What to do when wet bulb reading is too low to kick on compressor?

[Larry]

How do you get a sufficient water supply?

[jimF]

Do you have a water line going into the well for the wick? Does it have a float valve to allow flow as the level drops?

[doc henderson]

Jim, airflow can facilitate evaporation so too much air seems would give a false reading as well.  you would need a representative sample of air moving past the wick.  water moves in a gradient, and more evaporation drops the temp and dryer air causes more evaporation.  When you add a time such as cfm then the amount of water that can evaporate into the local environment never comes to any equilibrium, and more water is evaporated as the flow increases.

[K-Guy]

Posts: 7274
Age: 75
Location: NW Arkansas
Gender:



Re: What to do when wet bulb reading is too low to kick on compressor?
« Reply #25 on: Yesterday at 09:45:30 PM »
QuoteAdd Multi Quote
How do you get a sufficient water supply?

How do you get a sufficient water supply?

Larger kilns have tray and use a sock or sleeve type wick. The tray has a float valve connected to a water line to keep them full.

[jimF]

Wetbulb temperature is a measure energy transfer by evaporation, or a measure of the potential to evaporate water - a partial potential to evaporate water. To get an accurate measure full airflow is needed at the temperature of the entering air.

A side note: the condition of the wick needs to be clean and not coated with salt or lime build up from hardwater being used, nor a bacterial film build up. These contaminations can alter the the temperature and make it appear to dry out.

[doc henderson]

yes, wet bulb depression and it seems it could be enhanced (increased depression) with increased air flow.  There is an energy required for a phase change (evaporation) from liquid to vapor, and that drops the temp of the wet bulb in the wick.  It is supposed to be from gradient from saturated to dryer air, not wind speed.  The dryer the air, the more evaporation and drop in temp from dry bulb to wet bulb.  Is there a limit to the airflow that results in an accurate reading?

[jimF]

As you said "There is an energy required for a phase change (evaporation) from liquid to vapor". Energy is supplied by the air and there by transferred to the wood/water system. If the airflow is insufficient there is insufficient amount of energy to evaporate the full potential of water, thereby not accurately indicating the wetbulb temperature. If I remember correctly, about 200 ft/min is the minimum limit of airflow to provide equilibrium heat transfer to the wood/water and evaporation of the water to the air.

[TBrown99]

Whoa! A SECOND page here. I still haven't fully processed the first one though I'm working on it. (I have a full copy of "Drying Hardwood Lumber" by USDA in my hands as I write!).

I've noticed that the three good thermometers which I have in the kiln all -- and on average -- suggest that the L-53 dry bulb figure is 1.5-2 degrees warmer.   
 
I made a short video showing our L-53 setup with narration ( you might have to activate the sound ),

Shared album - Tobias C. Brown - Google Photos

The video doesn't show the drain & bucket just by the L-53 control box.

The main fix list includes redoing the front door, installing floor over uninsulated concrete, and putting the one radiant section down into the main area. I may also have to make a quick access door in order to get the main door right.

Thanks!

[doc henderson]

Nice job on the kiln!

[GBar]

TBrown99,
You may consider your Govee to be giving you false RH readings.  As Blackhawk said, the cited numbers would be below 4% EMC (e.g. 18RH and 120 Degrees = 3.6 EMC). it is not likely.  As others have alluded to: How does it compare to your other source - the Nyle DB/WB readings?

There are some handy calculators online to provide exact calculations and better than interpolating charts.
For RH Calc from DB/WB: Dew Point And Relative Humidity Calculator
For EMC from Temp/Humidity (my favorite): Wood Equilibrium Moisture Content Table And Calculator
CSG cites formula derivation from US Forest Products Laboratory.

I have three temp sources in my kiln to compare and all are within one degree: Penn/Johnson Controller, Fireboard BBQ thermometer with 6 100K Thermistor probes, and AC Infinity Swiss made Temp/RH sensor that is super accurate.  For moisture: the AC Infinity sensor and the Lignomat EMC sensor.  They match in EMC reasonably.

You may consider another source of RH to compare with Nyle DB/WB.  The AC Infinity App records temp and RH, can view readouts, graphs, change settings on phone, download CSV file to PC, and more. WiFi allow monitor of kiln RH and Temp anywhere there is internet to your phone.  I can monitor kiln and change settings anywhere in the country while away from kiln.  I would attach a screen shot, but the Gallery is off line.

[K-Guy]

Nice Job
I have a couple of suggestions for you. Call me at 800-777-6953 ext. 6 to discuss them.
Stan

[TBrown99]

Hi Stan,

I will be in touch. I'm still catching up with things.

Toby

[TBrown99]

Stan gave me some excellent guidance today which I'll act on:

• Move fan truss out to 3 feet (It's at 2'-4"). This will improve air flow.
  
