I was recently asked a question about how cool the cold aisle should be in a data center using hot/cold aisles to manage temperature.
This question is difficult to answer without other background information. I’ve seen specifications reference ASHRAE guidelines, Uptime Institute recommendations, and so on. For me, TIA-942 (which is the basis for the international standard on data center design), is a good framework to lean upon.
TIA-942, Appendix G states the following for the capabilities of the raised floor area environmental air:
- 20 degrees C to 25 degrees C (68F to 77F)
- Normal set point: 22 degrees C (72F) +/- 1 degree C (2F)
- Relative Humidity: 40% to 55%
- Normal set point: 45% RH +/- 5%
Now, all that may be easier said than done, of course. The whole point of the cooling is to keep the equipment happy (operating in the prescribed temperature range). Heat is generated by the equipment’s consumption of electricity, the level of utilization, and the density of the technology used in your data center (which may also vary by location on the raised floor, creating a non-uniform temperature pattern).
This is also modulated by the power density capabilities of the data center’s MEP infrastructure. If you have a relatively old facility, chances are that the power density capabilities of the facility are less than 50 Watts per Square Foot (W/SF). If you have a modern facility, you may enjoy capacities of 85 W/SF, 100 W/SF, or even 150 W/SF (higher than that are somewhat rare these days). A well designed MEP infrastructure has cooling capacity matched to power density capacity.
Regardless of that though, it’s possible that you may use technologies that squeeze a very high amount of power consumption (and heat generation) into a small area. Hot/Cold aisle arrangements may not be enough to cool those spots, and may cause consideration of supplemental cooling on the raised floor. There are several in-row cooling technologies with which you can place a floor-standing cooling unit in-row with your equipment racks to deliver extra cooling capacity to selected areas. One should be careful when using supplemental approaches though, that the redundancy of MEP infrastructure supporting your intended Tier Level is not obviated by such an implementation.
Do you have any experiences with specifying hot/cold aisle metrics that you’d like to share?