poor man's trombe wall
vmpo...@gmail.com
Hi,
I am interested in passive solar. I am a renter. I have approx 7 m^2
of south-facing windows in one room. My location is the cloudy
pacific northwest USA, approx 47.5 degrees north latitude. I am
thinking of conducting an experiment by putting some landscaping
blocks, painted black, near the window. Obviously I am not going to
go all out here, just a few hundred pounds worth. I know this is not
the same thing as a trombe wall because it will not be large enough to
have convective airflow, but there are the same basic concepts at
work. I will take unscientific measurements with an IR thermometer to
see how long the blocks retain their heat in the evening.
Will this have any effect at all or should I find something else to
waste my time on?
Thanks,
Viktor.
Morris Dovey
It will have /some/ effect - but what effect and how much is difficult
to predict from here. :-)
The only you'll ever find out is to give your idea a try and take the
measurements. Good karma accrues to those who try their ideas and share
the results with others.
Don't forget to take a few photos so we can see...
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
vmpo...@gmail.com
Morris thank you. I can start with one block and just see how it
goes, does it get above and remain above ambient temp on a typical
cloudy day and if so how much. With the IR thermometer I can
determine this. The heat capacity of concrete is listed as 0.88
joule g^-1 deg. C^-1 by wikipedia. Let's say a 40 kg block, about as
heavy as I care to pick up and move around unassisted. 35.2 kJ/deg.
C. per block.
Let's pick 2 deg C for the block's temperature above ambient after a
sunny day. I don't know if this is realistic or not, I'll find out. .
074 MJ/day/block.
At my current gas rate of $1.03/MJ and let's say $10 per block ($142/
MJ/day), payback is 138 sunny heating season days. This does not
include amortization of fixed costs for the furnace, etc.
If I were building my own place I would design to make maximum use of
passive solar. I think that by working with the forces of nature
instead of in opposition there is savings to be had, whatever one's
political position on environmental questions. But for now I am a
tenant in an over-inflated housing market. So I adapt and do things
on a small scale to learn.
Viktor
Morris Dovey
> Morris thank you. I can start with one block and just see how it
> goes, does it get above and remain above ambient temp on a typical
> cloudy day and if so how much.
Well, one block is a start. If you're going to paint the sunward face
flat black, I'll suggest Rustoleum flat black aerosol paint. It's
available at most hardware stores and works better than the same paint
in a can. Use just enough to completely blacken the concrete - I've
found that too much paint can work as insulation...
...and for the sake of interest, you might buy two blocks and leave one
unpainted as a control.
I suggest putting your blocks on something that'll insulate them from
the floor so that your results aren't skewed by heat flowing to/from the
floor.
<snip>
> If I were building my own place I would design to make maximum use of
> passive solar. I think that by working with the forces of nature
> instead of in opposition there is savings to be had, whatever one's
> political position on environmental questions. But for now I am a
> tenant in an over-inflated housing market. So I adapt and do things
> on a small scale to learn.
Sounds like a good plan to me. The experiment is simple, inexpensive,
and safe - and might provide a good learning experience.
Malcolm "Mal" Reynolds
@news.qwest.net:
If you are the curious type, you might try a 5 gallon bucket of water.
nicks...@ece.villanova.edu
>I am interested in passive solar. I am a renter. I have approx 7 m^2
>of south-facing windows in one room.
... 75 ft^2.
>... I am thinking of conducting an experiment by putting some landscaping
>blocks, painted black, near the window.
They might store overnight heat. Does the room get very cold by morning,
after an average day?
>I know this is not the same thing as a trombe wall because it will not be
>large enough to have convective airflow, but there are the same basic
>concepts at work.
Inefficient ones. Trombe walls lose lots of heat back through the glazing
at night.
>Will this have any effect at all or should I find something else to
>waste my time on?
It might be more interesting to turn some of the windows into air heaters
that lose little heat at night by pushing in a tight-fitting piece of dark-
painted foil-foamboard insulation with an air gap at the top.
Or make a "heat storage counter" a 4'x2'x30" tall box with insulation on
4 sides and a 4'x30" glazed south wall (eg discarded windows) south of
a light-colored floor with lots of 2-liter water or soda bottles inside
the box stacked in a horizontal hexagonal pattern.
Water can store 2-3X more heat by volume than masonry (about 4.4 Btu/F for
a 4" diam x 1' tall 2-liter bottle, vs 5 Btu/F for an 8"x8"x16" hollow
concrete block), and glazing can make the box warmer than the room temp,
so the water can store more heat.
