I’ve invested a great deal of time, effort and energy to ensure that my garage is comfortable and efficient for working, this is no secret, but that ancient forced-air wood furnace in there is just not congruent with my VISION OF AWESOME for the finished Garage. Among the final stages of my renovation schedule, after the floors, walls, between-stud-insulation, windows and ceilings are all dealt with, I intend to add siding to my building, and along with that house-wrap (like tyvek) and some 2″ rigid board insulation. The siding will go on over that whole mess. That said, a candle and a few warm bodies should heat that place in the wintertime, and it’ll be tight as a drum. I’ll need a dehumidifier running and some air filtration/purification to keep the space dry and fresh, but that’s a minor thing. What concerns me most is that big-dirty woodstove. Fortunately, I have a solution: Solar.
According this BTU calculator, based upon the dimensions of my shop, the coldest outdoor temperature (-51C / -65F last January) and the desired room temperature, I require 1,869 BTU/h. No problem. My issue is that this contraption is capable of production a rated 35,000 BTU. After I put R40/R60 in the ceiling, R20 in the walls, seal the floor and then wrap the exterior in 2″ rigid foam (~R10) and then several extra dimensions of air-tightness with the house-wrap, insulation should not be a problem. Given that the heat-loss, especially since I’m removing all the windows and insulating-in those spaces, will be nearly zero, it won’t take 35,000 BTU to heat the space. Ima get rid of the furnace. I may get a little dinky woodstove, a barrel with a chimney or a potbelly, I may not. I could save the cutoffs for sawing into pieces big enough for summer fires around the patio. The fact remains, I don’t need anything as big as bertha, in there. I’ll need to get rid of the chimney, cap that sucker off, and clear away all that mess. It’ll free up a ton of space and allow me to use that whole corner, close to 100 square feet!
Now, if I’m not using my woodstove/furnace, and as much as I hate oil, what’s my alternative? Geothermal has been spec’d out and is grotesquely expensive up here; prohibitively so. Then I had a dangerous thought: My shed’s roof peak runs east-west. The large sloping side faces due-south. I could use solar! “Solar?” You say? “At +50 degrees latitude? MADNESS” But I’m not looking for photovoltaics, I’m looking to harvest the thermal properties of solar energy; radio-thermal energy.
It’s been used in Africa to cook food, been used in Spain, Australia and the American South West in the Solar Thermal Towers. I don’t want it for energy, but the properties of heat cannot be discounted, even this far north (ask anyone driving a black car with tinted windows). My trick is a HUGE collection area, and a relatively small heated area with minimal thermal loads/losses.
Consider, if you will, the existing roof of this building. For argument sake, we’ll call it “My garage”. Let us also pretend that I am heavily invested in not only making it better, but making it ÜBER. Now, the side room near the stack of tires (16″ spares for the RV that we own) has walls that end above the window and have full triangular trusses. That space above the lower beams is not being used. That must change! Part of my hair-brained scheme is to remove the roof from that, the lesser building, and extend the existing roof down over the side building. In essence, creating something more like this. The first image is simply a facsimile of the garage as-is (or as well as I could do in 20 minutes) and the second image is the modification with the roof continuation. It gives me fewer seems to risk damage or leaks, extends my roof-lines up higher and gives me more solar-facing roof angles. Upon this roof, and the vertical south-facing wall, I intend to mount the apparatus that will heat my garage. The roof renovation is necessary anyway, since the existing roof is in hard shape and I need to give it some attention next year. There are already three spots that leak.
I drew some inspiration from a Newfoundland company, CanSolair, and their solar thermal furnaces that use pop cans and lexan greenhouse-like shields. I realized that they aren’t THAT complicated, and I was sure that I could design my own versions. Albeit without the experience and practical experience of J. P. Meaney, the business creator, but as they saying goes, “How do I get to Carnegie hall?” and the answer, “Practice, baby, practice.” So I’ve done my typical mountain of research and came to a stunning conclusion: The product isn’t complicated at all! I also discovered, to my delight, that the methodology is not limited to solar thermal air heating, but also solar thermal water heating. I should have guessed this, since I’d seen those black bags of water you hang in the sun and use for a shower while camping, and this is fundamentally the same principle.
