WhiteWhite Paper:Paper: ReducingReducing WaterWater ConsumptionConsumption inin CompressedCompressed AirAir SystemsSystems
Survey1. This study, “Estimated Use of Water in the United States”, has been conducted every five years since 1950. Data for 2010 water use will first become available in 2014.
The report indicates that national water use remained roughly the same as in 2000 and that water use has declined 5 percent from the peak in 1980. This leveling off of demand has occurred despite the population growth of 31 percent from 1980 to 2005 (230 to 301 million people)2. This population growth has led to a 33 percent increase in public supply water use over the same period. Fortunately, water use
Population growth in the U.S. has fueled a 33% (since 1980) increase in demand for Public-Supply water. for thermoelectric power generation, irrigation, self-supplied industrial uses, and rural domestic/livestock have stabilized or decreased since 1980. Reducing Water Consumption Power Generation and Irrigation in Compressed Air Systems Water Use Stabilizes Thermoelectric power has been By Nitin G. Shanbhag, Senior Manager, Air Technology Group, Hitachi America the category with the largest water withdrawals since 1965, and in 2005 made up 49 percent of total withdrawals3. Thermoelectric-power Compressed air systems are water is required for the inventory of water withdrawals peaked in 1980 at sometimes called the “4th Utility” air compressors in their factories along 210 billion gallons of water per day due to their presence in almost all with the related costs. An evaluation and were measured in 2005 at 201 industrial processes and facilities. can then be made, of the different billion gallons per day. Partially due The objective of this paper is to focus types of cooling systems, to ascertain to sections of the Clean Water Act, on the opportunity to reduce the water and cost reduction strategies. that were amended in 1972, power water consumption of compressed plants have increasingly begun to air systems. Water consumption has Section I: Offsetting the use wet recirculating cooling systems leveled off in the U.S. as reductions Increase in Public-Supply (cooling towers or ponds) and/or in the power, irrigation, and industrial Water Use in the U.S. dry recirculating cooling (air-cooled) segments have offset increases in systems instead of using once-through the public-supply segment driven by Total water use in the United States cooling systems. This has played population growth. Energy managers in 2005 was estimated at 410 billion a leading role in reducing demand should understand how much cooling gallons per day by a 2009 study conducted by the U.S. Geological for water in power plants.
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Irrigation is the second largest category Table 1: Total Water Use in the U.S. for water use and is also declining. Estimated water use in 2005 was 128 Total Water Use in the Billion gallons per % Change billion gallons of water per day – down U.S. day in 2005 % of Total 1980-2005 15 percent from the peak in 1980 and Thermoelectric Power 201 49% -4% representing 31 percent of total use.
Irrigation 128 31% -15% • The average application rate Public Supply 44 11% +33% for irrigation water has declined steadily from 3.55 acre-feet per 31 8% -31% Industrial acre in 1950 to 2.35 acre-feet Rural Domestic/ per acre in 2005. 6 1% -7% Livestock • This decline is attributed to Total 410 — -5% greater use of more efficient 230 million 301 million Population +31% sprinkler systems rather than in 1980 in 2005 flood systems4.
Source: 2009 Circular 1344, U.S. Geological Survey, “Estimated Use of Water in the United States in 2005”. Note: Data for 2010 water use will first become available in 2014.
Table 2: Trends in Total Water Withdrawals by Water-Use Category (U.S. Geological Survey)
Source: 2009 Circular 1344, U.S. Geological Survey, “Estimated Use of Water in the United States in 2005”. Note: Data for 2010 water use will first become available in 2014.
2 Public Supply Water Use • Domestic use made up 58 Self-Supplied Industrial Water Increases percent of the total while Use Decreases commercial/industrial made Public supply refers to domestic, Industrial water use includes water up 42 percent. commercial, and industrial users of used for such purposes as fabricating, public water supply systems. Public • The commercial/industrial number processing, washing, diluting, cooling, supply water use was 44.2 billion is a catch-all including industrial or transporting a product; incorporating gallons of water per day in 2005 – facilities, wastewater treatment water into a product, or for sanitation up 33 percent from 1980. This is a plants, firefighting, pools, parks, needs within the manufacturing facility. system losses, and all buildings reflection of the population increase Some industries that use large amounts with more than 15 connections5. over the same period of 31 percent. of water produce such commodities
Table 3: Trends in Population and Freshwater Use by Source (U.S. Geological Survey)
Source: 2009 Circular 1344, U.S. Geological Survey, “Estimated Use of Water in the United States in 2005”. Note: Data for 2010 water use will first become available in 2014.
