enhanced solar drying

[openspaceman]

I've been doing small experiments with air drying, where essentially the sun is heating air and increasing its capacity to absorb moisture, and in free air (i.e. log standing by itself) and seeing oak dry from green to 20% mc wwb in 44 days.

 

So as heat speeds drying up and solar heat has no fuel cost I started looking at small scale solar drying. I found just using cheap corrugated acrylic sheeting I could make a simple greenhouse where in the last 2 days the temperature has stayed above 40C for much of the day in sunshine with relative humidity falling to 24%. This is consistently more than 10C hotter than outside in the sun. RH is about the same because there is free air flowing and out.

 

Last week I was employed dragging tops and stuffing an ancient chipper on a commercial refurbishment where the previous tenants had allowed the Leylandii and mixed broadleaved hedges run away. I noticed a pair of old cycle racks had been removed and set aside.

 

I mentioned the possibilities of these being the beginnings of a solar log drying kiln for the boss's son, who runs a log round with about 40 customers in his college holiday.  Boss being a petrolhead was not at all interested. I made an enquiry and they were available for sale (these things new cost about £5k erected) I sent a photo to the son and explained my thinking and he was interested. At this point father and son took over and bought the shelters. Now I'm not sure if they are going to implement the idea but I estimate placed side by side and south facing they will intercept 18kW(t) in sunshine. This is enough theoretically to evaporate nearly 30kg of water an hour if the air circulation is good enough.

 

With the shelters side by side and south facing and a roofed area behind and the back being a curtain side from a lorry he should be able to stock about 20m^3 of split logs in stillages.

 

I think wit a few low powered circulation fans and  a differential thermostatic switch only running them when  inside temperature is 10C above outside and a humidistat controlling a vent fan he should get good drying. If I am kept in the loop I will update progress.

Edited April 19, 2018 by openspaceman

[Martin du Preez]

I've been doing small experiments with air drying, where essentially the sun is heating air and increasing its capacity to absorb moisture, and in free air (i.e. log standing by itself) and seeing oak dry from green to 20% mc wwb in 44 days.
 
So as heat speeds drying up and solar heat has no fuel cost I started looking at small scale solar drying. I found just using cheap corrugated acrylic sheeting I could make a simple greenhouse where in the last 2 days the temperature has stayed above 40C for much of the day in sunshine with relative humidity falling to 24%. This is consistently more than 10C hotter than outside in the sun. RH is about the same because there is free air flowing and out.
 
Last week I was employed dragging tops and stuffing an ancient chipper on a commercial refurbishment where the previous tenants had allowed the Leylandii and mixed broadleaved hedges run away. I noticed a pair of old cycle racks had been removed and set aside.
 
I mentioned the possibilities of these being the beginnings of a solar log drying kiln for the boss's son, who runs a log round with about 40 customers in his college holiday.  Boss being a petrolhead was not at all interested. I made an enquiry and they were available for sale (these things new cost about £5k erected) I sent a photo to the son and explained my thinking and he was interested. At this point father and son took over and bought the shelters. Now I'm not sure if they are going to implement the idea but I estimate placed side by side and south facing they will intercept 18kW(t) in sunshine. This is enough theoretically to evaporate nearly 30kg of water an hour if the air circulation is good enough.
 
With the shelters side by side and south facing and a roofed area behind and the back being a curtain side from a lorry he should be able to stock about 20m^3 of split logs in stillages.
 
I think wit a few low powered circulation fans and  a differential thermostatic switch only running them when  inside temperature is 10C above outside and a humidistat controlling a vent fan he should get good drying. If I am kept in the loop I will update progress.

Sounds good that! Well thought through, you can get massive Ones 45ft by 65ft for about 4 grand or less. Wish my staff were as motivated and intuitive as you !

[richardwale]

Could a similar situation be created using poly tunnels?

 

[Rough Hewn]

I worked for a guy years ago who used big commercial poly tunnels for drying. Worked ok.
I'm guessing height would be an issue for loading etc in a smaller one.

[AHPP]

Interesting post. Can you talk us through your calculations please.

[Con]

That's brilliant.

I'd like to have a go at something similar myself. Is it critical to have the fans on a thermostat? I was thinking of putting the fans on in the day and turning them off at night? Is it easy to set them on a stat? Thanks

[scbk]

Surely the answer would be a fan running directly off a solar panel - so therefore only runs when it's sunny!!

[Will Heal]

I’ve just put this polytunnel up. Yet to fill it with logs. I’m hoping that cutting the bottom 2 feet of plastic sheet on both sides and leaving the ends open will give me a good balance between being heated by the sun and airlflow.

[openspaceman]

On 4/20/2018 at 22:09, Martin du Preez said:

 you can get massive Ones 45ft by 65ft for about 4 grand or less.

I guess you mean polytunnels? I have never had one for logs but my brother in law had an expensive disaster when one suffered in a gale and lost many bedding plants.

 

We had an expert on polytunnels and their various plastic sheeting on the forum but someone got offensive so he left

 

 

 

This is covered in some sort of clear polycarbonate and budget will be only 10% of that but if I had access to an existing polytunnel I'd try that rather than this DIY approach.

[openspaceman]

On 4/21/2018 at 08:06, Rough Hewn said:

I worked for a guy years ago who used big commercial poly tunnels for drying. Worked ok.
I'm guessing height would be an issue for loading etc in a smaller one.

Yes and I was aiming to be able to load crates from the back and have about 20m3 capacity as he doesn't sell a great deal yet. I was thinking it would only need about 3 weeks in the summer but the last load could be stored until sold.