CCS - Castle Computer Suites Ltd.

Computer Rooms | Mechanical Services

Air Conditioning Systems

Generally speaking, smaller computer rooms/heat loads are most economically cooled using direct expansion. This is the system that the domestic refrigerator uses.

Chilled water systems become economic only for larger loads. Their heat exchange may be bypassing the water through water towers, or bypassing it over coils cooled by direct expansion or a combination of both. Additional efficiency is obtained by adding Glycol to the circulating water in closed systems.

Air Handling Units

Although a central plant arrangement located outside the room can be specially manufactured to suit, a less expensive and more versatile option is to purchase specialised modular units and stand them inside the room.

An air handling unit will contain: Cooling coils, scroll fans, heating elements/banks, condensate tray, drain and controls. It may also contain a humidifier and compressor (in the case of direct expansion).

They can be arranged so that conditioned air is supplied through their bases, tops or face panels. Return air can be arranged to be collected from similar positions – but not the same top or bottom. Delivery from the top of the face panels and collection through a lower portion is available – called point supply and return.

However, the heat producing computer equipment housed inside the room obstructs the path of air and so we use the floor and ceiling voids as clear plenums to deliver and collect it.

Where there is sufficient room height, as indicated in the sketch above, we do not need to use the ceiling void for return air collection, where we are supplying the cool air via the floor void. This is because there is sufficient unimpeded space at high level.

Where the room height is limited, we may connect the air handling unit to the ceiling void and use it for return air purposes. This means that perforated ceiling tiles are required to collect the return air from the room.
Where the computer equipment has a problem withstanding the thermal shock of cold conditioned air entering it via the floor void, we simply reverse the design for the airflow and deliver the conditioned air from the suspended ceiling void, or at high level within the room.

An in-room modular air handling unit either sits on top of the raised modular floor – with appropriate cut-outs beneath it, or on a purpose made steel plinth, with the flooring built up to it.

When in operation each air handling unit takes and commands its own territory. If it stops, then others take over the load. The units are positioned such that they are working together, rather than fighting one another!

We always provide at least one separate unit within the room, to act as a standby in the event of another failing.

The standby unit can either be left running or automatically operated cyclically with the other units.

Heat Exchangers

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

They pass the 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

Whilst the air conditioning system’s prime job is to remove the heat produced by the computer equipment, building fabric, lighting, fan and solar gains etc. it also requires a heating facility.

This is because the returned air from the room is passed over the cooling coils inside the air handler and reduced in temperature to a level at which the air releases the moisture it contains – condensate. Once this has been done, the air needs to be warmed back to the temperature required to maintain room conditions – usually 20 degrees C +/- 1 degree.

It is worth mentioning that every effort is made to provide an even temperature throughout the room – at mid height. It is this constant temperature that the computer equipment/engineers require and which can only be achieved by circulating the air at a rate of between 30 and 50 room changes per hour. The resultant turbulence is uncomfortable for long-term human occupancy.

We therefore consider desk positions inside a computer room to be entirely inappropriate.

Heating is provided inside the air handling unit, after the cooling coils. The medium may be electrical, hot water or steam, usually electrical.

Filtration

The computer room environment requires cleanliness because particulate deposits can cause damage to some computer components.

The computer manufacturers’ environmental engineers determine the degree of filtration. It will depend on the construction of the computer circuitry and the filtration safeguards built into their equipment.

Varying filtration levels are standard and filter banks readily inserted in the air handling units. Problems arise when protecting from the finest particulate pollution – which happens to be lamp black – carbon – emitted from diesel engine exhausts. Here we need to insert high efficiency carbon filters – which are expensive.

Humidification

A computer room environment requires maintenance of a humidity level of 50% +/- 5%. This is a standard that relates back to the days of paper tape and card readers, when the medium was required to be regulated in size. Nowadays we use it as a safeguard against the build-up of static electricity.

Humidifiers mounted inside the air handling units, or as separate humidifying units achieve it. Both work by simply producing steam and injecting it into the room air – where it immediately diffuses throughout the room. Control is by means of a humidistat.

Boiling a container of water – by electricity or heating element, usually produces the steam. Spinning discs in the path of a fine spray of water used to be used in central plant systems – in case anyone still has one and feels left out!

Fresh Air

We define a computer room as a machine room. Human occupancy is considered to be occasional and temporary – operators and installation/service/maintenance engineers. As such there is no requirement for fresh air.

However, we need to discourage the ingress of dirt pollution from outside the room, which might be drawn in by low pressure zones caused by the rapidly circulating air or through the entrance doors.

We achieve this by pressurizing the room – with air. The source is usually taken outside the premises. Taking it from inside could affect conditions in that area because of the negative pressure produced.

We cannot simply pump fresh air into the computer room without treating it, because it is at the wrong temperature and may be polluted. We therefore introduce the air via an entrainment unit, which may adjust its temperature (depends on size of room etc. - not always required) and filters it before it enters the room.

We introduce the fresh air near to the air handlers so that it is quickly conditioned before being recycled.

Call 01938 552 975 Email ccs@computer-rooms.com