enhanced solar drying

[Martin du Preez]

16 minutes ago, openspaceman said:

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.

yea thats the one, you get the agricultural ones for sheep and pigs but i assume they are built with shade in mind, maybe a frame and some thick heavy sheeting 

 

[openspaceman]

On 4/21/2018 at 10:04, AHPP said:

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

The figures I suggested are theoretical  so probably no achievable in practice but do consider that they will be in addition to normal summer drying as the outside air will still be contributing if the ratio of recirculation to venting air movement is right. It is important to get the fans right as they cost electricity to run and it may be more economic to take longer and minimise fan use.

 

Anyway I calculated the chord of the curved surfaces  and multiplied that (average) by the total length to give 23m^2 facing the sun at about 50 degrees, so near enough optimal and perpendicular to the sun's rays at midday in summer. As we intercept 1.1kW(t) per m^2  at best and the average during daylight is only 35% of this I guess at a figure of 18kW for a few hours in direct sunshine.

 

In practice I would leave a temperature and humidity logger in the device to see what it achieves and would hope to be able to weigh crates before and after to give an idea of water loss and decide how to optimise the running conditions.

[openspaceman]

11 minutes ago, Martin du Preez said:

yea thats the one, you get the agricultural ones for sheep and pigs but i assume they are built with shade in mind, maybe a frame and some thick heavy sheeting 

 

Ian suggested there were heavier grades of clearish plastic  available if longevity was more of a consideration than light transmission. It does seem a cheapish way of storing large volumes of logs. I had wanted one at my last job, with the intention of sitting it on pedestals to allow a loader to operate inside but it never happened.

[openspaceman]

23 hours ago, Con said:

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

Not critical but so cheap that it must be worth doing, there's not much point running the fans if it's raining outside

13 hours ago, scbk said:

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

Grid electricity tends to be cheaper and the heap of wood will still have heat able to evaporate water when a cloud passes over. To my mind the problem is more of optimising the air passing over a log because from my experiments of logs in free air the actual drying time can be fast if the air passing the log is able to carry the moisture away.

 

[openspaceman]

11 hours ago, Will Heal said:

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.

Will that all looks good and ideal as a log store but I was looking to be able to shift crates in and out so that more drying cycles could be accommodated in the few months the sun can do a bit of work. Hence the idea of an 8m south facing "window" with the body of a curtain side behind it to load through.

[Will Heal]

Will that all looks good and ideal as a log store but I was looking to be able to shift crates in and out so that more drying cycles could be accommodated in the few months the sun can do a bit of work. Hence the idea of an 8m south facing "window" with the body of a curtain side behind it to load through.

Ah, mine have all got to be thrown in and out by hand sadly.

[scbk]

5 hours ago, openspaceman said:

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.

If you want a more storm proof poly tunnel look up "polycrub"

[Stere]

You could shed out of timber and clad in vistulux

 

 

http://www.arielplastics.com/~/media/Ariel-Plastics/Files/Installation-Guides/Vistalux-Installation-Guide.pdf

 

Dunno how overall price would compare to a polytunnel though

 

[openspaceman]

4 hours ago, Stere said:

You could shed out of timber and clad in vistulux

 

 

http://www.arielplastics.com/~/media/Ariel-Plastics/Files/Installation-Guides/Vistalux-Installation-Guide.pdf

 

Dunno how overall price would compare to a polytunnel though

 

I'm trying to reply on my cellphone so bear with me: this is the material I used for my experiment and what I proposed to use prior to finding the bike shelters . It costs about £6/m^2 and I have a lean to roofed with it that lasted 35 years before it became too opaque and started splitting. The replacement is 3 years old and shows no deterioration yet.

Edited April 22, 2018 by openspaceman
posted prematurely

[AHPP]

The figures I suggested are theoretical  so probably no achievable in practice but do consider that they will be in addition to normal summer drying as the outside air will still be contributing if the ratio of recirculation to venting air movement is right. It is important to get the fans right as they cost electricity to run and it may be more economic to take longer and minimise fan use.
 
Anyway I calculated the chord of the curved surfaces  and multiplied that (average) by the total length to give 23m^2 facing the sun at about 50 degrees, so near enough optimal and perpendicular to the sun's rays at midday in summer. As we intercept 1.1kW(t) per m^2  at best and the average during daylight is only 35% of this I guess at a figure of 18kW for a few hours in direct sunshine.
 
In practice I would leave a temperature and humidity logger in the device to see what it achieves and would hope to be able to weigh crates before and after to give an idea of water loss and decide how to optimise the running conditions.

Very helpful indeed. Thanks very much.