Development and Testing of a Prototype Pilot Expansion Valve for Vapor Compression Systems
Youmsi Pete, Edwin Larry
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The Vapor Compression Cycle (VCC) is the fundamental thermodynamic principle behind most Heating, Ventilation, Air Conditioning and Refrigeration (HVACR) systems. HVACR systems account for a vast majority of the energy used in residential and commercial buildings. There is a growing need to make these VCC systems and their respective components more energy efficient. This thesis proposes a prototype pilot expansion device. Preliminary results have shown that this prototype expansion valve outperforms most of the expansion devices currently being used in HVACR applications. Valve hunting and superheat control are very important elements in the operation of expansion valves. They reduce system efficiency and increase energy consumption. To address these problems, the combination of conventional expansion valves with other expansion devices or components is still a relatively unexplored area. This approach has the potential to improve the energy efficiency of HVACR systems thus reducing cost of operation. This thesis discusses the development, design and proof-of-concept testing of a Prototype Pilot Expansion Valve (PPEV). A number of tests were designed and carried out in order to objectively compare the performance of the PPEV to that of an Electronic Expansion Valve (EEV) and a Thermal Expansion Valve (TEV) under a variety of operational conditions. These tests involve a superheat change test, startup test and external fluid flow rate test, all carried out at varying compressor speeds. The tests were carried out on a custom-built modulated water chiller system and a residential heat pump system. The results obtained from these tests validated that the PPEV performed significantly better than the EEV and the TEV. It was able to provide more cooling, better superheat control and consistently higher Coefficient of Performance (COP). In addition, this thesis also provides and proves the validity of a mathematical model for the Prototype Pilot Expansion Valve. Furthermore, an additional test was carried out to prove the possibility of an integrated design that will enable to PPEV to not rely on any external component to operate. This test demonstrates the possibility to use the compressor inlet and outlet to operate the PPEV thus confirming the possibility of a truly integrated design.