46
Unidrive M Modular Installation Guide
Issue Number: 2
Calculation of temperature rise in enclosure inputs
Table 5-3 Example data
For this example it is assumed the drive is in an altitude below 1000 m
and the enclosure it is mounted in has input and output ventilation.
Calculate open area % of venting and recirculation factor
= (0.27 + 0.15) x 100 / (2 x 0.8 x 0.5)
= 52.5%
From Figure 5-29 the re-circulation factor = 0.76.
Figure 5-29 Recirculation factor
This is an approximation of the amount of air that is re-circulated within
the enclosure due to inlet and outlet venting restrictions. The factor has a
safety factor built in to it to ensure a safe result. The factor has been
calculated using CFD software, testing the amount of heat flow back into
the drive when different vent restrictions are given. The factor can also
be applied to an Unidrive M size 9/10 E and separated Unidrive M size 9/
10 D.
Calculate loss which affects the drive inlet air temperature
Loss affecting drive temperature (Pr) = Lower choke Loss (Pc) +
(Total loss of single drive (Dp) x Recirculation factor (Rf))
= 250 + (4290 x 0.76)
= 3510 W
This is the loss from 1 drive unit only as simulations have shown that
with drives mounted inline and in a symmetric system the losses are
shared equally.
Calculate temperature rise
Table 5-4 Air flow rates
Calculating temperature rise in enclosure
dT = 3kPr/V
Where:
V
= Airflow in m
3
/hr (Unidrive flow rate = 305)
dT
= Temperature rise
Pr
= Loss affecting drive temp
k
= 1 / Altitude de-rate
Therefore ambient temperature rise (
dT
):
= (3 x 1 x 3510.4) / 305
= 34.5
°
C
So,
Ambient temperature inside enclosure = External a
temperature rise = 64.5
°
C
This shows that with the maximum allowable ambient drive temperature
of 40
°
C, the enclosure will overheat.
Processing results
Option 1:
If the absolute temperature inside the enclosure is still less
than 50
°
C, select a drive with the correct rating at 50
°
C.
Option 2:
Add more venting, if possible, to reduce the recirculation and
recalculate.
Option 3:
Add an enclosure fan.
Option 4:
Redesign the enclosure so that the drives can be through
panel mounted. This means that most of the heat can escape outside
the main enclosure, and the input air into the heat sinks will remain at the
external ambient and not be affected by recirculation. Refer to section
5.5.2
Heat loss through the front of the drive still needs to be considered.
Adding enclosure fan
Calculate required flow rate
•
Fan needs to remove the effect of re-circulation and the added
choke loss.
•
Loss effecting drive temp (Pr) = 3510.4 W
•
The above Loss of 3510.4 W is for one drive only, so with an
enclosure of 2 units the total loss to remove = 7020.8 W
Calculate the temperature rise allowed in the enclosure:
Temperature rise (dT) = (Allowable drive ambient - 5 {safety
factor}) - External ambient
= (40 - 5) - 30
= 5
°
C
Then using:
V = 3kPr/ (dT)
Flow rate required to remove loss = (3x1x7020.8) / 5
= 4212.5 m
3
/hr
Calculate back pressure on fan
Output sharing choke loss under single unit (L2)
250 W
Total loss of single drive
4290 W
Number of drives in enclosure
2
Width of enclosure
0.8 m
Depth of enclosure
0.5 m
Open area of roof vent (outlet)
0.27 m
3
Open area of inlet vent
0.15 m
3
External ambient
30
°
C
Altitude derate factor (Cf x Df)
1
Open area of venting %
Open area of roof + open area of inlet x 100
2 x cubicle width x cubicle depth
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=
1
0.8
0.6
0.4
0.2
0
Recirculation
factor
0
20
40
60
80
100
120
Open area (%)
1.2
NOTE
Modules
Flow rate (m3/hr)
Inverter
402
Rectifier
266
NOTE
Open area of venting %
Open area of roof + open area of inlet x 100
2 x cubicle width x cubicle depth
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