Kilning theory discussion

[Big J]

What about using an Air Source Heat Pump to provide both the heat & air flow?

 

You should get about 3 units of heat for every unit of elec.

 

 

Hmmm, very interesting. *Opens google......*

[TrollSpiel]

Jonathan, here's some spec from my kiln - a mix of hardwoods.

Over 12 weeks (between 1.5 - 2") @ 31-33 degrees, big fan, ebac dehu, duct extractor..

 

humidity per week > 75, 72, 60, 48, 40, 36, 31, 31, 29, (same for next 4 weeks)...

 

Results? despite meticulously cut & stacked

 

Pants! warp, twist, bend, cup, split, shake.....

 

Fortunately, a well stocked workshop to deal with such rubbish without cutting up those big boards.

 

This year, im looking more into natural seasoning, maybe kilning for the last bit..

[Big J]

Jonathan, here's some spec from my kiln - a mix of hardwoods.

Over 12 weeks (between 1.5 - 2") @ 31-33 degrees, big fan, ebac dehu, duct extractor..

 

humidity per week > 75, 72, 60, 48, 40, 36, 31, 31, 29, (same for next 4 weeks)...

 

Results? despite meticulously cut & stacked

 

Pants! warp, twist, bend, cup, split, shake.....

 

Fortunately, a well stocked workshop to deal with such rubbish without cutting up those big boards.

 

This year, im looking more into natural seasoning, maybe kilning for the last bit..

 

Your humidity is dropping too quickly I think. It should be at around 83% for the first two weeks or so, and it will then start to drop towards 30% when it should be ready to open. Mine's opening on Wednesday and it's currently 35 celcius and 30% RH in there.

 

Looking at air source heat pumps, I think they are too much for my application. Considering the heat requirement when utilising a heat exchanger is only 180w, it's unnecessary.

 

I'm setting up a new kiln at the new yard next month and will be using this kind of fan:

 

Industrial Extractor Fan 450mm, 18 inch, 240V, 900 rpm | eBay

 

instead of the centrifugal fan. Same air movement for a fifth of the power consumption. Spending about £700 on a heat exchanger and fan will reduce my electricity bill per cycle from £560 to £66 (or about 25 pence a cubic foot).

 

Jonathan

[Rob D]

Jonathan, here's some spec from my kiln - a mix of hardwoods.

Over 12 weeks (between 1.5 - 2") @ 31-33 degrees, big fan, ebac dehu, duct extractor..

 

humidity per week > 75, 72, 60, 48, 40, 36, 31, 31, 29, (same for next 4 weeks)...

 

Results? despite meticulously cut & stacked

 

Pants! warp, twist, bend, cup, split, shake.....

 

Fortunately, a well stocked workshop to deal with such rubbish without cutting up those big boards.

 

This year, im looking more into natural seasoning, maybe kilning for the last bit..

 

 

Could be too harsh in the first couple of weeks.... If any drying defects occur early on then that's it - there's no reversing it.

 

Also it could be the wood you're cutting - my timber tends to be bendy and through sawn which is a recipe for cupping - this year am going to do much more quarter sawing.

[Justme]

Does that 180watts run cont 24/7?

 

If so thats 4.3kwh per day so about 50p's worth.

 

A 3.5kw ASHP (smallest I could find quickly) will use 1.4kwh per day so about 17p's worth.

 

Cost about £400. So about 1200 days use to break even.

[Big J]

Does that 180watts run cont 24/7?

 

If so thats 4.3kwh per day so about 50p's worth.

 

A 3.5kw ASHP (smallest I could find quickly) will use 1.4kwh per day so about 17p's worth.

 

Cost about £400. So about 1200 days use to break even.

 

Could you please post the link to that particular heat pump? 1200 days is a long payback period but environmental credentials are important, so it might be worth it from that point of view.

 

Jonathan

[TrollSpiel]

Could be too harsh in the first couple of weeks.... If any drying defects occur early on then that's it - there's no reversing it.

 

Also it could be the wood you're cutting - my timber tends to be bendy and through sawn which is a recipe for cupping - this year am going to do much more quarter sawing.

 

Rob, John...

 

takes at least a week for the temp to get up and the wood to start warming.

 

Actually, it seems in the latter part that the defects have appeared - or perhaps it's just a slow progressive thing, which it seems to be because I look at it often as I have the means to via the setup.

 

Extraction is not too harsh - it's timer on/off so I don't suck too much heat out. Ebac has been on 24hr, maybe that's causing RH to drop to quick. Never sucks more than 5L out a day. At the start, first weeks, maybe.

 

Softwoods fine, big fat chestnut i left out for a year, fine.. But all that bendy "featured" oak, horrendous. Holm, so so; even the spiralling hornbeam wasn't too bad. the big stuff on the bottom of the stacks is alright i think, the smaller boards bit cuppy.

 

I also cut a lot of stuff that has just been lying around in the yard for years. What I'm not cutting is fresh, green, perfectly straight no-tension, quarter sawn... so I can live with the results. All a learning curve, and as I'm not a commercial mill, I can be a little phlegmatic about the results.

 

Might try and keep the RH up next time - which has been my 'gut feeling'

[Rob D]

All sounds fine to me.... it may be just the wood then as I have the same with a lot of the stuff I cut i.e. unless it's very straight and clean no matter how you dry it something will happen - if it stays flat there's be cracks if no cracks then it'll cup....

[Rob D]

Just noticed on the right hand side there is an advert saying 'grants for heat pumps'....

 

May be you could get a grant towards a more efficient system?

[Rob D]

https://government-grants.co.uk/air-source.shtml