There is also the extreme situation of HVAC systems installed in temperate areas. They can become the building’s heating system in cold weather.
If these potential problems can be avoided, dedicated air conditioning is an effective cooling technique, and in some cases the only practical solution to avoid damage by overheating.
Guidelines are not complicated; cool air should be delivered via a supply point high and in front of the rack, while the return for heated exhaust air should be located high and behind the rack.
Of the many types of analog and digital equipment being installed today, almost all fan-equipped components draw cooling air in front of their front panels and exhaust it to the rear. The arrangement described allows a ‘waterfall’ of cold air to fall in front of the rack where it can be pulled in, while a high-mounted exhaust fan in the top of the rack, or high on its rear panel, pulls heated air out into the return duct.
Integrators can accommodate those components without internal fans by placing passive vent panels below them. If the exhaust fan has been properly sized, it will pull conditioned air in. In some cases, it may be necessary to use one or more small fans inside the rack to prevent pockets of stagnant heated air from accumulating.
If the building’s HVAC system can accommodate the extra heat load, it may only be necessary to use the third rack cooling technique. This will provide active thermal management using only strategically-located fans, eliminating the cost and complexity of refrigeration.
Moving the necessary number of cubic feet or air through a rack every minute can be accomplished using ventilation systems available on the market. For freestanding racks, it is a matter of pulling heated air out from the top of the rack and replacing it with cool room air entering at the bottom (we have made the assumption that the rack is in a conditioned space, and that the building’s HVAC system can deal with the heat generated in the rack).
Fan systems are available which can be mounted near or at the top of the rack. They draw heated air up from below and discharge it through their front panel into the room. Other systems discharge the heated air straight up through the top of the rack.
Neither of these systems is effective when the rack itself is enclosed in a closet or millwork. In this case, we must first get the hot air out of the rack, and then get the hot air out of the closet. Systems are available that perform both functions; they pull air up from lower parts of a rack, then move it through flexible tubing to an area outside the closet.
Better ventilation systems represent a trade-off between moving air and generating noise. When the system is in a remote equipment room, noise is not an issue; when it’s in the board room, noise from fan motors and air movement becomes bothersome. Consulting with cooling system makers’ technical personnel is a great help during the design process.
Read an extended version of this article on CI sister site CorporateTechDecisions.com.