Heat Pump dehumidifier for Workshop

[Donwill]

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 practicality of this approach.

I have this link to a portable unit (Secco Piu or Prof):

may be better ones, I don't know, but it seems to be the right type of kit. I hoped it would solve the problem of heating the workshop for a relatively short time with the probability of condensation on machine tools when unoccupied and cold. At least when the unit was on, it would reduce the humidity to a level which may minimize condensation when the wksp cools. The other possibility would be to introduce some thermal mass within the insulated envelope (difficult). Heating continuously would be too expensive. Cheers Don

[Calvin Sambrook]

I have a small cheapish dehumidifier built under a seat in my new bathroom. It's controlled by a seperate humidistat and I've ducted the intake air from a high level with an additional fan. It works really well, extracts about half a litre a day (make that a litre if my daughter has had a shower in there!) and kicks out noticeable heated air. It's rated to consume about

240W so that's 240W of heating plus whatever you get from the latent heat of condensation, which feels about right - a fast stream of hot air. I really notice if it's not running for some reason, the windows and tiled walls are completely clear 20 minutes after showering when it's on otherwise they stay damp for a lot longer.

I think it would work well as a heater in your garage, 240W of heat would probably keep things dry anyway but doing it with a dehumidifier means you get drier air and some extra from the condensing process.

Now for a question I've been harbouring. How much heat is added by the condensation of the water? Condensing boilers use latent heat of condensation to add heat and hence efficiency but when I do the sums I calculate that 1 litre of water gives up about 600Wh which is insignificant. What goes?

[Geo]

for the last month's weather.

[Fredxx]

Most dehumidifies have a minimum temperate where below that the cold plate will simply ice up. Some have temperature sensors which can tell when this has happened. One I had did, but still iced up and took a day or so to unfreeze!

When it is cold, the air doesn't hold much water, so a few degrees of heat through a relatively small heater may sufficient to stop any condensation on tools and equipment.

[Andy Champ]

Desiccant Wheel dehumidifiers may be better for this kind of application. Supposed to work better at low temperatures.

Andy