Solar heating shed

[mike90045]

I've had my eye on this for a while, and think it is the way to go.
http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm
homebuilt collectors, large storage tank, in-slab PEX lines


(What I'm really here for is a Listeroid genset)

[quinnf]

What a great place to be a dog!

Quinn

[lowspeedlife]

Shed hell!! look at that view!!

[Ronmar]

That was a fantastic article.  Note the simple use of a TRV to mix in storage water as needed to maintain a constant floor temp untill the heat is exhausted.  Good practical engineering...

We have been planning our new house since last spring.  It will be on a full basement but we don't need all that room.  The house itself will be super insulated(15" in walls)  A major space taker in the basement will be a large heavily insulated thermal storage tank.  This tank will take inputs from various solar, generator waste heat if it is on line, and a chip bioler(pellet stove on steroids burning chipped yard waste and pelletized junk mail/burnable waste)...

[Ronmar]

We are looking at a Natural Spaces dome http://www.naturalspacesdomes.com/  They have a "super wall" construction that uses 2X8 frames for the triangles.  Off of these frames is a piece of plywood that supports a 2X4 inner wall frame for a 15" deep cavity.  With inner wall surface, isulation, air gap for outer wall ventilation and outer sheethig and roofing material, the wall is nearly 18" thick.  We are planning the dome on a basement of ICF block construction which yields a wall about 13" thick(8" concrete with 2.5" of foam on either side.  The slab will set on approx 4" of high density foam.  the basement floor will be dug into a hillside on our property so most of that basement will be below grade.

For thermal storage, I am figuring for at least 1500 gallons, but the actual heat needs of the house may change this size.  This tank will be homemade, similar to that done in the solar shed article.  basically a built up foam carcophagus with liner with a foam capstone.  The active collector I am planning should give me 18,000 BTU/HR for perhaps 6 hours on a sunny mid-winter day.  Not sure what the passive collectors will do yet as I havn't built one of those prototypes yet(maybe this winter:))

The chip boiler will use the heat exchanger design I have been playing with for the exhaust on the lister.  Should be easy to build and VERY easy to clean.  The burner will be basically pellet stove parts.  A auger and drive controller, a combustion blower on the outlet that draws air thru the burn grate to violently combust the fuel placed there by the auger. Then thru a particle separator to keep the bigger ash particles out of the heatex, and then thru the heatex to the blower inlet.  Where mine will differ from the typical pellet stove is that it will be manually lit(with auto stop/shutdown) I will also use a propane burner under the grate to Provide instant combustion at lightoff so there is no smoke at startup, like a pellet stove does.

If I can get my solar collectors sorted out, on a sunny day, the sun will heat the house and store enough heat for perhaps a day or two more.  3 days or more of no sun in the pacific northwest, when does that ever happen:)  The chip boiler is my sun in a can to recharge the thermal storage tank.  If thermal storage is high enough, it will also maintain the HW tank so electric bill should be limited to appliances, lighting and 3 or 4 small circ pumps that run intermittently, say 400W to heat the house along with an occasional boiler run at another 200W...    

[lowspeedlife]

My pellet stove has 30 Ft of 4 inch s/s pipe attached to it & it gets an amazing amount of ash (no creosote) build up in side, but i do burn about 5 tons of pellets each winter.

   scott r.

[Ronmar]

Don't make jokes about the roofing contractor getting a heart attack!  I will be doing the roofing... 

Pellet stoves don't really build up much of anything except fly ash which has about the consistency of fine sand.  I have only really found one type of buildup on the one I have been running for 3 1/2 years now and I can't really call that creosote as it does not appear to be flammable.  I get a few little pieces of black rough chunky buildup(looks like beach sand glued together) up at the screen at the flue rain cap.  You are pulling heat out of the pellet fire box right near the fire via pipe air-air heat exchanger tubes with room air forced thru them by a blower.  These only pick up a little carbon that is easilly scraped off with the built in tube cleaner.  I pull the cleaner rod every other day or so.  What the scraper dosn't get, is easilly removed with a plain paint brush during my more in depth cleanings of the burner grate every week or so.

The main reason for this is that the fuel is very dry, it has a lot of surface area exposed to the fire and it is combusted very hot/efficiently blast furnace style, hence the low emissions.  Woodstoves can be run like this, but they do not typicaly do so for very long as it is full throttle, sides glowing red hot, run you outta the house hot.  When run like that, the combustion process is much cleaner and there are less emissions to potentially buildup in the flue, and there is no real smoke.  The moisture content of firewood is typically higher also.  The wetter the wood, the dirtyer the combustion, emissions and the flue.  I grew up with woodstoves.  The standing rule was that the stove was ran to this point at least once, for at least an hour every day of operation.  This practice has served me well for many many years now...

No more info on the heatex yet, I am still playing with the prototype build, and I am going to set on it till I prove it out:). 

