Abstract

In a net zero energy building (nZEB), the energy demand from the operation of the building is met by renewable energy generated on site. Buildings require energy both in the form of heat and electricity, and solar energy utilization is important in order to reach a net zero energy balance. In projects with ambitious energy targets or limited available areas for local energy generation, solar thermal and photovoltaic (PV) installations will eventually compete for space on roofs and facades. Hybrid photovoltaic–thermal (PV/T) modules, in which heat and electricity is generated simultaneously, are therefore an interesting technology for building applications, which can potentially lead to a higher total efficiency and lower use of space. This paper describes a comparative simulation study of different solar energy solutions for a Norwegian residential building concept aiming for a net zero energy balance. Separate PV and solar thermal systems are compared to PV/T systems, and the resulting energy balances analyzed. The results show that the building with only high-efficiency PV modules comes closest to reaching a zero energy balance, but that the results depend greatly on the nZEB definition, the boundary conditions and the design of the building’s energy system.

Window panes, glass structures and electrochromic windows in buildings may be characterized by a number of solar radiation glazing factors, i.e. ultraviolet solar transmittance, visible solar transmittance, solar transmittance, solar material protection factor, solar skin protection factor, external visible solar reflectance, internal visible solar reflectance, solar reflectance, solar absorbance, emissivity, solar factor and colour rendering factor. Comparison of these solar quantities for different glass fabrications enables one to evaluate and thus select the most appropriate glass material or system for the specific buildings and applications. Measurements and calculations were carried out on various glass materials, including three electrochromic window devices, and several two-layer and three-layer window pane configurations.

Abstract

Modern office buildings often have large glazed areas. Incident solar radiation can lead to large cooling demands during hot periods although the solar radiation can help reduce heating demands during cool periods.
Previous studies have shown that large parts of the net energy demand of an office building is related to window heat loss and cooling demands induced by solar irradiance. In this article, the authors found that, even in what traditionally has been considered to be a heating-dominated climate, cooling demands dominate the net energy demand of an office building. Solar shading systems are vital to reduce the cooling demand of an office building.
Introducing shading systems might contribute to higher heating demands as well as higher demands for artificial lighting but at the same time it might be necessary in order to reduce glare issues.
Simulations of a number of shading strategies have been performed for south- and north-facing office cubicles with varying floor areas, window sizes and window parameters. Energy demands for heating, cooling, lighting and ventilation fans have been assessed. The simulations show that the choice of shading strategy can have an impact on the energy demand of the offices. Depending on strategy, the energy demand can either increase or decrease compared to an unshaded one- or two-person office cubicle.
In addition, the shading systems can contribute toward a lowered thermal transmittance value (U-value) of the window by functioning as an additional layer in the glazing unit when closed. Potential improvements of U-values have been studied in combination with the shading system’s effect on solar heat gains and daylight levels. Experimental investigations of in-between the panes solar shading system effects on window U-values are currently being carried out at the Research Centre on Zero Emission Buildings (www.ZEB.no).
It was found that automatically controlled shading systems can reduce the energy demands of south-facing, small office cubicles, but that they should not be installed without a thorough case-by-case investigation as increased energy demands were found if an improper shading strategy was chosen. Upgrading to four-pane glazing will, however, always have a beneficial impact on the energy demand compared to two- and three-pane glazing.