Greening of Facilities - Part V

8/6/2019 Greening of Facilities - Part V

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Energy Savings in MEP Systems -

Energy Systems

Course No: M08-002

Credit: 8 PDH

Steven Liescheidt, P.E., CCS, CCPR

Continuing Education and Development, Inc.9 Greyridge Farm CourtStony Point, NY 10980

P: (877) 322-5800F: (877) 322-4774

[email protected]


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52

GREENING FEDERAL FACILITIESAn Energy, Environmental, and Economic Resource Guide for Federal Facility Managers and Designers

Part V

ENERGY SYSTEMS

SECTION PAGE

5.1 Energy and Conservation Issues ............................ 54

5.2 HVAC Systems ............................................................. 56

5.2.1 Boilers .............................................................. 58

5.2.2 Air Distribution Systems............................. 60

5.2.3 Chillers ............................................................ 62

5.2.4 Absorption Cooling ....................................... 66

5.2.5 Desiccant Dehumidification ....................... 68

5.2.6 Ground-Source Heat Pumps....................... 70

5.2.7 HVAC Technologies to Consider ................ 72

5.3 Water Heating ............................................................. 74

5.3.1 Heat-Recovery Water Heating .................... 76

5.3.2 Solar Water Heating ..................................... 78

5.4 Lighting ........................................................................ 80

5.4.1 Linear Fluorescent Lighting ...................... 82

5.4.2 Electronic Ballasts........................................ 84

5.4.3 Compact Fluorescent Lighting .................. 86

5.4.4 Lighting Controls.......................................... 88

5.4.5 Exterior Lighting .......................................... 90


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53

5.5 Office, Food Service, and Laundry Equipment ... 92

5.5.1 Office Equipment .......................................... 94

5.5.2 Food Service/Laundry Equipment ............ 96

5.6 Energy Management.................................................. 98

5.6.1 Energy Management and

Control Systems ....................................... 100

5.6.2 Managing Utility Costs ................................ 102

5.7 Electric Motors and Drives ...................................... 104

5.7.1 High-Efficiency Drives................................. 106

5.7.2 Variable-Frequency Motors ........................ 108

5.7.3 Power Factor Correction ............................ 110

5.7.4 Energy-Efficient Elevators ......................... 112

5.8 Electric Power Systems ............................................ 114

5.8.1 Power Systems Analysis .............................. 1165.8.2 Transformers .................................................. 118

5.8.3 Microturbines ................................................ 120

5.8.4 Fuel Cells ........................................................ 122

5.8.5 Photovoltaics ................................................. 124

5.8.6 Wind Energy ................................................... 126

5.8.7 Biomass Energy Systems ............................. 128

5.8.8 Combined Heat and Power ......................... 130


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5.1 Energy and Conservation Issues

Technical Information

TheEnergy Systems section of this guide describes sys-tems that provide key opportunities for energy sav-ings. The following are some of these opportunities:

Integrated design is a process whereby the variousdisciplines involved in designarchitect, mechanicalengineer, electrical engineer, interior design profes-sional, etc.work together to come up with design so-lutions that maximize performance, energy conserva-tion, and environmental benefits. Integrated design isan important aspect of energy conservation and equip-ment selection because decisions made in one area(lighting, for example) will affect others (such as chillersizing). Refer back to Section 4.1 Integrated Build-ing Design for an overview.

HVAC system improvements offer tremendous poten-tial for energy savings in most facilities. Opportuni-ties include replacing older equipment with more effi-cient products, improving controls, upgrading mainte-nance programs, and retrofitting existing equipmentto operate more efficiently. Central plants contain manyinterrelated components, and upgrading them takescareful planning, professional design assistance, andcareful implementation. This guide covers chillers,boilers, air distribution systems, and other HVAC tech-nologies.

Water heating is a major energy user in facilities withkitchens and laundries. Beyond reducing the use ofhot water, various heat recovery and solar technolo-gies can also help reduce operating costs.

Lighting. More than$250 million could be saved an-nually if all Federal facilities upgraded to energy-effi-cient lighting. Light energy savings of up to 40% canbe achieved in interior applications by replacing lampsand ballasts. Savings of well over 50% are possible bydesigning and implementing an integrated approachto lighting that includes daylighting, task lighting, andsophisticated controls.

Office equipment is becoming an ever greater pro-portion of building loads. Green appliances that fea-

ture automatic power shutdown and more efficient elec-tronics can help reduce energy consumption.

Energy Management and Control Systems (EMCSs)are critical in avoiding energy waste and monitoringenergy consumption. Control technology should beapplied intelligently for each situation, and an opti-mized mix of local and central control should be used.

The Federal Government is the largest single user ofenergy in the United States and purchases $1020 bil-lion in energy-related products each year. With owner-ship of more than 500,000 buildings, including 422,000

housing structures, the Federal Government has a tre-mendous interest in energy efficiency in buildings. TheEnergy Policy Act of 1992 and Executive Order 13123set goals for energy reduction and provide some guide-lines for implementing conservation measures. Annualenergy use in Federal buildings has dropped from140,000 Btu/sq ft (1,600 MJ/m2) in 1985 to 116,000 Btu/sq ft (1,300 MJ/m2) in 1997. To meet the Executive Or-der 13123 requirement, annual energy use must dropto 90,800 Btu/sq ft (1,000 MJ/m2) by 2010. FEMP pro-vides information on technologies that have beenproven in field testing or recommended by reliablesources, such as the DOE national laboratories.

Opportunities

The time for planning, evaluating, and implementingis now! Facility managers should first implement en-ergy- and demand-reducing measures in their opera-tions and then look for opportunities to cost-effectivelyreplace conventional technologies with ones using re-newable energy sources.

Facility managers should also set goals for their op-erations that follow Federal mandates. Executive Or-der 13123 requires an energy reduction in Federalbuildings of 30% by 2005 and 35% by 2010, relative to1985. Industrial and laboratory facilities are requiredto reduce energy consumption by 20% by 2005 and 25%by 2010, relative to 1990. Executive Order 13123 fur-ther states that agencies shall use life-cycle cost analy-sis in making decisions about their investments in prod-ucts, services, construction, and other projects to lowerthe Federal governments costs and to reduce energyconsumption. When energy-consuming equipmentneeds replacement, guidance for purchasing productsthat meet or exceed Executive Order 13123 procure-ment goals is available through FEMPs Product En-ergy Efficiency Recommendations series.


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Electric motor systems that operate around the clock(or nearly so) consume many times their purchase pricein electricity each year. This makes inefficient, large-horsepower motors excellent targets for replacement.

If the driven load operates at reduced speed a major-ity of the time, installing electronic motor controls couldreduce both energy consumption and operating costs.

Electrical power systems can be made more effi-cient through (1) maintenance practices focused onidentifying potential trouble areas, such as loose elec-trical connections; and (2) selection of efficient electri-cal equipment, such as transformers. There may alsobe opportunities to use renewable power-generationequipment.

Making It Happen

Carrying out energy efficiency improvements in Fed-eral buildings is not simply about energy technologiesand systems, it is also about financing and budgets.Here are a few financing strategies that can be appli-cable to Federal buildings. Also refer to Section 2.4 Alternative Financing.

Energy Savings Performance Contracts provideFederal agencies with a means of increasing their in-vestment in energy-saving technologies. Because ap-propriated funds are shrinking for many agencies,ESPCs enable them to secure financing from energyservice contractors, or ESCOs, to identify and imple-

ment energy conservation measures. In effect, agen-cies can defer the initial costs of equipment and payfor the equipment through utility-bill savings. FEMPassists Federal agencies with ESPCs.

Super ESPCs are a facilitated form of ESPC. Theyare regional agreements in which delivery orders areplaced against a contract with selected ESCOs. A Su-per ESPC allows individual facilities to negotiate con-tracts directly with certain competitively selected com-panies, greatly reducing the complexity of the ESPCprocess.

Basic Ordering Agreements (BOAs) are written

understandings negotiated between GSA and a util-ity or other business that set contract guidelines forenergy-consuming products and services. For example,the GSA Chet Holifield Federal Center in LagunaNiguel, California, contracted with its electric utilityfor thermal energy storage, energy-efficient chillers,variable-frequency drives, efficient motors, and light-ing system retrofits. The contractor invested $3,800,000,

and the governments share of the savings is $1,400,000over 14 years. The GSA retains the equipment afterthe contract term. One prominent BOA specifying en-ergy-efficient chillers for Federal procurement has beendeveloped between GSA and five major chiller manu-facturers in the United States. Other BOAs are beingdeveloped and will be available soon.

References

Architects and Engineers Guide to Energy Conserva-

tion in Existing Buildings (DOE/RL/018-30P-H4), U.S.Department of Energy, Washington, DC, 1990.

Technology Atlas Series, E Source, Inc., Boulder, CO,1996-97; (303) 440-8500; www.esource.com.

Contacts

To access FEMPsProduct Energy-Efficient Recommen-dations series or obtain more information on financ-ing alternatives, visit the FEMP Web site at www.eren.doe.gov/femp or call the FEMP Help Desk at (800)DOE-EREC (363-3732).

Source: Farallon National Wildlife Refuge

The U.S. Fish and Wildlife service needed a cleaner, qui-

eter power source for the Farallon National Wildlife Ref-

uge, 30 miles (48 km) west of San Francisco. Applied Powerdesigned a 9.1-kW hybrid photovoltaic system to withstand

the extremely corrosive island environment. Before this in-stallation, the staff operated extremely loud, expensive die-

sel generators during daylight hours only.


