Performance Testing of a Unitary Split-system Heat Pump Utilizing an Energy Recovery Expansion Device

Nicholas J Czapla, Purdue University

Abstract

Due to the rising demand for a more efficient use of energy resources, the HVAC&R industry is facing the challenge of meeting stricter energy consumption requirements. The main objective of the research work presented in this thesis is the investigation of an energy recovery expansion device to improve the energy efficiency of a vapor compression cycle. Roughly 3 - 6% of the total system power consumption is wasted during the isenthalpic free expansion process of a conventional R410A heat pump. A partially isentropic expansion process in which energy is recovered and fed back to the system can have a meaningful impact on reducing the heat pump energy consumption. As a result, there is a significant potential for replacing the traditional passive expansion device by a power-generating device – the Viper expander. This device has been developed by the Regal Beloit Corporation and consists of a nozzle, turbine and a generator. The Viper expander functions by converting high pressure subcooled liquid into a jet of high velocity two-phase fluid which impinges on a turbine impeller. The kinetic energy is converted to mechanical shaft work as the Viper impeller rotates. The shaft of the impeller is connected to a generator that produces electric power which is fed back into one of the system’s fan motors. Ideally the augmented power from the Viper expander will supply an estimated 30-50% of fan’s power and thus, reduce the total system power consumption. The heat pump system, including the Viper Expander, is performance tested at Purdue University’s Ray W. Herrick Laboratories in accordance to ANSI/AHRI Standard 210/240. The heat pump is tested in both cooling mode and heating mode with several variations of the Viper expander. The highest isentropic efficiency was observed to be 12.1% with a 7.08% increase in COP. Experimental tests showed that the Viper expander generated up to 182 W for a condenser inlet air temperature of 110°F. These results suggest that a more efficiently designed Viper Expander could result in an even larger increase in COP. It was observed that the Viper expander has better performance when the refrigerant enters the device at higher vapor content and lower viscosity. Thus, installing it into a transcritical carbon dioxide (CO₂) refrigeration cycle is another possible application. A theoretical analysis quantifying the potential impact of the Viper expander in a transcritical CO₂ cycle has also been performed. The model was developed under the assumption that a more efficient Viper Expander has been developed based off past experimental testing. Isentropic efficiencies ranging from 30 - 50% can result in an increase in CO₂ system COPs by 2.9 - 10.8%.^

Degree

M.S.M.E.

Advisors

Eckhard A. Groll, Purdue University.

Subject Area

Engineering|Energy

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