Switching air conditioners with PIR occupancy sensors
Controlling the aircons with occupancy sensors can in many cases be done but it is technically a little bit challenging as there is no real standard way to do it. It depends very much on the type of aircon system and there are different interface options.
We have been receiving many inquiries about controlling aircon units with sensors recently and in the future we will document the possibilities more clearly (we also have a couple of ideas for customised products specifically for controlling aircon units).
In general, for aircon control you would choose the simplest sensor types which have no light measurement so that they will not switch off (unlike lighting control) when it is very bright as then usually cooling is required the most. So usually the PM/230V/5 or 5T or the PM/24V/5 MASTER (or 5T) would be the suggested sensor types.
In addition, the delay times should be on the longer side. I suggest a minimum of 10 minutes, not shorter.
Installation and possibilities depend a little on aircon systems type:
1.) Chilled water systems
In these systems one central chiller cools down water to around 4 degrees celsius or so and then this cold water is pumped around the building. In each are or room that is to be cooled there is a fan-coil unit in which the fan blows the room air across the coils (through which the cold water flows). The cold water supply to each fan coil unit is controlled by a valve which in turn is controlled by the room thermostat.
Some thermostats also have a control contact which you can use for turning them off or for setting back the setpoint (i.e. when the room is empty the thermostat would go up by a few degrees (e.g. from 21 to 26 degrees celsius). Sometimes customers prefer this behaviour over shutting down the aircon completely.
If there is no such input then shutting off the power to the fancoil unit (or air handling unit) with the sensor is also an option. How simple or complicated the wiring for this option is depends on the specific conditions.
2.) Small central systems
These are the ones described before. In these, one large evaporator creates cold air which is then divided into different ducts and then conducted to the different areas of the building. Each area will have an air outlet which can usually be opened or closed electrically by the thermostat in each area.
The sensor can shut off the air flow to an area.
Shutting off the air flow to one area will actually give you energy savings as the compressor will have to work less.
How and if the the vents can be controlled depends very much on the specific model and sytsems. Some vents will be "normally closed" if no power is applied to them so this type is quite suitable for sensor control (they open if the sensors gives them power and if open the thermostat controls the flow or open/close rythmn while the room is occupied).
3.) Multi-split systems
In this case one large outdoor unit feeds refrigerant to a several indoor evaporator units (usually one per area). So in this case the cold air is not divided into different air streams (ducts) but it is generated in each area individually.
So in this case the sensor could actually control the indoor unit per area. For this case, the information for the next item, "Single splits and window ACs" also applies
4.) Single Splits and Window ACs
These are also very popular for sensor control.
The challenge is that they do not behave in a uniform way when you cut the mains supply power (230V) to the aircon units.
When the power comes back on after a failure or when the sensor gives power to the aircon unit then
a.) some aircon units will automatically restart in the last mode of operation. These are immediately suitable for sensor control.
b.) Others will start in standby mode only and need to be activated manually to run again. The latter behaviour is typically not well accepted by the users of the room as you can imagine.
Finally, there are more and more systems in the market (even of single split type) which have a separate control input (usually voltage free contact) which is explicitly designed to be used with external sensors, timer switches, etc.
In this case you can often even choose if you want the aircon unit to turn off completely when the sensor switches of if you only want the thermostat to set back by a few degrees.
Which of the above applies, should be checked with the customer. We are happy to support you then to find the correct implementation.
Does this give you some clarification?
Over the nearer future we will also collect examples, photos and diagrams over the next weeks to turn this into a proper documentation.