Subject: Concrete slab

From: "Steve Sency" <[email-masked]>
Date: Thu, 15 Feb 2001 10:18:44 -0700

Hi,
I am considering a double glazed solarium that would be attached to my
house.  It would be 10ft. wide and 37ft. long.  That would give me a floor
surface of 370 sq. ft.  The floor would be concrete 6" thick.  It would be
insulated from the ground.  I thought maybe I could put tubing in the floor
and circulate the water through a radiant floor system in part of the house.

My questions are, will the concrete slab get hot enough to be effective for
radiant heat or would that just be a waste of money?  Are there any
calculations I can do to find out how hot the slab would get on any sunny
day?  I live in SW Colorado, we get about 300 days of sun here, the solarium
faces south.

Steve Sency

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From: "Jerry Ellinghuysen" <[email-masked]>
Date: Fri, 16 Feb 2001 20:02:20 GMT

I'd recommend taking a look at "The Passive Solar House" by Kachadorian,
James. What you describe is basically his plan, except that he puts the
concrete bed down on concrete blocks laid so that the "holes" or cores form
a heat transfer path as a means of distributing heat. Maybe not as efficient
as his plan, but living in the land of the Hanta virus, I'd think I'd
sacrifice a little efficiency for peace of mind (I've laid awake many a
night trying to mitigate the "breeding zone" this would create, but just
can't get comfortable with it).

Anyway, that aside, there's alot of good concepts and ideas along with a
great many worksheets for calculations that may not be EXACTLY your
situation, but ought to be a good approximation. Sounds like a great idea.
In the end, the ability to close things up at night might be your most
important design consideration.

I got my book at Barnes and Noble for ~$25, but I would suspect you could
get it through Amazon.com.
"Steve Sency" <[email-masked]> wrote in message
news:[email-masked]...

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From: "TyrannyOfGovt" <[email-masked]>
Date: Sat, 17 Feb 2001 08:11:25 -0700

I lived in South Korea for 13 months while in the Air Force. I had a little
one room apartment downtown that had the heated floor (just like everyone
there)
Before I moved in they installed the heated floor system while I hung out
and watched. First they laid out the gravel then topped it off with the wire
grid reinforcement. The tubing they used for water circulation appeared to
be 1/2 " vinyl hose like you can get from Home Depot for 25 cents a foot.
They laid out the hose in a back and forth manner with about 5" of space
between each run. They then used common nylon zip ties to anchor the hose to
the wire grid.
When they poured the cement the hose pattern was about 2" below the finished
surface.
The system was heated by what the called Ondoll. Ondoll is a 5 pound coffee
can size chunk of charcoal. The Ondoll was placed in a small cylindrical
furnace outdoors. The furnace had a water jacket about 3 inches thick
surrounding the Ondoll burning area.

The system worked great, so great the floor got pretty darn hot at times.
The system is good for sleeping on the floor but did a poor job in heating
the room. Many cold winter nights the floor would be an easy 110+ degrees
(F) with a room temp of near 40 degrees. But, in Korea most people slept on
the floor so room temp wasn't as important as floor temp.

.

--
Xabjyrqtr vf Cbjre

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From: [email-masked] (Nick Pine)
Date: 19 Feb 2001 16:25:23 -0500

>Hi,

Hi Steve,

>I am considering a double glazed solarium...

R4 glass with 50% solar transmission?

>...It would be 10ft. wide and 37ft. long.

And 8' tall, with glazed sides, and good roof insulation,
and thermal conductance G = 456ft^2/R4 = 114 Btu/h-F?

>The floor would be concrete 6" thick...

With about 10x37x0.5x25 = 4625 Btu/F of thermal mass...

>...will the concrete slab get hot enough to be effective for radiant heat
>or would that just be a waste of money?

It may be a waste of money, compared to covering it with dark carpet or
hanging 80% shadecloth inside the glazing and collecting hot air during
the day. Low-thermal-mass sunspaces can be more efficient housewarmers
than massy ones, since they can get warmer during the day and lose less
heat at night. 

