Interrelationship of charge, operating conditions, and type of expansion device on an air/air heat pump system
Abstract
The effects of the amount of refrigerant charge, different types of expansion devices and operating conditions on the performance of a heat pump have been investigated. Experimental tests were run on both heating and cooling modes of operation at different ambient conditions. Three independent steady-state heat pump computer models were compared in their strengths, weaknesses, and capabilities in simulating a heat pump system other than the one(s) with which they were first validated. One of these codes was further investigated in its capability of being sensitive to the refrigerant charge in the heat pump system. This program was modified to improve its predictions of mass inventory. Results obtained with this program using the mass inventory show that further improvements (primarily in the modeling of the evaporator) are necessary in order to be able to throughly simulate a heat pump with varying amounts of charge. Based on the experimental results a semi-empirical model is proposed which can represent the heat pump performance with varying charge in the system, and at different operating conditions. The approach used in this model indicates the potential of generalizing a limited number of experimental data based on a specific unit. Results of the present investigation show that means of controlling the amount of refrigerant in the heat pump cycle can improve its performance (in the order of 12% increase in heating seasonal performance factor) when equipped with fixed restrictor expansion devices. In the case of variable restriction (thermostatic valve) such a control can prevent condenser floodback which might cause system failure and decrease the system life expectancy.
Degree
Ph.D.
Advisors
Goldschmidt, Purdue University.
Subject Area
Mechanical engineering
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