Articles and whitepapers

Understanding Thermal Management: A Systems Approach to Effective Thermal Management Solutions for Electronic Equipment Enclosures (4/7/2007)

By Middle Atlantic Products

Maintaining the temperature inside racks and enclosures is critical to the proper functioning and survival of the circuits operating within. Most studies have shown that for every 5.5oC rise over 29.5°C, digital equipment life is reduced by approximately 40%. It is essential to ensure the heated air within the enclosure remains at a temperature of no more than 29.5oC to help protect the sensitive equipment mounted within.

There are two approaches to securing an adequate internal enclosure temperature for the successful operation of the components enclosed: passive and active thermal management. Passive makes use of the ability of a properly configured system to ventilate through natural convection. In certain cases, however, the use of fans to force air through an enclosure (active) is necessary to maintain the desired internal temperature. Please refer to the nomograph located on the back page to determine whether your system will require passive or active thermal management.

In addition to the proper configuration of your rack system, room design is critically important to the success of rack and enclosure thermal management. It is essential that not only does the equipment room have the ability to remove the heat generated by the racks, but also that racks are placed strategically within the room to ensure no re-circulation of air occurs.

Thermal technique: passive thermal management

The passive approach to thermal management involves capitalizing on natural airflow. Adequate vent openings in the top and bottom portions of an enclosure, as well as an unimpeded airflow, and placing hotter equipment lower in the rack will enhance the natural flow of air, as heat naturally rises. There is a wrong and right way to approach passive thermal management:

Thermal technique: active thermal management

In many instances, equipment located within an enclosure will produce too much heat for passive thermal management (convection) to properly ventilate the enclosure. In this event, the use of forced air (fans) is instrumental to maintaining the optimal 29.5oC temperature recommended. Keys to the successful implementation of active thermal design include the use of top-mount fan(s) and no venting in the upper 6 rackspaces, upper sides, upper front or upper rear door, to prevent short-circuiting of air at the top of the rack. There is a wrong and right way to approach active thermal management:

The key to successful active thermal management is ensuring there are no open vents at the top of the rack. The laws of static pressure dictate that fans will pull air from the easiest path (closest opening). This will create an undesirable recirculation of air, forming a stratification zone if upper vents are not blocked.

How to calculate ventilation required to provide an interior rack temperature of 29.5°C

This nomograph will show the minimum ventilation (active or passive) required, to provide an interior rack temperature of 29.5°C.

To calculate total waste heat (column B):

1. Obtain total waste heat output by combining the published waste heat BTU/Hr. of all amplifiers in the rack.

2. Add up total measured amperage draw from all other equipment and multiply by 800 (total amperage x 800 = total BTU/Hr. @220v.)

3. Combine BTU/Hr. totals from steps 1 and 2 to obtain total for all equipment. Mark total in column B.

* When voltage doubles, amperage draw is cut in half.

To obtain minimum ventilation requirements:

1. Mark ambient room temperature in column C and connect points in B and C with a straight edge.

2. The minimum cooling required providing an interior rack temperature of 29.5oC will be shown on column A, where the straight edge intersects the minimum cooling requirements column.

Common conversion formulas

1 M3/Min. = 35.31 CFM
1 Watt = 3.41 BTU
1 BTU/Hr. = .293 Watts
1 Watts = Volts x Amps

Nomograph

Calculate ventilation required to provide an interior rack temperature of 29.5°C.

Passive Ventilation requirements

(A) Fully vented rear door, vented rack top, in vented-face rack
(B) Fully vented rear door, vented rack top, in solid-face rack
(C) Solid rear door, vented rack top, in vented-face rack
(D) Solid rear door, 4 space vent in upper rackspace, solid top (E) Solid rear door, 2 space vent in upper rackspace, solid top

Middle Atlantic Products, Inc. is headquartered in Fairfield, New Jersey and is an ISO 9001:2000-registered leading manufacturer of state-of-the-art steel enclosure systems for a wide range of applications, including the custom residential, commercial audio video installation, broadcast, security, post production, structured cabling and premise wiring markets.

www.middleatlantic.com