Today we spend most of our day in closed rooms. For this reason, indoor air quality (IAQ) plants are installed, which are intended to create a pleasant indoor climate in the rooms. Ventilation plays an especially crucial rôle. On the one hand, it serves not only to provide fresh air, but also to remove pollutants, such as excessive humidity, from the rooms. Ensuring a sufficient air exchange rate, and therefore determining the volume flow, is an important quality factor in commissioning and operating IAQ plants. The reliable determination of the air velocity in ducts is one of the most challenging measurements a ventilation/air conditioning technician needs to take.
Follow this motto: “More is more” – IAQ plants are often run with excessively high air quantities. This surplus leads to increased operating costs. The energy consumption of a fan increases, since a greater amount of air needs to be moved through the plant. However, costs are also incurred for the conditioning of the air (cooling, heating, humidifying or dehumidifying), which can be reduced if the plant is correctly adjusted. In addition to this, a high air exchange rate often leads to draughts in the rooms, causing people to feel uncomfortable.
On the other hand, a too low volume flow can also be a problem. The people in the room have too little fresh air to breathe. The indoor air is “used up”, as the CO2 content in the room is excessive. Low volume flows can moreover have a negative effect on the plant’s hygiene: there is a risk of germ growth in the plant if the humidified air is moved too slowly through the ducts. A correctly adjusted IAQ plant thus not only helps to make the indoor climate comfortable, but also to save costs.
1. Introductory text
2. Significance of air velocity
3. Measurement of the right air velocity
4. The right measurement location
4.1. Flow profiles in ducts
4.2. Distance to sources of interference
5. The measurement method
5.1. Trivial method
5.2. Centroidal axis method
5.3. Calculation of volume flow
6. Analysis of the measurement values
7. The measurement report