Passive solar
Over 25% of UK primary energy goes towards heating buildings, more than for any other purpose. Passive solar design is an approach to building design which uses solar energy to provide some of the space heating and lighting of buildings and incorporates natural ventilation systems. A passive solar house provides cooling and heating to keep the building comfortable without the use (or minimal use) of mechanical equipment. The main benefits include a lower than conventional energy demand resulting in lower running and maintenance costs, with a corresponding lower carbon footprint.
Passive solar design is principally about maximizing solar heat gain in winter and minimizing it in summer. Some of the key design techniques used are:
- Orientating the building with its long axis running east/west
- Orientating and sizing glazing to optimize winter heat gain and minimize summer heat gain (sun tempering)
- Using south-facing overhangs to shade windows in summer and allow solar gain in winter
- Adding thermal mass in walls or floors for heat storage, such as concrete and masonry
- Using natural ventilation to reduce or eliminate cooling needs
- Using daylight to reduce the need for artificial lighting
Passive solar design can be best applied in new buildings, where the orientation of the building, the size and position of the glazed areas, the density of buildings within an area, and materials used for the remainder of the structure are designed to maximise free solar gains. Designing a property to maximise free solar gain need not add to the price of construction.
Passive solar measures can be applied to existing buildings to good effect. However, energy efficiency measures may well yield better results within a shorter payback period. Where passive solar measures are incorporated, these should be accompanied by energy efficiency measures.
Although it is relatively easy to orientate a single home to make best use of passive solar gains, it is also possible to achieve the same effect with larger developments of houses, without having to rely on homes in straight lines. This was first demonstrated on the Pennyland estate in Milton Keynes in 1983, where 177 highly insulated homes were arranged so that all but 9 of them were oriented to S, SE or SW. 132 of the homes were South facing, yet the roads (shown in brown on the attached plan) were free flowing rather than arranged on a rigid grid.
The retro fitting of conservatories, atria or greenhouses can be expensive and cannot be justified on the grounds of energy efficiency alone. However, a well designed conservatory can provide an extra unheated living space which also provides significant free solar gains. It should be borne in mind, however, that the positive energy gains of a conservatory are lost if the space is heated like the rest of the building.
A conservatory could save up to 20% of annual heating bills although this is strongly dependant on the size of the house, siting, design and materials used. A well designed conservatory acts as extra insulation for the house, preheats the ventilation air and provides direct solar heating to the intervening wall, which is convected into the house.
Sun tubes/pipes and fibre optics are also technologies which can be retrofitted into existing buildings to bring in more light.
