I live in a high desert climate, meaning low humidity and temps down into the low 70s F at night even during the height of summer. My passive cooling approach so far has been to cool the house down at night with a big fan, and tolerate a slow heating during the day. This works ok but not great. For a few weeks a year the house approaches 90F in the late afternoon, and ~ 85F peak for over a month. Not terrrible since humidity is low, but I know as the years pass we will get more spoiled. I could slow down the heat accumulation during the day if I closed all the windows but then the house humidity and air quality degrades too much to perceive an overall benefit. I'm wondering about incorporating an air/air efficient energy exchanger to cut down on heat entry while continuing to ventilate the house. I first read about them in zero energy homes in Germany, where they insulate like crazy for the winter, and then rely on an exchanger to bring in fresh air while not losing indoor heat. One example of a product sold in the US Intro to the topic. The advert blurb says "up to 70% of heat (or cooling) maintained, 100 watt power draw. The power draw sounds quite reasonable, but I cannot quite make sense of the efficiency because the home as a heat sink would seem to depend on heat capacity and heat transfer rate. Any ideas how to interpret the utility in terms of how many degrees the home is likely to heat up compared to without ? Perhaps I can just compare average ambient to average indoor air temperature with the exchanger ?