Study on Working Condition Adaptability of Transcritical Co2 Heat Pump Based on Intermediate Temperature Heating

Abstract

In the context of climate change, waste heat source transcritical CO2 heat pumps have received increasing attention. However, its discharge temperature is generally too low due to the high temperature of the waste heat source and high evaporating pressure, resulting in a limited system pressure ratio, so that the problem of not being able to produce a water supply of 80-100℃ is becoming significant. This paper provides a new type of waste heat source transcritical CO2 heat pump system with intermediate temperature regeneration. In this system, the gas cooler is divided into two parts, which are installed on both sides of the internal heat exchanger. This design improves the heat exchange effect of the internal heat exchanger and increases the amount of internal heat exchange capacity, addressing the problem of low discharge temperature. In addition, The single parameter optimization of the conventional type of heat pumps is explored in this paper for water inlet temperatures of 5, 15, and 30℃, with an outlet temperature of 90℃.,The results show that variations of the inlet water temperature exert minimal influence on the system’s optimal discharge pressure. The novel heat pump design incorporating an intermediate temperature parameter achieves equivalent discharge temperatures at 12.3MPa discharge pressure to those requiring 15.0MPa in conventional systems. This innovation substantially reduces the pressure ratio while enabling the gas cooler outlet temperature to approach the inlet water temperature more closely, thereby enhancing heat exchange efficiency in the high-pressure section. Consequently, the optimized system demonstrates 16.34% improvement in COP compared to conventional configurations. These results confirm that the novel waste heat pump not only fulfills high-temperature hot water demands under low pressure ratios but also elevates thermal efficiency and energy performance, ultimately optimizing overall system capabilities.

Keywords: Waste heat source transcritical CO2 heat pump, Intermediate-temperature internal heat exchange, low pressure ratio, coupled optimization, high discharge temperature