  • Stop using the individual accessory fans. The 4 fan bank is quite enough!
• Move fin tubes at least 6" off back wall
  
  • This will allow them to heat much better as they will have much more airflow.
• Move exhaust fan
  
  • Bad air flow with current install.
    
    • Install fan inside room and go directly out wall.
    • Use 14" vent duct
  • Stop exhausting moist or smelly air into shop.
  • Also recommended making intake vent straight too.
    
    • However, it seems the exhaust has been working very well... even with the intake blocked, so we may not change this. It takes about 2 minutes to reduce temp. I blocked it to avoid cold air exposure.
• Trim back the plywood stack top pieces
  
  • Extending these to the back wall restricts air flow
• Spray paint fin tube cooper with Rust-Oleum
  
  • Something that is not merely paint

Other longer term changes:
Thermostat for radiant tied into control box.

• In some cases it's better to avoid activating exhaust vent, other times desirable. So, control radiant fins with thermostat...

Add more insulation but not too much. If it's heating up okay, don't put more. That inner room could get very hot in the summer and be harder to cool.

[TBrown99]

I completed modifications to our chamber including:
--Move fan bank out 8-9" (stronger air flow)
--Move radiant fins out 4-5" off wall vs against wall (so air passes through better)
--Improve sealing around door and other spots
--Added a 2nd 7' radiant section so 2.5 total now.
--Because we use the fan bank model, we cut back our top plywood covers (no longer going to the back wall) to allow better air flow. This was a KEY change and greatly improved flow through the stack.
I didn't redirect the exhaust line yet as the current "curvy" line seems void excess heat rapidly.

I will still need to add "not too much" insulation on the exterior wall (to reduce some heat loss but not set conditions for overheating in summer months). I have 13 R now (but with a heated surrounding chamber, not exposed to outdoors directly) and will add 6-10 R layer. I'm considering putting a poly fabric barrier too. Also more sealing is needed around door as moisture is still showing from current load.

I installed our third "test" charge yesterday consisting of about 600 bf of the following:

All 9/4.

85% basswood, 20.3% with 19 readings, 30% high. Many readings below 20%.
10% white pine, 23% with 12 readings, 33.9%.
5% poplar, 24.3% with 6 readings, 27.4%.

Set to 120/90 schedule.

The kiln room heated up much faster with the additional radiant though I continue to use 2 - 800CFM accessory individual fans trained directly on the radiant vs. 4 before...).

Once temperature was reached, water started flowing as expected. However, over night flow stopped. I expect that wet bulb decreased below 90. Temp sensors indicate that exhaust came on 3-4 times.

I'm starting to expect that the Nyle dry bulb thermometer reports 3-4 degrees below actual temperature. I have TWO quality heat sensors just by the Nyle thermometer and this is what they show. So, I tried increasing dry bulb setting to 122-124 and flow resumed (wet bulb rising above 90 and holding).  I'll call Stan on this if I don't hear back here.

Steady as she goes!

[TBrown99]

I just did a short test as flow stopped. This occurred while WB was holding above 90 (compressor on) temp at 120.5 by Nyle thermometer. Aux fans trained on radiant were off. Nyle temp set to 122 (so l53 holding at the low range before kicking heat back on). I tweaked temp up to 123 and turned on the two aux fans. Within 30 minutes, temps rise 2-3 degrees and good flow from drain line resumes. Not much change in WB.

At this hotter level, Govee sensor shows 119.7 while 2nd sensor SensorPush shows 120.5.

How often is the Nyle thermometer off? Anyway. It appears that my system only works when DB is adjusted up a few degrees. This may explain original issue with WB not exceeding 90...   

[doc henderson]

good info.  did you mean dry bulb tweaked temp tweaked to 123 and by flow I assume you mean water coming out from the DH unit?  thanks.

"Anyway. It appears that my system only works when WB is adjusted up a few degrees"

"I tweaked temp up to 123 and turned on the two aux fans. Within 30 minutes, temps rise 2-3 degrees and good flow resumes. Not much change in WB"

[TBrown99]

Thanks Doc. You're right on with those two errors. FIXED in the original!

WB-->DB
Flow resumed... from the drain line.

I'm going to need to call Stan as I'm struggling to make this work. (I have DB temp 120 and WB above 90 but flow from L53 is inconsistent. Drips sometimes, doesn't other times. I can tweak up the temp and it picks up but the compressor isn't supposed to operate above 120.) I'm thinking I shouldn't need to micro manage like this.

