Modelling the thermal performance of complex glazing systems

Mylona, Anastasia 2007. Modelling the thermal performance of complex glazing systems. PhD Thesis, Cardiff University.

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Abstract

The aim of this research is to investigate the thermal performance of various shaded glazing options through the use of thermal modelling in order to reduce solar gains and as a result cooling loads in buildings. The review of early and recent research on the study of the radiation transport through glazing systems with slat-type blinds, and the more recent development of prediction tools, identified the elements affecting the thermal performance of various glazing systems, as well as the current needs in the calculation of the performance of such complex systems. The review demonstrated that no established and validated methodology is offering the flexibility that the study of the thermal performance of complex glazing systems with integrated slat-type shading is requiring. In order to serve the objectives of this work two existing simulation packages were selected and modified in order to better represent the properties of the various glazing systems and to examine their performance in a more holistic approach. The review of the calculation of the total solar transmittance, g-value, currently used as a representation of the performance of the various glazing systems, revealed that the variables that influence the g-value and so the thermal performance of a glazing system are the incident solar radiation, the optical and thermal properties of the glazing system and its components, and the temperature difference between internal and external environment, while it excludes any heat losses through the system. Introduced was a steady-state G-value to describe the thermal performance of different glazing systems under steady-state conditions and a dynamically calculated gd value under real climate conditions. The selected prediction tools were validated by comparing results against a validated reference model and measurements under real climate conditions. Results showed that although there is scope for further improvements in the calculation of the transmission characteristics of slat-type blind configurations, the prediction tools were able to distinguish between basic design alternatives, in the choice of similar shaded glazing options, in a sufficient to many applications in the design industry level of accuracy. The tools were applied to a variety of shaded glazing systems, under both steady-state and real climate conditions for three locations. The results showed that lower g-values could be achieved by higher slat angles (e.g. 70) and light colour blind material, while externally positioned blinds seem to be performing thermally better. Examples demonstrated that the above trends could be reversed if the performance of the various glazing systems is not carefully examined. The g-value also showed a high dependency on the angle of incidence, with higher values presented at angles of incident closer to normal and lower values at higher angles of incident. The above dependency of the g-value on solar angles revealed also the gd value's seasonal and latitude dependency. Comparisons undertaken between the steady-state G and the dynamically calculated gd, and also between predicted cooling loads, for keeping desirable internal temperatures in an office space, and both G and gd, highlighted the potential of the steady-state G to misinform the designer on the choice of glazing system, while the dynamically calculated gd is a more reliable indicator of the thermal performance of the various glazing systems, in practice. Examined was also the influence of various glazing systems on the performance of an energy efficient cooling system (chilled ceiling) in keeping desirable internal temperatures and preventing condensation levels, in a case study application. The performance of the chilled ceiling cooling system showed to be affected by the choice of glazing/blind option, but greater, in terms of both condensation and temperature control, was the effect of infiltration rates.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Architecture
Subjects:	T Technology > TD Environmental technology. Sanitary engineering
ISBN:	9781303181597
Date of First Compliant Deposit:	30 March 2016
Last Modified:	12 Feb 2016 23:14
URI:	https://orca.cardiff.ac.uk/id/eprint/55638

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