ML-11-016 -- Prevention of Compressor Short Cycling in Direct-Expansion (DX) Rooftop Units—Part 1: Theoretical Analysis and Simulation PDF

Compressor short cycling, recognized in the DX Rooftop Unit (RTU) operation, has not yet been successfully resolved. It drastically reduces the compressor reliability and degrades the system efficiency. This paper presents an advanced control algorithm to address this issue with minimized initial cost. It is based on the fundamental vapor compression theory that different evaporating temperatures will produce varied refrigeration effects. Elimination of the compressor short cycling can be achieved by extending the supply air temperature control band to match building load condition. Simulation results show short cycling to be completely eliminated with comparable or improved energy performance under various operating conditions. Field investigation was presented in a companion paper (Pang and Liu 2011).