An inverter-driven heat pump with a multi-tubular tube-in-tube heat exchanger for domestic hot water supply

Abstract

An inverter-driven heat pump prototype to supply domestic hot water (DHW) was built, within which a multi-tubular tube-in-tube counter-flow heat exchanger as condenser was installed including a desuperheater section and a condenser section. The heating coefficient of performance (COP) is reduced approximately 10% if the feed water temperature increases from 9 °C to 24 °C. When the inlet temperature of primary brine is 24 °C, the compressor frequency does not show any effect on the heating COP. While when the inlet temperatures of primary fluid are 5, 10, and 17 °C, the COP increases with the rise of the compressor frequency at first, but it stays almost constant when the compressor frequency is within 40–55 Hz. It is considered that the effects of opposite dependencies of heat transfer and the pressure drop in the condenser onto COP tend to cancel each other out to obtain a constant heating COP. When the produced hot water is 65 °C, the heating COP of our developed heat pump for DHW is the largest among those of other three different heat pumps.