Brands
- Rack-Supported
- Free-Standing/Floor Supported
- Rack-Supported
- Free-Standing/Floor Supported
- Ceiling Hung
The purpose of both hot and cold aisle containment (aka HAC/CAC) is to separate cold and hot air, increase efficiency and reduce hot spots.
There is a base power requirement to run a cooling system, not just the AHU’s in the white space but also the heat rejection system (i.e. taking the heat away from the AHU’s and, in most cases, putting it into the atmosphere). To minimise this cost, the aim is to maximise the Delta T so the difference between the supply and return temperatures.
Let’s just take a quick look at what preceded air containment.
The typical set-up would be a room with AHU’s around the perimeter delivering cold air to rows of racks via perforated tiles in the raised access floor. The racks would be set-up in a hot aisle/cold aisle configuration (fronts facing fronts and rears facing rears) with the AHU’s usually aligned with the hot aisle to minimise the return path for the hot air as shown below.
The issue was that the cold air didn’t evenly distribute across the room, with underfloor obstructions often making this worse, which restricted the placement of IT equipment and the hot air would always mix with the cold air before returning to the AHU’s lowering the Delta T meaning poor efficiency.
In rooms where the cold air is delivered under a raised access floor and through perforated tiles, the retrofit choice would be cold aisle containment. However, it’s recommended to have the airflow to the aisle checked before sealing it with a lid and doors – it must at least deliver the airflow required by the IT equipment in the racks!
In new rooms with slab floors and perimeter AHU’s (often at one end of the room only behind a louvred wall), HAC is used which acts as a chimney for the whole aisle of racks, the hot air then travels above the suspending ceiling back to the perimeter AHU’s. An alternative to this is chimney racks which can be added/removed individually.
With the exception of RDHx's, if using air-cooling as the sole method of cooling, the only way to achieve high efficiency/sustainability is to use CAC/HAC.
However, if CAC is to be retrofitted to an existing room, it’s essential to work out if the perforated tiles in each aisle can deliver the combined airflow required by the IT equipment you intend to put in those two rows of racks. At a minimum, basic measurements using a balometer should be taken but for rooms without a traditional hot aisle/cold aisle set-up with the AHU’s aligned with the hot aisle it would be safer to get a CFD study carried-out which could yield further OpEx savings as well as lowering risk.
If you need help with this, please contact us for further advice.