So how hot can you get yours!!??

[benbound]

I'm into my second season of kiln drying using a hot air system in a 20' container. I'm finding that stuff dries nicely from 30 degrees and above, if I really crank things up I can hit 50 degrees but even with a second heat source struggle to get above that.

 

Just wondering what other peoples' experiences were and if trying to go higher reaches the point of diminishing returns?

[ash_smith123]

I'm getting around 40-45 in the drying room and 20ft contained at the moment.

[big chris the log]

I'm into my second season of kiln drying using a hot air system in a 20' container. I'm finding that stuff dries nicely from 30 degrees and above, if I really crank things up I can hit 50 degrees but even with a second heat source struggle to get above that.

 

Just wondering what other peoples' experiences were and if trying to go higher reaches the point of diminishing returns?

 

My GF container runs about 45 to 48 most of the time but the top logs seem to go orange colour and smell a bit like singed cake this seems to affect the beech most.I would think making it hotter would not be the answer but more air flow .

Cheers Chris.

[Big J]

I get 65c at the end of the cycle with a 233kw boiler and a badly insulated 40ft container.

[benbound]

Those numbers are interesting thanks. I suppose the other issue is where you have the temp sensor as there seems to be a bit of a temperature gradient from top to bottom. Interesting about the logs going orange, not coma across that yet

[Duffryn]

Temperature rises as the logs absorb the heat. With an input of 80 degrees water into my heat exchangers and on an insulated kiln I get a 58 degrees at the bottom of the end of the kiln after 2 days. The heat exchangers on the lowest settings move a kiln of air every 90 seconds and so for me, temperature inside the kiln is more important than airflow in terms of reducing drying times.

[benbound]

That's useful thanks. There is clearly an optimum point to be reached in terms of airflow-v-tempertaure. Too much airlflow and you'll never reach the optimum tempertaure to drive water from wood. Also hi airflow seems to make the outside of a log dry but you don't get the much needed penetration of water release deep into the log which we all need.

For logs that are pretty well seasoned and just need the rainwater removing to make them saleable I think high airflow is the way to go and worry less about high temps. If you're drying green wood, I don't think that anything other than high tempertaure is going to do it in a reasonable time.

It would be good to see some science applied to this, can't find much on the interwebs.

[Guest the cleaner]

That depends if he is tired

[openspaceman]

That's useful thanks. There is clearly an optimum point to be reached in terms of airflow-v-tempertaure. Too much airlflow and you'll never reach the optimum tempertaure to drive water from wood. Also hi airflow seems to make the outside of a log dry but you don't get the much needed penetration of water release deep into the log which we all need.

For logs that are pretty well seasoned and just need the rainwater removing to make them saleable I think high airflow is the way to go and worry less about high temps. If you're drying green wood, I don't think that anything other than high tempertaure is going to do it in a reasonable time.

It would be good to see some science applied to this, can't find much on the interwebs.

 

I doubt you are far out. Of course the hotter you have your kiln the bigger the losses through the kiln walls, so extra capital cost in insulation becomes sensible. Also the hotter you go the higher the flue losses in your furnace but heat tends to be cheap compared with the power loss in having a fan moving lots of cold air.

 

You can make a fairly simple judgement as to how much airflow you need at a given temperature as evaporating water off the log converts the heat in the airflow to water vapour, this uses a lot of the energy in the air so its temperature drops. As long as the air going in is hotter than the air leaving and your heat losses are low then you are removing water. You can check the loss from the kiln by running it empty with the same air flow.

 

A simple kit would be two temperature and humidity logger and a power meter across the fan with a simple anemometer.

 

IIRC our high temperature kiln had to circulate 14m3+ for every kg of water removed and there was a substantial amount of energy needed just to get it to temperature.