The balometer is a specific flow meter for measuring the flow rate of the air leaving or entering a ventilation outlet within the airflow system of a building. Some balometers can also measure the temperature and relative humidity of the air stream along with its flow rate, as well as the atmospheric pressure of the room. 

Modern balometers measure the velocity and flow rate of an air stream using a differential pressure measurement system, which is very reliable and accurate for this type of application. This technique uses a measuring grid with many holes through which the pressure is measured in comparison to the atmospheric pressure, and provides an average flow rate over the entire measuring area. 

Specialisation on air vents 

A balometer is accompanied by different measuring hosts to be applied according to the size and shape of the air vents in a room, both supply and exhaust. This system allows to calculate very precisely the airflow that passes through a vent, and therefore the total airflow that enters or leaves a room. 

The balometer is precisely the only instrument capable of providing a reliable and accurate measurement on a certain type of air vent: diffusers, whose omnidirectional airflow is very difficult to measure with a conventional anemometer. 

Sufficient airflow facilitates the maintenance of the temperature and humidity levels targeted by the professionals in charge of managing the building's ventilation system. 

Note that as modern balometers are primarily pressure measuring instruments, they can also be used as micro-manometers by connecting Pitot tubes or simple silicone tubes to them. 

Key role in controlling the air change rate (ACR) 

The rate of air renewal inside a room is a very important parameter to know if the indoor air is sufficiently stirred to reduce the concentrations of harmful gases such as CO2 and VOCs, polluting particles, not to mention biological compounds such as viruses and bacteria. Insufficient air renewal will increase the concentration of these harmful and even dangerous components, especially when many people occupy the affected area. 
 
A balometer can easily measure the amount of air entering a room in a given time, and relate this to the total volume of the room to derive an air change rate. This rate is often expressed as the number of complete cycles of renewal of the entire volume of air in a room in one hour (that’s why it is also called ACH as for Air Change rate per Hour). 

The CO2 level is the preferred indicator of the air change rate in a room because it is relatively easy and reliable to measure using a CO2 Meter or a professional CO2 sensor, and above all because it takes into account the exhalation of the people occupying a room. Measuring the CO2 level thus makes it possible to determine the necessary ACR of a room depending on the number of occupants and the nature of their activity within a room. For instance, a gym requires a higher ACR than an office room for the same occupancy, as athletes exhale more CO2 (and also biological contaminants) per minute. 

To find out more about ACR, CO2 levels, viral and bacterial contamination and the role of balometers in general, there are several articles on our INsights blog that provide a lot of information: