Another option for switching is the use of a pressure-differential switch that senses the difference between outside barometric pressure and a pre-set inside pressure. These are made for use in mechanical rooms where heaters and other devices require make-up air. One commercially available unit appears to be a supplemental heat supply with a blower that has the current sensor in a single zero-clearance box (meaning it can be installed between rafters). We are putting that brochure in our "in case we need it" file but it is not currently planned for our installation because we anticipate no need for supplemental heating in our climate zone.
Reading through other blogs (including Green Building Advisor) , the placement of the make-up air supply vent is critical to avoid drafts while ensuring minimum conditioned air is drawn out by the range hood. Several placements are currently being considered but the one that we favor currently is the location either under or behind the refrigerator (this was suggested on other blogs). This affords the 'pre-heating' of the air entering during cold months while increasing the efficiency of the "fire under the ice-box" (quoting Anchorage Builder Corp's Chris Senior) effect of current refrigerator designs. Clearly there is some concern about hot moist air from the outside during summer months so we're still reviewing options. The placement near the refrigerator also avoids the penalties for supplemental heating elements for the supply air. Under no circumstances will the vent hood be connected to the ERV but we have not ruled out connecting the make-up air to the ERV system although that could mandate changes to the ERV design. We definitely don't want to create that infamous "ductopus" that robs efficiencies from any of the units so this design is still far from complete.