Total heat load consists of the heat
transfer from outside your panel and from the heat dissipated inside the
control unit.
Useful terms, and conversions:
1 BTU/hr = 0.293 watts
1 BTU/hr  0.000393 horsepower
1 Watt = 3.415 BTU/hr
1 horsepower = 2544 BTU/hr
1 Watt = 0.00134 horsepower
1 Square Foot = 0.0929 square meters
1 Square Meter = 10.76 square foot
1 BTU/hr  0.000393 horsepower
1 Watt = 3.415 BTU/hr
1 horsepower = 2544 BTU/hr
1 Watt = 0.00134 horsepower
1 Square Foot = 0.0929 square meters
1 Square Meter = 10.76 square foot
Typical fan capacity:
4" fan: 100 CFM (2832 LPM)
6" fan: 220 CFM (6230 LPM)
8" fan: 340 CFM (9628 LPM)
10" fan 550 CFM (15574 LPM)
6" fan: 220 CFM (6230 LPM)
8" fan: 340 CFM (9628 LPM)
10" fan 550 CFM (15574 LPM)
BTU/hr. cooling effect from fan 1.08 x
(temp. inside panel in ºF  temp. outside panel in degrees F) x CFM
Calculating
BTU/hr. or Watts :
1. Determine the heat generated inside the
enclosure. Approximations may be necessary. For example, if you know the power
generated inside the unit, assume 10% of the energy is dissipated as heat.
2. For heat transfer from the outside,
calculate the area exposed to the atmosphere except for the top of the control
panel.
3. Choose the internal temperature you
wish to have, and choose the temperature difference between it an the maximum
external temperature expected.
4. From the conversion table that follows,
determine the BTU/hr. per square foot (or watts per square meter) for the
temperature difference.
5. Multiply the panel surface area times
the BTU/hr. per square foot (or watts per square meter) to get the external
heat transfer in BTU/hr or in watts.
6. Sum the internal and external heat
loads calculated.
7. If you do not know the power used in
the enclosure but you can measure temperatures, then measure the temperature
difference between the outside at current temperature, and the present internal
cabinet temperature.
8. Note size and number of any external
fans. Provide this information to Nex FlowT to assist in sizing the appropriate
cooling system.
Temperature Difference in ÂºF

BTU/hr./sq. ft.

Temperature Difference in ÂºC

Watts/sq.m

5

1.5

3

5.2

10

3.3

6

11.3

15

5.1

9

17.6

20

7.1

12

24.4

25

9.1

15

31.4

30

11.3

18

39.5

35

13.8

21

47.7

40

16.2

24

55.6

Example:
The control panel has two frequency drives
totaling 10 horsepower and one module rated at 100 watts. The maximum outside
temperature expected is ºC. The area of the control panel exposed sides, except
for the top is 42 square feet or 3.9 square meters. We want the internal
temperature to be ºC.
Total internal power is 10 hp x 746
watts/hp  7460 plus 100 watts = 7560 watts.
Assume 10% forms heat = an internal heat load of 756 watts.
Assume 10% forms heat = an internal heat load of 756 watts.
Or
Total internal power is 10 hp x 2544
BTU/hp = 25440 BTU/hr plus 100 watts x 3.415 BTU/hr/watt = 25782 BTU/hr.
Assume 10% forms heat = an internal heat
load of 2578 BTU/hr.
External heat load: The temperature
difference between the desired temperature and the outside is ºC. Using the
conversions (and interpolating where necessary) we multiply the area by the
conversion factor:
42 sq. ft x 3.3  139 BTU/hr or 3.9 sq. m
x 10.3 = 40 watts
Total Heat Load: 756 + 40  796 watts or
2578 + 139  2717 BTU/hr.
You would use a Model 61040 for constant
operation or a Model 63040 for oneoff control. (Rated at 2900 BTU/hr or 849
watts).
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.