Many factors play a crucial role in the efficiency of a building in order to achieve a good thermal performance. We may perfect a building’s envelope, but if the building form is not intelligently designed it may not be a building that performs well. At Energy Rating Perth, our energy assessors urge our clients to include energy efficiency concepts early in their design process. There are many factors to consider when it comes to an energy efficient building but the conscious effort should start when designing the building form and a good thermal performance can be achieved.
Mainly, an intelligent building form is a balance between the floor area, shape of the plan, height of the building and surface area to volume ratio. The only way to determine the best outcome is by modelling different geometries of buildings into energy assessing software with variables like orientation and insulation considered to achieve the optimum outcome. Results from such modelling give a general idea for optimum building form but the true balance is dependent on complex factors like the prevailing climate and/or micro climate of a site and the eventual method of achieving thermal comfort in the inside of a building i.e. active or passive climatisation. At Energy Rating Perth, we are big believers of passive solar climatisation as it reduces the heating and cooling loads of a building significantly giving returns in the longer run.
Generally speaking, a building with a compact floor area and a low surface area to volume ratio takes more time to be effected by the outdoor temperature variations. If the building uses an active climatisation design, then a compact building will work best as both the heating and cooling loads will be lower. However, for a passive solar design, a higher surface area to volume ratio is preferred, as you want to maximise the solar heat gain in the winters for heating. For hotter climates, you want to achieve natural ventilation within the building, which is why elongated forms that increase the distance between entry and exit points of air is optimum. Similarly, the building height plays a role, the higher the ceilings are the more heat rises due to the stack effect and the colder air replaces the risen warm air hence causing a natural ventilation as well. However, this is not recommended if mechanical heating/cooling is used as there is a greater volume it will require more energy to cool/heat. Our energy assessors at Energy Rating Perth would like to inform our readers that the more compact and taller the building, the better it will perform thermally (to a certain extent as height also increases heat exchange i.e. heat losses/gains). In case of tall apartment building, when high buildings are bunched together, they effect the microclimate of the urban streetscape and the shading may reduce the overall heat gain of the area during the day. Furthermore, the shape of the plan and volume of the form also play a vital role. Wing walls in H and U shaped plans can provide self-shading. It can also benefit in producing air currents particularly if the courtyard is East/West facing. Such building forms see a slight drop in the heating loads but a significant drop in the cooling load of the building.
The energy assessors at Energy Rating Perth often feel that when a complete building design is given to us for 6 Star energy rating assessment, we feel the NCC energy efficiency requirements are enforced rather than dove-tailed into the design. As a result of this, there are design changes and retrofit solutions that have to be included into the building which results in an expensive exercise for the designer as well as the home-owner.