adding more heat to kiln

[kelLOGg]

I've been running my kiln (de-humidifier + window fans) for about a year now with good success and now I am considering adding additional heat to kill bugs. I can easily reach 120* w/ only the de-hum unit but in order to get 140* I have thought of 2 options which I want comments on.

1. Use an electric space heater. (Probably not a good idea since it will glow red hot and be more of a fire hazard.)

2. Use baseboard heaters (Surplus Center has many 220 volt units but my temp controller operates at only 120 VAC)Is there a problem operating them a 120 VAC? It is a purely a resistive load so I would get only half the heat but I see no problem with that. 

I operate my kiln only about 3 mo out of a year and it is small. (16 x 6 x 6 and insulated w/ 6 in batts and has a tightly fitting door.) Whatever I heat it with, it will be controlled by an instrument temp controller with dialable temperature with 1000 watts of power. Educate me.

Bob

[Kcwoodbutcher]

You can use either one as long as they have proper overtemp or in the case of the space heater overtemp and tip over switches. 140 is probably getting close to the temp limit. If you use a space heater use a forced air one like a milkhouse heater rather than a radiant one. they will not glow red. The bigger problem is the dehumidifier and the window fans. Neither one is designed to work at that temperature. You should turn the dehumidifier off before dialing up the temp. I'd worry about insulation failure with the window fans.

[red oaks lumber]

 i don't know if those kind of heat sources will put out more than 140 deg. maybe a couple of heaters might work

[Den Socling]

Use your controller output to energize a starter then you can put any voltage or current through as along as you don't exceed the rating of the starter. The controller needs to act as a thermostat.

[bck]

I use light bulbs on a thermostat in my small kiln.

I am more comfortable using light bulbs vs an electric heater.  I have had discussions online with people who insist an electric heater is safer ? any opinions ?

[sparky]

The following question was raised:
(Surplus Center has many 220 volt units but my temp controller operates at only 120 VAC) Is there a problem operating them a 120 VAC?

I am a recently retired electrical engineer. A 220 volt heater operated at 120 volts will produce only 25% of it's nameplate wattage. Power is related to the square of the voltage. If the voltage is reduced to 1/2, the power is reduced to 1/4. I agree with a previous post and use your controller to energize a contactor to deliver power to the 220 volt heaters.

Sparkt

[kelLOGg]

Sparkt,

Thanks. P=IV and when V is halved I is halved too, cutting the power to 1/4; now I get it. I will definitely use a relay.
It's easy for me to slip up on these things.

Bob

[solidwoods]

I like a wood fired water heater.
It can also heat a shop and home if they are located within 500' of each other.
Even an EL Cheapo shop built block walls/fire brick lined with steel pipe inside and or water filled heat exchanger chimneys works.

For kiln heat control use a Taco 3 way valve.  It has a 12vdc solenoid on it.  Low amps also.

For my kiln control I use the Pola egg discloser its about $600 and does everything you need, controls humidity and temp and vent. 
jim

[Sawyerfortyish]

I was told by nyle that 123 1/2 degrees is all that needs to be reached core temp in the wood for 24 hrs to kill all insects and eggs. When I'm finishing a load I turn the compressor off and the temp up to 130 degrees the day before I unload.

[kelLOGg]

Sawyer40ish,
Wow. 123 1/2 deg won't require much additional heat at all. I haven't added heat yet because I'm busy with other things but I'll try 130 deg initially as you do.

[solidwoods]

From the USDA Forest Svc. Book Drying Hardwood Lumber.
General
Technical
Report
FPL-GTR-118

It's free on line.

Sterilization is a procedure to kill any noxious insects and
their eggs (and perhaps any fungi) in the lumber. The procedure
is especially directed toward insects that originated and
lived in the standing tree. The objective of sterilization is to
prevent forest pests from spreading from one geographic
location to another. It is required for lumber being exported
to certain countries. All research indicates that when wood is
thoroughly heated to ³130°F (³54°C), this treatment will kill
all existing insects, their eggs, and any fungi associated with
wood. However, the sterilization procedure, as applied in
Canada and the United States, typically requires the center of
all the lumber in a kiln or sterilization chamber to be heated
to 133°F (56°°C) for at least 6 h, although shorter times are
certainly quite effective.
To ascertain the exact sterilization time, a company must
consider the lumber MC, lumber thickness, type of heat
used, and kiln or chamber characteristics. Usually, temperature
measurements are made within pieces of lumber (in the
slowest, coolest part of the kiln) to develop a specific procedure
and confirm that the required procedure is adequate.
The dryer is then “certified.”
Note: The temperature of wet lumber is closer to the
wet-bulb temperature than the dry-bulb temperature. As
the lumber dries, its temperature becomes closer to the
dry-bulb temperature.
The standard kiln schedules used in steam, hot air (direct
fired), and dehumidifier kilns will always achieve adequate
sterilization without the use of any special procedures. In
some older dehumidifier kilns, however, special care must be
used to ensure that the required temperatures are achieved
and are held for the required time.
When lumber is to be shipped green but sterilization is required,
heating must be done at very high humidity to avoid
drying. This can be accomplished by direct steaming of the
lumber. Because the steam temperature exceeds 212oF
(100oC) and because steam condensation on cold lumber
provides excellent heat transfer, steaming times seldom
exceed 1 h for most products and species. Sterilization in
hot-air kilns is difficult without drying the lumber because
high humidity levels are difficult to maintain.
When the wood is taken from the kiln, it can be reinfected by
insects. If the wood is not dried to <20% MC, it can be infected
by fungi. However, only a few insects will invade,
inhabit, and damage dry (<10% MC) wood. Three major
dry-wood insects are carpenter bees, termites, and lyctid
powderpost beetles. These insects are not the insects that are
of concern because they can be transported through cut
timber to forests in other geographical areas.
Note: Always check for special sterilization
regulations when the lumber is to be shipped to
another country to make sure that the procedures
discussed here are considered adequate.

[kelLOGg]

Use your controller output to energize a starter then you can put any voltage or current through as along as you don't exceed the rating of the starter. The controller needs to act as a thermostat.

I used a mechanical relay triggered by the output of the controller. But an immediate problem appeared: the controller is a proportional controller so it cycles the relay on and off (several time per second) as the temp reaches the set point. It is a laboratory controller and is designed for very accurate temp control and to prevent overheating. (gross overkill for drying wood) Under actual use it would burn up the relay in minutes with all the cycling. So I replaced it with a solid state relay which will take the fast cycling rate. Just installed it and will test it at operating temperature in the coming weeks. Fingers crossed. Bob