Achieving Optimal Energy Efficiency in Your Home Through Window Design
Windows play a crucial role in how energy-efficient your home is, and the design and configuration of windows are critical factors in regulating the entry of heat and light into your home.
Windows allow heat and light from the sun to enter your home, or to block it out completely. To obtain a 7-star NatHERS rating for your new home, you will need to consider windows very early in the design process.
Maximising the energy performance of a home involves optimising windows according to their orientation, selecting the right types and configuration of glazing, and choosing the right frames. Nick Rawson, Design Director for Hall & Hart explores the various factors that influence window performance and how to achieve optimal energy efficiency in your home through window design.
Optimising Window Design for Different Orientation
In regions with a temperate or cool climate, such as Sydney, Perth, Melbourne, Adelaide, and Hobart, the proper orientation and performance of windows are crucial for controlling heat and light. The Solar Heat Gain Coefficient (SHGC), which measures the amount of solar radiation passing through a window and entering a building, is a vital factor in window performance. In hot climates, windows with a low SHGC are necessary to minimise the amount of heat entering the building, whereas in colder regions, a high SHGC can be advantageous for capturing the sun's heat and naturally warming the building.
North-facing windows should have a high SHGC to allow direct solar radiation in winter, while being shaded in summer to prevent excess heat.
For east- and west-facing windows, shading devices such as deep overhangs can protect them from the summer sun early and late in the day.
South-facing windows are less critical since they receive less solar heat gain.
Selecting the suitable glass for various window orientations is a crucial factor in designing an efficient window system. Despite common belief, single glazing is not always the best choice for north-facing windows to achieve optimal energy rating. Both single and double glazing can allow direct solar radiation to pass through, but double glazing can also prevent heat loss, which is particularly advantageous in cooler climates.
To boost your home's performance by over half a star, optimizing window design according to orientation is essential, especially when endeavouring to utilise the benefits of thermal mass such as brick feature walls or concrete/tiled floors.
For thermal mass to work effectively, windows need to let in solar radiation during the day to warm it up, therefore you need to make sure windows are optimised to let in enough solar radiation during the colder months. In warm and hot climates, natural ventilation should be used on cooler evenings to let out the stored heat (night purging).
Controlling Air Leakage and Noise through Proper Window Sealing
Window sealing is important because it helps to prevent air leakage, which can impact your home's energy efficiency and comfort level. If windows are not sealed well, air can leak in and out of your home, causing drafts and temperature fluctuations. In the winter, cold air can seep in, and warm air can escape, leading to a colder indoor environment. Awning and casement windows, which seal by compression, control air leakage much better than sliding windows and doors. You can also control noise by using thicker and/or multiple layers of glass.
A well-sealed window can help to maintain a consistent indoor temperature and reduce your energy bills. Additionally, it can also help to prevent moisture and water from entering your home, which can cause damage over time.
Water will condense on cool surfaces. Efficient glazing assemblies will stay at the same temperature as the room, preventing condensation and the risk of mould. Less-efficient glazing will transmit exterior temperatures directly to the interior surface, thus creating greater differences between room temperature and glass surface temperature and causing condensation to form.
Impact of Different Types of Window Frames on Thermal Conductivity
The window frame is also an important factor that can affect the NatHERS star rating. The frame holds the glass in place and can greatly affect the thermal conductivity, also known as the U-value, of the window. Different types of frames have different U-values, which can impact how much heat flows through them.
Timber frames have a lower U-value than aluminium frames without thermal breaks, meaning they conduct less heat. This can make a significant difference in the energy efficiency of a home, especially in hot or cold climates where insulation is crucial to maintain comfortable indoor temperatures.
Importance of Window Design in Achieving a 7-Star NatHERS Rating
In summary, Nick Rawson, Design Director for Hall & Hart states that, “Modern designs with large fixed windows and minimal or no eaves will be very challenging to design to the new standard, especially homes with large connected spaces and voids.” Nick further explains that it will be critical to integrate the selection of windows into the design process as early as possible especially for sites that do not have ideal orientations and it will be critical that the design team has access to the appropriate software to assess ratings as part of the design process.
“Designing and configuring windows is crucial for achieving a 7-star NatHERS rating.” Nick says. You should optimise them based on orientation, have a high SHGC in the right direction, shade them in summer, let in enough solar radiation to warm the thermal mass, seal them well, control noise, and prevent condensation and fading (furniture, carpet etc). By taking all these factors into account not only will you increase the Nathers rating of your new home , you will also make your home more energy-efficient, reduce your energy bills, and have a lower environmental impact.