High Indoor Air Quality with Minimum Energy Costs

A random pattern of occupancy makes ventilation more difficult: the control system must be able to detect when ventilation is needed and to what extent. To ensure a cost-effective supply of fresh air, NuAire fitted its Smart Squrbo system with Vaisala’s CARBOCAP® carbon dioxide transmitters.

The current vogue for large open plan offices has created a need for many other smaller rooms for activities such  as meetings, briefings, appraisals, training  sessions, etc. These areas are notoriously difficult to ventilate  effectively because of their random pattern of occupancy. The time that the room is occupied and the number  of  occupants can vary significantly. How then can we design a ventilation system to cope with fluctuating demand?

A simple solution... and one that is even better

One simple method is to rely on a manual on/off switch and a speed control to alter the ventilation rate. The problem with such systems is the difficulty of matching the fan speed with the conditions and the number of occupants.  These  systems, moreover, are often left running in an empty room.  The result is usually one of two extremes: unhealthy stuffy conditions or too much ventilation, which is a waste of expensively heated or cooled air. The best solution is to fit a ventilation control system that will turn itself on and off and automatically adjust  the speed to match the level of occupancy.  Efficient fan and motor combinations are important, but it is much  more sensible and effective to switch off the fan or reduce the ventilation rate to match demand. Turning the fan down to half speed, for example, can cut the motor’s power consumption by up to 87 per cent. Add to this the savings that result from heating or cooling half the amount of make-up air, and the results can be staggering.

NuAire’s Smart Squrbo system
 

NuAire’s Smart Squrbo demand ventilation system incorporates a temperature sensor, an occupancy sensor and Vaisala's GMD20  carbon  dioxide transmitter. All these sensors are used to determine the level of ventilation necessary to keep the air fresh. Vaisala carbon dioxide transmitters were selected because of their  stability  and  long  life.

Stability minimizes the need for calibration and maintenance, helping to reduce the total operating costs of the system. The fan action is directly controlled by the sensors. When the occupancy sensor detects people in the room and the carbon dioxide level starts rising, the fan switches on, supplying the right amount of fresh air to the room. This prevents the rooms from becoming stuffy and provides  healthier conditions for the occupants. Since the  fan is used only when needed, this eliminates excess energy consumption. NuAire’s experiences with Vaisala instruments have been good. So far, we have installed ten  systems  with  Vaisala sensors,  and  they  have  measured up to our expectations. All the transmitters are working fine.

The article was first published in Vaisala News 148/1998/ Mike Fussell, NuAire Ltd.