U.S. Department of Energy - Energy Efficiency and Renewable EnergyFederal Energy Management Program – Energy-Efficient ProductsHow to Buy an Energy-Efficient Water-Cooled ChillerInformation about energy-efficient water-cooled chillers in this section includes the following:
Also provided is a portable document format version of How to Buy an Energy Efficient Water-Cooled Chiller (PDF 165 KB, 4 pp). Download Adobe Reader.
a Depending on the application, buyers should specify chiller efficiency using either full-load or integrated part-load values as shown (see text).
a The efficiencies of the base models are just sufficient to meet the current ASHRAE Standard 90.1. Metric Conversions: Cost-Effectiveness Assumptions: Annual energy use for the centrifugal chiller example is based on 2,000 equivalent full-load hours per year for a 500-ton chiller. The rotary screw chiller example uses a 250-ton machine operating for 2,000 equivalent full-load hours per year at part-load (IPLV) efficiencies, since rotary chillers are often installed in applications with variable load conditions. Assumed electricity price is $0.06/kWh, the federal average electricity price (including demand charges) in the U.S. Since this average cost figure does not incorporate the disproportionately large portion of demand costs that chillers usually contribute, actual cost savings may be greater. Using the Cost-Effectiveness Table: In the first example shown above, a 500-ton centrifugal chiller with a full-load efficiency of 0.56 kW/ton is cost-effective if its purchase price is no more than $100,000 above the price of the base model. The best available centrifugal model, with an efficiency of 0.47 kW/ton, is cost-effective if its price is no more than $170,000 above the price of the base model. Similarly, in the second example, the 250-ton recommended and best available rotary screw chillers are cost-effective if their respective purchase prices are no more than $125,000 and $135,000 above the price of the base model. Cost CalculatorTry the Energy Cost Calculator for Water-cooled Electric Chillers to compare the energy costs for your selection with FEMP-recommended and "Best Available" chillers. You can model different scenarios by varying electricity cost, capacity, efficiency, and hours of operation. Life-Cycle CostThe basic formula for estimating a chiller's annual energy use multiplies the average system load (in tons) by the relevant efficiency (full-load or IPLV) by the annual number of equivalent full- or part-load operating hours. The resultant annual kWh figure can then be multiplied by the average cost per kWh for electricity, yielding the annual energy cost: Annual Energy Cost = Avg. Load * Efficiency * Operating Hours * Electricity Rate For full life-cycle cost (LCC) analysis, this annual energy cost should then be multiplied by the regional electricity Uniform Present Value (UPV) factor for the estimated lifetime of the equipment, and then added to the initial cost of the chiller (or present value of the chiller's financed cost): Life Cycle Cost = (Annual Energy Cost * Uniform Present Value Factor) + Initial Cost Note that this simplified formula excludes operation and maintenance costs because they were assumed to be equal. Therefore, it does not represent a true life cycle cost calculation. If the operation and maintenance cost of the base and recommended models are substantially different the buyer should include these in the LCC calculation in order to get a truer picture of the potential savings. A manual with the appropriate UPV factors (Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis (PDF 497 KB, 75 pp)), as well as an LCC analysis guidebook (NIST Handbook 135, Life-Cycle Costing Manual for the Federal Energy Management Program (PDF 9.21 MB, 222 pp)) and LCC software (BLCC) are all available through the FEMP Help Desk, at (877) 337-3463. A large proportion of chiller energy costs is often attributable to demand (kW) charges. To incorporate demand and ratchet charges into the cost estimation of chiller options, the ERATES software is also available from the FEMP Help Desk. Rate schedules from ERATES can be imported by the BLCC program, enabling much more accurate estimates of life-cycle costs. FEMP provides a Web-based chiller "cost calculator" screening tool that simplifies the energy cost comparison between chillers with different efficiencies. Where to Find Energy-Efficient ChillersThe General Services Administration (GSA) has a Basic Ordering Agreement (BOA) that offers a streamlined procurement method for chillers based on lowest life-cycle cost. For more information, call GSA (817-978-8370). For chillers purchased through commercial sources, the BOA can still be used as a guide in preparing specifications, as can ARI and ASHRAE sources (see For More Information). An Energy Savings Performance Contract (ESPC) is an innovative method of financing a new chiller, as well as other associated energy conservation measures, with payments based on energy cost savings. Buyer TipsThe decision to specify chiller performance using full-load or part-load efficiency (kW/ton) levels depends upon the application. Part-load (IPLV) is preferred for more variable loads accompanying variable ambient temperature and humidity, the more