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as food, paper, chemicals, refined • The use of water in the mining Section II: Water petroleum, or primary metals. Water industry remained relatively flat. Consumption in Industrial for industrial use may be delivered • This reflects a decrease in Compressed Air Systems from a public supplier or be self- manufacturing employment Compressed air systems are present supplied. Stricter water-quality of almost 19 percent from in almost all industrial processes and standards for water discharges, 1990-2005. mandated by the Clean Water Act, facilities. They have been correctly may have also encouraged water • Employment in several major identified as an area of opportunity conservation. The data taken from water-using industries showed to reduce electrical (kW) energy even larger declines: this U.S. Geological Survey looks costs through measures like reducing at self-supplied industrial water6. –– Primary metal manufacturing compressed air leaks and identifying declined 31 percent. artificial demand and inappropriate • Self-supplied industrial water use uses. Water-cooled air compressors was 31 billion gallons of water –– Paper manufacturing and can also be significant consumers of per day, a decrease of 31 percent petroleum industries declined water and reducing these costs can from 2005 to 19807. 26 percent. represent a second area of opportunity. • Significant growth in water –– Employment in the chemical A very “typical” industrial plant use has been seen in the manufacturing industry declined running two 125 horsepower, water- “Aquaculture” industry – 12 percent. the farming of fish. cooled, single-stage, rotary screw,
Table 4: Cooling Water Requirements for Single-Stage Rotary Screw Air Compressors
Typical Lubricant-cooled Rotary Screw Cooling Typical Values for Air-Cooled Oil-Coolers Estimated Estimated Heat Rejection to Cooling Water (btu/hr)* Heat Rejection to Cooling Air (btu/hr)*
Air Water-cooled Air Air-cooled Compressor Oil-Cooler and Compressor Oil-Cooler and Capacity After-Cooler Approx. gpm Approx. gpm Capacity After-Cooler Approx. cfm CFM/HP** btu/hr at 70 ˚F at 85 ˚F CFM/HP* btu/hr Cooling Air
250/62 150,900 6 10 250/62 156,300 8400
350/83 200,300 7 12 350/83 208,500 8400
500/120 276,700 11 18 500/120 287,700 12000
800/215 445,500 16 27 800/215 463,100 17500
1000/250 550,400 23 39 1000/250 572,400 28700
1200/300 668,200 33 56 1200/300 694,700 28700
1500/350 889,709 33 56 1500/350 920,000 36000
2500/500 1,543,000 49 79 2500/500 1,543,000 45000
* This data is general in nature and should not be used to select equipment. It is necessary to look at the specific engineering data for all equipment being used. **System at 100 psig
4 air compressors can consume 11.4 of the water-consumption of all the million gallons of water per year. installed air compressors and of how The Clean Water Act A larger installation, with a 350 the water-cooling systems function. The Federal Water Pollution horsepower rotary screw under similar An evaluation should be made, in each Control Act of 1948 was the first circumstances, can consume 17 million facility, of the feasibility and benefits major U.S. law to address water gallons per year8. of switching to an air-cooled air pollution. Growing public awareness compressor or switching to a different and concern for controlling Many older facilities continue to use water-cooling system. water pollution led to sweeping two-stage, water-cooled, reciprocating amendments in 1972. As amended air compressors. Pulp and paper mills How Much Cooling Water is in 1977, the law became commonly and steel mills are perfect examples. Required by Air Compressors? known as the Clean Water Act Facilities, like these, can require 550 The standard rating, for air compressor (CWA). The 1977 amendments: million gallons per year of cooling water cooling water requirements, is how many for the air compressors. • Established the basic gallons of water per 1,000 btu/hr is structure for regulating Both air compressors and rejected into the cooling water flow. pollutant discharges into the compressed air dryers can be water- Air compressors generate a high waters of the United States. cooled. We highly recommend that rejection load due to their very basic • Gave EPA the authority energy managers, at multi-factory inefficiency – i.e. it takes 7 to 8 input to implement pollution corporations, take an inventory horsepower to supply 1 hp of work control programs such as setting wastewater standards for industry.
