Our customer instigated this project upon recommendation gained from an FEL Group risk analysis report. The report highlighted single point of failure potential at this business critical site. The upgrade initiated the need to provide true N+1 cooling to the technical space.

The site comprises of one main technical space that is currently fully populated with IT server cabinets. The technical space is very restricted for any future growth and there is simply no floor space for any additional cooling inside the same physical confines.

The internal wall space is very congested leaving no solution possible for any additional AHU around the perimeter. Maintaining the customers room build standards meant “InRow” type cooling was also unsuitable due to inadequate aisle clearances available from the existing IT equipment.



Providing true N+1 cooling to the technical space


International television & telecommunications company


Grimsby, North East Lincolnshire


8 Weeks

The existing air conditioning system comprised of two externally mounted air handling units with conditioned air delivered via ductwork into the IT suite and subsequently distributed by means of two separate textile duct arrangements.

This maintained even and well-regulated conditions throughout the room, but the conditions were dependent upon both of the air handling units running simultaneously at all times. Therefore, not providing N+1 cooling to the room.

Given this scenario, should either of the AHU’s fail, the respective half of the technical suite would have no cooling, leading to potential overheating/hot spots causing major technical issues, ultimately leading to server failure/outages.

Our first consideration was to seek a solution to connect the two independent textile ducts together, with a view of distributing the air from just one air handling unit in the event of catastrophic failure to the other AHU.

This could have been achieved with a modification encompassing a common header duct, enabling the available air to be evenly supplied throughout the whole room leaving no potential hot spots. After careful calculation and design it was found that just one air handling unit did not have the capacity to achieve useful air distribution.

Moreover, a single AHU in isolation did not entirely meet the overall cooling requirement, therefore this option was discarded.

In view of this, the new and final solution was proposed to add a third air handling unit, similar to the exiting two and replace the air distribution ductwork with one common system. To accommodate this third air handling unit, one of the existing air handling units was relocated.

The new air distribution scheme comprised of a new rigid supply air header external to the building. This was fed from all three AHU’s via motorised backdraught dampers. To keep the apertures through the wall to an acceptable size and enable the ductwork to be accommodated in the ceiling space of the IT suite, the air from this header entered the room via four branches feeding the newly proposed secondary header.

This new textile supply air secondary header was mounted inside the conditioned space. From this, eight branch ducts were arranged to distribute the air directly onto the IT equipment as required.

These branch ducts were all fitted with 30% of additional high velocity air nozzles to enable better commissioning permutations, for the supply air direction achieved by manually plugging the nozzles not required.

An optimisation measure

Furthermore, a new rigid return air header external to the building was installed and arranged to pick up the existing return air apertures, through the external wall and return it to all three air handling units. This scheme takes advantage of direct free-cooling whenever the ambient air temperature permits, allowing energy savings.

It also provides genuine N+1 cooling redundancy to the whole site. There is now sufficient cooling capacity to accommodate the IT load and existing hot spots were eradicated.

The potential to increase the overall useful cooling capacity was increased to accommodate future growth and there remains the potential to introduce cold aisle containment in the next phase of energy reduction measures.