Determining the size of your air conditioning system
Posted by Mike Gordon on 22 July 2015 12:22 PM

The effective output of an individual air conditioning unit or system may be given on the rating plate attached to the unit. It may also be stated in the operating and maintenance manual or from the manufacturer’s website. Alternatively, where the system is covered by a maintenance contract, the capacity should be known by the contractor and should be reported in the maintenance records they supply.

The guidelines below are an approximate indication of typical figures for installed capacity for various spaces and may help you determine whether your system is within the scope of the regulations. Cooling requirements depend on a wide range of circumstances, including the fabric, location and orientation of the building towards the sun, as well as the activities and the number of people in the building. Older systems are also likely to have higher rated outputs for a given floor area. Where more specific figures are needed these should be calculated taking account of the particular circumstances of the building and its use.

The guidelines below are for offices and shops. If it is not clear whether a building reaches the threshold the installed capacity of the system must be determined by appropriate inspection, calculation and enquiries. In other, more specialised, buildings, the wide range of factors which influence system capacity means that these systems should be determined by a suitably qualified person on a case by case basis if the information is not already available.

For larger systems, a central cooling system serving an office building of

2,000m2 is likely to be 250kW rated output. Cooling systems serving meeting rooms which may be used by large numbers of people, such as council chambers, may exceed the 250kW threshold for lower floor areas.