REGIONAL CHILLING NETWORKS AT THE UNIVERSITY OF ARIZONA: ANTICIPATING AN EVENTUAL BAN ON 1,1,1,2-TETRAFLUOROETHANE
Item Type text; Electronic Thesis
Authors Yarnall, Luke Brian; Batts, Iesha; Sia, Jasper; Zinyemba, Rodney
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/613808 REGIONAL CHILLING NETWORKS AT THE UNIVERSITY OF ARIZONA:
ANTICIPATING AN EVENTUAL BAN ON 1,1,1,2-TETRAFLUOROETHANE
By
LUKE BRIAN YARNALL
______
A Thesis Submitted to The Honors College In Partial Fulfillment of the Bachelors Of Science Degree With Honors in
Chemical Engineering
THE UNIVERSITY OF ARIZONA MAY 2016
Approved by:
______Dr. Kim Ogden Department of Chemical and Environmental Engineering Abstract 1,1,1,2-tetrafluoroethane, or R134a, is a hydrofluorocarbon refrigerant currently used in the University of Arizona’s central chilling networks. Due to its high global warming potential, environmental regulators in the USA and the EU have begun its phase-out. To determine the suitability of R134a substitutes, the UA central chilling plants were simulated through a purpose-built computational thermodynamic model constructed in Microsoft Excel with extensive coding in Visual Basic for Applications. The best currently available alternative refrigerant was determined to be 2,3,3,3- tetrafluoropropene, or R1234yf. However, R1234yf was substantially less apt than R134a. The Coefficient of Performance, which is the ratio between the cooling capacity provided and the energy input to the system, was estimated to be 0.081 for R1234yf, versus 1.065 for R134a.
Environmental analysis found that the CO 2 equivalent emissions from an R1234yf system would greatly exceed those of a comparable R134a system under typical conditions. Similarly, economic analysis revealed that the price of an R1234yf plant surpassed the price of a similar R134a plant by roughly an order of magnitude. Our work found no suitable replacement for R134a in this application with today’s technology. Therefore, we discuss a number of recommendations on both a plant level and a nationwide policy level in order to establish a path forward towards effective emission reduction in district cooling applications. Statement of roles and responsibilities of each group member
The technical core of the project was completed by two Honors students, Luke Yarnall and Jasper Sia. Luke Yarnall prepared the final document and carried out the majority of the thermodynamic and computational modelling, while Jasper Sia developed the economic analysis and much of the plant design. Rodney Zinyemba conducted health, safety, and environmental analysis, while Iesha Batts carried out much of the day-to-day project organization. A more detailed enumeration of each member’s contributions is available below: Iesha Batts
• Drafted introduction with Luke • Pricing and design of ice banks • Creation design day poster • Creation of preliminary Block and Process Flow Diagrams • Organizational duties, including o Preliminary Basis of Design o Gantt Chart o College of Engineering Design Day management • Aided other group members with specific smaller tasks Jasper Sia • Estimated the costs of all equipment except the ice banks. • Estimated the total capital investments, operating costs (total production costs), and NPV. • Designed and wrote equipment descriptions, rationale, and optimizations for all the heat exchangers. • Estimated the initial and annual costs of the refrigerants for R-134a and R-1234yf. • Estimated the electricity and gas cost for the plant using R-1234yf. • Estimated the workers’ salaries for the plant using R-1234yf. • Wrote appendices relating to the work done described above. • Developed the equipment table. Luke Yarnall • Developed the central thermodynamic model of the refrigeration cycle and its implementation in Excel and VBA, including determining the total area needed for the condensers/evaporators (credit to Jasper for help in conceptualizing/planning the solution and for auditing it for errors). • Found and fit most of the data required for the thermodynamic model (see Section Error! Reference source not found. ) • Total area calculations for heat exchangers • Horsepower and head calculations for pumps • Coordinated tour of facility • Sections of report written: o Introduction (with Iesha) o Much of section 2 o Equipment description/rationale for pumps, valves o Final BFDs and PFDs (Iesha produced the initial drafts early in the semester) o Stream tables o Appendices related to the above calculations o Conclusions & Recommendations o Edited and compiled final document
Rodney Zinyemba
• Wrote Safety and Environmental Section • Eliminated refrigerants that were undesireable a priori , e.g. CFCs, HCFCs, and inapplicable technologies. • Waste Management calculations: o Environmental analysis of refrigerants (double checked calculations with Luke) o Energy source comparison (double checked my work with Luke) o Leakage rate sensitivity analysis (checked my calculations with Luke) o Did the Clean Air Act Pollutant Calculations, Acidification Potential and Photochemical Ozone Formation Potential Calculations o Ran Data Query from EPA and U.S. Energy Information Administration for the Irvington Generation Station • Hazardous Waste Risk Assessment Calculation
Regional chilling networks at the University of Arizona: Anticipating an eventual ban on 1,1,1,2-tetrafluoroethane April 29, 2016
Prepared for CHEE 443 Taught by Dr. Kim Ogden
Iesha Batts Jasper Sia
Luke Yarnall Rodney Zinyemba
Batts, Sia, Yarnall & Zinyemba Pg. 2
Table of contents
Section 1. Introduction and Background ...... 4 1.1 Overall goal ...... 4 1.2 Current market information ...... 5 1.3 Project premises and assumptions ...... 6 Section 2. Overall Process Description, Rationale and Optimization ...... 8 2.1 Rationale for process choice ...... 11 2.2 Associated tables ...... 13 Section 3. Equipment Description, Rationale and Optimization ...... 19 3.1 Compressor design ...... 19 3.2 Ice Banks ...... 19 3.3 Heat Exchanger: Cooling Tower ...... 19 3.4 Heat Exchanger ...... 21 3.5 Heat Exchanger – Ethylene Glycol and Product Water ...... 24 3.6 Centrifugal pumps ...... 25 3.7 Valves ...... 26 3.8 Flash Vessel...... 27 Section 4. Safety/Environmental Factors ...... 27 4.1 Safety Statement – Overall Overview with Equipment Used in the Heating and Cooling System ...... 27 4.2 Microscopic View – Chemicals Present in the Heating and Cooling System .... 30 4.3 Environmental regulations associated with the chemicals used in the cooling system 34 4.4 Environmental Impacts ...... 35 4.5 Environmental Issues to consider with changes associated with new Refrigerant 38 4.6 Hazardous Waste Risk Assessment Analysis...... 41 Section 5. Economic Analysis ...... 41 5.1 Inflation ...... 42 5.2 Total Capital Investment ...... 42 5.3 Total Production Cost / Operating Cost ...... 45 5.4 Feedstock and Utilities ...... 46 5.5 Direct Manufacturing Cost ...... 47 5.6 Total Production Cost...... 49 Batts, Sia, Yarnall & Zinyemba Pg. 3
5.7 Net Present Value ...... 49 5.8 Sales Revenue ...... 51 5.9 Economic Hazards...... 52 5.10 Future Work: Reducing Costs to Optimize the Process ...... 54 Section 6. Conclusions and Recommendations...... 55 Section 7. References ...... 57 Section 8. Appendices ...... 63 8.1 Calculations ...... 63 8.2 Economics calculations ...... 74 8.3 VBA code to accompany Excel spreadsheet “Computational thermodynamics model – final.xlsm” ...... 79 8.4 Physical and chemical properties ...... 98
Batts, Sia, Yarnall & Zinyemba Pg. 4
Section 1. Introduction and Background
1.1 Overall goal The goal of this report is to evaluate the feasibility of replacing the refrigerant in the University of Arizona’s central cooling system with a more environmentally friendly option. The University of Arizona (UA) system delivers about 21500 refrigeration tons of cooling capacity to the campus under peak operating conditions. To power this system, UA purchases $14 million a year of electricity, in addition to energy provided by its natural gas turbines. The primary aim of this report, as it relates to central cooling systems however, is to evaluate the potential alternatives to R-134A, the refrigerant currently in use and a powerful greenhouse gas, in order to better prepare for future regulatory environments. Another aim of this report is to determine the impact of power sourcing upon direct and indirect greenhouse gas emissions from the regional cooling network as currently configured.
1.1.1 District cooling and the refrigeration cycle Central or district cooling is a favored method of cooling large facilities. District cooling is favored because of its low cost and high efficiency (Bush 2016). Insulated underground pipes send cool water to various buildings in a given facility from one or more centralized places depending on the size of the facility. This cold water circulates through radiators in order to provide air conditioning to individual rooms inside of each building. The UA creates chilled water with refrigeration equipment. Refrigeration works by using the vaporization and condensation of a fluid to move heat against a temperature gradient. The movement of the fluid generally requires a compressor, condenser, flash vessel, and an evaporator. The refrigerant enters the compressor as a low-pressure gas and leaves as a high pressured gas. The high-pressure gas then travels to a connected condenser where it condenses. The latent heat of condensation is directed to another heat transfer medium. This heat transfer medium varies by plant design. The now liquid refrigerant passes through expansion equipment, where the liquid’s pressure is significantly lowered. The liquid then moves to an evaporator where it vaporizes, delivering cooling capacity. The refrigerant then enters the compressor as a gas again and cycle returns to its starting point. Batts, Sia, Yarnall & Zinyemba Pg. 5
1.2 Current market information
1.2.1 Current market demand and pricing The International District Energy Association stated that there are over 700 district energy systems in the United States with some created as long ago as the 1800s. Central cooling is more favored outside of the U.S., especially under the European Union level program RESCUE, an acronym for The Renewable Smart Cooling for Urban Europe. The price for functioning district cooling systems varies by size and specific conditions of the system. RESCUE affirms the ambiguity behind pricing an individual cooling facility and applying it to all plants. RESCUE does say, however, that the price to extend a system requiring 60 MW to 72 GWh could “vary between 30 and 150 €/MWh with an EU27 average of 67 €/MWh” (Swedblom et al).
1.2.2 District cooling systems The University of Arizona (UA) has unique challenges in maintaining its district cooling system, deriving from the desert climate, providing high temperatures to overcome and increasing water prices. Engineers and refrigeration specialists across the country visit UA to tour its advanced facilities (Blowers 2016). Bush et al published an article in the beginning of 2016 that highlighted the innovation and new directions behind district cooling centers and focused mostly on the environment, energy and water usage in this diverse process. This paper did not address the unique challenges that the UA has overcome, such as producing cool air when the temperature is as high as 117 degrees Fahrenheit or the high water prices. While there are other areas in the world using district cooling with dry climates, the UA system is exemplary in many ways. Hong Kong’s warm weather, high humidity and production boom in the early 2000s made it particularly suitable to the development of central cooling systems. Hong Kong researchers performed comparative analysis between using fresh water and air in their cooling process and determined that water radiators were more energy efficient than using air (Chan 2010). This is the current setup at UA as well. Surveys sent to stakeholders and a life cycle analysis both confirmed that fresh water cooling towers were more economical, more energy efficient and less environmentally damaging than air cooling. Batts, Sia, Yarnall & Zinyemba Pg. 6
1.2.3 Environmental and regulatory implications of R-134a Widespread use of 1,1,1,2-tetrafluoroethane (R-134A) in refrigeration operations began in the 1990s as earlier chlorofluorocarbon (CFC) refrigerants were phased out in accordance with the 1989 Montreal Protocol. R-134A, a hydrofluorocarbon (HFC), is advantageous when compared to CFC refrigerants such as Freon-12 because it poses no ozone depletion threat (Fisher, et al, 1989). However, R-134A and other HFCs are potent greenhouse gasses, with R-
134A having a 100-year global warming potential (GWP) of 1300, compared to CO 2, which has a defined GWP of 1.0 (United Nations Framework Conventions on Climate Change, 2014). Because of their high GWPs, in recent years there has been considerable interest in the increased regulation of R-134A and other HFCs. In 2006, the European Community passed legislation that would completely phase-out of R-134A for use in motor vehicle air conditioning (MVAC) applications by 2017 (Council Directive 2006/40/EC). More recently, in April 2015 the Environmental Protection Agency (EPA) revised its regulations on substitutes of ozone-depleting refrigerants. Effective January 2016, the EPA has banned R-134A for most aerosol propellant applications, and will require the phase-out of R-134A for MVAC applications by the 2021 model year (Protection of Stratospheric Ozone). The automobile industry has now settled on R- 1234yf as a replacement for R134a. Given these signs by major regulatory agencies, as well as recent international commitments in the 2015 Paris Agreement, it is possible that additional regulations will restrict R-134A use in the coming decades.
1.3 Project premises and assumptions
1.3.1 Overview of UA regional chilling network The University of Arizona (UA) currently operates three central chilling plants that provide chilled water throughout multiple underground networks across the university campus which then provides climate control to university buildings. The UA regional chilling network utilizes a certain refrigeration cycle detailed schematically in Fig. 1 below. During the day, waste heat from the university buildings is removed by the chilled water network and transferred to a series of ice banks, which function as heat sinks. During the night, ice is produced by a refrigeration operation using R134a. Heat is removed from the hot, compressed refrigerant by exposure to an evaporative cooling tower.
Batts, Sia, Yarnall & Zinyemba Pg. 7
Fig. 1: Schematic of UA regional chilling network during the night
The University of Arizona operates natural-gas fired turbines in a Combined Heat & Power (CHP) setup to generate electricity and steam. Electricity from this process is used during the day to operate the regional chilling network, while electricity is purchased from Tucson Electric Power (TEP) during the nighttime, when electricity costs are lower. At night, TEP- sourced electricity is used to freeze water, which is stored in ice banks and used for heat disposal during the daytime hours (P. Blowers). Currently, the UA regional chilling system creates 910 tons of ice per hour at peak capacity (Tareola, Al). This information was used to determine the amount of energy needed to cool campus which was then used to size equipment for this process based on the number of sites, the standard sizing of equipment in industry and the optimization of finances for this project. As shown below in our process flow diagrams, it was assumed that each piece of equipment was organized in series for steps, with unit operations needing multiple pieces of equipment organized in parallel.
1.3.2 Greenhouse gas analysis of power sources in current use In short, global warming occurs because as solar radiation passes through the atmosphere, some of it is absorbed by the surface while some is reflected by clouds, aerosols, and the atmosphere. Greenhouse gasses reabsorb surface radiation and reradiate it back to the earth in a perpetual loop. This can destabilize the world climate, posing a threat to the health and welfare of current and future generations through effects like reduced crop yield, decreased arability, and risks to fisheries (Union of Concerned Scientists). The current power sourcing plan for UA’s regional cooling network—in which TEP- sourced electricity is used to freeze water during the nighttime, and a natural-gas fired CHP system is used to operate during the day—is financially advantageous because it buys cheap Batts, Sia, Yarnall & Zinyemba Pg. 8 electricity during non-peak hours. However, it is not known whether the regional cooling network’s power sourcing is optimized to minimize greenhouse gas (GHG) emissions.
Section 2. Overall Process Description, Rationale and Optimization We present similar but differentiated designs for the UA district cooling facilities under two scenarios: 1) using R134a, and 2) using R1234yf, which was determined to be the best alternative option through thermodynamic and environmental modelling as described below. Due to the similarities between the two systems, they are presented together in the our analysis. Block flow diagrams (BFDs) and process flow diagrams (PFDs) are provided below in order to better conceptualize the system. Stream tables, equipment tables, and utility tables are provided at the end of Section 2. Fig. 2: Block flow diagram for R134a system
Batts, Sia, Yarnall & Zinyemba Pg. 9
Fig. 3: Block flow diagram for R1234yf system
Fig. 4: Process flow diagram for R134a system
Batts, Sia, Yarnall & Zinyemba Pg. 10
Fig. 5: Process flow diagram for R1234yf system
The primary goal of this project was to replace the use of R134a, a potent greenhouse gas with a Global Warming Potential (GWP) of about 1400, in the cooling center facilities at the UA while optimizing the finances associated with construction and the operation demands. This process must be able to run 24 hours per day and 365 days per year. Refrigerant compatibility was determined by modelling the system thermodynamics based on the actual system cooling capacity, and then designing the equipment needed to meet these conditions. The design of this plant assumed standard process equipment operating in parallel or series to each other with the parameters provided in Seider, et al. As mentioned in the introduction, the University of Arizona chills water through a refrigeration cycle, and then provides this chilled water to radiators at the point-of-use. Batts, Sia, Yarnall & Zinyemba Pg. 11
The heat transfer medium was a 25% ethylene glycol, 75% water mixture, from this point forward referred to as EG25. The ethylene glycol serves as an antifreeze that enables the system to reach lower temperatures.
2.1 Rationale for process choice The process of choosing an alternative refrigerant for our project began by creating a list of potential refrigerants. We derived our list of potential refrigerants from the Environmental Protection Agency’s Significant New Alternatives Policy (SNAP) program which falls under Section 612 of the Clean Air Act (CAA). We used the EPA SNAP List because this program is designed to: a) Identify and evaluate substitutes in end-use that have historically used ozone-depleting substances (ODS) b) Examine overall risk to human health and the environment of both existing and new substitutes c) Promote the use of acceptable substitutes d) Provide the public with information about the potential environmental and human health impacts of substitutes. The EPA reviews characteristics when proposing a substitute that include: Ozone depleting potential (ODP), Global Warming Potential (GWP), Toxicity, Flammability, Occupational and consumer health/safety, local air quality and ecosystems (“Overview of Snap”). The current refrigerant being used at the University of Arizona (U of A), R-134a, is a hydrofluorocarbon (HFC) that poses health problems and can be especially dangerous if inhaled at high concentrations, since it can cause death without warning due to cardiac arrest. Other symptoms include dizziness, irregular heartbeat, drowsiness or weakness (“DuPont Instruments”). Not only does R-134a pose health hazards, it has a GWP of about 1400, or about
1400 times the potency of CO 2 (Gillenwater). In general, HFCs like R134a share the characteristic of having high GWPs. One hundred twenty-five refrigerants were derived from the SNAP list. The majority were eliminated a priori because they were unsuitable for various reasons. The remainder were analyzed computationally to determine their suitability as replacements for R134a. A priori reasons for the elimination of refrigerants were the following: Batts, Sia, Yarnall & Zinyemba Pg. 12
1. CFCs, HCFCs, perfluorocarbons, or other substances with nonzero ODPs 2. Substances with GWPs greater than R134a 3. Blends of substances that fall into the prior two categories 4. Cryogenic technologies 5. Technologies not applicable to district cooling systems, such as ammonia absorption or adiabatic expansion of compressed gasses 6. Substances that do not exist in the correct phase in the temperature and pressure regime required
After including some comparison refrigerants that fail the above criteria (e.g. R22, which has a nonzero ODP), we arrived at the following list of refrigerant candidates that were analyzed computationally using the techniques in Section 8: • C2H6 • R-134a • R-600 • C3H3F3 • R-143m • R-600a • CF2HOCH3 • R-152a • R-717 • R1234yf • R-22 • R-744 • R-1150 • R-290 • RE170 • R-125 • R-32 • R-1270 • R-410a
One thermodynamic measure of a refrigerant’s efficacy is the Coefficient of Performance (COP), which is the ratio of the cooling capacity attained to the energy input. Our computational thermodynamic model resulted in the following COP values: Refrigerant COP Pressure for which model converged (atm) R143m n/a did not converge CF2HOCH3 n/a did not converge R744 n/a did not converge C3H3F3 n/a did not converge R22 2.33E+00 16 R134a 1.07E+00 16 R125 4.57E-01 16 R32 1.36E-01 16 R410a 1.07E-01 16 Batts, Sia, Yarnall & Zinyemba Pg. 13
HFO1234yf 8.05E-02 16 C2H6 6.06E-02 16 R152a 5.72E-02 16 R290 5.21E-02 16 R1270 4.74E-02 16 R600a 4.50E-02 16 R600 3.95E-02 16 RE170 3.53E-02 16 R717 1.01E-02 16 R1150 8.94E-03 64
These thermodynamic results were used in conjunction with environmental calculations described below to estimate total CO 2 equivalent emissions per year for each refrigerant: Refrigerant Total Emissions (kg CO2 eq) R22 3.17E+07 R134a 6.83E+07 R125 1.72E+08 R32 5.79E+08 R410a 6.94E+08 HFO1234yf 8.90E+08 R1150 1.18E+09 C2H6 1.25E+09 R152a 1.38E+09 R290 1.51E+09 R600a 1.59E+09 R600 1.82E+09 R1270 1.92E+09 RE170 2.03E+09 R717 7.11E+09
After eliminating refrigerants for a priori reasons, the best alternative was R1234yf, which is the refrigerant used to replace R134a for MVAC applications.
