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Title: The development of a capacity controlled advanced cycle air source heat pump for domestic retrofit applications
Author: Quinn, Matthew Vincent
Awarding Body: University of Ulster
Current Institution: Ulster University
Date of Award: 2012
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Domestic heating for the majority of the housing stock within the UK and Ireland use a fossil fuel boiler, oil or gas, within a central heating system distributing heat to the living space through hydronic radiators. Current trends show a rise in the price of fossil fuels (through an increasing global demand) which is having a direct impact on the individual and the economy, increasing the price of all commodities through increased transportation costs and increasing the cost of energy (heating and electricity). The increasing costs and the environmental impact associated with the burning of fossil fuels are therefore driving the need for more renewable/more energy efficient means of supplying heat. Utilising a reversed Rankine cycle heat pump is a proven, well established method of providing high energy efficient heat transfer from a low temperature source to a high temperature sink through the manipulation of a working fluid about a pressure differential. The temperature and pressure differential across the compressor, have a large impact on the system performance. The aim of this work was to develop an air to water heat pump as an alternative to the fossil fuel boiler whilst using the existing heat distribution system and comparable water temperatures. This system could therefore be retrofitted into the majority of the existing housing stock providing an affordable energy efficient solution to the majority of homeowners whilst reducing national greenhouse gas emissions. An advanced cycle Economised Vapour Injection heat pump was utilised to improve the system efficiency when compared with a conventional system for the high temperature and pressure lift retrofit application. The COP was improved for the EVI cycle across the range of conditions tested. Between the minimum and maximum pressure differentials, the EVI cycle provided a performance improvement of between 1% and 27%. An off-the-shelf inverter was coupled to the BVI compressor to provide capacity control. The inverter-motor combination was evaluated detailing the maximum and minimum frequency limits. The heat pump performance was then evaluated between these limits comparing both the EVI and conventional cycles. As the frequency/compressor RPM was reduced, the improvement for the EVI cycle with respect to the conventional increased. The transient characteristics and the control strategies of the systems were evaluated showing large reductions of the start-up time-frame and power consumption when using the EV} cycle at increased speeds. When compare:d with the conventional cycle at 50Hz (nominal frequency), the maximum energy and time sav ings were 45% and 64%, respectively. This work concludes that th is set-up, using a nominal single speed compressor with an off-theshelf inverter is not ideal and creates reliability issues; however, it also highlights the potential benefits achievable when utilising capacity control which can be optimised by maximising the load matching range with a dedicated variable speed compressor.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available