Data Center Knowledge recently featured Upsite’s Lars Strong and his industry perspective on coldspots in data centers. From the article:
Data centers exist to provide continuous power, connectivity and proper intake air temperatures to IT equipment. Hot spots are a well-known difficulty that occurs when IT intake temperatures are above the recommended maximum.
Now, cold spots have become the new challenge, and opportunity, for data center operations. A cold spot is any IT intake temperature less than the established minimum. The minimum is established by data center personnel, or when ASHRAE recommended guidelines are followed, at 64.4 degrees F.
Historically, computer rooms have been kept overly cold. There are a number of contributing factors:
- Mainframes which primarily occupied data centers had less emphasis on front and back, and less airflow pattern or orientation that needed alignment with the room, so entire room was cool to compensate.
- Power was considered inexpensive.
- Densities were low relative to the area IT equipment covered so cooling capacity was not critical.
- Power was a much smaller portion of cost to run data center than today.
As IT equipment densities and power consumption increased, hot spots (HS) started forming. HS were recognized as damaging. For the last decade, the emphasis has primarily been on getting rid of HS. This has often been done by developing advanced AFM techniques, adding more cooling capacity, and turning down cooling set points.
As the cost of electricity has increased, and more significantly as the cost of electricity has become a much larger portion of operating cost, emphasis has been placed on reducing the power consumption of the cooling infrastructure, the largest consumer of power in the data center other than the IT equipment.
Thermodynamics
The increased efficiency and capacity of cooling units at higher return air temperatures is driving computer room operating temperatures up.
ASHRAE, working with IT manufacturers, have raised the recommended and allowable intake temperature ranges several times. The focus on the maximum intake temper has led to a lack of awareness of IT equipment intake temperatures being below the minimum recommended. As a result computer rooms often have a very wide range from the lowest intake temperature to the highest. There is a direct relationship between the range and efficiency: the wider the range, the lower the efficiency.
Data
Data from Upsite shows that cold spots are now even more prevalent in data centers than hot spots. Of the last eight data centers reviewed by Upsite, on average 7 percent of cabinets have hot spots and 35 percent of cabinets on average have cold spots. The sites reviewed totaled 84,600 sq. ft. of analysis. Not surprisingly, these same sites have an average rated cooling capacity that is 2.4 times the IT load.