• Maintained existing requirements to set Table 5: Cooling Water Requirements for Two-Stage Reciprocating water quality standards Air Compressors for all contaminants in surface waters. Two-Stage Reciprocating Air Compressor Cooling Water* • Made it unlawful for any Inlet Air 60 ˚F, Inlet Air 100 ˚F, person to discharge any Water 75 ˚F Water 95 ˚F pollutant from a point source into navigable waters, unless Discharge Air gpm Air gpm a permit was obtained under Bhp pressure Cap discharge water discharge water its provisions. Class psig acfm ˚F required ˚F required • Funded the construction 150 125 772 335 16 370 16 of sewage treatment plants under the construction 200 125 1050 335 21 370 21 grants program. 250 125 1300 335 26 370 26 • Recognized the need for 300 125 1560 335 32 370 32 planning to address the critical problems posed by nonpoint 350 125 1840 335 37 370 37 source pollution. 400 125 2035 335 41 370 41 Source: United 450 125 2340 335 52 370 52 States Environmental Protection Agency (EPA), http://www.epa. *This data is general in nature and should not be used to select equipment. It is necessary to look at the specific gov/lawsregs/laws/ engineering data for all equipment being used. cwahistory.html
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• Other critical data is needed such Today, the cost of disposing of the as OEM rated air flow (acfm at full heated cooling water has escalated as load pressure), compressor shaft various agencies may limit the dumping power (BHP), and motor input HP/ of the heated water into streams, rivers KW inclusive of motor/drive losses. and lakes due to potential thermal • GPM is typically provided, relative pollution. This is what has driven to cooling water requirements, the thermoelectric power plants to by the manufacturers of air alternative cooling systems. In many compressors. areas well-water supply is diminishing as the water tables are lowering and Three Primary Sources as the well gets older, the total flow of Industrial Cooling Water in gallons-per-minute (gpm) falls off. A modern air-cooled, oil-free, rotary screw Public Supply Water air compressor River Water/Lake Water Discussed in the U.S. Geological River and lake water have the same Survey as the category that continues limitations as well-water with regards in compressed air. This creates a heat- to grow in water use. Over the last to intake filtration and water treatment. of-compression generated during the 40 years these costs have escalated In many, if not most, areas today it is process reflecting this inefficiency. rapidly reflecting the scarcity of water no longer “free” and there often is a Energy input not converted to work and the cost of water treatment. It is charge for the discharge-heated water shows up as heat. This heat has to becoming the exception to the rule to the local body of water. There are be removed for the equipment to run today to see a compressed air system’s also EPA Clean Water Act regulations and for the plant to be able to use cooling-water supply coming from to be met and monitored with any the air. Particularly today, where dry the municipal utility. True costs are water being discharged to this type compressed air is often critical, it must not always evident. Additional costs, of water supply. be reliably and effectively after-cooled like sewer chargers, can’t be ignored. Often, city water will still require water and dried to a specified pressure dew Calculating the Basic Water point using compressed air dryers. treatment for effective performance Costs for Compressed in industrial cooling. These costs must Air Systems Calculating the required gallons- also be considered. per-minute (gpm) is dependent upon Regardless of what “rule of thumb” several critical variables: Self-Supplied Well-Water number is used for water cost (not including energy use) it will probably • Intake cooling water temperature Well-water has varying site-specific not be right for each particular to the air compressor or dryer. characteristics but it is generally not location. This cost is very site specific “Free”. After the well is drilled, in most • The allowable compressor and should be the first factor identified parts of the world the good news is discharge temperature – i.e. when embarking on a water cost, that the water is usually cool. The reciprocating, oil-free rotary energy-control program. All of these bad news is that it usually requires screw and centrifugals easily escalating costs, along with the significant intake filtration and water handle 350 to 400 ˚F discharge. man hours required to measure and Lubricant-cooled units are treatment for industrial use. Electric manage the process, have created limited by the cooling lubricant energy is required to pump it out of the a great incentive for industrial plants fluid but are usually a maximum ground and through the equipment. of about 200 ˚F.
