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Simulator testing of evacuated flat plate solar collectors for industrial heat and building integration
journal contribution
posted on 2018-04-25, 09:36 authored by Roger Moss, Paul Henshall, Farid Arya, Stan Shire, Philip EamesPhilip Eames, Trevor HydeThe concept of an evacuated flat plate collector was proposed over 40 years ago but, despite its professed advantages, very few manufacturers have developed commercial versions. This paper demonstrates the reduction in heat loss coefficient and increase in efficiency resulting from evacuating a flat plate collector: it is hoped that these results will stimulate interest in the concept. Evacuated tubes are now mass-produced in large numbers; evacuated flat plate collectors could in principle replace these tubes if the technical difficulties in creating extended metal-glass seals can be overcome. The experimental experiences described here should indicate targets for future research. Two different designs of evacuated flat plate solar thermal collector, each with a 0.5 × 0.5 m flooded panel black chrome plated absorber, were tested under a solar simulator. The cover glasses were supported by an array of 6 mm diameter pillars. Inlet and outlet temperatures were monitored via PT100 RTDs and glass temperatures were measured using thermocouples. Inlet temperature was controlled by a fluid circulator connected to a header tank with a Coriolis mass flow meter to measure fluid flow rate. Testing was conducted indoors with and without the use of a fan to cool the top cover glass. The test conditions spanned the range 200 < G < 1000 W/m 2 , 0⩽T M ⩽52°C. Evacuating the enclosure reduced the measured heat loss coefficient by 3.7 W/m 2 K: this was a close match to predictions and corresponds to an increase in aperture efficiency from 0.3 to 0.6 at T M /G=0.06m 2 K/W. The poor efficiency under non-evacuated conditions was due to the black chrome absorber coating being less selective than commercial panel coatings. The solder seals were developed from experience with vacuum glazing but the increased gap led to reliability issues. A vacuum pump maintained the enclosures under a high vacuum ( < 0.1 Pa) during testing. The enclosure based on a thin rear metal tray proved to be more effectively sealed than the more rigid enclosure with glass on both sides: the latter developed leaks as the front to rear temperature difference increased. The biggest challenge in the manufacture of evacuated flat plate collectors is to ensure a long-term hermetic seal such that no pumping is required.
Funding
The authors are grateful to the Engineering and Physical Sciences Research Council (EPSRC) for funding this work as part of a collaborative programme between Warwick, Loughborough and Ulster universities, reference EP/K009915/1, EP/K010107/1 and EP/K009230/1.
History
School
- Mechanical, Electrical and Manufacturing Engineering
Published in
Solar EnergyVolume
164Pages
109 - 118Citation
MOSS, R. ... et al, 2018. Simulator testing of evacuated flat plate solar collectors for industrial heat and building integration. Solar Energy, 164, pp.109-118.Publisher
Elsevier © The AuthorsVersion
- VoR (Version of Record)
Publisher statement
This work is made available according to the conditions of the Creative Commons Attribution 4.0 International (CC BY 4.0) licence. Full details of this licence are available at: http://creativecommons.org/licenses/ by/4.0/Publication date
2018Notes
This is an Open Access Article. It is published by Elsevier under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/ISSN
0038-092XPublisher version
Language
- en