I am seeking guidance on how to address a shelter's environmental control unit capability as a function of solar load specified by the contract.
The specification requires:
The system shall provide shelterized work areas capable of maintaining an effective internal operating temperature between 19 and 29.4 degrees Celsius (66.2 – 84.9F) per MIL-STD-1472.
a. The system environmental control unit's (ECU) shall maintain shelter internal operational temperatures when the external ambient temperatures are between -23.3 degrees Celsius (-10F) and 43.3 degrees Celsius (110F)
b. The system's ECUs shall maintain internal operating temperature while the shelter is exposed to a solar load of 355 BTU/ft2/hr, without suffering physical or functional degradation.
ANALYSIS
It is a closed unmanned shelter: 7.3'W x 7.2'H x 12.3'L (outside dimension). It has aluminum skin painted Woodland Camo. The shelter specification is R value of 3.6
Considering the solar load, I calculated resultant heat load using Stefan Boltzmann constant (radiation energy per unit time is proportional to the 4th power of the abs temperature). I used 2 surfaces for solar load (side and top) Perhaps optimistic, this calculates to a temperature of 342 F. However, the calculation determines how hot it could get without factoring in convection. The convection is discarded and all the heat (conduction) is assumed to go into the shelter in the next calculation (H = (A x T)/R. The point is to calculate a heat load, not the exact temperature of the shelter skin, right?
Can anyone offer any guidance on how to quantify the effects of the specified 355 BTU/ft2/hr? How would you estimate the resultant heat load from this solar load?