100% solar heated house for cold climate

[David Delaney]

I have posted to my web site a document describing a novel thermal
scheme for a solar heated house for a cold climate.

Drawings, graphs, and calculations may be seen at the web site. Text
below.

See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html>

I would be grateful for comments.

David Delaney, Ottawa

Start of text from web document

Thermosyphon solar air heater and overhead thermal crawl space for
100% solar heating

David Delaney [email protected] Ottawa, November 2004

keywords: solar air heater, thermosyphon, natural convection, flow
organiser, flow organizer, thermal crawl space, thermal closet, heat
store, passive solar, solar fraction, solar thermal energy, bed of
stones, bin of stones, rock bed, damper

A house in Ottawa, Ontario (45.3N, 75.6W, continental climate) can get
100% of its winter space heat from a solar air heater that operates by
natural convection to charge a heat store in an overhead thermal crawl
space. The house uses common materials, simple components, simple
control, and simple building techniques, but needs a stronger
structure than an ordinary house to support the weight of the
overhead thermal mass. There are no dampers requiring daily operation.
The only parts that move every day are the blades of a conventional
ceiling fan.

The heavily insulated thermal crawl space, lies above the living
space, and extends above a thermosyphon solar air heater that forms
the south facade of the house. When the sun shines, heating the air
heater, air moves by natural convection from the air heater to the
thermal crawl space and back. When the sun stops shining, air stops
moving between the air heater and the thermal crawl space, because the
air in the heater is then colder and denser than the air in the
thermal crawl space above it.

The flow organizer (flow organiser) allows the sheet of hot air rising
from the air heater to cross through the sheet of cool air moving
south along the floor of the crawl space. The sheet of cool air
eventually falls through an east-west slit in the floor of the crawl
space, then falls through the air heater against the glazing,
keeping the rising hot air away from the cold glazing.

A massive but relatively thin layer of small smooth river stones
provides heat storage. The stones are from 1-1/2" to 2-1/2" (35 mm
to 65 mm) in diameter. The stone layer is suspended one or two feet
above the floor of the crawl space on a wire mesh. There is a one
foot air space above the stone layer so that hot air from air heater
can spread out above the stones. The stone layer extends above the
whole of the habitable space below. The stones present an enormous
surface area for heat transfer between stone and air. There is very
little resistance to convective vertical flow through the stone bed
because of its very large horizontal cross sectional area. To match
the volume flow rate of air coming up from the air heater, air will
move down through the stones at a volume rate equal to the volume rate
of the air rising from the flow organiser. The rate of descent
through the stones will be the volume rate divided by the effective
duct area of the stones. The effective duct area of the stones will be
approximately the product of the void fraction and the area of the top
of the stone bed. Given that the stone bed extends over the whole of
the living area, the velocity of air descending through the stones
will not exceed about a twentieth of the velocity of the air rising
by natural convection through the flow organiser. As a result,
resistance to the flow through the stone bed should be extremely
small. 100 lb of stone per square foot of ceiling area (490 kg/m2)
is about right to produce the desired thermal capacity. 100 lb/ft2
corresponds to a 1 ft (0.3 m) depth of stone with a 40% void fraction.
The crawl space extends 3 to 4 ft (0.9 to 1.2 m) from its floor to
its ceiling.

A ducted ceiling fan moves hot air from above the stone layer down
into the living space. A conventional 4 ft (1.2 m) diameter ceiling
fan is located in the lower end of a 4.5 (1.4 m ) diameter circular
duct that runs from the ceiling of the living space up through the
crawl space and the stone layer to the top of the stone layer. The
ceiling fan operates at reduced speed, and consumes 50 watts or less
when running. It might be powered by a small area of solar
photovoltaic panel. Control of the temperature of the living space
can be very simple: a thermostat that turns on the fan when the
living space is colder than desired.

A large solar air heater, super insulation, and thermally efficient
windows that are not too large, are required to get all needed space
heat from the sun in Ottawa Ontario. Ottawa has a difficult December,
with 1483 F heating degree days below 64.4F, (824 C heating degree
days below 18 C) (according to NASA). The average December temperature
is 14F (-10C). In December, a total of 2.16 kWh per day of solar
radiation falls on each square meter of a south facing vertical
surface (NASA). Design calculations are currently based on the
assumption that the air heater can transfer 50% of the December
incident solar energy into the thermal crawl space as heat.

