
3
Server blade systems and 1U servers let you assemble high-density infrastructures; however, these
systems create much more heat per square foot of floor space and more hot spots. In instances like
this, the open-area approach cannot keep up with the demand for cool air.
Figure 2 compares two examples of server loading for a 42U rack. In Figure 2A, our rack contains
20 HP ProLiant DL380 G5 servers, each consuming approximately 424 watts for a total rack
consumption of 8.47 kW. In Figure 2B, our rack contains 42 dual-processor DL160 G6 servers
consuming 383 watts per server for a total rack consumption of over 16 kW of power.
Figure 2: Examples of power consumption in 42U IT equipment racks with different server loads
Higher power consumption produces more heat. Virtually all power consumed by rack-mounted
equipment is converted to sensible heat, which increases the temperature in the environment. The
sensible heat load is typically expressed in British Thermal Units per hour (BTU/hr) or watts, where
1 W equals 3.413 BTU/hr. The rack’s heat load in BTU/hr can be calculated as follows:
Heat Load = Power [W] × 3.413 BTU/hr per watt
For example, the heat load for a ProLiant DL160 G6 server in a 2P configuration consuming
383 watts is calculated as follows:
383 W × 3.413 BTU/hr/W =1307 BTU/hr
This means that the heat load of our fully-loaded 42U rack of DL160 G6 servers is 54,901 BTU/hr. In
the United States, cooling capacity is often expressed in "tons" of refrigeration, which is derived by
dividing the sensible heat load by 12,000 BTU/hr per ton. Therefore, the cooling requirement for our
rack of DL160 G6 servers is computed as follows:
54,901 BTU/hr ÷ 12,000 BTU/hr per ton = 4.58 tons
A: ProLiant DL380 G5 2U servers
(20 servers @ 423.9 W per server)
Power
consumption
B: ProLiant DL160 G6 1U servers
(42 servers @ 383 W per server)
Power
consumption
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