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.

Adding a Geographic Element to PUE Calculations

The PUE metric has become one of the most significant metrics for measuring the gross efficiency of a data center. As data center operators boast of PUE numbers that approach the optimal rating of 1.0, it's often difficult to separate out environmental or regional factors.

Is a PUE of 1.5 in Phoenix better or worse than a PUE of 1.4 in Seattle?

It depends. In absolute numbers, the lower PUE provides an indicator of the most efficient facility. However, achieving a PUE of 1.5 in Phoenix is much more difficult than an equivalent or slightly lower number in Seattle because Phoenix is so much hotter and requires more air conditioning. Moving data centers to cooler locations helps the PUE rating, but sometimes data centers need to be located in a specific city or region. How can you compare PUE values in regions with different environmental conditions?

One possible approach is to add a geographic compensating factor:

gPUE = G * PUE

The geographic compensating factor G would be determined by The Green Grid or other trusted body based on compiled weather data. Ideally, this could be calculated empirically through a formula using data maintained by the U.S. Department of Energy (refer to this blog link for information on that data and a free tool to visually represent that data).

This approach would allow somebody to measure the technical innovation of a given facility while providing an adjustment to account for geographic disparities in temperature, wind, solar loading, etc. It's not a perfect solution (since some cooling optimizations might not work in cooler or hotter climates), but it provides some measure of equalization to facilitate more equitable comparisons between PUE claims in different locations.

--kb

Truckin' Down the Information Superhighway

Last week, I was talking with a friend from Sun who is involved with Sun's containerized data centers. He mentioned that since they helped the Internet Archive put 3.2 petabytes of storage in a shipping container, they figured they could put the container on a truck, take 7 days to ship the container across country, and still average >40 Gbps over that 7 day period!

Coincidentally, two days later Amazon introduced Amazon Web Services Import/Export with a blog that starts off with the following colorful quote attributed to Andy Tanenbaum:

Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

Amazon Web Services Import/Export allows people to send USB or eSATA hard drives/media to Amazon for data sets that are impractical to send over available communications links.

It turns out that the bulk version of sneakernet may be the most expeditious way to move data. The more things change, the more things stay the same.

--kb
Note: Revised title on 5/29/09.

How a Good Metric Could Drive Bad Behaviors

The PUE (Power Usage Effectiveness) metric from The Green Grid has become a widely referenced benchmark in the data center community, and justifiably so. However, there can be a dark side to following this metric blindly.


Introduction

PUE is defined as follows:

PUE = Total Facility Power/IT Equipment Power

Using the PUE metric, a facility manager can judge what ratio of power is lost in "overhead" (infrastructure) to operate the facility. A PUE of 1.6 to 2.0 is typical, but facility managers are striving to approach a PUE of 1.0, the idealized state.

Companies willing to drive more sustainable practices may incent facility managers to improve facility PUE levels. However, if this is done without context towards the overall energy or other resource consumption, it could drive inefficient behaviors.



Issue #1: Dissimilar Infrastructure Power Scaling

If a facility manager tracks PUE over a variety of workloads, they will see how the data center's infrastructure power consumption tracks with the IT load. Ideally, the infrastructure overhead (HVAC system, UPS system, etc.) will match linearly with the consumption of the servers and other gear in the data center, but this is rarely the case.



In many cases, the fixed overhead for power and cooling systems will become a higher percentage of overall power consumption as the IT load diminished. In other cases, there will be significant step functions in overall power consumption as large infrastructure items such as chillers, CRACs, or other equipment is turned on or off (as depicted in the graph to the left).

In such situations, reducing the IT power consumption could increase the PUE even if it reduces the overall energy consumption of the data center. People will often act in the direction towards which they are incented (i.e., what improves their paycheck). Managers incented to improve PUE without any clear tie-in to overall energy consumption might be reluctant to shut off unused servers or aggressively implement power saving features on their IT infrastructure if it increased their PUE--even if doing so would reduce overall facility power consumption.

Ensuring overall energy consumption is part of the incentive package (not just PUE) is critical to driving the desired behaviors.

