I've asked this question on another NG and from the information I received from Peter Parry I'm contemplating using a dehumidifier/heatpump. The two conditions I want to achieve is low humidity to minimize the chance of condensation on machine tools, and to provide a comfortable temperature to work in. I have made a start by internally insulating with 50mm celotex. The up & over steel door will be replaced with a well insulated stud wall. I will also be fastening low resistance power resistors on the machine tools as reccomended by Bob Minchin. I thought to float the idea of using a dehumidifier/heatpump on this NG as there are many engineers with experience in aircon etc who might be able to discuss and advise me as to the practicallity of this approach.
I have this link to a portable unit (Secco Piu):
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may be better ones, I don't know, but it seems to be the right type of kit.
50mm would be OK for the walls, but you need over double that for the floor, and plenty of roof insulation too. Otherwise you will just be throwing your heating away. Although I turned ours into a dwelling, so it had to meet building regs, I needed 120mm Celotex on floors, and 250mm+ of loft insulation. Granted, you won't need as much if not trying to meet building regs, but whatever you can put in is going to help a lot, and certainly in the case of loft insulation, it will pay for itself in very little time.
I'm afraid I don't know a great deal about the dehumidifier aspect though.
absence of damp is more about keeping temperatures a little above ambient than anything else.
If air reaches the dew point, water comes out of it as dew, fog or rain. That runs away. If that air is heated marginally, it absorbs water by evaporation. it is now 'dry' and so will be anything stored in it.
De humidification is only really indicated if for some reason you want cold AND dry.
Otherwise a very small heater plus insulation will do the job, and keep the interiors a degree or two above ambient.
Some maybe, but before conversion, our garage floor felt freezing even in Autumn, let alone winter. Now it's bearable unheated, even with the recent cold spell.
True - depends on comfort levels I guess.
They were the B.C.O.'s requirements. He told me minimum 50mm polyfoam boards (incl plasterboard) for the walls - I went 55mm, as the thinnest Knauf board of that standard. The floor, you may be right about - perhaps less would have sufficed, but for a dwelling, I guess that 120mm raised it up suitably too. For the loft insulation, he said current local regs were at least 250mm (this site says 270mm :
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As it was dirt cheap (BOGOF @ B&Q, and BOGTF @ Wickes) at the time, it was a no brainer, and I actually went for 300mm. Cost me about £40 to insulate it the loft. It's now the most well insulated area in the house. I think the house loft (1997) has only 2-3" of insulation in it - which I'd like to improve, but there is too much clutter up there at the moment!
A dehumidifier will remove moisture from the air, and coincidentally acts as a heater, pumping out whatever its power consumption is (typically, 200-400W). Actually, you get a tiny bit more heat out, as removing moisture from the air also generates a bit, but you can probably ignore that. As protection against moisture damage such as rusting, this sould work very well. Whilst heat alone would work, you are getting a double benefit of the dehumidifying, which means you don't need anything like as much heating to achieve the same protection level. These units don't dehumidify so well when the temperature drops down near freezing, as they have to keep running internal defrost cycles. they are still generating heat though, and absolute humidity becomes quite low at low temperatures anyway. You can get ones with built-in humidistat, which will cycle on and off as the humidity raises and lowers. You want to make sure the Workshop/garage is quite air tight, or you'll be wasting the effect of the dehumidifier in air changes. Cost wise, running a 200W load
24x7x365 costs of the order £200/year. If you intend to leave it running when you're not there, you want one which can have a drain pipe connected, or it will switch off when the internal tank is filled. The ones I have have quite a sensible arrangement which allows you to plumb them in, but if the drain becomes blocked (e.g. frozen outside), the unit overflows back into the internal tank, and will carry on running until either that fills, or the external drain thaws out and runs again. If you keep timber in the workshop, this is not necessarily happy in the presence of dehumidifiers, as they all-too-easily dry the air out too much and you may lose dimensional stability and suffer cracking.
An air conditioning unit can be used both to pump heat in to the building (heating mode), or to pump heat out of the building (cooling mode). The air conditioning unit only dehumidifies in cooling mode, which is useful in the summer whilst you're working in there (for your benefit), but not so useful in the winter to keep things dry. You could use the unit simply as a heater in the winter. IME, they don't heat so well when outside temperature is between 0C and 5C (due to having to run defrost cycles), but either side of this range, and they're OK, although specific models may vary from this. Power consumption tends to be 1kW upwards, and they have quite a large switch-on surge each time the compressor starts up, which will create a noticable momentary voltage sag at the end of a long supply line.
It would be useful to calculate the heat loss from the workshop, to know what sort of heating power you're going to need both when you're using it, and when you aren't in there. Also how many hours you are likely to spend in there (in case it's too little for an air conditioner to ever pay for itself, verses using a simpler electric heater).
also on eBay as they're the sort of thing people buy and then find don't do what they thought they would, or no longer need. I guess freecycle might be good too, but I've never looked.
A dehumidifier, the compressor variety, is a small heater and will dry and warm the air. It will warm the air more for the same cost of electricity as a heater will.
If you want dry cold air an air conditioner will do that, not a dehumidifier.
Typically running around 20% of the time means a cost of about =A340 per year. It also means the mean 40w heating power will be insignificant. If you only dehumidify in winter and passively ventilate in summer instead, the cost's even less.
My limited experience of such is that it could be good for what you want. I've used drying rooms in YHs many times and those with dehumidifiers, with the room at about 20C, were far better than those with a fan and heated to
30C. A couple of times I cleaned the evaporator in one YH - for the second vist I took the tool for the job as it's small and light and saves half an hour.
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