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KinAlberta
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# Posted: 14 Oct 2017 09:36am - Edited by: KinAlberta
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I’ve long thought about building a stand-alone solar furnace / box to heat air and then blow it into our cabin. It would only likely take some of the chill off and provide a higher start temperature when I go out to the cabin but anything would help.
Plus I have a fair bit of space to work with so I can think big (beyond the little 3x5 DIY examples that are common.) I could easily fit in something more like 12’wx8’h or larger, maybe even something looking more like a fence (say 30’w x6’ h) but I’d guess that the costs would quickly become excessive considering the infrequent usage of the cabin.
So has anyone played around with these?
Here’s a good article (below) and YouTube has lots of DIY heaters that all look pretty creative and all seem primed for some simple further improvements.
Build a Simple Solar Air Heater - Renewable Energy - MOTHER EARTH NEWS I’m a retired aircraft engineer, but you don’t need a similar background to tackle this project. In fact, a solar air heater built into new construction or added to an existing building can be an easy and inexpensive heating solution. Following the simple principles and plan outlined here, you can heat your workshop, barn or even your home with free heat from the sun. If it works here in Bozeman, Mont., it’s bound to work wherever you are. https://www.motherearthnews.com/renewable-energy/solar-air-heater-zmaz06djzraw
The best thing about wall mounted heaters is one, it could be designed to also increase or decrease wall temp and therefore alter both winter and summer temperatures in the building.
Also:
MY ATTIC RE-THINK - SOLAR ATTIC HEATER:
For another thread, or maybe this one, would be a discussion of my thought to turning a conventional ventilated attic into a sealed attic cavity as in a typical gable ended cabin to passively heat a cabin, garage, etc. Add lots of insulation and run piping in it like one goes with fluid heated flooring and circulate it down into the living space. . Adding metal roofing to a our cabin and garage got me to rethinking that attic, but unfortunately I added whirley birds to our cabin when the metal went on.
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Just
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# Posted: 14 Oct 2017 05:37pm
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In 1975 I took a solar energy course as we intendrd on building our dream home . I came up with the idea of adding a warm air collecting element to our plans for the attached garage .We simply covered the south facing wall and roof with fiberglass panels .I insulated all other walls with R 20 .glass. Then I installed a fan in the ceiling rafters and ducked that to the isolated crawl space under the new home . The fan has a thermostat that turns the fan on when the air temp reaches 80 .
Not much gain November December or January. February March and April are good. I have seen it get 90 in the garage on sunny days in Feb.
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Just
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# Posted: 14 Oct 2017 05:44pm
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ps.. 43 parallel Ontario
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rockies
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# Posted: 14 Oct 2017 06:29pm - Edited by: rockies
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Too often people who are looking to improve their solar potential rely on these old 1970's ideas to heat their homes. Today building scientists are realizing that it's not so much using systems like solar boxes or solar attics that work but insulating and sealing up the cracks so that all your heated air doesn't escape.
If you look to the Passive house movement you'll discover that an investment in air sealing and a layer of rigid insulation applied to the EXTERIOR of the wall sheathing (under the siding) is far more effective than trying to regulate a passive solar heating zone (it's always going to be either too hot or too cold).
Passive houses can be heated entirely from the heat produced by the human body or a small hair dryer. However, even substantial gains in energy efficiency can be achieved just from air sealing. I would do a smoke pencil test around your cabin to find all the holes where your heat is leaking out first.
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Steve_S
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# Posted: 14 Oct 2017 07:09pm
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Have a look here at BuildItSolar http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm They have several working examples, details, and more... might help you out some.
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Wilbour
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# Posted: 14 Oct 2017 08:58pm
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There was a detailed build of a Passive Solar home on Wolfe Island Ontario. Too bad the site is now down.
Although you could build 3 homes for the cost of this Passive Solar Idea, the builder was not interested in just saving heating/cooling costs, he wanted to prove a Canadian home could be heated by the sun alone.