Dimensions and suitable R values for a small bungalow in Ottawa,
Ontario: Living space: 40 ft (12.2m) east-west, 30 ft (9.1 m)
north-south, 1200 square feet (112 m2). Insulation: ceiling of crawl
space: R 100 (RSI 17.6); walls of crawl space: R 57 (RSI 10); walls of
living space R 50 (RSI 8.8); underslab: R20 (RSI 3.5). Windows:
window R-value: R 4 (RSI 0.7 ); window area: 120 square feet (11.1
m2). Fresh air: 45 ft3/min (21 l/s) The air heater must have an area
of 430 ft2 (40 m2), which could be achieved with an east-west glazing
40 ft (12.2 m) long and 11 ft (3.4 m) high. These air heater
dimensions are based on the assumption that the air heater can
transfer 50 per cent of the energy of the solar radiation that falls
on the exterior of its glazing into the crawl space. The
calculations to justify these specifications, and to create the graphs
below, may be seen in 100% Solar heated house for Ottawa, Ontario,
with overhead thermal crawl space. (PDF)

AT 430 ft2 (40 m2) the air heater is sufficient for December space
heat, but 30% larger than is needed for either November or January,
the next most demanding months. The surplus heat available in the
less demanding winter months might be used to heat domestic hot water.
The air-water heat exchanger might be placed in the top of the thermal
crawl space directly above the air heater, where it would be
accessible for maintenance and repair.

A stone layer area of 1100 ft2 (102 m2) at 100 lb (45.5 kg) of stone
per square foot provides a thermal capacity of 22,000 Btu/F (11.6
kWh/C). Assume a non solar heat gain of 600 W, of which 200 W is due
to two human bodies. If the temperature of the stones is 100 F (38 C)
and the outdoor temperature is 14 F (-10 C) when the sun ceases to
shine for several days, and the fan is controlled to maintain a
desired temperature of 70 F (21 C), the temperature of the habitable
space will not fall below that desired temperature until after 120
hours of darkness, and will fall to 59.8F after 168 hours of darkness,
and to 39.1 F (4 C) after 20 days of darkness. This calculation is
quite conservative. In Ottawa, a prolonged period of no-sun days is
almost always accompanied by relatively warm weather, say around 32 F
(0 C). When the temperature descends to 14F ( -10 C) , as in this
calculation, or lower, there is almost always some clear sky each day.

The 430 ft2 (40 m2) air heater specified above can maintain the
average temperature of the heat store (the thermal crawl space) at 110
F (43 C) and the habitable space at 70 F (21 C) during an Ottawa
December of infinite duration but typical temperatures and sun. (with
600 W non-solar heat gain).

If the utility electricity fails in a typical December, but there is
PV power to run the fan, the temperature of the habitable space will
not fall below the desired temperature unless there is a long string
of no-sun days. (Assuming a 200 W non-solar heat gain, just the two
human bodies). As the graph to the right shows, the heat store (the
thermal crawl space) even in the absence of dark days, the
temperature falls to equal (a comfortable) habitable space
temperature, making it impossible to maintain this temperature during
multiple dark days. Backup heat might be desired to anticipate
multiple dark days during a prolonged December electrical utility
failure. Backup heat would not be needed for prolonged electrical
failures in other months. A wood or propane cooking stove would
provide sufficient backup heat.

If there is a failure of the fan or of the electricity supply that
drives the fan, a door, a window, or a special opening in the south
wall of the house may be opened during the day, producing the flow
pattern through the house and air heater shown to the right. The air
heater will be less efficient in this configuration, and much of the
benefit of the crawl space thermal mass will be lost, but substantial
solar heat gain will still occur. The thermal mass will still keep
the thermal crawl space hot, providing some heat at night by
radiation to the living space below and eliminating heat loss from
the living space through its ceiling.

End of text from web document

 

[Gunnar]

I have posted to my web site a document describing a novel thermal
scheme for a solar heated house for a cold climate.

Drawings, graphs, and calculations may be seen at the web site. Text
below.

See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html>

I would be grateful for comments.

David Delaney, Ottawa

100 lb of stone per square foot of ceiling area (490 kg/m2)
about 100 square meters area of stones? (wild guess here)

Total weight 49000kg = 49 tons. Wow, not too good for earth quake prone
areas I guess.

Why not use water as energy storage _under_ the house?

Gunnar.