[Part of this needs to be linked with overall productivity of the data center so that increased use of the data centers is encouraged while still incenting improved efficiency. I'll write about this in an upcoming post.]



Issue #2: Shifting Infrastructure Loads to IT

Another issue to watch is a desire to classify some infrastructure-like services as IT loads in order to improve PUE efficiencies. Examples of this include moving UPS systems into IT racks or putting large air-mover devices into equipment cabinets and trying to classify them as IT loads. This is "gaming" the system and should be actively discouraged.

The Green Grid is aware of this issue and is adding more guidelines to help people improve the accuracy and consistency of their PUE reporting.



Issue #3: Improving Infrastructure Efficiency at the Expense of IT

The third issue to watch is a move towards facility or equipment practices that reduce the infrastructure power consumption but increase the IT power consumption. In particular, the adoption of higher operating temperatures for data centers warrants particular scrutiny.

I've noted previously that there are significant gains possible by raising data center temperatures and making greater use of dry-side or wet-side economizers. However, it's important to compare the energy savings on the infrastructure side with the energy costs on the IT side. At higher temperatures, leakage currents in silicon increase and fans inside servers need to run faster to move more air through each server.

Increase the IT consumption and lower the infrastructure consumption and you get a two-fer: the PUE numerator goes down and the PUE denominator goes up, lowering the overall PUE. However, if the net power consumption doesn't go down, it usually** doesn't make sense to increase the ambient temperature. Once again, looking at overall power consumption in addition to PUE is important in incenting the proper behaviors.

--kb


**Note: For greenfield (new) data centers or substantial datacenter retrofits, raising the allowed data center temperature may eliminate or substantially reduce the CapEx (capital expenditure) cost for that data center even if the direct energy costs are slightly higher. For example, if a data center doesn't need to purchase a chiller unit, that could shave millions of dollars off the construction cost for a facility. In such cases, more complicated parameters will be needed to evaluate the benefits of raising the ambient temperature in the facility; these likely will include a net present value analysis for the CapEx savings vs. OpEx (operating expense) costs, consideration of real estate savings, etc. The real win is when both CapEx costs are avoided AND OpEx costs are lower.

SSD Potential Power Savings Writ Large

E-week has an interesting article about an iSuppli report suggesting that if all data centers moved 10% of their hard disks to SSDs (solid-state disks), it would save more power worldwide than the total 2006 power consumption of the African country of Gambia. This equates to more than 166,000 Megawatt hours.

However, since the analysis assumed an SSD averaged 7W, SSDs that use less than 2W could save more than 3x that amount. Adding in HVAC and power infrastructure savings, the savings could be even higher.

--kb

Building Codes and Roof Anchors

One of the biggest impediments to installing rooftop solar panels or wind energy devices such as helical windmills is the cost and risk associated with properly anchoring them to a building's roof. Extra effort is required to ensure retrofit roof penetrations do not leak; in many cases, installation of the roof anchors takes the majority of the installation time. The noise from cutting through the roof can significantly disrupt those on the floor or two below.

If "rooftop renewables" are designed into a building during initial construction, the cost is substantially lower. However, it may not be feasible to install these rooftop renewables when the building is first built (due to limited capital or other reasons).

A middle ground is to provide rooftop anchors during initial construction, regardless of whether or not rooftop renewables are installed with initial construction. That way, solar or wind devices could be installed at a later date much more easily and with no need to breach the roof seal.

All new data centers should be designed for the later installation of rooftop renewables, even if they aren't part of the initial build-out.

Taking this a step further, I advocate the following: building codes should be revised to **REQUIRE** all new commercial buildings with a roof area greater than 1000 square feet to install roof anchors every x (20?) feet, with a TBD load rating for each anchor. (These anchors should also be required when major roof renovations are initiated as well.) Requiring these anchors will facilitate the broader adoption of rooftop renewables in data centers and other commercial buildings.

