Superheat Control: A Hybrid Approach
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This paper examines the perennial problem of evaporator superheat control. While standard mechanical devices can operate effectively under design conditions, many behave poorly as conditions vary or under transient operation, resulting in degraded system performance, such as thermostatic expansion valve (TEV) hunting. Technological advances enabling electronic control help alleviate these problems by allowing more sophisticated control approaches to regulating superheat—for example, electronic expansion valves (EEVs). However, poorly tuned EEVs can still exhibit undesirable behavior, and frequent valve adjustments raise concerns about device longevity. In this work, we propose a cascaded control approach, which regulates evaporator pressure and superheat and is achieved with a feedback control device that uses a hybrid of mechanical and electronic feedback. Analysis of the fundamental dynamic behavior of evaporator superheat motivates this approach, while experimental evaluation of two separate systems demonstrates the efficacy of the approach as compared to standard control devices, such as TEV and EEV. © 2009 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
author list (cited authors)
Elliott, M., Walton, Z., Bolding, B., & Rasmussen, B. P.