Subject: Re: A zero-fossil-fuel studio?

From: mnjheldt@I\interaccess.com (Julie Heldt)
Date: 10 Mar 1996 21:15:09 GMT

In article <[email-masked]>, [email-masked] says...
>
>Your comments using 55 gallon barrels under the floor intrigue me.

EPA may eventually nail you for latent chemicals from the barrels even if
you think they are clean.  Try buying 5 gal "Stinkers", bottles from your
local water bottling company that the water company doesn't feel meet
their cosmetic requirements for use with customers.  They are small and
could save you from unnecessarily digging up your house.

---

From: [email-masked] (Nick Pine)
Date: 12 Mar 1996 07:26:35 -0500

Mike Youso  <[email-masked]> wrote:

>A major concern with any thermal storage system is the moisture from 
>condensation on the surface of the thermal storage modules if a remote 
>storage bank is used.

I agree this is a good thing to avoid. I don't see a problem with moisture
condensing on these containers of water while the containers are heating
the house on a cloudy day, do you? Would moisture condense on the containers
of water as they are being heated by sun-warmed air? Perhaps, if the air is
moist. But the air should be fairly dry in the winter, if the house is
reasonably-well ventilated and the sun heats it up. Do you think condensation
will occur in this system, or are you just saying it's a concern? If so,
I wonder under what conditions might it occur, and how might we avoid it?

>If the storage bank gets much above 60% rh some rather nasty organisms
>will be growing in the air supply system with possibly serious considerations
>for IAQ. 

I wonder how the humidity would increase to 60%? It seems that, say, 32 F air
at 100% relative humidity will have a much lower RH at 68 F, and on an average
day in December, this solar closet should be about 130 F inside.

>The most succesful thermal storage uses direct-gain solar mass walls
>rather than ducting warm moist air to a storage bank.

Again, where does the moist air come from? During charging, the air in a
solar closet is completely self-contained. There is no mixing with house air...

And when you mention "successful" direct gain solar mass walls do you mean
Trombe walls? 

A few years ago, I spent some time explaining to a local architect, a more
technical person than most, who had taken a few engineering courses on the
way to architecting, that a "Trombe wall" with some dark-colored insulation
on the outside and an air gap between the insulation and glazing and some
to the inside of the house that opened up during the day was a lot more
efficient at collecting and keeping solar heat in the house than a plain old
"traditional" Trombe wall, with masonry right behind the glass, with no
insulation. Here's what I said:

  A modified "Trombe wall" with insulation on the outside, and 1 ft^2 of south-
  facing single-glazed area and an R-value of 20, will receive about 1000
  Btu/day of heat on an average 32F December day, where I live. If the room
  behind it has a constant temp of 70F, and the sun shines 6 hours a day,
  on the average, the energy that leaks out of the glass will be about 6 hours
  x (70F-32F) x 1 ft^2/R1 = 228 Btu during the day, and 18 hours x (70-32) x
  1 ft^2/R20 = 34 Btu at night, a net gain of 1000 -228 -34 = 738 Btu/day.
  Simple, no? (~750 Btu, net, with double glazing, which passes less sun.)

  A standard unvented Trombe wall (Table IV-14b of Mazria's book says vented
  ones don't work much better) with a very large uninsulated thermal mass
  right behind the glass and an R-value of, say 2 (roughly 1' of masonry),
  would have an average temperature at the outside wall surface of about
  32F + R1 x (70F-32F)/(R2+R1) = 45F, if there were no sun. If you add a
  heatflow of 1000 Btu/day of sun to that model, falling on the outside
  of the wall, the outside wall surface will have an average temperature
  of about 45F + 1000/24 x (R=2/3) = 72.4F, which contributes 24 hours x
  (72.4F- 70F) x 1 ft^2/R2 = 29 Btu/day to the room behind the wall.

  So the "improved Trombe wall" above, (actually an air heater with the
  thermal storage inside the house) is _more than 25 times as efficient_
  (738/29) at collecting and keeping heat in the room behind it, than
  the usual Trombe wall. This is a bit oversimplified...

Trombe walls are also thermal disasters during long strings of cloudy days.
When the sun goes in for a week or two, they lose their stored heat in less
than a day, and then leak house heat badly, dramatically raising backup
heat or other solar thermal storage requirements.

>Two or three layers of drywall is a good compromise since only the first
>1.5" to 2" is diurnally active.

Seems to me that a few "accent drums" full of water sprinkled around
the house might be cheaper...
 
>a zero fossil fuel studio is quite feasible almost anywhere south of the 
>arctic circle.

We seem to agree on that :-)

Nick

---

From: eteam <[email-masked]>
Date: Tue, 12 Mar 1996 15:25:44 +0000

In article <[email-masked]>, Nick Pine <nick@vu-
vlsi.ee.vill.edu> writes

-- 
eteam

This modified Trombe wall sounds interesting however could you clarify the
constuction as we are still  a bit confused. i.e. is the dark insulation
exterior or merley outside a wall sandwiched between glass. Put another way,
does it go : outside / glass / dark insulation / wall / interior ?  If so , how
does the heat transfer through the dark insulation ?

Chris & Scot ---  The eteam

---

From: Mike Youso <[email-masked]>
Date: 12 Mar 1996 00:54:26 GMT

A major concern with any thermal storage system is the moisture from 
condensation on the surface of the thermal storage modules if a remote 
storage bank is used.  If the storage bank gets much above 60% rh some 
rather nasty organisims will be growing in the air supply system with 
possibly serious considerations for IAQ.  The most succesful thermal 
storage uses direct-gain solar mass walls rather than ducting warm moist 
air to a storage bank.  Water modules work well in the lower 48, and 
gypsum board is better than masonry.  Two or three layers of drywall is a 
good compromise since only the first 1.5" to 2" is diurnally active.

*

---

From: [email-masked] (Nick Pine)
Date: 13 Mar 1996 18:00:55 -0500

eteam  <[email-masked]> wrote:

>>... a "Trombe wall" with some dark-colored insulation
>>holes to the inside of the house that opened up during the day was a lot more
>>insulation...
 
>exterior or merley outside a wall sandwiched between glass.

The insulation is north of an air gap under the glass.
I guess this was not very clear.

>Put another way,
>does it go : outside / glass / dark insulation / wall / interior ?
                              ^
                              |
              Almost...        air gap
                              
>If so , how does the heat transfer through the dark insulation ?

The sun warms the air in the low-thermal-mass air gap, and the warm air moves
up and through a hole in the top of the insulation and wall into the house,
then back out of the house into the air gap through a hole in the bottom of
the wall and insulation during the day, circulating between the house and the
air gap. At night, a one-way plastic film damper covering the top hole or the
bottom hole or both, closes to prevent reverse air flow and cooling, and the
air gap quickly gets cold and stays cold all night, losing no heat to the
outside world, except what flows through the rest of the insulated wall. The
two holes might be equal sized, each 5% of the wall area, if this operates by
natural convection, or they might have less area if what moves the air is a
fan in series with a cooling thermostat in the air gap and a heating thermostat in the house. 

Nick

PS: The airflow by natural convection is on the order of 

    Q = 16.6  x Av   x  square root ((Tairgap - Thouse) x h)

    cfm    ft^2 of each hole          degrees F      wall height in feet.