Impact of Elevated Ambient Temperatures on Capacity and Energy Input to a Vapor Compression System -- Literature Review

Published

August 1, 2000

Author(s)

S F. Yana Motta, Piotr A. Domanski

Abstract

Operation of a system at elevated ambient temperatures inherently results in a lower coefficient of performance (COP). This conclusion comes directly from examining the Carnot cycle. The COP relation, COP=T_evap/(T_cond-T_evap) indicates that the COP decreases when the condenser temperature increases at a constant evaporation temperature. The theoretical indication derived from the reversible cycle is valid for all refrigerants. For refrigerants operating in the vapor compression cycle, the COP degradation is greater than that for the Carnot cycle and varies among fluids. The two most influential fundament6al thermodynamic properties affecting refrigerant performance in the vapor compression cycle are refrigerant's critical temperature and molar heat capacity. (e.g., McLinden, 1987, Domanski, 1999). For a given application, a fluid with a lower critical temperature will tend to have a higher volumetric capacity (Qvol) and a lower coefficient of performance (COP). The difference between COPs is related to different levels of irreversibility because of the superheated vapor horn and the throttling process, as shown conceptually in Figure 1. The levels of irreversibility vary with operating temperatures because the slopes of the saturated liquid and vapor lines change, particularly when approaching the critical point.

Citation

Letter Report to Air-Conditioning and Refrigeration Institute

Pub Type

Journals

Keywords

air conditioning, alternative refrigerants, coefficient of performance, refrigeration

Citation

Yana, S. and Domanski, P. (2000), Impact of Elevated Ambient Temperatures on Capacity and Energy Input to a Vapor Compression System -- Literature Review, Letter Report to Air-Conditioning and Refrigeration Institute (Accessed April 23, 2024)