The basis of intelligent cooling is that it allows us to deliver only the cooling that is required to meet our temperature requirements. By reducing the flow of air down to that which is actually needed (rather than just blowing as fast as we can) it is possible to reduce the energy demand of our cooling subsystems (conventional, free or fresh). We do this by varying the rate of flow or the temperature of input air or both to individual areas of a data centre or to a particular cabinet.
There are largely two approaches to determining what we need to do to drive intelligent cooling in data centres. The first involves measuring the temperature of exhaust air in each cabinet the other is to measure the input power per cabinet. The first involves retrofitting temperature sensors and cabling to bring the results back to a control system, the second involves leveraging intelligent PDUs (iPDUs) that measure and report on (via IP) the power draw from each cabinet and power strip.
During my time at BT I installed intelligent Power Distribution Systems (iPDUs) in the Rochdale and Cardiff sites. These provided us with data on rack level and facility power consumptions (in conjunction with the Supervisory Control And Data Acquisition (SCADA) system). Using output from iPDUs via the SCADA system allowed us to calculate the power consumption by room, rack, and aisle.
The diagram above shows an example of relatively low and relatively high power draw in different zones of the data centre halls. There are two aisles and the addition of power from all adjacent cabinets sums to provide a real time picture of the total energy delivered to the zone. As almost all of the input power is converted to heat we can also see zones of the data centre which are operating at higher or lower power draw. This introduces the potential of controlling our cooling airflow supply according to demand and in real time.
Active Airflow Control (AAC) is a new concept in data centre cooling. AAC can be used in a macro way using fans and remotely controlled vented plenum floor tiles – Room Scale Adaptive Cooling, it can also be used in servers in a micro way with each individual server managing it’s own airflow by speeding up and slowing down internal fans. Intel have a very good movie showing AAC in action on a server.
Floor grilles can open or close dependant on the cooling demand of each zone of the data hall. This is linked to under-floor pressure sensors which, in conjunction with the power data provided by the SCADA system, allows automatic airflow control. This is linked to variable fan speed DFUs which, when the fan speed is reduced, will facilitate a huge reduction in energy consumption.
