Solar Kiln for Use in our Cold Canadian Winters

[Coon]

I was just doing some reading on Solar Kilns but, to no avail have I found any information on using them in our cold winter climates.  As I would like to build a kiln to use year round I was wondering if anyone has the answers to some of my questions concerning winter use.

1.  I have read that when building a solar kiln the angle  of the solar collector is equall to latitude + 10degrees.  Does this angle also collect the same amount in winter as in the summer?

2.  Is there any way that a person could use another heat source besides solar during the winter months?  If so, could one simply add a wood heating source onto the kiln?

  Thanks in advance, Brad.

[jimF]

The wood does not have a brain to know where the heat is coming from!

[Coon]

Another thing I am trying to get at is --  When drying in the winter will the lumber dry out at the same rate as in the summer?  If using wood heat to assist the drying do I need to have any kind of different baffle and fan system to blow the air through the lumber different than say just the regular system in a solar kiln?

[slowzuki]

The colder it is the slower water evaporates but if you can warm the air in your kiln you won't need as much circulation as you live in a dry climate plus the air is naturally drier during the winter.

In fact you may have a problem of being too dry if it gets really warm.  I have no experience with solar kilns but this is the HVAC side of me talking!

[Coon]

Slowzuki can you fill me in more about the HVAC??

[Don_Lewis]

You can do a conventional heated kiln or you can do a solar kiln. But it really isn't a good idea to do a combination. I expect there will be a bunch of posts disagreeing with me. Solar kilns are for hobbists and not for people who are in business.

[fencerowphil (Phil L.)]

A well-built solar kiln has a primary limitation, when compared to commercial
conventional heated kilns:   It is slow and therefore financially impractical on a commercial scale.
A secondary limitation would be the lack of monitoring and control.

Technically, a well-built solar kiln has a primary limitation, if it is used
in tandem with conventional heat:   Heat loss via the glazing.

There is a remedy, however, for us ingenious (though lowly) "hobbyists."  In a cold area
subject to brutally low temps and low relative humidities, monitoring would be essential.
Secondly,  a means to insulate the glazing would be needed.   A sliding or folding insulation
panel assembly would handle that part of the challenge.

Phil L.

[Coon]

I am asking all of the questions because I want to build some sort of drying system that will speed up my drying time for a variety of different woods. I have little to no money to invest in a kiln but I do have lumber, windows, a couple of rolls of poly sheeting, used furnace fans, an old wood heater, etc...

The woods that I cut and dry and resell consist of white spruce, white birch and, white poplar (aspen) mainly.  I also do some Manitoba Maple, tammarack, red birch, jack pine, willow.  I have also done little amounts of apple, plum, cedar, black poplar, and a few small pieces of aldar and hazelnut.

[slowzuki]

HVAC is just short for heating, ventilation and air-conditioning.  I'm a mechanical engineer in training so I run into hvac stuff ever so often.

The basic principles for HVAC and drying something are this, the warmer the air the more water it can hold.  How fast wood dries is based on its temperature and how much moisture is in the air around it.

Relative humidity is an expression of how much water the air is holding at a given temp.  For example, 100% humidy means the air is hold all the water it can hold at that temp.  Any more humidity at that temp will fall out as dew.

What all this means in a kiln is you have to get the relative humity to a certain point in order for water to evaporate out of the wood into the air in the kiln.

Leaving wood in the direct sun in a high solar gain kiln with a big blower will dry the outside and ends of the wood faster than water can move inside the wood.  I'd also expect the colder the wood the slower water migrates out of it as well but don't know this for sure.

So you can heat your kiln with sun or wood heat what ever but you don't want to dry out the air too fast.  Putting a wood burning stove or big blower in may result in too much dry air from outside being drawn in.

If you want to experiment you may get a system down that works well, if you need to make it work well asap you should get a set of commercial controls for a heater etc.

If I were to build a solar kiln for year round use, I would put a divider between the collector and storage and have a fan on a temp switch in the storage side.  I would also put a fan between the storage and the outdoors on a relative humidty control like what a dehumidifier uses.  I would insulate the storage area very well.

If using wood for a heat source I would put it in with the wood with a variable draw between outdoor cold air feed or from the storage area with a grill on the far side.  I would have a humidity meter and adjust between the direct pipe to the stove or pulling though the wood.   If it is too dry, pull from direct outside to stove, too wet pull through the storage area.

[fencerowphil (Phil L.)]

Hello again, Brad!

When I used the phrase, "control and monitoring" above one would
immediately think I meant pricey dials, gadgets and digital readouts.
Not necessarily.
On the other hand, monitoring can be a matter of careful old-fashioned
checking with samples and your microwave oven, etc.  Of course a knowledge
of the drying personalities of all your primary woods would be helpful, too.

For example,  I noticed last week how quickly Sweetgum gets splotches of
mold, when I saw a split off of a poorly felled tree.  It had lain pretty as can
be in bright sun.   It rained two days and the third day that newly wetted
gum scrap was m-o-l-D-y.   The spores had roosted and were all ready to go!

On the other hand,  the heartwood of White Oak, Post Oak, or Mulberry or
Black Locust and many other woods would not do that.

To make it short...
     You can still monitor closely and do it cheap!

Phil L.

[Quebecnewf]

Brad

I built a solar kiln and it works but slow in the winter. I do not need large amountsof wood. My kiln is 6 by 12 I dry birch and some larch and a bit of special spruce and fir. I use a solar powered fan as my kiln is located of grid on an island. I live in Quebec Northern part. I think there are pictures in my gallery of my kiln.

I am more than pleased with mine. I have sold about 500 ft of my KD birch to a local very picky cabinet maker and he was very impressed with it.

Paul