Data Sheet

3 - 5
Technical System Catalogue/Climate control
TopTherm fan-and-filter units
Calculation basis for enclosure climate control
In natural convection, heat loss is dissipated to the outside
via the enclosure panels. The prerequisite for this is that the
ambient temperature must be lower than the temperature
inside the enclosure. The maximum temperature increase
(
ΔT)
max.
which may occur inside an enclosure compared with
the ambient air is calculated as follows:
Note:
If the heat loss inside the enclosure is not known, this basic
formula can be used to calculate actual heat loss, by meas-
uring the ambient temperature T
u
and the enclosure internal
temperature T
i
:
(ΔT)
max.
=
Qv
k  A
.
Q
S
= A  k  ΔT (watts)
.
Q
v
= Heat loss installed in the enclosure [W]
Q
s
= Heat emitted by the enclosure surface [W]
Qs > 0: Radiation (T
i
> T
u
)
Qs < 0: Irradiation (T
i
< T
u
)
Q
K
= Required cooling output of an enclosure cooling unit [W]
Q
H
= Required thermal output of an enclosure heater [W]
q
w
= Specific thermal output of a heat exchanger [W/K]
V = Required volumetric air flow of a fan-and-filter unit to main-
tain the maximum permissible temperature difference
between the supply air and the exhaust air [m
3
/h]
ΔT=T
i
– T
u
= Max. permissible temperature difference [K]
A = Effective, heat loss-dissipating enclosure surface area to
IEC 890 [m
2
]
k = Heat transfer coefficient [W/m
2
K]
for sheet steel k = 5.5 W/m
2
K
.
.
.
.
.
.
.