Subject: Extremely simple solar thermal problems

From: [email-masked] (Nick Pine)
Date: 23 May 1996 19:20:29 -0400

William R Stewart  <[email-masked]> wrote:
>Nick Pine wrote;
: Here's a big hint: If a "solar house" has a heat loss of 150 Btu/hr-F and
: a thermal capacity of about 8,000 Btu/F, so RC = 8,000/150 = 53 hours, and
: the house starts out with an interior temperature of 68 F when it's -10 F
: outside, with no electric or wood heating, and no sun, the interior temp after
: a couple of days will be approximately - 10 + (68-(-10))exp(-48/53) = 31.5 F.

>If the solar house you describe does not have a direct gain thermal storage 
>capability, aside from room temperature walls and floors, then you could see 
>something like the above.

I see that _with_ your water walls...

>However, if one *does* have thermal storage, such as 4000 lbs of water walls
>that are heated by direct solar gain, then these will raise to a higher
>temperature that the ambient indoor temperature without raising the indoor
>temperature uncomfortably, and heat by convection and radiation.

R-values include convection and radiation.

>If they were only 10 degrees warmer, then the storage would be 40,000 Btus.

And on a 36 F day with no sun, your 66 F house will need about 24(66-36)150
= 108K Btu to keep itself warm. 216K Btu for 2 days, 324K for 3 days, etc...

>BTW, any passive solar homeowner without a backup heat source in an area
>of -10 F days is asking for cold times, indeed.

I disagree. References please...
You have my numbers, Will.
Where are your numbers?
 
>Masonry heaters are natural complements,
>as they are relatively efficient and are themselves thermal flywheels.

References please... Did you say you cared about air pollution? 

: Another slightly less accurate way to do this is to find the energy lost
: during the first hour, assuming the interior temperature is constant over
: the hour, find out how much the thermal mass has to cool to supply that
: heat loss, find the new interior temperature, find the energy lost in the
: second hour, and so on...

>Or learn calculus.

Or learn high school physics, and use arithmetic.

You have failed to answer my many numerical questions...

A couple of people have asked me,

"Who is Will Stewart,

and
WHY are you
arguing with him?"
 
Nick

---

From: William R Stewart <[email-masked]>
Date: Fri, 24 May 1996 22:23:34 -0400

[Followups set to alt.solar.thermal]

Nick Pine wrote:
> 
> >BTW, any passive solar homeowner without a backup heat source in an cloudy
> >area of -10 F days is asking for cold times, indeed.

> I disagree. 

As is your right.

> References please...

Talk to a mechanical engineer, physicist, HVAC professional or a person 
who is living in a *passive* solar house under those conditions.

> You have my numbers, Will.

I've posted them earlier this week and you've already forgotten?
Don't forget you were going to revisit the multiple mistakes you had
made in your calculations.
 
> References please... 

I'm sorry, I assumed that you knew about Masonry heaters.
Reference: 

> Did you say you cared about air pollution?

Let me get this straight; You're the one consuming 700 kWh per month 
and you're acting holier-than-thou?

Heater Type	Particulate Emissions
		    g per kg

Open Fireplace      17.3

Masonry Heaters      2.8

Reference:  Home Power Magazine, Feb/March 1996

> : second hour, and so on...

And avoid adding error on top of error, on top of...
 
> Or learn high school physics, and use arithmetic.

Natural logs are not a part of arithmetic.  And you should
have taken the hint when others confirmed that questions such
as yours require calculus.
 
> You have failed to answer my many numerical questions...

You have failed to provide truly coherent questions, much less
coherent calculations.  A little knowledge is a dangerous thing,
indeed.
 
> A couple of people have asked me,

A private citizen that does not pretend to be the avatar of
all energy knowledge.

> arguing with him?"

Some quotes from people who have mailed me about you;

    "As an aside, if Mr. Pine was an actual working engineer
     (one with clients and projects), I would doubt that
     he would have time to indulge in as many "discussions"."

    "I notice you got sucked into Nick's "black hole" as well.
     Nick thinks he's god with a capital g, and doesn't have the
     background to support his raves."

    "I wouldn't mind if he weren't so arrogant.  I'm beginning 
     to think he's really a kid, out to impress himself."

    "If you're like me, you'll probably either toy with him
     or killfile him."