 

[Eric Swanson]

I have posted to my web site a document describing a novel thermal
scheme for a solar heated house for a cold climate.

Drawings, graphs, and calculations may be seen at the web site. Text
below.

See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html>

I would be grateful for comments.

David Delaney, Ottawa

Start of text from web document

Thermosyphon solar air heater and overhead thermal crawl space for
100% solar heating

David Delaney [email protected] Ottawa, November 2004

I'm building something similar to what you describe, except that I plan
to use a water tank for thermal storage.

You have a big problem with your design. Connecting the living space
to the crawl space by circulating air would eventually cause all the
moisture in the house to end up on the glazing of the hot air collector(s).

That's if you can pay for the extra structure for the 100 psf load for the
stoan bed on your ceiling. Do the structural calculations and you might be
surprized at the extra cost. Also, the extra insulation (R 100? That's
about 2 feet of fiberglass!) would be another negative.

Good luck!!

 

[[email protected]]

I have posted to my web site a document describing a novel thermal

scheme for a solar heated house for a cold climate.

Drawings, graphs, and calculations may be seen at the web site. Text
below.

See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html>

I would be grateful for comments.

What's the "novel" part of this?

I don't see any reason why the heating chamber shouldn't be wider,
6-8' deep would make it useable as living space during the day,
and possibly even as greehouse space during much of the year.

I'd also consider extending the roof overhang farther, enough
to block sunlight during the non-heating seasons. (although that
may not take much overhang, in ottawa.

Is the air-flow diagram really optimal? It seems like there's an awful
lot of air going in strange directions, to no real good purpose.
What happens if you move the fan and add some ducting,
to force air OUT of the living-space by shoving it into the
greenhouse during the day, or up into the overhead at night,
and suck heat down from the overhead through ports scattered
around the ceiling. That would reduce the draftiness, and
if you put the intake(s) down near floor level, you wouldn't have
to worry about stratification.

Also, if you can reduce the depth of the overhead assembly to 24"
(And I don't imagine you really NEED more than 6" of airspace
to get flow, do you?) then you can build the ceiling with standard
flat trusses, and stuff your thermal mass between them.

--Goedjn

 

[SQLit]

I have posted to my web site a document describing a novel thermal
scheme for a solar heated house for a cold climate.

Drawings, graphs, and calculations may be seen at the web site. Text
below.

See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html>

I would be grateful for comments.

snipped

Zome Works in New Mexico especially the bead window
Trumbal wall (spelling?)
Best of luck I have friends in Iowa that tried some thing similar to this. I
helped rip it out after the first winter. Worked ok in the day time. Brought
in cold air at night.

 

[Gunnar]

Heat rises?

exactly! with no power to run fans, having some means of manually adjusting
the heat transfer into the living area is a Good Thing. (IMHO).

Gunnar.

 

[Are we there yet?]

Look into "Hambro floor systems" and "Blue Max" style wall systems.

Go massive with lots of concrete - it'll make your house like a thermos
bottle.

What is the grade level? Why not go deeper into the earth and take
advantage of the free heat? More economical for storage too.

 

[Lorence M]

I have posted to my web site a document describing a novel thermal
scheme for a solar heated house for a cold climate.

Drawings, graphs, and calculations may be seen at the web site. Text
below.

See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html>

I would be grateful for comments.

David Delaney, Ottawa

I don't get it Dave. Some time or the other you will have
to move air against convection.

Why not just put the stone down in the crawl space, force
the heat down during the day then let it rise at night.

I'm in the process of building a "Normal" house. Looking at
your design, I just shake my head.

Don't get me wrong, I admire the work and thought you've put
into this project. I just don't think you've done a lot of
building.

The further you stray from the norm, the more it's going to
cost. You'd be lucky to build this place for double the cost
of a regular house, and it won't be worth sweet tweet when
your done.

You build a house to live in, not to live for.

Are you married? I'm shaking my head again.

"Ho-ney, I'm co-old. Turn up the heat pleeeaze."

Your a dead man.

Lorence

 

[[email protected]]

Go massive with lots of concrete - it'll make your house like a thermos
bottle.

You seem to have confused the difference between thermal mass and insulation.

Nick

 

[Eric Swanson]

I have posted to my web site a document describing a novel thermal
scheme for a solar heated house for a cold climate.

Drawings, graphs, and calculations may be seen at the web site. Text
below.