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5.2 HVAC Systems

occupied periods. Existing control systems will oftenaccommodate this very simple measure. Sections 5.6,5.6.1, and 5.4.4 (for lighting) address energy controlsin more detail.

Optimize for part-load conditions. Buildings usu-ally operate under conditions in which the full heatingor cooling capacity is not required. Therefore, signifi-cant improvements in annual efficiency will result fromgiving special consideration to part-load conditions.Staging multiple chillers or boilers to meet varyingdemand greatly improves efficiencies at low and mod-erate building loads. Pairing different-sized chillers andboilers in parallel offers greater flexibility in outputwhile maintaining top performance. Units should bestaged with microprocessor controls to optimize sys-tem performance.

Isolate off-line chillers and boilers. In parallel sys-tems, off-line equipment should be isolated from cool-ing towers and distribution loops. With reduced pump-ing needs, circulation pumps can be shut off or modu-lated with variable-speed drives.

Use economizers. In climates with seasons havingmoderate temperatures and humidity, adding air- andwater-side economizer capabilities can be cost-effec-tive. When ambient conditions permit, outside air pro-vides space conditioning without the use of the coolingplant. To prevent the inappropriate introduction of out-side air, careful attention must be given to economizerlogic, controls, and maintenance. With a water-side

economizer, cooling is provided by the cooling towerwithout the use of the chiller.

Remember that ventilation systems have a tre-

mendous impact on energy use because of the highcosts associated with heating or cooling outside air.Buildings should be ventilated according to ASHRAEStandard 62. The outside air requirements15 to 20cfm (7.19.5 L/s) per person in most commercial build-ingsof Standard 62s most recent version (62-1989)do not apply to buildings constructed before it was pub-lished, although for new additions of 25% or more, thisgrandfathering is not permitted by the major build-ing codes. The indoor air quality benefits of complyingwith ASHRAE 62-1989, such as higher productivityand decreased sick leave, may often make the addedexpense worthwhile, even when not required by law.

Upgrade cooling towers. Large savings are possiblewhen cooling towers are retrofitted with new fill, effi-cient transmissions, high-efficiency motors, and variable-frequency drives. Good water chemistry is needed tominimize the use of environmentally hazardous chemi-cal biocides. Ozone treatments also may be useful.

Heating, ventilating, and air-conditioning systems canbe the largest energy consumers in Federal buildings.HVAC systems provide heating, cooling, humidity con-trol, filtration, fresh air makeup, building pressure

control, and comfort controlall requiring minimalinteraction between the occupants and the system.Properly designed, installed, and maintained HVACsystems are efficient, provide comfort to the occupants,and inhibit the growth of molds and fungi. Well-de-signed, energy-efficient HVAC systems are essentialin Federal buildings and contribute to employee pro-ductivity. Boilers, air distribution systems, chillers, ab-sorption cooling systems, desiccant dehumidification,ground-source heat pumps, and new HVAC technolo-gies are covered in the sections that follow.

Opportunities

Consider upgrading or replacing existing HVAC sys-tems with more efficient ones if current equipment isold and inefficient; if loads have changed as a result ofother conservation measures or changes in buildingoccupancy; if control is poor; if implementing new ven-tilation standards has caused capacity problems; or ifmoisture or other indoor air quality problems exist. Besure to have a plan in place for equipment change-outand failure. The phase-out of CFCs is another factorencouraging chiller replacement. In all these cases, anintegrated approach should be utilized that looks at theentire cooling system and the entire building to take

advantage of synergies that allow for downsizing, aswell as boosting the efficiency of, a replacement chiller.


Strategies for reducing HVAC operating costs in largefacilities include the following:

Reduce HVAC loads. By reducing building loads, lessheating and cooling energy is expended. Load reduc-tion measures include adding insulation; shading harshwind and sun exposures with trees, shade screens,awnings, or window treatments and minimizing theuse of heat-producing equipment, such as office equip-ment and computers; daylighting; controlling interiorlighting; and capturing heat from exhaust air. SeePart 4of this guide for more on building design issues.

Incorporate building automation/control sys-tems. These systems can be added or upgraded to im-prove the overall performance of the building, includ-ing the HVAC equipment. Perhaps the simplest mea-sure and the first to be considered should be to ensurethat HVAC systems are in setback mode during un-


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Interconnect mechanical rooms for greater

modularity and redundancy. This increases effec-tive capacity while improving part-load efficiency.

IMPORTANCE OF MAINTENANCE

Proper maintenance helps prevent loss of HVAC airbalance (return, supply, and outdoor air); indoor air qual-ity problems; improper refrigerant charge; fouling ofevaporator coils by dust and debris; poor water quality

in cooling towers; and water damage from condensate.

Provide a monitoring and diagnostic capability.An important part of maintaining the rated efficiencyof equipment and optimal performance of HVAC sys-tems is understanding how they are functioning. In-corporate systems to track performance and identifyproblems quickly when they occur.

Ensure that air handlers are maintained. Toachieve better indoor air quality and reduce operatingcosts, steam-clean evaporator coils and air handlersat a minimum three-year rotation. Also service filtersfrequently.

Service the ventilation system.A good balance re-port is required. Airflows can then be periodicallychecked. Periodically lubricate dampers and check theiroperation by exercising the controls.

Prevent or repair air distribution system leak-

age. In residential and small commercial buildings,air duct leakage can be a huge energy waster. Leakscan also cause comfort and air quality problems. Checkventilation rates after duct repair to ensure that

ASHRAE standards are met and that desired pressurerelationships are maintained.

Eliminate or upgrade inefficient steam systems.Leaks are a common problem with older central steamdistribution systems. Regularly inspect for evidence

of leaks; repair problems as they occur or upgrade thesystem.

Check for improper refrigerant charge. Refriger-ant-based HVAC systems require precise levels of re-frigerant to operate at peak capacity and efficiency, andto most effectively control interior humidity in moistclimates. Loss of refrigerant charge not only wastesmoney but also damages the environmentmost re-frigerants deplete stratospheric ozone. Inspect for leaksand promptly fix problems. Consider replacing olderequipment with new, more efficient, ozone-safe systems.

Provide or consider ease of maintenance whenmaking any HVAC system modifications or equipmentpurchases. Make sure that access to filters (for clean-ing or replacement), ducts (for inspection and clean-ing), controls, and other system components remainseasy. Label components that will need servicing, andpost any necessary inspection and maintenance in-structions clearly for maintenance personnel.

References

ASHRAE Standard 62 (ventilation), Standard 90.1(energy performance), others; American Society ofHeating, Refrigerating and Air-Conditioning Engi-neers, Atlanta, GA; www.ashrae.org.

A Design Guide for Energy-Efficient Research Labora-

tories, Lawrence Berkeley National Laboratory; avail-able online (also downloadable) at ateam.lbl.gov/De-sign-Guide.

Space Heating Technology Atlas (1996) and Commer-cial Space Cooling and Air Handling Technology Atlas(1997), E Source, Inc., Boulder, CO; (303) 440-8500;www.esource.com.

Contacts

HVAC retrofits and maintenance opportunities arethoroughly covered in the FEMP-sponsored TrainedEnergy Manager course. Contact the FEMP Help Deskat (800) DOE-EREC (363-3732) for course information.

Information about the Laboratories for the 21st Cen-tury project is online at www.epa.gov/labs21century/.

For written material and software to assist with evalu-ating HVAC systems, contact the EPA ENERGY STAR

Building Hotline, (202) 775-6650; www.energystar.gov.

Chillers have changed dramatically in recent years.

Todays models are far better for the environment than

older products. Photo: McQuay Air Conditioning


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5.2.1 Boilers

Decentralize systems. Several smaller units strate-gically located around a large facility reduce distribu-tion losses and offer flexibility in meeting the demandsof differing schedules, as well as steam pressure and

heating requirements. Estimate standby losses bymonitoring fuel consumption during no-load periods.

Downsize. Strive to lower overall heating demandsthrough prudent application of energy conservationmeasures, such as increased building insulation andimproved glazings. Smaller boilers may be staged tomeet loads less expensively than large central plants.Many new units are designed to ease retrofit by fittingthrough standard doorways.

Modernize boiler controls. Direct digital controlsconsist of computers, sensors, and software that pro-vide the real-time data needed to maximize boiler sys-

tem efficiency. They allow logic-intense control func-tions to be carried out, such as temperature reset, op-timizing fuel/air mixture based on continuous flue-gassampling, managing combustion, controlling feedwaterand drum levels, and controlling steam header pressure.

Install an economizer. Install a heat exchanger inthe flue to preheat the boiler feedwater. Efficiency in-creases about 1% for every 10F (5.5C) increase infeedwater temperature. If you are considering an econo-mizer, ensure (1) that the stack temperature remainshigher than the acid dew point in order to prevent fluedamage, and (2) that excess flue temperature is due toinsufficient heat transfer surfaces in the boiler rather

than scaling or other maintenance problems.

Install an oxygen trim system. To optimize thefuel/air ratio, these systems monitor excess oxygen inthe flue gas and modulate air intake to the burnersaccordingly.

Reduce excess air to boiler combustion. The com-mon practice of using 50100% excess air decreasesefficiency by 5%. Work with the manufacturer to de-termine the appropriate fuel/air mixture.

