|
Roberto Felisi, senior product manager, mission critical cooling, Emerson Network Power EMEA, considers the practicalities of thermal management
Thermal management an ever-present consideration where equipment utilizes integrated circuit board technology. Caused by the passage of electrons, the heat can be minimised by designing the integrated circuit to monitor and control processing speed to match actual system demand. If there is still excess heat, this is generally transferred away to be released into the surrounding air, or to be dealt with by, or as part of, a supporting environmental system.
In many instances, the eventual release of the transferred heat into the surrounding air will not cause a further problem. Careful placement of the equipment should enable the normal circulation of air or the operation of a general air conditioning system to dissipate the waste heat. However, where processing equipment is concentrated it may be necessary to install a dedicated environmental system and this is particularly true in the case of a computer room or data centre. In such a setting, an under floor air cooling system is generally installed that releases chilled air through floor tiles that cools the waste heat generated by server microprocessors.
The growth of blade server technology has, however, shown that the waste heat being generated can overwhelm even specialized cooling systems of this sort, which should generally only be expected to handle loads of up to 5kW per industry standard rack with racks positioned in alternate hot aisle/cold aisle formation. Consequently, additional cooling capacity needs to be installed if high-density server consolidation is to be possible. Cold Comfort
Supplementary cooling may take the form of units suspended above the server racks, or placed on top of the racks, neither solution taking up valuable floor space. These units capture the excess heat being transferred away from the equipment in the racks and release it as cool air into the cold aisle. Solutions of this nature are currently available that are able to deal with all of the excess heat generated by fully populated racks of blade servers. Another currently available solution offers a completely different concept, as it takes the form of a cabinet with built in power distribution and closed loop cooling capacity that provides a dedicated environment for one standard rack.
The cabinet is, in effect, a stand-alone data centre, with the operation of the closed loop cooling system module removing the need to discharge the transferred heat load from the rack into the environment surrounding the cabinet.
The self-contained nature of the cabinet is re-enforced by the inclusion of back up ventilation, fire extinguishing and monitoring capabilities with full redundancy. As further high density racks need protection, additional stand alone cabinets can be deployed, connected via a LAN to enable immediate activation of a standby cooling unit in the event of failure.
This novel all-in-one concept has one further special feature. As the cabinet cooling system has a short and close air circuit, the cooling capacity must precisely match the heat load. Part of the essential heat transfer process is to compress the gas refrigerant to the desired discharge pressure, using scroll compressor technology, based on two spiral scrolls. The movement of the scrolls creates a series of gas pockets travelling between the two scrolls and these pockets are continually compressed towards the centre of the scrolls, where they are discharged as high-pressure gas. The need to match the cooling capacity to the heat load created a design challenge, as modulation normally involves powering the compressor on and off. This would not provide the continuing accurate match required, as the on/off action of the compression cycle would result in either an under-shoot or an over-shoot.
The design solution is an innovative feature that utilises a solenoid valve, piston and spring to separate the scrolls, controlling the compression cycle, without involving powering on and off, allowing continuous modulation to precisely suit the system’s needs, in a range from 2 to 23kW.
Moving On
Thermal management has played an important part in the design of electrical equipment, leading to the development of sophisticated methods of heat transfer. The necessary subsequent control of the waste heat has also involved innovative solutions and as microprocessors increase in density, which can be expected to continue for some time yet, thermal management will remain a hot topic.
|
