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The IEC Committee SC 48 D has developed a new Standard for the cooling of cabinets (Picture 1). The aim of this standard is the provision of guidelines for the selection of air/water heat exchangers with a performance up to 35 kW for cabinets and subracks and the indication of parameters, which result from the various configurations.
Planning of cooling concepts
The factor that is known in relation to the cooling of an installation is the expected performance loss. Here the first decision has to be made with regard to the cooling concept. If the expected performance loss lies above 1 kW, it may be necessary to deploy other mediums, such as Water, for the cooling. There are multiple air/water heat exchangers on the market: base or side assembly (Picture 1), with either horizontal or vertical air flow, bolt-on versions to the top or bottom etc. However, the solutions can seldom be compared. The new standard, which was developed together with manufacturers and users, solves these problems and offers assistance with diagrams, calculation examples for a professional planning process.
Planning of cooling concepts
The factor that is known in relation to the cooling of an installation is the expected performance loss. Here the first decision has to be made with regard to the cooling concept. If the expected performance loss lies above 1 kW, it may be necessary to deploy other mediums, such as Water, for the cooling. There are multiple air/water heat exchangers on the market: base or side assembly (Picture 1), with either horizontal or vertical air flow, bolt-on versions to the top or bottom etc. However, the solutions can seldom be compared. The new standard, which was developed together with manufacturers and users, solves these problems and offers assistance with diagrams, calculation examples for a professional planning process.
Picture 1: Water-cooled VARISTAR with side assembly of air/water heat exchanger LHX20
The new Standard
It is expected that the new IEC/TS 62454 Ed.1.0 will be issued at the beginning of 2007. It relates to cabinets, for which the dimensions were defined in the well-known standards IEC 60297 (19") and IEC 60917 (metric). The standard divides the water cooling in cabinets into three levels.
Level I - cabinet platform: cabinet with an air/water heat exchanger (base or side assembly). A global view point, whereby the entire control cabinet/electronic enclosure is cooled with an air/water heat exchanger.
Level II - Shelf (subrack) platform: cabinet with a smaller air/heat exchanger, which is located at the side, to cool an individual or a group of subracks.
Level III - Board platform: The most profound platform, where the water cooling has a direct impact on the boards or chips.
Level I
This level describes the framework conditions and supplies calculation examples for applications with air/water heat exchangers, which are either assembled at the base or the side of the cabinet.
Independently of which solution is selected (base or side assembly), the user can now establish the required footprint for his application with the aid of a diagram or through the calculation with formulas. The dimensions of the assembled components are defined with a depth of 400 mm and the cabinet widths is defined at 600 mm. For the noise generation the air speed vmax plays a substantial role. A diagram establishes the values at an air speed of vmax 3 m/s, which corresponds to a noise level of ≤ 45 dB(A) in accordance with DIN EN ISO 11690-1. A second diagram is valid for an air speed of vmax 5 m/s, which corresponds to a noise level of ≤ 55 dB(A) in accordance with DIN EN ISO 11690-1. The starting values for the establishment of the required cabinet depth are the Δ T between the internal cabinet and ambient temperature in Kelvin as well as expected performance loss Q in kW.
Example 1 (Picture 2):
It is expected that the new IEC/TS 62454 Ed.1.0 will be issued at the beginning of 2007. It relates to cabinets, for which the dimensions were defined in the well-known standards IEC 60297 (19") and IEC 60917 (metric). The standard divides the water cooling in cabinets into three levels.
Level I - cabinet platform: cabinet with an air/water heat exchanger (base or side assembly). A global view point, whereby the entire control cabinet/electronic enclosure is cooled with an air/water heat exchanger.
Level II - Shelf (subrack) platform: cabinet with a smaller air/heat exchanger, which is located at the side, to cool an individual or a group of subracks.
Level III - Board platform: The most profound platform, where the water cooling has a direct impact on the boards or chips.
Level I
This level describes the framework conditions and supplies calculation examples for applications with air/water heat exchangers, which are either assembled at the base or the side of the cabinet.
Independently of which solution is selected (base or side assembly), the user can now establish the required footprint for his application with the aid of a diagram or through the calculation with formulas. The dimensions of the assembled components are defined with a depth of 400 mm and the cabinet widths is defined at 600 mm. For the noise generation the air speed vmax plays a substantial role. A diagram establishes the values at an air speed of vmax 3 m/s, which corresponds to a noise level of ≤ 45 dB(A) in accordance with DIN EN ISO 11690-1. A second diagram is valid for an air speed of vmax 5 m/s, which corresponds to a noise level of ≤ 55 dB(A) in accordance with DIN EN ISO 11690-1. The starting values for the establishment of the required cabinet depth are the Δ T between the internal cabinet and ambient temperature in Kelvin as well as expected performance loss Q in kW.
Example 1 (Picture 2):
Picture 2: Diagram to establish the cabinet depth with an air/heat exchanger assembled at the side
Air/water heat exchanger assembled at the side (horizontal air flow), air speed vmax = 3 m/s and a ΔT = 15 and an expected performance loss Q = 10 kW. If these values are entered into the corresponding diagram, a necessary cabinet depth of 700 mm is obtained. With an air speed vmax = 5 m/s the necessary cabinet depth is less with 600 mm.
