Posted by Todd Boucher
on 10/24/2010
Many of our customers today are struggling to find ways to extend the lifecycle of their existing data centers through reconfiguration and energy savings. As potential ways to save energy are reviewed, the more “glamorous” strategies of improving data center efficiency traditionally get all the attention – containment, economizers, in row cooling, etc. While all of these strategies can yield significant energy savings, they also cause data center operators to overlook a simple tactic that is cost effective and relatively simple to implement: improving humidification controls.
Most existing (over 3 years old) data centers today are cooling with large CRAC units that are run independently and rarely customized beyond the default manufacturer settings. The data center also relies on these CRAC units to control relative humidity, which means each individual CRAC unit can do four things:
1. Cool (if air is too hot)
2. Humidify (if humidity is too low)
3. Heat (if air is too cold)
4. Dehumidify (if humidity is too high)
Although these CRAC units are trying to maintain one central temperature setpoint and one central relatively humidity setpoint in the data center, they are rarely linked together with integrated monitoring and/or controls. Furthermore, air mixing in the data center and the location of CRAC units’ exhausts and intakes in proximity to one another causes the CRAC units to mistakenly identify actual environmental conditions in the data center. In other words, it is very common to find two CRAC units located side-by-side with one unit dehumidifying and the other unit humidifying simultaneously (we have found this in multiple data centers during energy audits). Not only is this extremely energy efficient, it impacts the long-term reliability of your CRAC units.
There are a few simple solutions to this issue. The first is to implement an integrated control system for all of your CRAC units; instead of each unit independently monitoring temperature and relative humidity, install one or two temperature and RH sensors that all CRACs read from. This will help eliminate the condition of units working in opposite modes.
A second point to consider (although not appropriate for all data centers) is to turn disable dehumidification. In most data centers there is little, if any latent load for two reasons: IT equipment produces hot, dry air and most data centers do not have personnel working in them full time. Before considering this approach, it is important to ensure you have an adequate vapor barrier in your data center – if the environment is right you probably only need humidification turned on in your CRACS.
The last point to consider is opening up the relative humidity bands that you are trying to maintain in the data center. Most data center operators set the RH setpoint on their CRAC when it was installed 5 years ago and haven’t adjusted in since. In that timeframe, they have probably had 1-2 IT equipment refreshes in their data center and, moreover, ASHRAE has widened the acceptable RH ranges supported in the data center space. While we don’t suggest you take it to an extreme level (30% RH, for example), it will help if you are not forcing your CRACs to try to maintain exactly 50% RH.
It is easy to focus on widespread changes to improve energy efficiency in the data center. These longer term strategies may yield larger savings (and more utility company rebates), but companies looking to make immediate efficiency and operational improvements in their data center should review their humidification strategy. Our customers are recognizing quick implementation times and immediate energy savings from these simple changes.
