Arya, Farid, Moss, Roger W., Hyde, Trevor, Shire, G. S. F., Henshall, Paul and Eames, Philip (2018) Vacuum enclosures for solar thermal panels part 1 : fabrication and hot-box testing. Solar Energy, 174 . pp. 1212-1223. doi:10.1016/j.solener.2018.10.064

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Abstract

Non-concentrating solar thermal collectors are generally available in two forms, flat plate or evacuated tube. Recently a third configuration, the evacuated flat plate, has attracted interest due to enhanced performance and aesthetic characteristics. By isolating a solar absorber in a vacuum space (<1 Pa) heat loss from the absorber can be minimized resulting in improved efficiency. In addition the improved thermal insulation performance of evacuated panels over conventional glazing systems makes them attractive solutions for integration into energy efficient building facades.

This two part paper describes the design, construction techniques and thermal performance of two vacuum enclosures, fabricated at Ulster University, as prototype components for evacuated flat solar collectors. The first enclosure consists of two glass panes sealed to an edge spacer and separated by an array of support pillars on a regular square grid to form a narrow evacuated space. The second enclosure incorporates an uncooled copper sheet to represent a solar thermal absorber. The enclosures were tested at three conditions i.e. with an internal pressure of high vacuum (0.0021 Pa), low vacuum (8.4 Pa) and no vacuum (atmospheric pressure).

Part 1 of this paper describes the fabrication process for the vacuum enclosures and the measurement of their thermal insulation properties using a hot box calorimeter. The theory of heat transfer through an enclosure with support pillars is discussed; experimental results are compared with mathematical models predictions. A fabrication methodology has been successfully established and a U-value of 1.35 W/m2K for an enclosure with an internal pressure of 0.0021 Pa has been demonstrated. The experimental results are in good agreement with the predictions.

Part 2 of this paper describes solar simulator testing of the enclosure containing a copper plate. The highest stagnation temperature (121.8°C) was reached under steady-state conditions in the high vacuum test and was in good agreement with predictions. The transient plate and glass surface temperatures were measured and found to be consistent with the predicted curves.

Item Type:	Journal Article
Subjects:	T Technology > TJ Mechanical engineering and machinery
Divisions:	Faculty of Science > Engineering
Library of Congress Subject Headings (LCSH):	Solar thermal energy, Solar collectors -- Testing, Vacuum technology, Calorimetry, Plates (Engineering) -- Thermal properties
Journal or Publication Title:	Solar Energy
Publisher:	Elsevier Ltd.
ISSN:	0038-092X
Official Date:	1 November 2018
Dates:	Date Event 1 November 2018 Published 28 October 2018 Available 25 September 2018 Accepted
Date of first compliant deposit:	29 November 2018
Volume:	174
Page Range:	pp. 1212-1223
DOI:	10.1016/j.solener.2018.10.064
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access
RIOXX Funder/Project Grant:	Project/Grant ID RIOXX Funder Name Funder ID EP/K009915/1 [EPSRC] Engineering and Physical Sciences Research Council http://dx.doi.org/10.13039/501100000266 EP/K010107/1 [EPSRC] Engineering and Physical Sciences Research Council http://dx.doi.org/10.13039/501100000266 EP/K009230/1 [EPSRC] Engineering and Physical Sciences Research Council http://dx.doi.org/10.13039/501100000266

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