2.2 Associated tables
Stream table to accompany Process Flow Diagram for R134a system Batts, Sia, Yarnall & Zinyemba Pg. 14
Stream 1 2 3 4 5 6 7 Temperature 297 300 299 300 312 251 251 (K) Pressure (kPa) 101 101 101 101 2296 122 122 Vapor 0 0 0 1 0 1 0 Fraction Mass flowrate 250 499 749 250 879 544 335 (kg/s) Compound Water Water Water Water R134a R134a R134a
Stream table to accompany Process Flow Diagram for R134a system Stream 8 9 10 11 12 13 14 Temperature (K) 251 251 348 289 262 300 279 Pressure (kPa) 122 122 2296 101 101 618 618 Vapor Fraction 1 1 1 0 0 0 0 Mass flowrate (kg/s) 335 879 879 892 892 856 856 Compound R134a R134a R134a EG25 EG25 Water Water
Stream table to accompany Process Flow Diagram for R134a system Stream 1 2 3 4 5 6 7 Temperature (K) 297 300 299 300 312 251 251 Pressure (kPa) 101 101 101 101 1882 139 139 Vapor Fraction 0 0 0 1 0 1 0 Mass flowrate (kg/s) 3400 6790 10190 3400 13840 13430 410 Compound Water Water Water Water R1234yf R1234yf R1234yf
Stream table to accompany Process Flow Diagram for R134a system Stream 8 9 10 11 12 13 14 Temperature (K) 251 251 339 289 262 300 279 Pressure (kPa) 139 139 1882 101 101 618 618 Batts, Sia, Yarnall & Zinyemba Pg. 15
Vapor Fraction 1 1 1 0 0 0 0 Mass flowrate 410 13840 13840 890 890 860 860 (kg/s) Compound R1234yf R1234yf R1234yf EG25 EG25 Water Water
Equipment Table - Heat Exchanger T101-103 T201-231 Name Cooling Towers Cooling Towers Type Fin-fan with water mist Fin-fan with water mist Total Area (m^2) 31,540 430,000 MOC Tin Plated Carbon Steel Tin Plated Carbon Steel Number of units 3 31 Heat Duty (kW) 147,000 1,020,000 Flow rate refrigerant (kg/s) 880 13843 Flow rate water (kg/s) 250 3400 Refrigerant Inlet Temp (K) 348.2 339.2 Refrigerant Outlet Temp (K) 311.7 311.7 Tube Pressure (atm) 16 16 Chemical inside Tube R-134a R-1234yf
Equipment Table - Heat Exchanger E101-107 E201-207 Name Evaporators Evaporators Fixed Head Shell and Fixed Head Shell and Type Tube Tube Heat exchanger Area (m^2) 7000 7000 Number of units 8 8 Tube Length (ft) 20 20 Pressure (atm) 1 1 COM (Shell/Tube) C Steel / C Steel C Steel / C Steel Tube OD (in) 0.75 0.75 Shell ID (ft) 4.5 4.5 Number of Tubes 2413 2413 Total Surface Area per units (ft^2) 9475 9475 Pitch Type 1" Triangular Pitch 1" Triangular Pitch Tube type 16 BWG 16 BWG Flow type Countercurrent Countercurrent # tube pass/# shell pass 1/1 1/1 Batts, Sia, Yarnall & Zinyemba Pg. 16
Shell Fluid Ethylene Glycol Ethylene Glycol Tube Fluid R-134a R-1234yf Shell Flow Rate (kg/s) 892 892 Tube Flow Rate (kg/s) 880 13843 Shell inlet temperature (K) 289 289 Shell outlet temperature (K) 262.3 262.3 Tube inlet temperature (K) 251 251 Tube outlet temperature (K) 251 251 Phase Shell Fluid liquid liquid Phase Tube Fluid liquid/gas liquid/gas Shell and Tube Side Pressure (atm) 1 1
Equipment Table - Heat Exchanger E108-112, E208-212 EG25 & HOH Heat Name exchanger Fixed Head Shell and Type Tube Heat exchanger Area (m^2) 4914 Number of units 5 Tube Length (ft) 20 Pressure (atm) 1 MOC (Shell/Tube) C Steel / C Steel Tube OD (in) 0.75 Shell ID (ft) 4.75 Number of Tubes 2704 Total Surface Area per units (ft^2) 10618 Pitch Type 1" Triangular Pitch Tube type 16 BWG Flow type Countercurrent # tube pass/# shell pass 1/1 Shell Fluid Ethylene Glycol Tube Fluid Water Shell Flow Rate (kg/s) 892 Tube Flow Rate (kg/s) 856 Shell inlet temperature (K) 262.3 Shell outlet temperature (K) 289 Tube inlet temperature (K) 300 Tube outlet temperature (K) 279 Batts, Sia, Yarnall & Zinyemba Pg. 17
Phase Shell Fluid liquid Phase Tube Fluid liquid Shell and Tube Side Pressure (atm) 1
Equipment Table - Compressor C101-104 C201-243 Name Compressor Compressor Type Centrifugal Centrifugal Drive Electric Motor Electric Motor # stage 2 2 Fluid R-134a R-1234yf Power Requirement (kW) 71000 940000 # units 4 43 Efficiency 0.75 0.75 MOC Carbon Steel Carbon Steel Temperature (K) 348.2 339.2 Pressure in (atm) 1 1 Pressure out (atm) 16 16 Flow Rate (kg/s) 880 13843
P102-111A/B, P217- Equipment Table - Pumps P101A/B P201-216A/B 226A/B Pump HOH Pump HOH Name Condenser Condenser Pump EG25 Type Centrifugal Centrifugal Centrifugal Drive Electric Motor Electric Motor Electric Motor # stage 1 1 1 Fluid water water Ethylene Glycol # units 1 16 10 MOC Carbon Steel Carbon Steel Carbon Steel Efficiency 0.6 0.6 0.6 Flow Rate (gpm) 4000 54000 11000 Pump Head (ft) 50 52 1074 Fluid Density (kg/L) 1 1 1.32 Power consumption (Hp) 69 61 547 Pressure (atm) 1 1 1 Temperature (K) 300 300 289
Equipment table--Ice TK1101- Banks 1181,TK2101-2181 Batts, Sia, Yarnall & Zinyemba Pg. 18
Name Ice Banks MOC Carbon Steel # units 181 Inner Diameter (ft) 20 Length (ft) 40 Volume (ft^3) 2.3 million Weight (lbs) 36000
Utilities Table – Electricity Generation Refrigerant Compressor Price Annual Annual Total Cost ($) Power (kWh) ($/kWh) Electricity Natural Gas Cost ($) Cost ($) 1 R-134a 71,400 196.08 14,000,000 12,000,000 26,000,000 R-1234yf 941,000 196.78 185,169,588 158,716,764 343,886,352 1: Refer to the Operating Cost and Capital Cost Final and NPV for this calculation
Utilities Table – Water Usage 1 Refrigerant Flow Rate of Price to Annual Present Price to Cost to Water from Cool Cost to Water in the replace lost add Fresh our system to Hot Cool Hot System Cool Water Water in the Cooling Water Water ($) (gal/yr) from the system Tower ($/gal) Cooling ($) (gal/yr) Tower with Fresh Water ($/gal) R-134a 426,329,649 7.5*10 -5 31,975 12,200,000 0.027 329,400 R-1234yf 5,801,690,005 7.5*10 -5 435,1267 12,200,000 0.027 329,400
Utilities Table – Water Usage 2 Refrigerant Mass of Flow Rate of Water Price of selling cooled Annual Revenue ($) in our system (tons/yr) water ($/ton) R-134a 50,803 1.20 60,964 R-1234yf 50,803 1.20 60,964
Batts, Sia, Yarnall & Zinyemba Pg. 19
Section 3. Equipment Description, Rationale and Optimization
3.1 Compressor design In designing the cooling plant as is, we chose to have centrifugal compressors operated in parallel with our system next to the outlet of the evaporation system. This is the type of compressor used for 90% of processes because they are inexpensive and effective. The four restrictions centrifugal compressors have is the flow rate be between 10 and 5000 gallons per minute, that the head pressure be between 50 and 3200 feet, that the viscosity of the fluid in the compressor be higher than .0001 m2/s and that the NPSH be larger than 5 feet. The wide range of centrifugal compressor types made it so that at least three of these conditions had to be met in order for centrifugal pumps to not be the best choice and most of these constraints applied to the design criteria (Seider, Seader and Lewin). For the R134a system we needed 4 such compressors; for the R1234yf system we needed 43.
3.2 Ice Banks The ice banks in this process is used to store ice as a heat sink during nighttime operation. During the day when it is hot and the cycle is switched forward, this ice is melted to provide cooling. According to a personal interview with Chris Bansil, the maximum amount of time needed to create enough ice to chill campus on an extremely hot day was 14.75 hours where the real facility creates 910 short tons of ice an hour. This means the maximum capacity of ice the ice vessels at the designed facility must be 13422.5 tons or 26,845,000 pounds a day. This required about 2.3 million cubic feet of storage. Based on economic calculations, it was decided to use 181 vertical large vertical vessels with a height of 40 feet and a diameter of 20 feet.
3.3 Heat Exchanger: Cooling Tower After the refrigerant leaves the compressor, it passes through the cooling tower where it is liquefied at a high pressure. In this section, we discuss what kind of cooling tower to use. The chilling plant would be located in the desert, which has relatively high temperatures and relatively low humidity. Typical refrigeration units use air to remove the heat from the refrigerant during the condensation step. But since the desert has high air temperature, we cannot cool the refrigerant down very much using this method. So it is not very inefficient. Instead, we Batts, Sia, Yarnall & Zinyemba Pg. 20 decide to use the concept of an evaporative cooler to condense our refrigerant. A similar method is already done by the current UA chilling plant. Vaporizing water would absorb heat from the surrounding air and cool the air that would remove the heat from the refrigerant, condensing the refrigerant. Since the desert is relatively arid, we can vaporize much water and drive the air temperature down. We use this evaporating water method instead of using liquid cooling water to cool the refrigerant, because this method uses latent heat to absorb heat rather than sensible heat. And latent heat of water is orders of magnitude higher than its sensible heat. So, to remove the same amount of heat as using latent heat, the sensible heat would have to increase its temperature significantly. So the liquid cooling water’s temperature would turn very hot and not only pose a burns hazard but also pose an additional challenge of cooling the now hot liquid cooling water. Each refrigerant have different amount of heat to be removed in the cooling tower depending on its thermodynamic parameters. We will use the refrigerants R-134a (1,1,1,2- tetrafluoroethane) and R-1234yf (2,3,3,3-tetrafluoropropene) for this cooling tower analysis. We want to use condensing equipment that has similar effects as an evaporative cooler, where the evaporation of water cools the air. This air would then cool the refrigerant. Air-cooled heat exchangers such as a fin-fan heat exchanger can be modified by adding a water mist system to deliver the water evaporation. Since the water would be delivered in mist form, the small water mist would evaporate faster. We decided to use this kind of equipment because the equipment is not entirely new that would limit cost estimation and equipment availability. We are using a fin-fan heat exchanger which companies already manufacture and are just adding a pump system to deliver the water and valves to create the mist. We will use a carbon steel construction with tube outer layer of tin for the 2,3,3,3- tetrafluoropropene, and an outer and inner layer of tin for the 1,1,1,2-tetrafluoroethane. We use a carbon steel because it is cheap, can withstand our maximum temperature, and fits our application. According to Seider, et al, typical applications for carbon steel include water contact (Seider et al p697). Also, the 2,3,3,3-tetrafluoropropene manufacturer packages R-1234yf in disposable steel containers which we assumed to be carbon steel because it is cheaper (Alibaba, R-1234yf). We add the outer layer of tin to reduce rusting from the water vapor. We add the inner layer of tin for the 1,1,1,2-tetrafluoroethane to prevent potential interactions between the Batts, Sia, Yarnall & Zinyemba Pg. 21
aerosol and the carbon steel since tinplate is commonly used in aerosol containers (G3 Tinplate Aerosol Cans). For the fin-fan heat exchanger, the upper limit on the bare-tube surface area for each unit is 150,000 ft 2, as seen in the purchase cost calculation from Seider et al (Seider et al p592). Since for both R-134a and R-1234yf, the required bare tube heat transfer area is greater than 150,000 ft 2, then we need multiple units. R-134a requires a surface area of about 32,000 m 2 which is about 340,000 ft 2 (See: Computational Thermodynamics Model Excel Sheet). This means we need 3 units in parallel, each with about 120,000 ft 2 bare-tube surface area (See: Equipment Descriptions, Rationale, and Optimizations Excel Sheet). In contrast, the considered replacement refrigerant, R-1234yf, requires a surface area of about 430,000 m 2 which is about 4.7 million ft 2 (See: Computational Thermodynamics Model Excel Sheet). This means we need 31 units in parallel, each with about 150,000 ft 2 bare-tube surface area (See: Equipment Descriptions, Rationale, and Optimizations Excel Sheet). Clearly, we need ten times more fin-fan units for the R-1234yf than for the R-134a. So, the R-1234yf is much less efficient than the R-134a.
3.4 Heat Exchanger This heat exchanger refers to the part of the process where the refrigerant cools the ethylene glycol. As the refrigerant vaporizes, it cools the ethylene glycol which remains as a liquid. Since the temperature and flowrate of the ethylene glycol has been set by the process constraints and the heat capacity of the ethylene glycol, they remain constant regardless of the type of refrigerant we are using. As such, the heat exchanging area of about 7,000 m 2 is constant regardless of the refrigerant used (See: Computational Thermodynamics Excel Model). Since different refrigerant have different latent heat, the refrigerants with higher heat of vaporization would have faster flow rates while the refrigerants with lower heat of vaporization would have slower flow rates so that regardless of the refrigerant, the heat exchanging area between it and the ethylene glycol is constant. Numerous kinds of heat exchangers are available. We quickly eliminate fin-fan heat exchangers because we have to process streams and both are not utility streams like air or water. We eliminate double-pipe heat exchangers because according to Seider, et al, it is not recommended for vaporizing applications, which in our case: the refrigerant is vaporizing (Seider, et al). Also, the nature of the double-pipe heat exchanger limits it to relatively low Batts, Sia, Yarnall & Zinyemba Pg. 22
surface areas as low as 200 ft 2, insufficient to the massive scale of our operation to provide chilled water to the University of Arizona (Seider et al, p571). We eliminate plate-and-frame heat exchangers as our option because they are not well suited to evaporation (Seider, et al p482). So, our options reduce down to shell-and-tube, spiral plate, or spiral tube heat exchangers. Economic calculations done on the shell-and-tube, spiral plate, or spiral tube heat exchangers show that the spiral plate and the spiral tube heat exchangers cost more than the shell-and-tube heat exchanger. These two heat exchangers also require significantly more units than the shell-and-tube. To illustrate, the spiral plate requires 38 units and have a total purchase cost of $5.7 million and the spiral tube requires 151 units and have a total purchase cost of $31.5 million. This is in stark contrast to the shell-and-tube heat exchanger, where were require only 8 units and have a maximum total bare modulus cost of $3.9 million. Note that the $3.9 million is for the purchase cost plus the installation cost, unlike the cost listed for the other two heat exchangers which are only the purchase costs and do not include the installation costs. Also note that the reported $3.9 million is for the kettle reboiler design shell-and-tube heat exchanger, which is more expensive than the other designs: floating head, fixed head, and the U-tube (See: Equipment Description, Rationale, and Optimization Excel Sheet). The flow pattern is chosen to be countercurrent flow. This allows for the most efficient heat exchange between the ethylene glycol and the refrigerant. The refrigerant would be in the tube side so that in case the refrigerant leaks, the ethylene glycol that is in the shell side may act as a barrier rather than directly escaping to the atmosphere. Single tube pass and single shell pass heat exchanger would be used to maximize the efficiency of heat transfer. The tube and the shell fluids are entirely countercurrent in a 1-1 heat exchanger while some parts are co-current in a multiple tube pass or multiple shell pass heat exchangers. We also do not need the increase in shell fluid velocity from the multiple passes as our flow rates are already relatively high: about 900 kg/s (See: Copy of Computational Thermodynamics Model Excel). We do not have large temperature differences between the refrigerant and ethylene glycol (max difference: 40 K) so we do not worry about the effects of differential expansion (See: Equipment Description, Rationale, and Optimization Excel Sheet). As a result, we do not need the floating head configuration. We may want to clean the inside of the tubes later so we eliminate the U-tube configuration. This leaves us with the fixed head configuration. The fixed head allows us to clean the inside of the tubes, though it does not allow us to clean the outer surface of the tubes. Batts, Sia, Yarnall & Zinyemba Pg. 23
This drawback is a trade-off we are willing to make to use the cheaper fixed head than the more expensive floating head. Because we cannot clean the outside of the tubes, care must be taken to ensure the cleanness of the ethylene glycol in the shell. We choose a carbon steel shell and a carbon steel tube. Carbon steel is cheap, fits in our temperature range, and is suitable to handle ethylene glycol (Seider et al, p697). For 1,1,1,2- tetrafluoroethane, we will coat the inside of tubes with a layer of tin. This tinplate is commonly used in aerosol storage so it may prevent potential interactions between R-134a and the carbon steel (G3 Tinplate Aerosol Cans). For the 2,3,3,3-tetrafluoropropene, we do not need to coat the inside with tin because the 2,3,3,3-tetrafluoropropene vendor sells them in disposable steel cylinders (Alibaba, R1234yf). So we assume we can use steel as our tubes. Since stainless steel is more expensive than carbon steel, we assumed that they are using carbon steel as a disposable container. We choose a tube length of 20 ft because it provides the highest heat transfer area to cost ratio compared to shorter tube lengths (Seider et al, p571). We choose ¾” O.D. tubes because according to Heuristic 54, that is a good estimate to be used in preliminary calculations (Seider et al, p475). In addition, we chose the tube O.D. to be 0.75 in because we do not want to have it too small that the energy lost due to friction would be too high. We do not want the O.D. to be too large that we have a large temperature gradient across the perpendicular cross section of the tube because heat transfer is not as efficient. 16 BWG tubes are used because they are commonly used. Tubes are arranged in a 1” triangular pitch configuration because that allows more tubes in a specific shell area than if they are arranged in a square pitch. 1” pitch is chosen to balance enough shell fluid to flow between the tubes and fitting more tubes in the shell. To optimize the cost, we want the total surface area of all the heat exchangers to be as close to the heat transfer surface area that we need. So, as described for the shell and tube heat exchanger in the equipment sizing section in the appendix, we determined the specification of such a heat exchanger. So, we calculated that we would need 8 units each with 4.5’ inner shell diameter and approximately 2413 tubes. These heat exchanger units would be in parallel. The 1-1 fixed head shell-and-tube heat exchanger is not perfect but is sufficient for the refrigerant and ethylene glycol heat exchanger. The outside of the tubes cannot be cleaned so extra caution and care must be done to ensure that the ethylene glycol in the shell is clean. However, using the fixed head is cheaper than using the floating head, and we are willing to Batts, Sia, Yarnall & Zinyemba Pg. 24
make this trade-off especially since we do not need the differential expansion benefit of the floating head configuration.
