Improvement and validation of unitary air conditioner and heat pump simulation models at off -design conditions
Abstract
So far, there have only been a few in-depth research studies related to system simulation of unitary air conditioners and heat pumps at off-design conditions. However, it is clear that the current simulation tools and tuning methodologies do not provide accurate predictions at some off-design conditions. This report focuses on improved modeling methods for these situations. Comprehensive experimental and simulation studies are performed in this report to support this effort. Specific accomplishments of this work include identification of improved modeling methods for handling two-phase refrigerant entering the compressor, investigation of the effects of non-uniform distribution of refrigerant flow, investigation of the effects of a suction line accumulator in a heat pump, and development of an improved tuning method for charge modeling. The charge tuning method significantly improves simulations in the case of two-phase refrigerant entering the fixed-area expansion device. An existing system simulation model (ACMODEL) is the major tool that is used for this work and multiple improvements have been made in its capabilities. Based on an exhaustive literature search, the most appropriate up-to-date research results have been incorporated into each component model of the system simulation tool. In addition, a flexible heat exchanger modeling scheme has been developed that allows specification of heat exchanger design and circuiting. Extensive tests with detailed measurements were performed for two R-410A air conditioner units, one R-407C air conditioner unit, and one R-22 heat pump unit, which included over 350 points in different test series. All the tests have been simulated and analyzed in the report. The simulations were conducted at both the component level and system level. The overall accuracies of the improved ACMODEL in predicting cooling capacity and compressor power consumption of unitary air conditioners and heat pumps at off-design operating conditions are within 3% for the cases of no two-phase refrigerant entering the compressor or expansion device. In the cases of, two-phase refrigerant entering the compressor or expansion device, the overall accuracies of the improved ACMODEL in predicting compressor power consumption are within 5%, and the overall accuracies of predicting cooling capacity are within 10%.
Degree
Ph.D.
Advisors
Braun, Purdue University.
Subject Area
Mechanical engineering
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