Relacing business-critical air-conditioning equipment without interrupting vital functions


The data hall had four chilled water, close control CRAC (computer room air-conditioning) units, with a total duty of 240kW, supported by two ageing R22 chillers. The client wanted to replace these with new run and standby chillers, with free cooling, but as data hall provides services to the company and a number of clients, switching everything off to make the changes was out of the question.


We decided to support the data hall with temporary air conditioning while the work was undertaken in stages. The first step was to record the existing room performance, so our temporary cooling solution replicated the existing environment.

Over a 48-hour period we captured the room temperature, return air temperature at each CRAC, sub-floor supply air temperature at each CRAC, air flow, and temperatures within specific racks,.

We used this information to specify the temporary cooling of two external run and standby chillers, each with the capacity to support the room. The chillers would support a dual air-handling unit, with two run and standby generators providing the power.

The supply and return ductwork would run from the air handlers into the room at high level, terminating at the top return section of the internal CRAC units. The CRAC fans would run and take the temporary cooled air as return air from the room and discharge it into the floor void, ensuring the existing air distribution and balancing of the room would be unaffected.

The temporary system incorporated a building management system that interfaced with the existing site BMS, allowing it to be physically checked every four hours. Our solution also covered the data hall’s physical security, access to the IT equipment, along with the fire detection and suppression system.

With the existing chillers operational, we undertook an initial set-up of the temporary plant independent of the data hall to check the plant, changeover and monitoring systems were all working optimally. Following this successful test, the temporary cooling systems went into operation in the data hall.

The chilled water service to each CRAC unit was isolated and the temporary cooling set to match the figures recorded in the initial room analysis. The complete system was again function-tested under load; the temporary cooling was left to support the room for 48 hours, with the existing chillers still available, to prove the system.

Throughout this process the room was monitored and conditions recorded in the same way as the initial room analysis to ensure the performance of the temporary cooling matched the fixed system. Finally, the temporary cooling was signed off to enable the replacement works to commence.


With the new chillers proven, the temporary cooling system was carefully disassembled and removed from the site, without any disruption to the normal function of the IT equipment within the data hall – an operation that took considerably less time than planning and implementing the temporary cooling solution.