How to Calculate Heat Load for Your Enclosure
To determine the correct model for your application, it is first necessary to determine the total heat load to which the control panel is subjected. This total heat load is the combination of two factors – heat dissipated within the enclosure and heat transfer from outside into the enclosure.
| Temperature Conversion Table |
| Temperature Differential °F |
Btu/hr/ft.2 |
| 5 |
1.5 |
| 10 |
3.3 |
| 15 |
5.1 |
| 20 |
7.1 |
| 25 |
9.1 |
| 30 |
11.3 |
| 35 |
13.8 |
| 40 |
16.2 |
To Calculate Btu/hr:
- First, determine the approximate watts of heat generated within the enclosure.
Watts x 3.41 = Btu/hr.
- Then, calculate outside heat transfer as follows:
- Determine the area in square feet exposed to the air, ignoring the top of the cabinet.
- Determine the temperature differential between maximum surrounding temperature and desired internal temperature. Then, using the Temperature Conversion Table, determine the Btu/hr./ft.2 for that differential. Multiplying the cabinet surface area times Btu/hr./ft.2 provides external heat transfer in Btu/hr.
- Add internal and external heat loads for total heat load.
Example: Internal heat dissipation: 471 Watts or 1606 Btu/hr.
Cabinet area: 40 ft.2
Maximum outside temperature: 110°F
Desired internal temperature: 95°F
The conversion table (above) shows that a 15°F temperature differential inputs 5.1 Btu/hr./ft.2
40 sq. ft. x 5.1 Btu/hr./ft.2 = 204 Btu/hr. external heat load.
Therefore, 204 Btu/hr. external heat load plus 1606 Btu/hr. internal heat load = 1810 Btu/hr. total heat load or Btu/hr. refrigeration required to maintain desired temperature.
In this example, the correct choice is a 2000 Btu/hr. Cabinet Cooler System. Choose a Cabinet Cooler model by determining the NEMA rating of the enclosure (type of environment), and with or without thermostat control.
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| Temperature Conversion Table (Metric) |
| Temperature Differential °C |
Kcal/hr/m2 |
| 3 |
4.5 |
| 6 |
9.7 |
| 9 |
15.1 |
| 12 |
21.0 |
| 15 |
27.0 |
| 18 |
34.0 |
| 21 |
41.0 |
To Calculate Kcal/hr:
- First, determine the approximate watts of heat generated within the enclosure.
Watts x .86 = Kcal/hr.
- Then, calculate outside heat transfer as follows:
- Determine the area in square meters exposed to the air, ignoring the top of the cabinet.
- Determine the temperature differential between maximum surrounding temperature and desired internal temperature. Then, using the Metric Temperature Conversion Table, determine the Kcal/hr./m2 for that differential. Multiplying the cabinet surface area times Kcal/hr./m2 provides external heat transfer in Kcal/hr.
- Add internal and external heat loads for total heat load.
Example: Internal heat dissipation: 471 Watts or 405 Kcal/hr.
Cabinet area: 3.7m2
Maximum outside temperature: 44°C
Desired internal temperature: 35°C
The conversion table (above) shows that a 9°C temperature differential inputs 15.1 Kcal/hr./m2.
3.7m2 x 15.1 Kcal/hr./m2 =56 Kcal/hr. external heat load.
Therefore, 56 Kcal/hr. external heat load plus 405 Kcal/hr. internal heat load = 461 Kcal/hr. total heat load or Kcal/hr. refrigeration required to maintain desired temperature.
In this example, the correct choice is a 504 Kcal/hr. Cabinet Cooler System. Choose a Cabinet Cooler model by determining the NEMA rating of the enclosure (type of environment), and with or without thermostat control.