6 to supply or replace all their own “Rule of Thumb” Formula plant water utility. to Calculate Water-Cooling Costs of Air Compressors The net result of these cost factors for cooling water have resulted (a or b) + c with most design engineers using Formulas: a “default cost” of $3.00 (USD) per 1,000 gallons of cooling water – when a. Untreated Cooling Water Cost = (Gallons per year/1000) the actual site situation is unknown. x $3.00 The accompanying water treatment A modern air-cooled, oil-free, rotary screw Treated Cooling Water Cost = cost is about specific situations and b. air compressor (Gallons per year/1000) x $4.20 can be much higher depending on site c. Compressor Enclosure conditions and maintenance diligence – Switching to Air-Cooled Air Vent Fan Electric Cost = $1.20 per 1,000 gallons based on Compressors (Input kW x hours x ($/kWh) 40 grains of hardness, alkalinity 10, In light of escalating water costs Example: and biocide treatment included. and regulations, plants have sought A water-cooled, two-stage, rotary screw, lubricant-cooled, 100 horsepower air compressor. Table 6: Comparing Costs of Water- and Air-Cooled Systems: Assumptions: Two-stage, Lubricant Cooled, 100 hp, Rotary Screw Air Compressor • 8600 working hours per year (to take into account down-time) Two-stage Lubricant-Cooled • Cooling water use volume of 11 GPM at 70 °F Comparing Cooling 100 hp Class • Untreated Cooling Water Cost Requirements 547 acfm /111 bhp of $3.00 per thousand gallons Lubricant-Cooled, Two-Stage, at 100 psig Rotary Screw Compressor • Compressor Enclosure Vent Discharge 180–200 ˚F Fan Input Power of 1.1 kW Water Air • Electrical energy cost of $0.06 per kWh Gpm at 50 ˚F Electric $.06 kWh 5.5 fan hp/ 8 at 8,600 hours/yr. 5kW/$2,580 yr. Solution: Gpm at 70 ˚F 11 N/A • Step 1 to Calculate a: 8600 hours x (11 GPM x 60) = Gpm at 80 ˚F 18 N/A 5,676,000 gallons of water Total H O pressure loss (psid) 21 N/A per year 2 • Step 2 to Calculate a: Vent fan Input Power 1.1 kW N/A (5,676,000/1000) x $3.00 = Cooling Cost at 70 ˚F H O $17,028.00 untreated cooling 2 $17,028 (H O costs at 3.00 — water cost per year 2 per year per 1,000 gallons) • Step 3 to Calculate b: 1.1 kW x 8600 hours x $0.06 kWh = $568 Vent fan cost N/A $567.60 vent fan electric per year cost per year • Step 4: $567.60 + $17,028.00 = Water & Electrical Energy Cost $17,596 $2,580 $17,596.60 total annual at $.06 kWh/8600 hrs/yr. per year per year cooling costs Total Heat Remaining 303,000 btu/hr
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to decrease their cooling water 100 horsepower air compressor will Using a similar example, an air- requirements. Compressed air have 85% lower water and electrical cooled, 200 horsepower oil-free, air systems have become prime targets energy costs – compared to a similar compressor will see 89% lower water for continuous duty air-cooled air water-cooled unit. The air-cooled unit and electrical energy costs – compared compressors. Some air-cooled rotary will simply deploy a 5 kW fan creating to a similar water-cooled unit. The screw compressors have seen design an energy cost of $2,850.00 per year. air-cooled unit will simply deploy a improvements and can accept higher Assuming 8600 working hours per year 10 kW fan creating an energy cost of ambient temperatures than in the past. to take into account down-time, the $5,160.00 per year. Assuming 8600 water-cooled unit, with cooling water working hours per year to take into The benefits of switching are readily at 70 °F, will use 5,676,000 gallons per account down-time, the water-cooled apparent in terms of reduced water year at a cost of $17,028.00 per year. unit, with cooling water at 70 °F, will consumption and costs. Using the Add the small compressor enclosure use 7,236,600 gallons of water per year prior example, an air-cooled, two- vent fan and the total annual cost at a cost of $44,892.00 per year. Add stage, rotary screw, lubricant-cooled, is $17,597.00. a small compressor enclosure vent fan and the total annual cost is $45,279.00.