3.5 Heat Exchanger – Ethylene Glycol and Product Water This heat exchanger refers to the part of the process where the cold ethylene glycol absorbs energy from the warm water coming from The University of Arizona’s buildings. The resultant chilled water is the plant’s product that would cool The University of Arizona’s buildings. The temperature of the inlet and outlet water are set by our project’s constraints. Before arriving and after leaving this heat exchanger, the ethylene glycol passes through the ice banks where its temperature decreases by the same amount regardless of the kind of refrigerant. So, this heat exchanger is the same heat exchanger we use regardless of the refrigerant we choose. So, the heat exchange area between them is constant at around 4,900 m 2 (See: Equipment Description, Rational, and Optimization and Cost excel sheet). Many different types of heat exchangers are available, however some are inappropriate for this application. We will not use the fin-fan heat exchanger or modifications of it because we want to retain all of our process fluids. Double-pipe heat exchangers are eliminated from potential heat exchangers because of their limited heat exchange surface area. Similar analyses as was done on the equipment design of the evaporator shows that the spiral plate and spiral tube heat exchangers are more expensive than the shell-and-tube heat exchanger. Analysis on the potential plate-and-frame compact heat exchanger reveals that it is more expensive than the shell-and-tube heat exchanger. So, we will use the shell-and-tube heat exchanger. From the shell-and-tube heat exchanger, we can choose a specific type from the floating head, fixed head, U-tube, and the kettle vaporizer. We will not use kettle vaporizer since we do not have phase changes in both of our streams. We do not want to use the U-tube because then we cannot clean the inside of the heat exchanger. We want to clean the inside of the heat exchanger because of the water. The water may pick up junk as it goes through the buildings and bring it back to the heat exchanger. Since the temperature difference between the hottest part of the water and the coldest part of the ethylene glycol is not very large, so we do not have a differential expansion problem. So, we do not need this benefit in using the floating head configuration. Batts, Sia, Yarnall & Zinyemba Pg. 25
That leaves us with the fixed head configuration. However, a downside of the fixed head is that although we can clean the inside of the tubes, we cannot clean the outer surface of the tubes. However, if we place the cleaner ethylene glycol in the shell and the dirtier water in the tubes, we do not need to clean the outside of the tubes. So, we choose the cheaper fixed head configuration. The flow pattern would be countercurrent because this will provide more efficient heat exchange between the ethylene glycol and the water. We choose a single tube pass and single shell pass heat exchanger to maximize the efficiency of the heat transfer. Since we cannot clean the outside of the tubes, we must ensure that the ethylene glycol remains clean. We choose a carbon steel shell and a carbon steel tube. Not only is carbon steel cheaper, but it fits our temperature range and is suitable to handle ethylene glycol and water (Seider et al, p697). For similar reasons as discussed in the evaporator section, we choose tubes with length of 20 ft, ¾” O.D., are made of 16 BWG, and are arranged in 1” triangular pitch configuration. To optimize the cost, we want the total heat exchange area of all the heat exchangers to be close to the heat transfer are we need. We determine the specification of the optimum heat exchanger by using the techniques described in the equipment sizing section for the shell and tube heat exchanger in the appendix. So, we calculated we would need 5 units of heat exchanger. Each unit would have a shell I.D. of 4.75 ft and have around 2704 tubes. The 5 heat exchangers would be arranged in parallel. The fixed head shell and tube heat exchanger is not perfect since we cannot clean the outside of the tubes. However, fixed head is cheaper than floating head, and we are willing to use the fixed head especially because we do need the differential expansion benefit of the floating head configuration.
3.6 Centrifugal pumps Pumps are required to circulate EG25 through its heat exchangers and the ice banks, as well as to provide water to the cooling towers. Based on the outputs of our thermodynamic model, the necessary pump horsepower was determined as described in Section 0. A typical pump efficiency of 60% was assumed. The necessary pump horsepower depends primarily on the pump’s flowrate and the head that it must generate. The head that the pump must generate, in turn, depends on the energy Batts, Sia, Yarnall & Zinyemba Pg. 26
barriers that it faces. In the case of the pumps providing water to the cooling towers, the majority of the head derived from the height of the cooling tower. In contrast, for the EG25 pumps, the majority of the head derived from friction with the long lengths of plastic tubing within the ice banks. Because the pump flowrates and heads were not excessive, chemical engineering heuristics suggested that we use centrifugal pumps in our design (Seider, Seader and Lewin). In contrast to positive-displacement pumps, centrifugal pumps are generally preferable because of their lower cost, steady flow, and durability. Based on the economic calculations presented in Section 5, we determined that the EG25 system should have 10 centrifugal pumps in parallel with 550 hp each (this system remains the same regardless of refrigerant selection). In a similar fashion, we determined that the cooling tower water would require 1 pump at 70 hp when using R134a as the refrigerant. The switch to R1234yf would require 16 pumps in parallel with at least 60 hp each.
3.7 Valves In general, the UA central chilling facility requires a complex network of piping, valves, and fittings that are outside the scope of this design report. However, four valves in particular merit additional attention and are shown on the respective process flow diagrams. Valves V101, V102, V201, and V202 are mixing valves that combine two streams, as shown in the process flow diagrams and stream tables above. V101 and V201 integrate the inlet of fresh water to the cooling tower with the recycle stream of unvaporized cooling tower water. In turn, V102 and V202 divert the vapor stream from the flash vessel directly to the compressor. Bypassing the evaporator with this vapor stream ensures that only liquid refrigerant enters the evaporator, which helps ensure good nucleate boiling and lower resistance to heat transfer in the evaporator. Valves V103, V104, V203, and V204 are three-way valves used to redirect the flow of the EG25 heat transfer medium. During nighttime operation, these valves connect the ice banks to the refrigeration system so that ice can be stored. However, during daytime operation, these valves change so that the ice banks are instead connected to the EG25-chilled water heat exchanger in order to deliver cooling capacity to the end users. Batts, Sia, Yarnall & Zinyemba Pg. 27
3.8 Flash Vessel The objective of the flash vessel in this process is to decrease the temperature of the liquid before it enters the evaporator. Southwest Tech maintains that there is an orifice connected to the outlet of condenser in order to change the pressure. Because of the ambiguity with the amount of size needed to enter a vessel and consequent price ambiguity, it was decided to use an expansion valve over treated the flash process as a pressurized tank. Due to the specific need for this piece of equipment to meet the needs of the refrigeration cycle, it was decided to use Alibaba.com to price an expansion valve marketed with the intent of being used for R134a, our current refrigerant.
Section 4. Safety/Environmental Factors
4.1 Safety Statement – Overall Overview with Equipment Used in the Heating and Cooling System Several key pieces of equipment used in the heating and cooling system include: gas fired combustion turbines, heat recovery steam generators, compressors, heat exchangers, evaporators, condensers, chillers, boilers, cooling towers, and ice banks. We performed a Hazard and Operability (HAZOP) study on the cooling towers, ice banks, evaporators, and compressors in the cooling plant. The majority of mechanical hazards associated with this plant will come from the compressor. If the compressor is fed too much power the evaporator downstream will become too cold which can log the pipes in the ice vessels. Too much power to the compressor can also decrease the cooling efficiency of the cooling tower; the fins can be powered enough to force hot water back into the system. Too much power also risks losing additional money for the process. As a large customer of Tucson Electric Power, UA is fined if it expends more than 29 Megawatts in the temperature control processes. These considerations make the compressor of high concern. The implementations and observation of a voltage regulation meter should inform plant operators on the amount of electricity consumed by the compressor and prevent such problems. However, excess power is not the only caution associated with having compressors in this plant. If the flow into compressor is too high -perhaps due to a liquid carryover from interstage cooling or a sudden process change- it can affect all the other downstream equipment, leading to Batts, Sia, Yarnall & Zinyemba Pg. 28 less effective heating and cooling system. A valve with a feedback loop could easily be installed into the process to prevent this. Dirty liquid can also enter into the compressor due to contamination build up in our system and lower the overall efficiency of the compressor, and periodic cleaning can preclude these issues. Carbonate buildup is extremely common in processes moving water around. Carbonate buildup can also affect the performance of the compressor and periodic lime and soda washing could prevent this. Lastly, corrosive elements can hinder the overall performance of the compressor and one solution for this would be to replace the compressor after a certain drop in efficiency. Another important component to this plant are the cooling towers. The study node analyzed was the cooling water pumps. If the power of these pumps is too high it is due to an operator error. This leads to a waste of power and could be a fire hazard since the motor in the cooling tower can burn. To prevent or reduce the effect of this fire, required actions include the installation of sprinklers to prevent the fire from increasing in intensity and conveniently placing emergency response plans for fires near the cooling towers. Teaching these locations and protocols to operators should be done at least yearly and especially during training. If the power into the cooling tower is too low, it is from the induction load being off due to a low power factor from the pump from the pump motor. Adding specialized meter on the pump with a user- friendly display to operator interfaces to indicate when the power factor drastically deviates should help prevent this problem.. The collection basin is another study node analyzed in the cooling tower. If the water quality is high, possible sources include algae, dust particles and carbonate build up in the system. Possible consequences include the clogging of pipes since unwanted particles are entering into our system after passing through the cooling tower. This leads to less water flowing through the cooling tower making the tower less effective. One could reduce this threat by regularly collecting data on proper concentrations of dissolved solids and chemistry and then to apply the right remediation steps to maintain the quality of water. For the ice banks, ethylene glycol was a study node examined in the HAZOP analysis. If the ethylene glycol concentration is too high or low, then this was because an incorrect composition of ethylene glycol was introduced to the system. This could also happen if the water and ethylene glycol evaporate or leak from the system at unequal rates. When the water to ethylene glycol ratio is askew, a different heat capacity is introduced in the fluid, making the system inefficient. Regularly monitoring the composition of ethylene glycol can easily prevent Batts, Sia, Yarnall & Zinyemba Pg. 29 this situation. Temperature is another parameter within the ethylene glycol node that was analyzed. If the temperature is too high it would be due to a heat exchange problem from the refrigerant or due to friction loss. Both of those scenarios block the production of ice, and to fix this one should check the heat exchanger with the refrigerant for any clogged pipes and clean it. By having a temperate of the ethylene glycol-water mix that is too low, the likely cause is reduced water in the tank. With that issue, the system is inefficient which increases the economic and environmental cost with ice being less or not even made. Correcting that situation would be done by checking the water level in tanks, checking the system for leaks and then adjusting deviations as they appear. The evaporator was the last HAZOP done with regards the overview of the equipment. The study node that was looked at was the inlet stream which consists of the refrigerant. If the temperature is high, it is due to a malfunction of the flash vessel. This would result in an insufficient refrigerating capacity and an action required would be to inspect the flash vessel. If temperature is low, then it is due to the malfunction of the flash vessel. This would in turn cause freezing of the heat transfer medium, leading to broken pipes and pumps. A solution would be to again inspect the flash vessel and then increase the heat transfer medium to prevent the freezing process. Another study node on the evaporator is the outlet stream for the refrigerant. If the vapor fraction is below one, then that is because there is a high refrigerant flowrate or it can also be due to a low flow rate from the heat transfer medium. This in turn can cause wet compression which damage the compressor. A solution would be to increase the EG25 flowrate (refer to PFD to see this) and/or decrease power to the compressor. The main key operation concern for the heating and cooling system is the power supply because if there is a power outage, the plant would shut down until power is restored, causing a lag in the cooling production. Even if we had generators, it would not entirely as well power the heating and cooling for the U of A for a long period of time. However, the overall analysis for the HAZOP is that by having industry-standard equipment and safety measures, the overall equipment is reasonably safe.
Batts, Sia, Yarnall & Zinyemba Pg. 30
4.2 Microscopic View – Chemicals Present in the Heating and Cooling System To achieve the maximum safety in our heating and cooling system, a process of in depth analysis with regards chemicals present in our system was needed. A Process Hazard Analysis (PHA) was conducted to identify, evaluate and control chemical hazards. The table below displays the exposure hazards and proper response for chemicals used in this process: Exposure Hazards and Response for Process Chemicals Hazard Response Compound Skin Eyes Ingestion Inhalation Skin Eyes Ingestion Inhalation 2,3,3,3 – Cold Irritant Burns Unknown Wash with Flush Medical Administer Tetrafluoro burns water (15 with attention oxygen propene min), water
(C 3H2F4/R- apply (15 1234yf) a sterile min) dressing, and seek medical attention Sulfuric Corrosi Corrosi Irritant Irritant Flush with Flush Medical Administer Acid ve, ve, water (15 with attention oxygen
b (H 2SO 4) burns burns min.) water (15 min.) 1,1,1,2 – Irritant, Irritant Non- Suffocate Flush with Flush N/A Administer Tetrafluoro cold Applicabl due to loss water (15 with oxygen ethane burns e (N/A) of oxygen min) water
(CH 2FCF 3/ (15 R-134a) c min.) Ethylene Irritant Irritant Toxic Irritant Wash with Flush Medical Administer Glycol soap and with attention oxygen
d (C 2H6O2) water water Batts, Sia, Yarnall & Zinyemba Pg. 31
(15 min.)
Water Non- Non- Non- Non- N/A N/A N/A N/A
e (H 2O) corrosi irritant hazardou sensitizer ve s a: MSDS for R-1234yf supplied by Brins Oxygen Company (BOC) b: MSDS for Sulfuric Acid supplied by Science Lab c: MSDS for R-134a supplied by DuPont d: MSDS for Ethylene Glycol supplied by Science Lab e: MSDS for Water supplied by Science Lab
Looking at each of the chemicals from Table 1, one could see for each of those chemicals there is hazard that takes place based upon how the chemical enters an employee’s body at the Heating and Cooling System. The Hazard part represents the “if”, mainly the damage that takes place on the U of A Heating and Cooling employee’s body when exposed to chemical and the response is the “what”, the correct remediation step that one has to take to prevent further damage on the worker at the U of A Heating and Cooling System. Out of all the chemicals that are present in the U of A Heating and Cooling System, sulfuric acid is the most dangerous. Also, it can degrade the pipes and other parts of our operation if they are made out of aluminum, copper or steel. Sulfuric acid is also toxic. The Permissible Exposure Limit (PEL), the legal limit in the United States for exposure of an employee to a chemical substance, sulfuric acid threshold limit value (TLV) is 1 mg/m 3. This maximum value of the concentration of a chemical in air to which workers may be exposed over their occupational lifetimes was made by Occupational Safety Health Administration (OSHA). Looking at the refrigerants respectively OSHA does not have a PEL value for R-134a and since R-1234yf is a new refrigerant that is now in the market, we also see as well that there is not a PEL value present for this as well. By knowing the maximum range of the TLV that was made the American Conference of Governmental Industrial Hygienist (ACGIH), we can conclude that our plant would require a high degree of training and year of field experience for all operators working on it due to the danger of the chemicals. Batts, Sia, Yarnall & Zinyemba Pg. 32
Even though sulfuric acid is the most dangerous in terms of carcinogenicity, ethylene glycol follows next. It has a high TLV value of a 100 mg/m 3 meaning a worker would not want to be exposed more with ethylene glycol. Its main entry with regards the toxicity pathway is through the skin or absorption and in case of a chemical spill the right PPE would be used. The last on the list of being dangerous are the refrigerants. Since the refrigerants as gas form, the main point to entry upon an employee would be mainly through inhalation and if close to the source of a spill it will be damaging either the eyes or skin. With the R-134a being replacement with R-1234yf, one key main difference to just take a note off is that R-1234yf is a flammable gas which R-134a was not. Also, it is extremely corrosive and mixing that with the sulfuric acid is something that one should be aware of. In case of an accident spill, the correct Personal Protective Equipment (PPE) is needed, respirators to not inhale the gases since they lead to suffocating since vapors are heavier than air and as a result lead to reduction of oxygen in the lungs. By using respirators, training in using the Self-Contained Breathing Apparatus (SCUBA) can be done as employees would only were these on emergency situations. Besides SCUBA, the right safety eyewear is needed to avoid liquid splashes, and the right gloves to needing to fix the problem, steel toe shoes and flame resistant/retardant clothing. To strengthen such training looking at an accident spill, incident handling techniques could be used to handle an unplanned release of hazardous materials or hazardous waste. Factors that are used to consider the right proper incident management and mitigation techniques are the chemical hazard and the physical situation. To be able to apply incident handling techniques and have a command post and zoning during the incident, employers must be trained responders, as set forth by OSHA in 29 CFR 1910.120 (Woodside, p. 336-337). When forming an incident technique that suits the U of A Heating and Cooling system, one can see guidance in forming an emergency response thanks to the National Fire Protection Association (NFPA) from their NFPA 471 and 472 documents. The NFPA 471 and 472 documents are standards that were recommended by OSHA as an excellent method of response to a hazardous materials release. Combining NFPA 471 and 472 with NFPA 1561, an incident command system can be formed for any issue that can be seen with the U of A Heating and Cooling System. To form an effective response to an emergency seven personnel that are required from the table below which has the personnel role’s name and responsibilities. Batts, Sia, Yarnall & Zinyemba Pg. 33
Personnel that Might be Needed During a Hazardous Materials Incident Personnel Responsibilities Incident commander Establish and manage the incident response plan; allocate resources, assign activities, manage information, and ensure response is completed per plan Sector officers Manage geographical areas, including hazardous materials response teams in that area, as needed; provide specific functions such as serving as safety officer Command staff Assist incident commander and/or sector officers; gather data such as chemical information, weather data, and status of other operations Police or security Manage the location and activities of the general public Hazardous materials response teams Directly manage and mitigate the hazardous materials release under the direction of a specified team leader Communications personnel Perform central communication function for incident including requests of additional emergency resources; notify proper agencies of the release; answer media questions Technical information specialist Provide expertise directly to the incident commander in terms of chemical information and exposure hazards
Batts, Sia, Yarnall & Zinyemba Pg. 34
In conclusion, for chemicals if they are used right, there will be minimal chemical hazards. With industry-standard equipment and safety measures, and few chemical hazards, this overall process is reasonably safe.
