4-6
b
1
) Forced ventilation with heat exchanger in closed panels:
It can be used when either the “harsh” environments or the high dissipated power don’t allow for natural
convection. A heat exchanger with a fan pulls the air into the cabinet and forces it into the heat exchange plates
that are cooled by the external ambient air moved by a second fan. By using such an exchanger, provided it is
efficient and well maintained, the allowable power dissipation for equal temperature rise can be 5 to 6 times higher
than in A1.
b
2
) Forced ventilation in open panels:
Here filtered air is taken from the bottom cabinet openings by one or more fans creating an air flow through the
equipment which exits at the top of the cabinet. Fan dimensioning must be such to guarantee the required air flow,
as expressed by the formula:
Q
P
t
=
⋅31.
∆
Q = required minimum air flow in m3/h
P = power in watts to be dissipated in the cabinet
∆t (°C) = temperature rise of the cabinet
For the example cabinet (neglecting the cooling contribution of the side surfaces) for a ∆t = 10 °C (18°F) and a
power of 1000 W the minimum required air flow is
Q m h=
⋅
=
31 1000
10
310
3
.
/
c) Air conditioned cabinets:
This approach offers the advantage of obtaining a cabinet temperature equal or even lower than the ambient
temperature, becoming the ideal solution for hot climates. A specific refrigerating system can be used or, when
applicable, the existing air conditioning system can be used also for cabinet conditioning. In each case the
refrigerator size is related with the amount of heat to be removed due to the internally dissipated power.
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