My solar air furnace will be filled with identically sized 8oz (typical soda-sized) cans, nearly 300 of them. Each unit is built inside an 8′ x 4′ frame, portrait orientation, and hung on a french cleat, surprise surprise. There will be a vent in the top and bottom that allows a circuit of air to flow. Passive heating (involving no electricity) will cause the air to circulate via convection currents. In my version, the cans feed air into a special manifold that will only allow the air to pass through one tower at a time. Think of a single volume of air traveling through every single can before it leaves the system, snaking up and then down each sequential tower until it’s hot. This system runs parallel towers that feed in parallel, not series. I need to capitalize on as much of the heat as possible, and in a give few hours the heat from the sun will penetrate the front greenhouse glazing, onto the black painted can towers. The air in the garage will get sucked in through the intake and through each can in succession until it leaves the final can in the final tower and into the outlet that vents back into the garage. As the air heats up, it will cool down the cans, and reduce the efficiency of the system. My goal, with the series setup, is that there is a greater efficiency since the ENTIRE system area is used for heating, and the system should work a little more smoothly. The cans, of course, need to be super-clean and sterile, and HEPA filters used to keep the dust contamination out of the system. This is another reason for the dehumidifier. Dryer air has a decreased chance of getting trapped in the system and mildew forming. I will build three or four of these systems to install on the south facing wall of the extension room, and use that to pump incredible heat into the lumber storage solution described here.
Insofar as the secondary system, I wanted to have a series of radiators in the garage that can be heated using a circuit of water, heated by roof-mounted collectors. Functionally identical to the previous air-heated system, but the water system is a closed-loop where the air system is an open-loop. What I mean is the air pumps through a vent into the entire garage, and outtake sucks the air closes to the intake vent back into the system. The entire garage (plus whatever air leakage takes place) is the reservoir for the open-loop system. For a closed-loop, like the water heater, the water is pumped through the heater and into a radiator where it is cooled, heating the room, a sealed unit, and the water is then pumped back into the heater where it is heated, cooling the collector that the sun, then, warms again. I will be using an anti-freeze/water mixture for the water system, and it will be controlled by a digital thermostat attached to it’s power. If the temperature drops below 20C (68F) the heater pump will engage, day or night. Remember that I am not HEATING water with my electricity, just moving it. Sort of like a heat-pump, without the compressor. The solar can furnace will likely run forever, since a sealed environment full of rapidly heating air is liable to explode. Besides, a shop that’s too-warm can be more easily vented than a too-cold shop can be heated. The energy is free anyway, once the system is installed, so energy consumption a rather moot point.
The larger southern-facing roof segment is 12′ by 34′ and the “new” roof segment over the lumber storage extension room is 8.5′ by 18′. Even at 51 degrees latitude and a 50 degree perpendicular angle of the winter sun at my location, I feel that 900 square feet of area will do fine for my needs. I will give the shingles on the roof an extra heavy coat of tar, then lay my plumbing on the roof. Using 1/2″ flexible tubing, black, I will need approximately 2 miles (10,800 feet, 3218.69 meters) of tubing, locally available Pex in-floor heating pipe for example, assuming a 1/2″ spacing between the tubes. This would cost me nearly $4,000.00 CAD for the piping alone. Good god. THEN I’d need to cover those tubes with a glass, plexiglass, lexan, pallet wrap, something. Alternatively, I could arrange the tubing in such a way to effectively drain-away the water/ice/snow, but a sheath of greenhouse glazing would REALLY increase the efficiency of the system. I fear for the heating potential, since my roof-slope is 20d and not 50d, but I’m sure that shear area can accommodate. I can’t effectively make stilts to angle the system up, like the image seen to the right, because the wind here is enough to suck siding and shingles off well-built homes. These little stands wouldn’t “stand” a chance. I need to build for my climate as well as for my solar-day energy potential. So, no artificial stands.
It is my hope to install this system within the next 4-5 years, to completely negate my dependency on a wood-burning furnace. I also want to build a greenhouse later on, and that can be used as supplemental heat collection, but the humidity generated by that room may not be ideal for a woodworking shop. Will have to consider it wisely. The combination of air and water solar energy collection will go a long way towards making my shop self-sufficient and keeping me working in my shop and not out collecting wood, mending chimneys or refurbishing aging furnace equipment. When you think about it, even spending $4,000.00 on this heating solution is cheaper than some home-heating renovations.
I’d, ideally, have some 120vAC electric heaters to pick up the slack in the winter, what slack there would be, and MAYBE a little potbelly for hella-cold and overcast days. I can burn cutoffs and old scraps, dispose of sawdust, that sort of thing. I’ve also looked into artificial log packing equipment that squeeze sawdust into little jiffylogs. There are a bunch of sawmills locally that I could probably get free sawdust by the truckload and then pack them into little logs at my leisure. A GREAT stopgap until I can AFFORD this passive, environmentally solution. This would also be a great source of supplemental income for my shop, if I could rig up some sort of efficient system and spend a weekend making a few hundred of these little fireplace logs. An interesting thought presented to me by Dr. Tim Grede, my former PhD adviser. Every little bit helps, and I see no reason why anything rational should be beyond consideration! (That may be obvious by now)