Subject: Meanwhile, in Oklahoma...

From: [email-masked] (Nick Pine)
Date: 11 Oct 1996 11:54:51 -0400

>I am building a house and plan to have a solar closet and sunspace as
>you describe except that the solar closet will be in the sunspace instead of
>in the house.

There would be more heat loss from the closet that way at night to the
low-thermal-mass sunspace, when the sunspace gets cold, than if 5 walls
of the closet were inside the warmer house at night, with only the south
wall exposed to the sunspace, but it seems to me that the sunspace can be
a less-expensive space than the 24 hour living space of the house, and
you can just use a little more insulation in the solar closet walls...

For instance, the sunspace might be a plastic film greenhouse costing less
than a dollar per square foot, with a pebble floor over some plastic film as
a vapor barrier, and the solar closet walls might be strawbales. So, that
makes sense to me.. Why waste $75/ft^2 house living space for a solar closet
if it can live "outdoors" in a $5/ft^2 sunspace?

I'm planning to put the solar closet inside the sunspace in our youth
hostel project, vs extending the living space. If we put it inside the
existing 10x12' structure, there would be a lot less living space.

We may end up with something that looks like this

                       -------------
  south               |    |        |
                      | ss |existing|
                      | ---|  shed  | 12'
                      || DD|        |
                      || DD|        |
                      || DD|        |
                      | ---|        |
                       ---- --------
                         8'    10'

                         ^
			 |
			 new 8'x12' sunspace, with 2 layers of 6 drums,
surrounded by 6" of fiberglass insulation... (We would need fewer drums
without the recent architectural additions of 72 ft^2 of single pane windows
and sliding doors, and 12 ft^2 of single pane skylight, but hey, who wants
to live in a refrigerator.)

I wonder about shading within the sunspace... if your house and solar
closet and sunspace look like this

                            -----------------
                           |                 |
                           |                 |
                           |                 |
                       ----|                 |
                      |    |                 |
                      |    |                 |
  south               |    |                 |
                      | ss |                 |
                      |    |---              |
                      |    |   |             |
                      |    | sc|             |
                      |    |   |             |
                       ---- -----------------

  and the
  sun is
  over here,

then the solar closet does not shade the sunspace, but

if your house and solar closet and sunspace look like this

                            -----------------
                           |                 |
                           |                 |
                           |                 |
                       ----|                 |
                      |    |                 |
  south               |    |                 |
                      |    |                 |
                      | ss |                 |
                      | ---|                 |
                      ||   |                 |
                      ||sc |                 |
                      | ---|                 |
                       ---- -----------------

  and the
  sun is
  over here,

it seems to me we have less sun falling into the sunspace, ie the NW corner
of the solar closet is in shade. Am I confused about this? Probably :-)
The sunspace receives the same amount of sun through the glazing in either
case, right? So who cares what the internal shade patterns are? It receives
the same amount of daily solar energy in either case. If I keep writing that,
I may end up believing it.

>I plan to have a gas or electric water heater upstairs above the closet in a
>system as you described. I have a couple of  details that I hope you will
>help me with.

OK. I'll try.

>1. Since the solar closet will be used to heat domestic hot water the closet
>would need to be heated year round.

Right. But not exactly "heated." The solar closet glazing needs to be unshaded,
but the sunspace does not have to have a high temperature in the summer. The
solar closet will be happy in its normal winter environment, eg 70 F during
the day. It makes sense to keep the solar closet in the sunspace to help avoid
heating the house in the summer. (My old stone house has a "summer kitchen"
off the north side, which I use as a walk-in refrigerator/kitchen in winter.)
If the solar closet were inside the house, it would leak some heat into the
house, undesirably in summer.

>This seems to me to be a problem in my hot Oklahoma summers. Air conditioning
>is actually more of a concern in our hot humid climate than heating since
>I don't yet have a non-electric solution except to sweat :-).

I see your point. Perhaps you could use a fan. Or a heat sink. Or an unheated
waterbed? A swimming pool? A floating pool chair filled with water? A beanbag
filled with copper BBs, or Cryogel Iceballs? A cold water bottle worn inside 
your shirt, with some tubes to allow warmer water to flow up into your
double-walled convective pith helmet shaped cooler or clip-on hollow Martian
antennae? (Real Goods might carry these.) Wear fighter pilot pants inflated
with water instead of air? Use a tiny air conditioner to inflate your pants,
or a hemispherical hair dryer hat, raining a shower of cool dry air over your
body, after it passes through a sun-baked but now cooler dessicant cartridge?
(Why don't those hair dryers suck the warm air back into the heater at the
bottom of the helmet, instead of spraying it out into the room?) Live in the
basement? Lose a little weight to decrease your internal energy generation 
and increase your surface to volume ratio? Grow heat-conductive hair? Some
sort of rectal heat exchanger? Just a few suggestions :-)

>I've thought of one solution. To eliminate the need to heat the closet in
>the summer I could have a separate solar water heater that sits away from
>the house that would be used only in the summer.

