When choosing a residential ducted HVAC design, you have the option between different air-handling configurations. There are two types: constant air volume (CAV) or variable air volume/flow (VAV/VAF). VAV air conditioning systems are variable systems, which means they have the ability to accommodate for the difference in temperatures between rooms, with a ducted system in place.
House orientation: understanding heating and cooling with VAV air conditioning
Let’s start by looking at how VAV air conditioning works. Every house is oriented in a certain way, facing North, East, South or West. Because the sun rises in the East and sets in the West, the orientation of your home will affect how much sunlight (and therefore heat) each room is exposed to and how warm it gets during the day.
With a ducted system, the circulated air is sourced by the indoor unit in the roof or sub-floor space. Ducts are positioned for individual rooms, with inlets leading into each room from which the cool air is emitted. There needs to be a balance between the amount of air going into each room to compensate for the heat load that forms as the sun moves around the house during the day.
When it comes to heating the rooms, there are other considerations. Let’s look at a cold ground floor room in a house that faces South East, as an example. In summer, the amount of cold air from the air conditioner that this room is going to need to control the climate at a comfortable 24 degrees will be minimal. However, in winter, the room will be icy, so to warm it up to 24 degrees, you’re going to need substantially more air coming into the room.
How air balancing works
The discrepancy between how much air you need to cool or heat a room is one of the significant limitations of ducted systems. One way we can assist is by performing an ‘air balance’. We place dampers in the roof, which allows us to change the settings to adjust the amount of air that goes into each room.
Another option is to install a VAV air conditioning controller like Daikin’s new linear AirHub. It is connected to dampers that you use to control the air, but these have motors on them. This allows you to set the temperature in each room or zone individually via a wireless temperature sensor. (The sensors have individual batteries that last about 18 months.)
The sensors send a temperature reading back to the central controller, and the controller adjusts the damper in the ceiling accordingly. It responds by providing more air or less air to keep the temperature within two degrees of the main controller’s set point.
This system automatically adjusts as the temperatures change throughout the seasons, and the sun rises and sets daily. If this was installed in the ‘cold’ house we discussed earlier, the damper would automatically ensure that much more air goes in there when running on the heating cycle to keep that temperature where it needs to be. Conversely, it will wind it right back in summer because it doesn’t need so much air. This is why they are referred to as ‘variable air volumes’.
How a damper works
A damper is a type of barrel, all sized with different diameters, with most being about 500mm long. Dampers are placed in the middle of a duct run. Some have motors that run back to the controller, while others are set manually.
The motor opens and closes the damper in 5-degree increments with the option of 90 degrees of swing. Inside the barrel, the damper contains a round bit of metal, which keeps it wide open under normal circumstances. It would be at 90 degrees to the air coming in and offers no resistance. The controller can send a signal to the damper motor and shut it in 5-degree increments to slow the airflow.
A damper can be installed on an existing ducted air conditioning system, but it’s preferable to have them placed in the duct during the initial installation. The price of a VAV air conditioning system will depend on the number of zones you have (you can have up to eight zones). A four-zone kit would cost about $1,500, for example.
Get the temperature right with VAV air conditioning!
If you don’t achieve comfortable climate control with your existing air conditioning system, chat with us about installing a VAV controller or damper. If you are installing a new ducted air conditioner, ask us about the benefits of variable air control.