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KinAlberta
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# Posted: 15 Oct 2017 05:16pm - Edited by: KinAlberta
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Yeah here in central Alberta we understand the value of sealing up gaps and stopping drafts. My city home is pretty well weatherstripped including foam doohickeys on all the exterior receptacles. It also has triple pane, argon etc windows, the highest R value garage door available 20 yrs ago, probably about R-80 in the attic, etc. The perimeter gap between the drywall and the floors have all been sealed, basement rim joist foamed, etc. But it’s still 70s construction and the cheap gains have been achieved.
Our cabin though has an uninsulated floor. It also has coal and wood stoves so the air gaps are useful. In this instance a solar box might be a cheap source of some extra heat.
As for new construction super insulation would be my first choice but if it were s canin, icvalso want a lot of glass. Creates a bit of a wash.
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creeky
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# Posted: 18 Oct 2017 04:30pm
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i think the best solar heating is probably 4 solar panels and an air source heat pump.
Justs system looks like a good one. Might be for shoulder seasons, but I know a farmer who did his/her garage doors in the 80s with a similar idea and she/he's still reaping extra free heat.
my favorite is the screen door mesh box ... you can find it here. simple build too. I've been meaning to build one for years.  I'll get to it. Right after ...
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Jr23
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# Posted: 23 Oct 2017 01:47pm
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Google vacuums tubes 4 ft tubes trap heat I first saw a YouTube a guy in Canada had a shell heater for farm that was wearing out and he discovered the tubes .there sold on amazon and eBay individual and as units might be what your looking for
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KinAlberta
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# Posted: 24 Oct 2017 12:26pm - Edited by: KinAlberta
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Found this (link below). Interesting. Thanks! I’d sure prefer this over the incredible hassle of cutting, gluing and painting a bunch of coke cans. (Plus I can turn pop cans into cash those in at the bottle depot.)
I’m thinking that I’d need something that couldn’t reverse in the night and draw heat out of a building as a fully conducive loop might do so.
So, I’m thinking that just basically a fairly large surface area that could heat up and transfer the heat into the cabin and hopefully bring up the cabin temperature by 5 or 10 or more degrees (so arrive to a -10 and not a -20 cabin) thus reducing any output from stoves or electric heaters. Every degree of ‘free’ heat is a degree of free heat and less money and ongoing effort out.
A heavily back insulated glass faced box with black tubes might fairly cheaply capture and build up and even retain increasing but initially uncirculated heat that could all be ducted through a short insulated pipe into the cabin. Maybe a solar fan would run out of battery power about the time the box cooled thus keeping more heat in the cabin.
Now, another way might be through a seal-able attic* with modified insulation might be a way to capture the heat of the sun and duct it down into the cabin. Could maybe caputure heat on south face of our cabin roof, insulate the north face, and circulate cabin air up through the attic and back down into the cabin. (Dealing with any trapped moisture issues might be tough.)
* so we just cleared the insulation from the long blocked soffit vents and added two whirlybird vents on the new metal roof. Thus we have a cooler cabin in the summer but maybe we’ve ignored the free spring, fall and winter heating possibilities right over our noses.
Say, add a whole lot of ceiling insulation that can become a reservoir for built up heat captured as the attic heats up from the sun and convects and radiates downwards into this ceiling insulation plus this ceiling insulation also captures heat convecting upwards into it from the living space below. Then run piping through it to circulate the heat down into the cabin.
Everyones thoughts????
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Steve_S
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# Posted: 24 Oct 2017 01:35pm - Edited by: Steve_S
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Why not just run 2, 150' long 6" O-Pipes (unperforated) 5' underground (southern side). 1 side of each as Air Entry & 1 side of each as air exit. Powered by 2, 100CFM 12v, 0.5a box fans (like the computer fans).
In summer you'll gain cooling from the ground which averages 52F which will bring temps down and in winter which will pull in the ground heat to 52F which is a net gain. The key is to feed "from" house & back while not drawing air from exterior or picking up humidity. The Humidity is the trick through as it will take it from your home and condense in pipe if your not cautious about your input source point... drier air in the better.
In fact, you could use a simple 12V Gel Battery (RV type) and a single 12v / 100W Coleman type solar panel to keep a charge on the battery which would effectively run the two fans on both ends...
NOTE in Summer you gain more cooling is the ground is shaded &/or grassed and in winter leaf / grass cover is a bit of an insulating blanket.
