Draught sensor

Is the ventilation causing discomfort due to draught?

Draught depends on a combination of the air:s average velocity, temperature and turbulence. Swema 3000 and the directionally independent sensor SWA 03 measure all these entities and also presents the draught automatically in units called DR (Draught Rating).
EN ISO 7730 defines DR as the percentage of people who are predicted to be bothered by draught.

ISO7726 gives all the required and desirable characteristics of measuring instruments of the four environmental factors. However, the air velocity could be the most difficult case to measure due to fast air velocity changes.

SWA 03 meets the requirement of ISO 7726 to be used for ISO 7730 - Ergonomics of the thermal environment :

1: The air velocity sensor must be direction independent. The air velocity in room air movements is quite low (0.05...0.4 m/s) and there are often changes in direction and velocity (turbulence).

2: The response time of sensor must be as short as possible.
The turbulence of air is an important component of air velocity in the draught rating formula. The room air movement is very unstable. It can change from 0.05 m/s to 0.4 m/s in very short time. It is important that a suitable sensor should follow these changes. ISO 7726 indicates that the desirable response time of an air velocity sensor should be below 0.2 second (90%). The EC project SMT4-CT97-2172 proposed a sensor test method for frequency response with sinus formed oscillated air velocity. SMT4-CT97-2172 also proposed a desirable sensor frequency of minimum 2 Hz. Swema 03 fulfills booth the response time in ISO 7726 and the minimum frequency proposed by SMT4-CT97-2172. See technical data. Swema 03 achieves the desirable levels by using a fast microcontroller and a small sensing element. (Other larger sensors have greater inertia and therefore a longer response time).

The result is a draught sensor with especially good dynamic qualities for turbulence.

The Swema 3000 also makes it possible to use the SWA 03 without a computer for draught measurements in the field.


History:
1995: Swema bought and improved a draught sensor concept originated from the Swedish Building research center. Probe name: SWA 01. Max velocity 1 m/s.

1997: Tested in EC (European Community, today European Union) project MAT1 CT93 0039

1999-2000: The design was improved in EC (European Community, today European Union) project SMT4-CT97-2172.
Turbulence sensivity improved. Air velocity range extended to 3 m/s. Probe name SWA 03.