Install air preheaters that deliver warm air to theboiler air inlets through ducts. The source of warm air

can be the boiler room ceiling, solar panels, or solar-preheat walls. Managers should check with boilermanufacturers to ensure that alterations will not ad-versely alter the performance, void the warranty, orcreate a hazardous situation.

Most medium-to-large facilities use boilers to gener-ate hot water or steam for space heating, domesticwater heating, food preparation, and industrial pro-cesses. For boilers to run at peak efficiency, operators

must attend to boiler staging, water chemistry, pump-ing and boiler controls, boiler and pipe insulation, fuel-air mixtures, burn-to-load ratio, and stack tempera-tures.

Opportunities

Every effort should be made to upgrade boiler systemsto peak efficiency in order to reduce operating costsand environmental impacts. When replacing old equip-ment or installing new equipment:

Consider the advantages of multiple boiler systems,

which are more efficient than single boilers, espe-cially under part-load conditions.

Consider solar-assisted systems and biomass-fired

boilers as alternatives to conventional boiler sys-tems.

Consider opportunities for cogeneration (combinedheat and power), including the use of fuel cells and

microturbines as the heat source.


Note recent trends in boiler systems, which in-

clude installing multiple small boiler units, decentral-izing systems, and installing direct digital control(DDC) systems, including temperature reset strategies.Because these systems capture the latent heat of va-porization from combustion water vapor, flue-gas tem-peratures are low enough to vent the exhaust throughpolyvinyl chloride (PVC) pipes; PVC resists the corro-sive action of flue-gas condensate.

Replace inefficient boilers. In newer units, morefuel energy goes into creating heat, so both stack tem-peratures and excess oxygen are lower. Estimate effi-ciencies of existing units by measuring excess air, flueand boiler room temperatures, and percent of flue-gas

oxygen and carbon dioxide. Some utilities will providethis service free of charge. Boilers are available thathave efficiencies greater than 90%.


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Install automatic flue dampers to reduce theamount of boiler heat that is stripped away by naturalconvection in the flue after the boiler cycles off.

Retrofit gas pilots with electronic ignition systems,which are readily available.

Add automatic blowdown controls. Uncontrolled,continuous blowdown is very wasteful. A 10% blowdownon a 200 psia steam system results in a 3% efficiencyloss. Add automatic blowdown controls that sense andrespond to boiler water conductivity and pH.

Add a waste heat recovery system to blowdowns.Capturing blowdown in recovery tanks and using heatexchangers to preheat boiler feedwater can improvesystem efficiency by about 1%.

Consider retrofitting boiler fire tubes with

turbulators for greater heat exchange, after check-ing with your boiler manufacturer. Turbulators arebaffles placed in boiler tubes to increase turbulence,thereby extracting more heat from flue gases.

Insulate boiler and boiler piping. Reduce heat lossthough boiler walls and piping by repairing or addinginsulation. The addition of 1 inch (2.5 cm) of insula-tion can reduce heat loss by 8090%.

OPERATION AND MAINTENANCE

Proper operation and maintenance is the key to effi-cient boiler operation. Any large boiler plant should

maintain logs on boiler conditions as a diagnostic tool.When performance declines, corrective action shouldbe taken.

Reduce soot and scale. Deposits act as insulationon heat exchangers and allow heat to escape up theflue. If the stack temperature rises over time underthe same load and fuel/air mixture, and deposits arediscovered, adjust and improve water chemistry andfuel/air mixture accordingly. Periodically running thesystem lean can remove soot.

Detect and repair steam leaks. Though they arenot directly boiler-related, leaks in underground dis-

tribution pipes can go undetected for years. Monitorblowdown and feedwater to help detect these leaks.Repair them promptly.

On systems operating with negativepressure, air may enter the system af-

ter combustion and give false indications of ex-cess air measured with flue-gas oxygen.

ReferencesBrecher, Mark L., Low-Pressure System Gets HighMarks from College,Heating/Piping/Air Condition-ing, September 1994.

Payne, William,Efficient Boiler Operations Sourcebook,3rd Edition, Fairmont Press, Lilburn, GA, 1991.

Washington State Energy Office,Boiler Efficiency Op-erations (WAOENG-89-24), Olympia, WA, 1989.

The Multi-Pulse boiler from Hydrotherm offers an annual

fuel utilization efficiency (AFUE) of over 90%. Multipleunits can be ganged for higher output requirements.

Source: HydroTherm


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5.2.2 Air Distribution Systems

further from the thermostat and VAV box location tobe uncomfortable. Local ceiling diffusers ducted from theVAV box to individual rooms can modulate the amountof conditioned air delivered to a space, eliminating the

inefficient practice of overheating or overcooling spacesto ensure the comfort of all occupants. VAV diffusersrequire low duct static pressures0.25 inches of wa-ter column (62 Pa) or lessand thus save on fan energy.

Increase duct size to reduce duct pressure dropand fan speed. Eliminate resistance in the duct sys-tem by improving the aerodynamics of the flow pathsand avoiding sharp turns in duct routing. Increasingthe size of ducting where possible allows reductions inair velocity, which in turn permit reductions in fanspeed and yield substantial energy savings. Small in-creases in duct diameter can yield large pressure dropand fan energy savings, because the pressure drop inducts is proportional to the inverse of duct diameter tothe fifth power.

Specify low-face-velocity air handlersto reduce

air velocity across coils. Oversizing the air handlerincreases the cross-sectional area of the airflow, allow-ing the delivery of the same required airflow at a slowerair speed for only a relatively small loss of floor space.The pressure drop across the coils decreases with thesquare of the air speed, allowing the use of a smallerfan and smaller VFD, thus reducing the first-costs of thosecomponents. Air traveling at a lower velocity remainsin contact with cooling coils longer, allowing warmer

On an annual basis, continuously operating air distri-bution fans can consume more electricity than chillersor boilers, which run only intermittently. High-effi-ciency air distribution systems can substantially re-

duce fan power required by an HVAC system, result-ing in dramatic energy savings. Because fan powerincreases at the square of air speed, delivering a largemass of air at low velocity is a far more efficient designstrategy than pushing air through small ducts at highvelocity. Supplying only as much air as is needed tocondition or ventilate a space through the use of vari-able-air-volume systems is more efficient than supply-ing a constant volume of air at all times.

Opportunities

The largest gains in efficiency for air distribution sys-

tems are realized in the system design phase duringnew construction or major retrofits. Modifications toair distribution systems are difficult to make in exist-ing buildings, except during a major renovation.


Design options for improving air distribution efficiencyinclude (1) variable-air-volume (VAV) systems, (2) VAVdiffusers, (3) low-pressure-drop ducting design, (4) low-face-velocity air handlers, (5) fan sizing and variable-frequency-drive (VFD) motors, and (6) displacement-ventilation systems. These are described below.

Deliver only the volume of air needed for condi-tioning the actual load. Variable-air-volume systemsoffer superior energy performance compared with con-stant-volume systems with dual ducts or terminal reheat

that use backward-inclined or airfoil fans. VAV systemsare becoming an increasingly standard design practice,yet even greater efficiency gains can be made throughcareful selection of equipment and system design.

Use local VAV diffusers for individual tempera-ture control. Temperatures across a multiroom zonein a VAV system can vary widely, causing individuals

$

Designed for use with access flooring systems, these passiveair diffusers from Krantz swirl air, causing it to mix veryquickly with surrounding air.

Source: Krantz

1. Floor-mounted twist outlet

2. Throttle device

3. Dirt-collection basket

Facility managers can evaluate the ben-efits of reducing the size of fan systems

in facilities by running EPAs QuikFan software.The software is available to Green Lights andENERGYSTAR Building Partners.


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chilled water temperatures. This can yield substantialcompounded savings through downsizing of the chilledwater plant (as long as all air-handling units in a fa-cility are sized with these design strategies in mind).

Size fans correctly and install VFDs on fan mo-

tors.Replace oversized fans with units that match theload. Electronically control the fan motors speed and

torque to continually match fan speed with changingbuilding-load conditions. Electronic control of the fanspeed and airflow can replace inefficient mechanicalcontrols, such as inlet vanes or outlet dampers. (SeeSection 5.7.2 Variable-Frequency Drives.)

Use the displacement method for special facility

types. Displacement ventilation systems can largelyeliminate the need for ducting by supplying air througha floor plenum and using a ceiling plenum or ceilingducts as the return. Raised (access) floors providing

air delivery are commonly used in Europe and rapidlygaining popularity in the United States. This designstrategy is best used in (1) facilities that already in-clude, or can accommodate, low-wall duct mounts or afloor plenum; (2) spaces with high ceilings, in which onlya small band of air at the floor level needs to be condi-tioned for occupant comfort; (3) clean-room or labora-tory spaces that require high-volume ventilation orlaminar airflow; or (4) facilities in which other benefitsof access floors, such as telecommunications wiringneeds and high churn rate, are important. Because ofthe air delivery characteristics, the conditioned sup-ply air does not have to be chilled as much, resultingin additional energy savings.

References

Variable Air Volume Systems: Maximum Energy Effi-ciency and Profits (430-R-95-002), U.S. Environmen-tal Protection Agency, 1995; www.epa.gov.

Cler, Gerald, et al., Commercial Space Cooling and AirHandling Technology Atlas, E Source, Inc., Boulder,CO, 1997; (303) 440-8500; www.esource.com.