See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html>

I would be grateful for comments.

David Delaney, Ottawa

[snip]

I like the out-of-the-box thinking, but I'm concerned about efficiency
gains here.

I'm sure you're aware of Kachadorian's book *The Passive Solar House*
on a similar principle, but moving the air through the floor rather
than the wall and ceiling.

How come you don't store the thermal mass in the floor? The expense of
storing it in the ceiling [added expense of engineering] and forcing
it down surely won't pay for any efficiency gains [if any]. Three-four
days of no sun and you won't be running your PV fan anyway, and the
mass in the ceiling won't do you any good if you heat it up in some
other way, because you have to still force the air down, losing the
efficiency of storage.

I'm designing a solar-gain straw bale house and am storing the thermal
mass in the floor and some walls, and I won't be forcing the air
around anywhere. So at first blush, your idea looks impractical from a
simplicity standpoint, and you always want simplicity.

Good luck,

D

i had a passive system in central ohio. glass on the south heat rose a
fan blew it to the crawspace filled with large gravel. it worked
alright. where i lived, the solar gain was not as good as other parts of
the country. the house was built with 2x6 16 on center. double sliding
doors(which was great) there was a 18 inch space between the two. outer
one had a small roof over it. i believe in a well insulated house and
tight doors for central ohio area. there is a map somewhere that shows
areas that are great for solar gain.

Yes, the basic problem with simple passive systems is that they lose heat
rapidly t night or on cloudy days. And, if the collector efficiency is good,
they can overheat at the end of a sunny day.

Straw bales are good insulators, as long as they can be kept dry. It's hard to
build with them as they tend to sag when loaded, so using them as a structural
element is not a good idea. This can be a real problem around windows, as
there is less straw to sag, thus there can be differential sag across the
window (or door) area.

 

[[email protected]]

I'm sure you're aware of Kachadorian's book *The Passive Solar House*...

Ah yes...

Warm air rises. Why would it want to flow under the floor? Lots of warm
air needs to touch Lots of thermal mass surface to raise the slab temp
on a sunny day without overheating the house and ensure a low day/night
temperature swing. During a cloudy week, such a house gets exponentially
colder and colder, without woodstoves and so on.

Moving most of the solar glazing to a low-thermal-mass sunspace (one
that gets cool overnight and stays cool during a cloudy week) with an
insulated wall between the living space and the sunspace allows the same
or more solar gain when warm air flows between the sunspace and the house
during the day, but reduces the nighttime and cloudy-day heat loss from
the living space...

Dr. Rich Komp (author of Practical Photovoltaics and president of the
Maine Solar Energy Association) says warm hollow floors like his
(which predates Kachadorian's) aren't new. Romans built hypocausts,
hollow floors heated with warm air from hot water or fires. So did
Chinese peasants. Warm hollow floors make good homes for dust and
varmints. Rich's friend Ernie the Ermine takes care of that problem.

Living inside the heat battery, we are subject to its temperature swings,
and if there are no temperature swings, there is no solar heat storage.

We can't charge the slab up to a high temperature because we have to
live with it in the room. The same amount of thermal mass at a higher
temperature stores more useful heat than lower temp mass, and it allows
keeping a constant room temp until the mass cools to something close to
that room temperature.

Floor slabs don't usually have much insulation between themselves and
the room air, and they are difficult to insulate because of their shape.
The same amount of insulation applied to a cube with equivalent mass
lowers the rate of heatflow a lot more.

And water stores about 3X more heat than masonry by volume. It can also
be cheaper and more useful, even in sealed containers.

K's slab uses a fan. It might make more than a 40% heating fraction, with
lots of airflow and slab channels (ie heat transfer surface) and a carpet
on top of some foamboard over the slab and a low thermal mass sunspace with
separate 100 F air ducts between the sunspace and the slab and lots of house
insulation, eg 12" R48 SIPs.

Then again, we might make the house walls hollow block with the holes
lined up so air can naturally flow vertically through the walls, with
lots of insulation (eg Dri-Vit) outside the block.

But either way, we have lots of inaccessible nooks and crannies to attract
dust and spiders and varmints.

