ASHRAE Journal - March 2009 - (Page 28)

Thermosiphon heat exchangers operate with a refrigerant that condenses in a heat-transfer coil in the fresh air duct, transferring heat to the fresh air. It evaporates in a coil in the exhaust duct, drawing heat from the exhaust air. The thermosiphon operates like a heat pipe using a condensing and evaporating refrigerant, but the liquid travels from the condenser coil to the evaporator coil by gravity and not by capillary action. A thermosiphon does not require the exhaust duct to be adjacent to the fresh air supply duct as does a heat pipe. It is only necessary for the supply duct to be at a higher elevation than the exhaust duct for the liquid condensate to flow into the evaporator coil by gravity. A thermosiphon does not require an intricate series of capillary tubes as does a heat pipe and is less costly to make. The condenser and evaporator coils are shown in Figure 1 (RC-1 and RC-1A, respectively). The second heat recovery unit consists of transferring the heat of the warm water from the AC units’ condensers into the fresh air supplied by FAU-1. The water is diverted from the cooling tower to a series of heat transfer coils in the fresh air ducts supplied by FAU-1. The fresh air duct splits into two downstream of FAU-1 as can be seen in Figure 1. One set of heat transfer coils is in each branch of the supply duct. The heat transfer coils are shown in Figure 1. They are called RC-2A and RC-2B. RC-2A and RC-2B consist of two compact heat exchanger coils each. Both heat recovery units together are capable of recovering enough energy to heat the fresh air all winter. Figure 3: DDC screen view of UAF-1. Results and Benefits The first complete winter, after the energy-saving measures were implemented, ran from October 2007 to May 2008. The total consumption in natural gas was 5,223,675 ft3 (147 918 m3) for a cost of $68,008 (Canadian). The degree days for the same winter amounted to 7,608°F · days (4227°C · days). The natural gas savings were in excess of 60% of the original consumption with a 60% reduction in cost as well (even after a standard degree-day adjustment is applied). During the 12-month period beginning in October 2007 and ending in September 2008, the electrical consumption totalled 5,469,600 kWh for a cost of $383,080 (Canadian). That is 738,000 kWh (or 12%) less than the consumption during the year before the electrical measures were installed (Jan. 1 to Dec. 31, 2006). However, during the 12 months from October 2007 to September 2008, the average occupancy rate had risen to 97% from 89.7% during 2006. When the increase in occupancy rate is taken into account, the electrical savings amount to at least 20%. Despite the increased occupancy, the peak electrical demand did not increase. The total project cost was $527,600 (Canadian). The Canadian government and the local natural gas and electrical utility companies offered grants of $202,000 (Canadian). An analysis demonstrated that our goals were achieved. 4 Expected savings were exceeded and, 700 tons (635 Mg) of equivalent CO2 emissions were eliminated from the atmosphere per year. The owners and managers of this building have made great progress in their pursuit of environmentally sustainable buildings. References 1. Environment Canada, Service Météorologique du Canada. 2. 2004 ASHRAE Handbook—HVAC Systems and Equipment, pp. 44:14 – 44:15. 3. ANSI/ASHRAE Standard 62.1-2004, Ventilation for Acceptable Indoor Air Quality. 4. Efficiency Valuation Organization. 2007. “International Performance Measurement and Verification Protocol, Concepts and Options for Determining Energy and Water Savings.” Vol. 1. www.info.hotims.com/23933-42 28 ASHRAE Journal March 2009 http://www.unitedmetal.com http://www.unitedmetal.com http://www.info.hotims.com/23933-42

Table of Contents Feed for the Digital Edition of ASHRAE Journal - March 2009

Contents Commentary Industry News Letters Meetings and Shows Special Section 2009 ASHRAE Technology Awards Feature Articles Heat Recovery for Office Tower Air Motion Control in the Hospital Operating Room Anniversary Feature: Five Defrost Methods for Commercial Refrigeration Groundwater Issues: Commercial Open Loop Heat Pump Systems Used Filters and Indoor Air Quality Building Sciences Emerging Technologies Washington Report Products Special Products People Classified Advertising Advertising Index

ASHRAE Journal - March 2009

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