Using fabric ducting for exposed appli-cations can help avoid duct cleaning dif-

ficulties. Conditioned supply air inflates theducts and diffuses through the fabric into theoccupied space, providing final filtration of thesupply air in the process. Textile ducting can beremoved and washed in conventional clotheswashers at low labor costs, an importantsavings opportunity for sensitive areas thatrequire frequent cleaning, such as food process-ing facilities.

Half-round textile ducts in the Carlsson companys din-ing room (in Sweden) retain their shape even when notinflated with supply air. Source: KE Fibertec North America

Be certain that proper ventilation andhumidity control is provided by the air

distribution system even when heating and cool-ing loads are low. If fans are set up to respondonly to space temperature requirements, spaceventilation can fall below acceptable limits dur-ing mild weather. This is a very important airquality issue.


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5.2.3 Chillers

controls. Electric chiller classificationis based on thetype of compressor usedcommon types include cen-trifugal, screw, and reciprocating. The scroll compres-sor is another type frequently used for smaller appli-

cations of 20 to 60 tons. Hydraulic compressors are afifth type (still under development).

Both the heat rejection system and building distribu-tion loop can use water or air as the working fluid.Wet condensers usually incorporate one or several cool-ing towers. Evaporative condensers can be used in cer-tain (generally dry) climates. Air-cooled condensersincorporate one or more fans to cool refrigerant coilsand are common on smaller, packaged rooftop units. Air-cooled condensers may also be located remotelyfrom the chillers.

REFRIGERANT ISSUESThe refrigerant issues currently facing facilitymanagers arise from concerns about protection of theozone layer and the buildup of greenhouse gases in theatmosphere. The CFC refrigerants traditionally usedin most large chillers were phased out of productionon January 1, 1996, to protect the ozone layer. CFCchillers still in service must be (1) serviced with stock-piled refrigerants or refrigerants recovered from re-tired equipment; or (2) converted to HCFC-123 (for theCFC-11 chillers) or HFC-134a (for the CFC-12 chill-ers); or (3) replaced with new chillers using EPA-ap-proved refrigerants.

All refrigerants listed for chillers by the EPAStrategic New Alternatives Program (SNAP) are

acceptable. These include HCFC-22, HCFC-123,HFC-134a, and ammonia for vapor-compression chill-ers (see table on page 63). Under current regulations,HCFC-22 will be phased out in the year 2020. HCFC-123 will be phased out in the year 2030. Chlorine-freerefrigerants, such as HFC-134a and water/lithium bro-mide mixtures, are not currently listed for phase-out.

A chiller operating with a CFC refrigerant is notdirectly damaging to the ozone, provided that the re-frigerant is totally contained during the chillers op-

erational life and that the refrigerant is recovered uponretirement. If a maintenance accident or leak resultsin venting of the CFC refrigerant into the atmosphere,however, damage to the Earths ozone layer occurs. Thisrisk should be avoided whenever possible.

In large Federal facilities, the equipment used to pro-duce chilled water for HVAC systems can account forup to 35% of a facilitys electrical energy use. If replace-ment is determined to be the most cost-effective op-

tion, there are some excellent new chillers on the mar-ket. The most efficient chillers currently available op-erate at efficiencies of 0.50 kilowatts per ton (kW/ton),a savings of 0.15 to 0.30 kW/ton over most existingequipment. When considering chiller types and spe-cific products, part-load efficiencies must also be com-pared. If existing chiller equipment is to be kept, thereare a number of measures that can be carried out toimprove performance.

Opportunities

Consider chiller replacement when existing equipment

is more than ten years old and the life-cycle cost analy-sis confirms that replacement is worthwhile. New chill-ers can be 3040% more efficient than existing equip-ment. First-cost and energy performance are the ma-jor components of life-cycle costing, but refrigerant flu-ids may also be a factor. Older chillers using CFCs maybe very expensive to recharge if a refrigerant leak oc-curs (and loss of refrigerant is environmentally dam-aging).

An excellent time to consider chiller replacement iswhen lighting retrofits, glazing replacement, or othermodifications are being done to the building that willreduce cooling loads. Conversely, when a chiller is be-ing replaced, consider whether such energy improve-ments should be carried outin some situations thoseenergy improvements can be essentially done for freebecause they will be paid for from savings achieved indownsizing the chiller (see Section 4.1 IntegratedBuilding Design). Be aware that there can be lead timesof six months or more for delivery of new chillers.


Electric chillers use a vapor compression refrigerantcycle to transfer heat. The basic components of an elec-tric chiller include an electric motor, refrigerant com-pressor, condenser, evaporator, expansion device, and


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Proper refrigerant handling is a requirement forany of the options relating to chillers operating withCFC refrigerants. The three options are containment,conversion, or replacement:

Containing refrigerant in existing chillers is pos-sible with retrofit devices that ensure that refriger-

ant leakage is eliminated. Containment assumesthat phased-out refrigerants will continue to be

available by recovering refrigerants from retiredsystems.

Converting chillers to use alternative refriger-ants will lower their performance and capacity. The

capacity loss may not be a problem with convertedunits since existing units may have been oversizedwhen originally installed and loads may have been

reduced through energy conservation activities.

Replacing older chillersthat contain refrigerants

no longer produced is usually the best option forcomplying with refrigerant phaseout requirements,

especially if load reductions are implemented at thesame time, permitting chiller downsizing.

SPECIFYING NEW CHILLERS

Chillers have been significantly reengineered in re-cent years to use new HCFC and HFC refrigerants.New machines have full-load efficiencies down to 0.50kW/ton in the 170- to 2,300-ton range. Some have built-in refrigerant containment, are designed to leak nomore than 0.1% refrigerant per year, and do not re-quire purging.

Other important energy efficiency improvementsin new chillers include larger heat transfer surfaces,microprocessor controls for chiller optimization, high-efficiency motors, variable-frequency drives, and op-

tional automatic tube-cleaning systems. To facilitatereplacement, new equipment is available from allmanufacturers that can be unbolted for passagethrough conventional doors into equipment rooms.Many positive-pressure chillers are approximately one-third smaller than negative-pressure chillers of simi-lar capacity.

Thermal energy storage may be added when replac-ing chillers and may enable the use of smaller chillers.Although this strategy does not save energy per se,operating costs may be reduced by lowering electricaldemand charges and by using cheaper, off-peak elec-tricity. Thermal storage systems commonly use one ofthree thermal storage media: water, eutectic salts, orice. Volumes of these materials required for storage of1 ton-hour of cooling are approximately 11.4, 2.5, and1.5 ft3 (0.33, 0.07, and 0.04 m3), respectively.

Multiple chiller operations may be made more effi-cient by using unequally sized units. With this con-figuration, the smallest chiller can efficiently meet lightloads. The other chillers are staged to meet higher loadsafter the lead chiller is operating close to full capacity.If an existing chiller operates frequently at part-loadconditions, it may be cost-effective to replace it withmultiple chillers staged to meet varying loads.

Double-bundle chillers have two possible pathwaysfor rejecting condenser heat. One pathway is a con-ventional cooling tower. The other pathway is heat

(continued on next page)

COMPARISON OF REFRIGERANT ALTERNATIVES

Criteria HCFC-123 HCFC-22 HFC-134a Ammonia

Ozone-depletion potential 0.016 0.05 0 0

Global warming potential (relative to CO2) 85 1,500 1,200 0

Ideal kW/ton 0.46 0.50 0.52 0.48

Occupational risk Low Low Low Low

Flammable No No No Yes

Source: U.S. Environmental Protection Agency


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recovery for space heating or service-water heating.Candidates for these chillers are facilities in cold cli-mates with substantial hours of simultaneous coolingand heating demands. Retrofitting existing water heat-

ing may be difficult, because of the low temperaturerise available from the heat-recovery loop.

Steam or hot water absorption chillers use mix-tures of water/lithium-bromide or ammonia/water thatare heated with steam or hot water to provide the driv-ing force for cooling. This eliminates global environ-mental concerns about refrigerants used in vapor-com-pression chillers. Double-effect absorption chillers aresignificantly more efficient than single-effect machines.(See Section 5.2.4 Absorption Cooling.)

Specifying and procuring chillers should includeload-reduction efforts, careful equipment sizing, and

good engineering. Proper sizing is important in orderto save on both initial costs and operating costs. Build-ing loads often decrease over time as a result of con-servation measures, so replacing a chiller should beaccomplished only after recalculating building loads.Published standards such as ASHRAE 90.1 and DOEstandards provide guidance for specifying equipment.Procuring energy-efficient, water-cooled electric chill-ers has been made considerably easier for facility man-agers through the BOA developed by DOE and GSAthat specifies desired equipment parameters.

UPGRADING EXISTING CHILLERS

A number of alterations may be considered to makeexisting chiller systems more energy efficient. Carefulengineering is required before implementing any ofthese opportunities to determine the practicality andeconomic feasibility.

Variable-frequency drives provide an efficientmethod of reducing the capacity of centrifugal chillersand thus saving energy. Note that VFDs are typicallyinstalled at the factory. Savings can be significant, pro-vided that (1) loads are light for many hours per year,(2) the climate does not have a constant high wet-bulbtemperature, and (3) the condenser water temperature

can be reset higher under low part-load conditions. (SeeSection 5.7.2 Variable-Frequency Drives.)

