Experimental Investigation on an Ultra-High Temperature Air Source Heat Pump Water Heater

To generate boiling water beyond 100 °C via heat pump technology, the prototype of an ultra-high temperature air source heat pump water heater (ASHPWH) based on a single-stage compression cycle of R134a was established, and an experimental investigation on it was conducted under an environment temperature of 25 °C. Then, thermodynamic analyses were carried out on the basis of the experimental results, especially when the prototype produced 95.9 and 100.3 °C water. The experimental and analytical results indicate that water beyond 100 °C was achieved through the prototype. When producing 100.3 °C water, the discharge temperature and compression ratio of the compressor of the prototype are only 108.4 °C and 4.07, respectively, which are in moderate levels. Correspondingly, the work input of the compressor is 0.622 kW, the heating capacity is 2.786 kW, and the heating coefficient of performance is 4.48. In addition, when producing 95.9 and 100.3 °C water, the system exergy efficiencies of the prototype are 50.76% and 49.73%, which are larger than those of the existing ASHPWHs, demonstrating that dividing the condensing process into two parts of high-grade exergy and low-grade exergy and utilizing them separately is effective. That is the essential reason of generating boiling water beyond 100 °C as expected only through the single-stage compression cycle.