4.3 Environmental regulations associated with the chemicals used in the cooling system Federal agencies (usually the EPA for environmental legislation) provide detailed regulations, which are then published in the Code of Federal Regulations (CFR) under Title 40, the section on Protection of the Environment (Watts, p. 13). Out of the many environmental laws that were passed in the U.S. the six major laws are: Emergency Community Right to Know Act (EPCRA), Clean Air Act (CAA), Clean Water Act (CWA), Safe Drinking Water Act (SDWA), Resource Conservation and Recovery Act (RCRA), Federal Pollution Prevention Act of 1990, and Comprehensive Environmental Response, Compensation, and Liability Act/Superfund Amendments and Reauthorization Act (CERCLA/SARA). With the chemicals and structure of the U of A Heating and Cooling Plant. One knows that the site is not abandoned so the CERCLA/SARA environmental regulation law does not apply. There is a need in the plant of having emergency response plan in case accident spill or any other incidents and based off of that EPCRA is one regulation that is needed. With regards a spill and leakage occurs there are several scenarios that need to be looked at and they are: one, when the refrigerant is deposited into the system it contains some liquid and gas, so when leakage occurs: gas is emitted out of the plant and it pollutants are entering the surrounding air, meaning the CAA is an environmental regulation associated with our plant. If the liquid of the refrigerant be it R-134a or the alternative refrigerant R-1234yf is mixed with water, ethylene glycol and sulfuric acid drips down from the system onto the ground, if the ground is porous, the contaminated liquid can go down the soil all the way to groundwater meaning CWA and SDWA environmental regulations are in play and part of our systems environmental regulation. The spill itself needs to be cleaned up and put into the right disposal which a proper container and label. That operation in itself means RCRA is also involved in our environmental regulation. One of the goals of the UA cooling system is trying to prevent as much waste produced and that common sense initiative also implies that the Federal Pollution Prevention Act of 1990 is the last environmental regulation. Batts, Sia, Yarnall & Zinyemba Pg. 35
4.4 Environmental Impacts
4.4.1 TEP Past vs. U of A Heating and Cooling System One project goal was to compare the environmental impacts of energy sourcing between TEP and the U of A natural gas fired turbines. At night the U of A Heating and Cooling System buys electricity at night from TEP to make ice and during the day, the U of A melts the ice whilst generating power with its own natural gas. The limit that U of A cannot pass is 29 MWh/day. If the U of A does, it will pay a fine from TEP. The typical operation of the current system is 20MWh/day. During monsoon season, this current system might increase but still not reach 29MWh/day. The maximum capacity for the U of A in terms of producing power is one-third of 29MWh/day meaning only 9MWh/day is how much the current U of A system produces (C. Bansil). The generation station that provides electricity for Tucson is the Irvington Generating Station. There are 4 units that are present at the Irvington Generating Station: unit 1 which burns natural gas, the same as units 2 and 3, and lastly unit 4 which burns natural gas and coal (H Wilson). Looking at the Units present at the Irvington Generating Station, they are four oil/gas boilers generating steam for four condensing turbine generators. Units 1 and 2 have pressurized, natural circulation boilers designed in 1956 and rated for full load steam generation of 575,000 pounds per hour each. Unit 3 has a pressurized, natural circulation Combustion Engineering boiler designed in 1960 and rated for full load steam generation of 800,000 pounds per hour. Unit 4 had a pressurized, natural circulation Foster Wheeler boiler designed in 1965 and rated for full load steam generation of 1,140,000 pounds per hour. There is total of approximately 900 acres on the site, most of which, if required are available for new facilities such as coal handling (Cochran, p. 86). During early phases of the Irvington Generating Station Coal Conversion Project, a review of all alternatives was done and was concluded that at the Irvington Generating Station, the straight coal conversion will be applied whilst maintaining the oil and gas system. Coal would be acquired from New Mexico and approximately 21,600 tons is the maximum storage space available for coal (Cochran, p. 86 - 102).
Batts, Sia, Yarnall & Zinyemba Pg. 36
To compare which system is better the TEP or the U of A generation of electricity using natural gas, a comparison to see which system is better was based off the Tucson Electric Power Irvington Generating Station Air Quality Permit#1052 Technical Support Document (TSD) from
May 18, 2007. This document provided data of particular matter (PM), nitrogen oxide (NO x),
sulfur oxide (SO x), carbon monoxide (CO), and volatile organic compound (VOC). The emission rates that were calculated were changed from lb/hr to ug/m3 to see how bad TEP vs. U of A Heating and Cooling System are with regards emitting air pollutant to the surrounding air. Below is a table showing the results of the calculations.
U of A and TEP Irvington Generation Emission Rate U of A Emission TEP Irvington Generation Emission Rate Rate Pollutant lb/kWh lb/kWh with Coal PM 1.07E-06 1.88E-07 NOx 3.11E-07 5.70E-09 SOx 8.48E-08 1.02E-08 CO 1.19E-05 5.80E-08 VOC 7.77E-07 1.05E-06 CO2 1.70E-02 N/A
Looking at that table one can clearly see that the Irvington Generating Station with Coal was producing more bad pollutants that the U of A, making the Heating and Cooling System better. Without the coal, there is a drastic decrease with the pollutant emission levels. To see if TEP obeys the Acid Rain program due production of high NOx and SO2, one can be worried that TEP might be violating the Acid Rain Program under the Clean Air Act and under National Emission Standards for Hazardous Air Pollutants (NESHAP), for Generating Stations there are required Emissions Reductions (Masters, p. 374 - 375). After running a Toxic Release Inventory for the Irvington Generating Station after referring to the Waste Management Excel, one can see that the TEP Irvington Generating Station produces 0.023 ton of Mercury. This is far below the Acid Rain Program requirements, meaning they have great filters within their power plant and monitoring to ensure that no large pollutants are being released in the environment. This can be supported as well with the Air Quality Permit#1052 that showed the Acid Rain Permit (Technical Support Document, p.24). Using the Batts, Sia, Yarnall & Zinyemba Pg. 37
EPA website and in the Waste Management Excel, it showed SO 2 1,151.28 tons, NOx being
1197.55 tons and CO 2 being 666,947.347 short tons.
4.4.2 TEP Present vs. U of A Heating and Cooling System When TEP decided to stop using coal and switch to natural gas, it became interesting to see if U of A Heating and Cooling System is still better. In terms of pounds pollutants per kWh, the UA emissions are much less than TEP’s emission output due to more efficient Combined Heat and Power turbines. U of A Emission Rate
TEP Irvington Generation Emission Rate
4.4.3 TEP Future vs. U of A Heating and Cooling System Decarbonization strategies that could be used would reduce the amount of carbon going into the atmosphere by looking at: efficiency improvements of the current system at the Irvington Generation and U of A Heating and Cooling System, Fuel shifting as for example the switch from coal to natural gas that TEP did, carbon capture strategies to reduce carbon being permitted into the atmosphere and overall fossil fuel displacement of switching from natural gas to solar. Future generation technologies are: gas combined-cycles, supercritical coal steam, coal- Batts, Sia, Yarnall & Zinyemba Pg. 38
integrated gas combined-cycles, wind, solar, new-generation nuclear, small nuclear and large- scale hydro (although this last is not applicable in Arizona due to lack of exploitable rivers). In addition, better information technology tools with how the Irvington Generation Station works can help in reducing the pollutant emissions. Ideas of improvements include better meter data acquisition systems (MDAS), meter data management systems (MDMS), field area networks, customer information systems (CIS), billing systems, power settlement systems, trading systems, risk management systems, customer networks, and energy management systems.
4.5 Environmental Issues to consider with changes associated with new Refrigerant The environmental impact of all phases of industrial activity, from raw materials acquisition and R&D to the final disposition of a product and its packaging, is having a far- reaching effect on environmental quality and on public health. As result, industry, environmental groups, and governments are attempting to identify a systematic means of evaluating and minimizing the environmental impact of products and processes. One of the more promising systematic approaches for identifying and evaluating opportunities to improve the environmental performance of industrial activity is a term called life cycle analysis (LCA) (LaGrega, p. 391). LCA provides a framework for investigating the entire range of environmental impacts (e.g. air emissions, wastewater, solid and hazardous water, renewable sources, and energy utilization). With attention to the U of A Heating and Cooling System, in our process, the refrigerant is added into our system to provide the needed cooling for the U of A’s various buildings. If a leak were to occur, the refrigerant will leak and be emitted mostly as gas since the phase of the refrigerant, the pollutant emission coming out of our U of A Heating and Cooling System, gas and a little liquid. So based upon that, the leak creates an entry point of an environmental impact of an air emission and it is through this air emission were most of our LCA calculations will be based off. The current refrigerant in the U of A Heating and Cooling System is R-134a, an HFC. The alternative refrigerant that is going to be replaced in our system is R-1234yf, which is as well in the class of HFC but has a low GWP of 4. Analyzing the global warming potential to Batts, Sia, Yarnall & Zinyemba Pg. 39
figure out the direct and indirect emission, to yield the total air emission would be how in the family of air emissions our focus will be on. The total emission for the direct and indirect was determined for R-134a and R-1234yf which is shown by the table below assuming that the leakage rate was 2% per year and using factors to convert from power consumption to indirect emissions (Waste Management Excel).
Table 10: R-134a and R-1234yf Total Emission kg CO 2 eq at 2% Leakage Rate
Type of Refrigerant Total Emission kg CO 2 eq R-134a 68,321,233 R-1234yf 889,923,687
Comparing both of the refrigerant one can see that R-1234yf has a much higher total emission than R-134a and due to the fact that after looking more in depth in the Waste Management Excel that the indirect emissions are higher for R-1234yf than for R-134a. The direct and indirect emission came from the equations shown below.
kg CO2 eq Direct Emission ( ) %mass = leakage rate ( ) ∗ refrigerant charge (mass) kgCO2 eq ∗ GWP ( kg CO2 eq Indirect Emission kg CO2 = conversion factor ∗ compressor power (kWh ) ℎ 365 days ∗ melting ice (14 hrs ) ∗ ( )
The driving force in these calculations the indirect is bigger than the direct emission and when leakage starts to leak it becomes an independent variable and the overall total emission becomes the dependent variable. The more the leakage greater than 2% in the U of A Cooling Batts, Sia, Yarnall & Zinyemba Pg. 40
System, the worse the environmental impact since more kg of CO equivalent are being released into the atmosphere increasing the greenhouse effect. Below is a graph of the Leakage Rate vs.
Total CO 2 Emission and graphing that data, we were interested to see where the two refrigerants intersect. Fig. 1: Leakage rate vs. Total CO 2 Emissions
1.00E+18 1.00E+17 1.00E+16 1.00E+15 1.00E+14 1.00E+13 1.00E+12 1.00E+11 1.00E+10 R134a 1.00E+09 1.00E+08 1.00E+07 R1234 1.00E+06 yf 1.00E+05 1.00E+04 Total CO2 Emission (kg CO2) 1.00E+03 1.00E+02 1.00E+01 1.00E+00 10% 100% 1000% 10000% 100000% 1000000% Annual leakage rate (%)
The intersection occurs at (1010%, 5.93* 10^8 kg CO2 eq) for R-134a and at (1010%,
9.20*10^8 kg CO 2 eq). This means that for R-134a, the leakage rate has to be so drastic over 1010% for it to be worse for the environment than R1234yf. Once it goes over the 1110%, R- 1234yf is the better refrigerant to use. Using the common sense initiative, from the Federal Pollution Prevention Act of 1990, it makes sense that if one wanted to keep R134a, leakage rate prevention could be implement to have less of an environmental impact. As the refrigerant leaks it is not only CO2 that is the only emission pollutant that is present. There are many others like PM 10 , NO x , SO x , CO, and VOC. Looking at those pollutants, another environmental impact category is the acidification potential (AP). Acidification originates from the emissions of sulfur dioxide and oxides of nitrogen. In the atmosphere, these oxides react with water vapor and form acids which fall down to the earth in Batts, Sia, Yarnall & Zinyemba Pg. 41
the form of rain or snow or as dry depositions. The acidification potential measures the
contribution of an emission substance to acidification. AP is measured in SO 2 eq (Keulenaer, slide 4).Looking at the waste management excel, one can see that R-1234yf will have a lower -7 -6 acidification potential value of 1.37* 10 lb SO 2 eq/kWh than R-134a that has 1.82 * 10 lb SO 2 eq/kWh. The same can be applied as well to photochemical ozone creation potential (POCP), it is an environmental impact that is formed by the reaction of a volatile organic compound and nitrogen oxides in the presence of heat and sunlight (Keulenaer, slide 8). When one looks at R- -7 -6 1234yf, it has a lower POCP value of 5.04*10 lb NO 2 eq/kWh and 1.26*10 lb VOC eq/kWh, -6 -5 whilst R-134a has 6.66*10 lb NO 2 eq/kWh and 1.67*10 lb VOC eq/kWh.
4.6 Hazardous Waste Risk Assessment Analysis The assessment of health effects on workers, the general public, and the environment is often required in hazardous waste management. With attention to chemicals, they can have different environmental pathways from the source (area where the contaminant is released) to the receptor (area accepting this contaminant) (LaGrager, p. 872-873). The source of contamination at the UA Heating and Cooling System, is from the emission of natural gas through the chimneys of the boiler and leakage of refrigerant. The receptors for these two different scenarios are the operators and other workers that come to the U of A Heating and Cooling System to work. To analyze the risk associated of working at the U of A Heating and Cooling System, all the contaminants were looked at the only data that possible to
find was the reference dose value for PM 10 and NO 2. After performing the hazardous index (HI)
calculation for the non-carcinogenic risk of PM 10 and NO 2, the total HI value was 0.41. This value is less was that 1 which meant that this is an acceptable risk. In conclusion, the workers to a larger extent do not have to worry about acquiring any sort of health diseases from working at the U of A Heating and Cooling System.
Section 5. Economic Analysis The University of Arizona currently has three chilling plants. All our data acquired from them like utility costs, number of workers, amount of ice made, etc. are combined for the three plants. So, our thermodynamic and economic calculations were for the three plants combined. If we want to estimate the costs associated with just one plant, then we will divide our numbers by Batts, Sia, Yarnall & Zinyemba Pg. 42
three and round up. We round up to account for roles that cannot be divided evenly by three like managerial and supervisory positions. For our economic analyses, we will be doing the economics of the model plant we created using HFC-134a as if we are building the plant from scratch. We will then do economics for the model plant using the replacement refrigerant, R- 1234yf. The economic analyses we will do include estimating the total capital investment, the operating costs, and the net present value.
5.1 Inflation The equipment costs calculated using equations from Seider et al. use a Chemical Engineering Plant Cost Index (CEPCI) from 2006 with an average value of 500 across various types of equipment. The CEPCI fluctuates every year. In 2014, the average CEPCI across various types of equipment is 576.1 ("Chemical Engineering Plant Cost Index (CEPCI)."). During 2015, this value is slowly declining. However, for our analysis, we will use the relatively higher 2014 CEPCI of 576.1 because the fluctuating market may increase again in the near future. We apply the inflation amount to the bare module costs of the equipment. Since many of the calculations ultimately depend on the value of the total bare module costs of the equipment, the inflation correction factor carries over to them.
5.2 Total Capital Investment A summary of the total capital investments calculations for the refrigerants R-134a and R-1234yf is found in the following figures:
Batts, Sia, Yarnall & Zinyemba Pg. 43
We are conceptualizing the project as a greenfield plant. We are assuming we are building the plant from the beginning and no other chemical plants nearby the UA exist. We are not attaching the refrigeration plant to another chemical plant so it is not an integrated complex. However, since the plant is in the UA or such close proximity to it, the UA has provided the offsite facilities like the cafeteria, offices, etc. The heat exchangers, the compressors, and the pumps are the main types of equipment in the plant. Their purchase prices have been estimated using the equations and formulas from Seider, et al. Their purchase prices calculations are explained in the appendices of this report. We estimate the direct and indirect costs from the materials of installation, the labor of installation, freight, insurance, taxes, etc. by using the bare module factor. We multiplied the purchase cost by the bare module factor to estimate the bare module costs for each piece of equipment. Summing all the bare module cost, we acquire the total bare module cost. For our spares, we do not need any catalysts. The spares we need include extra pumps, one or two for each part of the plant that has a pump. Since the plant will be for a grass-roots system yet is already somewhat connected to the UA, we estimated the site preparation costs to be at the lower end of the range, to be around 10% of the total bare module cost. The cost of building the buildings is also estimated to be 10% of the total bare module investment. Since the chilling plant would be located near the University of Arizona, we do not need to build additional cafeterias and medical clinics, and utility lines would not be as expensive. So our service facilities costs are smaller. We estimate it to be 5% of the total bare module investment. Whatever power we need comes from Tucson Electric Power or from burning our own natural gas. The latter is not an offsite plant but exists within the plant. So, we do not have allocated costs for utility plants. We also do not have allocated costs for waste disposal because Batts, Sia, Yarnall & Zinyemba Pg. 44
we either dispose our waste through University of Arizona or treat it within the chilling plant. As a result, we do not allocate for utility plants and related facilities. The total direct permanent investment is the sum of the total bare module investment, the cost of the buildings, and the cost of site preparations. We allocate 3% of the direct permanent investments to the contractor fee, while 35% to contingencies. We use 35% because more unaccounted costs may occur since we are at an early stage in development for this plant. We did not choose 100% because the project is not entirely new and it is many parts of the process are already understood. The sum of the direct permanent investments, contingencies, and contractor fee is the total depreciable capital. According to Seider, the cost of land can be approximated to be 2% of the total depreciable capital. Our process does not have any patents associated with it so we do not have costs associated with royalties. In regards to startup, since running the refrigeration system is independent of other plants and current employees at the UA refrigeration plant already knows the refrigeration process very well, then the cost of plant startup can be approximated to be 2% of the total depreciation capital. Summing the total depreciable capital, the cost of land, and cost of plant startup gives us the cost of total permanent investment. Since the refrigeration plant is to be built near UA, which is located in the U.S.
