aalto1 untyped-item.component.html
Experimental assessment of the thermal performance of two different photovoltaic/thermal collectors
Loading...
URL
Journal Title
Journal ISSN
Volume Title
School of Engineering |
Master's thesis
Unless otherwise stated, all rights belong to the author. You may download, display and print this publication for Your own personal use. Commercial use is prohibited.
Authors
Date
Department
Major/Subject
Mcode
Language
en
Pages
96
Series
Abstract
In Nordic countries, interest is growing in the use of photovoltaic/thermal (PVT) collectors as sources for borehole regeneration in ground source heat pump systems. A PVT collector is a combination of a photovoltaic (PV) panel and a solar thermal collector (STC), allowing for the simultaneous generation of electricity and heat as the STC cools the PV. By setting the temperature of the working fluid under the ambient temperature, heat gains can also be observed at times of no irradiance, improving the thermal performance (TP) of the system. To optimise heat exchange between the working fluid and the ambient, fins are added to the back of the PVT absorber to increase the heat exchange surface area.
This study compares the TP of two prototype box-channel PVT collectors, assessing the impact of fins in low temperature operating conditions. The two PVT collectors are tested simultaneously at an outdoor testing facility at KTH Royal Institute of Technology in Stockholm, Sweden. The outdoor environment allows for the analysis of a variety of weather conditions, such as solar irradiance, wind speed and wind direction. The impact of different working fluid flow rates and roof installations on the TP are also evaluated. Quantifying the impacts of these different conditions will show whether an increase in TP due to the fins justifies their additional cost. To obtain thermal performance coefficients, the equation for modelled thermal power of a STC presented in ISO 9806:2017 is simplified. These coefficients serve as key performance indicators to compare the TP of the two PVTs under the conditions studied.
The results show that increasing irradiance and wind speeds improve the TP of the PVTs. However, it was observed that the same increase in either irradiance or wind speed does not result in the same improvement in specific thermal power under all operating conditions. An optimum flow rate of 0.021 kg/s/m2 was identified. Additionally, it was found that fins do improve the TP of the PVT collectors. Improvements in specific thermal power, when compared to the PVT with no fins, as larger as 16% were observed, at a flow rate of 0.028 kg/s/m2. When the airflow around the PVTs was restricted, through the addition of roof installations, the improvement in specific thermal power dropped to 6 or 7% depending on the roof installation.