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.
Geothermal heat pumps (GHPs), also referred to as ground-source heat pumps or Geo-exchange, have been proven capable of producing large reductions in energy use and associated carbon emissions for space conditioning and water heating in buildings. However, the current adoption rate of GHPs in the United States is still low, and GHPs receive little attention from either the public or policy makers. This report gives an overview of the status of GHP technology and its application in the United States, cost and performance of the state-of-the art GHP systems, barriers preventing wider adoption, and technologies under development that have potential to help overcome these barriers.
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