With energy prices skyrocketing, we are all looking for ways to reduce our power consumption. From using more energy efficient light bulbs, to better seals around doors and windows, there are numerous ways and various strategies that can be employed to reduce energy usage and save money. However, as with most things starting with a properly designed system to begin with provides distinct advantages.
In this case, a house designed using solar passive design principles is the best starting point. These design principles utilise “passive design” aspects to maximise thermal comfort, i.e. they use the climate and local environment, such as the sun and natural breezes, to reduce the need for artificial heating and cooling. In Australia, these costs can account for approximately 40% of energy costs in the average home, but may account for even more in some other climates.
Design principles for solar passive house designs are:
- Orientation
- Thermal Mass
- Insulation and sealing
- Ventilation
- Active users
Orientation
Homes built in the northern hemisphere should be oriented such that their long axis is aligned east/west, with larger windows in the south-facing walls to encourage solar heating during the colder months. If possible during the design phase, these windows should not be obstructed from the sun by such things as other buildings, trees or other structures between the hours of 9am to 3pm allowing sunlight to stream in.
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A house designed using solar passive design principles. Image credit: Thinkstock, 2014.
In the hotter months, when the sun is higher in the sky, it is important to limit the amount of sunlight entering the house using things like eaves, awnings, natural shade from trees etc., curtains, blinds or shutters.
Note; for homes in the southern hemisphere, the situation is reversed and the main windows should be located in north-facing walls.
Thermal Mass
The other component to solar heating is thermal mass. Things like cavity brick walls, concrete floors and internal brick walls all add thermal mass to a home.
In the winter months, when the sunlight is allowed to enter via north-facing windows, the heat entering the house is absorbed and stored in the thermal mass, i.e. concrete floors and internal brick walls and then released into the home during the cooler night, with warmth being trapped inside by closed blinds.
In the warmer months, the thermal inertia of a house with a cavity brick construction takes longer to heat up compared to a lightweight house.
In a detailed study instigated by the Australia brick industry using full-sized housing modules it was found that, increasing thermal mass, increases thermal lag. Thermal lag helps to damp the diurnal temperature variations and reduces the effects of the daily maxima and minima. In fact during the summer, the outside temperature might reach its highest around 13:00, but the inside temperature may not until about 18:00 or 19:00.
Furthermore, the maximum temperature experienced inside a lightweight house was significantly greater than that experienced in a cavity brick house. The temperature fluctuation inside the lightweight house also closely followed the outside temperature profile. In comparison, the heavier cavity brick house reached its maximum internal temperature several hours after the daily external maximum was experienced. The thermal lag meant that heat was also being drawn out of the brickwork and back into the atmosphere as the external temperature dropped during the daily cycle, reducing the amount of heat available to be transferred into the house, leading to greater levels of thermal comfort compared to the lightweight house, and reduced requirements for energy hungry air conditioners.
Insulation and Sealing
Heat naturally flows from hot regions to colder regions. It can do this via three mechanisms:
- Conduction
- Convection
- Radiation
The majority of domestic (thermal) insulation products work to prevent conduction and will be located in the walls and ceiling. This means during the cooler months, a properly insulated house will work to prevent heat from escaping from living spaces. Conversely, in the hotter months, the insulation works to minimise heat entering the living spaces from the outside.
Convection is the natural flow of heavier, cooler gases or liquids to lower levels. A properly sealed house will prevent hot air from entering during the summer months through leaky doors, windows and even floors. Similarly, a sealed home will prevent the loss of heat during the cooler, winter months.
Ventilation
Here, good local knowledge of the location is invaluable. While windows should be located to take advantage of passive solar heating, the window orientation and type should also consider the ability to allow breezes to ventilate the house to help flush out heat in the summer. Good ventilation will also benefit air quality within the dwelling.
Active Users
While a correctly designed home can deliver energy savings, active users, i.e. those who understand the solar passive design principles and can implement them, will bring the ultimate benefits. Such activities would include opening windows at specific times to utilise breezes to flush unwanted heat from the house and using shade devices such as awnings to limit heat entering the house in hotter months.
Summary
Solar passive design principles are an effective way to reduce the energy consumption and greenhouse gas emissions of a house. They need to be included in the initial house design to have maximum impact, but can be applied to existing homes and still provide significant benefits. When combined with active users, households will generate the maximum economic and environmental benefits.
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