Southwest, then according to Table 22.13 of Seider et al., the investment site factors, FISF , is
0.95. The FISF takes into account the inherent differences between locations such as differences in standard of livings, differences in laws, etc. Multiplying the investment site factor by the total permanent investments gives us the corrected or adjusted total capital investment. For our working capital, we estimated it by taking 1/12 or a month of the yearly operating cost (will be discussed later) without depreciation. We then add to this number the initial cost of our refrigerant. This amount should cover the initial expenses of the plant before the revenue comes in. The working capital would be recovered at the end of the plant’s life. However, realistically, the value of the used refrigerant in the system would be lower than unused refrigerant. Summing the adjusted total permanent investment and the working capital gives us our desired total capital investment. We estimated the total capital investment for R-134a to be around $310 million while we estimated it to be much higher, around $1.6 billion for R-1234yf. Batts, Sia, Yarnall & Zinyemba Pg. 45
5.3 Total Production Cost / Operating Cost A summary of the total production cost, also known as, operating cost for refrigerant R- 134a and R-1234yf is found on the figure below:
Batts, Sia, Yarnall & Zinyemba Pg. 46
5.4 Feedstock and Utilities The feedstock is the added refrigerant lost through leakage in the system over time. We assumed that the annual leakage is 2% of the refrigerant (P. Blowers). To get the amount of annual leakage, we need the mass of the refrigerant in the system. The UA has 21 machines with some using refrigerant R-134a and some using refrigerant R-123 (Questions UA Cooling System). The machines that use R-134a have around 6200 lbs R-134a per machine (Questions UA Cooling System). The machines that use R-123 have around 3700 lbs R-123 per machine (Questions UA Cooling System). However, we do not know how many machines are associated with each refrigerant. So, we took the average of the mass of refrigerants per machine and multiplied it by 21 machines to estimate the total mass of the R-134a for the plant. We then calculated the residence time of R-134a in the system by dividing the calculated total mass by the flow rate of R-134a. We calculated a residence time of about 54 s. We assumed the residence time to be constant regardless of the refrigerant used. We multiplied the flow rate of R-1234yf by the residence time to acquire the mass of the R-1234yf in its system. Afterwards, we use the 2% annual leakage rate to calculate the annual leakage mass. We then multiply the price of each refrigerant to acquire the initial cost and yearly costs for each refrigerant. The feedstock of warm feed water coming in from the UA buildings was approximated using the cooling water equation in Seider et al. (Seider et al, p604, Table 23.1). We used the cooling water equation because according to Seider, the cooling water is estimated to be at 90 oF which is close to the 80 oF return temperature as constrained by Dr. Blowers (Blowers personal interview). Since there is no accumulation of water in the system, the flow rate of the warm water into the system is the same flow rate as the chilled water leaving the system. The daily amount of energy to make ice at 32 oF from liquid water at 32 oF in 14.75 hours at 910 tons per hour is the same daily amount of energy needed to cool feed water from 80 oF to 42 oF, by conservation of energy (Questions UA Cooling System ). So, we calculated the amount of water that can be cooled per day, hence the flow rate. One third of the cooling water in the cooling tower is assumed to evaporate to cool the refrigerant in the condenser (P. Blowers). So, taking a third of the water flow rate through the condenser calculated before, 14.75 hours of ice making time per day, and using the same cooling water equation in Seider et al. as mentioned in the previous paragraph, we calculated the cost of cooling water in the cooling tower. Batts, Sia, Yarnall & Zinyemba Pg. 47
The electricity cost per year and the natural gas cost per year for the current system of the UA chilling plants which uses R-134a are $14 million and $12 million respectively (Questions UA Cooling System). To estimate the yearly cost of electricity and gas for the system that uses R-1234yf, we assumed that the compressor demands the most significant power in the entire plant so the power usage is approximated solely by the compressor. We calculated the price per year per kilowatt for R-134a using the numbers that we have and assumed the same price per year per kilowatt for the R-1234yf. Multiplying the compressor power of the R-1234yf and using the same ratio of electricity and gas cost as the R-134a, we estimated the R-1234yf’s yearly cost of electricity and gas to be about $185 million and $159 million respectively.
5.4.1 Operations (Labor-related) The current UA chilling plants’ number of employees and their wages are estimated from the number of employees and their total income working under the Facilities Management – Utilities department. These values are assumed to hold for the R-134a plant. We estimated the number of workers and salaries for the R-1234yf plant by taking ratios using the respective total number of equipment for the two refrigerants. According to Seider, the direct salaries and benefits is estimated to be 15% of the direct wages and benefits, and the operating supplies and services is estimated to be 6% of the direct wages and benefits (Seider et al., p604, Table 23.1).
5.4.2 Maintenance To ensure that the process equipment function properly, maintenance personnel regularly inspect, clean, and test the equipment. The maintenance costs include the wages and benefits which depends on our type of process which in our case is fluid handling process, the salaries and benefits of the maintenance crew, the materials and services, and the maintenance overhead (Seider et al., p604, Table 23.1). The wages and benefits associated with the fluid handling process are estimated to be 3.5% of the total depreciable capital (Seider et al., p604, Table 23.1). Taking the resulting amount, 25%, 100%, and 5% of that goes to salaries and benefits, materials and services, and maintenance overhead, respectively.
5.5 Direct Manufacturing Cost The direct manufacturing costs are the sum of feedstock, utilities, operations, and maintenance expenses. Batts, Sia, Yarnall & Zinyemba Pg. 48
5.5.1 Operating Overhead Operating overhead are costs not associated directly with the manufacturing of the product, but the company still spends. It is estimated as a fraction of the labor related operations and the maintenance expenses. We used the fractions suggested by Seider et al (Seider et al., p604, Table 23.1).
5.5.2 Property Taxes and Insurance According to Seider, annual property tax is estimated by 1% of the total depreciable capital in low population areas and 3% in high population areas (Seider et al, p612). Since the chilling plant is for the University of Arizona, so it is near UA, many students live near there so we estimate the property tax to be 2% of the total depreciable capital. According to Seider, the insurance costs is around 0.5 to 1.5% of the total depreciable capital, depending on the pressures, temperatures, explosion risks, etc. (Seider et al, p612). Our chilling plant has streams with high pressures and temperature after compressing the refrigerant and has streams with low temperatures, particularly after flashing the refrigerant. So, we estimate the insurance costs to be around 1% of the total depreciable capital. So, a total of 3% of the total depreciable capital goes to property taxes and insurance.
5.5.3 Depreciation We used a simple straight line depreciation of all our total depreciable capital over ten years. So, our depreciation is 10% of our total depreciable capital each year for ten years. We assumed a zero salvage value after the 10 years even though the plant is expected to operate for 20 years.
5.5.4 Rental Fees and Licensing Fees We assume that the UA chilling plant do not have rental fees for offices since we assume that The University of Arizona already has existing office spaces for the overseers of the project. Once the plant is complete, the workers will have offices inside the plant so no office rentals are needed. Since our refrigeration process is not patent protected, then we do not have licensing fees.
5.5.5 Fixed Costs The fixed costs is the sum of the costs from property taxes, insurance, and depreciation. Batts, Sia, Yarnall & Zinyemba Pg. 49
5.5.6 Cost of Manufacture The cost of manufacture is the sum of the direct manufacturing costs, total operating overhead, and the fixed costs.
5.5.7 General Expenses The chilling plant’s consumer is solely The University of Arizona. As such, the selling and transfer expenses is only the transportation of the chilled water from the plant to the rest of the university. So, we estimated this value to be 1% of the sales revenue (Seider et al, p604, Table 23.1). Note that the sales revenue estimation will be discussed later in the net present value subsection. The direct research and allocated research is estimated to be 4.8% and 0.5% of sales respectively (Seider et al, p604, Table 23.1). We allocate some money to research to continually improve the process and for potential discovery of innovative ways to produce chilled water and cool the UA buildings. Administrative expenses and management incentive compensation is estimated to be 2% and 1.25% of sales (Seider et al, p604, Table 23.1). We allocate money here to cover the costs not directly involved in manufacturing the chilled water but still required for the operation of the plant. The management incentive compensation is for bonuses that accompanies outstanding work. The sum of the selling and transfer expenses, direct and allocated research, administrative expenses, and management incentive compensation is the total general expenses.
5.6 Total Production Cost The total production cost is the sum of the cost of manufacture and the total general expenses. We estimated that the yearly total production cost for R-134a is around $100 million while we estimated it to be around $730 million for R-1234yf.
5.7 Net Present Value The calculations for acquiring the net present value can be found in the submitted excel spreadsheet. This is presented in the following figure: Batts, Sia, Yarnall & Zinyemba Pg. 50
The operating life of the chilling plant is assumed to be twenty years. We also assume that it takes three years to build the chilling plant with a third of the total depreciable capital expended each year of the three years. So the total plant life from start to finish is 23 years. The cost of the working capital and the value of the depreciation are as described above. Since we are depreciating only for 10 years with no salvage value, we start our depreciation on year 4 of the 23 years and we end after 10 years, on year 13. The net earning is calculated using an assumed state and federal tax of 37%. Note that the taxes are applicable only if the net earning is positive. When calculating the cash flow, we add the amount depreciated to the net earnings because the depreciation was taken out when calculating the net earnings. This method enables Batts, Sia, Yarnall & Zinyemba Pg. 51
the plant to not pay taxes on the amount equal to the amount of depreciation. So that amount goes to the cash flow into the company. The discount factor used to adjust the cash flow to present value is calculated using a nominal interest rate of 5%. This interest rate depends on the company and is usually 15% (Seider et al, p633). However since this is in a way a utility plant, then we estimate it to be 5% (Ogden personal interview). The value of this interest rate strongly affects the present value, and therefore affects the cumulative net present value.
5.8 Sales Revenue The sales revenue impacts the profitability of the chilled plant. We calculated the sales revenue of chilled water using the chilled water equation, 40 oF, from Seider et al (Seider, et al., p604,Table 23.1). We used the same flow rate of water as the “warm” feed water discussed above in the feedstock and utilities section because of conservation of mass. This flow rate is one of the constraints in the problem statement and is constant regardless of the used refrigerant. We calculated the revenue of chilled water per year to be around $22 million (See: Operating Cost and Capital Cost and NPV sheet) .
5.8.1 Impact of Sales Revenue Using the calculated $22 million in sales revenue, we quickly see that for both refrigerants, the production cost is higher than the revenue. The total production cost is around $100 million for the R-134a while it is around $730 million for the R-1234yf (See: Operating Cost and Capital Cost and NPV sheet). So our net earnings is negative. So, we do not pay state and federal taxes. Also, our net present value is always negative. So, the chilling plant should not be built regardless of the refrigerant. However, the sales revenue can be adjusted. The chilling plant is the only refrigeration provider to The University of Arizona. So, it can more easily increase the prices of the output chilled water compared to other kinds of plants which have many competitors. So keeping everything else constant (state and federal tax is 37%, nominal interest rate is 5%), we can compute, using Excel’s Solver, the sales revenue required so that the cumulative net present value at the end of the plant’s life is zero. For the R-134a plant, the yearly sales revenue must be around $105 million while for the R-1234yf plant, the yearly sales revenue must be around $750 Batts, Sia, Yarnall & Zinyemba Pg. 52
million (See: Operating Cost and Capital Cost and NPV sheet). In this case, since the cumulative net present value of the plant is zero at the end of the plant’s life, the investor’s rate of return (IRR) is equal to the nominal interest rate chosen of 5%. This is presented in the following figure:
5.9 Economic Hazards The economic hazards involve the raw materials: water and refrigerant and the product: chilled water. In the evaporative cooler, we evaporate around 400 million gallons of water every year for the R-134a and around 5.8 billion gallons of water every year for the R-1234yf (See: Operating Cost and Capital Cost and NPV excel). A four member American family, on average, uses 400 gallons per day ("Indoor Water Use in the United States."). So the R-134a plant uses Batts, Sia, Yarnall & Zinyemba Pg. 53 about the same amount of water per year as 3,000 American families while the R-1234yf plant uses about the same amount of water per year as 40,000 American families. This is a lot of water especially considering that the chilling plant would be built in the Sonoran Desert. The amount of water that would be used is an economic hazard since the government may levy a heavy fine on the plant for consuming water above a certain maximum. A way to mitigate this potential economic hazard would be to develop technology to use treated wastewater instead of drinking water in the cooling tower condenser. Another economic hazard would be consuming too much electricity from Tucson Electric Power (TEP). Currently, TEP limits the amount of electricity The University of Arizona chilling plant uses otherwise, TEP will fine the UA. The university currently uses R-134a which has a lower energy requirement instead of the R-1234yf which requires more energy. If the chilling plant that uses R-1234yf would be built, then UA will surely exceed the maximum energy usage currently imposed by the UA. In order to mitigate this economic hazard, a new agreement with TEP must be made to allow UA to use more energy without the penalty. Otherwise, UA must acquire the additional required energy from burning more of its own natural gas. Economic hazard from the type of refrigerant used also exists. The current R-134a refrigerant may be banned soon in large scale refrigeration systems because of its environmental impacts (Blowers personal interview). So we are looking for an alternative refrigerant to replace R-134a. But as we have seen in the case of R-1234yf, the cost to build and operate this R-1234yf plant is too high. The economic hazard would be that it is too expensive to actually build and operate a plant that uses the R-1234yf. To mitigate this hazard, UA ought to focus on reducing the leakage rate and prevent R-134a from getting banned by arguing that the focus must be on reducing the leakage rate and that the alternative is too expensive. Another way to mitigate this hazard would be to develop a better refrigerant that would not only have less impact to the environment, but also the plant that uses this refrigerant must also be cheaper to build and operate. In fact, reducing the leakage rate to be close to zero may reveal that some already banned refrigerants may have lower environmental impact than currently allowed refrigerants for this type of applications. Another economic hazard would be from the product: chilled water. The plant produces chilled water with the purpose of cooling the UA buildings. The cold air from this chilled water is indispensable; people will always want, and in some cases, need it. Since the UA has no Batts, Sia, Yarnall & Zinyemba Pg. 54
competitor for this product, it can increase the price of chilled water relatively easily. However, if the price of UA’s chilled water becomes too high, then the UA will search for alternative sources of cold air. They may conduct calculations and find that individual air conditioning units are cheaper than the chilled water approach. Although finding the cheapest option is good for the UA, the chilling plant’s chilled water demand would become zero. This is the economic hazard. To mitigate this hazard and ensure that the UA will “buy” the plant’s chilled water, we must keep the price of the plant’s chilled water low. So, we must produce it cheaper. So, we need to do the same things as discussed in the refrigerant economic hazard in the previous paragraph.
5.10 Future Work: Reducing Costs to Optimize the Process The total bare module costs of the equipment is high for both R-134a and R-1234yf. Many of the estimations for the other expenses in both the total capital investment and the operating costs are based ultimately on the amount from the total bare module costs. However, the total bare module cost associated with the R-1234yf is around 5 times higher than that associated with the R-134a. Also, the total bare module costs is related to the number of equipment the plant needs. So for future work, reducing the number of equipment the plant needs is the primary way to cut costs and optimize the process. Looking at the fraction of each cost that comprise the operating cost to the total production cost, we see that the cost of electricity and natural gas are the most significant. It comprises a total of 26% of the total production cost for the R-134a plant while it comprises a total of 47% of the total production cost for the R-1234yf plant. We, for our future work, would also concentrate in reducing these costs to continue optimizing the process. Specific optimization would include increasing the compressors’ efficiencies since they consume the most energy. An area where the estimated costs can be reduced is the estimated contingencies. We estimated contingency to be 35% of the total direct permanent investment. We chose this fraction because according to Seider et al, designs that are in their preliminary stages like student designs require 35% (Seider, et al., p551). In our future work, we can reduce this 35% by optimizing the economic analysis and acquire costs estimates closer to actuality. Thus, the 35% estimated contingencies would be lower and would cut that cost. Batts, Sia, Yarnall & Zinyemba Pg. 55
Section 6. Conclusions and Recommendations As regulatory bodies continue to develop policies that promote the usage of environmentally sustainable chemical products and processes, it is imperative that wise decision- making takes into account the holistic effects of new regulations. In this report, the future banning of 1,1,1,2-tetrafluoroethane (R134a) as a refrigerant for the UA district cooling system has been analyzed and discussed. Although the research and design presented in this report is not a complete discussion of all aspects of the problems of environmentally sustainable refrigeration systems, there are a number of key conclusions that can be drawn from this study. Perhaps the most crucial result of this study is the identification and analysis of the best existing replacement for R134a. At this point in time, the best replacement for R134a in the UA district cooling system is R1234yf, which is also the R134a replacement currently promoted by the worldwide automobile industry. Unfortunately, replacement of R134a with R1234yf is is inadvisable because of the following reasons: 1) The financial costs of an R1234yf system greatly exceed those of an R134a system. As discussed at length in Error! Reference source not found. , an R1234yf system would require both greater capital costs and greater operating costs than an R134a system. Fundamentally, the high costs of an R1234yf system stem from its fundamental thermodynamic deficiencies, leading to a low COP value. The R1234yf system costs are roughly an order of magnitude greater than those of an R134a system. 2) The total greenhouse gas emissions of an R1234yf actually exceed those of an R134a system. Although R1234yf has a negligible GWP, it has poor suitability as a refrigerant in the temperature range in which the UA plant operates. This leads to very high indirect emissions from the power required to run the system. As shown in Section 4, the crossover point for which the R1234yf system is environmentally advantageous occurs around a leakage rate of 1000% per year. This leakage rate is extremely high and in practice, leakage rates are often 10% per year or less. Under typical leakage rates, an R134a system would actually be more environmentally friendly than an R1234yf system despite the high GWP of R134a. 3) In the case of UA, an R1234yf would require more equipment and an expanded footprint. In addition to the cost of expanding the UA central chilling plants, space Batts, Sia, Yarnall & Zinyemba Pg. 56
would become a concern as footprint demands for the chilling plant would compete with footprint demands for classroom and administrative buildings. After studying this problem at length, it can be concluded that at present, there does not currently exist a suitable replacement for R134a for this application. Although it is desireable to reduce the usage of R134a due to its very high GWP, there simply is no better alternative product currently available. As next-generation refrigerants continue to be developed, similar analysis should be carried out on these alternative refrigerants to determine if any of them offer better results than R134a. If R134a is banned before a suitable replacement is developed, a central chilling facility producing chilled water to be circulated through radiators may no longer be the most viable way to provide climate control for the university. We recommend that other alternatives be considered before making the decision to redesign the existing central chilling facility to use a different refrigerant. Other options that were not studied in this report include: • Room air-conditioning units or building air-conditioning units instead of a centralized system. These systems generally use the outside air as a heat sink instead of chilled water, which means they operate in different temperature and pressure regimes. This change in temperature and pressure regime means that other, potentially more efficient or more environmentally-friendly, refrigerants could be used. Currently, this approach is far more expensive than a centralized system using R134a, so it is not currently employed. • Water evaporative coolers (also known as swamp coolers) for each building, which are not currently used because of their inability to provide effective cooling when the ambient humidity is high. However, they are inexpensive and environmentally benign. • Passive temperature control. In the future, new buildings could be designed with architecture that minimizes their need for cooling capacity. In addition to concrete recommendations for the UA central chilling system, this study carries important implications for national and international climate policies. Firstly, although it is a potent greenhouse gas, R134a should not be banned for applications in the same temperature range as the UA central chilling network. There is no currently available alternative better than R134a. Developing an effective R134a replacement is a desirable goal. To this end, more research should be carried out on modelling, developing, and producing next-generation Batts, Sia, Yarnall & Zinyemba Pg. 57
refrigerants that provide high COP values while having low ODP and GWP. If the US federal government wishes to tackle this source of greenhouse gas emissions, it should aggressively fund research and development in this area. In the meantime, rather than banning specific compounds with high GWP, like R134a, policymakers should consider placing overall greenhouse gas emissions caps on facilities. An overall cap on GHG emissions, both indirect and direct, would provide the desired emissions reduction, while providing facilities with the freedom to choose the most effective path toward this goal. As emissions caps become progressively more restrictive over time, the University of Arizona would be able to select between several attractive options, such as the following: • Replacement of R134a with a more benign refrigerant, if a suitable candidate is developed in the future. • Invest heavily in advanced leak-detection and leak-prevention technologies, like automated sniffer and scrubber equipment or tertiary leak containment, greatly reducing R134a leakage. • Make no changes to the UA central chilling plant, but instead update building infrastructure and/or climate control conditions in order to reduce the total amount of cooling capacity required. If these policy goals are aggressively pursued over the next few decades, we expect that it will be possible to drastically reduce greenhouse gas emissions from the UA central chilling plant and similar facilities nationwide. However, at current technological levels, continued restrictions on the use of R134a as a refrigerant are counterproductive and inadvisable, and organizations that rely on R134a in similar applications should lobby the EPA, the European Commission, and other regulatory bodies accordingly.