Storing heat for 5 cloudy 30 F days in a house that cools from 75 to 65 F
means 65=30+(75-30)exp(-120h/RC), so RC = -120/ln((65-30)/(75-30)) = 477 h.
A 48'x48'x8' house with an 8" 25 Btu/F-ft^3 slab with C = 48x48x8/12x25
= 38.4K Btu/F needs a max thermal conductance G = 38.4K/477 = 80.5 Btu/h-F,
or 57.5 for 3748 ft^2 of R65 walls and ceiling, after subtracting 4% of
the floorspace as R4 windows, with no air leaks or internal heat gain.
Sounds Herculean...

Making the house 32x32x16' tall with a 17K Btu/F slab and 2048 ft^2 of
5 Btu/F-ft^2 block walls makes C = 27.2K Btu/h-F, so G = 27.2K/477 = 57,
or 36.5 for 2990 ft^2 of R82 walls, with no air leaks. More Herculean.

K's book has lots of whopping mistakes. For instance, he thinks a house
needs 2/3 ACH for health, 27X more than the 0.025 ACH Swedish standard
and 83X more than the Canadian IDEAS standard.

Page 17 says "As you can see, the reduction in solar benefit increases
exponentially as you rotate the home's orientation away from true south."

Page 30 says

If this combination of poured concrete slab over horizontally laid blocks
is ventilated by air holes along the north and south walls, air will
naturally circulate through this concrete radiator when the sun is out...
the south wall will be warmer than the north wall... air that is next to
or alongside the south wall will rise. Warmed air will then be pulled out
of the ventilated slab, and the cooler air along the north wall will drop
into the holes along the north wall. This thermosiphoning effect will
naturally continue to pull air through the Solar Slab.

Page 49 says "Incorporate an air lock entrance" with miniscule energy savings
except for a department store, or a house with a huge active family.

Page 53 describes "reflective" foil smack up against plywood

The interior foil face will reflect heat back into the room, even though
it is sealed inside the thermo-shutter... The outside foil face of the
insulation contained within the wood veneers will reflect the sun's summer
heat back out the window.

Page 94 belies the natural air circulation described on page 30

The duct shown running down the middle of the bgase under the poured slab
is included in all cases. It should always be used as the return-air duct:
do not reverse the air flow pattrern shown on the control diagrams. By
using the Solar Slab as part of the return-air duct system, the Solar Slab
will constantly assist the furnace by preheating the return air. Even if
the home will be heated with a woodstove and emergency electric furnace,
the return duct should be included and the air mover hooked up per the
appropriate control diagram...

Page 101 says

2. Size of electric heating system = 9.25 kilowatt=hours,
with an annual consumption of 7.616 kilowatts,

Page 102 says

The calculation for the electric backup option determined that
we would need 9.25 kilowatts per hour for the Saltbox 38...

Page 106 says "The theoretical minimum temperature to which a home with
a Solar Slab will drop is the ground temperature under the solar slab..."
(Yes, that will keep the pipes from freezing in most parts of the US,
if a perfectly airtight house with infinite insulation

Page 107 says "it also costs more to cool air than to heat air," as if
K. is unaware of evaporation, night sky radiation, or the phrase
"coefficient of performance."

Page 137 ignores one-way passive backdraft dampers

It may seem that a sunspace that is gathering enough heat to become
90 degrees Fahrenheit on a cold, 15-degree but sunny winter day would
be beneficial to the home. And yes, it can be beneficial. However,
the same overglazed sunspace that accumulated all that heat during
the cold but sunny day will need lots of added heat when the sun goes
down to prevent it from freezing, which means that the sunspace or
greenhouse will tend to draw heat from the rest of the house as its
flow of solar heat reverses course, back out through the glazing.

but his solar slab is a good way to store overnight heat from inexpensive
passive air heaters or a low-thermal mass sunspace that can add valuable
floorspace to a house. One drawback is dust--it's hard to clean the rough
passages in the hollow concrete blocks. Another is fan power. A vertical
thermal mass (eg a chimney with extra flues open at top and bottom) might
store and release heat to a house with no fan power at all...

Page 46 says

Let there be no misunderstanding about where the fresh air makeup
is coming from. The walls and roof of your home should be very
tightly constructed... Fresh air will enter your home through
controlled or deliberate openings... not through gaps in the insulation
or poorly sealed windows and doors.

A 3,000 ft^2 house with 2/3 ACH has 267 cfm, enough for 18 full-time
occupants, using the 15 cfm/occupant ASHRAE standard.

