The influences of the operating characteristics of an Electronic Expansion Valve (EEV) on the operational stability of an EEV controlled direct expansion air conditioning system

• EEV's operating characteristics on a refrigeration system's stability were studied.
• Theoretical results using classical control theory were experimentally verified.
• A larger proportional or integral gain would very likely lead to instability.
• Slowing down EEV's temperature transfer may help mitigate instability.

This paper reports on a study on the influences of the operating characteristics of a proportional–integral (PI) controlled Electronic Expansion Valve (EEV) on the operational stability of a direct expansion (DX) air conditioning (A/C) system. Using the classical control theory, EEV's PI settings and time constant of EEV's temperature sensor were analyzed. The theoretical analysis results using the classical control theory were further verified experimentally using an experimental DX A/C system. The study results showed that a larger proportional or integral gain would lead to a high chance for the EEV–evaporator control loop to become unstable, while slowing down the rate of degree of superheat (DS) signal transfer by increasing EEV's time constants may help mitigate system's operational instability. The results confirmed that the operating characteristics of an expansion valve in a refrigeration system could impact its operational stability.