An energy efficient house is simply one that uses less energy than an average home. This is good for the environment, reduces your bills and makes your home more comfortable all year round. An energy efficient house design can be broken down in three main categories: Passive Design, Energy & Water. In this article I’ll briefly explain some of the key principles I use to design an energy efficient home.
Passive House Design
Passive design is a design that considers the climate and site conditions specific to a home or building. Following good passive design principles is an important part of creating an energy efficient house. Energy and Water efficient design is also important but can easily be upgrade or changed over time. Many principles of passive design need to be applied at the very start of planning a new home, renovation or extension and are difficult to change later.
Solar Passive Design and Orientation
A solar passive design considers the direction of the sun at different times of the day and year. This can make a big difference to your heating and cooling costs. A solar passive design uses the sun to warm the house in winter while reducing cooling costs in summer by keeping windows and external walls protected from the sun. The placement of windows according to the direction of the sun will either allow more or less energy efficiency. Here are some basic details about different window orientations (this also applies to walls but to a much lesser extent if they’re well insulated):
- North Windows – North facing windows allow light to enter the home during the day. In winter this can help to warm the house. North facing windows can also be protected from the sun in summer reducing cooling costs. As the suns angle is lower in winter than in summer a fixed eave over a window can block the summer sun while allowing the winter sun in. This is one of the most important considerations in designing a solar passive house.
- South Windows – South facing windows let in very little sunlight but they do allow heat to escape. In cooler climates like Hobart and Canberra it’s particularly important to minimise south facing windows. In hot climates south facing windows can be useful for letting a breeze through the house to help keep it cool without having the sunlight heat the house. It is however important to consider that even in hot parts of Australia it can still get cold, particularly at night. If a homes design entirely around staying cool it can make these cold nights very uncomfortable.
- East Windows – East facing windows receive direct sun in the mornings but are shaded from the sun in the afternoon. In hot climates east facing windows can be useful as they can warm the house in the morning which can be good after a cold night. In cooler climates it’s better to reduce east facing windows as they don’t generate much heat gain but do allow a lot of heat to escape in the afternoon and at night.
- West Windows – West facing windows get direct sun in the afternoon. In hot climates it’s better to reduce or shade these as much as possible as the afternoon is when the sun heats a home the most. This can be beneficial in cooler climates when the warmth can heat the houses.
Solid building materials like brick, stone, tile and concrete have a high thermal mass and can be used to store thermal energy. This is a important part of designing an energy efficient house as thermal mass can regulate fluctuations or changes in temperature over a short period (day and night temperature changes).
Materials with high thermal mass use a lot of energy to change temperature and also release energy slowly. Direct sunlight can be used to heat thermal mass. This heat will then be slowly released over night when there’s no sunlight available to warm the house. It can also be useful in climates with hot or warm days but cold nights as it will moderate the temperature by absorbing heat when it’s hot and releasing it when it’s cold.
Thermal mass in generally less effective or can even have a negative effect in hot or tropical climates. It can be used to cool a house by absorbing heat during the day and can then be cooled over night by allowing a cool night breeze to flow through the house. This reduce the effect of a cool night breeze so should only be used if this is carefully considered. It will also heat a house if it’s exposed to direct sunlight which can have a very negative effect on the homes energy efficiency.
Adding external shading can protect exposed windows from direct sunlight that can cause unwanted heating. It can also be used to protect walls that can heat up and radiate heat into the house.
Louvered awnings or pergolas are particularly useful as they can shade a house from the summer sun but still allow direct winter sunlight though. These can be fixed at an angle that will block the higher angle of the summer sun or they can be adjustable so they can be opened or closed as needed. other shading options that are useful in hotter climates are large eaves, verandahs and screens.
Insulation prevents heat escaping a house in winter and keeps heat out in summer. A materials insulating ability can be determined by it’s R-value (thermal resistance value) the higher the R-value the more resistance it has for preventing heat to pass through it.
Heat is lost or gained through a homes roof, walls, windows and floor so it’s important to allow for insulation to all of these areas. All building materials have an R-value but most are very low which is why added insulation is normally needed.
Insulation is available in two main types: reflective & bulk. Bulk insulation contains small air pockets that reduce heat transfer. Reflective insulation, which is normally aluminium foil over a paper or plastic sheet has a shiny surface that reflects heat. Composite materials that combine the two types of insulation are also available.
