Issue link: https://cp.revolio.com/i/148754
Figure 7 - Temperature Plane at 3' AFF. 75 °F SA, with Hot Aisle Containment Figure 7 is again the temperature plane at 3 feet above the floor at a 75 °F supply air temperature, given the containment scenario described above. The ambient temperature averages 76 °F (~ supply air temperature) with much more contained and significantly higher temperatures within the hot aisles. Notice that the ΔT across the hot and cold aisles almost exactly matches the 20 °F ΔT as modeled across the servers. Figure 8 below displays rack inlet temperatures (°F) throughout the data center. The maximum rack inlet temperature is 92°F with many racks above the ASHRAE maximum recommended temperature of 80.6 °F, as given previously in Table 1. Although the allowable range is above 80.6 °F for various server types, we will focus on the maximum recommended value here. Figure 9 below displays rack inlet temperatures (°F) throughout the data center for the containment scenario. The maximum rack inlet temperature is 79°F with all racks below the ASHRAE maximum recommended temperature of 80.6 °F. There is only a 4 °F variation in rack inlet temperatures across all racks. The previous rack inlet temperature variation was nearly 18 °F across all racks without containment. "SCENARIO-BASED" ENERGY MODELING Figure 8 - Rack Inlet Temperatures at 75 F SA At this point we know how far we can comfortably raise the supply air temperature within the data center and what modifications are required to get there (containment). The next question to ask is, "How does all this affect the energy consumption of my facility?" The energy model constructed previously can be expanded to calculate total plant energy consumption and various data center metrics. A metric that is commonly utilized in the industry is Power Usage Effectiveness, or "PUE". The basic formulas are given below: Total Facility Power PUE = ___________________ IT Energy 1 PUE = _______ + 1 COP Total Facility kWh = It kW x PUE x 8,760 hrs Figure 9 - Rack Inlet Temperatures at 75 F SA, with Hot Aisle Containment A PUE of 3.0 is considered very inefficient whereas 1.2 is considered very efficient. These same metrics were also generated and compared in the same energy model for operation with a highly efficient UPS. This is shown in Figures 10 and 11 above. Once one of the energy has been set-up for a particular scenario, 45 °F CHWS for example, additional scenarios can quickly be modeled by copying the first and making minor adjustments. For this case it is assumed that a 45 °F CHWS corresponds to a 55 °F SA temperature off the cooling coils of the CRAC units. The actual control strategy may differ slightly, but is a reasonable estimate. Figure 12 is a plot of monthly averaged facility-wide PUE, with and without the installation of a new UPS. The solid RED line indicates a 45 °F CHWS temperature (55 °F SA) operating with a water-side the economizer and a highly efficient UPS operating in "Eco-mode" (~98.5% efficiency). The dashed light RED line is the same scenario 24 | THE DATA CENTER JOURNAL www.datacenterjournal.com