heat transfer through multiple surfaces and air gap

[XOsirisX_]

Hi all, first post here

I am attempting calculate the heat load of a room generated by a roof section. There are multiple layers of the ceiling, then a 0.5m air gap and then multiple layers for the roof. I have seen other forums state that conducting an energy balance will give me the heat load entering the room, however I'm unsure how correct this is. If I obtain all the temperatures at each ends of the layers (say for example I could do that), would the heat load entering the room not simple be the UA(DeltaT) and deltaT would be the difference between Temperature above the first layer above the room and the room temperature.

Additionally, would you not also subtract the energy used to heat up that layer?

 

[IRstuff]

THAT is the way to solve the problem You have conservation of energy, which means that the UA(deltaT) for each layer is the same value. Therefore, you have a series of simultaneous equations

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[georgeverghese]

Heat transfer by radiation through the multiple layers also should be taken into account.
See equations 11-119, 11-120, 11-121 in Perry Chem Engg Handbook (chapter on heat transfer equipment, subsection on cryogenic processes) to get some idea of how to go about this.