# COP value for a DX coil that results in a specific EER

Dear forum, My past practice has been to derive the COP need to produce a specific EER (e.g., the EER specified as minimum for ASHRAE 90.1)

I was "cleaning house" recently and revised the spreadsheet where that COP is derived. Now it doesn't work :( The derivation is shown below.

Using Eqn #3c for this example, the derived COP is 3.497 to produce an EER of 10.0, but E+ thinks the EER is 8.7. Something in my derivation must be off, but after reviewing it about 100 times, I can't see it.

If any of you has an equation that works properly, that would be a great help. If you can point out my reasoning flaw, that would be even better.

Thanks in advance.