De-humidifier

Martin

I have run a dehumidifier in the garage/workshop for about a year now and there is no doubt that it does a lot of good, don't however expect miracles. The first thing to do is buy a cheap humidity meter (hygrometer?) - about £4.00 from garden centres, at least then you know how effective it is. My industrial dehumidifier is in a large brick built double garage and will keep the humidity below 80% under most circumstances during the winter, it removes 2 to 3 litres a day in damp weather. Don't forget that most dehumidifiers will not work efficiently at low temperatures as they can't defrost so it helps to provide a little background heat if possible during cold spells. Your theory about humidity increasing as the weather gets colder is a bit suspect - have you ever been to Florida in the summer? Setting the humistat is irrelevant in cold weather, just set it about halfway and hope, with a small unit you will find that it needs to run constantly to be effective. The main objective is too keep your workshop below the dew point and I find that this achieved OK.

Gaspode

I didn't think of that, of course the evaporator will freeze up! I need to heat the intake, but that will affect the humidity.... I have a 750W oil filled radiator on "frost", probably not enough, wish I had thought to run a radiator off the house into the garage before the patio was laid down.

I don't trust in heavier than air flight, but I take your point, One reason for purchase was to move it into the house in the summer.

It just occured to me that the dewpoint is 100% humidity, so it must increase as you approach the dew point.

So another 200W of heat to my 750, getting better.

Thanks for the input. I had set it to be just off, and in 30 mins I had turned it on, I assume that my respiration increased the humidity a little.

Regards

Martin

It sounds very much like the one I successfully use in the workshop for keeping the dreaded rust at bay, and is much cheaper to run than heating. All else being equal, you are right that lower temperatures will reduce the dew point BUT, you can have very low temperatures in winter and yet still have low humidity so the two properties are not inextricably linked.

Mine has a hose connection inside to allow the condensed water to be piped out of the back of the machine and through a hole in the wall. It is worth doing this if you are able, as it saves the chore of emptying the condensate tank every day.

I have also found that it will not defrost at temperatures lower than about

5º so a huge block of ice accumulates inside. A refridgeration engineer friend suggested that being a domestic machine it may rely on ambient heat from the air to melt the ice, and as the workshop is unheated most of the time the air is not warm enough. I have no solution to this problem except to turn it off in low temperatures.

It has this, but I thought that the pipe will likely freeze outside.

Does it hurt to leave it running when it is frozen? I'm not going to run outside to check in the cold.

If I had designed it, I would cycle the pump so that it auto defrosts, and hot freon runs back through the evaporator.

Thanks again,

Martin

I have been running one of the cheaper domestic de-humidifiers in both the railway room and the workshop. I don't heat either room and run the de-humidifiers continuously all year round. In five years I have had no rust and no problems from freezing up. I haven't bothered to run the pipe outside - just in case it does freeze and the condensate cannot escape. Of course, I do have to remember to empty the containers when they fill up. On really humid days they will each pull around 5 litres of water - either put into a 25 litre drum for the loco or into a smaller container for SWMBO's steam iron - or onto her plants.

Cliff Cogg> =

snip

It won't if there is a fall on the pipe to ensure it drains completely.

I guess the ice block will eventually grow until it damages a gas line or the fan. I am not prepared to take the chance to find out.

The extra valve required to do this would add to the cost.

Cliff.

You might find, that as the temperature drops, the condensing coil

start to frost -up. I don't think this presents a hazard to th de-humdifier, but once the coils frost, they sort of self insulate ergo no reduction in humidity.

As a matter of experience, the de-humidifier in my basemen TV/computer/hobby room is useless below about 15 centigrade. In th humid summers, when the basement temps go to 22 degrees and beyond, can collect 2 to 3 litres of water per day.

BTW this is precisely the water that you want to save to top up you lead acid (car) batteries, provided your collection bucket is clean.

(the other) Marte

- Marten - ..teach monkeys to fly.