[vdubnut62]

In my experience wood stoves generally give trouble when they are "idled" (combustion air severely limited).
I have had a ducted wood burning furnace for over 20 years. It is either wide open, or the draft is cut completely off.
I believe that it will burn anything without trouble, I have even fueled it with green Virginia pine with no creosote buildup.
That's my story and I'm sticking to it.
Ron

[Ronmar]

Yep, my story also.  Run full out, woodstove flues stay clean.  The pellet stove is run full out always, with a small intense lean fire. Fuel input rate is used to control heat output.  This same method could be used with a wood stove, but is typically not as it requires constant attention to add small ammounts of fuel.

The little bit I have experimented with burning air dried softwood chips has shown me that they appear to burn pretty clean.  They do produce a more conventional ash.  That is where the particle separator comes in.  This ash will probably want to move more in the forced airflow.  The particle sep will allow a velocity change, as well as a cyclonic action to help shake out the ash from the hot gas flow before it heads into the heat exchanger..

[BruceM]

Looks like a very interesting home project, Ronmar, looking forward to seeing more.

My new offgrid home is double framed, 12" wall, super-insulated design, though just a small single story ranch house.

In running in-floor heating design models, I found that insulating the slab from the stem wall with 4" of foam (bridged by that wide wall), and another 1" on the exterior of the stem wall, made a 50% heating BTU reduction over a more typical insulation job.  In practice, it was easy as it really isn't that much insulation to add.  The floor is uniform in temperature, not chilly towards the outside edge, with heating off.  The house loses 1.5 degrees per day without heat if the windows are covered with Astrofoil at night.

I also used 2" foam under the entire slab. With two layers of 6" insulation (John's Mansville's Formaldehyde free bats) and an R80 attic with lifted truss heels for depth over the outside walls, it sure doesn't need much heating. I was also absolutely anal about sealing the Tyvec to the slab and every where else, as it's a high wind area.   It takes about $30/month on top of the domestic hot water (propane now, was to be part of the active solar hot water system) for the house at 71 and the day temps 45F/10F.  The house is totally uniform in temperature, the whole thing is on just one 10watt circ pump, no need for zoning.  There is only one outside door, in a semi heated entryway which reduces door losses greatly.

The shop is 50 feet away, with space and pre-plumbing for an 600-800 gallon solar hot water storage tank.  The 10x40 foot shop south wall is ready for hot water panels below the high windows, but my operating costs on a $350 no-electric hot water heater  (65% efficiency) are so low, I'm having a hard time justifying the expense on hot water panels and storage tank.  The payback would be never.

I thought I might have to do cooling, but based on last summer, it appears unnecessary.  There is so much mass in the interior (5.5" slab, 5/8 sheetrock, all floors and walls ceramic tile, that the temperature just doesn't change much during the day.  (Most nights are cool even if the day temps are over 100F.)  

So I'm a believer, now, in super-insulation and a double framed wall. It only took two of us two days to do the second wall, not a big deal. The beauty of insulation is that there is zero ongoing maintenance, while all other systems do

[Ronmar]

Yes, I think super insulated is the only way to go if you are building. It lowers your needs in so many other areas.  Yes it is a big expense up front, but as you mentioned, it is a no maintenance system and a one time known expense.  Who knows what a BTU of either heating or cooling is going to cost you 10-20 years from now...  IMO it is better to just not need very many to begin with to maintain a comfortable living space.

[BruceM]

It is hard to part with the extra thousands up front for super insulation when you're on a budget, but I'm sure glad I did.  I really tried to take the whole off grid living situation seriously, in thinking about how to significantly reduce my energy needs while still living in comfort.

My cooling  plan was to do in-floor cooling (cool off the slab mass with the existing in floor heat pex) via night-time, evaporatively chilled water. The super insulation saved me from that project's expense and maintenance, plus the active solar hot water system.  So cost wise, it turned out to save me from my grand $ engineering plans.  Pity, I thought a big bong cooler on the side of my shop was going to be fun.

What I haven't seen yet is a good, low cost flat plate solar collector design using something affordable (not red gold- copper).  Plenty of homebrew Pex designs out there, but they are nuts;  if your pump fails once while the sun is shining, stagnation temps will melt the pex.

Plus pex systems typically are very low efficiency compared to copper tube and fin,  as the thermal conduction from formed aluminum fin to pex to water is so poor, so water temps are very disappointing in the systems where people have documented it. 




I

[Cornelius]

I observe that the trend here in Norway are 14"-16" in the walls. I think the new required standard are min. 10" in the walls and 16" in the roof.

So-called 'passive houses' built here, have 14"-16" in walls, 20" in the roof, and 14" in floors on ground.

It makes sense to invest a bit more in insulation; it will guaranteed pay back over the years. Here, it is usually below zero (celsius) in the winter, and sometimes 25-30+ in summer...

I myself lives in a wooden house, built in 1913, and that means hollow walls; 5" thick... (Just bought it, so i'm working in it... )