I hope others will adopt this cause; together we can effect real changes,
--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

More on Google's Battery-backed Servers

As noted in Evaluating Google's Battery-backed Server Approach, there are a number of benefits to Google's recently-disclosed practice of putting VRLA batteries on every server, but there are quite a few drawbacks as well.

One of the drawbacks not discussed in the prior post is a set of issues related to power transients and harmonics. With a conventional data center, there are multiple levels of power transformation and isolation between the individual server and the grid. Power usually comes in at high- or medium-voltage to a transformer and comes out as low voltage (<600v) before going to a UPS and a PDU.

In an effort to improve efficiency and reduce capital costs, facility managers are looking at removing some of these isolation layers. This is fine to a certain extent. After all, there are a lot of small businesses that run one or two servers on their own, and there aren't major problems with them. In those cases, however, there are usually relatively few computers hooked together on the same side of the electrical transformer that provides power to the building. This transformer provides isolation from building to building (or zone to zone in some installations).

When you scale up into a large data center, however, you get thousands and thousands of servers in the same building. If you remove those extra layers of isolation, the burden for providing that extra isolation falls to the power supplies in the individual servers. If servers use traditional AC power supplies, issues like phase balancing and power factor correction of all the separate power supplies becomes more of an interdepent issue.

The issues can be helped or hurt depending on what's nearby. Servers without isolation near an aluminum smelter, sawmill, subway, or steel mill may see wide fluctuations in their power quality which can result in unexplained errors.

I've seen cases with marginal power feeds where individual racks of servers seem to work fine, but the aggregate load when all servers are operating causes enough of a voltage sag that some servers occasionally don't work right. Let me tell you, those are a real pain to diagnose.

On the other hand, if you're somebody like Google or Microsoft who can locate data centers in places like The Dalles, Oregon or Quincy, Washington that are just a stone's throw from major hydroelectric dams or other sources of power, perhaps you can rely on nice clean power all the time.

External power factors may be the least of a data center manager's problems, however. The big concern with eliminating the intermediate isolation is that transients and other power line problems from one power supply can affect the operation of adjacent systems, and this can build up to significant levels if fault isolation and filtering is not supported.

Another issue that bedevils data center managers is the issue with phase balancing. In most AC-powered systems, power is delivered via three phases or legs (A, B, and C phases), each 120° out of phase with each other. At some point (usually the PDU), a neutral conductor is synthesized so that single-phase currents can run from one of these legs to neutral. In a properly balanced system, there will be equal loading on the A leg, the B leg, and the C leg. If the phases are not properly balanced, there are several bad things that can occur, including the following:

• The neutral point will shift towards the heaviest load, lowering the voltage to the equipment on that line, resulting in premature equipment failure and undervoltage-related errors
• An imbalanced load may cause excess current to flow over specific conductors and overheat
• Breakers or other overcurrent mechanisms may trip

Phase imbalance can occur when network administrators do not follow a rigorous process of plugging every third server into alternate phases. Additionally, shifting workloads could cause some servers to be more heavily utilized than others--and phase balancing is almost certainly not a factor considered in allocating applications to specific servers. An even more pernicious issue can arise with systems employing redundant power supplies, such as blade servers: in an attempt to maximize efficiency, management software may shut down certain power supplies to maximize load on the remaining power supplies--all without considering what the impact to phase balancing is when the load is not equally shared among all power supplies.

Data centers that employ conventional PDUs don't generally have these issues (or have them at lesser severity), since the PDUs and their transformers are usually designed to handle significant phase imbalances without creating problems.

Additional considerations with the Google battery-backed server approach:

• Acid risks from thousands of individual tiny batteries (i.e., cracked cases in thinner-walled batteries)
• Shorting risks from batteries that can deliver thousands of amps of current for a short period
• More items to monitor, or higher risks of silent failures (albeit with smaller failure domains) when you most need the batteries

This is a complex issue. I'm not convinced that Google has determined the optimal solution, but kudos to them for finally being willing to publicly discuss some of what they consider to be best practices. Collectively, we can learn bits and pieces from different sources that could end up delivering more efficient services.

