Any advise on modeling an ERV?

I am attempting to recover 4,000 cfm exhaust to partially temper ~20,000 cfm OSA. I have the ERV modeled as an enthalpy wheel. The program is computing approx. 30% gas savings. This seems extremely high given I am only recovering 20% of the air. If I change the exhaust recovery to 20,000 cfm, the results are about the same as recovering 4,000 cfm.

Has anyone had any luck accurately modeling and ERV? Are there certain settings I need to look for in my system?

Thanks-

Nick Schmit