Diane McArdle Mechanical Option Skye Laboratories, Inc. Building Fort Worth, Texas December 04, 2002 Proposal

Executive Summary

Skye Laboratories, Inc. Building E is a 220,559 square foot energy intensive animal testing research facility located in Fort Worth, Texas. The thesis project preformed for this building will decrease the total annual energy consumption. Energy is wasted by the primary-secondary pumping system that maintains a constant chilled water flow through the evaporators at partial loads. The first design alternative will convert the primary/secondary pumping system into a variable primary pumping arrangement. Variable-primary pumping system is less expensive and more efficient than a primary/secondary system. Energy is saved by varying the flow through the chiller which reduces the work done by the variable-primary pumps.

The second alternative will eliminate the requirement for the post cooling coils and the glycol chiller. The chiller plant was designed with the capability of future integration with the chilled water campus loop. The new plant and campus chilled water loop provide 44°F chilled water. Since 44 °F chilled water was not sufficient to cool the supply air serving the animal holding areas, post-cooling coils were piped to a small glycol chiller loop with 40°F water. The second alternative will be the installation of dehumidifier heat pipe in the six air handling units serving the animal holding zones. By dehumidifying the air leaving the cooling coils, the room air temperature of 66°F/55 % RH can be achieved with a higher supply air temperature. Dehumidifier heat pipes provide dehumidification with no moving parts, pumps, or additional energy.

The breath analysis will include the redesign of the electrical system. With a decrease in energy consumption, electrical components such as circuit breakers and feeders will have to be resized. The addition of the dehumidifying heat pumps will add a significant load to the current structural system. An analysis and possible redesign of the structural system will be preformed as the second requirement topic for a breadth analysis.

1 Background

Skye Laboratories, Inc., Building E is located in Fort Worth, Texas. The building site is situated north of the existing facilities operated by Skye Laboratories, Inc. Before construction the site was previously a parking lot that serviced employees working in the facility west of Building E. Ewing Cole Cherry Brott, a full service design firm, received the design bid and began producing construction documents in July 2001. Building E is two stories high with a total floor area of 220,559 square feet. The cost of construction is 45 million dollars. Site excavation started in August 2002 and construction is scheduled to be completed by October 2003.

View of the South facade

On the first floor, the floor plan is a basic repetitive grid. The northern half of the building is essentially used as an animal testing laboratory. A large corridor extends across the southern façade of the plant. This hallway serves as a link that connects the new parking lot east of Building E to the facility west of the construction site. The architects designed this hallway to shield employees from the hot Texas climate since the designated parking area had to be relocated farther away from the western existing facility. A strip of offices divide the hallway from the laboratory area. All the conference rooms have full skylight ceilings that extend into the corridor. The second story functions primarily as the mechanical mezzanine. It contains air handling units as well as data processing rooms.

Skye Laboratories, Inc. Building E is an energy intensive animal testing research facility. The estimated total energy consumption is 3200 kW/year. According to the project engineer, 70% of the energy is consumed by the HVAC system. During the design process, special consideration for the well being of the animals was a central focus. Through redundancy the mechanical system was reinforced so that in the case of extreme weather conditions the system would operate efficiently and valuable research would not be lost.

2 Skye Laboratories, Inc. Building E contains the fourth chiller plant on the grounds. The plant was designed with the capability of future integration with the chilled water campus loop. The new plant and campus chilled water loop provide 44 °F chilled water. Since 44 °F chilled water was not sufficient to cool the animal holding areas, post-cooling coils were piped to a small glycol chiller loop with 40 °F water. The chiller plant could be run with 40 °F chilled water but the chillers operate more efficiently supplying 44 °F water. The building is divided into six zones according to their indoor design conditions. The most critical area of the building is Zone 1 which is animal holding rooms that are maintained at a constant year round temperature of 66 °F/55 RH with a sensible heat ratio of 0.77. Six handling units with heat pipe energy recovery service this area with 175,000 cfm of 100% outside air. Zone 2 is a surgery area located within Zone 1. It requires 68°F/45% RH supply air that is provided by the air handling units for zone 1 and reheated and dehumidified. The remaining area of the first floor is a cage wash area and offices. The cage wash area is supplied 100% outside air at 72°F/50% RH in summer and 35% RH in winter. Zone 4 is the office area. It is supplied 35,000 cfm at 75°F/50% RH in summer and 35% RH in winter. The office area complies with ASHRAE 62’s outdoor air requirements and is a variable air volume system. Zone 5 is the chiller plant. It a constant volume system that is supplied 7000 cfm at 65°F in winter and 80°F/55 RH in summer. The chiller plant’s maximum outside air ventilation was determined by the code for the amount of refrigerant present. The minimum outside air is 0.5 cfm/sq. ft. at normal conditions and maximum outside air in the event of a refrigeration leak. The second floor of the building is zone 6 which is primarily the mechanical mezzanine. It is supplied 30,000 cfm at 80 °F/55 RH in summer and 65 °F in winter. The mechanical mezzanine and chiller plant are conditioned because the climate is particularly hot in Texas. Both spaces are provided enough air to keep the system operating properly.

Statement of Problem 1

Energy is wasted by maintaining constant chilled water flow through the evaporators at partial loads. Chillers operate on a primary-secondary pumping system as shown in the appendix. When the chillers supply constant chilled water flow to the load, the extra chilled water not required by the chiller is bypassed. The water bypassed combines with the return water from the system and provides a low temperature differential across the chillers. The chillers do not operate at optimal efficiency at low temperature differentials and energy is wasted.

Proposed Solution of Problem 1

Alternative solution #1 will be converting the primary/secondary pumping system into a variable primary pumping arrangement as shown in the appendix. According to Bahnfleth, variable-primary pumping system is less expensive and more efficient than a primary/secondary system. Energy is saved by varying the flow through the chiller which reduces the work done by the variable-primary pumps.

