Essential HVAC Guide – Air Conditioning Control Systems

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People often talk about getting some form of temperature control included with their reverse cycle ducted air conditioning system. So what are the different forms of air conditioning temperature control and how do they work? We will look at the common types of air conditioning temperature control systems and how they work below.

Basic Air Conditioning Controller

The basic controller that comes with your reverse cycle air conditioning system comes with a thermostat that reads the air conditioners temperature. Usually this temperature is read either from the controller itself or more commonly inside the return air box of the unit that sits inside the roof space.

If the temperature is read inside the return air box, it is sometimes not an accurate representation of the temperature in the room. The room itself may be quite cold but by the time the air is recirculated to the return air box it may have warmed up significantly which means the air conditioner will keep running (e.g. the controller in the living room is set to 22 degrees but once the air reaches the return air box it has heated back up to 30 degrees, which in turn causes the air conditioner to keep running).

In this situation, the unit will keep running even though people are becoming cold. There are however two options to counteract this. Firstly, increasing the temperature of the controls will cause the unit to cycle off quicker. It needs to be remembered that the temperature set on the controller is usually not accurate, instead it works as a scale (i.e. if you set to 22 degrees, it does not necessarily mean the room will cool to 22 degrees).

Secondly, some people put a ducted fixed constant in their hallway near the return air grille. This constant as it name suggests is always on. This allows the conditioned air to return easily back up to the return air box of the unit, which helps the unit cycle off. In this instance if you were running just your bedrooms that were all a long way from the return air, the air from the rooms would heat up too much before getting back to the return air. The fixed constant however would bleed air directly back into the grille which will make the unit cycle off and ultimately save you money in running costs.

VAV Air Conditioning Controller

VAV stands for Variable Air Volume system. This is where the zone motors for your reverse cycle ducted air conditioning system allow some temperature control to the rooms you are in.

A zone is basically a series of blades that close the ductwork if you want to stop the air to a room. For instance, if you turn off your bedroom, the blades close restricting the air flow from proceeding down the ductwork and into your bedroom. Likewise, when you want air, the blades fully open and air starts to flow out the diffuser and into your room.

VAV systems work differently however. Instead of the blades simply opening or closing, they can constantly adjust what percentage they are open. This constant adjustment lets you control the amount of airflow you get into a room which ultimately controls the temperature of the room.

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