Laboratory Tests Of A Prototype Carbon Dioxide Ground Source Air Conditioner

Author : Harrison Skye
Publisher :
ISBN 13 :
Total Pages : 79 pages
Book Rating : 4.:/5 (113 download)

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Download or read book Laboratory Tests of a Prototype Carbon Dioxide Ground-source Air Conditioner written by Harrison Skye and published by . This book was released on 2019 with total page 79 pages. Available in PDF, EPUB and Kindle. Book excerpt: Environmental concerns are driving regulations to reduce the use of hydrofluorocarbons (HFCs) with high global warming potential (GWP) as refrigerants in heat pumps. CO2 is an attractive alternative refrigerant because is it environmentally friendly in terms of direct emissions, with GWP=1, and no ozone depletion potential (ODP). However, CO2 heat pumps generally have a lower efficiency than HFC-based systems, and therefore have higher indirect emissions, related to generating the electricity that powers them. The indirect emissions dwarf the direct emissions for most heating, air-conditioning and refrigeration applications, so it is critical for the equipment to operate with high efficiency. CO2 air-source heat pumps (ASHPs) provide cooling with particularly low efficiency at high ambient temperatures where the CO2 operates in a transcritical cycle. Using CO2 in a ground-source heat pump (GSHP) offers the potential to overcome the low efficiency since a GSHP operates with lower heat-rejection temperature (for cooling), enabling the system to operate some of the time in a more-efficient subcritical cycle. This report details the laboratory tests of a prototype residential liquid-to-air ground-source air conditioner (GSAC) using CO2 as the refrigerant. The tests were performed in an environmental chamber and followed the ISO 13256-1 standard for rating GSHPs. The CO2 GSAC operated either in a subcritical or a transcritical cycle, depending on the entering liquid temperature (ELT). The test results included the coefficient of performance (COP), capacity, sensible heat ratio (SHR), and pressures. The system incorporated a liquid-line/suction-line heat exchanger (LLSL-HX), which was estimated to cause a COP penalty of (0 to 2) % for ELTs ranging (10 to 25) [degrees]C, and benefit of (0 to 5) % for ELTs ranging (30 to 39) [degrees]C. The CO2 system was compared to a low-cost , commercially-available R410A-based GSHP. With ELTs ranging (10 to 39) [degrees]C the CO2 system cooling COP ranged (7.3 to 2.4), whereas the R410A system values ranged (6.1 to 3.2). At the standard rating condition (ELT 25 [degrees]C), the CO2 GSAC cooling COP was 4.14 and the R410A GSHP COP was 4.57. At part-load conditions (ELT 20 [degrees]C) both systems had a COP of ?4.92. Further effort is needed to increase the CO2 system efficiency at ELTs greater than 20 [degrees]C, since it underperformed the R410A system in that temperature range.