Existing systems may already be in place to serve other parts of a premises and maybe these can be expanded. However we always prefer a system entirely dedicated to the facility we are constructing.

For the purpose of this exercise we have assumed a modern closed system using refrigeration gas as the cooling/heating medium with heat exchange to/from fresh air. Such systems are becoming quite sophisticated, able to provide both heating and cooling from one external unit.

Conditioned air
To counter heat produced within the room or lost/gained through the fabric we need to be able to cool and heat the space, as the heat load fluctuates.

We have an opportunity here to use the air handling devices shunned by us in the other protected areas: Computer Rooms, Server/Telecoms and Ops/Control Rooms.

Suspended ceiling mounted cassette air handling units provide an ideal means of silent distribution of conditioned, and collection of return, air throughout this type of facility.

Arranged in zones, the units can deal with differing levels of occupancy and densities of heat producing equipment.

Fresh air
This is extremely important. The last problem we want in such a room is a stuffy atmosphere promoting sleep!

The fact that a premises was built according to the Building Regulations, does not mean that a room will have sufficient fresh air available to it – for the purpose we wish to use that room. Building Regulations permit opening windows to be used as a means of providing the requisite fresh air. This is of no use for controlled environment situations – because of the pollution collected as soon as windows are opened.

A mechanical means of injecting fresh air into the room – without upsetting conditions within it, is required – see pitfalls.

Heat removed from the room by the air handling unit cooling coils is carried by pipework to externally mounted heat exchangers. Depending on the cooling medium used, these are referred to as condensing units, condensers, chillers or water towers.

They pass the air handling unit air heated cooling medium through an arrangement of tubes, over which air or water is passed to collect the heat, before the medium is returned to the air handling units for the cycle to be repeated.

The closer the units are located to their associated air handlers, the lower the pipework installation cost. There are limits to height and distance for their location.

These units need access to fresh air or a mains water supply. There are alternative means of achieving this, both outside and inside the building – usually the former.

All emit sound, and so consideration has to be taken regarding local environmental impact. There are means of reducing the sound levels to residentially acceptable levels.

Planning permission from relevant bodies may also be required.

Heating is best provided by the provision of heating elements inside the air handling equipment. An alternative, in the case of direct expansion cooling systems, is a reverse cycle valve – heat pump.

It is therefore only necessary to provide coarse filtration within the return air path in the air handling equipment and the fresh air source.

However, the fresh air intake needs to be checked to ensure fine particulate pollution is not likely from engine exhausts and the like.

Humidity control is not usually required. However in large installations it might be considered prudent to install humidification to reduce static build up. In which case, stand-alone units are available which produce water vapour by either boiling a body of water with a heater element or its surface by means of an electrode.

This is most important because whilst the regulatory fresh air might be available by opening windows, doing so would destroy the carefully controlled environment we are attempting to maintain.
We therefore need to introduce fresh air throughout the room in a controlled fashion.

The source needs to be fresh by definition, and forced. It is best introduced via the room air handling equipment in order to facilitate rapid dispersion.

Its volume needs to be taken into account when calculating the room heat load – for the comfort conditioning design.