Air intake louvres at most major hospitals lead into a larger supply air plenum from which multiple AHU intakes draw in the ambient air.
Health Technical Memorandum 03-01 Part B (HTM 03-01) recommends the maximum (12mm) and minimum (6mm) opening that should be used on insect mesh and it is this product that you will find immediately behind the weather louvre.
This insect mesh is not always easy to remove and that makes cleaning a little difficult. In one example, the mesh removal and reinstallation took at least 10 man hours which is a shameful waste of valuable labour resource.
Compliance issues mean that this task must be completed but with shortages of staff and other, more important PPM’s falling behind the waste of energy caused by blanket covering of vermin screens is the least of an Estate Managers problems.
Vermin screens add to the cost of running AHU plant which has been sized to cope with the combined resistance of louvre and mesh + a significant factor to allow for debris build up. Debris which should be cleaned on a regular basis to prevent additional resistance which causes fan motors to use more power.
The solution at this particular NHS Trust has been to completely remove the difficult to maintain mesh. Instead a RABScreen BHC air intake filter has been installed. It has a much lower resistance and a much higher particulate capture rate to prevent smaller insects (fruit flies, mosquitoes etc.) from entering the plenum. To ensure ease of maintenance a simple drop in framework was installed which allowed maintenance personnel to remove, vacuum and replace all panels within one hour.
The added bonus is that at 2.0m/s face velocity this new system only creates a resistance of 12.45 pascals so that the fans will draw higher volumes of cleaner air which will protect filters and reduce energy use.
