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And with it, the indoor humidity is dropping! ![[Linked Image]](https://pbs.twimg.com/media/BBJlX9cCYAAH9Bo.jpg) This is the lowest I've seen this year - how about you?
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I've seen the RH as low as 8 % here last month already. It's BUTT COLD here in Michigan, around 1 degree and lower with the wind chill.
Jerry Groot RPT Piano Technicians Guild Grand Rapids, Michigan www.grootpiano.comWe love to play BF2.
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Around 14% here at school this morning. The weather in Chicago has been so mild the last few years that everyone seems to be treating the cold as something unusual - it IS January after all! Dipped just a bit below zero this morning... Time to pull out the bigger coat and the flannel-lined jeans! Just last week, most indoor humidity was still in the mid to upper 30% range...
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14°F makes for a brisk bicycle ride into work. (wool, baby!)
It also makes for frozen brake cables... much fun to find that out as you are headed down a hill!
My piano doesn't like the low humidity, that's for sure!
Forrest
Mompou, Cancion y Danza #6
some Chopin, some Bach (always), Debussy
My beliefs are only that unless I can prove them.
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5 deg F here in Fort Erie this morning. Outside RH is 56%, inside it is about 27%. Have to feed my DC unit water every week and half now. At this point I convert from both celciaus and fahrenheit to the more appropriate and universally understood $%&@# its cold scale.
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Does that thermometer read 79.4 degrees??? If so, that's one of the main reasons the humidity is at 18%.
Eric Gloo
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Certified Dampp-Chaser Installer
Richfield Springs, New York
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Yup, the heat in that room was crazy! It was still 20% downstairs in another studio where the temp was 61 degrees...
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RH is an interesting thing that not everyone understands. I, myself, only really understood it about ten years ago, after being a tuner for three years and having a degree in engineering. Another tuner explained to me.
It is a percentage that describes the Actual Water Content in the air (call it AWC), relative to the Total amount of Water that the air is Capable of holding (call it TWC). RH = AWC/TWC
Higher temperature and lower atmospheric pressure increases the total amount of water that the air is capable of holding. (Higher temperature increases TWC, which reduces the fraction AWC/TWC, and therefore reduces RH.)
That is why Eric says the high temperaure reading is contributing to a lower RH reading on the hygrometer.
Cold temperature actually produces high RH (outside that is). As the temperature drops, the total amount of water that the air is capable of holding (if there was excessive water around to be held) decreases. (TWC decreases) And AWC/TWC (RH) actually increases. When the temperature gets really low, the air cannot hold very much moisture at all, we see it all around us as snow; the water has been "squeezed" out of the air. But then we bring the air into our homes and heat it up. So AWC has decreased (condensation) and TWC increases due to higher temperatures, and AWC/TWC (or RH) decreases.
So, for example, keeping a piano in a cold garage (not below 32 deg F, 0 deg C, that can cause swollen wood when the water freezes in the wood fibres) can actually put it in a decent RH environment.
I once left a hygrometer in my car in the summer time. When I came back, it read 44 deg C. (111 deg F) and 42% RH! (TWC was very high due to high temperature, and therefore AWC/TWC was lower than outside.)
There are many more implications to this when considering air conditioning which strips AWC and humidifiers and drafts and cold basements and hot upper floors, etc.
E.g. Air from an air conditioner, immediately leaving the unit, has a very high RH (the air has just been cooled down to 100% RH and lower. That's why there's condensation out the back). Yet, we generally assume an air conditioned home has a lower RH, which in most cases is has, but not right next to the A/C.
100 year old pianos with no soundboard cracks, may have spent many years in poorly heated and drafty homes, which kept the RH from going too low. Today, the efficient homes' insulation allows us to keep the heat up but results in lower RH than an older inefficient home would produce.
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RH is an interesting thing that not everyone understands. I, myself, only really understood it about ten years ago, after being a tuner for three years and having a degree in engineering. Another tuner explained to me.
