Performance Enhancement of Small-Scale Heat Pumps Using Thermoelectric Active Subcooling: A Simulation-Based Assessment
Achieving climate-neutral buildings requires compact and efficient heating technologies suitable for small-scale residential applications. This study evaluates the integration of thermoelectric (TE) modules as an active subcooler in a 5 kW air-to-water heat pump (HP) and compares its performance with a conventional passive subcooler and reference HP. An equation-based model of the TE module under constant-voltage operation is developed, validated, and coupled with the heat pump to simulate multiple operating scenarios combining different heat sources (-12 °C, and 12 °C), sink temperatures (35 °C, and 65 °C), and refrigerants (R290, R1234zee, and R1234yf). Results show that TE-assisted subcooling consistently contributes to the total heating capacity (5 kW) by 10–17%, with contribution of 0.54–0.96 kW. Highest COP improvements of up to 13% are achieved under high-lift heating conditions (65 °C Radiator/DHW, dT: 15K), while lower-temperature floor-heating (35 °C Floor Heating dT:5 K) conditions yield capacity gains but minimal efficiency improvement. Despite the added TE electrical input of 0.09–0.11 kW, the active system consumes less total power than the passive subcooler configuration due to reduced compressor work which reaches to more than 20% saving of electrical energy consumption. The findings demonstrate that active TE subcooling provides clear advantages over passive subcooling and offers the benefits under high-lift operation compared to reference HP. Overall, TE integration is shown to be a promising and technically viable approach for enhancing the efficiency of next-generation small-scale heat pumps in residential and urban heating applications. Future work should examine the impact of TE coupling position within the refrigeration circuit, as placement may influence subcooling effectiveness and system-level performance. Additionally, a comprehensive economic and techno-economic assessment is recommended, particularly for scaling TE integration to medium and large heat pump systems exceeding 50 kW, where cost-performance trade-offs become increasingly critical.