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Views: 84 Author: Site Editor Publish Time: 2022-06-24 Origin: Site
a) What is a Computer Room Air Handler
The Computer Room Air Handler (CRAH) is used for the same purpose as a CRAC unit. However, CRAHs use only fans and cooling coils. They typically use a chilled water circulation system from a larger unified cooling system, using the same compressor and refrigerant system as a CRAC, but with better economies of scale, transferring heat from the data center floor to the outside of the building at a lower cost.CRAH systems utilize cold water, allowing multiple cooling methods to cool the water circulation. The energy transfer is not done directly on the data center floor, which is why CRAH is referred to as an indirect system. In addition, the different designs of CRAH significantly affect the cooling range; for example, one design can only reduce the air temperature by 12 degrees, while another design can reduce the air temperature by 23 degrees. As a rule, the higher the outdoor temperature, the more powerful the unit is required.
b) Other considerations for CRAH
CRAH systems are usually not equipped with supercooling facilities, so they help eliminate some of the problems of CRAC condensation in actual data halls. However, CRAH requires a larger supply and distribution network, which may mean that large water pipes must flow through the data center. This can create a risk of water spillage if a water pipe breaks or leaks. This is an important reason why data centers need to include leak detection systems.
In the early construction of large server rooms and data centers, almost all server rooms had raised floors. The raised space under the floor is an important conduit for airflow distribution. Cooling equipment sends cool air under the floor and distributes it evenly to the racks between equipment. In addition, data cables and power cords can be placed in the raised floor space. However, in recent years, more and more data centers are laying flat flooring while elevating cooling channels and power cables above the racks.
a) Raised Floor
The diagram below shows a raised floor environment where the CRAC/CRAH units are integrated directly under the data center floor along with the power and network. Therefore, cooling is accomplished by the cold air rising from under the floor through a ventilated floor placed in front of each cabinet or row of cabinets.
However, if the ventilated floors are too close to the cooling units, these ventilated floors may create a venturi effect, creating a low-pressure adsorption effect that reduces the cooling effect. At this point, the air velocity above the ventilated floor increases the pressure above the floor and reverses the air flow at the air ports due to the proximity of the CRAC or CRAH unit.
In most cases, the raised floor does not need to be very deep. However, installing a raised floor system uses a very costly hard floor. Therefore, data center designers and builders should carefully evaluate the environment in which the raised floor will be used.