K. doesn't mention heat recovery, although he talks about an "air exchange
or ventilator system." HRVs seem useless for most US houses, since natural
air leaks can easily supply most of the ventilation air. A 3,000 ft^2 house
only needs 30x60/(3000x8) = 0.075 ACH for 30 cfm. We might run a ventilation
fan if the house feels stuffy or the RH exceeds 60% in wintertime...

We might store more heat with better room temp control by circulating
100 F air from a sunspace under the floor...

If a solar house needs, say, $200 per year of electrical energy to operate,
we might heat a superinsulated house at the same cost, and forget about
fans and mass and glass...

A 2K ft^2 2-story house with R40 6.5" Urethane SIP walls and 130 ft^2 of
U0.38 south windows with 46% solar transmission (SHGC = 0.46) and a thermal
conductance of 214 Btu/h-F needs 24h(65-27.4)214 = 193K Btu on an average
December day in Worchester, MA. If 300 kWh/mo of electrical energy use
contributes 34K of that and 0.46x130x860 = 51K comes in south windows,
we only need 107.6K more.

A square foot of R1 vertical south air heater or sunspace glazing with 90%
solar transmission and 80 F air on the inside would gain 0.9x860 = 774 Btu
of sun and lose about 6h(80-27.4)1ft^2/R1 = 316, for a net gain of 458. We
might heat the house on an average day with 107.6K/458 = 235 ft^2 of extra
south glazing, eg a 32'x8' tall single layer of polycarbonate glazing on
the outside of an open stud wall with SIPs on the inside, or over exposed
posts and beams at the south edge of a second floor cantilevered 4' to the
south of the first floor, forming a 4'x32' arcade with a transparent wall
beneath, for a medieval look. UK planners might like this, from a distance.

We need about 18h/24hx193K = 145K Btu of overnight heat. With a 10 F daily
temp swing, 7K Btu/F of inherent house thermal mass and furnishings with
a short (2 hour) time constant could store 70K Btu. We might store the rest
in 150 10'x4" PVC water pipes among rafters in 600 ft^2 of basement ceiling.

We need 5(193K-34K) = 795K Btu for 5 cloudy 27 F days, at (65-27)214 = 8132
Btu/h. With 2250 Btu/h-F of thermal conductance to room air, the pipes could
warm the house with 65+8132/2250 = 69 F water. A 4x8x8' tall EPDM-rubber-
lined R40 SIP boxful cooling from 69+795K/(256+64) = 118 to 69 F would lose
24h(118-65)256ft^2/R40 = 8,140 Btu/day to house air. We might add 50K Btu/day
for showers, with a 42 gallon galvanized pressurized tank inside and two
unpressurized plastic drums to warm house air as greywater heat exchangers.

A square foot of 45 degree south roof would get 0.707(860+480) = 948 Btu on
an average December day. Trickling 130 F water between a dark metal roof and
2 layers of polycarbonate glazing, we might gain 0.8x848 = 758 Btu and lose
about 6h(130-30)1ft^2/R2 = 300, for another net gain of 458 and 58140/458
= 127 ft^2 of roof collector, eg a 12'x12' patch...

Nick

 

[Thomas Lee Elifritz]

November 23, 2004

You seem to have confused the difference between thermal mass and insulation.

Which is why you want to insulate the concrete, and earth shelter it.

But NOOOO ... humanity insists on burning all the plastic insulation.

Thomas Lee Elifritz
http://elifritz.members.atlantic.net

 

[Eric Swanson]

Ah yes...

Warm air rises. Why would it want to flow under the floor? Lots of warm
air needs to touch Lots of thermal mass surface to raise the slab temp
on a sunny day without overheating the house and ensure a low day/night
temperature swing. During a cloudy week, such a house gets exponentially
colder and colder, without woodstoves and so on.

Moving most of the solar glazing to a low-thermal-mass sunspace (one
that gets cool overnight and stays cool during a cloudy week) with an
insulated wall between the living space and the sunspace allows the same
or more solar gain when warm air flows between the sunspace and the house
during the day, but reduces the nighttime and cloudy-day heat loss from
the living space...

Dr. Rich Komp (author of Practical Photovoltaics and president of the
Maine Solar Energy Association) says warm hollow floors like his
(which predates Kachadorian's) aren't new. Romans built hypocausts,
hollow floors heated with warm air from hot water or fires. So did
Chinese peasants. Warm hollow floors make good homes for dust and
varmints. Rich's friend Ernie the Ermine takes care of that problem.

