Nyle L200M, heating question once you reach 120º

[jimbarry]

I have another batch of firewood in the kiln. Stats attached.  The MC target is 20%

I went ahead this morning and shut off the heat, and the exhaust fan, to see how well the compressor can hold up the temp. Who's tried this already? Is this a mistake to do or not? I'm figuring the compressor's heat will add heat but the temp will slowly go back down. The question is, will it drop too fast such that it hinders evaporation? Or, would it be better to keep the heat on because maintaining at that temp will shorten the time necessary to run the kiln?

[K-Guy]

Hi Jim
A lot will depend on how tight and well insulated your kiln chamber is. Also the more moisture there is in the chamber, the harder the compressor has to work to remove it and the result is more heat.

[jimbarry]

Thanks. Well, let's see how tight the kiln is then.

[YellowHammer]

Normally, yes, assuming the kiln chamber is well insulated and the door seals are tight, the compressor will provide more than enough heat to keep the temp at your set point.

There is no need to turn the heat switch off, if the unit can maintain heat, then it will not call for it even though the switch is on.  

If it actually calls for heat, that will tell you right off that it needed it.

[doc henderson]

Jim I am not a kiln expert.  the compressor removes water (in the form of water vapor) from the kiln (back in liquid form).  it is the heat the moves the water from the wood to the air in the kiln.  airflow helps the water on the surface transition to the air.  If I had a great kiln like yours, I would run full bore for firewood and get it done.  the wet bulb depression reflects the RH in the air, and the higher the temp, the more water the air can hold ( lower RH)  and a greater gradient from liquid to gas.  promoting evaporation.

[jimbarry]

Starting point. 8pm



 

Day 1 morning reading 8am

 

Day 1 evening reading 8pm


 
Day 2 morning reading 8am

[doc henderson]

good data.  I would assume the compressor is running full tilt, since there is only a small dry and wet bulb difference.  If you lower the temp too much, you will get condensation on colder surfaces in the kiln.  approaching 100% RH if you like to think in those terms.  

[doc henderson]

I assume you have a ton of water coming out of the dehumidification unit, I would consider have the vents operate to get the extra water out, but I would defer to @YellowHammer   and @K-Guy  for practical applications.  I know the venting will loose some heat, but not much evaporation from the wood at the low wet bulb depression.  You should get a rebate from nyle for such great pics of the data and control unit!
8)  

[jimbarry]

...  You should get a rebate from nyle for such great pics of the data and control unit!
8)  

Yeah! Hey Stan, you hear that? ;) 

[YellowHammer]

The little "o" indicator below the text on the controller indicates if the circuit is being called, and if the switch is in in "auto" or "on" position, then the circuit will be energized.  If the switch is in "off" mode the circuit is being called, but is not able to energize.

So in your last picture, the compressor is being called a shown by the indicator, and is operating because the switch is in the "on" position, but the heat is not being called (no indicator) and wouldn't be operating even if you hadn't put the switch in the "off" position.  However, if the kiln temp cools off with the compressor running, you will see the "o" indicator reappear under the heat label, and if the switch is on the "off " mode the strips can't turn on, and chamber will cool down.

Also, always leave the vent in the "auto" position, again turning it on and off at the switch is not necessary, as it will only turn on when called by the controller.  However, if the compressor is generating excess heat, and the auto vents can't turn on as it should, the temps in the kiln will climb and eventually hit the high pressure freon cutoff, and then you get to meet the infamous "Little Red Button".

[jimbarry]

Batch 2, Day 2 , 8pm



I had turned off the heat at 8am so the kiln's been running 12 hours and it lost 1º. I attribute that to when I opened the door once noon time and went in for a quick check of things. It typically drops a degree whenever I do that.

[jimbarry]

Batch 2, Day 3, 8 am - With heat switched off for 24hrs now, with 32ºF outdoors, the kiln's managed to maintain its heating capability overnight while progress in dry down the firewood.



 

[jimbarry]

Batch 2, day 3, 8pm - Stepped into the kiln a couple times today, to toss in 6 bags of kindling (1 cu ft mesh bags). Mostly as a test to see what happens. Kiln temp did drop three degrees. Seems every time the door is opened it drops about 1.5ºF. But, as you can see, the kiln has recovered that temp. I took one more look this evening at 8pm just to check on things. All cruising along well.




  -

[doc henderson]

Jim this is great, I feel like I am right there with you drying that firewood!  thanks!!!