Section 7. References
2016 New Refrigerant R1234yf. Alibaba.com . N.p., n.d. Web. 25 Apr. 2016.
"Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importers ." Alibaba Manufacturer Directory - Suppliers, Manufacturers, Exporters & Importers . Web. 27 Apr. 2016.
Blowers, P, K.F. Tetrault and Y Trujillo-Morehead. "Estimation of gas-phase heat capacities for hydrofluoroethers with two carbon atoms." Ind Eng Chem Res (2007): 6600-6604.
Blowers, Paul. Personal communication L Yarnall. 3 February 2016.
Calm, James M., P.E., and Glenn C. Hourahan, P.E. "Refrigerant Data Summary." Engineered Systems 18.11 (2001): 74-88. Print.
"Calculating the Carbon Footprint." Materials Today 11.3 (2008): 61. Leiceistershire County Council. Web. 10 Apr. 2016.
"Dupont Instruments." Analytical Chemistry Anal. Chem. 39.3 (1967): n. pag. Web. 3 Apr. 2016. DuPont Suva. "Thermodynamic properties of Dupont Suva 410a refrigerant." Technical Information. n.d. DuPont Suva. Thermodynamic Properties of HFC-134a . Technical Information. Wilmington, DE: DuPont Fluorochemicals, 2004. Elliott, J Richard and Carl T Lira. Introductory Chemical Engineering Thermodynamics . Pearson Education, 2011. Print. "EPA Releases New Delisted Refrigerant List - HVAC.com." HVAC.com . N.p., 10 Sept. 2015. Web. 05 Apr. 2016.
Greenhouse Gas Protocol. "Global Warming Potentials." Greenhouse Gas Protocol, n.d. Web. 10 Apr. 2016.
"Publication 946 (2015), How To Depreciate Property." Publication 946 (2015), How To Depreciate Property . IRS.gov, n.d. Web. 05 Apr. 2016.
Woodside, Gayle. Hazardous Materials and Hazardous Waste Management: A Technical Guide . New York: Wiley, 1993. Print. Yang, Changsheng, et al. "Excess Molar Volumes, Viscosities, and Heat Capacities for the Mixtures of Ethylene Glycol + Water from 273.15 K to 353.15 K." J. Chem. Eng. Data (2003): 836-840. Yokozeki, A, H Sato and K Watanabe. "Ideal-gas heat capacities and virial coefficients of HFC refrigerants." Int. J. Thermophys (1998). 89-127. Yokozeki, A, H Sato and K Watanabe. "Ideal-gas heat capacities and virial coefficients of HFC refrigerants." Int. J. Thermophys (1998). 89-127.
Section 8. Appendices
8.1 Calculations
8.1.1 Core thermodynamic model A computational thermodynamics model was constructed in Excel to compare the different alternative refrigerants studied in this report (see the uploaded Excel spreadsheet “Computational thermodynamics model – final.xlsm” and 8.3, which details the extensive VBA code working behind-the-scenes in this spreadsheet).
8.1.1.1 Cooling tower parameters The performance of the cooling system depends greatly on the environment in which it must run. Because Tucson is much warmer and drier than a typical location, the cooling tower temperature parameters differ from those found in chemical engineering heuristics. We designed for the worst-case conditions that the system would likely have to endure: a record high temperature with moderate humidity. National Weather Service records put Tucson’s record high at 117 °F (National Weather Service). In the Tucson summer, the humidity is typically very low unless it has rained recently, in which case the temperature will be lower and the conditions less stressful. Therefore, we assumed a low-moderate humidity level of 20% relative humidity. The wet-bulb temperature was determined from psychometric charts for water (Felder and Rousseau). Air conditions were traced along an adiabatic evaporation line from the ambient Batts, Sia, Yarnall & Zinyemba Pg. 64
conditions to 100% humidity, representing a cooling tower outlet at equilibrium. The worst-case wet-bulb temperature was determined to be 81 °F, which was used as the outlet temperature of the cooling tower.
8.1.1.2 The refrigeration cycle and its parameters The core thermodynamics of the refrigeration cycle were modeled by a modified Standard Vapor-Compression Cycle, which reflects the energy flow of refrigeration equipment with a high degree of accuracy (Stoecker). The Standard Vapor-Compression Cycle is diagrammed below in Fig. 7: Fig. 7: The Standard Vapor-Compression Cycle (Stoecker pg. 55)
In the Standard Vapor-Compression Cycle, heat is removed from the source via the isothermal evaporation of the refrigerant in the evaporator until the refrigerant is a saturated gas at the design temperature of the evaporator. The refrigerant is then directed into a compressor and compressed at constant entropy to the condensing pressure. The assumption of constant entropy is, of course, an idealization in which the compression work is reversible; our modified cycle accounts for nonideality by introducing a compressor efficiency. The work of the compressor superheats the refrigerant beyond the vapor saturation point. The refrigerant then enters a condenser, where it is cooled and then condensed at constant pressure to its vapor saturation point, dumping the source heat and the compressor work into the Batts, Sia, Yarnall & Zinyemba Pg. 65 heat sink. Leaving the condenser, the refrigerant is flashed adiabatically through an expansion valve in order to achieve the low temperature required to draw energy away from the heat source. The Standard Vapor-Compression Cycle is diagrammed on a pressure-enthalpy diagram below in Fig. 8: Fig. 8: Pressure-enthalpy relations in the Standard Vapor Compression Cycle (Stoecker pg. 55)
Although our calculations were based upon the Standard Vapor-Compression Cycle, we accounted for nonideality in the following ways: 1. Real compression is not isentropic. As described below, we adjusted for nonideality by first calculating the ideal compression work, and then using a correction factor to account for the efficiency of the compressor. 2. Real refrigeration systems often heat or cool the refrigerant beyond the vapor saturation point, leading to a superheated vapor entering the compressor and a supercooled liquid entering the flash vessel. Preliminary calculations showed the sensible heat involved in superheating or supercooling the refrigerant to be many orders of magnitude less than the Batts, Sia, Yarnall & Zinyemba Pg. 66
latent heat of vaporization or condensation, so this nonideality was neglected to simplify the analysis. 3. Frictional losses in the heat exchangers and piping lead to pressure drops in a real system. Chemical engineering heuristics suggest pressure drops of about 1.5 psi for boiling and condensing fluids (Seider, Seader and Lewin). These pressure drops were neglected because they are much lower than the pressure increases and drops from the compressor and flash vessel of more than 235 psi. Accounting for frictional losses would have led to slightly (less than 2%) higher power requirements at the compressor.
The parameters for the refrigeration cycle were as follows: 1. The evaporation temperature was set by the freezing temperature of our heat exchange medium (NIST), adjusted by a 20 °F heat exchanger approach, as suggested by chemical engineering heuristics (Seider, Seader and Lewin). The resulting evaporation temperature was 251 K. 2. The condensation temperature was an iterable variable used in both the core thermodynamics and the condenser pinch analysis, and was varied until the model converged (see VBA code to accompany Excel spreadsheet “Computational thermodynamics model – final.xlsm”). 3. The refrigerating capacity (i.e. the energy removed from the heat source) was calculated by a heat balance on the current operating conditions. 4. The vapor saturation pressure of the refrigerant at the evaporation temperature was used as the system low pressure. The system high pressure was analyzed at 16, 32, and 64 atm, corresponding to 2, 3, and 4 stage compression, assuming a typical compression ratio of 4 and a low pressure equal to atmospheric pressure (Seider, Seader and Lewin). In general, increasing the system high pressure decreases the system efficiency (due to the nonideality of the compressor), so we used the lowest number of stages that would lead to the model converging in any particular case.
8.1.1.3 Refrigeration cycle calculations The refrigeration cycle model contains interrelated expressions based around the unit operations of refrigeration: compression, flash, condensation and evaporation. Batts, Sia, Yarnall & Zinyemba Pg. 67
8.1.1.3.1 Compression Beginning at the compressor (the process between points 1 and 2 on Fig. 7 and Fig. 8), the expression for the isentropic work of compression was derived from thermodynamic principles. The second law of thermodynamics relates the change in entropy to the system’s heat and temperature:
= Meanwhile, the first law of thermodynamics relates the change in internal energy to the work and heat provided to the system.
dU = δq + δw = δq − PdV Replacing the heat term in the second law with the expression from the above equation yields:
dS = Expressing the internal energy change as a function of temperature gives:
dS = + Replacing the pressure and temperature in the second term using the ideal gas law leads to:
dS = + For an ideal gas, Cp = Cv + R, so:
dS = + − Taking the total differential of the ideal gas law,
RdT = d(PV ) = VdP + PdV And from the ideal gas law,
T = Including these relations in the derivation leads to:
dS = + − − = −
Substituting this relation into the derivation and setting the entropy change to zero for an isentropic process leads to: Batts, Sia, Yarnall & Zinyemba Pg. 68
∆S = 0 = − Rln T1 and P 1 are the vapor saturation point leaving the evaporator, as described above in The refrigeration cycle and its parameters. The upper pressure P 2 was a model parameter. Eqn. A.1.3.1-10 then permits one to calculate the upper temperature of the compressed vapor in the isentropic case. This relation was implemented in VBA as shown in Subroutine IdealCompHighT. The isentropic work was calculated by determining the sensible heat required to increase
the refrigerant’s temperature from T 1 to T 2. Depending on the particular refrigerant considered, different empirical expressions were used to relate heat capacity to temperature. This calculation was implemented in VBA as shown in Function SensibleHeatGas. The isentropic work was adjusted for nonideal, polytropic conditions via an efficiency factor, η.
ηW = W Then, the nonideal compressor exit temperature was determined by iteratively considering exit temperatures until finding one for which the sensible heat required was equal to the real compressor work. This calculation was implemented in VBA as shown in Subroutine NonIdealCycleCalc. The real compressor power was then calculated by the following relation:
= ∗ 8.1.1.3.2 Flash In our analysis, the flash of the refrigerant from high to low pressure was assumed to be isenthalpic (adiabatic). An isenthalpic flash maintains the system enthalpy constant while the temperature of a liquid drops. The heat removed via the temperature drop serves to partially vaporize the liquid. Since enthalpy is a state function, the transition between the two thermodynamic states can be conceptualized as a sum of any set of paths that connect the two states. The computationally simplest path for a flash vaporization consists of first cooling the liquid to the second temperature, followed by a partial vaporization to the second pressure. The enthalpy balance becomes:
ℎ = ℎ Batts, Sia, Yarnall & Zinyemba Pg. 69
C dT = x ∗ ΔH where x is the vapor quality. The quality out of the flash vessel was derived from a heat balance to be
= ∆
8.1.1.3.3 Condensation The heat duty at the condenser was calculated as the sum of the heat absorbed at the evaporator and the additional heat added by the compressor.
Q = Q + P In our design, the condensers use water cooling towers as heat sinks. A one-pass water vaporization ratio of 1/3 was chosen as a compromise value between two competing desires: to reduce the flowrate and hence the power to the pumps on the water side, and to increase the flowrate in order to avoid steam film dynamics and maintain effective heat transfer coefficients. This vaporization ratio is effective in industrial practice (P. Blowers). In practice, the actual vaporization ratio will be somewhat different depending on the atmospheric temperature and humidity. New tap water was assumed to enter the system at 75 °F. A schematic of the condenser temperature profile is displayed below in Fig. 9. Condenser dynamics were analyzed by defining heat balance functions for each segment of the heat exchanger, and then iteratively changing the parameters until the minimum approach temperature was achieved and the results converged with the core thermodynamic calculations (see 8.3). Batts, Sia, Yarnall & Zinyemba Pg. 70
Fig. 9: Temperature profile across condenser
Heat balances provided the following relations:
= ∗ = = ( ∗ + )
= ∗ ∗ = = ∗ where v is the single-pass vaporization ratio for water.
8.1.1.3.4 Evaporation The heat duty of the evaporator was assumed to be equal to the refrigerating capacity. The rate at which refrigerant evaporates in the evaporator is the ratio of the refrigerating capacity and the refrigerant’s latent heat of vaporization:
m = ∆ Batts, Sia, Yarnall & Zinyemba Pg. 71
Because only the liquid remaining after the flash can provide refrigerating capacity through evaporation, the net recirculation rate of refrigerant is the quotient of the evaporation rate and the quality out of the flash vessel.
= The heat balances along the exchanger are similar to those for the condenser, except that the refrigerant is isothermal and the EG25 heat transfer medium does not vaporize. The resulting temperature profile is displayed below in Fig. 10. . Fig. 10: Temperature profile across evaporator
The heat balance becomes
= ∗ = = ∗ Batts, Sia, Yarnall & Zinyemba Pg. 72
8.1.1.3.5 Other thermodynamic and refrigeration cycle calculations Vapor-saturation relations were modelled with varying forms of Antoine’s Equation, which has the general form
log P = A + where P sat is the vapor saturation pressure and T is the temperature. The specific forms and constants used for each compound are available in 8.4. Vapor and liquid heat capacities were estimated by empirical relations also available in 8.4. Latent heats of vaporization were estimated by the Clausius-Clapyeron equation, which relates the change in saturation temperatures and pressures to the heat of vaporization (Elliott and Lira):
∗ ΔH = One useful measure of a refrigerant’s thermodynamic suitability is the Coefficient of Performance (COP), which is the ratio of the refrigerating capacity achieved to the energy expended, and is a measure of the system’s efficiency. A higher COP implies that the system is more efficient.
=
8.1.2 Heat exchanger sizing Heat exchangers were sized with the following equation:
= ∗ where A is the exchanger area, U is the overall heat transfer coefficient, and ∆TLM is the log mean temperature difference:
Δ = In evaporating or condensing systems, the heat transfer resistance on the refrigerant side greatly exceeds that of the other side because of mixed-phase film phenomena (Stoecker). Therefore, we simplified the analysis by neglecting the resistances from the heat transfer medium and from the heat exchanger wall and instead used representative evaporation and condensation Batts, Sia, Yarnall & Zinyemba Pg. 73
heat transfer coefficients for similar systems (Seider, Seader and Lewin) (Cavallini, Censi and Del Col).
8.1.3 Pump sizing The same procedure was used to size the various pumps required in our analysis. First, the required pump head was calculated as the sum of head from different sources:
= + Δℎ + + where the terms on the right side of the equation are the head due to differences in kinetic energy, potential energy, flow work, and friction, respectively. The contributions of kinetic and potential energy changes were estimated using the terms in the above equation. The head loss due to flow work through heat exchangers was estimated using chemical engineering heuristics (Seider, Seader and Lewin). Meanwhile, the frictional losses were estimated based on tables of head loss per length as a function of flowrate and pipe diameter (The Engineering Toolbox). The required pump power was determined based on the flowrate and head, and was adjusted depending on the viscosity of the liquid being pumped (Seborg, Edgar and Mellichamp):
∗ ∗ ∗ ℎ = ∗ where H is the total head, g s is the fluid’s specific gravity, η is the pump efficiency, and α is a viscosity correction factor. A typical pump efficiency of 60% was assumed.
8.1.4 Ice Bank Pricing The ice bank in this plant is conceptually the most specialized piece of equipment there is. The equipment decided to use was a vertical pressurized vessel or tower. Because the ice must be packed. The total cost of each ice bank can be calculated from the equation below from chapter 22 of Sieder et al:
= +
Batts, Sia, Yarnall & Zinyemba Pg. 74
Where is the total price, is the material factor, is the cost of the empty vessel and is the cost of ladders and platforms needed for the tower. For towers holding 9,000 to 2,500,000 pounds, the Cv can be calculated as:
. . ( ( )) . ( ( )) =
W, the weight should be calculated by based on the thickness of the walls and shells inside of the vessel.
= ( + )( +. 8 )
Where is the inner diameter, is the shell wall thickness, L is the height of the tower, and is the density of the carbon steel. The design thickness of the shell is .25 inches.
The bare module cost is the cost of purchase multiplied by the bare module factor which was decided from Table 22.11 in Sieder.
8.2 Economics calculations
8.2.1 Equipment Costs All the economic calculations for the equipment are estimated from Seider, et al Chapter 22.
CB is the base cost of the equipment. CP is the purchase cost of the equipment. CBM is the bare module cost of the equipment which takes into account the installation and other cost associated with the equipment. Heat Exchangers The cost factor is A, heat transfer surface area in ft 2. Shell and Tube A, tube outside surface area, must be between 150 to 12,000 ft 2 for the equations for base costs to work. Batts, Sia, Yarnall & Zinyemba Pg. 75
Fixed Head Base Cost, : = exp {11.2927 − 0.9228 ln ( ) + 0.09861 ln ( ) } Floating Head Base Cost:
= exp {11.9052 − 0.8709 ln ( ) + 0.09005 ln ( ) } U-tube Base Cost:
= exp {11.3852 − 0.9186 ln ( ) + 0.09790 ln ( ) } Kettle vaporizer:
= exp {12.2052 − 0.8709 ln ( ) + 0.09005 ln ( ) } Material Factor, : = + 100 Where a and b depends on the material. In our case, we have carbon steel shell and carbon steel tube, a = b = 0.
Tube Length Factor, FL depends on the tube length. In our case, 20 ft tube length
corresponds to FL = 1.
Pressure Factor, FP, is based from the pressure on the shell side, P, in psig. P must be between 100 and 2,000 psig for the equation to work.
= 0.9803 + 0.018 + 0.0017 100 100 The purchase cost, CP, is the price of the equipment.
= Spiral Plate A must be between 20 – 2,000 ft 2. This is for a stainless steel construction.
. = 6,200 Spiral Tube A must be between 1 – 500 ft 2. This is for a stainless steel construction.
= exp {8.0757 + 0.4343 ln ( ) + 0.03812 ln ( ) Plate and Frame A must be between 150 – 15,000 ft 2. This is for a stainless steel construction.
. = 8,880 Air-cooled Fin-fan Batts, Sia, Yarnall & Zinyemba Pg. 76
A, bare-tube heat-transfer area, must be between 150 – 15,000 ft 2. This is for a carbon steel construction.
. = 8,880 Pumps Centrifugal The purchase cost depends on the size factor, S.
. = ( ) Where Q is the flow rate through the pump in gallons per minute and H is the pump head in feet of the fluid. The purchase cost for the pump without the electric motor depends on the base cost, the material factor, FM, and the pump-type factor, FT.
