Office air con sizing calculation

If a workplace becomes too hot then staff effciency will be reduced. There are also health concerns as in extreme temperatures there is a risk of serious fatigue or heat stroke. Whilst British legislation does not set a maximum working temperature, it is interesting that the World Health Organisation recommends a maximum air temperature of 75°F/24°C for workers to work comfortably.

Uncomfortable levels of heat are more likely to cause accidents because it lowers concentration levels.

Putting aside the health and safety implications of having a hot working environment, by installing air conditioning the workplace becomes a much nicer place to spend a considerable part of your day-to-day life.

Air conditioner size calculation
In order to calculate the size of air conditioner that you require you will need to know:

The floor area of the room
The size and position of the windows
The number of occupants (if any)
The heat generated by the equipment in watts
The heat generated by the lights in watts

Once you have this information perform the following calculation:

Room area (length in m x width in m) x 300
Length (m) x width (m) of south facing window x 870
Length (m) x width (m) of north facing window x 165
(if there are no blinds on the windows multiply windows results by 1.5, also if you are in the southern hemisphere reverse these conversion factors so a south facing is x 165 and a north facing is 870))
Number of occupants x 400
Wattage for all equipment, e.g. computers, faxes, printers, etc x 3
(the wattage for equipment is based on maximum power consumption)
Lighting wattage x 4.25

Add all your results together and divide by 3412. This is the size of air conditioner you require in kW.

Office air conditioning issues

- Portable air conditioners are suitable for areas up to 38m2. Alternatively, portables are ideal for spot cooling certain areas within an office. However, for large offices and areas that require very quiet conditions, split systems should be installed.

- If you are using portable air conditioners and are not near a window or door, then it is often possible to vent the exhaust hose up through a suspended ceiling system. The tiles can be easily pushed up or to the side.

- If you are going to install a wall-mounted split system then this will involve installing a fan unit in the room to be cooled and an external unit on an outside wall. Most regions in the UK do not require you to obtain planning permission for this type of installation but some do. You will need to check with your local council if you are unsure

- Always try to install the inside fan unit of a split system on an external wall as it removes the need to run piping along walls and can make condensate removal much easier as a condensate pump may not be required - a gravity drain can be used instead.

- When considering the positioning of a split system, consider how the air flow will effect the people positioned closest to it. Being situated directly under a unit may be uncomfortable. Also, if you have a long area always try to have the air flow travelling down the length of the room rather than across.

- Air conditioners will produce condensation internally on the cold surfaces of the unit. In portables this is dealt with either by pumping the moisture out of the vent hose, by incorporating an internal water tank that you will need to empty or through plumbing the unit in to the drain. In wall-mounted and through-the-wall systems, condensation is automatically drained outside of the building. On hot days this can be up to five litres.

- An air conditioner will need servicing every six months to maintain efficient operation.

- Many air conditioners can also heat making them useful in the winter as well as in the summer.