In a tight, well-sealed building ventilation is very important for:
INDOOR AIR QUALITY. It is important to remove stale humid air that may contain pollutants and to provide a supply of fresh air to the interior. But if you just make the building leaky or open a few windows you are at the mercy of the weather. So some form of controlled ventilation is called for. Controlling humidity levels by exhausting steam from cooking, washing, and breathing is important because high indoor humidity can lead to excessive condensation on windows, walls, and in inside the building fabric. This, in turn, can lead to mould growth which can cause serious health problems as well as rot in the building structure.
HEAT DISTRIBUTION. Without some form of air movement it can be difficult in larger buildings to move heat from the north side when the sun is shining to the rest of the building. Or from the second floor (where rising heat can accumulate) back down to the ground floor.
SUMMER COOLING. In the Southern Highlands of NSW, summer cooling is best accomplished by closing the house during the day and opening it up during the night to allow cool air to flow through.
Ventilation in the Greeny Flat is achieved with the use of three exhaust fans. One small fan in the bathroom runs continuously through the winter (when the house is closed up) and the flow can be adjusted up or down as required to keep the relative humidity around 50% and to maintain good indoor air quality. Another small fan in the bathroom comes on at full speed whenever the lights are turned on. And the small kitchen rangehood is turned on whenever anyone is cooking. All three of the these fans are ducted directly to the outside of the building via hoods with dampers that face away from the prevailing winds.
When any or all of the exhaust fans are running, fresh air is drawn into the Greeny Flat via an “Earth Tempering Tube”. In our case this is a 90mm PVC pipe that is laid (as shown above) under the living room floor and comes up underneath the refrigerator. The pipe runs under the part of the slab that is warmed by the sun during the day so the incoming air is warmed as it passes through the pipe. It is still cooler than the interior air when it arrives under the fridge so it helps to cool the air around the refrigerator. This helps to make the fridge more efficient and the fridge helps to warm the air a bit more.
This is an inexpensive way to ensure that there is a constant supply of fresh air to the interior. When we installed the pipe we also installed a thin rope inside the pipe which allows us to pull a sponge through the pipe to clean it so that the incoming air does not get contaminated as it passes though the pipe.
A better way to ventilate a well-sealed building (but more expensive and hard to find around here) is a Heat Recovery Ventilation (HRV) system (and I don’t mean one that takes warm air from your attic and blows it into your house). A true HRV provides two, balanced air flows. One that exhausts stale air from the building and another that provides a constant supply of fresh air to the interior. As the two air flows pass each other the heat is recovered from the stale air and transferred to the fresh air via a heat exchanger.
An HRV is essential in a very cold climate and will probably become more common in Australia soon.
Energy Recovery Ventilators (ERV) are similar to HRV but they recover humidity as well as heat and are better suited to air-conditioned buildings.
One of the reasons why ventilation is so important in relatively tight buildings is the potential for condensation. Here we see condensation on a window in the Greeny Flat after a few days of not running the exhaust fans. Condensation can lead to mould which can become a serious indoor air quality and health problem. Rot in the building structure is another potential effect of too much condensation. If you can see condensation on your windows there’s a fair chance that there will be condensation in other areas that you can’t see which could lead to real problems. So condensation is a good sign that you need to ventilate more.
The tried and tested formula for making buildings that are healthy, comfortable, safe, durable, and energy efficient is to “Build Tight, Vent Right”.
It is also important to consider natural cross-ventilation for cooling the building in summer. Any time the outside air temperature is cooler than the inside it can be used to help cool the building. This only works if adequate provision has been made for air to flow through the building (even when, or especially when, bedroom doors are closed at night). So bedrooms typically require at least two openable windows in different walls and preferably as far apart as possible to allow breezes to flow through the room.
In the Greeny Flat we anticipate that, in summer, we will be able to keep the building cool by closing it completely during the day (including the blinds) and opening it up at night to let the cooling breezes through as shown above. This should have the effect of cooling down the floor slab at night so that the thermal mass of the concrete can help to keep the interior cool throughout the day.