# Effect of solar heating

We have an electronics enclosure that has a top with 23.3 square feet. It is painted white and I have read that a glossy white paint will absorb only 14 percent of the solar heat. That tells me that of the the 97 watts per square foot from solar radiation this top will will absorb 13.58 watts for a total of 316.414 watts. I understand that 316.414 watts is converted to btu via the constant 3.413 resulting in 1079.9 btu per hour.

The top has an R value of 9. How many watts of this solar radiation will get though the top? In other words, how much load will the solar energy put on my air conditioner?

Thank you,
B Kelly

## Answers and Replies

Q_Goest
Homework Helper
Gold Member
I think you're going to have to determine the surface temperature of the panel at equilibrium.

As the surface temperature warms up, part of that 316 watts is lost through convection to the atmosphere. It is going to heat the air as it passes over the panel.

Part of that 316 watts will also be conducted through your insulation and warm the enclosure.

So the total 316 watts can be broken up into heat rejected to atmosphere (A) due to convection and heat rejected into the box (B) which must be removed by your air conditioner. The relative portions of A and B must be determined by calculating the equilibrium temperature of the box surface where the solar energy is 'deposited'.

Hello Q,
Somehow I knew this was more complicated that I was planning on. I don't know how to come up with the equilibrium temperature. The only thing I think I know is that with the small size of the top and its r-value, the heat from the electronics inside overwhelms the solar gain. I will just work it from that angle. I expect to average about 2000 btu per hour during normal operation, but can spike up to about 5700 btu. I figure about 6000 btu unit will do fine.

Thanks for your time,
Bryan

Q_Goest