Today’s Data Center Cools it—Economically
The latest approach to data center cooling uses separate hot and cold aisles for the data equipment. Equipment runs at higher temperatures than in the past. The cool, low-humidity northwest climate allows total reliance on outside air for cooling.
A robust high-density power and cooling infrastructure is designed to deal with a heating load of 150w/sf scalable to 230w/sf, with 100 percent free cooling.
The cold aisle is to be maintained at 78 °F (max) between 20 % and 80 % RH (the relative humidity limits are intended to prevent static discharge and condensation). The hot aisle is designed for a 20 °F rise across the servers. This hot-aisle/cold-aisle segregation optimizes the outdoor-air economizing potential. Direct evaporative cooling and humidification can support all of the cooling needs of the raised floor area. This design differs from the conventional method of delivering 50 °F to 55 °F supply air that mixes with the heat rejected from the server racks. The design will provide up to 75 % energy savings compared to traditional chilled water system cooling.
The tile floor is divided at regular intervals by return air grids. Racks of computer servers in the data center are set up on each side of these grids, and air warmed by the data equipment (the hot side) is drawn into the space below. The data center occupies the building’s second story, while the first story serves as a return air plenum. Exhaust fans in the first story space serve to balance the air pressure inside.
From the first-story space the heated air is moved to the third story, where it is mixed with outside air as needed to cool the computer servers. In addition to air handlers, this space contains new evaporative cooling equipment that can be used to bring the air temperature down on the warmest days. On very cold days (15 °F) heat from data servers will warm the building. The evaporative system will also run during the winter to maintain the minimum relative humidity in the space. But that, according to McKinstry engineer Michael Frank, will be rare.
“We will be in economizer operation, mixing return air with outdoor air with no mechanical cooling or evaporative cooling required, for approximately 8,500 hours out of the year, with only 260 hours where we will be using evaporative cooling,” Frank said. “Mechanical cooling is not required for the data
center space at all.” The existing chilled water system will serve some support spaces and equipment rooms that were left unchanged during the retrofit.