Seeking a new throttle to substitute the thermostatic expansion valve in vapor-injection process for an air-source heat pump: An experimental study

Abstract

Air source heat pump (ASHP) as a sustainable energy technology is playing an essential role in achieving carbon neutrality for almost countries. The operational stability of ASHP is related to throttles. The selection of thermostatic expansion valve (TEV) types is sometimes limited by a wide range of outdoor temperature conditions. In order to find a substitutable throttle of TEV, this paper compares a pulse width modulation driven (PWM-driven) solenoid valve coupled with a capillary with TEV to control vapor-injection based on a two-stage compressed air-source heat pump (TCASHP) prototype. The experiment results show that the TCASHP unit can operate in a wider temperature range if the TEV capacity is selected properly to control vapor-injection. While the on-off periods and times of PWM-driven set out of place make the TCASHP situate at a hunting problem state. The solenoid valve should be installed behind the capillary to control vapor-injection by experiments and entropic analysis. Furthermore, the shorter on-off periods and longer opening time of PWM-driven solenoid valve reduce the risk of hunting problems. Besides, the operation stability is the best for TCASHP unit with PWM-driven solenoid valve coupled with capillary to control vapor-injection, which has the same performance as the TEV.