Investigation of a novel micro-channel, mini-channel PV/T and thermal modules based solar heat pump systems

Zhou, Jinzhi

Engineering
November 2018

Thesis or dissertation


Rights
© 2018 Jinzhi Zhou. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
Abstract

Regarding the building energy consumption optimisation, there is a developmental trend to replace traditional fossil fuel sourced energy with, rapidly growing, clean renewable energy. The main source of energy consumption is from hot water, cooling and space heating, which is normally provided by electric heater, gas boiler and/or coal boiler. However, these existing systems have their own drawbacks, such as high operating costs (electric heater), being inconvenient to obtain (gas boiler) and causing environmental pollution (coal boiler). Therefore, it is necessary to develop a clear and convenient energy system to replace these traditional ones, i.e., solar energy, biomass energy.

This research aims to investigate two kinds of novel photovoltaic thermal modules (PV/T) based heat pump systems, one with direct-expansion and the other with an indirect-expansion style, to be used for the purpose of space heating, hot water supply and power generation. Compared to existing PV/T modules, the new modules possess novel features that lead to enhanced heat transfer, improved solar efficiency and extended module lifetime. The strength and innovation of PV/T technology in this thesis are as follows: (1) a micro-channel and mini-channel tube is selected as the heat exchanger tube. This special structure improves the heat transfer rate of working fluid inside, enhancing both solar, thermal and electrical efficiencies; (2) compared to existing copper tube heat exchanger, the micro-channel has a much larger contact area, increasing the heat transfer rate; (3) the material of the micro-channel tube and header is aluminum, which has a low cost. These designs were intended to overcome some of the drawbacks and provide experimental data for the development of PV/T technology.

For the solar direct-expansion heat pump system, more than one-month time testing was carried out, and according to the result on a sunny winter day, the average electrical, thermal and overall efficiencies of the micro-channel panels were 13.1%, 56.6% and 69.7% respectively, which were respectively higher by 11.0%, 11.8% and 11.4% than the similar system. The Coefficient of Performance (COP) of the system had a similar variation trend to the solar radiation, with the average COP in the testing day being 4.7.

For the solar indirect-expansion heat pump system, again tested in winter, it was found that the average electrical, thermal and overall efficiencies of the mini-channel PV/T panels were 14.5%, 31.7% and 46.2% respectively, which has 9.0%, 5.8% and 6.2% higher efficiency than the existing similar systems. In addition, the mean thermal efficiency of the mini-channel thermal panels is 49.9%, which is a 5% increase compared to existing collector. The average COP of the heat pump is 4.6 during the working time. In summer, the average electrical efficiency of the PV/T panel was 11.5%, and the average thermal efficiency of the thermal panel was 46.8%. The temperature of water in the tank increased from 23oC to 60oC, therefore this water could be used for various applications.

The annual economic and environmental analysis results, based on the local weather data, indicate that although the two systems have a higher initial cost, they have a much lower operating cost. Based on the weather data of Taiyuan city, the payback time of these direct and indirect expansions systems are 8.7 years and 5.8 years, respectively. Additionally, these direct and indirect expansion systems can, respectively, reduce CO2 emission by around 91.4 t and 109.1 t annually. Based on the weather data of London, the payback time of the two systems are 6.6 years and 3.5 years, while the CO2 emission reduction are 44.8 t and 76.2 t, respectively.

Based on these research results, some amendments are required to improve and promote the systems in the future. These include improving the structure and material of the PV/T panel, reducing manufacturing cost, further optimisation of the system and long-term measurement under real-world conditions. Additionally, seeking policy support is needed from the government to reduce the initial and operating cost.

This research shows that these two solar heat pump systems provide a reasonable alternative to the traditional heating system for space heating in rural house. Most of the existing solar energy systems are small scale and designed for producing hot water, while the large-scale solar energy system for space heating in rural houses is rarely researched. Therefore, the experimental and simulation results on these two systems provides fundamental data for developing and improving large-scale solar energy systems.

Publisher
School of Engineering and Computer Science, The University of Hull
Supervisor
Zhao, Xudong
Sponsor (Organisation)
University of Hull
Qualification level
Doctoral
Qualification name
PhD
Language
English
Extent
11 MB
Identifier
hull:17278
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