An interesting couple of questions, lets deal with each detail... > From: Robert Scott <rscott@wwnet.net> > When correcting for low humidity, the evaporation pad is heated to > add moisture to the air. Then the moist air rises and bathes the > soundboard with moist air - until the RH reaches 50%. > > Question 1: Although the soundboard is the primary target, how effective > is this operation at raising the RH at the pin block? I assume you're discussing an upright (or vertical) piano... The soundboard _is_ the primary target, but the rest of the piano benefits by the coincidence of inhabiting the same space as the soundboard. The easiest way to think about the whole thing is that the area within the case of the piano has its own micro-climate created by the D/C system. Firstly, the reason that warm air evaporation is used (ie the pads over a heater bar) is that warm air evaporation circulates throughout the whole piano (not just the the soundboard area), it is also better than say steam which condenses against the nearest cold item (probably the strings or the frame) causing rust. Whereas warm moist air will readily travel imparting its moisture to absorbent items like wood and felt. The first materials to absorb will be the softer materials like spruce, felt, leather etc but also hardwood later or more slowly. > > After the RH reaches 50%, the dehumidifier takes over. It doesn't > remove any water from the air, but it raises the temperature of the > air so that what water there is becomes a smaller percentage of what > the air is capable of holding. A typical situation might be 80 degrees F > and RH of 90% (a very humid summer day). If I understand the vapor > tables correctly, it would take a temperature of 102 degrees F to make > the 90% humidity come down to 45%. This is a 22 degree rise. Yep! That's why when you first open a piano with a system in it you can feel the warm air drifting out of the top. > > Question 2: Is it possible for a Dampp-Chaser operating in dehumidify > mode to keep the air around the soundboard 22 degrees higher than > ambient? I'm sure the air immediately around the heating rod is > hotter than this, but when that air diffuses with ambient air and > reaches the edges of the soundboard, how hot can it be? If it is > lower than 102 degrees, then the RH is higher than 45%. Not necessarily kimosabe! When you first set-up a system and plug it in, it may well encounter what you describe here, but as time goes on, it builds up it's own little microclimate inside the case, and while fairly extreme things can be happening outside the piano, inside is a different story. This is why it takes a couple of weeks, or even longer in really extreme environments, to get the piano where it wants it and stabilises there. The warm air used by the system to control the moisture content of the wood in the piano generates its own kind of thermal protection from the undesirable stuff trying to get in from outside. This is also why the Back Side Cover even further enhances the protection of the soundboard by creating a layer of "controlled air" on both sides of the board. With a properly installed system and a Back Side Cover (I wish they'd change that name!!My back side cover is called trousers... but I digress) the variation in moisture content of the soundboard can be less than 1%. Precisely what we want. Let's face it, if the system was having to cope with 22 degree temp differences on a day to day basis, it wouldn't work nearly as well as it does! And there would be dead soundboards all over the place The grand offers a different story, it's control of the soundboard is good in ideal circumstances (ie no drafts which remove the controlled air). The Grand Underside Cover which is currently being tested will solve that problem. But it doesn't solve the pinblock question in grands Another point, is that while it might be 90% RH outside the house (ie the humidity readings that are recorded in the paper or on the weather on TV) inside the house it is rarer to find things that extreme...I've already got my flame suit on for those of you who know of homes where this is the case or worse...but it is not the rule, there are always exceptions! So there are two buffer zones, the house protecting the piano, and the microclimate inside protecting and stabilising the EMC of the wood. Sorry about the length of this post, but I have tried hard to understand the vagaries of RH and EMC as they relate to the piano and Dampp-Chaser's part in this...this is why I finally decided to become the Australian distributor for the product ...it works! It's a fascinating area and I never stop learning, I look forward to others opinions. Cheers Mark Bolsius Bolsius Piano Services Canberra Australia > > - -Robert Scott > Ann Arbor, Michigan
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