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How to Cool a Small Server Room and Control Room Temperatures

If you do not have a purpose-built server room or data centre it can be difficult to control room temperatures and humidity. This time of year, our projects team are often asked to assist sites with small server rooms or computer rooms, whose temperatures will be expected to rise over the summer period and even more so during those occasional ‘heatwaves’ we have in the UK. So why is server room cooling and temperature control so important?

Server Room Size and Heat Containment

All electronic devices will generate heat. The greater the processing power of the microprocessor or central processing unit (CPU), and the workload being undertaken (server utilisation), the greater the amount of heat generated.

Computer and server manufacturers build cooling facilities into their hardware designs. An air-cooled server will have a heatsink and variable speed fans. Air is typically drawn in through the front of a computer or server case, passes over the CPUs and heatsink and exhausts through the rear. This flow of exhaust air leads to a Delta-T or temperature difference as it is also referred to in the HVAC industry, which can be up to 15⁰ higher at the rear of the server compared to the air intake.

In a data centre a heat containment system may be installed in the form of hot and cold-aisle containment. This prevents cold air from the cooling system mixing with the hot exhaust air from rear of the server racks installed. Containment improves cooling and energy efficiency.

In a small computer room or server room (2×2m or 3×2m) with only one or two server racks, containment is not a viable solution. There will be room size restrictions as well as budget. Yet the problem remains of how to ‘channel’ hot air away from a server rack and to cool the overall room ambient.

Portable Air Conditioners

Portable AC units should only be considered as a temporary solution to the problem of how to cool a computer or server room. Portable air conditioning units are easy to install and can supplement existing cooling arrangements i.e. during maintenance or service an existing air conditioner or to cover a short-term rise in room temperatures.

The three main downsides of using portable ac units include:

  1. Condenser Trays: as air conditioners cool, they remove moisture from the air and in a portable AC unit this is collected in a tray that must be emptied. In extreme circumstances this could be daily. If the condenser tray is not emptied, the air conditioning could stop working.
  2. Exhaust Piping: portable AC units must be connected to an exhaust tube to carry the heat removed from the computer room or server room to an are external to the building. A typical exhaust tube may be only 3-5m in length.
  3. Poor Energy Efficiency: the exhaust tube must be connected securely to a vent or window with adequate sealing to prevent warm air from leaking back into the cooled space. Portable AC units tend to cost more to run than fixed installation air conditioners due to sealing issues and their overall design.

Portable air conditioning should only be considered as a temporary solution. Manufacturer warranties tend to reflect the ‘temporary’ nature of most portable AC units. 12-24 is the norm compared to 5-7 years for an equivalent sized air conditioning system installed and maintained by a manufacturer certified engineer.

Air-Conditioned Server Racks

An alternative to a portable AC unit can be an air-conditioned server rack. This is server cabinet with a bolt-on or built-in air conditioner. Whilst this will cool the servers and storage devices built-into the rack, the heat still must be exhausted through some form of tubing or piping to the outside of the building and an external condenser. Air-conditioned server racks can be a viable solution in more extreme environments or where a fixed air conditioning system cannot be installed.

Fixed Installation Server Room Cooling Systems

The optimum solution to cool a small computer or server room is a wall mounted air conditioner. This will be connected via piping to an external condenser unit. The header unit will be installed in the room along with a wall mounted or hand-held (Wi-Fi) remote-control panel that can be used to set the required ambient temperature.

The AC unit may have a built-in interface to report alarm conditions using volt-free contacts (VFCs) or SNMP (simple network management protocol) over a local IP network.

Wall mounted is the ideal solution for a small computer or server room and works best when the air conditioning unit is placed above the rear of the server rack(s). Cool air then flows over the top of the rack(s) and drops to the front of the server for intake into the units. Warm air is expelled through the rear of the rack(s) and is drawn into the intake area of the air conditioner for cooling via the condenser circuit.

In larger server rooms and data centres with raised access floors, DX cooling and in-row units can be installed to provide the cooling required by a larger number of server racks. As with containment, this is a more expensive solution and one that can be avoided with a suitably sized wall mounted air conditioning system.

For added resilience, two (or more) wall mount air conditioners can be installed in an N+1, N+X arrangement. The air conditioners are sized so that if one fails the other can support the cooling load. During normal operation, the AC units will cycle with one in sleep mode and the other cooling the load. This practice improves energy efficiency.

Controlling Server Room Temperatures

The control unit for an air conditioner sets the ambient temperature that the unit is to achieve. How hard the air conditioner must work, and the energy used will depend upon several factors which our projects team will assess as part of a server room cooling site survey.

Server Room Design and Layout

A small computer room or server room may have originally started out as a storage area or have been created using partitioning in an office area.

From an airflow and cooling point of view one of the first things to inspect during a survey is the sealing of the room. If there is a door into and out of the room, is it shut with controlled access either via a lock, keypad, or access control?