3 Solution Method for Alternative 1

The simulation method to model the benefits of variable-primary pumping will follow the method outlined by Dr. William P. Bahnfleth1 in a HPAC Engineering article comparing variable-primary speed pumping to constant speed. Carrier’s Hourly Energy analysis program can also be used to compare variable-primary speed pumping to constant speed primary pumping.

Tasks and Tools for Alternative 1

Task 1. Develop model of building in Carrier’s Hourly Energy analysis program a) Enter spaces and conditions into HAP b) Enter equipment from design drawings c) Input chilled water leaving temperature, condensing water temperature Task 2. Compute total pumping energy a) Generate energy results in HAP for primary/secondary setup b) Generate energy results in HAP for primary-variable setup c) Compare energy results Task 3. Develop models for chillers, cooling towers, and pumps a) Find information on the systems equipment from manufactures b) Derive polynomial equations from the components Task 4. Develop plots that illustrate the pump head as a function of chilled water flow a) Develop for existing primary/secondary configuration b) Develop for variable-primary pumping configuration c) Compare generated plots and determine if energy is saved through the variable-primary configuration Task 5. Perform economic analysis

Task 6. Summarize results

Statement of Problem 2

The six air handling units servicing the animal holding areas need post cooling coils to maintain the room air temperature of 66°F/55 % RH in the labs. The chiller plant was designed with the capability of future integration with the chilled water campus loop. The new plant and campus chilled water loop provide 44°F chilled water. Since 44 °F chilled water was not sufficient to cool the supply air serving the animal holding areas, post-cooling coils were piped to a small glycol chiller loop with 40°F water. The current heat pipes only exchange sensible heat between the outdoor air supply and the exhaust air. An enthalpy wheel that recovers latent energy could not be used because it would cause cross contamination between the supply and exhaust air.

4 Proposed Solution of Problem 2

Alternative solution #2 will be the installation of dehumidifier heat pipe in the 6 air handling units serving the animal holding zones. The dehumidifier heat pipes will eliminate the need for the post cooling coils and the glycol chiller. The dehumidifier heat pipes will enclose the cooling coils as illustrated in Figure 1. Since dehumidifier heat pipes do not have any contact with the exhaust air, cross contamination will not occur. By dehumidifying the air leaving the cooling coils, the room air temperature of 66°F/55 % RH can be achieved with a higher supply air temperature. Dehumidifier heat pipes provide dehumidification with no moving parts, pumps, or additional energy. The process uses the same heat in the reheat that is used in the precool section of the heat pipe. The heat from the hot outside air causes the liquid in the heat pipe to evaporate and is transferred to the heat exchanger on the other side of the cooling coil. Once the cold air from the cooling coil comes in contact with the heat pipe, the fluid in the heat pipe condenses and returns to the other plate by means of gravity or capillary action. Heat pipes on average have a payback of three years and do not require a lot of maintenance.

Figure 1 Solution Method

Solution Method for Alternative 2

The design of the heat pipe humidifier will follow the procedure presented by the Dinh Dehumidifier Heat Pipe Principle2. Trial and error will have to be used to select the appropriate size heat pipe humidifier. Calculations require use of the existing cooling coil conditions and a psychometric chart. Software provided by manufactures to size software can be used if applicable.

5 Tasks and Tools and for Alternative 2

Task 1: The first step is to select a temperature differential across for the precool and reheat. The greater the temperature difference will result in a lower sensible heat ratio which means that a greater percentage of cooling effort will conduct latent cooling.

Task 2: Next the new air wetbulb and drybulb temperatures leaving the cooling coil needs to be determined.

Task 3: The air wetbulb and drybulb temperatures leaving the reheat plate can be determined using the psychometric chart.

Task 4: The efficiency of the pipe can be determined by dividing the temperature differential across the precool and reheat panels by the difference in temperature of the air entering the heat pipe and the supply air.

Task 5: The number of heat pipe rows to meet the heat pipe efficiency can be sized off a table from the manufacture to meet the required efficiency.

Task 6. Repeat tasks 1-5 until a heat pipe is selected

Task 7. Preform economic analysis

Task 8. Summarize results

Additional Issues

Breadth Analysis: The proposed thesis will resize the electrical system in response to the changing energy consumption. With a decrease in energy consumption, electrical components such as circuit breakers and feeders will have to be resized. The addition of the dehumidifying heat pumps will add a significant load to the current structural system. An analysis and possible redesign of the structural system will also be preformed as the second requirement topic for a breadth analysis.

Task 1: Resizing electrical system to comply with NEC standards Task 2: Analysis and redesign of structural system

Thesis presentation: The presentation will be designed and rehearsed during the first two weeks of March.

6 Timetable

Time Table Alternative 1 Alternative 2 Breath Analysis Month Week Task Month Week Task Month Week Task December 1 1 & 2 December 1 - December 1 - 2 3 & 4 2 - 2 - 3 - 3 - 3 - 4 - 4 - 4 - January 1 - January 1 - January 1 - 2 - 2 - 2 - 3 - 3 - 3 - 4 5 4 - 4 - February 1 6 February 1 - February 1 - 2 - 2 1-6 2 - 3 - 3 7-8 3 1 4 - 4 - 4 2 March 1 - March 1 - March 1 - 2 - 2 - 2 -

7 Bibliography

1. Bahnfleth, W. P. 2001. “Comparative Analysis of variable and constant primary-flow chilled-water-plant performance.” HPAC Engineers

2. EPA Heat Pipe Effectiveness study, “Gulf Breeze Laboratory Installation.” www.heatpipe.com

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