Heating / cooling an insulated shed

I have had them at work. Yes, it does ice up, so the control system runs it in reverse for a while - it melts the ice, but blows cooler air indoors. On balance it seemed to work, though it might be less comfortable in a smaller space.

Chris

Don't forget to factor in ventilation - you should have a small amount of trickle ventilation available either by design or by accident[1] and air changes do add to heat loss quite significantly on an otherwise well insulated building.

I'd work on 1kW peak at the worst times of the year - in or out.

In winter I'd look to maintain it at 10C with rapid rise when required (good convector or fan heater) and in summer if you are not opening windows, you need to factor in the heat produced by your body and any equipment your are using.

A little crossflow exchanger could much reduce ventilation losses

NT

I have one in the workshop. They work well apart from 0 to 4C. The efficiency drops off below freezing but it keeps the place at a nice healthy 26C IME. The AC is useful in hot weather, a couple of days a year. Very painless to operate.

And solar gain through the windows, particularly any that catch the sun. I'd say that cooling will be required in the summer.

A heat pump that can work in either direction seems the obvious choice and if this shed has a couple of south ish facing windows around a couple of square metres and 3 kW unit may well not be to far off the size required to keep the place cool.

An air source heat pump won't ice up at below freezing outside air temps as the air will be pretty dry. The problem is air temps above freezing to around 5 C when it can have considerable water vapour in it, that condenses on the collector when it's below the dewpoint and then freezes when the collector is sub-zero.

Dennis, could you check your computer's clock or timezone? Messages from you seem to come through with the next day's date.

James

OK, thanks. Its a new computer and I must have slipped when I set it.

Yes, looking at south-facing French windows / doors and another small-ish window on that face. Also east and west facing windows to catch morning and evening sun.

Thanks to all for replies. It's beginning to look like an A/C unit might not just be an indulgence, but might actually be a sensible choice. But I'm particularly interested in running costs / efficiency.

If it takes, say, 500 Watts over the winter months to keep the room warm for, say, 50 hours a week for 30 weeks, that's 750 kWh or ~75 quid. If the heat pump cuts that to a third then that's a saving of 50 quid a year. Over ten years it pays for itself.

Is that a realistic calculation?

I have only had mine since November but it hasn't frozen yet. The temp drop through the outside unit is only about a degree so its not going to get to freezing point very often. If it does freeze then the unit will heat the outside just enough to melt the ice so it can drip off. It makes you wonder why they don't coat it with that water repelent stuff so it all runs off before it can freeze. I might buy some of the spray on stuff and try it.

More a case of how long I have to carry on working to keep Fevric Junior and Fevrica fed and clothed...

If its a damp environment a dehumidifier will warm it a bit and dry it out at the same time. You can get quite a bit of "free" heat from drying damp air.