>Are there any calculations I can do to find out how hot the slab would get
>on any sunny day?

You might calculate how warm it would get on an average day, with an
average amount of sun...

>I live in SW Colorado... the solarium faces south.

January is the worst-case month for solar house heating in Alamosa, with
a 14.7 F 24 hour average outdoor temp and an average daily max of 33.3 F,
and 1720 Btu/ft^2 of sun that falls on a south wall on an average day.
East and west walls get 680 and 690, and a horizontal surface gets 950.

Say the slab has temp Tn at dawn and Td at dusk, and the solarium glazing
collects 0.5x8'(16x685+37x1720) = 298K Btu of sun over 6 hours on an average
day. Say it all ends up in the slab. (How would you arrange that, since
the sun only rises to 90-23.5-37.45 = 29 degrees on 12/21? Maybe this slab
should be a wall...)

          --------www--------*--- Ts = Tn at dawn and Td at dusk
         |       1/114       |
         |                   |
       -----  T(t)          --- 4625 Btu/F 
        ---                 ---
         |                   |
         _                   _

Ts = 14.7+298K/6h/114 = 451 F during the day and 14.7 at night, and
RC = 4625/114 = 41 h and Td = Tn+(451-Tn)(1-exp(-6/41) = 0.864Tn+61.4
and Tn = 14.7+(Td-14.7)exp(-18/41) = 0.644(0.864Tn+61.4-14.7)+5.2, so
Tn = 79.6 F and Td = 130.2.

If the hydronics cooled it to say, 80 F over an average day, the solarium
would lose about 6h(80-14.7)114 = 44.7K Btu during the day, and the slab
would cool to 14.7+(80-14.7)exp(-18/41) = 56.8 by dawn. Reheating it to
80 F would require 4625(80-56.8) = 107.3K, so the house would gain about
298K-44.7K-107.3K = 146K Btu/day, with a 24% solar collection efficiency.

This would work better with less concrete. With none, the solarium could
provide 298K-44.7K = 253K Btu of warm air for the house, with 42% solar
collection efficiency, and you might replace the R4 windows with cheaper
R2 windows with 80% transmission to raise the solar input to 478K Btu/day
while raising the solarium loss to 6h(80-14.7)228 = 89.3K, for a net gain
of 388K Btu/day, with 65% efficiency, or more, if you redo these calcs
using a (14.7+33.3)/2 = 24 F outdoor temp during the warmest part of
an average day.

Nick

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From: "Bill Kreamer" <[email-masked]>
Date: Tue, 20 Feb 2001 12:40:32 -0500

Nick,

Could I prevail on you to do either a numerical or a features/benefits
comparison of sunspaces and active heating collectors?

Near the end of the analysis below, your thinking seems to be trending
toward recommending the characteristics of an active air-heating collector
over those of a sunspace.  It has the least mass (lowest thermal capacity),
the quickest response to changing conditions (quickest turnover to the
heated space), the least loss at night, and the least expense.

Unless one saw a specific secondary benefit to "living inside the solar
collector" (there could be some), why would one choose to build a sunspace?
I have a unambiguous opinion, of course - our SHVC (Solar
Heating/Ventilation Cooling) solar system is 72% efficient, and never causes
discomfort (it ventilates in warm weather).

Thanks, as always, for your clear information, humor, and generosity - Bill

Bill Kreamer, President
Sol-Air Co.
129 Miller St.
Belfast, Maine, U.S.A. 04915

tel  207-338-9513
fax  603-853-9339
mailto:[email-masked]

"Nick Pine" <[email-masked]> wrote in message
news:[email-masked]...

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From: [email-masked] (Nick Pine)
Date: 21 Feb 2001 12:40:18 -0500

>comparison of sunspaces and active heating collectors?

Sure.

>over those of a sunspace.

Oh?

