There are several smart ways to keep your home comfortable all year round. The two most common ways of becoming energy efficient are installing double-glazing and insulation. These are also an integral part of your home’s building envelope, which is made up of the ceiling, floor and external walls.
Although critical, they don’t show a complete picture of energy efficiency in a house. For all these expensive building elements that make up the building envelope air leakage into the building must be tackled.
The air inside your home, with its heating or cooling energy contained in it, always moves through a building envelope and escapes to the outside. This air movement is caused by holes and gaps in air conditioning duct work, walls, ceiling and floor systems, and can be exacerbated by air pressure difference between inside and outside.
The holes and gaps are often small, but there are 100’s of them throughout your home: power points and switches on external walls, gaps under skirting and around window architraves, attic access, ceiling exhaust fans, down lights, to name but a few.
The Wind, blowing against a house is one of the main causes of air pressure difference, while another one, is caused by turning on an exhaust fan in the bathroom, or a leaky ducted heating system.
The result of all this air movement is expressed as an air leakage rate, or air change per hour (ACH). For example, if your home has one (1) ACH at ambient pressure, it means that total volume of air in your house has been replaced by outside air, even with little or no wind blowing outside. If the wind picks up, the ACH of a house multiplies many times.
|ACH50||Natural Air Change||Rating||% of bill||% saving potential||Ventilation Requirements|
|1.5||.075||Super||2%||none||Constant energy recovery ventilation|
|3.5||.18||Excellent||6%||1 to 3%||Occasional forced ventilation|
|5||.25||Better||10%||2 to 4%||Occasional|
|7||.35||Good||14%||2 to 5%||Small|
|10||.5||Fair||20%||3 to 10%||Rare|
|20||1||Bad||40%||5 to 20%||Little to none|
|Standard||House Leakage based on floor area of: 210 square metres||ACH50|
|ATTMA TS-1||UK, Best Practice, residential||3.4|
|Oregon||3.5 to 5 is Tight, great||3.5|
|ASTM E779||LEED, 1.25 sq in at 4 Pa / 100 sq ft. Envelope||4.7|
|PA Housing||Tight < 5 Housing Research/Resource Center (PHRC)||5.0|
|EEBA||Energy and Environmental Building Association Guidelines||5.2|
|EN13829||Most European countries||6.1|
|Oregon||5 to 7 is good||7.0|
|PA Housing||Moderate < 10, Leaky > 10 Housing Research Center||10.0|
The following graph explains the relationship between wind speed and the pressures it creates on the building envelope. To test the air leakage of a building, a pressure difference of 50 Pascal (Pa) is applied. This test is performed through the use of a ‘blower door’, a mechanical device designed to determine the air tightness of a building envelope.
Air leakage testing at a pressure difference of 50Pa is an internationally accepted standard. If for example, the building leaks at a rate of 10 ACH at this pressure, it is expressed as 10ACH at 50 Pa. As seen in the graph, a 50Pa pressure difference is comparable to a wind speed of 32 km/h blowing against the building, while a 1.5Pa pressure difference is equivalent to a 5km/h wind.
Once you have made the decision to address the air leakage of the home, the question then becomes how (air) tight the building should be. If it’s too tight, it will impact the indoor air quality, or if it’s too leaky, it will affect the energy efficiency. Here is where an air leakage test can provide the answer. Not only will this test give you an ACH at 50Pa of your home, but it will also pinpoint all of the invisible holes and gaps.
Another useful diagnostic tool in this testing process is the thermal imaging camera. This camera can pick up temperature differences in a building envelope, as well as show where insulation in the wall or ceiling is missing. If 5% of the building is not insulated correctly, the overall efficiency of the insulation drops by roughly 35%. Therefore it is important to have a continuous insulation barrier for the whole house!
If after sealing, the ACH of your house drops below 10ACH at 50Pa, a well thought out ventilation strategy should be considered. One such strategy is the installation of a mechanical whole house ventilation system, which introduces tempered fresh air to the living and bedroom areas, and removes stale, moist air from the bathroom, laundry, and kitchen.
In most cases, however, a building envelope can be sealed to the right level and thus provide a balance between energy efficiency and healthy indoor air quality.
And on the topic of ventilation, it is important to make sure that exhaust fans in kitchen, bathroom, and toilets can do their job, by allowing sufficient make-up air to be introduced back into those areas of the house. Poorly running exhaust fans are more than often the cause of mould and mildew.
There are many benefits of having a well-sealed building envelope: It makes the house substantially more energy efficient and comfortable, reduces moisture issues (mould!), and keeps dust, insects, and noise out.
Compared to double glazing and extra insulation, sealing your home is extremely cost efficient and relative simple to do. It is an investment with a substantial payback and can represent in many cases a 25% reduction in the overall energy cost.
Now for the most important question: How energy efficient is you home?
Contact us Efficiency Matrix, for an appraisal of your home…
|210 square metre home with basement||ACH50|
|Excellent- Less than 5%||1.5 - 2.0|
|Good- Best 30%||2.5 to 5|
|Poor- 55 %||5 to 10|
|Very bad- 10%||10 +|
By Jan Brandjes