The windows to the north and south elevations have a number of features that assist in the heating and cooling processes in the building. Simply, the treatment is designed to provide a barrier to 'heat gain' into the building in the summer and 'heat loss' from the building in winter.
The following features contribute to this process:
- double-glazing
- timber window frames, which are a low conductor of heat when compared with aluminium, reducing the 'heat bridge' effect
- external sunshade from balconies (from the floor above) and from fabric shades above the door to each balcony
- chilled beams over the window cooling the air and creating a protective curtain of falling cold air across the window when heat gain is an issue
- underfloor hydronic heating grilles, located adjacent to the window, providing a protective curtain of rising warm air when heat loss is an issue.
Timber window frames
All of the window frames to the north, south and east elevations are timber, rather than aluminium. When resourced correctly timber is a more sustainable material than aluminium and also enables the window system to contribute to the thermal performance of the building. Timber window frames are a low conductor of heat when compared with aluminium, and therefore reduce the ‘heat bridge’ effect that occurs with metal frames. Other features of the timber frames include:
- timber was chosen on the basis of being a product with low embodied energy and well understood performance and maintenance regimes
- finger-jointed construction was used for less waste
- the windows were designed for repair and disassembly (screw construction) and have an anticipated life-span of over 100 years
- laminated fabrication was used to ensure a well-sealed and air-tight system.
Upper and lower windows and use of blinds
Each window has an upper and lower section, each with a separate blind, which has the following benefits:
- the use of blinds can be optimised. The upper section is well protected from the sun by the balcony above and blinds are only needed in the winter when the sun is very low in the sky. The upper blind also is raised rather than lowered and can therefore be set in an optimum position
- the lower blind is required for sun protection more often than the upper blind. In this instance the use of the blind is optimised by having only a partial blind, 900mm high. The blind can therefore be set at the optimum level up the window to protect from the direct rays of the sun, without unduly reducing the amount of natural light entering the building.
Staff can control the use of the blinds to optimise the protection from the sun’s rays and the amount of natural light entering the building at any time.
Glare control
Glare is caused by sharp contrasts and is often treated by brightly lighting inner walls or using blinds. Both of these methods waste energy. CH2 reduces glare while using energy by framing external views with leaves on the northern balconies and on the south with vertical planters.
Additionally, CH2’s window treatment incorporates features to control glare:
- Use of reveals: the air supply and exhaust ducts are located either side of the windows on the south (supply air) and the north (exhaust air) facades. These ducts give the external wall enough thickness to form reveals to the windows. The window reveal is a splayed framing to the window which mitigates the contrast between the very bright outside light and the internal relatively dark wall. Glare is caused by sharp contrasts and the half light on the reveal helps to reduce glare. This is an old device used particularly in Georgian interior architecture.
- External plants: each of the windows on the northern façade has a balcony with trellised planting on each side, running the full height of the building. These plants provide both lateral protection from the sun’s direct rays and help control glare by diffusing light.
- Internal plants: plants were successfully trialled in the existing Council House for glare control and have been installed in moveable internal planters on each side of the most windows on the south elevation. The south-facing windows can be subject to glare reflected from buildings across the street.