--kb

Evaluating Google's Battery-backed Server Approach

As noted previously, Google has disclosed that they put batteries on every server (see this picture of a Google rack), essentially powering their servers like the way laptops have traditionally been powered. The batteries are needed on laptops because they need to be mobile, which is not generally a consideration for servers.

Are batteries in servers a good idea?

There are some definite advantages in Google's approach:

1. No need to pay for UPS systems (saves CapEx dollars)
2. Eliminates two conversion stages found in a traditional AC double-conversion UPS
3. Reduces dedicated floor space/real estate commonly devoted to UPS/battery rooms
4. Localizes fault domains for a failed server to just one server
5. Scales linearly with the number of servers deployed

All of these add up to a solution that works just as well for one server as it does for one thousand servers. Coupled with Google's efforts to increase energy efficiency through founding and support for the Climate Savers Computing Initiative (CSCI) and its target of 92% power supply efficiency, this solution appears to be very efficient.

However, there are some down sides to Google's approach:

1. A lot of batteries to wire up and monitor
2. Increased air impedance from blocking airflow
3. Lower battery reliability with increased ambient temperatures
4. Higher environmental impact due to increased battery materials
5. Individual server supplies are exposed to a higher level of power transients and harmonics
6. Potential phase imbalances and stranded power in data centers

Issue #1 is self-obvious. Issue #2 can be seen from this picture from Green Data Center Blog; the physical mass of the batteries blocks a good portion of the air space in front of the server, which increases the resistance and in turn requires more fan power to move the same amount of air.

Issues #3 and #4 are somewhat related. Google, Microsoft, and other leading internet companies have advocated moving the ambient temperatures of data centers to higher temperatures, with some advising 35°C, 40°C, or even occasionally 50°C ambient temperatures. There are clear savings to be had here, but it may run counter to the battery approach used by Google. Assuming the Google batteries are conventional lead-acid batteries, a common rule is that the useful life of batteries drops by ~50% for every 10°C above 25°C ambient temperatures. Thus, a 4-year battery would only be good for ~2 years in a 35°C environment. In comparison, conventional UPS batteries are often rated for 10, 15, or 20 years. When consolidated in a UPS battery cabinet, the batteries can be protected from the higher ambient temperatures through localized cooling (batteries dissipate almost no heat) for increased life.

Lots of little batteries like Google uses results in more materials usage compared to the use of larger batteries. Couple that with reduced battery life at higher temperatures, and the result is not as good as it first seems. According to http://www.batterycouncil.org/LeadAcidBatteries/BatteryRecycling/tabid/71/Default.aspx, more than 97% of lead from lead-acid batteries is recycled, but this also states that 60-80% the lead and plastic of new batteries is recycled material. Looking at this last stat a different way, 20-40% of lead-acid battery materials are not recycled. Thus, even if Google performs 100% battery recycling, using lots of new batteries still results in the use of a lot of new materials.

I'll address issues #5 and #6 in a future post.

--kb

Google's Server Power Supplies

This past Wednesday, Google finally provided a peek into their data centers. Green Data Center blog has a great roundoup of various articles related to this workshop, including pictures from Google's container data centers.

One of the more interesting aspects revealed Wednesday was the fact that Google has batteries attached to each of their servers.

At first, this seems rather odd. Google's explanation for this is that they use this arrangement as a 99.9% efficient replacement for UPS (Uninterruptible Power Supply) systems. Wow...99.9% efficient!

This is definitely a different approach from what most data centers do today, and it seems really far out there--until you break it down in its component parts. A simplified block diagram looks like the following:

Broken down this way, the arrangement really starts to look like a laptop. The Google server power system apparently operates just like a laptop:

• External power supply provides ~12Vdc
• Battery is included with every computer
• When the external power supply fails, the battery provides power until the generator starts or power is switched to a different source

Graceful shutdown in power outages may or may not be an issue for Google's applications (likely not an issue).

Google certainly thinks they've got a winner with this approach, and goodness knows they've had experience deploying this at scale. In a future posting, I'll look at some of the pro's and con's of this approach.

