HVAC Essentials: Air Conditioning Control Systems

People frequently discuss incorporating temperature control into their reverse-cycle ducted air conditioning system. What are the various types of temperature control for air conditioning, and how do they operate? We will examine the common types of temperature control systems for air conditioning and their operation below.

Standard Air Conditioning Control

The basic controller included with your reverse cycle AC maintenance system includes a thermostat that reads the temperature of the air conditioner. Typically, this temperature is read from either the controller or, more commonly, the return air box of the unit located in the attic.

If the temperature is measured within the return air box, it is not always an accurate representation of the room's temperature. The room may be quite cool, but by the time the air is recirculated to the return air box, it may have significantly warmed up, causing the air conditioner to continue to operate (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 circumstance, the unit will continue to operate despite the fact that people are becoming cold. There are however two possible countermeasures. Increasing the temperature of the controls will accelerate the unit's shutdown cycle. It is important to keep in mind that the temperature set on the controller is typically not accurate; rather, it serves 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 individuals install a ducted constant near the return air grille in their hallway. As its name implies, this constant is always on. This facilitates the return of conditioned air to the unit's return air box, allowing the unit to shut down. In this case, if you were to run only the bedrooms, which are located far from the return air, the air from the rooms would heat up excessively before returning to the return air. However, the fixed constant would bleed air directly back into the grille, causing the unit to cycle off and saving you money on operating costs.

Controller for VAV Air-Conditioning

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

A zone is essentially a series of blades that close the ductwork in order to prevent air from entering a room. When you turn off your bedroom, for instance, the blades close, preventing air from travelling through the ductwork and into your bedroom. Similarly, when air is desired, the blades fully open and air begins to flow from the diffuser into the room.

However, VAV systems operate differently. Instead of simply opening or closing, the blades can continuously adjust their percentage of openness. This constant adjustment allows you to control the amount of airflow into a room, which ultimately regulates the room's temperature.

For instance, if your room is approximately 30 degrees and you set your VAV controller (which is located in the room) to 22 degrees, air would rush in to attempt to cool it. Once the room temperature reaches approximately 22 degrees, the blades will begin to close to restrict airflow in order to maintain that temperature. As soon as the room temperature begins to rise above 22 degrees, the blades will reopen to allow additional airflow in order to return it to 22 degrees. This allows the VAV system to maintain a room's temperature.

The VAV system is one of the most fundamental forms of temperature control for air conditioning. It is an inexpensive method for adding temperature control to a few rooms (say your master bedroom, office and living room for instance).

This system is not comparable to VRV. Multiple head units (wall splits) are powered by a single large outdoor compressor in VRV air conditioning systems.

Full Temperature Control of the Air Conditioner

Fully ducted temperature control operates similarly to the VAV system described previously. The temperature is read by a controller in each room, causing the blades to open or close to allow the correct airflow to heat or cool the room.

The difference between partial and full temperature control is that the entire house, as opposed to just a few rooms, is controlled by temperature. As a result, the fully temperature-controlled air conditioning system will provide the greatest level of comfort, as individuals will be able to set their preferred temperatures for their own living spaces.

Due to their energy savings, these temperature-controlled air conditioning systems are also more economical and cheaper to operate than standard systems. This is because once the rooms reach the desired temperature, they can be easily turned off, allowing the unit to cycle off and saving the owner money on operating costs.

Why Choose an Air Conditioning System with Temperature Control? 

Essentially, air conditioning temperature control permits each user to set the desired temperature. People are diverse and frequently desire varying temperatures in their living environments. Other factors, such as the heat load from devices and people, the individual's clothing, and which side of the house the sun is on, also contribute to determining the optimal temperature for a room. Temperature control systems, on the other hand, circumvent these issues by granting each person control over their own environment.

These systems are unable to perform separate cooling and heating operations. If the air conditioner is set to the cooling mode, it can only cool the space. If someone desires heating in one room and cooling in another, the air conditioner will not be able to accommodate both needs.

I hope this clarifies some of your questions about reverse cycle (refrigerate) air conditioning systems' temperature control systems. For additional information, speak with the manufacturer and ask as many questions as possible.