We do run the air con during hot days Mike. And as you say, it's "free." In addition Yuri prefers to sleep with the air con on. Once the batteries are in, this will also be "free."
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^ we have a similar set up exc the batteries as i decided we didn't need them, cost benefit etc. You'll notice the benefit of the insulation and that alone will help a lot, One of my problems with Thailand is aircon/fans as they dry my eyes out, i hate having them running and especially at night so as mentioned we try to shut the bedrooms up day time and run the aircon to cool them and as the rooms are well insulated (30cm in the ceiling and 20cm QCon) they tend to remain cool all night.
Its lovely in the cool season being able to sleep with no fan/aircon and the windowns open
peciacake...house is looking great. But I hope you have a ride-on mower, or gardener, with all that grass ?