I leave Varroa trays in to reduce wind blowing up through the mesh floor. I also put a super full of drawn comb under the brood box to reduce wind swirl further. I agree Nigel insulated hives use less food. The utimate question must be how little air exchange do they need. CO2 may well be the limiting factor rather than the need for water removal. Bees are able to tolerate high levels of CO2 but from what I have read, start fanning to remove it at a concentration around 1%. As well as heat loss, too much air exchange can lead to dessication and extra trips for water carriers in marginal conditions.