[NicknamedBob]

" I'd like to have A/C here for more comfort but can't justify the expense for the few days we need it, though the furnace/air handler we put in a long time ago will accept an A/C addition. The Scot in me prefers low-cost solutions."

Sounds like you could use a "ground loop". These vary in configuration, from a trenched-in buried plastic pipeline to a vertical bore with drop-in plastic loop, backfilled with the same dirt you dug out.

If you have access to a pond, you can put the loop in the bottom of the pond.

The basic idea is to circulate water or other fluid to pick up heat or drop it off, and then use a copper coil or such inside the house with a regular box fan on it.

The coolness of the ground will be transferred to the house, and when you no longer need it just turn off the circulating pump and the fan. Or put it on a thermostat.

[sionnsar]

I'm somewhat familiar with ground-loop heat pumps. The Reichstag went to those (really deep ones!) in its renovation in the later 1990s. I've also seen industry standards for sizing same for sale, but for our locale there's a pretty high upfront cost in drilling for the downloop end. OTOH, the subsurface water flow through our property could significantly reduce the size of the required wellhole if we planted the downloop in the path of that flow.)

We're way up on a hill on glacial moraine; there are no ponds nearby as indicated by my annual tally of mosquitoes usually being less than what I can count on my fingers & toes.