This "Incidentally" happened to me without any intention of doing so... My Pump/Power house has 2, 4" O-Pipes running 75' from it to cabin (water pipe & electric conduits) and I realized this summer who my cabin was partly so cool, the cooled air was being pulled into the cabin through the pipes and it made a significant difference ! In fall & spring I found the cabin to warm up faster & to be warmer than outside / ambient air temps till ONE DAY I was working at ground level where the 2 O-Pipes are and noted the airflowing in.... quick digital thermometer check and low & behold ! I put Caps on the O-Pipe in the Pump House and within two days I watched the temps differentiate between the buildings and the cabin take on it's own (more natural I assume) heat / cool profile.
Fact that Romans & even Babylonians did this over 2200 years ago using clay pipes with good effect should have been a clue that it could work today with plastic O-Pipes as well.
On the gluing of pop cans together ? Seriously, what a tedious and uneconomical time killer.... unless you have a bunch of cans, are bored to death and NEED a project to stay out of criminal activities. Why not just use 2" or even 3" expandable aluminium pipe (like that dryer & range hood piping) and use a flat black paint to cover the aluminium pipe & the back tin... a variation on the BuildItSolar projects...
As for the roof.... That situation is more complex and others have made a variety of attempts with limited luck... I have read about them over the years... It's a trade off / Exchange of issues and with many potential caveats. Best thing with the roof is to design it to keep the heat in during winter and to deflect it away in summer with a good thermal break between the outside & inside to prevent heat/cold transfer in & out.
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KinAlberta
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# Posted: 25 Oct 2017 04:10am
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The pipe idea is neat. I’d have to go deeper here.
Our basements essentially do the same thing since they allow ground heat to rise into the building.
On capturing heat in the attic, I’m curious if just embedding a matrix of pipes in the attic’s ceiling insulation (like a heated floor system) wouldn’t be a useful means to capture heat that’s left the living space and about to leave the building, and then say cycle it into the basement and back. It might change the dew point if that can be an issue.
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Steve_S
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# Posted: 25 Oct 2017 05:43am
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These Ground Air Tube heat exchangers are commercially available as products but can easily enough be done ala DIY and is quite effective & efficient. I am now reconsidering my happenstance implementation and thinking about how I will harness that - I like Free Heating & Cooling it's a cost I can certainly handle. My HRV won't handle such a thing so I'll ponder on it a while and consider options... May also be an idea for the Greenhouse to provide heat for extending grow time & cooling in summer for less stress on the plants....
You might want to look at these articles.... 5-6 feet (18"+ below frost line) is perfectly suitable for our climate.
http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/my-earth-tube-story
Slightly newer article / review +
http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/do-earth-tubes-make-any-s ense
and from BuildItSolar too....
https://www.builditsolar.com/Projects/Cooling/EarthtubeNotes.htm
https://www.builditsolar.com/Projects/Cooling/passive_cooling.htm#Other
One of the Key Tricks is managing the air source humidity and one system uses an HRV / ERV type system to exchange the air and dehumidify it. Some are pulling air from outside and bringing "fresh air" in while others circulate building air out, through & back. Both could have positives & negatives so careful thinking & planning is required.
BTW: At HomeDepot, Lowes & TSC similar too, a 100' long 4" Big-O Agricultural Pipe is about $75
REF: https://www.homedepot.ca/en/home/p.4-inch-x-100-foot-solid-tubing.1000124225.html
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KinAlberta
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# Posted: 25 Oct 2017 10:05am - Edited by: KinAlberta
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I found this for the Edmonton area so our cabin would be even deeper:
“I was surprised to hear that you use footings as shallow as 42". I am near Edmonton, Alberta. Most of the geotechs in this area specify 5' minimum for continuously heated buildings and 8' deep for open, unheated foundations.†http://www.eng-tips.com/viewthread.cfm?qid=267021
I know the pipe.
Just bought a 100’ feet of the correlated pipe at Home Depot for a beaver dam leveller device we in put in last weekend.
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creeky
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# Posted: 26 Oct 2017 06:39pm
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Be real careful with the ground source heat tube. The reason no one does them is mold. In the summer the hot humid air dumps water into the tube. what happens to water in the dark with a bit of fertilizer from pollen etc?