Living inside the heat battery, we are subject to its temperature swings,
and if there are no temperature swings, there is no solar heat storage.

Hi Nick,

I see you are still at it. Did you ever build your sunspace house?

I'm finishing mine up now (finally!). I hope to move in before Christmas,
if I can get past the last inspection. My south wall house has a 5500 gal
water tank in the middle that's 19 feet high. There won't be any big
temperature swings, if I can get it all to work as planned.

 

[[email protected]]

Hi Nick,

Hi Eric,

I see you are still at it. Did you ever build your sunspace house?

I've built several small versions, and may tweak the large retrofit version
this winter, as well as building a modified sunspace-Barra structure...

I'm finishing mine up now (finally!).

Congratulations (almost .

My south wall house has a 5500 gal water tank in the middle that's 19 feet
high. There won't be any big temperature swings, if I can get it all to
work as planned.

A stack of 7' diameter sewer pipes? Lots of pressure at the bottom,
and possible pump power savings...

Nick

 

[Eric Swanson]

Hi Eric,


I've built several small versions, and may tweak the large retrofit version
this winter, as well as building a modified sunspace-Barra structure...


Congratulations (almost .


A stack of 7' diameter sewer pipes? Lots of pressure at the bottom,
and possible pump power savings...

Yes, a 7 foot diameter corregated drain pipe. It's galvanized and it's
sitting in concrete. I still haven't figured out what to put on top. I
started with the idea of using a surplus carbon steel tank from some oil
company, but they were not very tall. My tank still needs to be coated
inside to deal with corrosion. I may just get a PVC tank liner. Looking
back, I wish I'd taken the plunge and bought stainless steel, but they are
about $6k and I thought I could save some bucks. The sewer pipe cost about
$1200, but there was the extra expence of welding the seams, which took me
2 weeks.

BTW, the pressure at the bottom will be about 8 psi. Pumping losses are
mostly from pipe friction. The electricity used to run the pump(s?) will
not be wasted, as it will go into heating the water. My backup heating
system will use propane. Around here, propane at $2 per gallon costs more
per BTU than electricity at $0.08 per kWh.

 

[News]

snipped

Zome Works in New Mexico especially the bead window
Trumbal wall (spelling?)
Best of luck I have friends in Iowa that tried some thing similar to this. I
helped rip it out after the first winter. Worked ok in the day time. Brought
in cold air at night.

That's a bit drastic. How about installing insulated dampers to close it
off? Must be cheaper and a control system may have made it work properly.

 

[News]

exactly! with no power to run fans, having some means of manually adjusting
the heat transfer into the living area is a Good Thing. (IMHO).

Gunnar.

The problem with a passive solar house is that you live in the heat
generator, which may be uncomfortable. Storing solar gained heat and then
directing that heat to the living areas is better for comfort levels. This
design dose that and simply too.

 

[News]

Hi Nick,

I see you are still at it. Did you ever build your sunspace house?

I'm finishing mine up now (finally!). I hope to move in before Christmas,
if I can get past the last inspection. My south wall house has a 5500 gal
water tank in the middle that's 19 feet high. There won't be any big
temperature swings, if I can get it all to work as planned.

Do you have a web site, or a house description?

 

[David Delaney]

100 lb of stone per square foot of ceiling area (490 kg/m2)
about 100 square meters area of stones? (wild guess here)

In this particular example 1100 ft2, 102 m2

Total weight 49000kg = 49 tons. Wow, not too good for earth quake prone
areas I guess.

It "just" costs money for an appropriate structural design.

Why not use water as energy storage _under_ the house?

More fan power for charging. More complicated control required.
Dampers required. I want a brutally simple system with minimal
maintenance.

 

[News]

Ah yes...

Warm air rises. Why would it want to flow under the floor? Lots of warm
air needs to touch Lots of thermal mass surface to raise the slab temp
on a sunny day without overheating the house and ensure a low day/night
temperature swing. During a cloudy week, such a house gets exponentially
colder and colder, without woodstoves and so on.

Moving most of the solar glazing to a low-thermal-mass sunspace (one
that gets cool overnight and stays cool during a cloudy week) with an
insulated wall between the living space and the sunspace allows the same
or more solar gain when warm air flows between the sunspace and the house
during the day, but reduces the nighttime and cloudy-day heat loss from
the living space...

