Heat generated in units and parts installed in a cabinet raises the
temperature of the air inside the cabinet, compared with the external air.
Since the generated heat is radiated from the surface of the cabinet, the
temperature of the air in the cabinet and the outside air balance at certain
heat levels. If the amount of heat generated is constant, the larger the
surface area of the cabinet, the less the internal temperature rises. The
thermal design of the cabinet refers to calculating the heat generated in the
cabinet, evaluating the surface area of the cabinet, and enlarging that
surface area by installing heat exchangers in the cabinet, if necessary.
Such a design method is described in the following subsections.
The cooling capacity of a cabinet made of sheet metal is generally 6 W/°C
surface area, that is, when the 6W heat source is contained in a
cabinet having a surface area of 1 m
, the temperature of the air in the
cabinet rises by 1°C. In this case the surface area of the cabinet refers to
the area useful in cooling , that is, the area obtained by subtracting the area
of the cabinet touching the floor from the total surface area of the cabinet.
There are two preconditions : The air in the cabinet must be circuited by
the fun, and the temperature of the air in the cabinet must be almost
constant. The relationship between the temperature rise inside the cabinet
and the temperature of the external air is represented in the following
Internal heat loss P [W] x
⋅°C] × surface area S[m
]×rise in temperature[°C]
For example, a cabinet having a surface area of 4 m
has a cooling capacity
of 24W/°C. To limit the internal temperature increase to 10°C under these
conditions, the internal heat must not exceed 240 W. If the actual internal
heat is 320W, however, the temperature in the cabinet rises by 13°C or
more. If the ambient temperature of the unit under the installation
environment cannot be satisfied, the cooling capacity of the cabinet must
be improved using the heat exchanger described next.
If the temperature rise cannot be limited to the permissible temperature
or lower by the cooling capacity of the cabinet, a heat exchanger must be
added. The heat exchanger forcibly applies the air from both the inside
and outside of the cabinet to the cooling fin to obtain effective cooling.
The heat exchanger enlarges the surface area.
A heat exchanger is to be prepared by the customer.
OF THE CABINET
within the Cabinet
Cooling by Heat