Second Solar Kiln Build. Looking to improve

[tagolong]

 I'm getting ready to start building a second kiln.  I will be making some changes to my first build.  The first build was pretty much exactly sized and designed off the VT Solar design.  Mostly I'd like to improve on my ventilation controls.  I'm wondering if anyone has tried the design in the photo below.  

[doc henderson]

it looks like it would be hard to build heat if all the air passes once and is exhausted.  most VT kilns will circulate, and vent only a small portion.  the humidity is higher so you do not get surface checks.  what issues are you having with your first kiln?  I think if it was for firewood it would be ok.  my concern is drying too fast for some or many types of wood.  you are almost power air drying.  interesting.  @GeneWengert-WoodDoc 

[pineywoods]

Might work ok in a dry climate, here in the deep south not so much. (update your profile,so we can see where you are) Need to re-circulate the air. The black sheet metal under the roof makes a big difference in the heat. I've seen 180 F in mine. I use a cheap room de-humidifier to pulll out the moisture, instead of venting. Planman1954 built a nice version of mine and did a nice job of documenting the build.

[GeneWengert-WoodDoc]

This design is called a single pass dryer.  It is used for very fast drying species like pine and will not achieve low final MCs, which is ok for pine construction lumber.  As mentioned by others, without recirculating the air in the kiln, you will not get the heat required and therefore not the lower humidities, which are essential in the middle of the cycle and toward the end.  The vent air volume is rather small compared to the recirculated air volume.  In fact, the last few days in a kiln, the venting is close to zero.  This design is also likely to have too low of a humidity the first few days of drying green oak, leading to checking.

[tagolong]

I updated my location.  Gene should be pretty familiar with the climate.  The most important thing we need to improve is the fans.  We are currently using three box fans that are plugged in.  It requires constant attention so first off I'd like to go solar.  I'm definitely looking for some do's and don'ts with the fans, brands or types that people have liked.  
Second we put the vent adjustment on the inside of the kiln.  I'd love to see other peoples means of sealing their vents from rain while being able to adjust them from the outside.  Thanks

[GeneWengert-WoodDoc]

The box fans do indeed need frequent replacements they use inexpensive bushings instead of bearings.  They could be put on a timer, which is what I used at VT.  Basically turn them On about 2 hours after sunrise and turn off about two hours after sunset.  This is somewhat inefficient during a rainy time, but so what?

The vents can be a door with a hinge on the outside, top.  My preferred design is to have a sliding door cut a little larger than the opening and mounted on the outside that uses a small molding on the top, bottom and one side that holds the door and allows it to slide open.  Also I suggest a screen on the inside to prevent birds, etc. from entering.  OK?