Combined domestic hot water and house heating system

[BruceM]

Marcus-  I like the masonry stove as thermal cooling mass idea. The masonry stove might be an even more effective cooling mass if you could move air through it at night;  if you could put a fan to move cool outside air down the chimney and out into the house, that might chill out the masonry faster than blowing warm house air up. It's another situation where some buried thermisters might help work out the optimum design.  It might be less annoying with the fan up topside; fans at night can be bothersome depending on sound character.

Also-  5/8" sheet rock is a fairly cheap way to add a lot of mass throughout the house, while having nicer walls at the same time. (Stone or masonry is always nice but hurts the pocket book.)   It is "fast mass"- if you leave windows open when it's too hot or cold, it has a lot of surface and will dump it's heat/cold fairly quickly.  But well managed, mass is mass, and "fast mass" can be helpful for passive (windows open) night time cooling, it will cool off quickly if there is good air flow.

[mbryner]

Hmm.  You guys got me thinking more outside the box again, especially Bruce with your last reply.   Thanks!    Since the masonry stove needs outside combustion air, what about taking the air from the cooling tubes into the air inlet of the masonry stove, in the normal direction and not just at night.  It would keep the stove cool all day to help keep the house cool.   The air wouldn't get into the living space; it would just go out the chimney.   The chimney could act like a draft tube.   Any mold that formed on the inside of the masonry stove would get burned out every fall at the first firing.   Wonder if that would work?   In winter the draft from the fire would suck air through the underground tubes and warm it a bit.   Probably negligible increased efficiency because of warming the air a few degrees for a 1000 degree firebox.

Marcus

[Geno]

That is out of the box thinking....and may just be a very good idea. If the fireplace will draw its own draft in the summer you'd definitely be on to something.

Thanks, Geno

[Ronmar]

Feeding combustion air directly to the firebox from outside is a good idea in general.  If you draw air from the building, that air has to be made up from somewhere else.  This happens by cold air being drawn in thru every crack in the envelope...

I had a wood stove, and changed it out for a pellet stove.  We were very dissappointed with it's initial performance as our main living space was far colder than with the woodstove.  After a little bit I figured out what was happening.  A pellet stove is a lean burn device and pumps a very large ammount of air out the exhaust.  What was happening in my drafty old house, was that drawing the combustion air from the home, pulled in as much, if not more cold air thru the cracks as I was heating.  You get around the doors and windows and you could actually feel the cold air moving.  I hard plummed a 2" air line to the combustion air inlet from outside.  The difference was night and day in room comfort... 

[mbryner]

I was going to feed outside air through a 4" pipe for combustion anyway, this just makes a possible passive A/C out of it.

OK, now here's another idea building on the concept.   Geno, says:

If the fireplace will draw its own draft in the summer you'd definitely be on to something.

Why not extend the chimney with uninsulated pipe about 6 feet or so higher than required.   Sunlight shining on the black flue pipe will heat it, heating the air inside and causing even greater draft, slowly sucking cool ground-air into the firebox and cooling the masonry.   What do you think?

[BruceM]

Sorry to dampen the enthusiasm for this, but there's no way to pull colder, heavy air up out of the chimney by convection!  You'll have to use a blower.

[mobile_bob]

there is if the stack is tall enough, and is painted black

look up thermal chimney

i have several books from back in the 70's and 80's that show illustration

my old 3 story victorian house would "thermal" cooler air from the basement hard enough to
blow my daughters hair back while standing in the doorway.

what was even with the attic stairs door closed!

when that heat rises, and if it has a runner to go up, it will draw up heavy cold air behind quite well
in my experience.

bob g

[BruceM]

OK, I'll partially buy the big solar chimney concept.  The air coming out of the solar chimney must be substantially lighter than the column of cold air it's pulling up the shaft, which means you'll need a substantial thermal chimney.

The draft of solar chimneys can be very impressive...but they don't usually pull a column of earth cooled air through tubes. 

Plan for a fan just in case...

There's a solar chimney about 24" in diameter on a solar/green demonstration home nearby. The house is built into a south facing hill.  The summer airflow up the shaft  is very impressive, you can hear a whooshing sound and feel it near the opening.  I asked where is the air inlet for the house...they looked at me with blank, confused faces.  One tried to tell me it came down the center of the flow.    The only inlets for that tremendous flow up and out were leaks in the building envelope- I thought it smelled "earthy" ! 

