Finding A Good DH

[Charles]

I have a small DH kiln (250 bft) and use a 30 pt home dh unit and  run the kiln at 80-90f 
I have read several posts about using the same thing and drying lumber to 7% at slightly higher temps.
I can get 7-8% but can't  go any higher on the heat which I would like to do.
In order to achieve my 7-8% mc I maintain 80-90f and achieve a 35% rh in the kiln simple enough.
The problem I have is my evaporator coil in the DH has a hard time maintaining the needed temp to extract water between 80-90f
From my dew point chart 80-90f  @ 35% RH needs a condensing temp of between  approx. 50-60f
At 80f kiln temp the evaporator coil is about 52f and as the temp rises to 90f the  evaporator coil temp also goes up to about 58f.because of the kiln heat on the DH compressor. I have added a little extra r12 to the compressor so as to semi flood the evaporator to almost a freeze up to take the heat ,this helped. I have mounted another  fan in front of the compressor to help cool this helped. But short story is how does everybody else get these things to work and I can't
When the RH starts to get close to 35% it takes forever to extract water. I have posted about this before but I thought I try again I am getting tried of screwing around. One last thing is I have found a hvac guy who is going to build me a water cooler for the return side of the compressor to cool the freon but hasn't happened yet

This is pic of the the kiln, it is inside in my shop in the basement



 

[Tom L]

I have seen some basement /crawlspace dh units that say they run and work to 120 degrees.
they are very expensive though. have not had the guts to pull the trigger on a unit that costs 1g and not sure if it would work. the units are large and would take up too much space in my small kiln also.

wish you luck,

[GeneWengert-WoodDoc]

If the air is warmer, a coil at 40F will produce lower humidities.  That is why the smallest commercial DH will run at a peak of 115 F, and larger ones up to 150F.

Note that at 35%RH, the surface fibers will reach 7% but the core will likely not go below 9% MC.  You need to achieve a lower RH, which will take more heat with a DH.  Unfortunately, home DH units will not live long if you add much heat...that is a result of the new gasses used...they do not lubricate as well.

[Charles]

Tom
I have looked into crawl space DH units and phoned the rep from Ebac and Honeywell and they got a little nervous when I told them what I wanted it for . I agree that dropping a G plus on a poke at a pig is something I don't want to do
But what are the other guys doing to get with their DH's that I am not doing????
thanks for the input
Charlie

Gene
I know I have to go to higher temps to get the right MC . You are so right with the lower MC on the outside and the higher in the center I get that all the time that's what ticks me off. If others are getting results of 7% dried lumber with a house DH then what am I doing wrong, higher temps just shove my evaporater temps up as well.
Gene do you think the design of the kiln is wrong. By that I mean I built it vertical because of space. Someone mentioned to me that why would you try to push thin air up when it is easier to keep it down, meaning it would be easier to dry the air if everthing was on the same plane like all the rest of the kilns. Just grabbing at straws but maybe they had something. I use R-12 and have added a little extra in the system to almost flood the evaporater for extra cooling and added an extra fan to blow on the compresser for cooling. maybe I shouldn't be forcing dry air up
Any thoughts
Thanks
Charlie

[kelLOGg]

Interesting thread.
I have a home DH unit also and I need to buy my third one because they can't take the heat as Gene says. I let them go to as high a temp as they can (~130°F) and that is a mistake. So, when I replace my second unit I am thinking about turning off the DH unit when it reaches about 80 - 90°F as Charles does. Then turn on aux heat to ~140 or so and then:
1. let it cool back to 80 - 90 and turn on the DH again.  It would take days to cool. Would the wood re-absorb the moisture while cooling?
or
2. just vent it until it reaches 80 - 90°F the turn on the DH again?

Bob

[GeneWengert-WoodDoc]

Up or down air has no difference.

Your experiences with your DH unit are common.  Some folks are not as picky as you are, so they do not complain.  Yet, your pickiness is best.

kelLog...I would opt for faster cooling.

[Charles]

kelLOGg
If you look at the pic of the kiln on the top of it there is a 5,000 btu air conditioner.
I run the DH till the temp gets to 90f then it shuts off and the a/c starts up on low and cools the temp back down to 82f, this takes about 20 min then the DH comes back on and runs for about 40 min. this gives a little more than a 60% duty cycle. By doing this I don't have worry about venting or anything just let it run. But you would have to some sort of PLC or electronic control for this.
I am very happy with the way everthing works except I wish I could get the temp up a little while keeping evaporator temp down which at this point seems impossible if I want good dry lumber.
I am hoping that this water cooling system that is being made for the suction side of the compressor will be the answer
I see Nyle has a new small DH the L53 foe 300 to 1000 bf. That would do the trick but when you only dry for yourself 3 grand or so is fair chunk of change

[kelLOGg]

Charles,
I have looked at the Nyle L53 but for my small operation the cost is prohibitive.  I like the A/C alternative for cooling but I think I will go for venting for now.
Bob

[Tom L]

Charles,
I have looked at the Nyle L53 but for my small operation the cost is prohibitive.  I like the A/C alternative for cooling but I think I will go for venting for now.
Bob

I've been running my air conditioner in the kiln full time with the temp set at 85 degrees. so I don't fry the dh unit. seems to work OK  would be nice to get the temp up in the 100's

[kelLOGg]

kelLog...I would opt for faster cooling.

Gene,
I assume your above comment refers to my option 2: "just vent it until it reaches 80 - 90°F the turn on the DH again" rather than install an A/C?

Bob

[Charles]

Tom
do you have the A/c unit right inside the kiln and running all the time to keep the kiln at the right temp while the DH is running also. How big is the kiln??

[Tom L]

yes, the kiln I have doubles as a walk in cooler for hanging deer in the fall,
so I cool the cooler with a 8000btu air conditioner mounted in the wall. hooked up to a special controller
to bring the temp down in the mid 30's to age deer.

so when hunting season is over, I stack my wood inside with the dh unit and let it run. with the air conditioner running the whole time, so I don't fry the dh unit . it will get up to 130 degrees in there if I do nothing and just let the dh run.

then with drying pine, I cover the air  conditioner, (so it doesn't melt anymore) take out the dh unit and can get the kiln up to 160 degrees to set the pitch with a heater and fan.

the kiln is 6ft x 6 ft x 8 ft tall

[Charles]

interesting Tom
never heard of running a A/C with the DH
Neat way to cool the venison also

Charlie