Friday, 10 June 2016

Calculate Heat Loads from the Sun for Outdoor Control Panels

I am always happy to see the sun rise each morning. But, electrical panels that are exposed to the sun are not.  Solar heat adds significant BTU’s to the overall heat load in an electrical panel.
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A customer had a VFD to control a 300HP blower motor for a dust collection system. The VFD was getting an over-temp error and shutting down the system.  He contacted EXAIR to get a Cabinet Cooler to keep the VFD cool.  We went through our normal questions to determine the heat load, i.e. the size of the cabinet, the temperature inside, the temperature outside, the maximum external temperature and the desired temperature.  As we went through the questions, he stated that the cabinet was located outside.  This is not an issue for our Cabinet Coolers as EXAIR has NEMA 4 and 4X (IP66) Cabinet Coolers.  It did stem another question; was it under cover?  He mentioned that it was not.
NEMA 4 Cabinet Cooler
NEMA 4 Cabinet Cooler
Generally in calculating cooling capacities with our Cabinet Coolers, we size the units by adding the ambient heat load and the electrical heat load. With the panel exposed to the sun, this adds another component to the total heat load.  To get an estimation on the amount of solar heat, color becomes a big factor as the darker colors will draw more heat.  Here is a good approximation to follow:
Solar heating by color
Solar heating by color
In this application, the customer had a gray panel, a common color. With an exposed surface area of 16 ft^2 (1.47 M^2), Exair would have to increase the heat load by 16 ft^2 * 7 Watts/ft^2 = 112 Watts.  This equates to 112 Watts * 3.41 BTU/hr/Watt = 382 BTU/hr of added heat.  (Or 112 Watts * 0.86 Kcal/hr/Watts = 96 Kcal/hr).
If an electrical panel is outside and cannot be shaded from the sun, we can still protect the sensitive components inside.  With the proper sized Cabinet Cooler, your equipment will remain running cool.  
Vivek Engineers,
#22, 1st. Floor, 1st. Cross,
Adj. IIMB Compound, Bilekahalli Industrial Area,
Bannerghatta Road, Bangalore - 560 076.
Ph : 080 -  3297 0358, 4170 1145
TeleFax : 080- 2648 1309.
E- mail : sales@vivekengineers.net
URL : www.vivekengineers.net
CONTACT PERSONS :
Mr. Durga Madhab Praharaj - Sales & Opearations Manager.
Mob : 097404 39220. E -mail : durga@vivekengineers.net

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