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Owing to their high cooling efficiency in summer and frost-free characteristics in winter, heating tower heat pumps are becoming increasingly popular. However, the solution will be diluted during heating due to absorbing moisture from the air, and should be properly regenerated for continuous operation. In this study, a novel heat recovery solution regeneration system using an internally heated regenerator is proposed for antifreeze solution regeneration. A test bench is fabricated to investigate the regeneration performance of the internally heated regenerator. Correlations of the heat and mass transfer coefficients are proposed, and agree well with the experimental data. The influences of inlet parameters on the moisture removal rate, latent heat ratio, and humidity effectiveness are evaluated and compared to those for internally heated liquid desiccant regeneration. The results indicate that: the regeneration performance of the internally heated regenerator is affected mainly by the air flow rate, heating water flow rate, and inlet temperature of heating water. The moisture removal rate increases remarkably with increasing the heating water flow rate and inlet temperature of heating water. The latent heat ratio decreases significantly with increasing the inlet temperature of heating water. The humidity effectiveness decreases remarkably with increasing the air flow rate. The influences of the above inlet parameters on performance indices in the present study exhibit the same trends as those reported for internally heated liquid desiccant regeneration. However, compared with internally heated liquid desiccant regeneration, the regeneration temperature for internally heated antifreeze solution regeneration is much lower. This suggests that a low-grade heat source can be used to meet the antifreeze solution regeneration demands.

A heat-source tower heat pump (HTHP) is a potential heating source for space heating due to frost-free characteristic. The heat and mass transfer between the antifreeze solution and air at low ambient temperatures is a key issue for performance enhancement. In this study, a test bench for evaluating the cross-flow closed-type heat-source tower (CCHT) is fabricated to investigate its performance under variable working conditions. Based on the experimental results, correlations of heat and mass transfer coefficients are developed, which can be used to predict the performance of the CCHT. As a result, the mass transfer coefficient between the solution and the air of the CCHT is 0.015–0.051 kg m−2 s−1, while that of the liquid desiccant dehumidifier is 0.0037–0.015 kg m−2 s−1. However, the latent heat ratio of the CCHT is 6–31%, while that of the liquid desiccant dehumidifier is 42–124%.

The heat-source tower heat pump, a frost-free heat pump with superior energy efficiency, has been used for heating in cold regions. Because the solution in the heat-source tower absorbs moisture continuously from the outdoor air and becomes diluted during heating, solution regeneration is necessary. However, existing regeneration technologies have various disadvantages, such as a reduced heating capacity, decreased system efficiency, or the need for additional equipment. Hence, it is urgent to develop a regeneration technology with low cost, high energy efficiency and little impact on heating capacity. In this study, a heat-source tower heat pump with a self-regenerator is proposed and experimentally investigated. To regenerate the weak solution in the tower, the system uses the subcooling heat of the refrigerant at the condenser outlet as a heat source. The operating characteristics of the system in three heating modes are investigated experimentally. The results indicate that in the heating mode with self-regeneration, the heating capacity of the system is similar to that in the heating mode without regeneration under the same operating conditions. The system realizes efficient regeneration and can operate continuously, although the system efficiency is 2.5–5.1% lower than that of a system without regeneration. In addition, the regeneration efficiency of the proposed system reaches 3.13–11.98 under the condition where the regeneration temperature ranges from 18 to 45 °C. These results demonstrate that the proposed system can be used in cold regions.

Conventional absorption refrigeration systems (ARSs), which are mainly driven by heat, have a competitive primary energy efficiency (PEE) compared with chillers driven by electricity. In the typical ARS, a large quantity of high-temperature heat is supplied into the generator, while a substantial amount of low-temperature heat is rejected to the environment from the condenser, it’s a huge waste. In order to decrease the input heat for generator and enhance the performance of conventional ARS, a kind of absorption-compression hybrid refrigeration system recovering condensation heat for generation (RCHG-ARS) was ever proposed. In the present study, the models of both RCHG-ARS and double-effect absorption refrigeration system (DEARS) are established, and the effects of different parameters on them are simulated and compared with each other. As a conclusion, the PEE of RCHG-ARS can be 29.0% higher than that of DEARS, and RCHG-ARS has a wider working conditions than DEARS due to the existence of the compressor.

To prevent frosting of air source heat pump used for space heating in winter, heat-source tower heat pump has been developed for its advantages such as frost-free, stable and reliable. Due to the mass transfer process between air and solution, however, the solution can continue to absorb the moisture of air, which results in the decrease of solution concentration and the increase of freezing point. It’s very essential to regenerate the dilute solution to ensure the stability and reliability of the operation of heat-source tower heat pump. Therefore, in this paper, the experimental test of closed-type heat-source tower is built to study the effect of inlet parameters of three fluids on heat and mass transfer performance under low temperature condition. According to the experimental results, with the increase of air volume, flow rate of internally heating water, so does the solution regeneration performance of closed-type heat-source tower.

Traditional single source heat pump systems, e.g., air source heat pump (ASHP) and ground source heat pump (GSHP), cannot work efficiently in the whole year. To develop an energy-efficient heat pump system for year-round operation, temperature grades of common natural energies are compared with each other. Based on the comparison, the combination principle of hybrid sources with complementary characteristics is discussed firstly. Then three typical types of heat pumps with hybrid sources are selected as representatives to show how to take full advantages of different heat sources or sinks for energy-efficient operation and how to extend functions of hybrid source heat pumps for new solutions to the disadvantages of conventional heat pumps. Finally, the annual performances of these three selected types of hybrid source heat pump systems for three corresponding specific cases are simulated by TRNSYS. The results show that hybrid source heat pump systems can maintain nearly the same heating capacity as they do without frost during the defrosting period; maintain energy-efficient year-round cooling with no risk of freezing during winter; keep the thermal balance of soil and maintain reliable cooling and heating over long periods of operation; fully utilize solar radiation of different intensities; and achieve year-round energy-efficient performance. In contrast to a conventional ASHP and GSHP system, the energy saving rate of a typical hybrid source heat pump system is approximately 15%, and the payback period is approximately five years. Hybrid source heat pumps provide a way to match multiple heat sinks/sources for different levels of building demand in different climates.