Dr. Rich Komp (author of Practical Photovoltaics and president of the
Maine Solar Energy Association) says warm hollow floors like his
(which predates Kachadorian's) aren't new. Romans built hypocausts,
hollow floors heated with warm air from hot water or fires. So did
Chinese peasants. Warm hollow floors make good homes for dust and
varmints. Rich's friend Ernie the Ermine takes care of that problem.

Living inside the heat battery, we are subject to its temperature swings,
and if there are no temperature swings, there is no solar heat storage.

We can't charge the slab up to a high temperature because we have to
live with it in the room. The same amount of thermal mass at a higher
temperature stores more useful heat than lower temp mass, and it allows
keeping a constant room temp until the mass cools to something close to
that room temperature.

Floor slabs don't usually have much insulation between themselves and
the room air, and they are difficult to insulate because of their shape.
The same amount of insulation applied to a cube with equivalent mass
lowers the rate of heatflow a lot more.

And water stores about 3X more heat than masonry by volume. It can also
be cheaper and more useful, even in sealed containers.

K's slab uses a fan. It might make more than a 40% heating fraction, with
lots of airflow and slab channels (ie heat transfer surface) and a carpet
on top of some foamboard over the slab and a low thermal mass sunspace with
separate 100 F air ducts between the sunspace and the slab and lots of house
insulation, eg 12" R48 SIPs.

Then again, we might make the house walls hollow block with the holes
lined up so air can naturally flow vertically through the walls, with
lots of insulation (eg Dri-Vit) outside the block.

But either way, we have lots of inaccessible nooks and crannies to attract
dust and spiders and varmints.

Storing heat for 5 cloudy 30 F days in a house that cools from 75 to 65 F
means 65=30+(75-30)exp(-120h/RC), so RC = -120/ln((65-30)/(75-30)) = 477 h.
A 48'x48'x8' house with an 8" 25 Btu/F-ft^3 slab with C = 48x48x8/12x25
= 38.4K Btu/F needs a max thermal conductance G = 38.4K/477 = 80.5 Btu/h-F,
or 57.5 for 3748 ft^2 of R65 walls and ceiling, after subtracting 4% of
the floorspace as R4 windows, with no air leaks or internal heat gain.
Sounds Herculean...

Making the house 32x32x16' tall with a 17K Btu/F slab and 2048 ft^2 of
5 Btu/F-ft^2 block walls makes C = 27.2K Btu/h-F, so G = 27.2K/477 = 57,
or 36.5 for 2990 ft^2 of R82 walls, with no air leaks. More Herculean.

K's book has lots of whopping mistakes. For instance, he thinks a house
needs 2/3 ACH for health, 27X more than the 0.025 ACH Swedish standard
and 83X more than the Canadian IDEAS standard.

Page 17 says "As you can see, the reduction in solar benefit increases
exponentially as you rotate the home's orientation away from true south."

Page 30 says

If this combination of poured concrete slab over horizontally laid blocks
is ventilated by air holes along the north and south walls, air will
naturally circulate through this concrete radiator when the sun is out...
the south wall will be warmer than the north wall... air that is next to
or alongside the south wall will rise. Warmed air will then be pulled out
of the ventilated slab, and the cooler air along the north wall will drop
into the holes along the north wall. This thermosiphoning effect will
naturally continue to pull air through the Solar Slab.

Are you saying this would not promote circulation through the south wall,
floor and north wall?

Page 49 says "Incorporate an air lock entrance" with miniscule energy savings
except for a department store, or a house with a huge active family.

Page 53 describes "reflective" foil smack up against plywood

The interior foil face will reflect heat back into the room, even though
it is sealed inside the thermo-shutter... The outside foil face of the
insulation contained within the wood veneers will reflect the sun's summer
heat back out the window.

Page 94 belies the natural air circulation described on page 30

The duct shown running down the middle of the bgase under the poured slab
is included in all cases. It should always be used as the return-air duct:
do not reverse the air flow pattrern shown on the control diagrams. By
using the Solar Slab as part of the return-air duct system, the Solar Slab
will constantly assist the furnace by preheating the return air. Even if
the home will be heated with a woodstove and emergency electric furnace,
the return duct should be included and the air mover hooked up per the
appropriate control diagram...

Using the hollow floors as a return air duct will sue purchased heat to
charge up the floor. Not what you ant. Although using dampers and controls
can eliminate that.