Terry Farthing, head of communications at Trox UK, explains the importance of good air distribution and two new developments which could affect the future market
ROOM air movement is critical to comfort levels. Good air distribution should be draught-free and include a good mixing of air so an even temperature is produced throughout the space. It should also include low air velocities so that the entire space is neutral to the occupants.
In other words they should not even notice the air conditioning system is there.
Conversely poor air distribution creates draughts or high temperature gradients and gets the occupants complaining about comfort levels. How often do people talk about the air conditioning system not working properly when what they really mean is that the grille or diffuser has been poorly selected? Yes, a simple diffuser costing less than £30 can condemn the entire ac system worth millions of pounds if air distribution engineering has not been employed.
All too often, particularly on the smaller project, the contractor chooses the cheapest products available which are mostly imports sold through distributors and not well supported by design advice.
They are sold on the basis of cheap commodity products off-the-shelf and are usually simply filling a hole in the ceiling where the ducting terminates. Not ac engineering or air distribution engineering at its best.
I often make the distinction between grille and diffuser manufacturers and air distribution engineers. As you can probably guess Trox falls into the second category since our air distribution performance figures are backed by our own test laboratories and supported by design advice, which seems to come into its own on the larger projects.
On the larger projects, the consulting engineer is more liable to produce a detailed schedule providing specific air distribution performance criteria that must be met. The ability of manufacturers to demonstrate room air conditions via a mock-up is becoming an increasing consideration.
Sophisticated computer analysis such as CFD (computational fluid dynamics) can relatively quickly look at a wide range of variants. However they cannot accurately predict the velocities that will exist in a room in specific circumstances and that is why there is no substitute for real live testing.
Clearly not every job is big enough to warrant this type of testing but even in relatively standard applications diffuser performance data supported by such test facilities is a vital consideration.
Many new ideas and concepts have been effectively introduced to the market place as a result of this investment in r&d. Two such concepts are integrated service modules - ISM - and VAV fan coil systems.
With the ISM we looked at the chilled beam market to see if any factors could be used to influence innovations with grilles and diffusers.
Service integration
The major driver in the beam market has been multi service chilled beams - the main reason being the integration of all the services into one module.
This integration need not be restricted to chilled beams only. Integrated service modules (ISM) include the air distribution devices, lighting and other components forming a complete prefabricated assembly installed into the ceiling. The ISM system has already been used on a few projects.
This multi-service approach to air distribution could be extended to most fan coil systems since there are a number of interesting benefits. The multi service approach means that the air distribution and other components can be designed to give a high quality aesthetic appearance.
It also gives the architect more freedom to design and integrate the air distribution and to achieve the best overall finish. The ISMs are pre-fabricated and assembled in the factory and delivered to site as a composite unit. This pre-fabrication within a controlled factory environment gives improved quality and reduces installation time.
Another interesting development potentially affecting the air distribution market is the introduction of variable air volume (VAV) fan coil units.
One very serious consideration with VAV fan coils is that with standard diffusers there is a risk that the air will dump below, say, 60% of maximum. With conventional VAV, the risk of dumping was a major concern for many designers.
Anti-dumping devices
For VAV FCU to succeed, this risk needs to be eradicated either through a thorough review of each diffuser's performance or by utilising anti-dumping devices such as the Varyset plenum.
This is a very simple device comprising a segmented plenum box and counter-balanced air-operated damper. Note the damper covers only 2⁄3 of the spigot area.
At 100% air flow the damper is fully open and air can flow into the plenum box as though it were a conventional unit. But as the air flow reduces so the damper closes, providing constant velocity to part of the diffuser which maintains the coanda effect.
As VAV fan coils become more popular this will drive the market to a more systemised approach and enforce the importance of good air distribution engineering.
So next time you are feeling uncomfortable don't blame the ac system, get the air distribution checked out.
Trox UK
01842 754545