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Air Conditioning for Cooling Server Rooms


Server rooms and indeed any enclosed environment where a lot of computers are in use are temperature critical environments. All computer equipment has a maximum operating temperature above which efficiency drops or thermal shut-down occurs so it is critical to keep server rooms at a stable temperature. Humidity is also an issue and it is important to control this at the same time.

In reality this means providing some form of air conditioning to the room to maintain a constant temperature irrespective of outside ambient conditions and to dehumidify the air to remove excess humidity as well.


Any air conditioning system used in a server room must be large enough capacity to cope with removing the heat generation from the computer equipment but also the natural heat energy from the room itself. Furthermore, as the equipment is operational 24 hours a day, 7 days a week, the air conditioner must be a continuously rated unit designed for the application, not just a simple light domestic unit designed for infrequent use.


When choosing a suitable air conditioner there are basically two types on the market, portable (or monoblock air conditioners as they are also called) and fixed split air conditioning systems.


Portable air conditioning units are, as their name suggests, single self contained units that are simply placed in the server room. They extract the heat (and most also take the excess humidity) down a flexible tumble-drier type hose that is typically 125mm in diameter. The open end of this hose needs to vent to outside the room either by opening a window or making a vent aperture through the wall. All portables are the same – you CANNOT get portables that are totally self contained without a vent pipe – the heat HAS to be ducted somewhere. The flexible hose has a maximum length of typically 2 to 2.5 metres. This cannot be extended as the hose is radiating heat back into the room and the longer the hose the more heat is radiated straight back into the room you are trying to cool thus lowering the efficiency of cooling. Beyond a certain length you also get back pressure build up in the machines stopping the hot air escaping. This causes thermal cut-outs in the machines to trip stopping the cooling process. Because you are exhausting hot air down the vent hose fresh air has to be able to enter the room from elsewhere to balance this through a vent/door/window.


Operationally, portables are largely the same as a fixed system – you get fully automatic thermostatic control of temperature which can be adjusted up and down to suit the application. Generally, however, portable air conditioners do not have sophisticated timers.

Fixed air conditioners are generally two part systems. Inside the server room a high wall unit is mounted. This is connected by an umbilical cord carrying the refrigerant and power to an outside unit. These are generally a bit quieter in operation, and are more efficient. The indoor unit simply re-circulates the same air so there is no need for external ventilation supplies – this makes the units cool more efficiently. The outdoor unit is typically mounted on the ground or up on wall brackets. Self install systems are available which have a pre-charged refrigerant umbilical with a quick coupling connector to join the indoor and outdoor units together. Maximum length of the umbilical is typically 4-5 metres and this cannot be extended. If you need a longer run than this then you will have to have the air conditioner professionally installed (it I against the law to install any air conditioning system that requires the venting of refrigerant pipes to the atmosphere – you HAVE to use an approved contractor in the same way as you use a CORGI registered installer for gas).


Self-install air conditioning units come with a full featured remote control allowing the units to turn on and off at certain time of the day if required as well as fully automatic control of temperature.


DIO will be pleased to offer any advice to customers with server room air conditioning applications. We can calculate cooling requirements, advise on installation and supply the recommended portable or fixed air conditioner to suit your application and budget.