Author Topic: Heating the mass  (Read 4259 times)

FreeBTU

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Heating the mass
« on: November 02, 2013, 02:48:31 AM »
There are all sorts of way to get free heat.

Some people have near infinite access to free firewood. They can use wood as fuel.
Some live in a climate with enough temperature swings to benefit from thermal mass.
Others have lots of sun all year around and go a long way with their solar panels.
But others have a little of everything but never enough to rely on one system.


I'm looking into, as asking for advice, to make efficient use of thermal mass heating. I'm not a good writer so I'll just sum up the idea's I have because they pretty well explain my aim.

I'm possibly moving to... an empty piece of land :-)
I'll build a house to my own preferences. One of those preferences is a stable low cost indoor temperature. Lot's of high mass walls inside.
--> I would welcome advise on cost vs effiency of various high mass walls.

Good insulation, etc etc.

I'm also considering a very high mass "object" that weights thousands of pounds to store heat (or cold in the summer).
I have two main options. A raised floor. Or a 2 feet thick wall.
I want to heat (or cool) that wall with water. Likely by running tubes/pipes through it.
--> Advice on thermal stress is welcome.

Obviously that water  needs to be heated so I'm thinking about a combination of various sources.
- As a backup natural gas heating.
- Electric heating from solar panels. --> Saves on batteries to store electricity.
- Mass rocket stove. (wood)
- Other ways like geo thermo heat?

So that would mean:
- Pipes running trough a the wood burner.
- Electric heating elements in the water. Or perhaps directly in the wall
- Connected to a regular gas heater which will have all the required safety valves, pump and stuff.

During the summer the water should be cooled down.

Feedback please?

worms

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Re: Heating the mass
« Reply #1 on: November 02, 2013, 05:07:56 AM »
This is probably not the best place to ask these questions.  Lots of useful stuff on places like permies.com or green building forum.

Rural

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Re: Heating the mass
« Reply #2 on: November 02, 2013, 05:59:49 AM »
I second the suggestion to look elsewhere and add Mother Earth News to the list -- the website is fairly extensive.

Have you considered earth sheltering or partial earth sheltering? That gives you extremely high thermal mass without the moving parts of your water (always a weak point in a system). Our new hose is earth sheltered on three sides (and not the roof). We're stable at 58 degrees with passive solar heat gain working pretty well when the leaves are off the trees to heat it. We did cool some this summer, but that will be less when we have our porch roof on.

If you have a spring or well on the property, look into geothermal heating and cooling with a heat pump. My parents' place has run extremely efficiently in that for near forty years now. The water comes only to the pump, not throughout the walls, which removes some of the nightmare scenarios of leaky pipes that sprang to my mind when I read your (otherwise very cool-sounding) plan.

nico demouse

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Re: Heating the mass
« Reply #3 on: November 02, 2013, 06:48:53 AM »
I'm assuming you've already found these guys, but just in case: http://www.builditsolar.com/

Wealth of information. All kinds of projects, from low to high tech.

m8547

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Re: Heating the mass
« Reply #4 on: November 02, 2013, 08:28:49 AM »
Solar hot water is a good way to go, if you live in a sunny enough area. It even works in the winter if you get the right type (vacuum tubes, I think).

I did some calculations for ground source with a heat pump, and it never made sense over natural gas heat with current pricing in my area. Natural gas is so cheap, and electricity is relatively expensive, and the ground source didn't improve the COP enough to bring the electricity consumption very low. It might have been slightly cheaper to operate than gas, but it would never pay back the cost of getting the system installed (thousands for the heat pump/heat exchanger parts, and tens of thousands up to 100,000 to get ground source piping installed). If you live in an area with true geothermal, where you can extract heat from the ground without a heat pump, that's awesome and you should take advantage of it. But as far as I know, most places require a heat pump so you don't get free energy.

If you live in a place with cold winters, where it's cold all day, insulation is probably more important than thermal mass. Thermal mass is great for places like Colorado where it might get up to 60 in the day and the sun can heat the thermal mass, but then it gets cold at night. The key is that the sun heats it. If you have to heat the mass yourself, you might as well skip the mass and just heat the interior space. Thermal mass is good for things that provide free heat some of the time, like solar hot water. Using solar photovoltaic panels to heat thermal mass electrically is likely not a good use of resources. Solar panels are expensive and not very efficient, converting on the order of 15% of the sun's energy to electricity. If you are using them to replace an expensive energy source like electricity, it can make sense, but using them for heat is not usually worth it. You could use solar to run a ground source heat pump, but then you have the problem of a super expensive system with a long payback period.

