Where's the Hi Moisture Comin' from?

[RK Ron]

Hi Folks,
Can't figure out where the high moisture is commin' from.  I made a sleeve that fits around the wood stove's exhaust flue.  I installed a pipe on one end for incoming air, and installed another pipe on the other end for the air(now heated) to exhaust from, everthing is sealed tight.  This heated air is  ducted to the kiln (15'-0" total run, 4" dia. pipe). The pipe continues inside the kiln along the fans, where I drilled out holes in the pipe to allow venting to happen @ center of fans.  A 1/4 hp. suirrel cage blower completes the system, and now I have a heat exchanger on the cheap. 
As the stove heats up, so does the incoming air(duct is directly over stove @ ceiling).  Because the incoming air is heated, it also has a lower humidity than before it got warm. Then it passes thru the heat exchanger, where I'm measuring a pick up of 40+degrees(measured @ end of run@ last fan).  Trouble is, it also measures a higher R.H. than the cooler,incoming air.
EXAMPLE:  Today-  incoming air @ duct entrance= 106degrees, <19% R.H.
                             end of run @ last fan =             156degrees, 49% R.H.
This was just before a storm front moved in and screwed the drying up, so I shut it down.
The weather change had no effect on the incoming air side --  still below 19% R.H.  All the seams have been "furnace taped".  I have 10 holes for venting into fans, all are blowing out VERY well, none sucking in.
I'm in that familiar stance again- scratchin" my head...

Help
RK Ron

[Don P]

I'm real suspicious of your input rh today, we were 90 degrees and 80% before the front, about 70% later in the day. Can you fiddle around more with how you get that reading?

[beenthere]

RK Ron
I'm also wondering how you are measuring RH ?? 

'cause what you are saying, doesn't seem to add up (and apparently it doesn't in your mind either). 

[KGNC]

RK
Are you sure you are not missing a decimal place? If I'm reading my chart right (need my glasses) 20% at 100F should be about 4.9% at 160F.

[RK Ron]

Hi Fellas,
Had a function last evening and here's what was being measured @ the time I shut it down(6pm).  By the way, I switched guages around to double check accuracy, then re-checked the ducts, taping @ spots w/furnace tape just because I have a lot of it. 
Incoming air  <19% RH   105.3 degrees f.
Exhaust air @ last fan   28% RH   136.6 degrees f.
Temp. outdoors  90.5 degrees   36% RH

Ehaust temp. wasn't being monitored which is why it read 20 degrees "cooler" than I want it to be.  Preferred target is 155 degrees.

KGNC- What chart are you reading from?  I LOVE CHARTS!  (not that I understand or follow them, but people think your smart if their taped to the kiln....)

RK RON

[BBTom]

Ron, 

I know you said everything was sealed up tight, but it almost sounds like an exhaust leak into your heat exchanger.  Or it could be that the instrument you are using to measure the humidity does not read correctly over 120°.   

[Don_Lewis]

Clearly you are getting erroneous readings of humidity at the higher temperatures. There are a number of psychrometric charts on the internet. Check the absolute moisture content of the outside air and then using that moisture content (usually expressed as pounds of water per pound of dry air) and temperature, you can determine the relative humidity. It will be very much lower than you are reporting unless you are spraying water into the heated air. If you are only adding heat, it will very low.

There are better ways of measuring humidity but they all cost money and don't really add any useful information

[KGNC]

RK
I was looking at a standard humidity chart, also call a psychometric chart in one of my old engineering books. I did a quick search but did not fine a good one on the web.  I'm sure they are out there but most of the ones I found stop at around 100 deg. I'll dig a bit deeper and see if I can find a good one.

[Don P]

Don, can you post the formula's behind the charts?

[Jeff]

Don P, I smell the makings of a calculator... :D

[Don P]

If there's not a good one out there now. But don't let me stop you if you want to  ;D. I gotta column calc open thats teaching me patience.

I do like the thought of having an answer in actual amount of moisture as well as RH. My pea wraps easier around grains per cu ft or something similar.

[RK Ron]

THank you fellas for your input. I would never have questioned all those guages being erroneous >120 degrees.  Now I know I won't be shutting it down so early, or starting it up so late.
RK Ron