It is a percentage that describes the Actual Water Content in the air (call it AWC), relative to the Total amount of Water that the air is Capable of holding (call it TWC). RH = AWC/TWC
Higher temperature and lower atmospheric pressure increases the total amount of water that the air is capable of holding. (Higher temperature increases TWC, which reduces the fraction AWC/TWC, and therefore reduces RH.)
That is why Eric says the high temperaure reading is contributing to a lower RH reading on the hygrometer.
Cold temperature actually produces high RH (outside that is). As the temperature drops, the total amount of water that the air is capable of holding (if there was excessive water around to be held) decreases. (TWC decreases) And AWC/TWC (RH) actually increases. When the temperature gets really low, the air cannot hold very much moisture at all, we see it all around us as snow; the water has been "squeezed" out of the air. But then we bring the air into our homes and heat it up. So AWC has decreased (condensation) and TWC increases due to higher temperatures, and AWC/TWC (or RH) decreases.
So, for example, keeping a piano in a cold garage (not below 32 deg F, 0 deg C, that can cause swollen wood when the water freezes in the wood fibres) can actually put it in a decent RH environment.
I once left a hygrometer in my car in the summer time. When I came back, it read 44 deg C. (111 deg F) and 42% RH! (TWC was very high due to high temperature, and therefore AWC/TWC was lower than outside.)
There are many more implications to this when considering air conditioning which strips AWC and humidifiers and drafts and cold basements and hot upper floors, etc.
E.g. Air from an air conditioner, immediately leaving the unit, has a very high RH (the air has just been cooled down to 100% RH and lower. That's why there's condensation out the back). Yet, we generally assume an air conditioned home has a lower RH, which in most cases is has, but not right next to the A/C.
100 year old pianos with no soundboard cracks, may have spent many years in poorly heated and drafty homes, which kept the RH from going too low. Today, the efficient homes' insulation allows us to keep the heat up but results in lower RH than an older inefficient home would produce. You will find that your understanding of what RH is in the above falls far short of reality. Air is not even required for an RH reading , nor does air "hold" water vapour. John Dalton (scientist) concluded that the vapor pressure of water in air is independent of the existence of the air back in 1803. There are numerous conditions that blow simplified, dummied down explanations of RH clear out of the water. Eg. RH can be determined in a non air environment because air is not a requirement for water vapour to be present. Secondly, the common accepted number of 100% RH is mistakenly associated with the transition point/saturation point for water vapour. Again this is not correct wince it applies to the waters' molecule structure over a flat surface. A non flat surface such as a cloud formation will reach saturation at higher levels...typically 101-103%. The reality is that a perfectly smooth container with no abberations and a completely dust/molecule free environment in it can hold water vapour up to even 200-300% concentration before saturation occurs. Best read this to fully understand what RH truly is, since numerous textbooks and other information sources dummy down the explanation to simple laymens terms which can be torn apart under close scientific scrutiny... http://www.atmos.umd.edu/~stevenb/vapor/
Last edited by Emmery; 01/22/13 01:12 PM.
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George Brown College /85
Niagara Region
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Thanks for that Emmery. I will certainly read it. But my interest is in practical applications of RH, in which my reasoning still applies. I'm not writing a thesis here, just providing practical advice that works in the real world that I live in, not space.
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I'm sorry Mark, but a definition of an extremely precise scientific measurement is exactly that, not a simplified explanation related to your own inferance of its specific use.
To put it in a nutshell, you state "RH is an interesting thing that not everyone understands. I, myself, only really understood it about ten years ago...It is a percentage that describes the Actual Water Content in the air (call it AWC), relative to the Total amount of Water that the air is Capable of holding (call it TWC)."
