Cooling consumption cannot accurately be measured in the data center. However, there are a few strategies that will help you approximate how much cooling your data center is consuming.
You can monitor and record power consumption. This is the major variable that correlates to cooling requirements. Get as accurate and precise as possible - right down to individual cabinet power strips, which are now available with both local and remote metering. This will also help you maintain load balance on dual UPS's and phase balance on 3-phase circuits, both of which contribute significantly to power stability.
Every 3,000 Watts (approximately 25 amps at 120 volts) requires 10,200 BTU of sensible cooling. If you're using conventional CRAC units with humidification, set them for 72F Return Air. This will require about one ton of total machine capacity. These are very "round numbers" but should give you a good guideline.
Install temperature and humidity monitors at key locations in the room. Preferably, install monitors in each cabinet, too, but at least in each "High-Density" cabinet. There are many systems now available to do this. The system won't tell you how much cooling you need, but this will certainly identify when and where cooling is needed.
This will also help you get the most from the air conditioning you already have. If it saves installing just one CRAC unit, the monitors will more than pay for themselves. Additionally, the information provided will be a very good way to know if your cooling design remains stable under all conditions.
ABOUT THE AUTHOR: Robert McFarlane is a pioneer in the field of building cabling design. He has been asked to speak at countless seminars on building infrastructure for electronic communications, evolving technologies and the requirements of trading floor and data center design. Mr. McFarlane served for twelve years as President of Interport Financial, Inc., a firm specializing in designs for financial trading floors and critical data centers.