It's going to take us a year or two to work out exactly what to do with the cooling and heating of the house. It will probably boil down to three different strategies: cooling, passive heating and active heating. There may be some gaps in between where we don't have to worry, but I suspect at any given time we should either be cooling the house in anticipation of impending heat or heating it in anticipation of impending cold. The weather and climate are changing but the seasons are here for a while.
We switched off the active heating April 10th, and the house has not been cold since. The last night below zero outside was 8th April, when it was minus 2, according to tenki.jp, although it was down to 3 degrees above freezing in the wee hours of 13th May and this year it didn't start getting really hot until the middle of July.
We're now in cooling mode and have begun a routine of opening up the windows when it drops below about 25, which is often at 7 pm, and closing them when the temperature outside rises above 25, which is around 7 am. July 21st was cool and rainy, in the low 20s all day, so the house was cooled a little more.
The bypass system on the ventilation is now working, so it will be pumping cooler air into the house throughout each night, exchanging all the air every two-and-a-half hours. Opening the windows substantially increases the air flow and cooling. In an ideal world they would open and close automatically, like the heat-exchanger bypass switches on and off automatically, depending on temperature difference.
The daily indoor temperature variation is bigger than I expected, probably due to the size of the windows on the south wall, and the lack of a decent awning to keep the heat off the terrace. At the moment we just have a little camping tarp over it.
