Anybody ever tried making the collector seperate from the kiln boxon a solar set

[LeeB]

Has anyone ever tried or given thought to building the collector  separate from the box, thus allowing a square box instead of one with a pitched roof?

[Dan_Shade]

how would you "move the heat"?

[LeeB]

With the fans, same as with a regular one. Just duct the air in and back to the collector. 

[GeneWengert-WoodDoc]

The US Forest Products Lab designed such a kiln in 1976.  Plans are on line.

[LeeB]

Gene, was it a successful design?

[GeneWengert-WoodDoc]

It did dry wood, but it was intended more for tropical countries.  It would be quite expensive here in the US compared to the designs where the roof is the collector.

[LeeB]

How so? Extra materials required?

[GeneWengert-WoodDoc]

You need to build a totally insulated box (a kiln that would be similar to most other home-built, non-solar kilns) and a totally separate collector.  Then you need a transportation system for the hot air (or hot water) from the collector to the kiln and back.  This transport system needs to turn off when there is no or little heat and then on when heat is available, so you also need a control system.  OK?

[5quarter]

Lee...I think your idea would be ideal for someone who wanted to run a solar kiln inside his shop. In fact a guy might be able to heat his shop in the winter when he wasn't drying wood.  ;)

[pineywoods]

We looked at doing that when LeroyC and I built our kilns. Might be the way to go if you want to put the lumber side inside an existing building. In fact, thats where we got the idea to put a black sheet metal collector on the bottom of the rafters on our otherwise conventional design. Didn't have an existing building, so all the extra material and construction nixed the idea.

[jimF]

If you have the opportunity to look up the reference, you will notice that the collector that is separate from the kiln, as Gene mentioned, is designed for the tropics. It was flat on the ground to be perpendicular to the sun's rays.  And there was duct work in and out of the kiln.

[LoneDuck]

One Idea I have been throughing around is to build one into a hill. Have a a-frame with collectors on both sides and then push the heat down with a fan. Have one side open to load and unload. I know with this style of earth home in a hill works great for heating and to maintain temputure. What would you say to something like that.

[GeneWengert-WoodDoc]

I think that you would still need a strong frame with insulation (hillsides are not warm...ever seen a warm basement?) and now you would need pressure treated wood and superior moisture control.  Plus you would need special venting ducts.  I am not excited about this idea for a dry kiln.

[GeneWengert-WoodDoc]

This may be well known info, but in case it is not, here it is.

To evaporate water from lumber at 100% efficiency requires a little more than 1000 BTUs per pound or pint of water that is evaporated.

Each species varies a bit, but for dense woods like oak, 32 pounds or pints evaporated from 1000 BF will change the moisture content by 1% MC.

Most drying processes use about 2000 BTUs to evaporate 1% MC from 1000 BF.  The number is higher because there are building heat losses, venting losses (but not very big in a DH kiln).  There are also boiler, or other heating system, losses.

Sunlight averages about 1000 BTU per square foot per day...higher on a sunny, summer day and lower on a cloudy day and/or in the wintertime.

For 100% solar heated kilns! the collector is around 1square foot for every 10 BF of lumber in the kiln.  More heat, which means a larger collector could be used with pine, poplar and other easy drying woods, although that would increase the cost.

If a 1000 BF solar kiln dries three loads a year and lasts for 10 years without major maintenance, that is 30 loads that must carry the amortization cost...a $1500 cost amortized  over ten years and 30 loads is going to be around $75 per MBF.  Then add labor costs, electrical fan costs, insurance, taxes, loading, stacking, and unstacking and maintenance; we see that solar drying costs are not cheap.  Note that a more expensive kiln would add a lot to the costs...that is why more expensive collectors and buildings are probably not economical.

A step upwards could be a small DH kiln.  Overall drying costs will be similar to solar...a bit more...but the DH runs 365 days, which can be an advantage.

[LoneDuck]

I think that you would still need a strong frame with insulation (hillsides are not warm...ever seen a warm basement?) and now you would need pressure treated wood and superior moisture control.  Plus you would need special venting ducts.  I am not excited about this idea for a dry kiln.