The minimum insulation requirements vary depending on a homes climate zone. Most areas require an R-value of 4.1 to 5.1 for roofs or ceilings, depending on the roof colour (dark colours require more insulation). Walls normally require 2.8 and floors vary from 1.0 to 2.25 depending on the climate. Alpine climates require higher r-values (6.3 for the roof, 3.8 for walls and 3.25 for floors).
Preventing the leakage of warm air in winter or cool air in summer can play a big part in creating an energy efficient house design. Air can escape through gaps around walls, ceilings, floors, doors, windows as well as fire places, fans, vents and even plumbing and electrical fixtures. Sealing these gaps can increase energy efficiency but can also cause moisture and condensation problems. When a house is well sealed it’s important to provide ventilation particularly in bathrooms, kitchens and laundries that can cause moisture, condensation and air quality problems.
Self closing extractor fans can provide ventilation when needed but close to reduce unwanted air leakage. another good option is a “Heat Recovery Systems” which works by using the heat from extracted air to warm cool external air being drawn into the house. They also work the other way by using cool air from inside to cool external air being drawn in.
My Passive Design Recommendations
Hot Summers with Mild or Cool Winters
This type of climate applies to many of Australia’s cities including Perth, Adelaide, Melbourne and Sydney. It’s generally better to reduce west facing windows as much as possible to reduce overheating in the afternoons in summer. North facing windows that are raised off the ground by at least 600mm and under an eave of at least 500mm are protected from most of the summer sun but allow direct sunlight in to warm the house in winter.
Hot and Humid
Northern parts of Australia where it’s hot and humid all year obviously need to focus on keeping the house cool. It’s important to protect most or all windows from direct sunlight. Unprotected west facing and full height north facing windows should be avoided as much as possible. It’s also important to be able to let a breeze through the house to keep it cool at night.
In cool climates like Tasmania and Canberra it’s important to capture heat from the sun during the day and to keep heat from escaping at night or on cold days. North facing windows that let in plenty of direct light will help to warm the house. This can then be kept in the house with insulation and air sealing. thermal mass can also be used to store heat from the sun but it’s important to make sure the thermal mass can easily be warmed or it can have a negative effect.
Energy Efficient House Design
The above passive design principles help to reduce energy consumption by maintaining a comfortable temperature inside your home. This results in less mechanical heating and cooling needs which can drastically reduce your energy use however there are some other design considerations that can also help create an energy efficient home. These include using energy efficient appliances, energy generation and energy storage.
Energy Efficient Appliances
Appliances such as fridges, freezers, dryers, washing machines and dishwashers can make up a large percentage of a homes energy use. Choosing high efficiency rated appliances will help to reduce your homes energy requirements. The governments rating system makes it easy to choose the right appliances for your energy efficient home. check out www.energyrating.gov.au for more info on energy ratings.
Energy Generation & Storage
Generating your own renewable power, most commonly with a solar PV (Photovoltaic) system provides energy that you can use in your home and feed back to the grid when not needed. The cost of solar PV systems is becoming more and more affordable. Government rebates may also be available which help to make a solar PV system an even more viable option.
Before deciding to install a Solar PV system it important to find out what your rebates are and what your feed in tariff is. A feed in tariff is the money you get back or deducted from you power bill for feeding power back to the grid. This is generally much less than the cost to use power from the grid. If you feed in tariff is very low it might be worth considering using energy storage with your Solar PV system. storing energy you generate during the day to use at night instead of feeding it back into the grid can make a huge difference to the energy savings of your Solar PV system.
Water Efficient House Design
Reducing a homes water use, collecting and storing rainwater and reusing grey water all contribute to creating an energy efficient home.
Choosing water efficient appliances like the above energy efficient appliances will help to reduce a homes water usage. Showers and toilets are two of the biggest water users in a home so choosing a water saving shower head and toilet will make a big difference. Efficient washing machines and dishwashers also offer a good amount of water savings and are worth the investment.
Collecting and storing rainwater from your roof either for use in your home or garden is a great way to increase your homes efficiency. Some council areas require the home owner to dispose of stormwater themselves. In this situation soak wells or leach drains are often used. Installing rainwater tanks with a smaller soak well or leach drain for overflow can help create an energy efficient home without adding very much to the overall build cost.
Another water saving measure that can be worth considering particularly if your having large areas of lawn or gardens is to reuse grey water. Grey water is water other than sewerage that’s been used in the house, often collected from showers, baths, hand basins and washing machines. This grey water can be treated in a specially designed treatment system or piped directly into the garden. If grey water is being used to water vegetables or fruit trees it’s important to use a good treatment system to reduce the amount of chemicals and bacteria in the water.