Chiller bypass systems can be retrofitted into cen-tral plants, enabling waterside economizers to coolspaces with chillers off-line. In these systems, the cool-ing tower provides chilled water either directly with

filtering or indirectly with a heat exchanger. Thesesystems are applicable when (1) chilled water is re-quired many hours per year, (2) outdoor temperaturesare below 55F (13C), (3) air economizer cycles can-not be used, and (4) cooling loads below 55F (13C) donot exceed 3550% of full design loads.

Other conservation measures to consider whenlooking at the chiller system upgrades include:

Higher-efficiency pumps and motors;

Operation with low condenser water temperatures;

Low-pressure-drop evaporators and condensers

(oversized chiller barrels); Interconnecting multiple chillers into a single system;

Upgrading cooling towers; and

Upgrading control systems (e.g., temperature reset).

Overall HVAC system efficiencyshould beconsidered when altering chiller settings.

The complex interrelationships of chiller systemcomponents can make it difficult for operators

to understand the effects of their actions onall components of the systems. For example, oneway to improve chiller efficiency is to decrease

the condensing water temperature. However, thisrequires additional cooling tower operation thatmay actually increase total operating costs if

taken to an extreme. In humid climates, increas-ing the chilled water temperature to save energymay unacceptably reduce the effective removalof humidity if the coil size is not also adjusted.

5.2.3 Chillers (continued)


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Carrier Corporations Evergreen line of chillers was the

first one specifically designed to accommodate non-ozone-depleting HFC-134a refrigerant. Source: Carrier Corporation

References

Energy Management: A Program to Reduce Cost andProtect the Environment, Facility Management Divi-sion, General Services Administration, Washington,DC, 1994.

Electric Chiller Handbook (TR-105951s), ElectricPower Research Institute, Pleasant Hill, CA, 1995;

(510) 934-4212.

Fryer, Lynn, Electric Chiller Buyers Guide: Water-Cooled Centrifugal and Screw Chillers, TechnicalManual, E Source, Inc., Boulder, CO, 1995; (303) 440-8500; www.esource.com.

Cler, Gerald, et al., Commercial Space Cooling and AirHandling Technology Atlas, E Source, Inc., Boulder,CO, 1997 (see contact information above).

Contacts

For more information about the Basic Ordering Agree-ment (BOA) for energy-efficient water-cooled chillers,contact the General Services Administration at (817)978-2929.

ROOFTOP RETROFITS

Many Federal buildings are cooled via roof-mounted direct-expansion (DX) air conditioners.If the individual rooftop DX units are old and in-efficient, it may be possible to retrofit them touse a single high-efficiency chiller (18 or higherenergy-efficiency rating [EER]). In the retrofitprocess, the existing evaporator coils areadapted to use glycol that is cooled by thechiller. Ice storage may be incorporated as partof the rooftop retrofit. The chiller can be oper-ated at night to make ice, which would provideor supplement cooling during the day. This ret-rofit system provides an efficient means of re-ducing on-peak electric demand, as discussedin this section under Thermal Storage. FEMP es-

timates a very high savings potential from thissystem. If all rooftop DX systems used in Fed-eral buildings were replaced by chillers, more than50% of the electricity used by rooftop unitscould be saved. Available space for the chillerand, if included, ice storage, is a considerationwith this type of retrofit.


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5.2.4 Absorption Cooling


An absorption cooling cycle is similar to a vapor-com-pression cycle in that it relies on the same three basicprinciples (1) when a liquid is heated it boils (vapor-izes), and when a gas is cooled it condenses; (2) lower-ing the pressure above a liquid reduces its boiling point;and (3) heat flows from warmer to cooler surfaces. In-stead of mechanically compressing a gas (as occurs witha vapor-compression refrigeration cycle), absorptioncooling relies on a thermochemical compressor. Twodifferent fluids are used, a refrigerant and an absor-bent, that have high affinity for each other (one dis-solves easily in the other). The refrigerant (usuallywater) can change phase easily between liquid andvapor and circulates through the system. Heat fromnatural gas combustion or a waste-heat source drives

the process. The high affinity of the refrigerant for theabsorbent (usually lithium bromide or ammonia)causes the refrigerant to boil at a lower temperatureand pressure than it normally would and transfers heatfrom one place to another.

Absorption chillers can be direct-fired or indirect-fired,and they can be single-effect or double-effect (explana-tion of these differences is beyond the scope of this dis-cussion). Double-effect absorption cycles capture someinternal heat to provide part of the energy required inthe generator or desorber to create the high-pressurerefrigerant vapor. Using the heat of absorption reducesthe steam or natural gas requirements and boosts sys-

tem efficiency.

Absorption cooling equipment on the market rangesin capacity from less than 10 tons to over 1,500 tons(35 to 5,300 kW). Coefficients of performance (COPs)range from about 0.7 to 1.2, and electricity use rangesfrom 0.004 to 0.04 kW/ton of cooling. Though an elec-tric pump is usually used (the principal exceptionsbeing the small hotel and recreational vehicle [RV] re-frigerators), pump energy requirements are relativelysmall because pumping a liquid to the high-side pres-sure requires much less electricity than does compress-ing a gas to the same pressure.

High-efficiency, double-effect absorption chillers aremore expensive than electric-driven chillers. They re-quire larger heat exchangers because of higher heat-rejection loads; this translates directly into higher

On the surface, the idea of using an open flame or steamto generate cooling might appear contradictory, but theidea is actually very elegant. And it has been aroundfor quite a whilethe first patent for absorption cool-

ing was issued in 1859 and the first system built in1860. Absorption cooling is more common today thanmost people realize. Large, high-efficiency, double-ef-fect absorption chillers using water as the refrigerantdominate the Japanese commercial air-conditioningmarket. While less common in the U.S., interest inabsorption cooling is growing, largely as a result ofderegulation in the electric power industry. The tech-nology is even finding widespread use in hotels thatuse small built-in absorption refrigerators (because oftheir virtually silent operation) and for refrigeratorsin recreational vehicles (because they do not requireelectricity).

Opportunities

Absorption cooling is most frequently used to air-con-dition large commercial buildings. Because there areno simplifying rules of thumb to help determine whenabsorption chillers should be used, a life-cycle costanalysis should be performed on a case-by-case basisto determine whether this is an appropriate technol-ogy. Absorption chillers may make sense in the follow-ing situations: where there are high electric demandcharges, where electricity use rates are high, wheresummertime natural gas prices are favorable, or where

utility and manufacturer rebates exist. Absorptionchillers can be teamed with electric chillers in hybridcentral plants to provide cooling at the lowest energycostsin this case, the absorption chillers are used dur-ing the summer to avoid high electric demand charges,and the electric chillers are used during the winterwhen they are more economical. Because absorptionchillers can make use of waste heat, they can essen-tially provide free cooling in certain facilities.

Absorption cooling systems can most easily be incor-porated into new construction, though they can alsobe used as replacements for conventional electric chill-ers. A good time to consider absorption cooling is when

an old electric chiller is due for replacement.


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costs. Non-energy operating and maintenance costs forelectric and absorption chillers are comparable. Sig-nificant developments in controls and operating prac-tice have led the current generation of double-effectabsorption chillers to be praised by end-users for theirlow maintenance requirements.

The potential of absorption cooling systems to use wasteheat can greatly improve their economics. Indirect-firedchillers use steam or hot water as their primary en-ergy source, and they lend themselves to integrationwith on-site power generation or heat recovery fromincinerators, industrial furnaces, or manufacturingequipment. Indirect-fired, double-effect absorption

chillers require steam at around 370F and 115 psig(190C and 900 kPa), while the less efficient (but alsoless expensive) single-effect chillers require hot wateror steam at only 167270F (75132C). Triple-effect

chillers are also available.

References

Cler, Gerald, et al., Commercial Space Cooling and AirHandling Technology Atlas, E Source, Inc., Boulder,CO, 1997; (303) 440-8500; www.esource.com.

ASHRAE Handbook: 1997 Fundamentals, pp. 1-20,American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Atlanta, GA; www.ashrae.org.

Wood, Bernard D., Application of Thermodynamics,Addison-Wesley Publishing Company, Reading, MA,1982, pp. 238-257.

Contacts

Distributed Energy Resources Program, Office of PowerTechnologies, EERE, U.S. Department of Energy, 1000Independence Avenue, SW, Washington, DC 20585.

Building Equipment Research Program, Energy Divi-sion, Oak Ridge National Laboratory, Oak Ridge, TN37831; (865) 574-2694.

American Gas Cooling Center, 400 N. Capitol Street,

NW, Washington, DC 20001; (202) 824-7141, www.agcc.org.

This York Millennium Direct-Fired Double-Effect Ab-

sorption Chiller/Heater replaces an electric chiller and

boiler, reducing the floor-space requirement by up to 40%.

Source: American Gas Cooling Center

TYPICAL INSTALLED COSTS OFVARIOUS TYPES OF CHILLERS ($/TON)

SMALL MEDIUM LARGECHILLER TYPE (


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5.2.5 Desiccant Dehumidification

Their ability to recover energy from conditioned airthat is normally exhausted from buildings.

The lower cost of dehumidification when low-sen-

sible load, high-latent load conditions are met. The greater comfort achieved with dehumidified air.

The promotion of gas cooling for summer air-condi-tioning by utilities in the form of preferential gascooling rates.

High electric utility demand charges, which encour-age a shift away from conventional, electrically

driven air-conditioning (which requires a heavydaytime loading).

