CONSCIOUS HOMES

Designing for thermal efficiency

Thermal efficiency often called “Passive Solar Design” is all about your home being an efficient shelter from the elements, working with the natural environment. For instance in Melbourne it is possible to design and build a home that needs no cooling or heating. The correct combination of orientation, insulation, glass and internal thermal mass will give you a home that is comfortable all year round and a pleasure to live in. A well designed passive solar home will have a natural temperature range of 18 to 26 degrees without heating or cooling. This range is well within human comfort levels, when we wear appropriate clothing for the seasons. Such a home would be rated better than 6 Stars on the SEAV home energy rating system.

An incredible amount of energy is used all over the world in air-conditioned buildings keeping building temperatures between 20 and 22 degrees Celsius. Often in air-conditioned buildings both the heating and cooling will be activated within the same day! The reason for these huge internal temperature swings is usually bad design.

An important part of passive solar design is the connection with the earth below. Because the temperature of the sub soil is constant all year in winter the soil below a slab is a source of base temperature supplemented by direct solar gain. In summer the soil below the slab becomes a source of coolth, drawing heat into the ground below. Dense products such concrete and masonry, which are not good at insulation, are good for storing heat within an insulated building, creating “thermal mass”. Good internal thermal mass moderates the internal temperature all year round.

Thermal efficiency is a pretty simple principle. Heat travels to the surface or air that is at a lower temperature. The resistivity or R value (insulating ability) of the material between will moderate that flow of heat. Double glazing does that with ambient air temperature. High energy direct sunlight will penetrate through glass (even double glass) and turn to low energy heat inside the building. The more square to the glass the rays are, the more effective the penetration - this is why north facing glazing works for positive heat gain in winter and why west facing glass turns your home into an oven in summer. North facing vertical glass with correctly proportioned eaves will allow full sun penetration in winter and full shade to the glass in summer. Well sealed windows and doors keep the heat inside in winter and outside in summer. Good cross flow ventilation capacity helps to air and cool your home naturally. In winter keep your home well sealed generally and then open windows to ventilate at the warmest time in the afternoon. In summer seal during the day and ventilate in the coolest times at night.