# Heat exchanger effectiveness

I am designing a heat exchanger to be used in a house to circulate air from the outside. I have very basic knowledge on the subject and would appreciate any input. I have looked up various topics on the subject and am using "introduction to thermal and fluid engineering" by Kaminski. However after reading the procedure in calculations I am still unsure.

I have decided on a counterflow heat exchanger with air to air properties.
I know the volume of the house, and the air change rate is 3 times this per hour.
I know the temperatures of Hot air in and Cold air in.
I also know or have calculated Specific heat Capacity, Density and Mass Flow Rate.

I have set my calculations up on a spreadsheet, however i am now stuck as some equations require Hot temperature out and cold temperature out.

## Answers and Replies

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mfb
Mentor
Those temperatures will depend on the efficiency of your heat exchanger (and maybe humidity).
In the limit of perfect efficiency, they are equal to the temperatures inside/outside.

and the air change rate is 3 times this per hour.
Are you sure this is necessary?

bigfooted
Gold Member
I don't know this specific book, but usually you will need to make an assumption on your heat exchanger like that it has a constant wall temperature at the contact surface, or a constant heat flux. You can then calculate the outlet temperatures. The book probably deals with these two cases for the heat transfer problem of a fluid flowing through a pipe or something.

AlephZero