You might reconsider your attitude towards others in the energy
field.

Cheers,

Will Stewart

---

From: William R Stewart <[email-masked]>
Date: Fri, 24 May 1996 22:24:48 -0400

[Followups set to alt.solar.thermal so as not to bore the rest
of the free world...]

Nick Pine wrote:
> : Here's a big hint: If a "solar house" has a heat loss of 150 Btu/hr-F

Assuming that you are alluding to my place, show me a 2250 ft^2 house with 
150 Btu/hr-F loss...

> : and

This would be fine for a house that undergoes these conditions.  My house is in 
an area that goes below 16 F exactly 1% of the time. (Reference: "Statistical
Abstract of the United States", 92nd edition, US Bureau of the Census)

I wouldn't have electricity off for a couple of days (will have photovoltaic panels
and battery storage).

I will have an energy efficient fireplace and will fire it up from time to time,
especially when extreme weather conditions occur. 

> I see that _with_ your water walls...

You push heaps of numbers around, but you fail to understand essential aspects
of thermodynamics.  It's no wonder you don't see...
 
> >that are heated by direct solar gain, then these will rise to a higher
> >temperature than the ambient indoor temperature without raising the indoor
> >temperature uncomfortably, and will also provide heat by convection and 
> >radiation.

> R-values include convection and radiation.

(This last line is a keeper, rabbits or no rabbits)

I rest my case.....

Cheers,

Will Stewart

---

From: [email-masked] (Nick Pine)
Date: 25 May 1996 05:41:02 -0400

>[Followups set to alt.solar.thermal so as not to bore the rest

You don't want to bore people, eh Will? :-)

>Assuming that you are alluding to my place, show me a 2250 ft^2 house with 

That seems like a non-seqitur... I'd say your place will be a very energy
efficient home, and that's good, and not easy to accomplish...

150 Btu/hr-F was about what we got for its thermal conductance
with the window insulation in place, as I recall.

:and
:a thermal capacity of about 8,000 Btu/F, so RC = 8,000/150 = 53 hours, and
:the house starts out with an interior temperature of 68 F when it's -10 F
:outside, with no electric or wood heating, and no sun, the interior temp after
: a couple of days will be approximately - 10 + (68-(-10))exp(-48/53) = 31.5 F.
 
>Abstract of the United States", 92nd edition, US Bureau of the Census)

That's a very nice reference, Will.
A good and powerful reference...
But where will your house be? 

The 1993 ASHRAE HOF lists the 99th percentile winter design dry bulb
temperature for Andrews Air Force Base (is that near your house?) as 10 F.
The 97.5% number is 14 F, ie the winter temp there will be less than 14 F
less than 2.5% of the time.

1% of 6 months is about 40 hours. What would the interior temperature of
your "solar house" be after 40 hours, if your house and its 3,300 pounds
of water walls and 3,000 Btu/F of drywall, concrete furniture, etc, start
out at 66 F one fine cloudy morning with the window insulation in place,
when it's 16 F outside, and you are not burning wood or using electricity?
RC = 6300/150 = 42 hours, so T(40) = 16 + (66-16)exp(-40/42) = 35.3 F.
That wasn't hard, was it?

Why call this a solar house, if 56% of its heat comes from the electricity
you use and your bodies, and a lot of the rest will come from burning wood?
And who cares whether it's a solar house? It's an energy-efficient house...
That's good. But it seems to me that it could be vastly improved and made
less expensive in the way it uses the sun for heat and hot water. 

>I wouldn't have electricity off for a couple of days (will have photovoltaic panels

Good for you... What does all that cost?
 
>especially when extreme weather conditions occur. 

Good for you... Bad for the earth, but nicely nostalgic.  

>of thermodynamics.  It's no wonder you don't see...

I wonder where you would find an error in the tiny heap of numbers above...
Never mind... My vision is unlike yours. 

>> >temperature uncomfortably, and will also provide heat by convection and 

I thought that was 3,253 pounds of water walls, by your last calculation. 

I suppose these water walls will not be insulated, and they were 4" thick, 
(and cost $2K, + how much per square foot of floorspace?), so they might
have a volume of 50 ft^3, and a surface area of 150 ft^2, on each side,
and the US R-value of a still air film is about 2/3, so they would have
their own RC time constant of 2/3/300ft^2x3253=7.2 hours. Not very long
compared to the time constant of the house, so I don't think their time
constant will matter much as your house cools. If we combined these time
constants by squaring them, adding them, and taking the square root, it
would add another half hour to make a 42.6 hour overall RMS time constant
for your house.

