Experimental investigation on a rotary compressor-expander heat pump performance

• Main Author: Kouhestani, Mohammad Salehi
• Published: Ulster University 2016
• Subjects: 621.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.698802

This research investigates the performance and impacts of integration of an internal expander within a typical heat pump system for the UK climate. In this novel system, the expansion process takes place within an expander rather than a traditional expansion valve, and it is expected that recovered work by the expander could provide a portion of the required power to drive the compressor. This project comprises a literature review, test rig design and fabrication, control system design instrument selection and calibration, data-logging system setup and installation, implementation of the BS standard for heat pumps performance testing, implementation of tests, and data collection according to relevant standards and data analysis. A test rig is developed and improved throughout this research. More than 20 sets of tests have been carried out between 2011 and 2014, and the most appropriate of them are presented and discussed. To determine the impact of expander integration, the rotary compressor-expander unit was tested with and without an expander, and the system COP, capacity, and isentropic efficiency are discussed. This thesis commences by introducing key drivers of this research, the energy crisis, global warming issues, and the contribution of the domestic sector to energy consumption in the UK. Then it continues by classifying heat pumps according to their energy sources. A detailed review and evaluation of major advanced heat pumps and refrigeration technologies then follows. Test rig design and development (according to the BS EN14511-2:2011) are discussed and outlined comprehensively. The test scenarios are presented, obtained data are discussed, test outcomes are evaluated, and the issues and their causes are addressed in detail. To address the issues and interpret the achieved results, theoretical analysis is carried out as well, then actual outcomes are compared with theoretical anticipated results and the differences are addressed. Results of compressor tests and system integration are presented separately and discussed comprehensively. The last chapter outlines conclusions and recommends further possible work on this research topic and offers practical suggestions to improve the performance of this developed system. However, this research reveals that such integration of an expander and compressor is not suitable in practice for typical UK winter conditions, though it may offer some benefits for extreme winter conditions where the ambient temperature drops to -10°C or below. In addition, it reveals that the designed compressor is not able to overcome a significant temperature increase (which is the case for medium-temperature heating applications and retrofit applications) due to internal refrigerant leakage.