[Crofter]

Sorry to dampen the enthusiasm for this, but there's no way to pull colder, heavy air up out of the chimney by convection!  You'll have to use a blower.

I agree.

If the house was totally sealed and the underfloor pipes were open to the outside you could probably create a pressure differential with the heated chimney that would pull cold air up a small way above ground level but any volume of it would cool the chimney and destroy the weight differential of the column in relation to outside ambient. Denser air does not flow uphill. flow will only exist when the average density of the lift column is less than the average density of the other column . I expect you would have a short circuited convection current going on in the heated portion of the chimney. You could induce flow if the outdoor temperature were very cold and the ground tubes open to it though.. I saw this one argued to great length about someone wanting to duct from the ceiling and have hot air pulled down into his crawl space to  by the chimneys draught sucking the cold air up into the room and into the stove intake.

[Ronmar]

Yes, the principals of thermosiphon apply here.  It will take a lot of energy to create enough of a vacume to lift cold dense air.  Also a single wall chimney might give you creosote buildup issues when burning the stove.  Chimney fires are not a very good time... 

[BruceM]

Duh oh, I forgot about the chimney liner- that would screw the whole concept, as it insulates the masonry from the flue. Thanks Ron.

Do the big European masonry heaters use flue liners?  That was what I thought Marcus was proposing since he was talking about large mass.

[mbryner]

OK, you're all bursting my bubble here!!!    Yeah, I was wondering if the concept would have enough draft effect.   But, at least maybe it would work together with a fan to increase the draft effect?   Yes, the big Euro-inspired masonry heaters have a chimney liner, but the creosote is a non-issue.   The fire is very hot and short-lived, and the stove is designed to hold most the heat instead of sending it out the chimney.   The smoke going out the chimney is not nearly as hot as a woodstove.  If it wasn't burning so hot and completely I would indeed worry about creosote.   But, if I extend maybe 6-10 ft of unlined black stovepipe above where the completed chimney stops, I don't see how it could hurt and it might just cut the blower fan wattage?

All the regular thermal chimney use a water mist at the top of a "chimney".   The evaporative-cooled air falls into the house.  Totally different concept (reversed flow from what I'm proposing).

Again, this forum has got to be the coolest on the net.   Where else could we talk about diesel engines running all kinds of fuels, heat recovery from engines, house design, thermal storage, chimneys, earth tubes, etc. etc., doing real number crunching (or at least real experience) and talking to no-nonsense decent people from all over!   (And I can still be my Libertarian self but be "green" without labeled a "greenie wacko".  No offense to anyone, I've never been politically correct, and if you're here you're probably running a "polluting" diesel engine.   OK, now I'm just rambling.   Just took a nap and still waking up; it took a little while to get my 2 y/o daughter to take her nap and I went to sleep next to her...)

[mobile_bob]

this place is sure nuff turning out to be greater than the sum of its parts!

and we got lots of parts!

bob g

[BruceM]

Too bad the liner blows the air thermal exchange.  Still, passively the masonry stove will help as "slow mass", as long as it's in the envelope and the house airflow is managed to keep the house cool.

If you are going to close up a lot during the day in the summer, then you might consider improving indoor air quality by materials selection.  Carpet is by far the worst offender, next is particle board. If you have an insulated slab, tile is very comfortable and durable, the best for indoor air quality. 

The low speed generator, off grid living, and ways to save energy for your climate is all part of the same game for many of us.  Planning for and off grid living especially gives us a new perspective on energy and energy conservation. 

[mbryner]

consider improving indoor air quality by materials selection.  Carpet is by far the worst offender, next is particle board. If you have an insulated slab, tile is very comfortable and durable, the best for indoor air quality.

OSB is not eliminated from our construction materials, i.e. roof panels, but yes, we have thought of such issues.  The bedrooms will have carpet (wool if it doesn't cost too much in the end), the bathrooms get tile, the kitchen will have cork, and the rest gets reclaimed wide plank clear heartwood yellow pine (used to be gym bleachers for 40 years).  The only slab is in the basement (workshop and garage).

Why does the liner blow the air thermal exchange?