common situation. Full-load is appropriate where chiller load is high and ambient temperature and humidity are relatively constant (e.g., for baseline chillers). To further optimize your selection, compare chillers based on non-standard part-load value (NPLV), which maintains the same weightings as IPLV, but allows the designer to prescribe other critical variables (entering condenser water temperature, evaporator leaving water temperature, flow rates, etc.). Proper determination of NPLV is described in ARI 550/590-98. Environmental TipsRefrigerants with ozone-destroying chlorofluorocarbons (CFCs) were common in older chillers but are no longer used in new equipment. The 1992 Montreal Protocol banned the production of CFCs in the U.S., beginning in 1996. Much of today's equipment uses hydrochlorofluorocarbon (HCFC) refrigerants, which have a much lower ozone-depleting effect. There are also many energy-efficient chillers on the market that use hydrofluorocarbon (HFC) refrigerants, with no ozone-depleting effect. When purchasing an HCFC chiller, buyers can request that the manufacturer conduct leak testing before shipment; leakage of 1% annually is considered good for new equipment (consult Green Seal, listed in "For More Information," below). Owners and operators of chillers with CFCs are faced with three options:
These options should be evaluated using life-cycle cost analysis (call the FEMP Help Desk at (877) 337-3463 to obtain LCC analysis materials). It is important when considering the continued operation of chillers with CFCs to assess the process of refrigerant recovery, followed by recycling or reclamation, and to factor in the likely substantial increase in the cost of obtaining replacement CFCs. When retiring a chiller that contains CFCs or HCFCs, the Clean Air Act requires that the refrigerant be recovered on-site by a certified technician. For compliance information, contact the EPA Stratospheric Ozone Information Hotline at (800) 296-1996. Early ReplacementMany facility managers are opting for early replacement of existing chillers with high efficiency units using non-CFC refrigerants. Good candidates for "early retirement" are CFC-based chillers with poor efficiencies or histories of high maintenance cost. Energy cost savings can add to the environmental benefits of non-CFC refrigerants. For example, replacing a 500-ton CFC chiller (0.85 kW/ton efficiency) with an efficient (0.56 kW/ton) non-CFC chiller can save $17,000/year, assuming a conservative $0.06/kWh. Demand charge savings may almost double this figure in some cases. In addition, many utilities offer financial incentives for efficient chiller replacements. SizingWhen replacing a chiller, careful attention to appropriate sizing is critical to achieving maximum energy savings. Many existing units are oversized. An oversized chiller not only costs more to purchase, it costs more to operate due to substantial energy losses from excessive cycling. Use the referenced ASHRAE calculation procedure (see For More Information) to properly determine the cooling load. It is often cost-effective to combine a chiller replacement with other measures that reduce cooling load, permitting specification of smaller equipment (see Integrated Chiller Retrofits, below). Replacing a single chiller with two or more smaller chillers to meet varying load requirements may be cost-effective. "Parallel staging" of multiple chillers is a common method of meeting peak load in larger installations. Multiple chillers also provide redundancy for routine maintenance and equipment failure. For many typical facilities, sizing one chiller at one-third and another chiller at two-thirds of the peak load enables the system to meet most cooling conditions at relatively high chiller part-load efficiencies. For example, one chiller could be optimized for peak efficiency at summer conditions (85°F condensing water) and the other chiller could be optimized for winter conditions (75°F condensing water). Integrated Chiller RetrofitsAn integrated chiller retrofit can provide enormous energy savings. It combines the chiller replacement or a refrigerant change-out with other energy conservation measures that reduce the cooling load or increase the efficiency of the cooling system itself. Examples of cooling system efficiency improvements are control system upgrades and increased cooling tower capacity. Cooling load reduction measures include tightening of the building envelope, and lighting system retrofits. The additional cost of these and other load reduction measures can be significantly offset by the savings from the downsized chiller they make possible. Lawrence Berkeley National Laboratory's "Cool $ense" project provides guidance on integrated chiller retrofits (see "For More Information". The first step in implementing an integrated chiller retrofit is a preliminary energy audit to assess the savings potential of various efficiency measures. A preliminary audit can often be provided by energy service companies, architecture and engineering firms, or utilities. FEMP can also provide this technical support, on a reimbursable subcontract basis. For information, contact FEMP's Technical Assistance Team at (202) 586-5772. For More Information
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