Secondary Control Strategies for Cycling of Air Conditioning and Refrigeration Systems

Seshadri, Swarooph Nirmal; Rasmussen, Bryan P.
October 2012
ASHRAE Transactions;2012, Vol. 118 Issue 2, p508
Academic Journal
A large percentage of air conditioning and refrigeration systems rely on compressor cycling strategies to meet cooling loads. This paper examines the impact of expansion valve and heat exchanger fan control strategies on system efficiency, assuming an on-off cycle of the compressor . The first step is the development of a start-up/shut-down dynamic simulation model that is used as a tool to understand the effect that valve/fan cycling has on the system's cyclic efficiency. Refrigerant migration due to valve strategies and fan delay at shutdown are determined as crucial issues that have an effect on system's cyclic efficiency. Optimization approaches are then used to search for the optimal cycle strategies. The simulation studies are followed by extensive experimental tests conducted on a 3-ton residential air conditioner , confirming the major conclusions of the simulation study, namely that the valve and fan control strategies during compressor shutdown can result in significant variations in cyclic COP.


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