= The base cost is given by the following equation and is applicable from S = 400 to 100,000.
= exp {9.7171 − 0.6019 ln ( ) + 0.0519 ln ( ) FM is given by the following table:
FT is given by the following table: Batts, Sia, Yarnall & Zinyemba Pg. 77
For the electric motor, the size parameter is given by its power consumption, PC, which depends on the theoretical horsepower, PT, the fractional efficiency of the pump, ηp, and the fractional efficiency of the motor, ηm.
= = = 33,000 The ρ is the liquid density in pounds per gallon. The can be estimated by the following equations.
= −0.316 + 0.24015 (ln ) − 0.01199( ) = 0.80 + 0.0319 (ln ) − 0.00182( ) Note that PB is between 1 and 1,500 Hp. The base cost of the electric motor can then be estimated using the formula:
= exp {5.8259 + 0.13141 ln ( ) + 0.053255 ln ( ) + 0.028628 ln ( ) − 0.0035549 ln ( ) } Then the purchase cost is given by the equation:
= Where the FT is the motor type factor given in the following table.
Batts, Sia, Yarnall & Zinyemba Pg. 78
Compressors Centrifugal
The base cost estimate of centrifugal compressors is based of consumed power, PC, in horsepower in the range of 200 to 30,000 Hp. It is given by the equation:
= exp {7.5800 + 0.80 ln ( ) } The purchase cost is given by the following equation:
= Where FD is equal to 1 if the compressor has an electric motor drive, 1.15 if it has a steam
turbine drive, and 1.25 if it has a gas turbine drive. The FM equals to 1 if it is cast iron or carbon steel construction, 2.5 if it is made of stainless steel, and 5.0 if it is made of nickel alloy. Bare Module Costs The bare module cost takes into account the purchase costs of the equipment along with the cost of installation and other direct and indirect costs associated with the equipment. The bare module factor, FBM , is the factor to which we multiply the purchase cost to get the bare module cost. The bare module factors for each equipment are summarized in the table below:
Batts, Sia, Yarnall & Zinyemba Pg. 79
Inflation According to Seider, the equations that would give the purchase costs and the bare module costs have a Chemical Engineering Plant Cost Index (CE) of 500, which is the average CE during the year 2006. To account for inflation, we found more recent CE data. We found an average CE of 576.1 for the year 2014 ("Chemical Engineering Plant Cost Index (CEPCI)."). The CE shows a decreasing trend after 2014, but to err on the possibility that the CE would rise again in the near future, we chose the CE from 2014 of 576.1 in our inflation correction. So for each equipment, we multiplied the bare module cost by (576.1/500) to account for inflation.
8.2.2 Equipment Sizing Shell and Tube We need to size the shell and tube heat exchanger that we would use for the evaporator and for the heat exchange between ethylene glycol and product chilled water. We need to specify the shell inner diameter, the number of tubes inside the shell and the heat exchanger length, and the tube other diameter. We have the shell inner diameter, length of the heat exchanger, and total surface area for three shell and tube heat exchanger (Seider, et al, p475, Heuristic 54). We estimated the number of tubes associated for each by using the surface area equation of a cylinder. We then fitted a quadratic equation on the three points. The quadratic equation works well because the surface area equation also is a second order equation. We now have an equation that gives the number of tubes as a function of shell ID. We use Excel’s Solver to minimize the bare module cost by changing the shell ID and keeping the shell and tube heat exchanger area less than or equal to 12,000 ft 2. Afterwards, we manually adjusted the shell ID to resemble more an actual shell we can buy.
8.3 VBA code to accompany Excel spreadsheet “Computational thermodynamics model – final.xlsm” The computational thermodynamics model described in Section 0 was implemented in a macro-enabled Excel workbook with substantial behind-the-scenes coding in Visual Basic for Applications (VBA). The code is provided below, as well as an explanation of its functions and subroutines. Although a general effort was made to adhere to good coding practices and style, Batts, Sia, Yarnall & Zinyemba Pg. 80 the emphasis was on producing an accurate, functioning model in the fewest weeks possible, rather than on producing an exemplary software engineering product (in other words, developer time was valued more highly than computer time). For this reason, the code contains sections that are inefficient or “hackish”, or that do not conform to good coding style. The sections below show the code and explain how the code works.
8.3.1 Selection of computational tool For this project, three computational environments were considered: Excel with VBA, Matlab, and Python with scientific computing modules such as pandas and matplotlib. Other options were not considered because these were the only environments with which any group member was sufficiently competent. Although both Matlab and Python offer superior tools for scientific computing, it was decided to use Excel with VBA because the front end (i.e. the Excel workbook) was very familiar to all group members.
Batts, Sia, Yarnall & Zinyemba Pg. 81
8.3.2 Conceptual map of VBA functions and subroutines Batts, Sia, Yarnall & Zinyemba Pg. 82
8.3.3 VBA functions and subroutines Numerical parameters were obtained from literature sources or fit to experimental data outside the scope of the VBA code. Not all data of the same type (e.g. not all vapor pressure relations) were fit to the same expression, so some functions and subroutines have to distinguish between different expressions for different compounds.
8.3.1.1 Function SensibleHeatGas Function SensibleHeatGas (RefName As String , LowT As Double , HighT As Double ) As Double 'This function calculates the sensible heat required to heat between two temperatures (i.e. integrate CpdT from T1 to T2) 'This function uses the Ideal Gas Heat Capacity Equation at constant pressure 'It takes the refrigerant name and the temperatures in Kelvin as arguments, and outputs the heat in kJ/mol
Dim A As Double Dim B As Double Dim C As Double Dim result As Double
Select Case RefName Case "R134a" 'Uses duPont 2004 reference A = 19.4006 B = 0.258531 C = -0.000129665 Case "R22" 'chlorodifluoromethane A = 25.33466 B = 0.15096 C = 0.000116143 Case "R290" 'propane A = 17.53 B = 0.219 C = -0.00006 Case "RE170" 'dimethyl ether A = 21.628 B = 0.1756 C = -0.00006 Case "R717" 'ammonia A = 19.99563 B = 0.049771 C = -0.000015376 Case "CF2HOCH3" 'difluoromethoxy methane A = 27.813 Batts, Sia, Yarnall & Zinyemba Pg. 83
B = 0.2016 C = -0.00009 Case "R143m" 'methyl trifluoromethyl ether A = 19.4006 B = 0.25834 C = -0.0001297 Case "R600a" 'isobutane A = 2.8157 B = 0.3541 C = -0.0001 Case "R1150" 'ethylene A = 19.685 B = 0.1024 C = -0.00003 Case "R600" 'n-butane A = 23.092 B = 0.2911 C = -0.00009 Case "C2H6" 'ethane A = 20.907 B = 0.0993 C = 0.00003 Case "C3H3F3" 'trifluoropropene A = 100.86 B = -2.008 C = 0.0009 Case "R32" 'difluoromethane A = -6.098682 B = 179.22 C = -122.3682 HighT = HighT / 1000 'Shomate Eqn LowT = LowT / 1000 Case "R410a" 'pentafluoroethane / difluoromethane mix A = 19.423 B = 0.153532 C = -0.000071 Case "R125" 'pentafluoroethane A = 21.732 B = 0.2702 C = -0.0001 Case "R744" 'CO2 A = 24.997 B = 55.18696 C = -33.69137 HighT = HighT / 1000 'Shomate Eqn LowT = LowT / 1000 Batts, Sia, Yarnall & Zinyemba Pg. 84
Case "R152a" 'difluoroethane A = 17.025 B = 0.1957 C = -0.00008 Case "R1270" 'propene A = 23.978 B = 0.127 C = 0.00003 Case "HFO1234yf" A = 26.625 B = 0.2081 C = 0.0000002 Case Else MsgBox ("That refrigerant is not currently supported" ) Exit Function End Select result = A * (HighT - LowT ) result = result + (B * (( HighT ^ 2) - (LowT ^ 2)) / 2) result = result + (C * (( HighT ^ 3) - (LowT ^ 3)) / 3) 'J/mol If (RefName = "R32" ) Or (RefName = "R744" ) Then result = result * 1000 'Shomate eqn SensibleHeatGas = result / 1000 'kJ/mol End Function
8.3.1.2 Function SensibleHeatLiquid Function SensibleHeatLiquid (RefName As String , LowT As Double , HighT As Double ) As Double 'This function calculates the sensible heat required to heat between two temperatures (i.e. integrate CpdT from T1 to T2) 'It takes the compound name and the temperatures in Kelvin as arguments, and outputs the heat in kJ/kg
Dim result As Double result = 0
Select Case RefName Case "R134a" 'Fit to Huber McLinden 1992 reference A = 3.32768483E-12 / 7 B = -5.11913813E-09 / 6 C = 0.00000324277588 / 5 D = -0.00108218945 / 4 H = 0.200604945 / 3 'avoid E as number formatter F = -19.5795658 / 2 G = 787.170101 result = A * (( HighT ^ 7) - (LowT ^ 7)) + _ B * (( HighT ^ 6) - (LowT ^ 6)) + _ C * (( HighT ^ 5) - (LowT ^ 5)) + _ Batts, Sia, Yarnall & Zinyemba Pg. 85
D * (( HighT ^ 4) - (LowT ^ 4)) + _ H * (( HighT ^ 3) - (LowT ^ 3)) + _ F * (( HighT ^ 2) - (LowT ^ 2)) + _ G * (HighT - LowT ) Case "Water" 'From NIST webbook A = -203.606 B = 1523.29 / 2 C = -3196.413 / 3 D = 2474.455 / 4 E = -3.855326 LowT = LowT / 1000 HighT = HighT / 1000 result = A * (HighT - LowT ) + _ B * (( HighT ^ 2) - (LowT ^ 2)) + _ C * (( HighT ^ 3) - (LowT ^ 3)) + _ D * (( HighT ^ 4) - (LowT ^ 4)) + _ E * (( 1 / HighT ) - (1 / LowT )) 'J/molK result = 1000 * result / 18 'MW of water --> kJ/kg Case "Ethylene glycol" 'Fit to data from Parks 1925 and Yang 2003 A = 0.00391315 / 2 B = 1.23046 result = A * (HighT ^ 2 - LowT ^ 2) + _ B * (HighT - LowT ) 'kJ/kg Case "R22" 'chlorodifluoromethane A = 304.0793 B = -1.72033 C = 0.03558 Case "R290" 'propane A = 119.6 B = 0 C = 0 Case "RE170" 'dimethyl ether A = 180.404 B = -0.7288 C = 0.001692 Case "R717" 'ammonia A = 173.0426 B = -0.77811 C = 0.001586 Case "CF2HOCH3" 'difluoromethoxy methane A = 182.6692 B = -0.59178 C = 0.0014002 Case "R143m" 'methyl trifluoromethyl ether A = 353.1475 B = -1.856471 Batts, Sia, Yarnall & Zinyemba Pg. 86
C = 0.003859 Case "R600a" 'isobutane A = 129.7 B = 0 C = 0 Case "R1150" 'ethylene A = 67.4 B = 0 C = 0 Case "R600" 'n-butane A = 132.42 B = 0 C = 0 Case "C2H6" 'ethane A = 74.48 B = 0 C = 0 Case "C3H3F3" 'trifluoropropene A = 114.88 B = -0.2481 C = 0.001 Case "R32" 'difluoromethane A = 7691.9 B = -48.354 C = 0.077 Case "R410a" 'pentafluoroethane / difluoromethane mix A = 701.323 B = -4.759926 C = 0.009513 Case "R125" 'pentafluoroethane A = 43.301 B = 2.648 C = -0.0059 Case "R744" 'CO2 A = -171.61 B = 0.798 C = -0.0006 Case "R152a" 'difluoroethane A = 117.31 B = 0 C = 0 Case "R1270" 'propene A = 98.9 B = 0 C = 0 Case "HFO1234yf" Batts, Sia, Yarnall & Zinyemba Pg. 87
A = -2.6272 B = 0.4417 C = -0.0004 Case "EG25" 'Fit to Yang 2003 reference A = 0.003255268 / 2 B = 2.321495905 result = A * (HighT ^ 2 - LowT ^ 2) + _ B * (HighT - LowT ) 'kJ/kg Case Else MsgBox ("That refrigerant is not currently supported" ) Exit Function End Select
If result <> 0 Then SensibleHeatLiquid = result 'in kJ/kg Else result = A * (HighT - LowT ) + _ B * (HighT ^ 2 - LowT ^ 2) / 2 + _ C * (HighT ^ 3 - LowT ^ 3) / 3 SensibleHeatLiquid = result / 1000 'J/kg --> kJ/kg End If End Function
8.3.1.3 Function EstdHvap Function EstdHvap (RefName As String , Temp As Double ) As Double 'This function uses the Clausius Clapeyron relation in order to estimate the latent heat of vaporization 'at a given temperature for a given refrigerant 'Inputs are the refrigerant name and the temperature in K 'Output is delHvap in kJ/mol
Dim PsatLow As Double Dim PsatHigh As Double Dim R As Double Dim LHS As Double Dim RHS As Double
R = 8.314 'J/mol PsatLow = RefPsat (RefName , Temp - 5) PsatHigh = RefPsat (RefName , Temp + 5) LHS = Log (PsatHigh / PsatLow ) 'log in VBA is natural log RHS = (( 1 / (Temp + 5)) - (1 / (Temp - 5))) / R
EstdHvap = (-1) * LHS / (1000 * RHS ) 'in kJ/mol End Function Batts, Sia, Yarnall & Zinyemba Pg. 88
8.3.1.4 Function RefPsat Function RefPsat (Refrigerant As String , Temp As Double ) As Double 'This function returns the saturation pressure for a given refrigerant at a temperature 'Temperatures should be provided in K; Psat returned in kPa
Dim Psat As Double Dim A As Double Dim B As Double Dim C As Double
Select Case Refrigerant Case "R134a" 'Based on Goodwin 1992 reference A = 14.21475 B = -2013.951 C = -37.217 RefPsat = AntoineEqnPsat (A, B, C, Temp ) Case "R22" 'Based on Goodwin 1992 reference A = 14.03798 B = -1890.641 C = -31.64 RefPsat = AntoineEqnPsat (A, B, C, Temp ) Case "R290" 'propane A = 4.53678 B = 1149.56 C = 24.906 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "RE170" 'dimethyl ether A = 4.49337 B = 1104.69 C = -1.64253 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R717" 'ammonia A = 4.86886 B = 1113.928 C = -10.409 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "CF2HOCH3" 'difluoromethoxy methane A = 5.794145 B = 802.2153 C = -54.1418 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R143m" 'methyl trifluoromethyl ether A = 6.38712 B = 1047.03 C = -10.1869 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Batts, Sia, Yarnall & Zinyemba Pg. 89
Case "R600a" 'isobutane A = 4.3281 B = 1132.108 C = 0.918 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R1150" 'ethylene A = 3.87261 B = 584.146 C = -18.307 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R600" 'n-butane A = 4.35576 B = 1175.581 C = -2.071 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "C2H6" 'ethane A = 3.93835 B = 659.739 C = -16.719 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "C3H3F3" 'trifluoropropene A = 4.37137 B = 937.142 C = -11.5361 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R32" 'difluoromethane A = 4.26224 B = 821.092 C = -28.554 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R410a" 'pentafluoroethane / difluoromethane mix A = 4.8073 B = 1073.737 C = 0.03259 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R125" 'pentafluoroethane A = 4.5817 B = 1022.719 C = -1.05339 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R744" 'CO2 A = 4.5588 B = 793.443 C = -10.0524 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R152a" 'difluoroethane Batts, Sia, Yarnall & Zinyemba Pg. 90
A = 4.23406 B = 896.171 C = -34.714 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "R1270" 'propene A = 3.97488 B = 795.819 C = -24.884 RefPsat = AntoineEqnPsatLog10 (A, B, C, Temp ) * 100 'convert bar --> kPa Case "HFO1234yf" A = 21.629 B = -2373.463 C = -8.689 RefPsat = AntoineEqnPsat (A, B, C, Temp ) / 1000 'convert Pa --> kPa Case Else MsgBox ("That refrigerant is not supported" ) End Select End Function
8.3.1.5 Functions AntoineEqnPsat and AntoineEqnPsatLog10 Function AntoineEqnPsat (A As Double , B As Double , C As Double , t As Double ) As Double 'Antoine's Eqn form 1 Dim LNP As Double LNP = A + B / (t + C) AntoineEqnPsat = Exp (LNP ) End Function
Function AntoineEqnPsatLog10 (A As Double , B As Double , C As Double , t As Double ) As Double 'Antoine's Eqn form 2 Dim LOGP As Double LOGP = A - B / (t + C) AntoineEqnPsatLog10 = 10 ^ LOGP End Function
8.3.1.6 Subroutine ModelAllRefrigerants This subroutine handles input/output for analyzing many refrigerants. The Application.ScreenUpdating lines reduce the needed computer time by preventing Excel from updating the graphical user interface. Without these lines, the code runs in about three minutes; with these lines, the code runs in about 70 seconds.
Sub ModelAllRefrigerants () Batts, Sia, Yarnall & Zinyemba Pg. 91
Application.ScreenUpdating = False 'Helps speed up code
Dim t As Double t = Timer 'Count how long code takes to run
RefList = Array ("R22" , "R290" , "RE170" , "R717" , "CF2HOCH3" , "R134a" , _ "R143m" , "R600a" , "R1150" , "R600" , "C2H6" , "C3H3F3" , "R32" , _ "R410a" , "R125" , "R744" , "R152a" , "R1270" , "HFO1234yf" ) 'List of refrigerants to analyze
Dim i As Integer i = 3 For Each Ref In RefList Sheets ("Cover sheet" ). Range ("$E$2" ). Value = Ref Call MasterMacro Sheets ("Model results" ). Select Range ("A" & i). Value = Ref Range ("B" & i). Value = Sheets ("Nonideal Refrigeration Cycle" ). Range ("$H$11" ). Value 'Nonideal Refrigeration Cycle results Range ("C" & i). Value = Sheets ("Nonideal Refrigeration Cycle" ). Range ("$O$2" ). Value Range ("D" & i). Value = Sheets ("Nonideal Refrigeration Cycle" ). Range ("$O$3" ). Value Range ("E" & i). Value = Sheets ("Nonideal Refrigeration Cycle" ). Range ("$O$4" ). Value Range ("F" & i). Value = Sheets ("Nonideal Refrigeration Cycle" ). Range ("$O$5" ). Value Range ("G" & i). Value = Sheets ("Nonideal Refrigeration Cycle" ). Range ("$O$6" ). Value Range ("H" & i). Value = Sheets ("Condenser Design" ). Range ("$P$2" ). Value 'Condenser Design Results Range ("I" & i). Value = Sheets ("Condenser Design" ). Range ("$P$3" ). Value Range ("J" & i). Value = Sheets ("Condenser Design" ). Range ("$P$4" ). Value Range ("K" & i). Value = Sheets ("Condenser Design" ). Range ("$P$6" ). Value Range ("L" & i). Value = Sheets ("Condenser Design" ). Range ("$P$7" ). Value Range ("M" & i). Value = Sheets ("Evaporator Design" ). Range ("$N$2" ). Value 'Evaporator Design Results Range ("N" & i). Value = Sheets ("Evaporator Design" ). Range ("$N$3" ). Value Range ("O" & i). Value = Sheets ("Evaporator Design" ). Range ("$N$5" ). Value Range ("P" & i). Value = Sheets ("Evaporator Design" ). Range ("$N$6" ). Value i = i + 1 Next Ref
Application.ScreenUpdating = True 'display resulting spreadsheet
t = Timer - t 'end timing length of code MsgBox t & " seconds elapsed running this code" Batts, Sia, Yarnall & Zinyemba Pg. 92
End Sub
8.3.1.7 Subroutine MasterMacro This subroutine calls the code necessary to recalculate the model for the refrigerant currently under analysis. The thermodynamic cycle calculations and the condenser pinch analysis calculations are interdependent, so the code runs until the model converges.