--kb

Eliminating the UPS Efficiency Penalty with -48Vdc

The Green Grid recently released Quantitative Efficiency Analysis Of Power Distribution Configurations For Data Centers, which shows how different power chains from 480Vac down to 12Vdc stack up in terms of efficiency. This showed -48Vdc to have the highest efficiency for systems at 60% of capacity and below--in an idealized world.

This is true when a UPS is required--but what happens if a UPS isn't needed?

Say what? Who would ever want to deploy servers without UPS
backup?

There are certain circumstances where a UPS is not needed:

• Services with sufficient geo-redundancy that a power failure at any one site doesn't have appreciable impact on the overall service availability


• Lower-priority services for which an infrequent service outage would be acceptable

In situations like this, how does a -48Vdc system stack up? Let's look at the data in the report from The Green Grid mentioned above:

• The best AC power supplies to go from 240Vac down to 12Vdc peak out at around 93% efficiency [Figure 31].


• The best DC rectifiers (with batteries) to go from 240Vdc down to -48Vdc peak out around 96.5% efficiency [Figure 29].


• The best DC power supplies to go from -48Vdc down to 12Vdc peak out at almost 95% efficiency [Figure 31].

Taken together, the 96.5% rectifier efficiency x the 95% power supply efficiency equate to ~91.7% efficiency, slightly less than the 93% efficiency of a pure AC to 12Vdc power supply solution.

However, this is using rectifiers with tightly regulated -48Vdc outputs designed to work with batteries along with wide-ranging inputs. This is a mis-match! It's understandable why this has traditionally been done (for applications needing battery backup), but it's overkill for applications not needing battery backup.

Since most -48Vdc power supplies can handle input voltages from -42Vdc to -56Vdc (or a wider range), think what could happen with a DC rectifier with a loosely regulated output well within this range. If a DC rectifier was allowed to vary its output voltage between -44Vdc and -54Vdc, the net efficiency of the -48Vdc system could meet or beat the approach with a straight AC power supply.

Without battery backup, a -48Vdc system could match an AC system; even with full-time battery backup, the -48Vdc system is within ~1.5% of the AC system without battery backup.

Next: the story gets even better when redundancy is considered...

Sealed Containers: Reality or Myth?

One of the interesting debates for those looking at containerized data centers is whether or not containerized data centers need to be serviceable in the field. Different products on the market today take different approaches:

• The Sun Modular Datacenter (nee "Blackbox") provides front and rear access to each rack by mounting the racks sideways and using a special tool to slide racks into the center aisle for servicing.
• The Rackable ICE Cube provides front access to servers, but the setup doesn't lend itself to rear access to the servers.
• HP's Performance-Optimized Datacenter (POD) takes an alternative approach: there's a wide service aisle on the front, but you need to go outside the container to get to the back side of the racks via external doors.

Some industry notables have advocated even more drastic service changes: James Hamilton (formerly with Microsoft, now with Amazon) was one of the early proponents of containerized data centers, and he has suggested that containerized data centers could be sealed, without the need for end-users to service the hardware. The theory is that it's cheaper to leave the failed servers in the rack, up until the point that so many servers have failed that the entire container is shipped back to the vendor for replacement.

How reasonable is this?

Prior to the advent of containers, fully-configured racks (cabinets) were the largest unit of integration typically used in data centers, and these remain the highest level of integrated product used in most data centers today. How many data centers seal these integrated cabinets and never open the door to the cabinet throughout the life of the equipment in that cabinet? This is perhaps the best indicator as to whether a sealed container really matches existing practices.

We had looked at the "fail in place" model in the company where I work, but it was difficult for managers to accept that it was okay for some number of servers to be failed in a rack. As long as the cost of fixing the hardware is cheaper than the cost of buying a new server (or the equipment is under warranty), most finance people and managers want to see the servers in a rack functional.

What do you think? Do you see people keeping cabinets sealed in data centers today? Does fail in place make sense to you?

