New ASHRAE Temp/Humidity Guidelines

FYI, ASHRAE (American Society of Heating, Refrigeration, and Air-conditioning Engineers) has released new guidelines for temperature and humidity conditions for IT equipment. Among the changes (see p.8), are new classes A3 and A4, which allow 5C-40C and 5C-45C temperatures in data centers (respectively), along with 8-85 and 8-90% RH.

There are even guidelines for lower humidity level if certain procedures are followed.

--kb

P.S. Thanks to Pasi Vaananen for the heads-up.

Cisco & Sun Servers Spar for Best Humidity Support

One of the clear trends in data centers is to improve data center efficiency by making greater use of HVAC economizer modes. For air-side (dry-side or outside air) economizers, one of the keys to broad adoption is to be able to use outside air across as broad a relative humidity (RH) range as possible.

Among the major blade vendors, Cisco appeared to have taken the lead by offering support for the broadest operating humidity range, but Sun appears to have matched Cisco recently:

• Cisco's Unified Computing System blades support 5 to 93% RH
• Sun's Sun Fire X2270 blades support "up to" 93% RH
• HP's c-Class BL260 G5 blades support 10 to 85% RH
• IBM's BladeCenter HS22 blades support 8 to 80% RH
• Dell's PowerEdge M600 blades support 8 to 80% RH

(All humidity ranges are non-condensing. All data is from vendor web sites as of 9/3/09).

Ever-widening ranges for supported humidity make the use of dry-side economizers more feasible. If vendors were able to support 0-100% relative humidity, data center operators wouldn't need to worry about humidifcation/de-humidification controls. Eliminating such controls and systems could lower capital costs, reduce operating costs, lower the carbon footprint of facilities, and lower their water footprint as well.

--kb

Human Side of Higher Data Center Temperatures

With all the talk of hotter data center temperatures, one item that has often been overlooked is what happens to the poor soul tasked with going in and servicing equipment in that data center. Imagine having to work in a facility at 40°C (104°F) for several hours at a time--and that's at the equipment input. The exhaust temperature on the back side of the rack could easily be 55°C (131°F).

One approach is to adopt a "fail in place" model where technicians never go into a production facility, but even Google has technicians adding and replacing individual servers in their containerized data centers.

Other approaches to consider:

• Localized spot cooling. A very small air conditioner could take the edge off the area in front of a rack.
• Perform service operations at night or when it's reasonably cool.

This last suggestion may seem too simplistic at first, but it's actually quite practical. In a facility with sufficient redundancy to ensure high availability, server replacement should be able to wait up to 24 hours. Operating a data center at consistently high temperatures will end up increasing power consumption in the IT equipment. It only makes sense to use higher temperatures in a data center when using optimizers to eliminate or substantially reduce HVAC CapEx and OpEx costs.

If a data center is using economizers, the temperature in the data center should drop when the outside temperature drops. Even in relatively warm areas during summer months, there are substantial times each day where the temperature drops to reasonable levels in which technicians can comfortably work.

--kb

Processors for Higher Temps

Higher Temperatures for Data Centers talks about emerging environmental standards that could well lead to increasing ambient temperatures in facilities. All other things being equal, higher ambient temperatures will lead to higher component temperatures.

In many cases, the maximum processor case temperature (Tcase) is the limiting factor for how high the ambient temperature can be raised. The Tcase limit is established by the semiconductor vendor as the maximum case temperature that the chip can experience and still meet the vendor's reliability goals.

This can put a crimp in plans to use outside air for cooling. In most likely data center locations, there are occasionally warm days that would increase the inlet temperature to the servers to the point that the processor Tcase would exceed the vendor's specified ratings.

The telecommunications market has had this issue for years. NEBS-rated equipment for central offices generally has to operate at 40°C ambient temperature, but they also need to operate at 55°C for short periods (up to 96 hours at a time and up to 360 hours per year).

To address the needs of the NEBS market, Intel provides some of their processors with dual Tcase ratings: one long-term T-case rating and a second short-term Tcase rating that is 15°C higher for up to 360 hours per year.

These processors with dual Tcase ratings may be a good fit for systems in data centers that use air-side economizers.

Higher Temperatures for Data Centers

As mentioned in Using Outside Air for Data Centers, there is increasing interest in using outside air to cool data centers. At times, this will mean higher ambient temperatures inside those data centers.

A couple years ago, the TEM-led SCOPE Alliance undertook the task of identifying the relevant environmental requirements for data centers and telecommunications from several different standards groups (Telcordia, ETSI, TIA, etc.) and came up with the Environmental Profile: Central Offices and Network Data Centers, eventually published last May. It was a lot of work, but I think we developed the most comprehensive overlay of those standards that has been published to date.

Last August, ASHRAE issued its 2008 ASHRAE Environmental Guidelines for Datacom Equipment, which changed the recommended setpoints in data centers from 20-25°C to 18-27°C. This may not seem like much, but it's a step in the right direction towards better allowances for dry-side (air) economizers.

Last November, Telcordia released GR-3160, NEBS(TM) Requirements for Telecommunications Data CenterEquipment and Spaces. [I had provided information for this to Telcordia through the two years this document was in process.] Though those outside the telecom world may not be familiar with Telcordia (or its predecessor, Bellcore), the Telcordia NEBS standards have become the de facto standards for how telecommunications facilties and equipment is designed in the U.S. and many places around the world. GR-3160 is effectively Telcordia's first major foray into data center standards, a clear recognition that telecommunications carriers like AT&T, Verizon, and Qwest have a large number of data centers and a growing need to ensure maximum availability in those facilities. Among the interesting elements of GR-3160 is Telcordia's expectation for allowable maximum ambient temperatures at the air inlet to the rack-mounted equipment:

• 30°C long-term max ambient
• 40°C short-term max ambient (up to 360 hours per year)

These two upper limits provide a reasonable target that equipment manufacturers can design to, while providing enough freedom that facility designers can make maximum use of economizers.

--kb

Using Outside Air for Data Centers

Conventional wisdom holds that it takes one Watt of cooling to remove every Watt of ICT equipment inside the data center. Today's data centers can do a bit better than that, but cooling costs remain a considerable OpEx cost for facilities.

One approach that's generating increased interest is the use of dry-side economizers, which bring in outside air to cool the data center. Using outside air saves the power that is normally used by compressors and chiller plants to cool facilities; even bigger gains may be achieved by avoiding CapEx (Capital Expense) costs by eliminating the purchase of chiller plants entirely or at least reducing CapEx costs by installing smaller cooling plants.

At first blush, this approach may seem to only be of marginal value. However, higher density data centers (such as those with blade servers) may have a relatively large temperature increase between inlet and exhaust temperature. Even if the desired inlet temperature is only 75°F, a facility with a 50°F temperature rise would have an exhaust temperature of 125°F--most ambient temperatures are well below this temperature. Bringing in outside air could take less energy than cooling the recycled air--humidity considerations notwithstanding.

To look at the impact of using outside air to cool data center equipment, several data center operators have performed small-scale tests to see how data center equipment is impacted by outside air:

• Microsoft's test: http://blogs.msdn.com/the_power_of_software/archive/2008/09/19/intense-computing-or-in-tents-computing.aspx
• Intel's test: http://www.intel.com/it/pdf/Reducing_Data_Center_Cost_with_an_Air_Economizer.pdf and http://www.datacenterknowledge.com/archives/2008/09/18/video-intels-air-side-economization-test/

Air economizers look promising, based on these results.

--kb