Consulting-Specifying Engineer - January 2008 - (Page 30) Equipment Lifecycles and project time disparities, or unequal service lives. An important aspect of a chiller selection is analyzing its energy use for operating cash flows. Assuming a selection of a watercooled, centrifugal chiller is required, a method to use is the chiller’s relevant pressure drop and flow rate information, and its Air-Conditioning and Refrigeration Institute (ARI) integrated part load value/ non-standard part load value (IPLV/NPLV) ratings. The ARI 550/590-2003: Standard for Performance Rating of Water Chilling Packages Using the Vapor Compression Cycle IPLV/NPVL ratings provide realistic off-design performance for chillers, and assists in making energy comparisons. To illustrate, assume two 2,000-ton chillers with 25-year life expectancies operate 8,760 h/yr at $0.10/kWh; discount rate 11%; and all other items (e.g. energy cost escalation, depreciation method, maintenance costs, etc.) are equal. The manufacturers’ information follows: Description Price Evaporator pressure drop Evaporator flow Condenser pressure drop Condenser flow Loading A = 100% (85 F) B = 75% (75 F) C = 50% (65 F) D = 25% (65 F) Chiller 1 $522,700 17.3 ft 4,000 gpm 13.0 ft 6,000 gpm kW/ton 0.588 0.505 0.460 0.588 Chiller 2 $462,700 19.7 ft 4,000 gpm 18.9 ft 6,000 gpm kW/ton 0.599 0.516 0.483 0.595 Compressor costs 2,000 tons x (8,760 h/yr) x ($0.10/kWh) x (NPLV kW/ton) = $/yr Evaporator and Condenser Pumping costs [(number ft) x (flow gpm) / (3,960 x 0.85)] x [(0.746 kW/hp) x (8,760 h/yr) x ($0.10/kWh)] = $/yr A NPV calculation over 25 years indicates that if Chiller 1 is selected, it would have a lifetime cost of $7.23 million, compared to Chiller 2, which would have a lifetime cost of $7.47 million. At present value (PV), Chiller 1 costs $50,541 more up front. In reviewing the cumulative lifecycle PV energy savings of operating Chiller 1, the savings of $62,804 in year 3 indicates the payback for the increase in capital expenditures occurs rather quickly. If the chillers had up-front equal costs, the energy savings would be immediate, but would not be equal to the mathematical difference of the savings if calculated using the formulas above. The owner would need to take the difference and invest it to achieve a cash flow. The cumulative PV energy savings of operating Chiller 1 compared to Chiller 2 over 25 years is $143,300. The $240,334 is the PV difference between the two selections, taking into account all costs (not assumed equal) for this example, which is only the first cost and the energy costs carried through a 25 year NPV calculation. A change in full or part load efficiencies can dramatically change the NPLV and operating costs. If there is a change in the NPLV for Chiller 1 to 0.507, the payback does not occur until year 17. The prediction of energy costs over a 25-year period can be a variable as anything else. The costs would be included in the NPV and discounted along with all the others equally contributed to both chillers. Schrecengost is a project manager in Stanley Consultants’ Austin, Texas, office. A certified energy manager, he has extensive knowledge of lifecycle costs. Use the following formulas to calculate the items necessary for a NPV comparison: NPLV kW/ton = 1/[(0.01/A) + (0.42/B) + (0.45/C) + (0.12/D)] And you thought Swiss watches were impressive. Jaeggi. It’s pronounced “Yay-gee.” It means Swiss-engineered cooling towers that embody unprecedented quality, reliability and water and energy efficiency. Available for the first time in the United States, this innovative, patented Hybrid Dry Cooling Tower technology will debut at the AHR Expo in New York. Visit our booth or website to learn how environmentally conscious companies are benefiting from significantly reduced operating costs and up to 80% water savings by using Jaeggi Hybridcoolers. You’ll be impressed. AHR EXPO New York January 22-24, 2008 Jaeggi Booth #8549 Jaeggi. Changing the language of industrial cooling. 760 541-9308 www.jaeggi.us Input #217 at csemag.com/quickResponse http://www.jaeggi.us http://www.jaeggi.us http://csemag.com/quickResponse
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