Discharge Temperature, Compressor Performance
Predicting the discharge line temperature (DLT) of air conditioning and refrigeration compressors is important to ensure sufficient lubricant properties and proper performance of components that are positioned in the exhaust stream. Understanding the DLT is also necessary for the design of waste heat recovery systems, which are of increasing interest. However, compressor performance information published by manufacturers does not typically include DLT values. Assumptions made in established thermodynamic models result in only modest correlation between predicted and observed DLT values. Numerous comprehensive DLT prediction models have been developed with excellent accuracy, but require many details of a particular compressor. This paper presents an assessment of various thermodynamic DLT prediction methods that do not rely on compressor-specific parameters. Prediction methods considered include an entropy-based model, a polytropic model and an energy model. The energy model was expanded to include an empirical component to account for high-side heat transfer and exhibits an accuracy that significantly exceeds the other established methods. The model was evaluated for both traditional refrigeration and air-conditioning operating conditions and translates well to vapor-injected, economizer cycles. Lastly, a study was conducted to determine the robustness of the empirical component by analyzing the relationship between the accuracy of the model and the number of experimental points used to produce the model.