Conference Agenda

To accelerate the electrification of air source heat pumps (ASHPs) in cold climates across the United States, various initiatives have been launched to enhance the effectiveness of ASHPs. One avenue of research involves incorporating thermoelectric (TE) technology into vapor compression refrigeration cycles. This study aims to assess the heating performance of a cold climate ASHP by employing TE modules as a liquid line subcooler. The tested system is a nominal 4.5-ton split heat pump utilizing R410A, equipped with a scroll compressor and an accumulator. An electronic expansion valve was employed for both cooling and heating modes. Two configurations of TE sub-coolers, one utilizing 2 TE bundles and the other 4 TE bundles, were integrated into the liquid line of the tested system. The heating performance of these configurations was evaluated. The results revealed that activating the TE subcooler led to a notable increase in total heat capacity, reaching 1318 W at -15.0 °C and 1164 W at -19.0 °C. The corresponding TE coefficients of performance (COPs) were 1.76 and 1.63, respectively. The activation of the TE sub-cooler resulted in a slight reduction in the overall system COP, with a decrease ranging from -2.6% to -4.2% for these two temperatures. The system COPs were measured at 2.10 and 1.86 for -15.0 °C and -19.0 °C, respectively. This prototype demonstrated a significant augmentation in heating capacity with a minimal sacrifice in COP.

A broad thermodynamic and heat transfer analysis is presented for a variable speed, vapor injection cold climate heat pump (VI CCHP) designed to meet the Residential Cold Climate Heat Pump Challenge from the U.S. Department of Energy’s E3 Initiative. The design is compared against a baseline non-vapor injection, non-variable speed compressor system. A case study is presented using a real-world calculated heating load at a 5 ℉ (-15 ℃) outdoor ambient temperature for an 1800 ft² (~167 m²) residential home located in Salt Lake City, Utah (Region V). Thermodynamic performance and heat exchanger sizing are evaluated. Design levers for the VI CCHP are discussed, such as the ratio of refrigerant injection mass flow to total mass flow. R454B was chosen as the working fluid due to its burning velocity and GWP value compared to R32. The vapor injection loop introduces components such as a secondary expansion valve and economizer in addition to the components of the baseline four-component refrigeration cycle. The sizing summary indicates that a large outdoor heat exchanger is necessary to meet the heating load. The sizing of the economizer is outside this paper's scope but is recommended for future work. The VI CCHP design meets three of the Residential Cold Climate Heat Pump Challenge specifications and had a 32% increase in capacity and a 32% increase in COP compared to the baseline design. It is shown that the VI CCHP meets the load of the case study, and the improved performance results in an estimated annual energy savings of $425.35. The validity of the design in cooling mode is also presented.

This paper investigates the integration of a solar-powered dedicated mechanical subcooling (SDMS) cycle into the basic vapor compression cycle (VCC), as proposed and energy-assessed by Barghash et al. (2021). The primary advantage lies in enhancing refrigerant by further subcooling through an internal heat exchanger (IHX), thus increasing cooling capacity and utilizing solar energy to power the secondary compressor, leading to utility energy savings. This paper aims to further analyze the modified SDMS cycle by conducting exergy, environmental, and economic (3E) analyses for a case study of hot climates such as Kuwait. When comparing the SDMS system with the baseline VCC system, exergy analysis showed an enhancement of approximately 3% in exergy efficiency during the operational summer months of May, June, July, and August. Furthermore, from the exergy destruction perspective, SDMS reduced the exergy destruction by about 8% to 11% compared to VCC during the summers months. Environmental analysis, employing the Total Equivalent Warming Impact (TEWI) methodology, showed a 5% reduction in yearly equivalent carbon emissions despite a minor increase in direct emissions. Lastly, the economic analysis estimated a break-even period to be about 9 years between the SDMS and VCC systems.