I have recently written about the relationship of CFM and cooling.
Most of the arguments in the industry about using slab floor instead of raised floor are effectively cooling higher density payloads beyond 4kW/rack. And that is a very low payload in today’s context.
The picture on the left is an example of a data center on slab floor (this is Sun’s Santa Clara data center). The theory behind cooling such a facility is to bring the cooling closer to the heat source and deliver it horizontally (row-based) or vertically (rack-based), instead of distributing over the sub-floor.
Lets look at what are the limitations of raised floors.
- Raised floor design makes it difficult to maintain an even and predictable server temperatures across the facility to support a heterogeneous mix of payloads and high density payloads. There are multiple factors that will limit the effectiveness and efficiency of cooling in a raised floor facility such as leakages, blockages at the sub-floor, etc.
- From a capital investment perspective, to design and build a facility with raised floor to support higher densities payload will require a much higher – and more expensive build – in order to maintain adequate CFM, pressure, etc. i.e. Building a 1m height raised floor is more costlier than a 500mm height raised floor.
- Higher density raised floors requires much more careful designs through possibly use of CFD modeling, therefore, increasing design costs.
- For fire protection, suppression strategy is generally focused on the zones which are isolated in that facility and putting in place sufficient capacity of clean agent as a suppression medium to extinguish a fire in that zone (should there be a need to). Therefore, with a raised floor, you instantly double the number of zones you must monitor, and deploy fire suppression system at.
- In terms of maintenance, the data center is a facility to house IT equipment to support the business. Hence, it is essential to maintain the facility to ensure that our IT equipment can run reliably and safely. Unfortunately, in most cases, unless there is a disciplined regime of cleaning the subfloor area, there will eventually be collection of dirt, dust, debris beneath. Pollutants and contaminants from such unwanted collection will lead to higher risk of failure. I once had a customer (no names) who had 24 hard disks crashed on the same day. After some investigation and root cause analysis, we found that they were using some insulation material lining the bottom of the subfloor and part of this material had ruptured, exposing fiber glass. Guess what – the expose fiber glass was just next to the down flow outlet of one of their CRAC.
At the end of the day, the decision to use raised floor or not will depend on your expected payload densities and how much will this change over the years in the future.
Tags: Air Management, airflow, Data Center, raised floor, slab floor