How do you calculate the change in temperature going through a wall assembly if you are only given the R values of the materials that the air is passing through?
Hi @rinair85 thanks for the question!
Is there a specific practice exam question you’re referring to, or is this a general question? If it’s a specific question feel free to PM me the content and I can look into it further.
Generally, you’d use this formula:
BTU/h = (U) x (A) x (Td)
which is found on page 183 of the ARE handbook. You’d need 3 of these 4 variables to be provided in order to answer the question.
In practice, this formula is usually used to calculate the heating load in order to size an HVAC system. So, you’d know the U-value of your wall that you designed, as well as the area and the worst case outside temperature that you’re solving for. For example, with an area with temperatures that reach 5 degrees, and an indoor goal temperature of 70 degrees, you’d be solving for a temperature differential of 65 degrees.
I hope this was helpful and good luck on your next exam!