I've heard that "heat wheels" are being torn out all over the country because of cross contamination issues between the supply and exhaust side. I had some back in the 80's that were junk and fell apart, but I haven't expierienced the contamination problem.
We work on alot of Munter units and have not heard that. Still selling them down here.
A lot of the older stuf fwas built without filters in the return airstream. This would allow the dirt from the building to load up the wheel making it lose effieicency. The newer systems typically do have filtration in both airstreams. We also start up and service a bunch of them. Some venues have gone to heatpipe as opposed to a wheel.
Maybe contamination was the wrong word to use. The two air streams mix which defeats the purpose of the wheel. The wheels I've had are filtered on both sides, but I haven't seen one with a good gasketing system between the 2 plenums that prevents the 2 air streams from mixing.
we have a building that has two micrometl energy with recovery ventilators with dessicant wheel inside fairly new last summer was the first summer they saw and when the monsoon season came here in az they just could not remove any humidity well maybe not enough for the building that takes 100% outside air but have not seen any cross contamination were actually in the process of installing some dx coils to help remove the moisture carrier aquasnap should work great then