>It has the least mass (lowest thermal capacity), the quickest response
>to changing conditions (quickest turnover to the heated space), the
>least loss at night, and the least expense.

I wouldn't say "least expense." Serving more than one purpose can change
the economics, even with sunspaces that cost more than mine...

>collector" (there could be some), why would one choose to build a sunspace?

Sunspaces can thermosyphon better than panels, with more height and depth
and less air velocity near the cold glazing... I have some dark shadecloth
hanging near the north wall of my sunspace to keep warmer air closer to
the house... My cat enjoys it...

I don't do much living inside my sunspace, but I store some stuff there
and I sometimes work in there, since it has lots of light and a 16' ceiling.
It can also be a nice place to read on a sunny afternoon, and I could grow 
things there if I wanted to. My sunspace is half of a gothic-arch commercial
plastic film greenhouse turned on the side, with the straight parts of the
bows supported by ground stakes (the "foundation" and the curved ends hinged
to the house under the soffit. It's 32' long x 12' deep x 16' tall, and the
parts cost about $500. It's cheap "living space," at $1.30/ft^2 :-)

It has an oak floor--shredded wood playground mulch over black plastic film. 

Our BOCA-township building inspector gave me a ($150 :-) permit to build
this thing, and classified it as "HVAC space," which doesn't raise real-
estate taxes. It looks a bit strange, facing the road 100' away, but so far
none of my neighbors have threatened to kill me. (I also have a couple of
100' greenhouses and a 6-ton pile of Unistrut on my front lawn.)

I sometimes wish I'd covered it with $1.50/ft^2 20 year clear Replex
polycarbonate vs 5 cent/ft^2 4-year cloudy greenhouse polyethylene film,
but the polycarbonate only comes in 4' widths (vs greenhouse poly in
folded rolls up to 40' wide and 100' long :-), so it would need attaching
to every curved metal pipe bow, and I have 300 more neighbors now than
a couple of years ago, so the privacy isn't unwelcome. Then again, it would
be nice to be able to see clearly out of the south windows of my house... 
Most people wouldn't want to obscure their house window views with cloudy
film. Clear plastic might raise the cost of a sunspace to $5/ft^2. 

>I have a unambiguous opinion, of course -

Of course :-)

>our SHVC (Solar Heating/Ventilation Cooling) solar system is 72% efficient,
>and never causes discomfort (it ventilates in warm weather).

Norman Saunders used to say "Sunspaces are always too hot or too cold."
Mine tends to overheat in summertime, even with 80% shadecloth over the
outside and a 6" slot at the top that vents into my solar attic, which
has 2 turbine vents and 4 small windows, open in summertime. (The south
roof of the attic is covered with corrugated polycarbonate, at a 45 degree
pitch, with serious summer overheating. I've measured 143 F up there.) 

Honestly speaking, my gut feeling about factory-built air heating panels
is that they are very expensive, and people often buy them in 1s and 2s
as toys, vs trying to heat a whole house that way. I reviewed one design
(Wolfe?) that appeared to consume more electrical energy than the solar
heat it collected :-) I realize yours works better, but it still seems
expensive. A new house might have economical corrugated polycarbonate
"solar siding." Then again, there's the big problem of storing heat from
hot air overnight, and for a few cloudy days in a row. Not everyone lives
in a supermarket full of canned goods on shelves.

>> ...you might replace the R4 windows with cheaper R2 windows with 80%
>> transmission to raise the solar input to 478K Btu/day while raising
>> the solarium loss to 6h(80-14.7)228 = 89.3K, for a net gain of 388K
>> Btu/day, with 65% efficiency, or more, if you redo these calcs using
>> a (14.7+33.3)/2 = 24 F outdoor temp during the warmest part of an
>> average day.

Let's try that... 478K-6h(80-24)228 = 401K Btu/day with 67% efficiency,
or about 800 Btu/dollar-day or 50 peak watts per dollar, using a plastic
film sunspace.

Nick