In December in Seattle, 420 Btu/ft^2 of sun hits a south wall. If a window
passes 80% of that and each of N layers of box glazing passes 90% of that
and adds R1 to the box and 336x0.9^N = 24h(T-70)1ft^2/N, with lots of water
in a 70 F room, the box temp T = 70+14N0.9^N on an average day, eg 82.6,
92.7, 100.6, and 106.7 F with N = 1 to 4 layers of glazing.
Nick
RicodJour
Jeff
> Hi,
>
> I am interested in passive solar. I am a renter. I have approx 7 m^2
> of south-facing windows in one room. My location is the cloudy
> pacific northwest USA, approx 47.5 degrees north latitude. I am
> thinking of conducting an experiment by putting some landscaping
> blocks, painted black, near the window. Obviously I am not going to
> go all out here, just a few hundred pounds worth.
This looks like adding mass to even out temperature swings. You will
have the same amount of solar gain with or without.
333.3 lbs at .3BTU/lb = 100BTU/F or 2K BTUs for 20F.
Not much.
Now lets look at 60SF of R1 glazing at say 40F temp change inside to
outside. That's 2400 BTU/hr, 28K overnight. 14K for R2 glazing.
The best thing you can do is minimize loss through the windows.
Jeff
David Williams
to the amount of solar energy coming in through the windows. It *may*
make a difference to the amount that's reflected out again, if the
blocks are black and the other stuff in the room is light coloured. And
it *will* make a difference to the heat capacity of the room, making it
get less hot in the daytime and less cold at night. If you pay to cool
the room in the daytime and to heat it at night, obviously this will
save you money. But if you're paying to heat it day and night, then the
net effect may be close to zero.
As Morris said, the only way to find out is to try it and see.
dow
Bob F
<vmpo...@gmail.com> wrote in message
news:8cb951f7-2d4d-479f...@z11g2000prl.googlegroups.com...
I open my shades during sunny days in Seattle, and the room does warm
significantly. It does not get hot, however, so I doubt if there would be
sufficient excess energy to store heat from the day for the night. Maybe, if you
have lots of south facing windows.
vmpo...@gmail.com
> It might be more interesting to turn some of the windows into air heaters
> that lose little heat at night by pushing in a tight-fitting piece of dark-
> painted foil-foamboard insulation with an air gap at the top.
I like this idea better. Cheap, simple, one-trip-to-the-store type of
project and no heavy lifting required. Would I put holes or air gap at
both the top and bottom to get some convection ailflow going (I think
I have seen this called a 'thermal siphon'). Thank you for this idea.
> Or make a "heat storage counter" a 4'x2'x30" tall box with insulation on
> 4 sides and a 4'x30" glazed south wall (eg discarded windows) south of
> a light-colored floor with lots of 2-liter water or soda bottles inside
> the box stacked in a horizontal hexagonal pattern.
>
> Water can store 2-3X more heat by volume than masonry (about 4.4 Btu/F for
> a 4" diam x 1' tall 2-liter bottle, vs 5 Btu/F for an 8"x8"x16" hollow
> concrete block), and glazing can make the box warmer than the room temp,
> so the water can store more heat.
This is suprising to me. Hollow cinder blocks I can believe, but how
about a solid block? Of course there I suspect the issue is the whole
block never reaches temperature.
nicks...@ece.villanova.edu
>> It might be more interesting to turn some of the windows into air heaters
>> that lose little heat at night by pushing in a tight-fitting piece of dark-
>> painted foil-foamboard insulation with an air gap at the top.
>
> ... Would I put holes or air gap at both the top and bottom to get some
> convection ailflow going
A 3' tall window might have a 3" gap between the foamboard and the window,
with a slot at the top but no slot at the bottom, so warm air can rise out
of the top slot during the day, with no airflow at night. With more thought,
we can make a foamboard insert with a flow organizer at the top that lets
cool room air flow down between a screen and the cool glass and lets solar-
warmed air rise up and out in another gap north of the screen.
>> Or make a "heat storage counter" a 4'x2'x30" tall box with insulation on
>> 4 sides and a 4'x30" glazed south wall (eg discarded windows) south of
>> a light-colored floor with lots of 2-liter water or soda bottles inside
>> the box stacked in a horizontal hexagonal pattern.
We might let room air flow through the box on a cool day. This could work
well with phase-change materials.
>> Water can store 2-3X more heat by volume than masonry (about 4.4 Btu/F for
>> a 4" diam x 1' tall 2-liter bottle, vs 5 Btu/F for an 8"x8"x16" hollow
>> concrete block), and glazing can make the box warmer than the room temp,
>> so the water can store more heat.
>
>This is suprising to me. Hollow cinder blocks I can believe, but how
>about a solid block?
Concrete stores about 25 Btu/F-ft^3, so 8x8x16" would store about 15 Btu/F.
Nick