Over the last few weeks while I have been traveling there have been some interesting bits of information released in the mission critical world.For example, Dell introduced their 12th generation PowerEdge servers. This generation of servers is warranted to handle temperature excursions up to 45 degrees C, or 113 degrees F, for up to 90 hours per year. One of Dell’s rationales behind marketing the server at those conditions was to allow fresh air cooling in virtually the entire continental US. Other research by Dell has indicated that their servers can operate 87% of the year in Washington, DC using fresh air cooling alone.
The energy saving potential of raising the inlet temperatures that high can be enormous. Instead of running chillers or compressors 8,760 hours a year they are only operating 1,138 hours per year.To put that into numbers is difficult but let’s try a little example.
If the PowerEdge server power consumption is 300 watts then the cooling system must remove 300 watts times 8,760 hours per year or 2,628 kwh of heat (8,961,480 btu). That can either be accomplished using mechanical cooling or fresh air cooling or a combination of the two.A pretty efficient HVAC system will remove about 4.5 watts of heat per watt of electrical energy used. So to cool that PowerEdge server using mechanical cooling will require 2,628,000 watts of heat divided by 4.5, or 584 kwh of compressor power.
To cool that same server using fresh air for 87% of the year will only require 75.8 kwh of compressor power. Of course, the fan energy stays the same in both cases but the compressor savings of 508.2 kwh PER SERVER can really start to add up. At an aggressive electric rate of 4.5 cents/kwh that amounts to $22.87 PER SERVER PER YEAR.At modest densities of, say, 40 servers per rack the savings amounts to $915 PER RACK PER YEAR. Now consider how many racks are in the typical server room or data center. If the data center has a server load of 1 megawatt then a density of forty, 300 watt, servers per rack will translate into 83 racks. So the annual savings would be almost $76,000 in this example.
To make the savings even greater the same HVAC unit that provides the fresh air could also provide indirect evaporative cooling and completely eliminate the compressor-based cooling…adding another $3.50 PER SERVER PER YEAR of savings. That would add another $11,620 PER YEAR in savings.