Both of these examples used Table 7: Comparing Costs of Water- and Air-Cooled Systems: conservative water temperatures of Two-stage, Oil-free, 200 hp, Rotary Screw Air Compressor 70 °F, did not add the potential cost of Two-stage $1.20 per thousand gallons for water Oil-free treatment, and did not add pumping Comparing Cooling 200 hp Class circulation costs. Requirement Oil-Free, Two-Stage 856 acfm/193 bhp at 100 psig Rotary Screw Compressor When evaluating a switch to an air- Discharge 350–400 ˚F cooled air compressor, however, Water Air particularly on units larger than Gpm at 50 ˚F Electric $.06 kWh 11 fan hp/10 kW/ 22 100 horsepower, it is important to at 8,600 hours/yr. $5,160 yr. seriously evaluate all the application Gpm at 70 ˚F 29 N/A variables like room ventilation, ambient Gpm at 80 ˚F 48 N/A temperatures, after-cooler and dryer performance capabilities, maintenance Total H O pressure loss (psid) N/A 2 personnel and processes. 1/.75 kW/ Vent fan HP 3,500 cfm All this considered, looking at the differences, it is obvious why plants are Cooling Cost at 70 ˚F H2O/$/yr.
(H2O costs at 3.00 $44,892 looking for air-cooled units whenever per 1,000 gallons) possible and/or looking at how to Vent fan cost $387 N/A minimize water cooling costs when Water & Electrical Energy Cost air is not viable. $45,279 $5,160 at $.06 kWh/8600 hrs/yr. Total Heat Remaining 599,000 btu/hr
8 An effective trim cooler should be well • Significant water loss due Section III: Six Different controlled to effectively modulate the to ambient evaporation Types of Cooling Systems flow and manage the power use. Often • Continued buildup of silt in the Most air compressors are designed to these trim coolers are sized to be able pond may significantly reduce receive cooling water, at the required to handle 100% of the load and keep heat absorption capability and flow, with a maximum inlet temperature the equipment running in the case not remain usable of 100 ˚F and expect maximum of an emergency. discharge water temperatures of • Water treatment is still necessary 120 ˚F to 130 ˚F. These values should The energy use of the circulation • Makeup water is usually with be kept in mind when evaluating any pumps is a function of the flow volume some kind of expense – i.e. well and the head. Poor fluid piping, sizing compressor cooling system. pump, etc. and configuration can add pressure Evaluation of the cooling system loss and head. Installing the cooler • A pumping station is still required for the compressor should include farther away from the compressors to circulate the cooling water the after-cooler performance as it or on the building roof will also usually relates to the inlet temperatures it will increase the cooling fluid “head” and Cooling System #2: Trim Coolers provide to the compressed air dryer. require larger pumps. A trim cooler is a smaller heat Compressed air dryers are almost exchanger to be used only in times all designed to receive inlet air to Cooling System #1: of excess or peak heat loads. They be dried at 100 psig and 100 ˚F. Recirculation Ponds are installed to complement a larger With temperatures to the dryer above Recirculation cooling water ponds system designed to handle all cooling 100 ˚F (the rated inlet temperature), are an option for a locally controlled need 85-90% of the time. A trim the moisture load per scfm to the dryer cooling water system supply. As cooler can allow a facility to go with will increase significantly reducing the long as the pond is large enough to a lower water consumption system flow rating drying capability. For proper handle the heat load under the worst by being there as an emergency back- application, be aware of the inlet condition and maintain an acceptable up during high heat load periods. air temperature to the dryer and the temperature, it can be very effective, A trim cooler might be a shell and design approach temperature to the particularly in large installations. They tube heat exchanger or a cabinet- incoming cooling media temperature – do have some inherent limitations: enclosed chiller. air or water.
With the exception of large water- cooled reciprocating compressors, most rotaries and centrifugal air compressors have relatively high pressure losses through them when compared to many others commonly fluid- cooled industrial pieces of equipment. Whenever possible, each compressor (or group of compressors) should be on their own system to avoid other pressure losses affecting the flow to the air compressors.
