I am planning a work-shed. Garden office, if you prefer. Fully insulated for year-round use.
I'm looking at 2m x 4m (ish) floor plan and 2m walls.
90mm thick Celotex on walls and ceiling, and as much as we can squeeze in on the floor.My back of an envelope calculation is that a perfect Celotex box of those dimensions needs 250W to maintain a 25 degree temperature differential. IOW in theory one person and a computer can stay comfortable when it's zero degrees outside.
Obv., nothing is perfect, and there will be a number of double-glazed windows and doors.
But I figure a fairly low-power heater would be sufficient.
However... my eyes were caught by various offerings of evaporative coolers at ~70 quid. And I thought it might be nice to have a cool office on those few days of the year that it actually gets hot.
But it turns out that by most accounts, those things are useless. OTOH for a bit more wodge one can get a proper real air conditioner, albeit one where you need to pipe hot air out of a window, using a pipe and a (supplied) blanking plate. And then in the winter you can turn the thing round and use it as a heater.
But then for a bit bit more wodge, you can get a real proper wall-mount air conditioner with external heat exchanger.
The big attraction is that these things can (allegedly) operate in reverse, so that you can get ~3kW of heating for ~1kW of input. Which could, in the long term, save quite a lot of money.
So... has anyone got any experience of this sort of thing? What's the *realistic* cost of heating a shed-like-this over the winter months? Can a heat pump (i.e. air conditioner in reverse) work in sub-zero temperatures? Won't it just ice up horribly?