This issue of frosting in HRV's in cold climate area seems to me be working in direct opposition to when you need it the most so after inefficient operation from frost, defrosting cycles or addition costs of pretempering intake air to prevent frosting is enough really saved to pay for it? Especially for a small home with clean lifestyle and few VOC's. Oxygen/CO2 are a concern but what level of ACH will cover just that? Does ACH have to be constant or can it be higher during daytime activity and less at night? Simpler/cheaper solar air collectors can supply a lot of heated fresh air during the day, would it be enough to make it through the night? Could some fresh air be preheated thru a graywater HX during non solar periods? I just know that an aggressive insulation/air sealing retrofit on our 50's doll house cut the heating bill by 2/3 and we have no HRV. We do get condensation inside DP windows on coldest days that needs to be wiped up some mornings. I counted an average of 20 times a day of opening/closing exterior doors(even in winter) how many ACH does that add to that would happen even with an HRV? I'm just not yet sure of an HRV real savings as its theory. A DIY one would certainly help if it lowered cost but they still have frost issue to overcome. Seen many energy projects installed that are now removed or in disuse from not being realistic. Yet some are good but it is buyer beware not to get sold a bad one.
My next home being designed and built has an advantage of better construction methods and energy conservation practices than retrofitting old ones. But there are not less "great ideas" to sort thru.
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