Desiccant systems offer significant potential for energysavings (0.1 to 0.4 quads nationwide). They also in-

hibit microbiological growth by maintaining lower hu-midity levels. Better control of humidity prevents mois-ture, mildew, and rot damage to building materials.

Desiccant dehumidification is particularly attractivein applications where building exhaust air is readilyavailable for an energy-recovery ventilator (ERV, orpassive desiccant system) or where a source of wasteheat from other building operations is available to re-generate an active desiccant system.

Desiccants are materials that attract and hold mois-ture, and desiccant air-conditioning systems provide amethod of drying air before it enters a conditionedspace. With the high levels of fresh air now required

for building ventilation, removing moisture has becomeincreasingly important. Desiccant dehumidificationsystems are growing in popularity because of theirability to remove moisture from outdoor ventilation airwhile allowing conventional air-conditioning systemsto deal primarily with control temperature (sensiblecooling loads).

Opportunities

Desiccant dehumidification is a new approach to space-conditioning that offers solutions for many of the cur-rent economic, environmental, and regulatory issues

being faced by facility managers. Indoor air quality isimproved through higher ventilation rates, and achiev-ing those fresh air make-up rates becomes more fea-sible with desiccant systems. At low load conditionsoutdoor air used for ventilation and recirculated airfrom the building have to be dehumidified more thanthey have to be cooled.

Properly integrated desiccant dehumidification sys-tems have become cost-effective additions to manybuilding HVAC systems because of:

Passive versus active desiccant wheels

Adapted from American Gas Cooling Center materials

An energy recovery wheel has a small amount of des-iccant, so it can transfer moisture. But with no heatfor reactivation, dehumidification depends on thedryness and temperature of the exhaust air.

A desiccant wheel rotates slowly and contains moredesiccant than a heat recovery wheel. By heatingthe reactivation air, the desiccant wheel removesmuch more moisture than heat recovery wheels.

Moisture Exchange(Energy Recovery, or Enthalpy Wheel)

Moisture Removal(Desiccant Wheel)

0.2 rpm

Outdoor Air

85120 gr/lb

Outdoor Air

85120 gr/lb

75

Exhaust Air

76

77 gr/lb

121

42 gr/lb

Reactivation Heater

Exhaust Air

85120 gr/lb

250120 gr/lb

20.0 rpm


19/8169

$

Source: American Gas Cooling Center

The DRYOMATIC Dehumidification System from the Air-flow Company may be installed indoors or outdoors.

Because the sizing of desiccant systemsis based on the airflow rate (cfm), costs

are typically given in terms of $/cfm. Passivedesiccant system costs have been estimatedby one HVAC manufacturer at $3 to $4/cfm. Forlarge, active desiccant systems, the cost isusually about $6/cfm, while smaller units (less

than 5,000 cfm) may cost up to $8/cfm. In-stallation costs vary according to specific siterequirements.


To dehumidify air streams, desiccant materials areimpregnated into a lightweight honeycomb or corru-gated matrix that is formed into a wheel. This wheel isrotated through a supply or process air stream on oneside that is dried by the desiccant before being routedinto the building. The wheel continues to rotate through

a reactivation or regeneration air stream on the otherside that dries out the desiccant and carries the mois-ture out of the building. The desiccant can be reacti-vated with air that is either hotter or drier than theprocess air.

Passive desiccant wheels, which are used in totalERVs and enthalpy exchangers, use dry air that isusually building exhaust air for regeneration. Passivedesiccant wheels require additional fan power only tomove the air and the energy contained in the exhaustair stream. However, passive desiccants cannot removeas much moisture from incoming ventilation air asactive desiccant systems and are ultimately limited in

sensible and latent capacity by the temperature anddryness of exhaust air leaving the building.

Active desiccant wheels use heated air and requirea thermal energy source for regeneration. The illus-tration above shows the operational characteristics ofactive and passive desiccant wheels. The advantage ofactive desiccant wheels is that they dry the supply aircontinuouslyto any desired humidity levelin allweather, regardless of the moisture content of thebuildings exhaust air. They can be regenerated with

natural gas combustion or another heat source, inde-

pendent ofor in combination withbuilding exhaustair, which allows more installation flexibility. The re-generation process, however, requires heat input to drythe desiccant; this usually increases the operating costof the system. Active desiccant wheels can remove muchmore moisture than passive systems and thus are theonly desiccant approach that allows truly independenthumidity control to any desired level.

References

Two-Wheel Desiccant Dehumidification System, Fed- eral Technology Alert, April 1997; www.pnl.gov/fta/

8_tdd.htm.Applications Engineering Manual for Desiccant Sys-tems, American Gas Cooling Center, Washington, DC,1996.

Contacts

Distributed Energy Resources Program, Office of PowerTechnologies, EERE, U.S. Department of Energy, 1000Independence Avenue, SW, Washington, DC 20585-0121.

Building Equipment Research Program, Energy Divi-

sion, Oak Ridge National Laboratory, Oak Ridge, TN37831-6070; (865) 574-2694.

American Gas Cooling Center, Inc., 400 N. CapitolStreet, NW, Washington, DC 20001; (202) 824-7141;www.agcc.org.

Advanced Desiccant Cooling & Dehumidification Pro-gram, National Renewable Energy Laboratory, 1617Cole Boulevard, Golden, CO 80401; (303) 384-7527;www.nrel.gov/desiccantcool.


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5.2.6 Ground-Source Heat Pumps

such as small-town post offices. In residential and small(skin-dominated) commercial buildings, ground-sourceheat pumps make the most sense in mixed climateswith significant heating and cooling loads because thehigh-cost heat pump replaces both the heating and air-

conditioning system. In larger buildings (with signifi-cant internal loads), the investment in a ground-sourceheat pump can be justified further north because air-

conditioning loads increasewith building size. Packagedterminal heat pumps, used inhotels and large apartmentbuildings, are similar exceptthat the heat source is a con-tinuously circulating source ofchilled waterthe individualwater-source heat pumps pro-vide a fully controllable sourceof heat or air-conditioning forindividual rooms.

Because ground-source heatpumps are expensive to installin residential and small com-mercial buildings, it some-times makes better economicsense to invest in energy effi-ciency measures that signifi-cantly reduce heating andcooling loads, then install lessexpensive heating and coolingequipmentthe savings in

equipment may be able to payfor most of the envelope improvements (see Section 4.1Integrated Building Design). If a ground-source heatpump is to be used, plan the site work and projectscheduling carefully so that the ground loop can beinstalled with minimum site disturbance or in an areathat will be covered by a parking lot or driveway.


Ground-source heat pumps are generally classifiedaccording to the type of loop used to exchange heatwith the heat source/sink. Most common are closed-

loop horizontal (see the illustration above) and closed-loop vertical systems. Using a body of water as the heatsource/sink is very effective, but seldom available asan option. Open-loop systems are less common thanclosed-loop systems due to performance problems (ifdetritus gets into the heat pump) and risk of contami-nating the water source orin the case of well wa-terinadequately recharging the aquifer.

Ground-source heat pumps are complex. Basically,water or a nontoxic antifreeze-water mix is circulatedthrough buried polyethylene or polybutylene piping.

Heat pumps function by moving (or pumping) heat fromone place to another. Like a standard air-conditioner,a heat pump takes heat from inside a building anddumps it outside. The difference is that a heat pumpcan be reversed to take heat from a heat source out-

side and pump it inside. Heat pumps use electricity tooperate pumps that alternately evaporate and con-dense a refrigerant fluid to move that heat. In the heat-ing mode, heat pumps are farmore efficient at convertingelectricity into usable heat be-cause the electricity is used tomove heat, not to generate it.

The most common type of heatpumpan air-source heatpumpuses outside air as theheat source during the heatingseason and the heat sink dur-

ing the air-conditioning sea-son. Ground-sourceand water-source heat pumps work thesame way, except that the heatsource/sink is the ground,groundwater, or a body of sur-face water, such as a lake. (Forsimplicity, water-source heatpumps are often lumped withground-source heat pumps, asis the case here.) The efficiencyor coefficient of performance ofground-source heat pumps is

significantly higher than thatof air-source heat pumps because the heat source iswarmer during the heating season and the heat sinkis cooler during the cooling season. Ground-source heatpumps are also known as geothermal heat pumps,though this is a bit of a misnomer since the ultimateheat source with most ground-source heat pumps isreally solar energywhich maintains the long-termearth temperatures within the top few meters of theground surface. Only deep-well ground-source heatpumps that benefit from much deeper earth tempera-tures may be actually utilizing geothermal energy.

Ground-source heat pumps are environmentally attrac-

tive because they deliver so much heat or cooling en-ergy per unit of electricity consumed. The COP is usu-ally 3 or higher. The best ground-source heat pumpsare more efficient than high-efficiency gas combustion,even when the source efficiency of the electricity istaken into account.

Opportunities

Ground-source heat pumps are generally most appro-priate for residential and small commercial buildings,

Horizontal-loop ground-source heat pumps typi-cally have tubing buried within the top 10 feet (3

m) of ground. Source: Al Paul Lefton Company


21/8171

This water is then pumped through one of two heatexchangers in the heat pump. When used in the heatingmode, this circulating water is pumped through the coldheat exchanger, where its heat is absorbed by evapora-tion of the refrigerant. The refrigerant is then pumpedto the warm heat exchanger, where the refrigerant iscondensed, releasing heat in the process. This sequenceis reversed for operation in the cooling mode.

