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Humidistat? for Andrews De-humidifier

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_Paul_23/12/2010 12:12:41
543 forum posts
31 photos
I am looking for some advice on Humidistats, I have been "bequeathed" an Andrews HD500 De-humidifier running in 240V mode.
Rather than have to guess what the humidity is and periodically run the machine "manually" I would like to (if possible) set this up so once the humidity reaches an unacceptable level it starts/stops itself.
Does anyone have a de-humidifier controlled by a Humidistat?
Any and all advice on the above would be greatly appreciated.
Paul Floyd
V8Eng23/12/2010 16:24:13
1644 forum posts
1 photos
Crikey as the saying goes thats a bigun!
Have you got a very sizeable workshop? because this is suitable for drying out large areas.
If your workshop is not large then this unit might be less than suitable for the job, it might cut in and out too frequently and be uneconomical as well.
These are sold by Andrews-Sykes so they might be able to supply humidistats, and advice on suitability for your application.
One place I used to work at they attached wall mount humidistats to basic (domestic size) de-humidifiers, that idea worked quite well.
RS list a wall mount humidistat.
(sorry, couldn't manage a link to the actual page so search for humidistat).
You would have to check that it could switch the load of this unit, plus of course all the usual safety aspects of doing something like this.

Edited By V8Eng on 23/12/2010 16:49:21

Richard Parsons23/12/2010 17:55:15
645 forum posts
33 photos

Why not buy/make a wet/dry bulb thermometer. To make one you need two ordinary garden/household thermometers mounted side by side. Get a small glass/plastic pot and a shot length of wicking. You can sew a wick up yourself from a bit of cloth. Put the wick around the bulb of one of the thermometer. Dip the other end into the pot and fill it with water. Leave to equilibrate, and then read. You will find the relative humidity from the table here.

Care and maintenance. Top the pot up with water as required and do not let it freeze.

Howard Jones24/12/2010 06:20:12
70 forum posts
112 photos
does  just sitting the wet bulb there actually work?
when we were doing survey barometery (using paired sets of Mechanisms Ltd Baromech instruments )we needed this info to correct for air density, the instrument we used was a psychrometer. this blew air over the wet bulb at either 2 or 5 meters per second. only after the wet bulb had stabilised in the air flow could we make valid humidity determinations. the wet bulb sitting there before the fan was turned on never gave valid values.
Frank Dolman24/12/2010 12:42:05
106 forum posts

     It seems to me that there is no sense in getting too concerned in accurate
 measurement of humidity.  The requirement is to keep the dew point of the air
 below the temperature of the machines and tools.  The dehumidifier has a
 limit to the maximum number of starts per hour ( usually six ) so you don't  want
 to leave it under the sole control of a humidistat, or it might kill itself.
     Semi-manual control could be quite simple if you fitted a timer, setting it to
 run for (say) five minutes every hour in damp weather and reducing it in dry.
V8Eng24/12/2010 18:05:42
1644 forum posts
1 photos
Possibly Richard is describing a Masons Screen Hygrometer.

I use a small domestic de-humidifier with built in stat control, which works fine for my shed type workshop (about 3 x 2.4).
De-humidifiers do need to be roughly sized to the application, hence my comments about the Andrews machine and workshop size.
Stub Mandrel24/12/2010 19:16:45
4311 forum posts
291 photos
1 articles
This thread should be a reminder for all of us whose workshops are currently sub-zero. If we get a front with warm, damp air coming through even those of us with well insulated and normally rust-free workshops must beware of sudden condensation. My advice is warm the workshop gently ahead of the big thaw (if it ever comes).
Richard Parsons24/12/2010 19:38:29
645 forum posts
33 photos

Howard   yes It does.  The two thermometers sit next to each other and the wet bulb is lower than the dry bulb.  The set is called a wet and dry bulb thermometer.  Not only can you get the Humidity from the thing but you can get the Dew Point here.  >>

Merry Christmas to all >>
Do not worry Stub you will get a thaw I get them every few days - Watch the Jet Stream it will tell you when one is comming

> >

Edited By Richard Parsons on 24/12/2010 19:40:00

Stub Mandrel26/12/2010 18:08:57
4311 forum posts
291 photos
1 articles
No thawing here for about 2 or 3 weeks. Last weeks snow is still loose powder. I ahevn't seen anything like this before, but apparently no-one else (living) has either!
Yesterday looked at the surface pressure forecasts and thought the fair weather for midweek looked unlikely with a huge low in mid atlantic. Lo and behold they are forecasting heavy snow for Tuesday now.
Where do you get a jetstream forcast?
Richard Parsons26/12/2010 21:29:22
645 forum posts
33 photos

To find the jet stream have a look here. It is quite usefull as it tells you what is coming. I have no idea how accurate it is, but it works in Hungary.

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