I knew a family that lives off grid, and they have solar hot water for hot water and heat, with free wood to supplement that when it's colder. They use a tank of water in the basement for thermal mass (it looked like a hot tub, but I don't know if you could swim in it). Their electricity comes from 2 sun tracking PV arrays, and they have a huge bank of batteries (most of a room) which could power them through a few days of cloudy weather. They also have a diesel generator for times in the winter when it's cloudy for a long time, and they said they use it once or twice a year.

If you are living on-grid, you can use the grid as your battery for solar power, saving lots of money.

I've heard stories about super insulated houses that get enough heat from the occupants and regular electricity use that no other heat is required. If it got too cold, they would just play with the dog for a while or turn on a 60w light bulb for an hour.

Derek

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Re: Heating the mass
« Reply #5 on: November 13, 2013, 06:35:38 AM »
Here is my experience with building a house in 2007 with these principals.  We went with a passive solar design.  Not a crazy wall of windows, just most of the windows facing south.  Not only do you get a lot of free heat on sunny cold days but the natural light is excellent and we never need electric lights during the day.  Also you do not get a lot of unwanted heat gain during the summer due to the angle of the sun.  We do not have overhangs and this works just fine.  We have spray foam insulation and it is wonderful but blown in cellulose/fiberglass is also good.  We did not make our house super air tight because I didn't want to rely on an an electric air heat exchanger to keep the air fresh in the house.  For thermal mass we have a masonry heater.  Think of a 16,000 lb. wood stove.  Keeps our house comfortable without excessively heating the room or drying everything out.  The only unmustacian issue with a masonry heater is the cost.  The kit we used (Temp-Cast) is about 6K.  By the time you pay the masons, build the foundation, buy facing material, get an insulated metal chimney, you are going to spend about 17K.  You could go with a regular wood stove and if you have an insulated slab foundation with tile floors you will still have a similar effect. 
   Thermal mass simply regulates the heat.  If you have a wood stove or passive solar, without thermal mass the house gets hot during the sun/burning time and does not stay warm at night or when you are not burning.
     We have regular central air and LPG heat.  We almost never turn on the furnace due to the masonry heater and our air conditioning bill adds about $30 a month.  This is for a 3000 sq./ft home in Missouri.



Derek

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Re: Heating the mass
« Reply #6 on: November 13, 2013, 06:39:42 AM »
I forgot to add, you can also place a heating element in the masonry heater to get hot water during the winter.  I wish we did this.  We have solar hot water.  Drainback system with flat plate collectors.  Works well 8 months a year.

Rural

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Re: Heating the mass
« Reply #7 on: November 13, 2013, 05:27:02 PM »
Here is my experience with building a house in 2007 with these principals.  We went with a passive solar design.  Not a crazy wall of windows, just most of the windows facing south.  Not only do you get a lot of free heat on sunny cold days but the natural light is excellent and we never need electric lights during the day.  Also you do not get a lot of unwanted heat gain during the summer due to the angle of the sun.  We do not have overhangs and this works just fine.  We have spray foam insulation and it is wonderful but blown in cellulose/fiberglass is also good.  We did not make our house super air tight because I didn't want to rely on an an electric air heat exchanger to keep the air fresh in the house.  For thermal mass we have a masonry heater.  Think of a 16,000 lb. wood stove.  Keeps our house comfortable without excessively heating the room or drying everything out.  The only unmustacian issue with a masonry heater is the cost.  The kit we used (Temp-Cast) is about 6K.  By the time you pay the masons, build the foundation, buy facing material, get an insulated metal chimney, you are going to spend about 17K.  You could go with a regular wood stove and if you have an insulated slab foundation with tile floors you will still have a similar effect. 
   Thermal mass simply regulates the heat.  If you have a wood stove or passive solar, without thermal mass the house gets hot during the sun/burning time and does not stay warm at night or when you are not burning.
     We have regular central air and LPG heat.  We almost never turn on the furnace due to the masonry heater and our air conditioning bill adds about $30 a month.  This is for a 3000 sq./ft home in Missouri.

I'll second the effectiveness of an insulated slab (no tile here yet, just concrete). That's the route we went for thermal mass, that and 10 inch concrete walls, and it works well for thermal mass. We do have a fairly crazy south-facing wall of windows, partly because all the other walls are underground. We don't yet have an overhang to block summer sun (we're well south of you), but we're in the middle of mature deciduous forest, so we're shaded when the weather's hot.

If we'd been further North, we'd have gone with a masonry stove, too. We looked at them but decided we'd burn up.

Seawolf

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Re: Heating the mass
« Reply #8 on: December 04, 2013, 01:16:27 PM »
I'm going to go ahead and 2nd the Masonry Heater proposition.  We have one that stretches two stories, and though it doesn't quite do all it needs to on very cold nights, when I'm retired I can fire it twice a day to cover that.  Heats a 3k sq ft Geodesic dome like none other.  Basement and upstairs stay warm if not boilingly toasty.