Parameter estimation based model of water-to-water heat pumps with scroll compressors and water/glycol solutions

Abstract

A recently developed parameter estimation-based steady state simulation model of water-to-water reciprocating vapor compression heat pumps (Jin H, Spitler JD, ASHRAE Trans. 2002; 108(1)) is built up from models of individual components. Various unspecified parameters for individual components are estimated from catalogue data for the overall unit performance. This approach has been shown to give better accuracy and extrapolation capability than polynomial fit models. It has also been shown to give accuracy similar to more detailed deterministic models that require additional information not typically available to an engineer performing energy analysis. This paper covers two important extensions to the model — scroll compressors and glycol/water mixtures. A five-parameter (including intake volumetric flow rate, built-in compression ratio, leakage coefficient and two efficiency-related parameters) scroll compressor model replaces the reciprocating compressor model previously used. While necessary in some applications for providing protection from freezing, water/glycol solutions adversely impact heat transfer performance. A procedure for adjusting the model parameters to account for the change in working fluids is presented. In addition, a preliminary field validation of the modified water-to-water heat pump model is presented. The heat pump utilized both a scroll compressor and a propylene glycol/water mixture as the working fluid.