[jimbarry]

With the record keeping between batches, its interesting to watch for performance variances along the same timestamps. Between the last batch and this one, at this time day 3, 8pm, the stats and electrical consumption are about the same. Only exception is the kiln DB and WB are about 7º higher on this batch.

[doc henderson]

if the second batch was dryer, it could be hotter with the same input.  is this with the heat off?

[jimbarry]

Batch 2 day 4 8 am



 

I turned the heat off in this Batch 2 after 36.75 hrs running.

Water sample taken, flow rate is 3 min/250ml (5L/hr).

Probe stats are clearly showing the varience in the 2 cords loaded. Probe 1 and 3 (closest to the dehumidifier) are for a cord of wood split a month ago from wood cut in Oct 2019 (crate F to H). Probe 2 and 4 are for wood cut and split in jan 2019 from logs harvested Oct 2018 (crates A to E).



 

[YellowHammer]

As a note, your dehumidifier is still showing that is it overloaded, due to the WB and DB being so close together.  So the air is carrying lots of moisture, and it's more than the coils can remove so it can't reduce the WB temp.  So if you want to speed things up, (I don't know that you do), then a strategy to dump the moisture laden air would work.  Typically, that is done by cracking a vent, while applying supplemental heat to keep the temps up.  So I typically do this by turning on heat lamps and turning the heat strips to auto.  Then crack a vent (without the blower working) and some of the moisture laden air will escape in a steady flow.  You'll see what looks like steam escaping, but its just the moist air.  If done correctly, you will still be able to maintain the 120 DB temps and you will see the WB drop substantially.  This is how a standard heat cycle kiln operates, except generally, it is using a much stronger heat source, such as gas or propane.  Some people even run heat from the OWB or such into the kiln chamber to provide lots of free supplemental heat.  

Anyway, the reason this is done in a standard kiln operation is to prevent sticker stain, which would have happened already unless the WB/DB depression is more than 10° for a day or two, and preferably 20°. With firewood, it obviously won't matter, but it will speed the drying process up, it you want to. 

[doc henderson]

what is the max temp that a nyle will operate.  is there an ideal operating temp as far as water removal.  each time you open it up and the temp drops, you are getting a bolus of dryer air.  I agree with YH, you are trying to dry the wood at nearly 100% humidity.  if the temp dropped, you would get condensation.  but the wood is getting dryer!

[doc henderson]

could throw a home dehumidifier in or open up and let in dryer air, but loose temp for a while, and have to heat it back up.  the wood would retain some heat, but it will drop with a phase change of the water  from liquid to vapor.  

[jimbarry]

I just went and checked the controller again and the DB and WB show a 3 point difference. I didn't crack any vents though. It did that on its own.

[WDH]

what is the max temp that a nyle will operate. 

About the mid-130's.  If the dry bulb exceeds this with the compressor "on" and running, the compressor will trip and have to be re-set. 

[jimbarry]

Here's my understanding of it all. I thought the idea was to get the heat up (thus increase thermal mass of wood) and the air moving to draw the moisture out of the wood. The condenser can only remove moisture at whatever rate its designed for, so excess moisture would be in the air until its drawn out. 

Wanting to dry the firewood as quickly as possible, should I continue as I am doing and also implement YH's suggestion? Anything else?

[WDH]

In normal lumber drying, you have to balance the load with the water removal capability of the dehumidification unit.  If you overload the kiln with lumber (or firewood), the humidity will be close to 100% for a longer period of time which can lead to sticker stain and discoloration (gray stain) from long periods of high temp and high humidity.  This is important in stain prone species, but is not an issue with firewood.  There is more water being evaporated from the wood than the system can remove.  If you crack a vent, you are dumping some of that super saturated air containing the excess moisture into the air outside the kiln.  This will also dump heat, so you may have to operate the kiln with the heater on to keep the operating temp at the desired level. 

One thing that I do in this situation is to open the kiln doors for a couple of minutes to dump the very humid air and replace with lower humidity outside air, thereby dumping out the water vapor in the kiln air.  Again, you are also dumping heat.  However, given the thermal mass of all the hot wood, the heat loss is not too big an issue due to the stored heat in the load.  You might have to have the heater on for a bit, but the temp will return fairly soon, and you will have dumped a lot of the evaporated water out of the chamber.  This will speed drying of the load.

[jimbarry]

Appreciate the info. I now have a much clearer understanding.