How to assess the indoor climate in homes and offices

Published 2023-12-14

“It’s too cold”, “The air is really bad”, “It’s drafty” … Sound familiar? The nature and experience of the climate in different indoor environments depends on factors such as air and surface temperatures, leaks and air movement. There are several things to consider when measuring and analyzing the indoor climate in homes and offices.

To find out what to do and what to consider, we consulted Anders Tennerhed of Energy Concept in Sweden, who has 20 years of experience in indoor climate assessments.

Measure the air temperature in the occupied zone

– A good place to start is by measuring the temperature of the air. And more importantly, measure in several places to get a representative value of the air temperature,” says Anders Tennerhed:

– Always measure temperatures in the occupied zone. Even if the tenant has their bed next to the wall and finds it cold when lying in bed, you should always measure 0.6 meters from the outer walls and 1.0 meters from the windows and between 0.1 meters above the floor and 2.0 meters in the air. That’s what the occupied zone is.

Watch out for cold walls

But air temperature readings alone do not always give a true picture of the indoor climate, Tennerhed points out. In stone and brick houses, the walls are often cold. They have a high so-called U-value (W/m2K (watts per square meter Kelvin) and thus a radiant temperature that affects the indoor environment. In these cases, an additional measurement should be made with a global thermometer to calculate the operational temperature, which is the same as the perceived climate. The operating temperature can be several degrees lower than the air temperature. To compensate for this ‘loss’, it may be necessary to turn up the heat slightly to increase the operating temperature.

Is it dense everywhere?

A thermal imaging camera is a relatively small investment that quickly reveals cold surfaces. Similarly, its thermal images show where there are leaks around windows and doors, for example, which can cause unnecessary, costly heat loss.

– Often, it is a matter of construction measures that need to be taken. A one-off cost for, for example, additional insulation or replacement of windows. Then it is solved. The result is more satisfied tenants and lower energy costs,” says Anders Tennerhed.

Map air flows and air speed

A common complaint is that it draws. In spaces with exhaust air ventilation, where unheated outdoor air is brought in, draughts often occur.

– Measure air flows to ensure that you are not blowing in too little or too much air. Also check that air speeds do not exceed 0.15 m/s during the heating season and 0.25 m/s during the rest of the year. If air flows and air speeds are within the limits but the rooms are still cold, you may need to increase the heating.

Common ventilation problems in offices

Over- or under-pressure can lead to poor indoor climate and complaints in offices. Negative pressure is usually the most common. Negative pressure causes outdoor air to enter through leaks in the building envelope, creating drafty indoor environments and increasing energy use if you have ventilation systems with heat recovery.

Short circuiting of ventilation systems is another common problem. Often due to misplaced supply and exhaust air vents.

– It is common to have exhaust vents in toilet rooms that are too close to a door. Most of the air that enters above or below the door does not have time to mix with other indoor air before it is discharged through the diffuser.

Short circuits can also occur if too hot air is blown into the premises. Normally, it is recommended that the supply air temperature should be three to four degrees lower than the room air in premises. A colder supply air has a higher density. That is, the air weighs more and will mix better in the room than if it had been warm.

How much air is exchanged?

Air exchange efficiency can also be good to check. That is, what percentage of the air is regularly exchanged in a room? And how much area does not get any new air at all?

-If you suspect that there is too little air exchange in a room, it can be measured with tracer gas. In a decay measurement, the room to be measured is filled with carbon dioxide. A carbon dioxide analyzer is then placed in the exhaust air and one in the middle of the room and a measurement is made to determine the percentage of air exchanged in the room. According to BBR, at least 40% of the air in a room should be replaced continuously.

Poor exchange efficiency can be due to several reasons. It may be that the wrong type of supply air device is used, that too much hot air is blown in and does not mix sufficiently with the air in the room. And again, donors can be misplaced so that there is a short circuit in the ventilation system.

Incorrectly adjusted flows

Ventilation should both ensure good air circulation and remove pollutants and excess heat from internal loads such as lighting and people. Problems arise when there are either significantly more or fewer people in the space than the ventilation is designed for.

More people than expected make the room hot and stuffy. And vice versa, if there are significantly fewer people, the room is cooled by the disproportionate airflow.

-Strikingly, airflows are often oversized, bringing in cold air that cools people down. Bringing in too much cold outdoor air to be heated lowers the relative humidity and increases static electricity. Residents complain that the air is too dry.

-“It is simply a matter of adapting the air flows to the needs of the business in question,” concludes Anders Tennerhed.

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