Taking control of the air supply
Luke Bigg of Waterloo Air Products explains the benefits of putting variable air volume (VAV) at the heart of a building’s air movement system.
Efficiency is the key to creating and maintaining good buildings. Everybody is busy, and budgets are tight in a competitive market, so it’s a matter of getting the most value out of the least resources.
When it comes to designing and installing air-movement systems, variable air volume (VAV) is growing in popularity because it offers efficiency across the whole life of the project.
VAV delivers the right volumes of cooled or heated air to aid the lowering or raising of room air temperature at the right time. Temperature and humidity are monitored via sensors connected to the air-handling unit (AHU). The AHU then controls the VAV to adjust air volume to help maintain an environment suited to the needs of the specific room. The technology is used to reduce wastage and keep running costs down.
Think of a school hall, which could be used for different purposes at different times of the day or year — and for different numbers of pupils. An assembly will bring together the entire school during the morning, but the hall will be used for smaller groups at other times. Even here, the amount of air required will vary massively between an active PE lesson and a sedentary gathering of the school.
In other words, it isn’t practical or economic to pump a consistent volume of air into the room, and that’s where VAV comes in. The system works behind the scenes to optimise airflow depending on occupancy and usage, which means a more efficient building. By choosing VAV for a new building from the start, the efficiency begins immediately.
A VAV system supports the original vision of the architect, giving the freedom to design ambitious buildings without worrying about the impact on airflow. It gives control to specifiers, who can recommend fully integrated and cost-effective air-movement systems. And it delivers reliable, all-year-round temperature to help those responsible for running the building.
Even though VAV technology has been around for a while, it is only in the past few years that specifying it has become more usual. This is partly to do with education. VAV is more widely taught to building engineers now than it was 10 or 20 years ago, and a new generation has entered the construction industry that is familiar and comfortable with using it. Alongside this, the ongoing development of the technology has made VAV more efficient and easier to install.
Like any air-movement system, getting VAV right means understanding what each room will be used for and who will be using it. The key is to keep the room comfortable regardless of the number of people occupying it, increasing the volume of cooled air as more people enter and temperature rises — all monitored using thermostats linked to the AHU.
Just as vital is to preserve the conditions in sensitive rooms where the temperature must be stable. In clinical environments such as operating theatres and laboratories, the flow of air must be optimised to keep conditions sterile and make sure that contaminants are circulated away from patients or experiments. A similar level of control is important in server rooms, where excess humidity or temperature can cause IT systems to fail.
Choosing VAV from the start of a project means that architects have more options when designing each room to meet specific needs. The temperature in rooms containing sensitive items can easily be controlled, so VAV is perfect for hospitals or scientific research facilities. But architects can also make a statement with big public spaces, safe in the knowledge that the VAV system will react quickly to match the volume of air to the volume of people. Due to these factors, VAV is ideal for any large building — offices, factories, schools or high-rise developments — which are occupied by varying numbers of people throughout the day and night.
Another benefit of integrating VAV into the building design in a project’s early stages means that specialist suppliers of air terminal devices can provide their expertise.
At Waterloo, we have long recognised the value of offering VAV alongside grilles, diffusers and other air-terminal devices. Offering a single source of supply simplifies procurement and means that we can work more effectively with architects and specifiers to devise the right systems.
The key to maximising efficiency from a VAV air-movement system is to work collaboratively as early in a project as possible. Once the right grilles or diffusers are selected — or bespoke products are engineered from scratch where required — they are set up with the appropriate size and shape of VAV unit, along with project specific settings.
Available in round or rectangular units, in a number of sizes, each of our VAV units has a flow sensor and a motorised damper, which are fitted in the ductwork and linked to the central building-management system (BMS). As the temperature or humidity changes, a signal is sent to the VAV unit, and the damper is opened or closed until the air flow is optimised.
Within each VAV unit, a building engineer can easily set their preferred range so that the VAV unit is always in line with the specific needs of the room.
Air movement is all about finding efficient ways to direct air where it is needed, regardless of the number of occupants in a room. VAV adds the ability to deliver air when it is needed, in a way that helps everybody involved in the creation and running of the building.
Luke Bigg, is test and development engineer with Waterloo Air Products.