Document Type

Theses, Ph.D

Rights

Available under a Creative Commons Attribution Non-Commercial Share Alike 4.0 International Licence

Publication Details

Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Technological University Dublin, March 2013.

Abstract

absorber and an asymmetric compound parabolic concentrator was applied to increase the intensity of solar radiation incident on the perforated absorber. A 2D ray tracing model quantified optical efficiency at different incident angles within 27o to 89o incident angles. The beam efficiency was found to vary between 72% and 79% and diffuse efficiency was found to vary between 48.2% and 65%. The average thermal efficiency was found to be approximately 55%-65% with average radiation above 400 W/m2 for flow rates in the range of 0.03 kg/s/m2 to 0.09 kg/s/m2. Experimental results at air flow rates of 0.03 kg/s/m2 and 0.09 kg/s/m2 showed temperature rise of 38oC and 19.6oC respectively at a solar radiation intensity of 1,000 W/m2. A comparison with a commercially available Unglazed Transpired Collector (UTC) showed that at an air flow rate of 0.03 kg/s/m2 and solar radiation intensity of 1,000 W/m2 the air temperature rises were 21oC for the UTC and 38oC for the new system. At an intensity of 500 W/m2, the air temperature rise was 12oC for the UTC and 19oC with the new system. Without a glazing cover and tertiary section, reverse flow effects were found to dominate the new system’s thermal performance. This problem was resolved by incorporating a 50 mm optically optimised tertiary section that acts as a heat trap. Regular maintenance was found to be necessary in unglazed concentrating collectors with exposure of the high reflectance reflector to outdoor conditions which reduce the lifespan of such collectors. Because the average number of reflections at any incidence angle is > 1, reflector reflectance crucially affects the optical efficiency of the collector. i The estimated indicative cost of the new system was €450/m2. The designed stationary system has the operational and economic advantages of no moving components. Incorporating a carbon fabric absorber with inherent perforations reduced overall life cycle cost significantly. As the pressure drop in the new system was found to be 10 Pa for an air flow rate of 0.1 kg/s/m2 between inlet and outlet, the required fan power consumption was very small in comparison to the recovered energy giving operational costs. A techno-economic analysis of the new system was carried out for a domestic dwelling considering space and water heating demand. The annual CO2 emission reduced by the new system was calculated as 280 kg/m2 against an electric heater, 112 kg/m2 compared to a gas boiler and 147 kg/m2 against an oil boiler which makes it an attractive air heating system for the residential sector. Considering 8% interest rate the Benefit Cost Ratio (BCR) of the new system was found 1 in year 9 of a 20 year lifespan.

DOI

https://doi.org/10.21427/D7NK67

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