Secondary Loop Residential Heat Pump Design, Performance, and Cost Analysis Utilizing R290

The use of alternative refrigerants and HVAC technologies is necessary because of the inevitable phase out of current refrigerants. Ammonia and Propane are desirable for air conditioning applications because of their superior thermodynamic and transport properties compared to many HFC refrigerant alternatives. However, these refrigerants are toxic or flammable. The idea to use a secondary loop cycle enables these refrigerants to be used while not bringing them in contact with people. An initial analysis of a secondary loop system for a residential heat pump using propane as the refrigerant was performed using ACHP showing a comparable performance to a traditional DX heat pump. This thesis presents a design for the secondary loop, the optimization performed for the system, the system testing data, and comparisons of ACHP model predictions with test data. The focus was to achieve a 3-ton cooling capacity with SEER 14 performance for a prototype R290 while achieving a mass production cost that would be competitive in the market today. Psychometric chamber testing showed that the secondary loop system fell short of the baseline system’s cooling and heating capacity as well as consumed more energy than the baseline DX system at all ambient conditions. The lower capacity was due to losses in the PHEX and secondary loop, low refrigerant flow rate, and low coolant flow rate. The test results for the R290 SL system showed approximately a 0.7 to 0.8 kW capacity drop between the PHEX refrigerant and the indoor coil air (secondary loop capacity losses). The power consumption of the SL R290 system was also greater than the R410A DX system leading to a lower COP. The increase in power was primarily due to additional pump power associated with the secondary loop and increased compressor power due to a larger pressure ratio and lower isentropic efficiency than the R410A compressor