Humidistat Accuracy

[Farrell]

The sling hygrometer is fine for the room RH, but not much use to determine the RH right next to the underside of the soundboard (unless you have a 9' Brambach with no framing!). Before I bought my high-end hygrometer, I had run my shop dehumidifier off several regular DC humidistats and several "DRY" DC humidistats. The regular ones would turn the dehumidifier on around 60% to 65%. The "DRY" ones would be a bit better, switching the dehumidifier on in the upper 50%s. Now with my better hygrometer, I see that my cheap hygrometers now read two or three percent high, so I guess my stated ranges should be a bit lower. Still though, it appears we are not close to low-40%s.

Now that I have a good hygrometer, I will make some new observations of humidistat performance.

BTW. I have a Sear basement-type dehumidifier in my shop (900 square feet). It has an "electronic humidistat" - whatever that might be - that you can set to a range of desired humidity levels - the range extends down to 40% RH. I keep mine set at 45% and keep a small fan on top of the dehumidifier to keep air circulating so that it gets a good average shop-RH exposure. I have been very impressed with its performance. Every time I check RH in the shop with my new hygrometer, it reads between 43% and 45%.

A few humidistats I ran across on the web:

Johnson Controls $130

Microprocessor controlled unit http://www.greenair.com/humidistat.htm

http://www.meaco.com/conservation_heating_humidistat.htm

http://www.saginomiya.co.jp/english/e_products/rle.html

BTW - here is a room humidifier for those in dry climates:  http://www.powerhousecatalog.com/product/481/

I don't know the price of most of these. I know also I have seen a couple in lab equipment catalogs - I think they were in the $200 to $300 range. I think to be fair, we must acknowledge that DC sells their humidistats at a VERY low price. I think that we, as piano technicians trying to provide some target environmental conditions for a piano, must decide for ourselves whether the DC humidistat performs adequately, or if some other humidistat might better meet our needs. Realize that most good ones cost quite a bit more than a DC. The problem I have with DC is their claim of maintaining 42% RH. I haven't observed it yet.

Terry Farrell
  
----- Original Message ----- 
From: "Dave Doremus" <algiers_piano@bellsouth.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Saturday, November 30, 2002 11:38 PM
Subject: Re: Humidistat Accuracy


> At 9:30 PM -0500 11/30/02, Farrell wrote:
> >I have a big pile of copies of a full-color beautiful Damp-Chaser 
> >marketing handout that describes how the use of their dehumidifier 
> >system keeps the relative humidity (RH) of the atmosphere in the 
> >area of the piano soundboard at maximum of 42% RH.
> 
> 
> Terry, This is a pet peeve of mine. I have just the last two weeks 
> had two dampp chaser control units running in a customers house 
> plugged into light bulbs. He has a curious mind and got the units 
> with a rebuild that I did not do. (The piano has many problems still 
> but that's another story.) One does not start to dry until the room 
> humidity is over 70%, anywhere below 60% it tries to add water. The 
> other one is always drying, never shuts off at New Orleans humidity. 
> I had 30% in my shop yesterday, the lowest since last winter, he told 
> me the unit was still heating. He has a fairly high end hygrometer, 
> still only accurate to 7%, and is talking about a sling psychrometer. 
> Meanwhile the dampp-chasers are only lighting the room. Neither is 
> accurate enough to be in a piano. I have two humidistats at home that 
> I hope to experiment on this week, but I dont think they are 
> wonderful devices unless you have no other option. You'd be better 
> off with room humidity control, IMHO.
> -- 
> ----Dave
> 
> 
> -----------------------------
> Dave Doremus RPT
> New Orleans
> algiers_piano@bellsouth.net
> ------------------------------
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