Sub MasterMacro () 'This routine currently automates the following sheets: 'Nonideal Refrigeration Cycle 'Condenser Design 'Evaporator Design Dim i As Integer
For i = 0 To 9 'Thermodynamics model + size condenser Call NonIdealCycleCalc Tout1 = Sheets ("Nonideal Refrigeration Cycle" ). Range ("H9" ). Value Call Condenser_Pinch Tout2 = Sheets ("Condenser Design" ). Range ("P2" ). Value 'Tolerance of 0.5% seems reasonable If (Abs (Tout1 - Tout2 ) / Tout1 ) < 0.005 Then Exit For Next i Call Evaporator_Pinch 'size evaporator
End Sub
8.3.1.8 Subroutine Condenser_Pinch Excel’s optimization functions Solver and GoalSeek can only be called upon cells, not upon variables in VBA. This has an unfortunate consequence of making it impossible to nest Solver optimizations inside other Solver optimizations. Instead, this function nests Solver inside of a structure that exhaustively tests all options the model converges. This method is inefficient and is the main reason that the code takes so long to run; however, it works and is much simpler than attempting to emulate Solver or GoalSeek.
Sub Condenser_Pinch () 'This routine conducts pinch point analysis on the condenser Sheets ("Condenser Design" ). Select Tupper = Range ("B5" ). Value 'Refrigerant inlet temperature Batts, Sia, Yarnall & Zinyemba Pg. 93
Tlower = Range ("B7" ). Value 'Water outlet temperature Dim i As Double Dim vap As Double Dim Flowrate As Double
For i = Tupper To Tlower Step -3 Range ("P2" ). Value = i 'New outlet temperature SolverReset 'Optimize water flowrate and vapor fraction SolverOk SetCell := "$G$15" , MaxMinVal := 2, ByChange := "$P$3,$G$4" , _ Engine := 1, EngineDesc := "GRG Nonlinear" SolverSolve UserFinish := True
'Exit condition for best pinch value If Not Range ("P4" ). Value Then Exit For Else vap = Range ("G4" ). Value Flowrate = Range ("P3" ). Value End If Next i
Tupper = i + 3 'More precise loop now For i = Tupper To Tlower Step -0.5 Range ("P2" ). Value = i 'New outlet temperature SolverReset 'Optimize water flowrate and vapor fraction SolverOk SetCell := "$G$15" , MaxMinVal := 2, ByChange := "$P$3,$G$4" , _ Engine := 1, EngineDesc := "GRG Nonlinear" SolverSolve UserFinish := True
'Exit condition for best pinch value If Not Range ("P4" ). Value Then Exit For Else vap = Range ("G4" ). Value Flowrate = Range ("P3" ). Value End If Next i
'Export values Range ("P2" ). Value = i + 0.5 Range ("G4" ). Value = vap Range ("P3" ). Value = Flowrate
SolverReset 'Optimize for flowrate alone SolverOk SetCell := "$G$15" , MaxMinVal := 2, ByChange := "$P$3" , _ Engine := 1, EngineDesc := "GRG Nonlinear" Batts, Sia, Yarnall & Zinyemba Pg. 94
SolverSolve UserFinish := True End Sub
8.3.1.9 Subroutine Evaporator_Pinch Sub Evaporator_Pinch () 'This routine applies pinch analysis to the evaporator 'This is simpler than the condenser because the temperatures are either design constraints 'Or calculated by the refrigeration cycle Sheets ("Evaporator Design" ). Select SolverReset SolverOk SetCell := "$H$6" , MaxMinVal := 2, ByChange := "$N$2" , _ Engine := 1, EngineDesc := "GRG Nonlinear" SolverSolve UserFinish := True End Sub
8.3.1.10 Subroutine NonIdealCycleCalc Sub NonIdealCycleCalc () 'This routine automates calculation of the thermodynamic cycle for the nonideal case Sheets ("Nonideal Refrigeration Cycle" ). Select Call IdealCompHighT Range ("$O$6" ). Value = Range ("$H$3" ). Value 'initial guess is ideal case SolverReset SolverOk SetCell := "H7" , MaxMinVal := 2, ByChange := "O6" , Engine := 1 SolverSolve UserFinish := True End Sub
8.3.1.11 Subroutine IdealCompHighT The numerical parameters here are the same as the SensibleHeatGas function. Although this is not excellent style, copy+pasting the code was simpler than rewriting the code to make it more modular. Excel only permits Solver to act on cells, and not on variables in VBA. As a workaround, this subroutine temporarily exports values and formulas to a worksheet, calls solver, and reads in the results from the worksheet.
Sub IdealCompHighT () 'This sub calculates the temperature leaving an ideal compressor (isentropic) 'It takes the refrigerant name, entering temperature (K), and pressures (any consistent units) as arguments, and outputs the exit T in K
Sheets ("Nonideal Refrigeration Cycle" ). Select Dim RefName As String RefName = Range ("B8" ). Value Batts, Sia, Yarnall & Zinyemba Pg. 95
Dim LowT As Double LowT = Range ("B5" ). Value Dim LowP As Double LowP = Range ("B19" ). Value Dim HighP As Double HighP = Range ("B20" ). Value Dim HighTGuess As Double HighTGuess = 300 'arbitrary guess, should be close though
Dim A As Double Dim B As Double Dim C As Double Dim RHS As Double Dim R As Double Dim sht As Variant R = 8.314 'J/molK Set sht = ActiveSheet
Select Case RefName 'Uses vapor heat capacity equation Case "R134a" 'Uses duPont 2004 reference A = 19.4006 B = 0.258531 C = -0.000129665 Case "R22" 'chlorodifluoromethane A = 25.33466 B = 0.15096 C = 0.000116143 Case "R290" 'propane A = 17.53 B = 0.219 C = -0.00006 Case "RE170" 'dimethyl ether A = 21.628 B = 0.1756 C = -0.00006 Case "R717" 'ammonia A = 19.99563 B = 0.049771 C = -0.000015376 Case "CF2HOCH3" 'difluoromethoxy methane A = 27.813 B = 0.2016 C = -0.00009 Case "R143m" 'methyl trifluoromethyl ether A = 19.4006 B = 0.25834 Batts, Sia, Yarnall & Zinyemba Pg. 96
C = -0.0001297 Case "R600a" 'isobutane A = 2.8157 B = 0.3541 C = -0.0001 Case "R1150" 'ethylene A = 19.685 B = 0.1024 C = -0.00003 Case "R600" 'n-butane A = 23.092 B = 0.2911 C = -0.00009 Case "C2H6" 'ethane A = 20.907 B = 0.0993 C = 0.00003 Case "C3H3F3" 'trifluoropropene A = 100.86 B = -2.008 C = 0.0009 Case "R32" 'difluoromethane A = -6.098682 B = 179.22 C = -122.3682 Case "R410a" 'pentafluoroethane / difluoromethane mix A = 19.423 B = 0.153532 C = -0.000071 Case "R125" 'pentafluoroethane A = 21.732 B = 0.2702 C = -0.0001 Case "R744" 'CO2 A = 24.997 B = 55.18696 C = -33.69137 Case "R152a" 'difluoroethane A = 17.025 B = 0.1957 C = -0.00008 Case "R1270" 'propene A = 23.978 B = 0.127 C = 0.00003 Case "HFO1234yf" Batts, Sia, Yarnall & Zinyemba Pg. 97
A = 26.625 B = 0.2081 C = 0.0000002 Case Else MsgBox ("That refrigerant is not currently supported" ) Exit Sub End Select If (RefName = "R32" ) Or (RefName = "R744" ) Then 'Shomate Eqn HighTGuess = HighTGuess / 1000 LowT = LowT / 1000 End If
RHS = R * Log (HighP / LowP ) 'Pushing values to excel to use Solver Sheets ("TempCalc" ). Select Range ("A1" ). Value = RHS Range ("B1" ). Value = HighTGuess Range ("C1" ). Formula = "=" & A & "*ln(B1/" & LowT & ")" & _ "+" & B & "*(B1-" & LowT & ")" & _ "+" & C / 2 & "*((B1^2)-(" & LowT & ")^2)" Range ("A2" ). Formula = "=abs(A1-C1)" 'objective function to minimize 'Running Solver SolverReset SolverOk SetCell := "A2" , MaxMinVal := 2, ByChange := "B1" , Engine := 1 SolverSolve UserFinish := True 'Reading in result If (RefName = "R32" ) Or (RefName = "R744" ) Then 'Shomate Eqn, adjust by 1000 HighT = 1000 * Range ("B1" ). Value Else HighT = Range ("B1" ). Value End If Sheets ("TempCalc" ). UsedRange.ClearContents sht.Select 'Refocus view Range ("H3" ). Value = HighT End Sub Batts, Sia, Yarnall & Zinyemba Pg. 98
8.4 Physical and chemical properties Table 1: Properties of compounds under analysis
Molecular Antoine's Antoine's Liquid Cp Liquid Cp Vapor Cp Vapor Cp Compound weight Equation Equation References expression coefficients expression coefficients (Daltons) form coefficients A = A = A = R22 304.0793 Cp[J/mol] (Goodwin, Cp[J/kg] = 25.33466 ln(P[kPa]) = 14.03798 chloro- B = - = A + Defibaugh and 86.47 A + BT[K] B = 0.15096 A - B / (T[K] B = - difluoro- 1.72033 BT[K] + Weber) + CT^2 C = + C) 1890.641 methane C = CT^2 (NIST) 0.000116143 C = -31.64 0.03558 A = Cp[J/mol] A = 17.53 Cp[J/kg] = A = 119.6 log10(P[bar]) 4.53678 R290 = A + B = 0.219 44.10 A + BT[K] B = 0 = A + B / B = (NIST) propane BT[K] + C = - + CT^2 C = 0 (T[K] + C) 1149.56 CT^2 0.00006 C = 24.906 A = A = Cp[J/mol] A = 21.628 (Blowers, Tetrault RE170 Cp[J/kg] = 180.404 log10(P[bar]) 4.49337 = A + B = 0.1756 and Trujillo- dimethyl 46.07 A + BT[K] B = - = A + B / B = BT[K] + C = - Morehead) ether + CT^2 0.7288 (T[K] + C) 1104.69 CT^2 0.00006 (Ihmels) C = C = - Batts, Sia, Yarnall & Zinyemba Pg. 99
0.001692 1.64253
A = A = (Blowers, Tetrault 182.6692 Cp[J/mol] A = 27.813 5.794145 CF2HOCH3 Cp[J/kg] = log10(P[bar]) and Trujillo- B = - = A + B = 0.2016 B = 82.05 A + BT[K] = A + B / Morehead) 0.59178 BT[K] + C = - 802.2153 + CT^2 (T[K] + C) (Satoh, Nishiumi C = CT^2 0.00009 C = - and Kasatani) 0.0014002 54.1418 A = A = R143m 353.1475 Cp[J/mol] A = 19.4006 6.38712 (Blowers, Tetrault Cp[J/kg] = log10(P[bar]) methyl B = - = A + B = 0.25834 B = and Trujillo- 100.04 A + BT[K] = A + B / trifluoro- 1.856471 BT[K] + C = - 1047.03 Morehead) + CT^2 (T[K] + C) methyl ether C = CT^2 0.0001297 C = - 0.003859 10.1869 Cp[J/mol] A = 4.3281 Cp[J/kg] = A = 129.7 A = 2.8157 log10(P[bar]) R600a = A + B = 58.12 A + BT[K] B = 0 B = 0.3541 = A + B / (NIST) isobutane BT[K] + 1132.108 + CT^2 C = 0 C = -0.0001 (T[K] + C) CT^2 C = 0.918 Cp[J/kg] = A = 67.4 Cp[J/mol] A = 19.685 log10(P[bar]) A = R1150 28.05 A + BT[K] B = 0 = A + B = 0.1024 = A + B / 3.87261 (NIST) ethylene + CT^2 C = 0 BT[K] + C = - (T[K] + C) B = Batts, Sia, Yarnall & Zinyemba Pg. 100
CT^2 0.00003 584.146 C = - 18.307 A = Cp[J/mol] A = 23.092 Cp[J/kg] = A = 132.42 log10(P[bar]) 4.35576 R600 = A + B = 0.2911 58.12 A + BT[K] B = 0 = A + B / B = (NIST) butane BT[K] + C = - + CT^2 C = 0 (T[K] + C) 1175.581 CT^2 0.00009 C = -2.071 A = Cp[J/mol] 3.93835 Cp[J/kg] = A = 74.48 A = 20.907 log10(P[bar]) C2H6 = A + B = 30.07 A + BT[K] B = 0 B = 0.0993 = A + B / (NIST) ethane BT[K] + 659.739 + CT^2 C = 0 C = 0.00003 (T[K] + C) CT^2 C = - 16.719 A = A = 114.88 Cp[J/mol] 4.37137 C3H3F3 Cp[J/kg] = A = 100.86 log10(P[bar]) B = - = A + B = (Duan, trifluoro- 96.05 A + BT[K] B = -2.008 = A + B / 0.2481 BT[K] + 937.142 Wang and Meng) propene + CT^2 C = 0.0009 (T[K] + C) C = 0.001 CT^2 C = - 11.5361 Batts, Sia, Yarnall & Zinyemba Pg. 101
A = Cp[kJ/mol] A = - A = 7691.9 4.26224 R32 Cp[J/kg] = = A + Bt + 6.098682 log10(P[bar]) B = - B = difluoro- 52.02 A + BT[K] Ct^2 ; t = B = 179.22 = A + B / (NIST) 48.354 821.092 methane + CT^2 T[K] / C = - (T[K] + C) C = 0.077 C = - 1000 122.3682 28.554 R410a A = A = 19.423 A = 4.8073 pentafluoro- 701.323 Cp[J/mol] Cp[J/kg] = B = log10(P[bar]) B = ethane / B = - = A + 72.60 A + BT[K] 0.153532 = A + B / 1073.737 (DuPont Sava) difluoro- 4.759926 BT[K] + + CT^2 C = - (T[K] + C) C = methane C = CT^2 0.000071 0.03259 mix 0.009513 (Yokozeki, Sato and Watanabe) (Tanaka and A = 4.5817 A = 43.301 Cp[J/mol] Higashi, R125 Cp[J/kg] = A = 21.732 log10(P[bar]) B = B = 2.648 = A + Measurements of pentafluoro- 120.02 A + BT[K] B = 0.2702 = A + B / 1022.719 C = - BT[K] + the Isobaric ethane + CT^2 C = -0.0001 (T[K] + C) C = - 0.0059 CT^2 Specific Heat 1.05339 Capacity for 1,1,1- trifluoroethane (R143a), Batts, Sia, Yarnall & Zinyemba Pg. 102
pentafluoroethane (R125), and difluoromethane (R32) in the liquid phase) (DuarteGarza, Stouffer and Hall) A = - Cp[kJ/mol] A = 24.997 A = 4.5588 R744 Cp[J/kg] = 171.61 = A + Bt + B = log10(P[bar]) B = (NIST) carbon 44.01 A + BT[K] B = 0.798 Ct^2 ; t = 55.18696 = A + B / 793.443 dioxide + CT^2 C = - T[K] / C = - (T[K] + C) C = - 0.0006 1000 33.69137 10.0524 A = Cp[J/mol] A = 17.025 4.23406 (Magee) R152a Cp[J/kg] = A = 117.31 log10(P[bar]) = A + B = 0.1957 B = (Yokozeki, Sato difluoro- 66.05 A + BT[K] B = 0 = A + B / BT[K] + C = - 896.171 and Watanabe) ethane + CT^2 C = 0 (T[K] + C) CT^2 0.00008 C = - (NIST) 34.714 Cp[J/mol] A = Cp[J/kg] = A = 98.9 A = 23.978 log10(P[bar]) R1270 = A + 3.97488 42.08 A + BT[K] B = 0 B = 0.127 = A + B / (NIST) propene BT[K] + B = + CT^2 C = 0 C = 0.00003 (T[K] + C) CT^2 795.819 Batts, Sia, Yarnall & Zinyemba Pg. 103
C = - 24.884
Cp Cp[J/mol] (Parks and Kelley) A = log10(P[bar]) Ethylene (kJ/kg*K) = A + (Yang, Ma and 62.07 3.193E-3 n/a = A + B / n/a glycol = AT(K) + BT[K] + Jing) B = 1.230 (T[K] + C) B CT^2 A = 3.3277E- 12 B = - Cp 5.1191E-9 (Goodwin, (kJ/kg*K) A = C = A = 19.4006 Defibaugh and R134a = AT(K)^6 Cp[J/mol] 14.21475 3.2428E-6 B = ln(P[kPa]) = Weber) 1,1,1,2- + BT^5 + = A + B = - 102.03 D = - 0.258531 A - B / (T[K] (DuPont Suva) tetrafluoro- CT^4 + BT[K] + 2013.951 1.0822E-3 C = - + C) (Huber and ethane DT^3 + CT^2 C = - E = 0.000129665 McLinden) ET^2 + FT 37.217 2.0060E-1 + G F = - 1.9580E1 G = 7.8717E2 Batts, Sia, Yarnall & Zinyemba Pg. 104
A = A = A = 173.0426 Cp[J/mol] 19.99563 4.86886 Cp[J/kg] = log10(P[bar]) R717 B = - = A + B = B = 17.03 A + BT[K] = A + B / (NIST) ammonia 0.77811 BT[K] + 0.049771 1113.928 + CT^1 (T[K] + C) C = CT^2 C = - C = - 0.001586 0.000015376 10.409 A = - HFO1234yf Cp[J/mol] A = 26.625 A = 21.629 (Tanaka, Higashi Cp[J/kg] = 2.6272 ln(P[Pa]) = 2,3,3,3- = A + B = 0.2081 B = - and Akasaka) 114.00 A + BT[K] B = 0.4417 A - B / (T[K] tetrafluoro- BT[K] + C = 2373.463 (Takana and + CT^2 C = - + C) propene CT^2 0.0000002 C = -8.689 Higashi) 0.0004 A = - 203.606 Cp[J/molK] B = = A + Bt + 1523.29 Ct^2 + C = - Water 18.02 n/a n/a n/a n/a (NIST) Dt^3 - Et^- 3196.413 2 ; t = T[K] D = / 1000 2474.455 E = - 3.855326 Batts, Sia, Yarnall & Zinyemba Pg. 105