Ya. So all summer/winter you then draw nice moldy air into the house.
Air exchangers are a great idea.
I would think you're best off with the solar heat exchanger. Simple to build. Dampers or simple S shape air flow gates solve the back flow problem. Lots of solutions online.
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KinAlberta
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# Posted: 26 Dec 2018 09:35pm - Edited by: KinAlberta
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Older interesting article:
Builder uses solar power to heat Fairbanks home in the winter
Molly Rettig / mrettig@newsminer.com Mar 13, 2011
http://www.newsminer.com/news/local_news/builder-uses-solar-power-to-heat-fairbanks-h ome-in-the/article_0e6654f8-6226-576b-a004-2870890894cb.html
2014:
Solar Thermal is Dead (NOT) “The DIYer can build a solar thermal system equivalent to the $6000 to $10,000 commercial system described above for not much more than $1000. This is not an exaggeration – my initial domestic water heating systemcost $1000 and I have heard from many people who have built similar systems from $500 to $2000. A number of these systems are described in detailed here... “ https://www.builditsolar.com/Projects/WaterHeating/Dead/Dead.htm
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Jebediah
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# Posted: 27 Dec 2018 06:01am - Edited by: Jebediah
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I have 2 old 4x8 solar water heaters panels that I'm not using right now(siphon system)...They get so hot, even in the winter you can't touch the copper piping, you can scold yourself if you let the antifreeze run onto your hand....I was thinking of connecting a couple of old cast iron heaters to the system...
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creeky
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# Posted: 27 Dec 2018 12:44pm
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That fairbanks alaska home is something. A 5000 gallon storage tank. Wow.
Reminds me of the old cisterns folks in our area used to build. I'm thinking I have to try something like that.
Hmmmm.
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slgerber
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# Posted: 29 Dec 2018 10:35am - Edited by: slgerber
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I wonder how well it would work to put a large thermal storage water tank inside a cabin and then locate a solar water heating panel ( filled with glycol) outside below the bottom of the tank. Connect the panel to a shallow height glycol filled vertical pipe coil inside the bottom of the tank using through-hull couplings and the system should work as a thermosiphon loop without the need for the added complexities of an electrical pumping system. Although a circulation pump would increase efficiency it also adds more points of failure especially if it must be powered by an off-grid solar powered electricity source. Seems like this could potentially work well enough to keep a well insulated cabin above freezing even if it is infrequently used.
I do actually have a selfbuilt 4x6 foot solar hot air panel on my house and it contributes a useful amount of heat on sunny days. The main drawback to a simple hot air panel like mine is that it doesn't really do very much toward storing up heat to use at night or on cloudy days. A tank of hot water is a much better thermal store compared to just filling a building with hot air.
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KinAlberta
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# Posted: 27 Sep 2019 11:05pm - Edited by: KinAlberta
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It seems to me that the best possible use for a solar air heater would be as a preheater for the cold air intake on a furnace.
It can’t replace a furnace but it can cut the cost of heating a house just like a higher efficiency furnace reduces fuel consumption.
I still wonder if heat couldn’t be captured as it rises into an attic and then returned into the house. Maybe heat could even be captured from right under the roof sheathing and also sent down into the house. A house with a metal roof where the snow slides off would then heat up. So maybe sheath the inside of the rafters to create channels on the sun facing side and capture heat using those channels for some other preheating benefit.
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Nobadays
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# Posted: 28 Sep 2019 11:35am
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Kin.... I did a bit of a search but couldn't find what I was looking. That said I have seen where heat was captured from under the sheathing by boxing in under the south side rafters, insulating the back side (toward open attic space) then an air duct connecting the "boxes" both top and bottom. The system I remember then used an insulated flexible duct from the top into the the home via a standard vent.... then an intake to the lower end with insulated flexible duct and inline duct fan to help push the air through. I think I remember that fan having a thermostatic controller to turn it 9n and off at pre-set temps.
We live in central AZ during the winter (5,000' in the mountains), lots of sun but not really warm so heating either wood or heat pump is a necessity. Have always wanted to experiment with solar hot air recovery/heaters. Maybe this is the year!