The same result can be obtained with the following formula:
D = DR + DF + DE
(D = cabinet depth; DR = distance between installed components and rear panel; DF = distance between component front panels and front door; DE = depth of the installed components)
DR = 1.25 x DF
D = 1.25 x DF + DF + DE
D = 2.25 x DF + DE
(Q = performance loss; ρair = air density; v = air speed; Heff = 1600 mm cabinet height; Cpair = heat capacity of the air; ΔT = temperature difference between internal cabinet and ambient temperature)
Example 2:
Air/water heat exchanger assembled at the bottom of the cabinet (vertical air-flow), air speed vmax = 3 m/s. At a ΔT = 15 and an expected performance loss Q = 10 kW a necessary cabinet depth of 1100 mm is obtained. With unchanged data but an air speed vmax = 5 m/s only a cabinet depth of 900 mm is necessary. Here, too, the cabinet depth can be calculated with formulas.
In all diagrams and formulas a 25 % tolerance is included. This takes into account such things as the air flow being obstructed at the front and rear of the installed components through for instance cabling.
Level II
This level describes the framework conditions and supplies the calculation examples for applications with smaller air/water heat exchangers, which are assembled at the side of the cabinet and only cool parts of the cabinet, such as individual subracks or groups of subracks (Picture 3). The air/water heat exchangers planned for this solution by the manufacturers and users and now defined by the standard work with vertical air flow. This means that above and below the subrack or subracks an area for air circulation and redirection has to be allowed. How many U the user has to calculate for this, can be worked out with diagrams or with formulas.
The same result can be obtained with the following formula:
D = DR + DF + DE
(D = cabinet depth; DR = distance between installed components and rear panel; DF = distance between component front panels and front door; DE = depth of the installed components)
| DF = | Q |
| ρair x v x Heff x Cpair x ΔT |
DR = 1.25 x DF
D = 1.25 x DF + DF + DE
D = 2.25 x DF + DE
(Q = performance loss; ρair = air density; v = air speed; Heff = 1600 mm cabinet height; Cpair = heat capacity of the air; ΔT = temperature difference between internal cabinet and ambient temperature)
Example 2:
Air/water heat exchanger assembled at the bottom of the cabinet (vertical air-flow), air speed vmax = 3 m/s. At a ΔT = 15 and an expected performance loss Q = 10 kW a necessary cabinet depth of 1100 mm is obtained. With unchanged data but an air speed vmax = 5 m/s only a cabinet depth of 900 mm is necessary. Here, too, the cabinet depth can be calculated with formulas.
In all diagrams and formulas a 25 % tolerance is included. This takes into account such things as the air flow being obstructed at the front and rear of the installed components through for instance cabling.
Level II
This level describes the framework conditions and supplies the calculation examples for applications with smaller air/water heat exchangers, which are assembled at the side of the cabinet and only cool parts of the cabinet, such as individual subracks or groups of subracks (Picture 3). The air/water heat exchangers planned for this solution by the manufacturers and users and now defined by the standard work with vertical air flow. This means that above and below the subrack or subracks an area for air circulation and redirection has to be allowed. How many U the user has to calculate for this, can be worked out with diagrams or with formulas.
Picture 3: Principle assembly of an air/water heat exchanger for the partial cooling of a subrack inside a cabinet
Example 3:
Smaller air/water heat exchanger assembled at the side of the cabinet (vertical air flow), air speed vmax = 3 m/s, W = 600 mm, W1 = 800 mm, W2 = 200 mm, DE = 400 mm and D ≥ 600 mm. With ΔT = 22.5 K and a performance loss of the subrack of Q = 2,5 kW this results in 3.82 HE (4 U are standardised) additional U for air circulation and redirection above and below the subrack. If the subrack has 14 U, the user has to plan for 18 U.
Level III
This level deals with water cooling of individual components/chips directly on the boards. The possible cooling solutions are so manifold due to the dimensions and positions of the components that need to be cooled, that the members of the standards consortium decided not to restrict this by tight definitions. Therefore Level III only defines that water connections have to be present in the cabinet, leading to quick-release connectors at the front or rear of the subracks. The principle of water cooling of individual components is outlined. The detailed configuration is left to the manufacturers/users.
Smaller air/water heat exchanger assembled at the side of the cabinet (vertical air flow), air speed vmax = 3 m/s, W = 600 mm, W1 = 800 mm, W2 = 200 mm, DE = 400 mm and D ≥ 600 mm. With ΔT = 22.5 K and a performance loss of the subrack of Q = 2,5 kW this results in 3.82 HE (4 U are standardised) additional U for air circulation and redirection above and below the subrack. If the subrack has 14 U, the user has to plan for 18 U.
Level III
This level deals with water cooling of individual components/chips directly on the boards. The possible cooling solutions are so manifold due to the dimensions and positions of the components that need to be cooled, that the members of the standards consortium decided not to restrict this by tight definitions. Therefore Level III only defines that water connections have to be present in the cabinet, leading to quick-release connectors at the front or rear of the subracks. The principle of water cooling of individual components is outlined. The detailed configuration is left to the manufacturers/users.
With this first standard for water cooling in cabinets, the user obtains a practice orientated tool, which provides rules and guidelines, concrete planning and calculation models, where requested and where freedom is required, this is not restricted.