Are there windows? Windows present a security concern and can also be opened in the belief that they can help airflow. Any window, especially south-facing can lead to solar gain issues heating up air in the room. Windows should be coated on the outside with reflective materials and ideally secured internally with bars or bricks, mortar, and plasterboard.
Doors should also be inspected to make sure that they fit their frames properly and do not contain vents. Are there any other vents within the room? If so, these may require further investigation and sealing.

Sealing may also be an issue if there is a suspended ceiling or raised access floor. The latter is less likely in a small computer or server room, but any misaligned tiles or broken tiles must be repositioned correctly or replaced.
Small computer and server rooms may tend to be used to store packing and other materials. These should be removed from the area as they represent a potential fire risk. A golden rule should be that if it is not needed as part of the IT network, then it should not be in the computer or server room.

Whilst it may not be necessary to carry out Room Integrity Testing (RIT) for fire and insurance purposes, a properly sealed room will help to improve the overall cooling and air flow.

Building and layout issues should be addressed and where necessary, a server room refurbishment project considered.

Server Rack Layout Blanking Panels

A server rack or cabinet is an ideal way to vertically stack IT servers, storage SANs and networking devices. Power protection systems can also be installed within a rack including rack mount UPS, UPS maintenance bypass switches, automatic transfer switches and PDUs.

Physical population of a server rack is important. Heat rises and so the more sensitive electronic and electrical devices should be near the bottom of a rack. This includes heavier component such as uninterruptible power supplies and their battery packs which could present a ‘toppling’ issue if placed higher up in a rack and extended out on a set of rack rails or shelf. The UPS batteries may also be sealed lead acid (SLA) which are temperature sensitive and need a 20-25⁰C ambient to prevent performance degradation.

If there are unpopulated front areas in a rack, these should be filled with blanking panels. Side panels should also be securely fitted as should the server rack front and rear doors. This practice helps cooling airflow efficiency (front to rear) and can help to prevent hot spots in the rack.

Server Room Air Conditioning

If there is an air conditioner already installed how is the IT equipment arranged in the room? Ideally a server rack should be used to vertically house all the IT devices. Not only does this help to organise and tidy up the space, but it also provides a more channelled airflow into and from the server rack to the air conditioner.

For best cooing practice a wall mount air conditioner is preferred. If there is a ceiling mounted AC unit this should not be directly over the server racks(s) to prevent moisture droplets failing into the rack(s) if there is an AC unit malfunction or problem. Incorrectly positioned floor standing AC units can be positioned incorrectly, leading to hot spots within the room.

Energy Efficiency

The more energy efficiency an electronic or electrical device, the less the energy wasted as heat. Almost all manufacturers of equipment for IT and general environments supply energy efficient devices.

IT servers and UPS systems are typically positioned high on an energy efficiency improvement program, but lighting and air conditioning should also be considered. LED lighting can reduce energy consumption within a server room by up to 30-40% compared to standard office or neon lighting.

Any improvement in energy efficiency will reduce the heat load placed on the air conditioning system.

Monitoring Server Room Temperature

An air conditioning system is a cybernetic system. It is a closed system that incorporates self-control in terms of thermostatic temperature control. But what happens when the air conditioning system is set incorrectly or malfunctions?

The installation of a suitable environmental monitoring solution in a computer room or server room provides immediate notification when temperature and other monitored environmental factors go outside of pre-set conditions.

A typical computer or server room monitoring system will have a temperature sensor and be able to provide alarm alerts via email and SMS text messages. On-premise software on the local network will provide quick access to historical data logs and a current state-of-play dashboard. This information may also be available over the internet via a secure HTTPS browser view.

Additional sensors are available for power availability, humidity, water leakage, smoke, fire, motion, door, and rack security. An environmental monitoring unit may also be able to pick up signal contact alarms from the local air conditioning system and report them.

With a 24/7 alarm notification system in place, it is easier to respond remotely to an event within a small computer or server room. Temperature related incidents, for example, can be immediately investigated to ensure that continued availability of the IT network and system. Sensors can also be placed within hot-spot areas within the room or server racks and cabinet heat-maps produced.


Data centre outages tend to make the headlines when there is a major incident and loss of service, be it an to an airline, bank or social media platform. Small computer and server room incidents are less reported for obvious reasons but their impact on their organisations can be just as significant to them. The majority of outages (36%) are due to power related incidents and these can have a more significant impact on a smaller computer or serve room whose air conditioning systems may not be backed-up by a local standby generator.

For more info on data centre outages:

It is relatively easy to control and monitor temperatures in a small computer or server room. The principles are like those used in a larger data centres and have similar features and levels of sophistication but without the large price tags. Air conditioners for a small computer or server room measuring 2×2 or 2×3m can be installed for under £2,000 and a typical monitoring system will cost less than £200.

The smaller the computer or server room the greater the need for cooling and temperature monitoring. In a confined space, temperatures can rise quickly (within a matter of minutes) to levels which can pose a fire risk to the room and building itself.

Having a suitably sized and installed air conditioner will provide adequate server room cooling. The addition of a temperature monitoring system will provide alarm notifications (email and SMS) if there are temperature or other environmental factors that could lead to system downtime and loss of service.

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