Directionally selective shading control in maritime sub-tropical and temperate climates: Life cycle energy implications for office buildings
Introduction
Occupants of office buildings depend on the careful consideration of solar penetration, provision of views to the outside and access to daylight in design of fenestration systems. For several decades the design trend in Europe and America has been towards highly-glazed facades [1]. Equator facing and western facades are particularly vulnerable to overheating causing occupant thermal discomfort as well as non-uniform daylight distribution. A sensible shading strategy can assist in reducing the energy costs associated with solar gains; however, additional shading devices have their own embodied energy demands that contribute to a building’s life cycle energy demand. Because shading also has a direct relationship to heating and cooling requirements for a building, if the shading can be controlled in a way that reduces the requirement for heating and cooling, energy reductions can also be translated to other components of the building which are sized to distribute heating and cooling. Examining the interaction between shading and the equipment for heating and cooling an office building can assist in selecting systems which use less energy over the building life cycle.
The aim of this study was to calculate and analyse the life cycle energy demands of an external directionally selective shading control which responds to real-time weather conditions in multiple locations. The contribution that external directionally selective shading control can make to reducing the HVAC systems’ sizing and hence embodied energy has also been considered.
Section snippets
Directionally selective shading of office buildings
The energy consumed by a newly installed HVAC system differs according to how directionally selective shading is operated and positioned relative to the glazing. Venetian blinds are one type of shading that have the potential to redirect sunlight to both improve the uniformity of daylight distribution within a space while at the same time reducing potential sources of glare from the sky or directly from the sun. Venetians perform a number of functions that affect the operation of office
Approach for determining blind slat tilts
This section describes the approach used to determine the slat tilt for the shading scenarios. The base case was to be consistent with a scenario in which occupants who are compelled to draw a blind down to control solar radiation will then leave them down for periods in which conditions are appropriate for daylighting, bringing about an unnecessary dependence on artificial lighting. Such a scenario follows reports of this being a common behavior in offices. One behavioural study by the BRE in
Comparing the life cycle energy performance of shading scenarios
The energy demands associated with maintaining thermal and visual comfort within an office building occur at various stages of a building’s life. A full replacement of major HVAC components, such as the chiller, only occurs on average once every 25 years [31]. This duration of 25 years was selected as the timeframe over which to perform the life cycle energy analysis. This study focuses on the effect of external venetian shading on the operational energy requirements (for artificial lighting,
Peak load and operational energy
This section presents and discusses the results of the life cycle energy analysis of the two shading scenarios. Table 2 shows the difference in sizing of the chilled beams between Melbourne and Brisbane and isolates beam sizes for the northern and eastern perimeter zones of the office space which were the most highly glazed zones bringing about the need for a greater surface area of chilled beams. Flow rates were restricted to no greater than an air supply rate of 14.3 l/s/m at a supply air
Conclusions
This study demonstrates that for the case study building analysed, the combination of external venetians and the adjustment of slat tilt according to sun position and sky condition delivered substantial energy savings when compared to a static overhang and static internal venetian blind base case. In comparison to static shading systems, which are designed for maximum heat gain reductions for a specific day of the year, the ability to make adjustments to slat tilts with the use of external
Acknowledgements
The authors wish to acknowledge the contribution made to reviewing and improving this work by Dr Eckhart Hertzsch, Dr Eddy Rusly, Adrian Rowe and the anonymous reviewers.
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