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KinAlberta
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# Posted: 28 Sep 2019 01:15pm
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I was in one of our Home Depot stores a few days ago and saw that they had long black downspout pipes for only about $20 each. Tempted to buy 10 or 20 of them and build a solar fence air heater to sit beside the cabin.
However could just lay a bunch of them vertically side by side on top of our metal roofing and create manifolds top and bottom (peak & eave).
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Steve_S
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# Posted: 28 Sep 2019 02:22pm
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you should seriously revisit http://www.builditsolar.com/index.htm and look at the projects and the updates.... They have all the how to on what you want to do, tested and working with results. no point in reinventing the wheel.
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Jebediah
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# Posted: 28 Sep 2019 05:40pm
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Cabin Depot sells these...
24" x 48" Solar Thermal Air Heater
Product Code: SIS50M2448 (Interior Use)
Highlights:
High efficiency interior application for sunny or partial cloudy conditions
Ideal for space under 150 sq. ft.
3-Dimensional stacked heat-absorbing collectors
Under good winter sun conditions, up to 30 degrees F (17 degrees C) may be added to the ambient temperature in the room with a maximum air flow from the solar fan of 80 CFM
Quiet solar powered waterproof recirculating fan distributes heated air and has adjustable speed control knob
12 Volt / 20 Watt photovoltaic panel provides plenty of solar energy to power the fan.
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gcrank1
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# Posted: 28 Mar 2021 02:16pm
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Im pulling the antique upright woodstove pipe out of the gable exit about mid-spring and installing a 'belled' ductwork pipe through the hole with a fan to pump the hot summer air that stacks up there out of the peak.
Im also thinking on leaving the old woodstove inside (it does look good and is a contributing 'heat sink' amount of metal) with the sgl wall black stove pipe going up to about 2' from the peak. That with a fan blowing down should suck the winter heated air out of the peak, down through the pipe and stove heat sink and back into the room at floor level through the draft control.
No need for combustion clearances or hearth either, just tuck the stove back next to the wall.
All that with just modding most of what I have without building another something from scratch.
But to the orig. question, I did build a warm air solar collector some 30ish years ago. It was a 2x8 box frame with a plywood back, rigid styro and black painted steel corrugated roofing, glazing was repurposed patio door glass. A 6" air inlet at the bottom feed from my basement to a 6" outlet at top to floor level of my living room did give us heat to help min. furnace run during a sunny day. Simple manual flap controls.
Cost analysis? I dont know....may have saved some, nothing big enough to say 'wow'. Once it started needing some rebuilding I concluded that the nice upgraded south facing windows we had put in were just fine so I gave the unit away to a young guy that wanted to play with the solar idea.
Thinking about this thread and if, say, a 10*f rise in the cabin from ambient would be nice, yes it would. That would be another 10* I wouldnt have to heat it up from whatever temp it starts at. I found this past winter, on the occasions we could get in, that typically I could get about a 10* rise in the first hour (about 45k btu's of lp in 2 wall heaters) so the math says that Id be about 1/2 gal. of propane ahead; not much in savings but the diff in creature comfort would be good as it warmed up quicker.
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scott100
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# Posted: 28 Mar 2021 10:33pm
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I did the second one in the link below a number of years ago. It produced quite a bit of heat. At the time, we were heating that house primarily with a wood stove in the cellar. I plumbed the air heater into the cellar to supplement the wood heat, and it made a noticeable difference in house temp when we got home from work on sunny days. We later put in a geo system at the house and I did away with the solar heater.
If I were to do such a project again, I would do one of the heaters with screen as the absorber instead of the downspout idea. The downspouts and associated ducting needed too high a pressure blower to get good flow and more electricity to run. Screen absorber collectors can be made to be pretty much passive. It was a fun experiment, though.
https://www.builditsolar.com/Projects/SpaceHeating/DownSpout/DownSpout.htm#Big
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KinAlberta
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# Posted: 3 Oct 2021 11:29am
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To take the chill off, I’m temped to build a passive solar heater fence next to our cabin. Say something just 4’ high by 16’ long. On the vertical it may not be the most efficient but wouldn’t accumulate snow.
Anyone try this?
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