If your were talking about the "relative humidity of an air-water mixture" you are reasonably correct in your understanding. I simply pointed out that it is neither correct, nor a full understanding of it, if you are talking about "Relative Humidity". As for your explanation of its practicality, perhaps you meant "widespread common layman usage". RH measurements have been done practically on all gaseous containments of water vapour, including a vacume.
Would somebody have a reasonably good understanding of what "speed" is if I told them that its the velocity of an object measured by a speedometer? They could immediatly conclude that sound and light have no speed by that definition.
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Well I don't know about this RH business too well, but I know it's freaking cold. I was in Chicago on Sunday on a lay over coming home to Delaware from vacationing in Hawaii for 2 weeks. What a shock coming off the plane at 5AM on Sunday in Chicago. 10 degrees and I hear Monday was colder. Ron I feel your pain.
Do or do not. There is no try.
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Emmery, your understanding of RH obviously is more in depth than mine. But I am working in an air water mixture and my limited knowledge has served me well. My perspective is as a teacher; one whose mandate it is to help other people who want to learn piano tuning, be able to learn it as quickly as possible (quicker than I did, aanyway) and with a reasonable level of proficiency.
This explanation of RH has helped many of my students grasp the concept better and also helped me to make decisions regarding actual real-world piano experience, with expected outcomes.
Is it perfect? Is it an absolute definition of the entire elemental relationship of the individual parts? Of course not. No scientific explanation of anything is, or else science is dead.
What I deal with as a teacher and technician is cold, hard, factual reality; the reality that helps me service pianos and students. As for the advanced knowledge you refer to, I wasn't blessed with the requisite mental capacity that you obviously have, nor the time. As for being cold, I figure this RH scientific discussion has gotten cold enough. I say let's bury it and get back to the weather.
-10 deg C. (14 deg. F) in PEI. No wind, thank God. We had our deep freeze last week. Working at the university where temperature changes as I walk from one room to the next, yikes!
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In the minus 20's celcius here and for the next dew days. Down to the minus 30s with the windchill. Brrrrr.
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If dew point is when the air temp drops to a point where it exceeds 100% RH, what is supersaturated air?
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What I deal with as a teacher and technician is cold, hard, factual reality; the reality that helps me service pianos and students. As for the advanced knowledge you refer to, I wasn't blessed with the requisite mental capacity that you obviously have, nor the time. As for being cold, I figure this RH scientific discussion has gotten cold enough. I say let's bury it and get back to the weather. Another cold, hard, factual aspect of reality, is that people often get annoyed when others try to give them a lesson when they haven't asked for it.  Your tone on the forum comes across (to me, at least) as a little condescending and opportunistic. I'm glad you enjoy teaching, but its good to know when to turn it off, or tone it down. That being said, you have a lot of good things to say and contribute.
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What I deal with as a teacher and technician is cold, hard, factual reality; the reality that helps me service pianos and students. As for the advanced knowledge you refer to, I wasn't blessed with the requisite mental capacity that you obviously have, nor the time. As for being cold, I figure this RH scientific discussion has gotten cold enough. I say let's bury it and get back to the weather. Another cold, hard, factual aspect of reality, is that people often get annoyed when others try to give them a lesson when they haven't asked for it. Your tone on the forum comes across (to me, at least) as a little condescending and opportunistic. I'm glad you enjoy teaching, but its good to know when to turn it off, or tone it down. That being said, you have a lot of good things to say and contribute. Another cold hard fact is that people don't like being told what to do. I'm here to educate. If you like my posts great. If not, stop reading them.
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After rereading my last post, I reaize it sounds obnoxious. But maybe if you understand that my posts are written with the beginning technician or student in mind, maybe you won't be so offended.
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"Another cold, hard, factual aspect of reality, is that people often get annoyed when others try to give them a lesson when they haven't asked for it."
...Especially if the lesson is incomplete, factually wrong, or coming from a tutor that knows less on the subject than they believe they do, and then dismisses the "extra" correct knowledge as inpractical or not of interest. Yeah, type A personalities will cringe from that.
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