Improve Indoor Air Quality
Modern homes have become almost airtight. That has the advantage to save energy and to keep outdoor air pollution from entering the home. Unfortunately, this also leads to an accumulation of indoor air pollution, which are now blamed for so many modern illnesses such as allergies and asthma. Since we spend more and more time indoors, be it at home or at work, indoor air pollution has become a bigger health problem than outdoor air pollution. Good ventilation has, therefore, become essential to protect your health. The purpose of ventilation is not only to remove bad smells from the kitchen or the toilet, ventilation also removes or dilutes potentially hazardous pollutants and gases; and it helps to control the indoor humidity and, as a consequence, limits the growth of harmful organisms.
An efficient air exchange also protects your home and its content. By removing excess moisture from the indoor air, it can prevent the rotting of timber components, such as window sills or timber floors and walls. Your TV, computer and stereo absolutely hate high humidity, because a combination of dust and moisture can create short circuits.
It doesn’t have to be expensive either. Strategically placed air vents and fans are cheap and normally manage to supply a home with sufficient fresh air. But what is sufficient? The answer isn’t simple, because there is always a trade-off between the need to preserve energy, the need to keep outdoor pollutants outside, and the need for fresh air supply into the home. Let’s first discuss some of the basics of air movement and the different types of ventilation systems.
Building design has become a science. Building scientists study the function of a house under hot and cold conditions and try to find ways to make the building comfortable and healthy. Sounds good? This is a far cry from only a few years ago when buildings were to be practical and cheap to build. Has this changed? In some countries, authorities have gradually introduced building codes that deal with such problems as indoor air quality. Unfortunately, the codes are voluntary measures in many countries or the population simply can’t afford the latest building designs.
We don’t have to be too scientific, however, and I try to make it simple. Mind you, I’m not an architect or designer of ventilation systems, so many terms and concepts of this so-called building science are way above my head anyway.
Natural Air Exchange
Let’s picture the car park of your local supermarket on a sunny day. The sun heats up the bitumen and the parked cars. The hot surface and vehicles pass on some of the heat to the air just above it. The warm air near the car park’s surface is less dense. It is, therefore, lighter than the slightly cooler air above it and rises. But unless the air is replenished, you would step into a vacuum when you walk to your car. This won’t happen, of course. The car park draws fresh air from somewhere. But from where?
Coincidentally, there is a playground nearby. The local council spent a considerable amount of money to plant nice green grass and many leafy trees. The air is much cooler on the playground than it is on the car park. The air won’t rise. Instead it has to move sideways to fill the ‘hole’ in the air above the car park. The movement is wind.
That reads like a lesson in meteorology. Well, the principles are the same when the air in your home is warmer than the outside air, as during the heating period for example. The warm air inside a room rises to the ceiling where it tries to escape into the attic and eventually outside. Older-style Australian homes had high ceilings with plastered air vents in every corner to allow the hot summer air drift into the attic. The room requires replenishment from the outside, though. Cooler and, hopefully, fresher air enters your home via every possible , joint, gap, crack and vent. On the other hand, if you use an air conditioner in summer, the heavier indoor air behaves like water and wants to spill into the lower parts of the building, or ooze out of gaps under doors or low vents into the outside. Warmer air will then be drawn into the home from the top. This is the natural way of air exchange due to temperature differences between the home and the outside.
Another natural force that influences indoor air is the wind. Most buildings aren’t designed by aeronautical engineers and are, therefore, a drag, so to speak. Wind is lazy, by nature, and doesn’t want to go around or over the obstacle. The air pressure is, therefore, mounting on the building’s side that faces the wind. The pressure is enough to force some of the air into your home. The opposite is true on the side that faces away from the wind, where the low air pressure literally sucks.
A third natural way of ventilating your home is too simple to be true – open the windows or outside doors now and then – even if you do so only briefly during the heating or cooling period. This is still better than not at all. My wife and I live in a cool region of Australia where the temperatures in winter sometimes plummet to around the freezing point. Nevertheless, the bedroom windows are open day and night (with security screen, if you wonder) and provide us with a good night’s sleep. “Lucky you,” you might say. I can understand the need to be energy conscious – I’m born in Germany, you know, where it can be very cold in winter. But even during bitter cold days my wife’s and my parents insisted that we open the windows for half an hour, at least once per day. Perhaps that was an excuse for not getting out of bed in the morning.
Natural air exchange is not always possible, not always desirable, or often not sufficient. That’s when mechanical devices come into play. Frying a steak is such a situation. If you like your steak cooked in a very hot cast iron pan, then air pollution is an unavoidable by-product, unless you have a kitchen fan or a range hood. Any device that removes the air while cooking is a must for the kitchen. The same goes for the so-called ‘wet-rooms,’ to remove excess moisture.
Short of complex ducted ventilation or filtration systems, two cost-effective methods can be used to replace stale air or remove pollutants mechanically:
spot ventilation and
In your home you are likely to have already some spot ventilation fans installed that remove localized pollutants in the kitchen or prevent excess moisture build-up in bathroom and laundry. You probably use the fan only when required. You may have to consider spot fans also for areas where other strong and short-term sources of pollution are present, such as in hobby rooms, workshops, or garages; and during home renovations.
Some pollutants, however, aren’t limited to only one area of the home. For example dust mites may be present in all rooms, and animal dander in rooms where the pet has access to. To keep pollutant levels down, you need to ventilate the whole building constantly with fans that run most of the time. As with spot fans, you can force the indoor air outside – you depressurize the building to some extent – and hope that enough cracks and gaps allow fresh air to fill the available space. This method is not always welcome, as it also draws gases form unwanted sources, such as radon from underneath the building; and may create a dangerous condition called ‘backdraughting.’ Alternatively, there are fans that do the opposite – they force outdoor air inside and slightly pressurize the building.
A more complex third and the best method is to combine the two: draw fresh air with one fan and expel it with another. This way you create an artificial draught with the advantage that you can control the situation: vary the speed of the fan and you increase or decrease the volume of air that is being exchanged, or simply switch the fans off. This system can also make good use of heating or cooling ducts.