The above statement is probably something we can all agree on, but getting there can be more complicated than you might think. Building regulations try to help us along the way by defining and setting requirements for the level of ventilation in homes.

"Buildings must be ventilated to ensure that occupants and users of buildings have an acceptable indoor climate. Ventilation must ensure that there is fresh air for users and that moisture and other contaminants do not occur in concentrations that can cause health problems, inconvenience to users or damage to the buildings"

- Building Regulations Ventilation §420 - §452

How is air change and ventilation demand determined?

The air change in existing buildings is typically assessed by measuring the CO2 concentration. By measuring the CO2 concentration, it is possible to see when people are in the home, how active they are and calculate the actual air change. By comparing these calculations with limit values set by the Danish Standard, you can determine whether the air change is theoretically appropriate and thus meets the ventilation needs.

The method is proven and recognized around the world, but has a built-in flaw: It requires the presence of people and therefore CO2 in the room, which is not always the only reason for ventilation. What about the humidity?

 A new and innovative method

Through our more than 500 indoor climate analyses in homes, CLIMAID has developed an alternative method for calculating ventilation levels. The method is based on relatively simple measurement data and has several obvious advantages.

What is the purpose?

As we have already mentioned, ventilation should not only remove CO2 from exhaled CO2, but more importantly ensure that the humidity conditions in the home do not cause damage to the building and thus unhealthy and harmful conditions for humans. Shouldn't we rather control the ventilation level based on the humidity conditions? CLIMAID has found a correlation between our calculation of moisture addition, the absolute moisture level and the traditionally calculated air change from CO2 measurements.

This context allows us to assess ventilation needs based on humidity conditions and ensure that the building is not damaged even when there is no high human activity.

A single person cooking without extraction or drying clothes indoors creates a greater ventilation demand than 2 people sitting and drinking coffee. The traditional CO2 method would say the opposite.

How do we measure?

We measure temperature and humidity in the home as you already know it from old-fashioned thermometers and hygrometers. In addition, we use weather data and information about the building to calculate the humidity conditions.

The simpler sensors that only measure temperature and humidity are 2-3 times cheaper than CO2 sensors and have a battery life that is 3-5 times longer. This makes it both cost-effective and practical to install in all homes, giving you a better overview of the building's ventilation level.

What about GDPR?

This is where one of the biggest benefits of avoiding CO2 sensors lies in the assessment of air exchange. With CO2 sensors, those who have access to their data can clearly see when and how much human activity has occurred in the home. They can see if anyone is home and whether activity is high or low. We can understand if residents are concerned about this data being available and don't want to give permission for this data to be collected. With temperature and humidity measurements, it is not possible to see the immediate level of activity or assess whether someone is home.

Are CO2 sensors never needed?

Yes, it does. Using CO2 sensors to assess air change in buildings with many people and high activity, such as schools and offices, makes a lot of sense and we use them there too. Here, a calculation of the moisture supply and the absolute humidity level will probably not be sufficient to assess the need for ventilation.

CO2 sensors may also be needed to document whether 0.30 l/s per m² of heated floor area is being supplied as required by building regulations, for use in a technical report or dimensioning of a new ventilation system.

However, if the goal is to find a robust, cost-effective and practical solution to quantify the ongoing ventilation demand in a residential building, we think it's worth considering whether there are better solutions.