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Performance of ventilation should be considered when looking for causes of indoor air problems


What makes us think that indoor air is poor? The causes are numerous, and the much-discussed mould is just a small part of the problem. In fact, much smaller than people generally think. Very often, problems are caused by microbial activity and microbial emissions, but how many factors have yet to be identified? Is there a chemical burden that may well continue to evolve and increase?


How much has our response changed over time and through the generations?


Typically, every building has microbial activity. It has always existed everywhere, and it will always exist. However, the question is what makes it harmful and when harmful growth and microbial activity are produced. Old strains may have been in a resting state for years or decades, but then something makes them become aggressive. If conditions are favourable, new growth also emerges. Building stock ages over the years, however, and weather conditions such as humid winters make its maintenance challenging. Not all microbial activity is harmful, however. Not even moulds. If you think about it, forests are full of decaying wood, growth and moulds but they do not make us ill.

Based on my experience, the common factor is some kind of change quite often related to ventilation



Are the problems caused by changes in ventilation?


Based on my experience, the common factor is some kind of change quite often related to ventilation. A problem building can be “demonised” and some times even torn down simply because air ducts have been swept poorly. Various solidified impurities can accumulate in the spiral seams. These include, for example, emission particles from outdoors, wool dust from fibre insulation, construction dust, fine sand, etc. If the material is not removed carefully after sweeping, the impurities can travel and have a long-term effect – and in the worst case, also the insulation of the diffuser boxes or silencers break as a result. In some instances, fire dampers have closed without anyone noticing, and the resulting pressure differences can cause significant problems. Even small holes in a building cause a sufficient leak when the flow is constant – from one second and minute to the next, all day long. This can carry impurities from surprising locations.

Even if the ventilation has been correctly adjusted, there can be changes to the ventilation system. These changes can impact the performance, which is why monitoring is important. Dirty or wet filters can radically change the pressure ratios.

When competitive tendering is heavily slanted towards cost saving, it may end up costing more because the performance of the solution is too low – sometimes both in principle and because the intended use or the number of people has changed. One common example of this is an increase in the size of daycare groups. Increased temperatures, insufficient ventilation and operation-related vast particle burden can lead to unpleasant conditions.


Even a small amount of finely ground insulation wool irritates the eyes and airways


When the pressure is strongly negative, ventilation can trigger problems by itself. In this case, the ventilation system tries to draw air from sources where the air is not clean at all. These impurities are not always moulds. They can also be concrete or other construction dust. Sometimes the source is surprisingly far from the premises where symptoms occur, making it difficult to identify. The source can even be in the basement or underground floors. In my experience, the problems may be caused, for example, by creosote when no clear general source of indoor air impurities can be found. This is typical in older buildings where creosote has been used. Creosote smells bad but it might be impossible to sense because even very low concentrations can cause irritation. Also, microbial activity can follow the same path from the underground level to the upper floors. Even very small connections are enough to cause problems.

The problem is often in the basement or downstairs, but symptoms can still occur upstairs


The cause of indoor air problems can even be found on another floor


Naturally, we first look for the cause in the same space where symptoms occur. It should be noted, however, that air almost always flows upwards, first to corridors, stairs and upstairs, and then into rooms. When the pressure is negative, air flows towards the rooms or classrooms where the exhausts are located. Naturally, each premise has supply and exhaust vents, but the pressure differences within a building are not that distinct. When the total pressure ratio is slightly negative, negative air pressure is lost in the vicinity of the vents, in areas like lobbies and corridors, every time the front door is opened. When a room has no direct connection to outside, the pressure stays negative and tries to stabilise. This means that the basic air flow is towards these rooms. As a result, symptoms occur upstairs even though the problem is often in the basement or downstairs.

What is good indoor air?

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