Direct-exchange ground-source heat pumps use cop-per ground-loop coils that are charged with refriger-ant. This ground loop thus serves as one of the twoheat exchangers in the heat pump. The overall effi-ciency is higher because one of the two separate heatexchangers is eliminated, but the risk of releasing theozone-depleting refrigerant into the environment isgreater. DX systems have a small market share.

Free Hot Water: When used in the coolingmode, a ground-source heat pump with a

desuperheaterwill provide free hot water. Build-ings in more southern climates that use a ground-source heat pump primarily for cooling can ob-

tain a high percentage of hot water demand inthis manner. Look for a ground-source heat pumpthat includes a desuperheater module.

Typical system efficiencies and costs ofa number of heating, cooling, and water-

heating systems for residential and light com-mercial buildings are shown in the table below(from EPA, 1993). Of all the systems listed,ground-source heat pumps are the most expen-sive to install but the least expensive to operate.

References

Space Conditioning: The Next Frontier, U.S. Environ-mental Protection Agency, Washington, DC, 1993.

Space Heating Technology Atlas, E Source, Inc., Boul-

der, CO, 1996; (303) 440-8500; www.esource.com.

GeoExchange in Federal Facilities, Geothermal HeatPump Consortium (see contact information below).

Malin, Nadav, and Alex Wilson, Ground-Source HeatPumps: Are They Green? Environmental BuildingNews, Vol. 9, No. 7/8, July 2000; BuildingGreen, Inc.,Brattleboro, VT; (800) 861-0954; www.BuildingGreen.com.

Contacts

Geothermal Heat Pump Consortium, 701 Pennsylva-

nia Avenue, NW, Washington, DC 20004; (888) 255-4436, (202) 508-5500, (202) 508-5222 (fax); www.geoexchange.org.

U.S. Department of Energy; www.eren.doe.gov/ orwww.energy.gov.

SEASONAL PERFORMANCE FACTORS(1)

Space-Conditioning System Heating Cooling Hot Water Installed Cost Ann. Op. Cost

Electric resistance with elec. A/C 1.00 2.32.6 0.90 $5,4155,615 $8712,945

Gas furnace with elec. A/C 0.640.87 2.33.2 0.560.60 $5,7757,200 $4611,377

Adv. oil furnace with elec. A/C 0.73 3.13.2 0.90 $6,515 $1,1621,370

Air-source heat pump 1.62.9 2.34.3 0.903.1 $5,31510,295 $3532,059

Ground-source heat pump 2.75.4 2.86.0 1.23.0 $7,52010,730 $2741,179

1. Seasonal performance factors represent seasonal efficiencies for conventional heating and cooling systems andseasonal COPs for heat pumps. Ranges show modeled performance by EPA in different climates.

Source: U.S. Environmental Protection Agency, Space Conditioning: The Next Frontier, 1993

$

Improving Performance: There are a num-ber of ways to improve ground-source

heat pump performance. Cooling-tower-supple-mented systems can reduce the total size of

the ground loop required to meet cooling de-mand. A cooling tower is added to the ground-

coupled loop by means of a heat exchanger.Solar-assisted systems use solar energy tosupplement heating in northern climates. Solarpanels boost the temperature of the ground loop.


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5.2.7 HVAC Technologies to Consider

Fort Carson uses a ventilation-preheatsolar collector wall to warm outside fresh

air before it enters an aircraft hanger. Intake air

is preheated by 3050F (1728C). Such sys-tems can reduce annual heating cost by $1$3per square foot ($11$32/m2) of collector wall,depending on fuel type, significantly reducing de-mand on boiler systems.

NATURAL GAS ENGINE-DRIVEN COOLING

An engine-driven cooling system is similar to a con-ventional electric cooling system, except that the com-pressor is driven by a natural gas engine rather than

an electric motor. Configurations include chillers, pack-aged direct-expansion units, and heat pumps, usuallyin sizes from 200 tons to 4,000 tons. Engine-drivensystems are variable-speed, have higher part-load ef-ficiencies, generate high-temperature waste heat (thatcan be used), and can often reduce operating costs.Consider engine-driven natural gas cooling when elec-trical demand charges are high or natural gas is par-ticularly inexpensive.

COOLING EQUIPMENT WITH ENHANCED

DEHUMIDIFICATION

Reducing indoor humidity is a prime factor in discour-aging microbiological growth in the indoor environ-ment. Section 5.2.5 addresses desiccant dehumidifica-tion. Heat pipes can also be used to efficiently removemoisture with direct-expansion or DX cooling. Heatpipes enable DX coils to remove more moisture by pre-cooling return air. Heat absorbed by the refrigerant inthe heat pipe can then be returned to the overcooled,dehumidified air coming out of the DX coils. The sys-tem is passive, eliminating the expense of active re-heat systems. Somewhat more fan energy is requiredto maintain duct static pressure, as is the case whenany new element is added to the ventilation system,but no additional pumps or compressors are required.

Increased fan energy must be considered when calcu-lating system energy savings. Energy savings up to30% have been reported. At least one manufacturerbuilds a variable-dehumidification system for DXequipment that precools liquid refrigerant rather thanthe air stream.

EVAPORATIVE COOLING TECHNOLOGIES

Evaporative coolers (also known as swamp coolers)have been used for many years in hot, arid parts of the

New (or generally unfamiliar) HVAC technologies canhelp facility managers lower energy costs, reduce en-vironmental impacts, and enhance indoor environmen-tal quality. Information is provided here on a numberof these technologies. Some of the new technologies

covered in this section of the first edition ofGreeningFederal Facilities (1997) are now in fairly widespreaduse and merit their own sections of the guide (ground-source heat pumps, absorption cooling, and desiccantdehumidification). Other technologies have been addedto this section. Although new technologies may be avail-able only from a single manufacturer, and althoughthe energy performance data are sometimes limited,these systems are worth considering.

Opportunities

Not every Federal facility will be able to try out rela-

tively new or unfamiliar technologies, but as these sys-tems become better known and trusted, potential ap-plications will grow. Ventilation-preheat solar collec-tors are demonstrated to be highly cost-effective inhundreds of cold-climate applications. A number of thetechnologies described here can help control indoorhumidity. In arid climates, evaporative cooling and aninnovative rooftop evaporative system can be effective.Where electrical power demand costs are high, natu-ral-gas engine-driven cooling may be appropriate.


VENTILATION-PREHEAT SOLAR

COLLECTORS (TRANSPIRED AIRCOLLECTORS)

This very simple solar collector passively preheats ven-tilation make-up air via a large, unglazed solar collec-tor. These collectors are most effective on south-facingbuilding facades, though significant deviation off truesouth (plus-or-minus about 60) results in only minorloss of performance. The Canadian company ConservalEngineering, Inc., has pioneered this system under thetradename Solarwall. The sheet-metal collector hasperforations that allow air to pass through into corru-

gated air channels under the outer building skin. Theventilation system air intakes are configured so thatmake-up air is drawn through the collector before itenters the building.

In new construction, installation costs are typically inthe range of $6 to $7 per square foot ($65$75/m2),though if the sheet metal facade replaces a more ex-pensive facing, such as brick, there may actually be anet reduction in cost for this ventilation preheat sys-tem. With retrofit applications, costs are usually some-what higher than with new construction.


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country. These systems are typically roof-mounted.Cooling is provided as hot, dry outside air is blownthrough an evaporative media that is kept moist.In-direct evaporative coolers can work in climates wheremoist air is not wanted in the building, though effi-ciency is lower.

On larger buildings in hot, dry climates, the benefitsof evaporative cooling can be achieved through roof-spray technology. A modified spray-irrigation system

can be used on the roof to drop daytime roof-surfacetemperatures from 135160F to 8590F (5771C to2932C). With a typical (poorly insulated) roof system,this can reduce interior temperatures significantly.

A newer, more innovative use of evaporative cooling isnight-sky radiant cooling. This approach works in cli-mates with large diurnal temperature swings and gen-erally clear nights (such as in the Southwest). Wateris sprayed onto a low-slope roof surface at night, andthe water is cooled through a combination of evapora-tion and radiation. This process typically cools thewater to 510F (2.75.5C) below the night air tem-perature. The water drains to a tank in the basement

or circulates through tubing embedded in a concretefloor slab. Daytime cooling is accomplished either bycirculating cooled water from the tank or through pas-sive means from the concrete slab. Developed by theDavis Energy Group and Integrated Comfort, Inc., thisNightSky system was used at the U.S. Customs bor-der patrol station in Nogales, Arizona, and monitoredby Pacific Northwest National Laboratory (PNNL) in1997. The average cooling efficiency was found to benearly 15 times greater than that of conventional com-pressor-based air-conditioning systems.

REFRIGERANT SUBCOOLING

Refrigerant subcooling systems save energy in air con-ditioners, heat pumps, or reciprocating, screw andscroll chillers by altering the vapor-compression refrig-erant cycle. Three types of refrigerant subcooling tech-nologies are being manufactured, and each adds a heatexchanger on the liquid line after the condenser: (1)suction-line heat exchangers, which use the suction-line as a heat sink; (2) mechanical subcoolers that usea small, efficient, secondary vapor-compression systemfor subcooling; and (3) external heat-sink subcoolersthat used a mini-cooling tower or ground-source waterloop as a heat sink. Subcoolers increase energy effi-ciency, cooling capacity, and expansion valve perfor-mance (i.e., decrease flash gas).

