Are we containing for Reliability or Efficiency? You need to plan in advance.
Are Data Centers actually designed from the outset to take advantage of the true benefits of airflow containment? Containing your hot or cold aisles will not only pave the way for benefits of fan turn down on the local CRAHs, but will also present the right conditions for the operation at raised chilled water (CHW) supply temperatures, which will further help the facility exploit the benefits of free cooling and improved Coefficient of Performance (COP) on primary cooling plant.
During my time as a MEP design consultant, I came across a number of clients that wanted to deploy airflow containment in their facilities shortly after commissioning and handover. The only problem was that their sites were designed to operate at 10C CHW supply, and so their mechanical infrastructure was selected around this parameter. To further compound matters, the cooling system was supporting other non-critical spaces along with the dehumidification load on the pressurisation air handling units; so it was not possible raise the CHW temp. This meant that savings from hot or cold aisle containment were limited to those from reduced fan power only, causing the ROI case for containment to suffer. Even so, with the CHW supply temp. fixed at 10C, slowing the CRAC fans down increased the system water temperature difference to about 13C, and led to reduced water flow rates in the system pipes and problems with stagnant branches of pipework. The phrases “too late” or “I told you so” come to mind.
If the client had committed to airflow containment from the outset, I would have designed the data center with a CHW supply temperature of 15C, which actually gives the plate heat exchanger a fighting chance to free cool, given the global air to water approach across the system. This way I could ensure that the chiller compressor remained offline for longer and increased my savings significantly over the course of the year.
But perhaps the client was more interested in reliability and wanted to minimise the possibility of detrimental effects such as depressurisation of cold aisles especially closer to the higher U-slots in the racks, or to create a partially sealed zone with cold air as a thermal buffer. Who knows? Either way one needs to plan for these things in advance to get the true benefits.
Ehsaan Farsimadan is a Mission Critical Consultant at Romonet Ltd, and has a PhD in Mechanical Engineering.