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The rate at which heat is lost depends on many factors, including:
Climate – ie the temperature, humidity, prevailing wind conditions and light levels in a region. Predicted changes in climate (due to increasing carbon dioxide emissions) can be accounted for in the design, construction and operation of new buildings. For existing buildings, it is only possible to reduce the impact of climatic conditions in small ways, such as through the installation of draught stripping, upgrading of insulation levels or the provision of external shading.
Weather – The greater the temperature difference between the inside and outside of a building, the faster the heat will be transferred from the warmer location to the cooler one. Therefore, energy consumption associated with heating will generally increase during winters that are colder than normal.
Exposed locations will usually have higher wind speeds which increase ventilation rates and heat losses in buildings.
Shape, orientation and layout – A building’s shape determines its external surface area. The smaller this is, the less opportunity there is for heat to escape, however, day-lighting and natural ventilation are also reduced.
South facing buildings help ensure maximum daylight enters the space but external shading may be required to prevent overheating and minimise glare. East/West facing buildings may experience variations in solar glare and heat over the course of a day on both sides of the building.
Properties of the building fabric – Different elements (eg windows, doors and walls) have different thermal (heat retaining) properties. The ability of material to retain heat is expressed as its U-value: the lower the U-value, the better the material is at preventing heat loss.
U-value: A measure of the amount of energy (heat measured in Watts) that is transferred through an area (measured in m2) of material when there is a 1°C difference in temperature between inside and out.
The air tightness of a building - The amount of fresh air entering a building (either by controlled ventilation through windows that open and dedicated air vents, or uncontrolled through poorly fitting windows, doors or joins in walls) affects the amount of heat lost. A ‘leaky’ building allows heat to escape through cracks and gaps and reduces staff comfort by allowing cold draughts to enter the space.
Recent changes to building regulations have helped to improve the air tightness of new buildings and the performance of the building fabric itself. Whilst this is mostly beneficial, it could, however, result in overheating problems as internal heat gains from occupants, equipment and lighting build up.
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