This is very possible, but it would have to happen inside the equipment family using formula-driven parameters. Basically all of the basic arithmetic functions you'd find in Excel can be done in a family, once you learn the syntax. In fact, that is how I would start: build a spreadsheet that does what you want, and then figure out how to get a family to do it.

I have terminal unit and duct heating coil families that do something similar to what you're talking about. They'll calculate heating coil Kw, leaving air temp, fan minimum speeds, etc. If I were making an ERV family, I would create parameters for the various temperatures (supply entering/leaving, exhaust entering/leaving) and simply calculate the heat being moved from one air steam to the other. Exhaust delta-T * Exhaust CFM * 1.08 = BTU of exhaust heat reclaimed. Take that BTU / 1.08 / Supply CFM to give you the temperature rise on your supply side. Add that to your entering supply air temp and there's your leaving supply air temp.

This will only work for sensible heat, BTW. If you're trying to calculate latent or total heat, or wet bulb temperatures, that is beyond Revit's capabilities. You'll need a psychrometric chart for that.

not exactly what you're asking but might give you ideas.