A Semi-Empirical Model for Studying the Impact of Thermal Mass and Cost-Return Analysis on Mixed-Mode Ventilation in Office Buildings

The heating capacity and coefficient of performance (COP) of conventional air-source heat pumps decreases towards lower ambient temperatures. Additionally, the heat pump stops running at very low ambient temperatures due to the high discharge temperature at the outlet of the compressor. Oil injected into the compression chamber absorbs the heat generated during the compression process and thus, reduces the compressor discharge temperature. This allows the application of air-source heat pumps in regions of low ambient temperatures during the winter month. In addition, the compressor power consumption decreases with oil injection. Furthermore, the system performance of a vapor compression system with oil flooded compression can be significantly improved when also using a regenerative heat exchanger. The work presented on this poster shows the simulation results applying the oil flooded compression with regeneration technology to a vapor compression cycle with a secondary loop for providing the required heating load. In addition, experimental results of a R410A 5-ton small packaged heat pump, which was retrofitted with an oil injected compressor and regenerator, are presented. Compared to the performance of the secondary loop baseline cycle without oil injection, the system COP increases by more than 13% at an ambient temperature of -30 C when liquid flooding and regeneration is used. The testing of the 5-ton small packaged heat pump modified for use with the oil injection and regeneration technology showed a system COP improvement of more than 7%. Additionally, a higher superheat at the compressor suction leads to larger improvement of the system COP if the ambient temperature stays constant.