I have had a great interchange from a subscriber to The Hot Aisle:- Darek Wichniewicz of ATM SA in Warsaw, Poland. Darek is looking for some real technical advice on building a new Data Center facility of 2000 – 3000 square meters utilizing fresh air cooling. Like many Data Center operators Darek is concerned about being too innovative with fresh air and taking risks that won’t work and require rework later at great cost.

“But for my technical department the main questions are: Is it possible not to use air condition? In case of failure of “fresh-air cooling” idea, will we have to add normal coolers later with more effort and cost?”

The first important fact is that using fresh air to cool computer equipment is more common than you would think. I have examples of where this is commonplace:

• Many vendors expect their equipment to be used in office environments without raised floors and dedicated air handling units. There are hundreds of thousands of small companies who have a few servers installed in a cupboard or in the corner of the office, all running at ambient temperature. The big difference between equipment located in an office space and in a dedicated data center is packing density, the number of KW per square meter.
• Telecommunications companies have used fresh air cooling for decades for their network equipment in telephone exchanges. Vendors manufacture most of their computer products to operate in this environment. Telecommunications companies specify operating temperature ranges up to 50 Celsius (122 F). Telecommunications companies expect power densities of 0.5 – 1.5 KW per square meter.
• At BT we constructed 106 21st Century Data Centers that work on fresh air cooling. These are not design studies but real live sites delivering service to customers. There are a large number of articles already on the Web that describe the design and operating principles. Green Data Centers, Efficient Data Centers, Sustainable Data Centers.

How practical is fresh air cooling? Depending on the location of your site and the maximum year round temperature the answer is very practical. But in almost any location, it is possible to reduce the amount of air conditioning required provided that the external temperature is cooler than the temperature of air exhausted from your equipment for at least part of the day.

Darek continues with some specific information and questions:

“Our planned data centre is located in Warsaw, Poland so expected average daily temperature is 16-19 degrees Celsius (in summer).” – (61-66 F)

My research shows that average maximum temperatures in Warsaw in the summer are actually 24 Celsius (75F). At this temperature it is perfectly possible to run fresh air cooling year round. Power densities of 1.5KW per square meter are practical. Fresh air must be delivered via a standard pressurized plenum floor just like a conventional 20th Century Data Center. Rather than using a conventional Computer Room Air Conditioning (CRAC) unit an air handling unit without refrigeration can be installed. It is very important to utilize hot and cold aisle separation preferably using curtains as described in my earlier post.

“According to technical specification of several manufacturers products (servers and telco equipment), we assume that the temperature in our fresh-air cooled data centre (measured in RACKs) must not exceed 40C, and the humidity should fit between 10-80%. We think that maintaining the temperature just below 40C (without air-conditioning) should be just fine for the servers regular operations. Considering your knowledge and practical experience, would you confirm correctness of our assumptions?” (40C = 104F)

Manufacturers specifications are generally for the air temperature at the inlet to the computer equipment not the temperature inside the computer cabinet. Note that higher inlet temperatures tend to cause the temperature controlled fans inside most equipment to operate at a higher speed, increasing the energy used. Provided that exhaust air from the hot aisle is not allowed to mix with fresh air in the cold aisle and that room air handling systems can deliver enough air keeping the inlet temperature well below 40 Celsius.

Humidity control is designed to prevent condensation on cold surfaces (80%) and the build up of static (10%). The absence of refrigeration means that there are no surfaces colder than the air flow making condensation impossible. As input air is warmed going through the room, relative humidity decreases further reducing the likelihood of condensation. Very dry input air is unusual in a temperate climate, usually only caused by refrigeration.

“Could you describe the parameters of the fresh-air cooled data centre you’ve had dealt with? I.e. avg/max: temp, humidity, power consumption / m2?”

Generally the data center operates at 5 degrees Celsius above ambient. BT 21st Century Data Center designs are 1.5 KW per square meter. There is no humidity control.

“What was the attitude of the equipment vendors concerning warranty terms and conditions, when it came up that the equipment was operating in data center without air conditioning? Were they accepting this innovative approach to meet the environmental conditions?”

Vendors have no option but to provide full warranty on products operated within their operating parameters. BT made it a condition of supply that all equipment would work with inlet temperatures of 50 Celsius.

“Do you have any experience with fresh-air cooled used in Service Provider model? Were they rented to external customers, not only used by the owner?”

I do not believe that the world is ready for fresh air cooled co-location data centers yet. BT was able to use fresh air cooling because the contents were for internal use. Most co-location customers would not have the skills or capability to lay the equipment out efficiently to maximize cooling capacity.