Steve,
While HRV/ERVs sound like the perfect solution, they have their limitations.
For example:
ERVs are supposed to remove humidity from incoming air and send it out with the exhaust air and they do .... but only to a certain degree. If you live in an area where the relative humidity remains low most of the time they will do you good but, in that case, so would anything that exchanges outdoor air for indooor air.
If you live in an area with high relatiive humidity, the dessicant wheel that does the transfer of humidity becomes saturated so quickly that it becomes ineffective almost immediately.
Also, ERVs are supposed to retain a percentage of the cool air that you would otherwise be ventiing outdoors. Great concept EXCEPT for the fact that folks with reef tanks hardly ever vent cool air. Even when the lights are off we are still heatiing the rooms because we keep our tanks at normal reef temperatures which are higher temperatures than most people keep their homes in warm weather.
When it comes to reef tank setups, I'm not a big fan of ERVs for those two reasons but, then again, I live in an area with a high relative humidity and keep my thermostat temperature set below the temperature that I keep my tanks.
HRVs are great but have a limited season as they are for use in cool/cold weather.