  

[doc henderson]

good idea to call stan.  not sure why it would produce more at a higher temp as that lower the relative humidity.  have you tried dropping the wet bulb setting telling the compressor to come on at an even lower RH, or wider gap in DB/WB, or in other words a larger WB depression.

although raising the DB, or lowering the WB creates a larger overall depression that correlates with a goal of a lesser RH.

I may be getting myself confused.    can you set the WB lower and see if you make more water.  are you saying that no water was flowing, despite the compressor running?

[TBrown99]

Stan said before that I should not simply set down the WB level and, indeed, I tried this and it would reliably begin the bucket filling drops of water   I expect it's problematic because you want to maintain a base level of humidity to avoid quality degrade issues (splitting? not sure exactly).

Instead, he recommended turning off compressor and leaving at 140 for a couple of days, forcing out humidity. Then back to 120 and hopefully higher WB.

My best idea now is that the Nyle thermometer is reading 2-4 degrees too low. I've read that Govee is accurate .5 deg. Not sure. But my other sensor also reads lower than Nyle. I have a third coming to test more.

I turned off my aux. fans used to generate heat and cut the water flow from my boiler (base board radiants) to 50% figuring I'd see how the system responds. It's been an hour so far and while the Nyle heater was on, it has stopped early 119.3... with WB close to target 89.6. I was hoping the rise to 122 would bring the compressor back on. But again, the heater cut on me. Not sure why. Back out to the barn! I'll open the radiant boiler water flow to full to maybe get a bit more heat out. (I'm not going to turn the aux fans on except for sterilization and initial heat up...)

I don't recall the dehumidification indicator coming on in the past but it is coming on. Maybe it also has, just seems new.

My sensors are showing falling humidity level so despite the lack of flow into my bucket, I expect it's not all wasted time. The humidity is getting out somewhere.

I'm starting to ramble. Getting tired! 

 

[TBrown99]

The big point here is that if I could turn up the heat 2 degrees, this would likely put me in 90 compressor area (sitting at 119.6/89.9 now... just sitting there...) But the compressor isn't supposed to be on above 120. My theory is that the thermometer isn't accurate, as suggested by two good quality sensors (Govee and Sensor Plus).

I will soon have a third sensor as I purchased a Inkbird WiFi ITC-308 to control my auxiliary heat fans (which blow directly on the radiants)... Stan had mentioned that I should add thermostats in my boiler water lines but this may be an easy alternative... thermostat tied to the fans automating switching on / off according to set points.

(Instead of just sitting there, I'm temped to set temp to 121 and WB to 89.)

[doc henderson]

Ok so the compressor is doing its job.  that was the only reason to suggest lowering WB was to make sure the compressor was not only on but doing its job.

I agree you do not want to create a schedule that dries wood too fast and degrades it.  you can turn off the compressor and turn up the heat to boil off water and when you reduce the temp the RH will go up and a higher WB setting will now turn on the compressor and put out water.

these are relativily soft woods, and wet.  so water should pour out. 

[doc henderson]

I think as long as you follow the MC loss each day and not overdo it you should be fine.  this is how we all learn.  thanks for letting me follow along!

I do not know when the compressor shuts itself off and if it relies on the unit temp to do that.  You could also do as stan suggested for a few days then drop the temp and sort of move water in a pumping fashion.  I do not know if any of these woods tend to stall, like walnut.  

[TBrown99]

Not wanting to see an empty bucket tomorrow morning (15 lbs of water first 24 hrs), I set WB down to 88.

Again, my only thought is that the dry bulb thermometer isn't taking correct readings. If it were adjusted just two degrees lower and matched the lower readings of my two other sensors (placed just by the Nyle one) the system would be working as expected. I need to know the odds of a mis-calibrated Nyle thermo.

I'm surprised that the Nyle heater struggles to maintain 120 even though I have two 7' radiant sections in the room. But those aren't so good at generating heat without air flow, so maybe it makes sense. The problem is that if I turn the aux fans on them, it gets too hot and the exhaust fan cycles. (I'm not totally clear why getting rid of the moisture that way isn't desirable.)

[doc henderson]

I do not think it is bad, but it may be why the compressor does not come on and or not much water comes out via the DH.  the thermostat that you plan to attach to control the heat may help not overheat.  It could be bad if you are way off schedule for a hard to dry wood like oak if it goes too fast.  I think it would be interesting to try what Stan suggested.  turn off the compressor, and heat to 140 like a sterilization cycle then turn off the heat and turn the compressor back on.  I think YH does something similar with walnut that has stalled.  can the directed fans be wired to come on only when heat is called for (by the radiant heat)?

[doc henderson]

a solar kiln gets rid of moisture that way and defeats the purpose of the DH to some degree, but it is fast.  if you are paying for the heat, then it is wasteful to overheat.  Do you have a current MC for the wood?  Stan is the man to ask about the temp probe calibration and or replacement.