Server Cost Adders for Higher-temp Operation

Numerous industry notables, including Microsoft's Christian Belady, have been advocating the operation of data centers with higher ambient temperatures. The cost savings by reducing or eliminating cooling plant costs could yield considerable savings. But what does it take to build servers designed to operate at these higher temperatures?

As mentioned in a previous post, telecommunications equipment is typically designed to meet the NEBS standards (55°C maximum ambient). Cost adders for NEBS equipment include the following:

• Higher temperature integrated circuits (ICs). Commercial-grade ICs are generally rated to 70°C; higher ambient temperatures could force the use of extended temp components.
• Heat sink costs. Higher temperatures often drive more expensive heat sink materials (i.e., copper rather than aluminum) and more use of heat sinks on components that don't need them at lower temperatures. For example, some servers need heat spreaders on DIMMs to be rated to operate at higher temperatures.
• Corrosive gases tolerance. Telecommunications equipment generally needs to pass tests to ensure reliability in the presence of corrosive gases, including high sulfur-content air. Before dismissing this requirement, consider the case of air-side economizers: if you're bringing in outside air, do you need to worry about contaminants in the air, such as diesel exhaust from nearby trucks or from diesel generators?
• Wider humidity range. Most NEBS equipment is designed for a wider range of allowable humidity exposure than most data center equipment. The broader use of economizers might make a wider humidity range desirable for data centers.
• Flame tests. NEBS flame tests may be overkill for most data center equipment, in part because most data centers have sprinklers or other fire suppression controls (unlike telecom central offices, which do not have sprinklers).
• Shake and vibe tests. NEBS equipment generally is tested to meet seismic Zone 4 earthquake tests. These tests could just as well apply to data center equipment, but it is something beyond what most data center equipment is validated against.
• Materials selection. The use of V0-rated plastics and HF-1 or better foams in data center equipment is not necessarily a cost adder if designed in up front, but it can add appreciable expense if retrofits have to be made after-the-fact.
• Air filters. Data center equipment generally doesn't need air filters, so these can be eliminated.
• Long life. This actually encompasses two aspects: extended availability of certain components and long-life reliability. Telecom products often require the availability of the same components for 5-7 years, much longer than typical data center products. Similarly, telecom products often are designed to meet usable lifetimes that are much longer than most data center refresh cycles.

Which of these attributes are needed for equipment in data centers with higher temperatures? What other attributes are needed for higher temps?

--kb

Containerized Data Centers in Buildings

Much of the focus with containerized data centers has been on mega-facilities that can house dozens of shipping containers.

Another use case where containerized data centers could make sense is in retrofitting buildings, though it may be somewhat counter-intuitive.

Building a state-of-the art facility can take a long time, but clearing out an open space and then lifting in a container could be a much faster approach to getting an optimized facility installed in a building than trying to get it built in place. Furthermore, it's possible to replace a set of equipment the same way.

This could be used with a single container, or there could be multiple containers placed together on the same floor of an office building.

--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

Temperature and Climate Data Around the World

One of the issues that affects the efficiency of data centers is the climate in which the data center is located. A well-run data center in Phoenix could draw more power than a poorly run data center in Toronto. When looking at measures of data center efficiency, it's important to consider these factors.

There's a nifty utility available from UCLA called Climate Consultant (see
http://www.aud.ucla.edu/energy-design-tools/tools/Climate4.exe or
http://www2.aud.ucla.edu/energy-design-tools/). This software allows you to draw
psychrometric charts, plot average/min/max temperatures, etc. for any location for which you have the proper type of weather file. For example, the graphic at the right shows a psychrometric chart for Hillsboro, Oregon.


Not only is this utility free, you can get weather data for many locations for free. The U.S. Department of Energy (DoE) maintains weather data for over a thousand locations around the world, including most airports at http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm. For example, http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data3.cfm/region=4_north_and_central_america_wmo_region_4/country=1_usa/cname=USA#OR provides data for several sites in Oregon. Just save the .EPW file to your local hard disk, and you're good to go.


Enjoy,
--kb

P.S. Thanks to Pasi Vaananen for the pointer to this tool.