Figure: A water-to-air trim cooler
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Cooling System #3: Dry Air Cooling System #4: Open Open tower coolers are very prevalent Cooling – No Water Required Evaporative Cooling Tower throughout industry and are often These coolers are closed loop cooling The cooling water system requiring the known affectionately as very effective systems usually using an appropriate lowest capital costs is the open tower “air washers” meaning they remove water (60%) and polyglycol (40%) mix type. In this system, the heated return the dirt and impurities from the (one-time fill) passing through finned water flows down a controlled open ambient air, generating a continual tubes. The coolers are in modules – path where it is cooled by continual cleaning of the tower. each with a small fan for air-cooling. evaporation by moving ambient air from The contamination factor, along with the As the heat load is reduced, the fans a fan and pulling an evaporating water high level of make-up water required, are shut-off individually as required and percentage into the ambient air. These makes proper and diligent water brought back on when needed. Dry air towers will have a smaller circulating treatment and condition monitoring a cooling systems are usually available pump to move the water through the prerequisite for a successful installation. from 160,000 btu/year rating at 250 cooling area and a large horsepower Open towers also inject oxygen into cfm class to 4,000,000 btu/hr rating electric motor fan to move ambient air the process water system which may at 6,000 cfm class – with special sizes over and through the cooling water or may not create corrosion or other for other levels. to optimize the evaporation cooling. maintenance issues. There is also a flushing or blow out system using water. Cooling System #5: Closed Circuit Cooling Tower with an The primary benefit of this type Auxiliary Evaporation Cooling of system is that as the ambient Assist for Hot Weather temperatures increase, generally In this type system the primary so does the evaporation rate which coolant is sealed in a closed loop means, in most North American system – unexposed to ambient air, locations, they will deliver about it may be water – but it more often 85 ˚F temperature cooling water Typical Dry-Air Fluid Cooling System – Usually is a glycol water mix appropriate to uses an appropriate water/glycol mix when operating properly within their the local ambient cold temperature design limits.
The air-cooled heat exchangers can be manufactured to deliver a 2 ˚F approach temperature but economics usually dictate a 5 ˚F approach. This means in parts of the country they may be able to handle a reciprocating compressor’s cooling needs with little or no trim cooling. Dry air cooling systems, when combined with a trim cooler, can provide factories with a very low-cost and reliable alternative to water-cooled machines.
Typical Evaporation Open Tower Typical Closed Circuit Cooling Fluid Tower with Counter Flow with Evaporator
10 Table 8: Direct Cooling Water/Fluid Comparison of a 600 hp, 3-Stage Centrifugal Compressor, 2,750 scfm at 100 psig at 290 bhp
Compressor Cooling 1,000 btu/hr gpm
1,000 btu/hr 1,547 — After-cooler Gpm at 85 ˚F — 124
1,000 btu/hr 145 — Oil-cooler Gpm at 85 ˚F — 29
Total 1,000 btu/hr/gpm 1,692 153
Once – through Open Closed Loop Municipal Evaporative Evaporative Dry Cooler Water Water Tower with Trim
Water cooled for compressor 153 Recirculated Recirculated N/A cooling – gpm/$yr. $236,844
Total gallon/year at $3.00/1,000 gallons 78,948,000 N/A N/A N/A
Spray circulation pump motor kW/100% kW/30% N/A at $.06 kW/8,600 hrs/yr. $516 $155
(12) 1.5 hp 75 hp 11 hp 18 hp at 50% Main cooling system fan driver motor N/A 60 kW 10 kW use kW/yr. at $.06/8,600 hrs/yr. $30,960/yr. $5,160/yr. 9 kW $4,644/yr.
Evaporative make up water – gpm 3.4 gpm 1.2 gpm N/A $/year $5,264/yr. $1,858/yr. N/A gallons/year 1,754,400 619,200
Flushing blow out water – gpm 45.9 1.7 ($3.00/1,000 gallons) $/year N/A $71,052/yr. $2,632/yr. N/A gallons/year 23,684,400 877,200
Total Gallons of Water for Water Treatment 78,948,000 25,438,400 1,496,400 N/A
Water treatment costs at 42 grains hardness, 10 alkalinity, with biocide $94,737 $30,526 $1,795 N/A treatment at $1.20 per 1,000 gallons
Trim cooler costs to operate during 30% utilization extreme hot weather; chiller cooler kW/% N/A N/A N/A 9 kW time at $.06 kWh/8,600 hrs/yr. $1,393/yr.
