Working in EXAIR’s International Sales Department at EXAIR can get a little tricky sometimes. Not only do we deal with multi-national companies who have R&D in one country, purchasing in another and the end use customer in a third, sometimes we are requested to make a calculated proof that what we recommend truly will do the job.
In a recent case, a design engineer in Singapore had instructed a purchasing agent in China to get a commercial offer for a system that met their needs. The need for the Cabinet Cooler System was in Kuwait with very hot, dry conditions. The customer’s panel was 2 meters high, 1 meter wide and 0.6 meters deep. The panel designer knew the heat load was going to be quite large, so he wanted to do all he could to mitigate heat going into the inside of his cabinet. His first decision was to implement a sun shade to keep the sun load from being a problem. The second thing he did was to specify foam insulation to be applied to all surfaces of the enclosure. With these couple of things in mind and a few other issues concerning the condition of the compressed air at the site, we were able to make the following proof to the designer that our recommendation would work according to his stated conditions.
Following are the basis calculations:
- Panel size: 2 m x 1 m x .6 m = 7.6 m2
- Internal heat load = 300 Watts
- Internal Heat Load = 300 Watts
- Maximum external temperature possible = 55°C
- Desired temperature inside panel = 45°C External Temperature differential = (55°C – 45°C) = 10°CΔT
- Insulation value = 0.5 W/m2/°K (insulation to be added) External heat load = 0.5W/m2/°K x 7.6m2 x 10°ΔT = 38 Watts
- No sun load due to shade structure.
- Panel is free standing and NEMA type 4
- Compressed air utility is at 60 PSIG maximum and 60°C.
Total Heat Load = (300 Watts internal load + 38 Watts external load) = 338 Watts x 3.41 = 1,153 Btu/hr.
Cooling power de-rating:
Model HT4880-240 produces 5600 Btu/hr. with 21C compressed air temperature and 35C target temperature of panel.
Total air consumption @ 60 PSIG = 52.1 SCFM
Total cold flow @ 60% CF and 60 PSIG = 31.3 SCFM
Temperature drop expected = 40.6°CΔT = (73°FΔT)
Net output temperature = 19.4°C = (67°F)
Target temperature = 45°C = (113°F)
Net cooling power = 1.0746 x (113°F – 67°F) x 31.3 SCFM = 1,546 Btu/hr.
We evaluated the net cooling power compared to calculated cooling power needed under stated conditions. Since we have at least 200 Btu/hr. spare capacity which we do, so this model is OK to recommend.
The customer in this case only had compressed air that could be piped to the location of the cabinet. So he really needed this to work. Fortunately, for him we did manage to make a reasonable recommendation. Of course, the recommended Cabinet Cooler System would go on to work well for the customer in this application. The keys to success were the ability of the customer to recognize how important it was to take the couple of steps to provide for the passive methods of heat mitigation with the use of the sun shade and application of foam insulation board to the outside of the panel. Also, the availability of EXAIR’s High Temperature style Cabinet Coolers afforded sufficient cooling power under these very demanding conditions.
Neal Raker, Application Engineer