Computer equipment is continually evolving to operate at higher power levels. Increasing power levels pose challenges with regard to heat management. For example, many data centers now employ individual racks of blade servers that can develop 20,000 watts, or more, worth of thermal load. Typically, the servers are air cooled and, in most cases, the data center air cooling systems are not designed to handle the thermal load.
To help address this problem, computer equipment in data centers are commonly arranged using a “hot aisle/cold aisle” configuration. According to this scheme, racks of computer equipment are arranged in a series of rows forming a series of aisles, such that the computer equipment draws cooled air from one aisle (a “cold aisle”) and expels heated air into another aisle (a “hot aisle”). A hot aisle/cold aisle configuration increases the efficiency of a data center cooling system by reducing mixing of the heated and the cooled air.
Cooled air is usually supplied to the computer equipment by an air cooling unit, e.g., via a cold aisle. The heated air expelled from the computer equipment travels back to the air cooling unit, e.g., by way of a hot aisle. At the air cooling unit, the air is cooled, completing a full cooling cycle.
Ideally, according to the cooling cycle described above, the cooled air travels directly to an air inlet in the computer equipment where it cools the equipment, is exhausted directly to a hot aisle and then returns to the air cooling unit so as to complete a direct loop through the equipment being cooled. Inefficiencies arise, however, when cooled air is supplied and returns directly to the air cooling unit without circulating through the equipment.
Inefficiencies can also arise when heated exhaust air, rather than returning to the air cooling unit, recirculates back into the equipment. There are a number of such recirculation possibilities. Air recirculation constitutes an energy loss, in that energy is spent circulating the flow, but cooling does not result. This problem is compounded in data centers where the hot aisle/cold aisle arrangement is not employed. In such cases, heated exhaust air from the equipment on one rack can flow directly into the air inlets of equipment on an adjacent rack.
Recirculation difficulties can be most severe for equipment located at the tops of racks. Namely, cooled air can be drawn off by equipment lower in the racks leaving only heated expelled air to be drawn into the equipment located higher in the racks.
Significant cooling system optimization is now required to handle the modern generation of servers and storage systems as data centers expand their capabilities. Thus, techniques for increasing the effectiveness and efficiency of data center cooling systems would be desirable.
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