Question
I have been running a 1,600 bd ft solar kiln for about 8 years now. Originally I built it to cure the white cedar for my boat project and have been renting time to other woodworkers ever since. One of my customers is a tree service and has a Wood-Mizer. He wants me to build him a kiln. I stopped by today and this guy has a pile of logs maybe 90' long and 20' high. 28" chestnuts, 24" black walnuts, 20" white oaks, rock maple and who knows what. We are talking a 4 or 5,000 bd ft kiln just to make a dent. The problem is he has no way to get power to his yard and solar powered fans for a kiln that big are way out of his budget, so I am looking for a design that uses natural convection.
Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
If you build a kiln on top of the solar collector, then as the air is heated it will rise and enter the kiln. Then, as it dries the wood, it will cool and flow back, possibly cooling the incoming air before the hot air can do any work. I have had people try to figure out a design, but there is none, especially for such a large kiln. The air flow provides warm, dry air around the lumber, carries the moisture away and also assures a good degree of uniformity of conditions.
The only possible design in your case is one that uses an exterior windmill that is mechanically linked to the interior fans. This design was used by Edward Peck around 1960 in Sauk City, WI. I have the article, but it is so simple, you do not need the article. The main factor to watch is the 1 sq ft of flat roof for 10 bf of lumber. Of course, a windmill connected to a generator would also work, but would be more expensive.
I am going to try to talk him into either bringing in power or springing for solar. If he doesn't do something he is going to lose a lot of valuable lumber.
Harbor Freight sells a solar panel kit (about $170) that delivers 45 watts that could power multiple muffin fans like in computers that could be turned on in stages with the same hot water heater thermostats.
Vents with a flap used on propane heaters from trailers could be used for exhaust. Very little pressure to open them because of balance. Greenhouse vents that open based on temperature could also be used. All designed to withstand kiln temperatures.
If you are in Ontario I would suggest applying for a micro fit setup and sell the solar energy back to the government at $0.802 per kilowatt. Then take the profits and buy another system to use on your kiln. If you qualify for the micro fit program, you will be guaranteed a loan from any financial institution as the contract is for 20 years and the payback is less than 8 years.
The small solar kiln might require 10 kW per day, so a solar panel should be 2kWh to assure enough electricity at medium to low sun angles, or about $4000. We also need to be concerned about cloudy days and frequent dirt on the collector and other efficiency losses over time. So maybe add another 50%. This is a lot of money for a kiln costing $700 or so.