That would work, but why have two? Moving heat any distance can be lossy
and/or expensive with insulated pipes, even as hot water.

You could vent the sunspace during the summer, without shading it...
Or even remove the sunspace glazing entirely, which might make it last
longer, if it were plastic film. The solar closet glazing is a smaller
area than the sunspace glazing (8x12', if you are making hot water?) so
maybe you could somehow shade part of the sunspace glazing by hanging some
shadecloth over it on the outside in the summer, without shading the smaller
solar closet glazing. Or put lots of insulation between the sunspace and
living space, so a warm sunspace won't heat up the house much. You can figure
this out with numbers, but I'd just use lots of natural ventilation in the
summer, maybe opening up the endwalls completely, floor to ceiling.

How about venting the sunspace to the outside, and unrolling a piece of
greenhouse shadecloth over the dark north sun-absorbing wall of the sunspace
during the summer, with an air gap between the shading and the house wall,
without covering the smaller solar closet glazing? That may be easier to do,
geometrically.

Come to think of it, this would make the sunspace more usable and a more
efficient solar collector in winter too, with cool house air flowing out into
the sunspace on a sunny day, so the sunspace is basically full of 70 F air,
which is then heated up to 100 F, maybe, as it passes from south to north
_through_ the shadecloth mesh absorber and back into the house. This is more
efficient and comfortable than having the entire sunspace filled with 100 F
air on a sunny winter day (we measured 157 F in our 2'x4'x8' tall outdoor
test structure sunspace last winter, and my 600 ft^2 solar attic was 125 F
a couple of days ago.) So maybe the shadecloth should be permanently hanging
a few inches away from the north wall of the sunspace, ie the wall between
the sunspace and house, except for the solar closet glazing. You might have
an umbrella over your picnic table in the sunspace, for shade...

This would also increase the solar collection efficiency of the sunspace
because some sun would pass through the shadecloth and heat up the wall
behind it, and the shadecloth would block reradiation. I wonder what the
optimum shadecloth density is. Allowing some sun to pass through it is
better than allowing none, or all of it. This arrangement would also
add the shadecloth area (both sides) to the sun-air heat transfer area,
decreasing the "absorber plate temperature" and reradiation loss.

                                              .
Like this, maybe:                           .  solar 
                                          .    attic?
					.. ..........
                                     .  >. . ==> 100 F air
                                   .    >.^.
                                  .     >.^.  house
                                 .  70 F>.^.
              reflecting pond?   .  air >. . <==  70 F air
....................................................................
                                         ^ dark shadecloth

Another thing: it seems to me that in hot humid places, it might be a good
idea to have some material that absorbs water vapor in the sunspace, eg
a vermiculite or zeolite or calcium chloride pebble or very thin reinforced
concrete floor, or a shallow polyethylene glycol pool or slow wet-wall
waterfall/fountain (PG can absorb 11x its weight in water.) We wouldn't want
too much thermal mass or and RC time constant much more than an hour or two
in the sunspace, but if we could vent the sunspace to the outside during the
day, and let the hygroscopic material, eg the floor, heat up and bake dry
in the sun, and then close the vents and let it cool off at night, and then
allow airflow between the house and the sunspace in the early AM before dawn,
we might be able to dehumidify the house this way.

Materials that do not change their chemistry when they absorb water heat up
the air as they do so, but Richard Komp says some materials which do change
their chemistry don't heat up the air as they absorb water, or they do,
but they cool off at the same time, so the net absorption reaction is not
exothermic.
 
>2. What diameter tube is typically used with the "fin tube" collector? You
>reference a fin tube base board heater. Would one or several of these work
>for the collector?

I'd use 3/4" baseboard. That's what Steve Baer uses in Big Fins, and they
seem to work fine by natural convection, as far as the water flow goes. 
Having to use a tiny pump would not be a disaster, in my book, but it seems
better to make the plumbing in the convection loop with few bends, and use
natural warmwater convection. If the fin tube is inside the solar closet,
up along the ceiling, you should not have to worry about freezing, but the
piping that connects through the sunspace to the water heater upstairs
might want to be insulated. 
 
>3.What about insulation under the floor of the house with a masonry floor?
>Do you feel it would be worth while? Seems to me that it would help in the
>winter but reduce the cooling effect in the summer.

Ground coupling could be an advantage. A cold source for better push-pull
house temp control, even in the winter, and a way to condense some water,
maybe, and heat sink, if you decide to build a closed cycle solar thermal
engine to make electricity with refrigerant gases or low boiling point
solutions of ethyl alcohol, hexane, etc, like those "hand boiler" toys :-)
A roof pond or reflecting pond might help cool the house in the summer,
in dry weather. 

>Your drawing shows it under the closet but not the house in your paper.

We didn't intend to show any floor details. 

Nick