Pump station electric motor kW – based on 7 kW 7 kW 7 kW 7 kW 160 gpm, 100 ft of head specific gravity 1.0 $3,612 $3,612 $3,612 $3,612 100% of time at $.06 kWh/8,600 hrs/yr.
Total Operating Cost Water $/yr. $335,039/yr. $136,666/yr. $13,350/yr. $9,649/yr.
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limitations. This is very good for the advantages which may be significant Conclusion equipment being cooled since it runs when the operating conditions dictate. for a significantly long time without As the population continues to grow In a compressed air system the significant water treatment requirement in the United States, industrial use process water must be capable of or replenishment. will need to continue to fall to help full capacity throughout the year. This offset the increases in Public-Supply The cooling system is equipped with means maintaining a clean, reliable water use. Compressed air systems a motor driven spray pump and spray cooling fluid loop is critical. To do provide an opportunity for energy header which delivers a spray over this in an open tower requires proper managers to reduce associated the air cooled heat exchangers during and diligent water treatment and cooling water consumption and costs. hot weather and creates evaporation maintenance. The closed loop system Understanding the costs and the auxiliary cooling similar to the open is basically isolating the compressor alternative types of cooling systems tower described earlier. cooling fluid from all air ambient is an important first step. out borne contaminants: Cooling System #6: Closed Loop All options are preferable to “once Cooling with Evaporation • This reduces the frequency of the through” municipal water. The ever- need to shut down the cooling growing regulations and controls will Closed Loop Cooling with Evaporation system for cleaning. just further increase these costs. The systems experience additional water • This type cooler has a lower true cost of the open evaporative tower use, the magnitude very much dictated volume of recirculating water and the closed loop evaporative tower by the ambient conditions. There is requiring water treatment filtration can be driven much higher with more also a motor driven coolant circulation significant water treatment cost, water pump and motor drive main cooling • The compressor cooling disposal regulations, sewer costs and air fan similar to the open tower. fluid usually requires minimal surcharges. If a facility can’t simply The standard pumping station treatment convert a water-cooled air compressor is also required. Some flushing • During periods of dry operation to an air-cooled air unit, a dryer-cooler or blow may also be required. (cooler weather) the need for spray evaporation and therefore system (with trim) has the lowest costs Depending on design and operating makeup water is eliminated and very predictable results. conditions, this type of cooling towers For more information, please use parallel flow or cross flow or • These units, like many central cooling water systems, are set up contact Mr. Nitin G. Shanbhag, counter flow. Compared to an open Senior Manager, Air Technology Group, with either another cooling water Hitachi America, tel: 704-494-3008, tower with evaporative cooling, the source or chiller cooler. These closed circuit cooling system has email: [email protected], trim coolers cool the fluid from www.hitachi-america.us/airtech a higher initial cost but also some the primary cooler when required by too high a temperature.
Endnotes 1 Estimated Use of Water in the United States in 2005, Joan F. Kenny, Nancy L. Barber, Susan S. Hutson, Kristin S. Linsey, John K. Lovelace, and Molly A. Maupin, U.S. Department of the Interior, U.S. Geological HITACHI AMERICA, LTD. Survey, Reston, Virginia, 2009, Circular 1344, page Air Technology Group 2 Ibid, Table 14, Trends in estimated water use in the U.S. page 43 3 Ibid, page 42 4 Ibid, page 45 5808-Q Long Creek Park Drive 5 Ibid, page 16 Charlotte, NC 28269 6 Ibid, page 32 Tel: 704.494.3008 7 Ibid, page 1 8 Figures taken from a data sheet of a single stage, lubricant cooled, rotary screw air compressors at 100 psig Email: [email protected] pressure, 8600 working hours, and 70 °F water temperature. www.hitachi-america.us/airtech
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