Heat sink subcooling can be used (1) where units arebeing replaced; (2) where building expansion isplanned; or (3) where current capacity is inadequate.The best applications are in climates that are hot year-round1,200 or more base-65F (18C) cooling-degree

daysand with DX systems. With external heat sinksubcooling, condensing units and compressors shouldbe downsized, making the technology more appropri-ate when existing equipment is being replaced, whenconstruction or expansion is planned, or when currentcooling capacity is inadequate. PNNLs evaluation ofsubcooling in Federal facilities is contained in aFederalTechnology Alert available from FEMP.

References

Space Conditioning: The Next Frontier, U.S. Environ-mental Protection Agency, Washington, DC, 1993.

Space Heating Technology Atlas (1996) and Commer-cial Space Cooling and Air Handling Technology Atlas(1997), E Source, Inc., Boulder, CO; (303) 440-8500;www.esource.com.

Natural Gas Cooling Equipment Guide, American GasCooling Center, Washington, DC, 1995.

Contacts

For information about all types of gas cooling equip-ment, contact the American Gas Cooling Center, 400N. Capitol Street, NW, Washington, DC 20001; (202)

824-7141; www.agcc.org.

Federal Technology Alerts and other publications aboutnew HVAC technologies are available from the FEMPHelp Desk at (800) DOE-EREC (363-3732), or see theFEMP Web site at www.eren.doe.gov/femp.

Conserval Engineering, Inc., 200 Wildcat Road, Downs-view, Ontario M3J 2N5, Canada; (416) 661-7057; www.solarwall.com.

Davis Energy Group, 123 C Street, Davis, CA 95616;(530) 757-4844; www.davisenergy.com.

Each innovative air tree above provides ventilation forsix offices at the National Renewable Energy Laboratorys

(NRELs) Solar Energy Research Facility in Golden, Colo-

rado. Air is cooled and humidified by direct evaporation,

or swamp cooling. Photo: Warren Gretz


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5.3 Water Heating

commercial kitchens where steam is also used for cook-ers. Where boilers must be kept operating during sum-mer months to supply small amounts of steam forkitchen purposes, changing to alternative water heat-

ing can be extremely cost-effective and possibly extendthe life of the boiler.

Standard gas-fired water heaters use natural gas orpropane burners located beneath storage tanks. Standbylosses tend to be high because internal flues are unin-sulated heat-exchange surfaces. Equipment should bedirect-vented or sealed-combustion to minimize the riskof combustion gas spillage into the building.

Condensing gas water heaters have higher effi-ciency because the latent heat of vaporization is re-claimed from the combustion gases. Flue gases are coolenough to permit venting with special PVC pipe.

Tankless or demand gas water heaters are usuallyinstalled near the point of use. These are often goodoptions for remote sites where there is adequate gaspiping, pressure, and venting. Some recent develop-mentsincluding higher-efficiency models with pre-cise controllability and potential for ganging multipleunits together for whole-building, staged useare ex-tending the practical applications for demand gas wa-ter heaters.

Direct-fire water heaters are gas-fired, demandwater heaters for users of large quantities of potablewaterup to several hundred gallons per minute. Using

technology in existence since 1908, they mix the heat ofcombustion (not flame) directly with incoming water,achieving in excess of 98% efficiency while eliminatingstandby losses. Though expensive, these systems (pro-duced by several manufacturers) can be very cost-ef-fective for facilities using large quantities of hot water.

Air-source heat pump water heaters are special-ized vapor-compression machines that transfer heatfrom the air into domestic water. Commercial kitch-ens and laundries are excellent opportunities becauseboth indoor air temperatures and hot water needs arehigh. In the process of capturing heat, the air is bothcooled and dehumidified, making space conditions more

comfortable. Air-source heat pumps are recommendedonly if the air source is warmed by waste heat.

Ground-source and water-source heat pump

water heaters are dedicated heat pumps that heatdomestic water from energy captured from a water source.

The heat source may be groundwater that is used forits stable year-round temperature, or a low-grade wasteheat source. Ground-source heat pumps circulate thewater through buried heat exchanger tubing.

Hot water is used in Federal facilities for handwashing,showering, janitorial cleaning, cooking, dishwashing, andlaundering. Facilities often have significant needs forhot water in one or more locations and many smaller

needs scattered throughout the facility. Methods forreducing water-heating energy use include maintain-ing equipment, implementing water conservation, re-ducing hot water temperatures, reducing heat lossesfrom the system, utilizing waste heat sources, and re-placing equipment with higher-efficiency or renewable-energy systems.

Opportunities

Reducing the demand for hot water should be the firstpriority, and it can be implemented at virtually anyfacility through efficiency measures and by matching

the water temperatures to the task. Beyond that, con-sider upgrading to higher-efficiency water-heatingequipment or shifting to other water-heating technolo-gies whenever equipment is being replaced or majorremodeling is planned. Rooftop solar water-heatingequipment should be consideredespecially at the timeof reroofing. Heat-recovery water heating can be con-sidered when modifying plumbing, HVAC, power-gen-eration, or industrial-process systems that generatewaste heat. Plan ahead and select a technology for usein the event that existing water-heating equipmentfails; dont just replace-in-kind.


WATER HEATING TECHNOLOGIES

Solar water heating captures energy from the sunfor heating water. These systems have improved sig-nificantly in recent years and make economic sensein many areas. See Section 5.3.2 Solar Water Heat-ing.

Standard electric water heatersboth heat and storewater in insulated storage tanks. Many older unitshave inadequate insulation and should be replaced orfitted with insulation jackets to improve performance.

Tankless or demand electric water heaters elimi-nate standby losses by heating water only as it isneeded. They are usually located at the point of useand are convenient for remote areas having only occa-sional use; however, because of very high power con-sumption, they can increase electric demand charges.

Steam-fired water heaters utilize centrally producedsteam for heating water. These units are popular in


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Desuperheaters are connected to air-conditioners,heat pumps, or refrigeration compressors. Hot refrig-erant gas from the compressor is routed to the gas sideof the units heat exchanger. Water is essentially heatedfor free whenever the air-conditioner, heat pump, or

refrigerator compressor is operating. When a desuper-heater is connected to a heat pump operating in heat-ing mode, some of the heat pumps capacity is devotedto water heating.

Drainline heat exchangers are very simple, passivecopper coils wrapped around wastewater drain lines.The cold-water line leading to the water heater passesthrough this coil, and water is preheated by hot watergoing down the drain. These low-cost systems are cost-effective in residential buildings (typically mounted tocapture waste heat from showers). They can also workwell in commercial buildings with significant hot wa-ter use.

IMPROVING WATER HEATERPERFORMANCE AND SAVING ENERGY

Insulate tanks and hot-water lines that are warmto the touch. Only recently have manufacturers in-stalled adequate amounts of insulation on water heatertanks. Hot-water lines should be continuously insu-lated from the heater to the end use. Cold-water linesalso should be insulated near the tank to minimize

convective losses (and everywhere if high humidity islikely to cause condensation).

Limit operating hours of circulating pumps.

Large facilities often circulate domestic hot water tospeed its delivery upon demand. By turning off thosepumps when facilities are not being used (nights andweekends, for example), both the cost of operating thepump and heat losses through pipe walls will be re-duced.

Install heat traps. Heat traps are plumbing fittingsthat block convective heat losses from water storagetanks.

Install water heaters near the points of mostfre-quent use to minimize heat losses in hot water pipes.Note, this location will not necessarily be where the

most hot water is used.Eliminate leaks. Delays in repairing dripping fau-cets not only waste water and energy but often lead tomore expensive repairs because of valve stem and valveseat corrosion.

Repair hiddenwaste from failed shower divertervalves that cause a portion of the water to be dumpedat a users feet. This leakage is usually not reported tomaintenance teams.

Reduce hot water temperature. Temperatures canbe safely reduced to 140F (60C) for cleaning and laun-dering.

Install quality low-flow fixtures. Good-quality low-flow showerheads and faucets provide performancealmost indistinguishable from that of older fixtures;avoid inexpensive models or pressure-reducing insertsthat provide unsatisfactory shower performance.

Setting the water temperature too lowcan cause problems. Reducing the hot

water set-point below 120F (49C) to save en-ergy may allow Legionella bacteria to grow inside

domestic hot water tanks.

Contacts

The FEMP Help Desk at (800) DOE-EREC (363-3732)can provide many publications about energy-efficientwater heating.

Source: Direct Fire Technical, Inc.

Though requiringa high first-cost in-

vestment, a direct-fire water heater is

so energy-efficientthat its payback

period can be short.


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5.3.1 Heat-Recovery Water Heating

pumped to a condenser for heat rejection. However, ahot-gas-to-water heat exchanger may be placed intothe refrigerant line between the compressor and con-denser coils to capture a portion of the rejected heat.

In this system, water is looped between the water stor-age tank and the heat exchanger when the HVAC sys-tem is on. Heat pumps operating in the heating modedo not have waste heat because the hot gas is used forspace heating. However, the heat pump system can stillheat water more efficiently than electric resistanceheating.

Double-bundle condensers. Some chillers have con-densers that make it possible to heat water with wasteheat recovery. Double-bundle condensers contain twosets of water tubes bundled within the condenser shell.Heat is rejected from the system by releasing super-heated gas into the shell and removing heat as the re-frigerant condenses by one of two m

Documents

Greening of Facilities - Part V