An assessment of the thermal performance of spaces fitted with different types of glazing systems in a central Mediterranean climate

Abstract

Driven by the challenges of energy performance of buildings in Malta coupled with the ever increasing demand for buildings featuring fully glazed facades, this dissertation investigates the thermal performance of different forms of glazing assemblies in the context of a southern Mediterranean climate during the cooling season. The dissertation first provides an understanding of the characteristics of the Mediterranean climate, followed by an insight into the properties of glass and design parameters in relation to the thermal performance. The study outlines different solar control technologies and distinguishes between the performance of each. Inappropriately considering these parameters may result In overheating In summer and heat loss in winter. The relevance of this topic in Malta is evident since the number of predominantly glazed facades is set lo substantially increase with the forthcoming major projects and high-rise buildings. The most important design and glass thermal performance parameters include the U-value and the g-value, with the latter still being omitted from even the latest revision of local legislation on the energy performance of buildings. The study delves into a number of testing-out field experimental setups that have been in place overseas and establishes a testing setup suitable for the carrying of field test experiments on the thermal performance of spaces fitted with different types of glazing assemblies. The dissertation adopts the comparative approach, whereby the thermal performance of a space fitted with four different types of glazing setups are compared with that of a reference setup along the four cardinal orientations. The analysis of the results of the temperature values with the test cells concludes that whereas double glazing units with a solar control coating perform best on the southern orientation due to the substantial incidence of short wave infrared radiation, a double glazed unit having a spectrally selective, low-emissivity coating performs better along the three other cardinal orientations. The study confirms that a low emissivity coating reduces long wave infra-red radiation from sources external to a space, hence being attentive at reducing heat gain even in a cooling-dominated Mediterranean climate. The study also confirms that the application of a solar control film over a single glazed unit only marginally improves the thermal performance of a space facing the south, east and west orientations. The research also confirms that uncoated double glazed units, currently being the local industry standard of glazing in most buildings, are not only the least effective in reducing solar heat gain, but effectively contribute to increased cooling loads due to their high g-value and the consequential containment of warm air within a space. From this study it was concluded that the g-value remains the most important parameter in thermal performance as it governs the solar gains, an element of significant importance within the local climate. This parameter has nonetheless been omitted again in the latest revision of the Technical Document Guide F (2016). The U-value proved to be a very complex parameter as there is a limit at which further reduction in its value, not only does not result in better performance but essentially leads to higher cooling loads. l he above conclusion confirms therefore that Government incentives intended to promote the installation of "double glazing" within buildings in a drive to achieve more energy efficient buildings may prove to be counterproductive. Future architectural trends will invariably result in the development of buildings with greater window-to-wall ratios, as we go high-rise, high-tech, with fully glazed facades. Considering today's expectations of thermal comfort, the use of active environmental control systems such as air conditioning is unlikely to change, especially when the façade is fixed or with limited openable area. The industry needs to focus on having buildings that are cheaper to run, albeit at a higher initial capital cost, and when external shading is not included on the façade, the use of the appropriate glazing is paramount In achieving lower running costs.