What is demand control?
Demand control (Dutch: vraagsturing) is a way of regulating the use of something in order to shift, reduce or increase that use (temporarily). In building services it mainly means that sensors and software decide whether a system runs, and how hard, based on actual need rather than a fixed setting or timetable.
Forms of demand control
- Technical (built in): sensors measure ambient conditions and control the system. For ventilation these are CO2 level, relative humidity or occupancy.
- Shifting in time: an appliance or charging point is switched on later, for example to avoid peak loads and grid congestion.
- Financial: price incentives, such as dynamic energy tariffs, move consumption to cheaper moments.
Demand-controlled ventilation
Ordinary mechanical ventilation runs at a fixed speed that the occupant switches by hand. With demand control:
- the fan speeds up when a CO2 sensor in a living room or bedroom measures a higher concentration (more people, sleeping with the door closed);
- a humidity sensor in the bathroom responds to showering and switches back by itself afterwards;
- the system runs low when nobody is home.
Benefits: better air quality when needed, and less fan energy and heat loss when not.
Tips
- Place CO2 sensors in habitable rooms, especially bedrooms; a sensor only at the ventilation unit measures mixed air and responds more slowly.
- Check whether your ventilation unit supports sensors. Many modern units have inputs for CO2 or humidity sensors; otherwise a replacement is needed.
- Keep air inlets and valves open and properly balanced; demand control cannot work if air cannot flow in.
- Budget from a few tens to a few hundred euros per sensor, depending on brand and type; a complete demand-controlled unit costs more.
Related terms
- Mechanical ventilation
- Balanced ventilation
- Natural ventilation
- CO2 detection
- Smart grid
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