Passive design is the process of designing a building envelope which does not require mechanical heating or cooling. As awareness of sustainability, internal climate control and desire for comfort in our dwellings increases it is important to consider passive design a guiding philosophy for the design and construction of new homes or buildings. Correct specification and selection of aluminium windows and aluminium doors can be an integral part of a successful passive design process, improving energy efficiency and comfort of your home. Homes that are passively designed take advantage of natural climate to maintain thermal comfort.
Incorporating the principles of passive design in your home:
- Significantly improves comfort
- Reduces or eliminates heating and cooling bills
- Reduces greenhouse gas emissions from heating, cooling, mechanical ventilation and lighting.
Building envelope is a term used to describe the roof, walls, windows, floors and internal walls of a home. The envelope controls heat gain in summer and heat loss in winter.
The performance of a building envelope in controlling climate extremes is significantly improved through passive design.
Well designed building envelopes maximise cooling air movement and exclude sun in summer. In winter, they trap and store heat from the sun and minimise heat loss to the external environment. Windows and doors are a critical component in this process.
The fundamental principles of passive design, are simple and can be applied in any climate zone throughout Australia.
DESIGN FOR CLIMATE
It is important to consider the climate zone where a building will exist. In Australia there are 7 core climate zones. The properties of a building in each of these zones would need to vary in order to accommodate the specific climatic requirements of that zone.
Where windows are concerned it is important to select a window suitable for the climate zone it will be used in. For example in a cool climate a window with high solar heat gain to maximize the use of free heating energy would be appropriate. In a warm climate you may wish to select a window which offers low solar heat gain properties to avoid unwanted heat entering the home through solar radiations.
ORIENTATION
A home that is well positioned on its site delivers significant lifestyle and environmental benefits. Correct orientation assists passive heating and cooling, resulting in improved comfort and decreased energy bills.
In hot humid climates and hot dry climates with no winter heating requirements, orientation should aim to exclude sun year round and maximise exposure to cooling breezes.
In all other climates a combination of passive solar heating and passive cooling is required. The optimum degree of solar access and the need to capture cooling breezes will vary with climate.
Where ideal orientation is not possible, as is often the case in higher density urban areas, an energy efficient home can still be achieved with careful attention to design.
Orientation for passive heating is about using the sun as a source of free home heating. Put simply, it involves letting winter sun in and keeping unwanted summer sun out. This can be done with relative ease on northern elevations by using shading devices to exclude high angle summer sun and admit low angle winter sun. Selecting windows and doors which have high Solar Heat Gain properties will assist free solar heat energy to enter your home.
SHADING
Shading of windows and doors is a critical consideration in passive design. Unprotected low performance glass is the single greatest source of heat gain in a well insulated home. Shading requirements vary according to climate and house orientation.
In climates where winter heating is required, shading devices should exclude summer sun but allow full winter sun to penetrate.
This is most simply achieved on north facing walls. East and west facing windows require different shading solutions to north facing windows.
In climates where no heating is required, shading of the whole home and outdoor spaces will improve comfort and save energy.
PASSIVE SOLAR HEATING
Passive solar heating is about keeping the summer sun out and letting the winter sun in. It is the least expensive way to heat your home.
Solar radiation is trapped inside the home using correctly oriented (north facing) windows exposed to full sun. Window frames and glass have a significant effect on the efficiency of this process. Trapped heat is absorbed and stored by materials with high thermal mass (usually masonry) inside the house. It is re-released at night when it is needed to offset heat losses to lower outdoor temperatures.
Design floor plans to ensure that the most important rooms (usually day-use living areas) face north for the best solar access.
Heat loss is minimised using insulation – select aluminium windows and aluminium doors with low Uw Values which offer good insulation properties. ,
Air infiltration is minimised with airlocks, draught sealing, airtight construction detailing and quality aluminium windows and aluminium doors.
Passive solar houses can look like any other home but they are more comfortable to live in and cost less to run.
PASSIVE COOLING
Passive cooling is the least expensive means of cooling your home. It is appropriate for all Australian climates.
Passive cooling maximises the efficiency of the building envelope by minimising heat gain from the external environment and facilitating heat loss to the following natural sources of cooling:
- Air movement.
- Cooling breezes.
- Evaporation.
- Earth coupling.
Air movement is the most important element of passive cooling. It increases cooling by increasing evaporation rates. Generally, cross ventilation is most effective for air exchange (building cooling) and fans for air movement (people cooling). Windows are a great source of cross flow ventilation.
Correct positioning of windowd and doors is essential to facilitate air movements. Use windows designed to deflect breezes from varying angles. Locate windows on walls with best exposure to common cooling breezes and design for effective cross flow of air through the building.
INSULATION
Insulation is an essential component of passive design. It improves building envelope performance by minimising heat loss and heat gain through walls, roof and floors.
THERMAL MASS
Externally insulated, dense materials like concrete, bricks and other masonry are used in passive design to absorb, store and re-release thermal energy. This moderates internal temperatures by averaging day/night (diurnal) extremes, therefore increasing comfort and reducing energy costs.
GLAZING
Windows and glazing are a very important component of passive design because heat loss and gain in a well insulated home occurs mostly through the windows and doors.
With good passive design, this is used to advantage by trapping winter heat whilst excluding summer sun. Cooling breezes and air movement are encouraged in summer and cold winter winds are excluded.
Windows in a typical insulated home can account for more heat gain or loss than any other element in the building fabric. In summer heat gain through an unshaded window can be 100 times greater than through the same area of insulated wall. One square metre of ordinary glass can let in as much heat as would be produced by a single bar radiator. In winter, heat lost through a window can be ten times more than through the same area of insulated wall.
Glazing is a key element of your home’s design providing, light, ventilation, noise control and security.
It can enhance the appearance and amenity of your home, providing views and connection with outdoor spaces. You can enjoy these benefits and have high thermal performance by selecting the right type of glass and frames and choosing the right size, location and shading of windows.
There are simple principles that can be followed, at design stage, to optimise the thermal performance of your home. These include:
- Locate and size windows and shading to let sunshine in when the temperature is cold and exclude it when it is its hot.
- Use thermal mass to store the sun’s heat and provide night-time warmth in cold conditions.
- Locate window and door openings to allow natural cooling by cross ventilation.
- Provide seals to openings to minimise unwanted draughts.
Incorporating passive solar principles at design stage is the most cost-effective way to achieve good thermal performance.
Including energy efficient windows and energy efficient doors in a well designed home can further improve its thermal comfort. Consider products like ThermalHEART™ which delivers substantially improved thermal performance, great insulation properties – Low Uw Values.