Vapor compression cycle enhancements for cold climate heat pumps
Abstract
In very low ambient temperature regions, both heating capacity and coefficient of performance (COP) of traditional air-source vapor compression heat pumps drop significantly with a decrease in outdoor air temperature. The current study investigates two alternative technologies for improving the efficiency of vapor compression cycles especially at very low ambient temperatures. The first method is liquid flooded compression with regeneration in which a significant amount of non-volatile liquid is mixed into the stream of refrigerant vapor entering the compressor in order to approach an isothermal compression process. The second method is multi-port refrigerant injection during compression and economizing which is similar to multi-stage compression in providing refrigerant cooling between compressor stages and a lower refrigerant quality entering the evaporator. Both technology improvements address the thermodynamic inefficiencies that are inherent within the simple vapor compression cycle that is employed in most heat pumping equipment. The benefits of oil flooding and saturated vapor injection are evaluated using experimental testing of an oil flooded R410A scroll compressor and a 2 port saturated vapor injection R410A scroll compressor and simulation. The results show that the performance of the compressor increases with oil flooding and saturated vapor injection especially at very low evaporation temperatures. The experimental compressor results were used for system analysis of liquid flooded compression with regeneration and saturated vapor injection. At -10°C ambient temperature, estimated COP (heating) of the flooded compression with regeneration cycle was 25% higher while that of the vapor injection cycle was 12.5% higher than the standard vapor compression cycle. For Minneapolis, the seasonal efficiency (heating) of a flooded compression with regeneration cycle was estimated to be 34% higher while that of the vapor injection cycle was 21% higher than the standard vapor compression cycle. Both technologies lead to higher energy efficiency and less degradation in heating capacity at low ambient temperatures. Also, a previously developed detailed flooded scroll compressor model has been validated with the oil flooding experimental data, for which good agreement was found.
Degree
M.S.M.E.
Advisors
Groll, Purdue University.
Subject Area
Mechanical engineering
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