As a matter fact I have seen a warm basement. I grew up in a house just like what I'm talking about. The house used a wood foundation and built into the hillside. Very easy to heat and we always had to put moisture into the air because it was too dry in the house. Plus it is about 4hr north of you near Antigo Wi. See I'm not that hooked up with the coast of it because for me being able to cut and dry my own wood for my projects is what I'm after. I do log and rustic furniture and are unable to get the quality of wood that I like to use. I should not say can't but I've see some of the slabs that I cut priced at half of what it would cost to build the kiln. I would like to keep coast down though and that is why I would like to build my own. I have learned in the past that its better to ask before then after. That is why I asked for suggestions and thoughts as to how and if this makes sense. So thank you for your suggestions but please remember there is more to this then money. Some of us like the feeling of doing some things ourselves.

[LeeB]

Lone Duck has made a good point. Not all of us consider the time we put into a project or hobby in terms of dollars and cents. I would actually imagine that most who build a solar kiln, or some mutation there of, never consider cost per load or amortization. For me, $75 a years is pretty cheap entertainment.

[GeneWengert-WoodDoc]

Indeed, cost, especially for a hobby, is not everything.  But when considering various design options for a solar kiln, which was the initial concern of this thread, the cost of the various options might be somewhat of a concern. 

Overall, the cheapest way to dry lumber in most cases will be to shed dry and then go into the kiln around 20% MC.

In fact, some people drive a really fancy, expensive car that will get from my home to California just as fast, although for more money, than the Ford Explorer that I drive.  So money is not always the overriding factor.  But driving to CA from WI is probably more expensive than flying, yet I will be driving.

[LeeB]

When I posed the original query, cost did not particularly enter my mind. Like a good many men, I'm a material recycler(wife says I have a lot of junk, don't know what's wrong with her) and have scrounged up everything I need to do this. The only thing I would have to pay for would be electric for the fans. I have to pay a minimum each month for my shop due to the power company labeling it as a commercial building and never come close to using that much. May as well get something out of it for my money,

[LoneDuck]

LeeB you and I sound a lot alike. We should start a club. :D We like to do something just to see if it can be done. There are just something's that are not available or too expensive. But with a little red neck ingenuity we get it done. Maybe not the prettiest or most efficient but they serve our needs. We barter what is needed and normally do not have much money in it. We are here just to ask of others the questions of how it works and get ideas that we can use. So if anyone would like to give any info that we may be able to use it is greatly appreciated. Thanks

[LeeB]

OK Gene, cost increases aside, is a separate collector such a far fetched idea?

[LoneDuck]

Don't know much about this but it may help in what you are looking at.

 

[GeneWengert-WoodDoc]

Heat is heat and if the "roof collector" is the same size as a separated collector, then the heat is the same.  So, there is more construction for a separate collector, as I mentioned earlier, both for the kiln and the collector.  I like the KISS principle, but then I also like FORD.

[GeneWengert-WoodDoc]

With an external collector, you can make it a hot air device and blow the hot air into to kiln.  The problem is that the air return can be a problem as the moisture can condense and / or the dirty air can cloud the clear collector. 

You can also use a hot water collector with antifreeze, water pump, and heat exchanger in the kiln.  There was a hot water kiln in Alabama or Mississippi a few decades ago and they noted that the outside of the collector was getting dirty almost every day, requiring a lot of cleaning.  Also, they had a water storage tank to store hot water for nighttime use.  However, solar was only able to provide half the energy required and not all. 

I guess calculations are one thing, and actual can be something else when the engineers are not familiar with solar collectors and wood drying.  It certainly is nice when making profit is not the main goal.

Incidentally, I worked on my first solar heat lumber dry kiln in 1961 with Ed Peck at the US Forest Products. Lab in. Madison

[LeeB]

Thank you Gene. The collector clouding due to moisture is something I had not considered. This is the kind of information I'm looking for. Would you not have the same issue with an integral collector? Is that not solved by venting?

[GeneWengert-WoodDoc]

If the roof is part of the collector, you will get condensation at night, (and this high RH removes casehardening stress in either case), but it is easier to evaporate.