Low Energy House Design Principles: Passive Design

 

‘Passive design’ is a design principle used to create energy efficiency in a building, reducing its ecological footprint. Passive homes are specifically designed to take advantage of the climate and maintain a comfortable temperature range in the home, resulting in ultra-low energy usage. 

According to the Australian Government, ‘Passive design reduces or eliminates the need for auxiliary heating or cooling, which accounts for about 40% (or much more in some climates) of energy use in the average Australian home.’ This standard is not just confined to residential properties though. Office buildings, schools, kindergartens and supermarkets have also been constructed using passive design.

The principles of good passive design (that suits your climate) are important to pay attention to as these design standards will effectively lock in thermal comfort, low energy bills and reduced greenhouse gas emissions for the life span of your home.

Here are a number of strategies that contribute to good passive design:

The Building Envelope

A building envelope describes how the combination of the roof, walls, windows and floors of a house help to isolate the atmosphere inside the building from the atmosphere outside. If you want to control heat gain during hotter months and heat loss in the cooler months, then a tight building envelope is very important. You will also likely need some form of mechanical ventilation in tight enveloped buildings to control your home’s air quality.

Passive Solar Heating

Good passive solar heating design captures and stores available heat from the sun. Passive heating keeps out the unwanted summer sun and lets in the winter sun, whilst still ensuring the building envelope lets any built up heat escape during summer and keeping the heat inside during winter. This is also the least expensive way to heat your home. All passive design are important when thinking about the design of a house that benefits from passive solar heating.

Passive Cooling

Most Australian climates require both passive heating and cooling. Using elements such as air movement, evaporative cooling and thermal mass are all techniques used to cool the house and create thermal comfort for the people inside.  Good wind ventilation or stack ventilation strategies and ensuring that windows are shaded are very effective measures for passive cooling. Like passive heating, passive cooling is the least expensive way to cool you home and will work well when applied to a range of different climate zones in Australia.

Orientation

The orientation of your home refers to the way it’s facing and its placement on your lot. You can do a lot to achieve an efficient home design based on the orientation of your home and by taking advantage of climatic features such as the sun and cool breezes. For instance, where the climate is generally warmer and humid in the top parts of Australia, direct sun exposure should be avoided and longer walls should face south. In the cooler parts of Australia, walls should face north to provide more heat during the winter months. The need for assisted heating and cooling is reduced due to good orientation, making your home more comfortable to live in and cheaper to run.

Shading

Did you know direct sun can generate the same heat as a single bar radiator over each square metre of a surface? By effectively controlling how heat is absorbed by your house and strategically  keeping heat off parts of your house where necessary, you can improve comfort and save energy. Using things like carefully designed eaves, awnings, shuttings, pergolas and plantings can block up to 90% of this heat. Unprotected glass is often the greatest source of heat gain in a house, so shading of glass is critical. However, poorly designed fixed shading can block winter sun. Another great way to maximise thermal comfort is to plant some deciduous trees that will lose their leaves and allow the sun through during winter.

Insulation

How well your building envelope performs can be based on how effectively your home is insulated. To ensure heat stays where you need it to, your walls, ceilings and floors need to be properly insulated. Insultation can also help you control how heat is dissipated from the thermal mass in your house. However, insulation must be installed correctly for it to work as intended.

Thermal Mass

Thermal mass is the ability of a material to absorb and store heat energy. It is important to understand thermal mass of the building materials used in your home and the impact they have on the way heat is absorbed, stored, released and distributed. Materials such as brick, concrete and tiles are excellent at absorbing heat because they are more ‘dense’ and are considered to have high thermal mass. A lot of heat energy is needed to change the temperature of high density materials. Lightweight materials such as timber have lower thermal mass. Using materials with high thermal mass throughout your home can save you a lot on energy bills. However, poor use of thermal mass can worsen already extreme climates by radiating heat on a hot summer night or absorbing all the heat on a winter night. For effective use of thermal mass, good passive design techniques must be combined and be appropriate for the climate.

Sealing Your Home

Sealing your home against air leaks can help winter heat loss in buildings and can contribute to loss of cool air in climates where the air conditioner may be used. The more extreme your climate is, the more you’ll benefit from sealing your home. This is also one of the most simple upgrades you can choose for your home to increase thermal comfort and energy bills. However, sealing your home and increasing insulation levels can create condensation and indoor air quality problems in your home, so have a good understanding of your climate zone and how you can limit its impact.

Glazing

Although glazed windows and doors bring in light and fresh air, they can cause your home to lose heat in winter and gain unwanted heat in summer. According the Australian Government (environment.gov.au), up to 40% of heat energy can be lost and up to 87% of its heat gained through glazing. Based on the orientation of your home and the climate zone you live in, choosing the right glazing system can help rectify these thermal performance issues.