---------------------------------------------------------------------------------- Posted from the RCGroups.com Discussion Forums Visit us at

The capacity of air to hold moisture increases with temperature. "Humidity" is the absolute water content of air. "Relative Humidity" is humidity expressed as a percentage of the maximum humidity possible at a particular temperature. If the air has 100% RH (relative humidity) any fall in temperature will result in condensation. A dehumidifier works simpy by cooling incoming air to a point where local condensation will occur so water is precipitated. This means that humidifiers tend to work well at high ambient temperatures and very high humidity levels as they only have to cool the air very little for condensation to occur. Of course at air temperatures of zero degrees C there is no free moisture and the air is "dry". Hope this helps

Chris R

Sorry forgot to mention On a practical note about condenser freezing. Most of the domestic humidifiers I have seen have a frost stat to cut off the compressor prevent the coils freezing. Chris R

The heavier-duty units have this feature. I managed to scavenge one with a switch for hot/cold weather, but it still doesn't help much when the temperature of the air rises faster than that of the machines, and droplets appear all over my mill :(

I thought a good compromise might be to add small heaters to the important things. Something simple like a heatsink-bodied power resistor bolted to the underside of the mill table or lathe bed, with a thermostat to keep the metal just warmer than the air in winter.

Only reason I haven't tried it is I'm too lazy to experiment with the power required. I reckon about 10 watts on every 2ft of table, or

5kohm directly across the mains - anyone tried this?

Guy

In article , Guy writes (Snip)

Sounds like a bloody good way to end up with a live machine! ;^)

There is an article on this entitled "Keeping Rust at Bay" in Model Engineers' Workshop No. 94 which gives details of a low voltage, regulated system devised for an ML7 lathe.

Cheers Brian

The message from "Chris" contains these words:

Of course at air temperatures of zero degrees C

Not really Chris, air can "hold" moisture at and below zero degrees C. Admittedly not very much, only a few grams per cubic metre.

This might explain why it was running at bedtime, and at breakfast time appeared to have been all night, yet there was only a trickle of water in the container.

Can anyone furnish me with a scan, photo or just the electrical details (i.e. wattage) from this article? I'd really like to give this a try, as I've got the dampest shed this side of the Amazon.

thanks Guy

Our dehumidifier in the house has been fairly useless of late, and had taken to mysteriously 'dumping' a load of water on the floor. It seems to have been freezing up for some time *before* the frost stat cuts it out. Once it does cut out, the accumulated ice melts, and.... :-(

Having removed various cabinet bits to see what's going on, it seems that the condenser coil freezes up at one end within a few minutes of switching on, while the rest of it is scarcely cold at all. I guess this indicates a problem with the refrigerant - anyone know?

I picked up, for peanuts, a couple of industrial dehumidifiers a couple of weeks ago. Was rather surprised on getting them home to find they're not the usual refrigeration/condenser type, but rather they use a very slowly rotating dessicant wheel.

a similar model. One worked for half an hour until the plastic belt driving the wheel broke, the other is showing some sort of fault. Anyone have any experience of these, to know whther they are likely to be worthwhile persisting with?

Cheers Tim

Tim Leech Dutton Dry-Dock

Traditional & Modern canal craft repairs

Tim I only have a little experience with desicant dryers used for compressed air. They are more effective than refridgerated dryers, as the url you posted indicates, especially at low temperatures. When they are working I believe they are very good. If you paid very little I would think there is probably something costly wrong with them.

Basically as you probably realise the dessicant extracts the moisture and some will then drain as the media is saturated. The media then has to be heated to regenerate its properties.

Compressed air dryers remove the water by mechanically by periodically blowing air over the media to dislodge the water. When the media is saturated it is regenerated by heat. As all the compressed air must be diied this system is usually duplexed so that as one unit is regenerating the other is on line but I guess for space dehumidification this would not be the case.

How all that works in the wheel system Im not sure though.

Chris

Gentleman

There is one very useful aid to keeping rust at bay which seems to have become forgotten in recent years -- a piano heater. This consists of a meter long sealed aluminium tube of about one inch diameter with a mains lead emerging from one end, the tube contains a fifteen watt heater. Under normal circumstances the thing is installed inside a piano with the intention of minimising damp. I have mine slung on wire under the Myford and switch it on every night beneath the old blanket which covers the machine.....no rust in an outside garage/workshop for 18 or so years. Although there is no thermostat fitted the power consumption is low enough to allow it to be switched on permanently if required.

I bought mine from a piano shop (Yellow Pages) for less than £20 in about 1985 and can highly recommend it.

--

Chris Edwards (in deepest Dorset) ..."There must be an easier way...!"

exactly why desicant dryers are used ChrisR