Another simple way to get a feeling for this is to see what the water wall
temperature will be in your 66 F house after 40 hours, if the house somehow
stayed at 66 F the whole time and the water walls were initially 10 F warmer
than the house. (How do these water walls 4" away from the windows affect
the view?) Anyhow... T(40) = 66 + (76-66)exp(-40/7.2) = 66.04 F, not much
warmer than the house... Such is the magic of time constants. They are really
quite useful and simple to use for things that cool. Find the R, find the C,
multiply them together and use that simple formula with the "e-to-the-x"
button on your $20 calculator (this is the inverse of the natural log button
on my Casio fx-991H, which I bought for $19.95 at K-Mart.)

>(This last line is a keeper, rabbits or no rabbits)

Here's a quote from pages 79-80 of _From the Walls In_, Little-Brown, 1979,
by Charles Wing, PhD, physics, formerly an Apollo lunar experimenter at MIT:

   H = A x delta T/R... Thermal resistance, R, is actually defined by
   this equation. In the laboratory the two faces of a slab of insulative
   material are maintained delta T degrees apart, the amount of energy
   per hour required to maintain delta T is measured, and R calculated
   as a result. Of course no house consists entirely of solid uniform slabs
   of material. More typically a wall consists of various layers of boards
   and plaster enclosing a cavity containing either air or a fibrous
   insulating material [or bubbles :-)] To complicate the picture further,
   there may be four surfaces facing air, each of different emissivity!
   How do we calculate the total thermal resistance of such a hodgepodge?
   Here it is worth noting the difference between an engineer and a physicist. 
   The physicist wishes to "understand" physical processes. This has led him
   from being a philosopher of nature (knowing a little about everything)
   through the process of specialization (knowing more and more about less
   and less) to his logical end (someone who knows everything about nothing.)
   On the other hand, the engineer typically cares not a whit for why
   something happens, only how to assign a number to it. Results are what
   counts! Thank God for engineers.

   Here's how the engineer does it. First he builds a sample wall, roof, or
   floor construction. Then he says, "I don't care whether heat is flowing 
   through that thing by conduction, convection or radiation or all three at
   once. The simplest formula I have is for conduction alone, so I'll use it."
   He then performs the conduction experiment (illustration 48), turns the
   calculator crank, and out comes apparent total thermal resistance, R. 

   After performing this experiment dozens of times with different assemblies
   of material and air spaces he can sort out the apparent thermal resistance
   contributions of air surfaces, air spaces, and solid materials. Reversing
   the procedure, he can then predict the total thermal resistance of any
   proposed construction by adding the thermal resistances of each of the
   component parts. And it works!

   Tables 15, 16, and 17 list the thermal resistances of surfaces, air
   spaces and solid materials as discovered by engineers...

Those are R-values. You can see them stamped in big letters and numbers
on rolls of insulation for sale at building supply stores. Ours are much
larger than Europe's. Perhaps we should be proud.

Cheers,

Nick

---

From: [email-masked] (Nick Pine)
Date: 25 May 1996 06:13:52 -0400

>I've posted them earlier this week and you've already forgotten?

I think you just told me to redo my numbers, for your house.

>made in your calculations.

No, I just agreed when you said somebody should. It's your house, Will.
 
>Reference:  Home Power Magazine, Feb/March 1996

Nice. I wonder where airtight woodstoves with catalysts fit in.

Speaking of logs...

>as yours require calculus.

You don't need logs or exponentials to size a solar closet, just arithmetic.
Direct gain houses need logs and exponentials. I try to ignore people who
desire to complicate solar house heating. I studied calculus, analysis, etc,
for about 7 years in school, on my way to a masters in electrical engineering,
but I'd like to simplify all this. It seems to me that if we just use some
common sense and arithmetic, we can build much better solar houses, even if
all the calculations are off by 50%. Improving today's solar house designs
is like shooting fish in a barrel. In 20 years, calculus, spreadsheets, and
other computer tools might be more helpful. For now, it seems to me we have
to try very hard just to get in the right ball park.

>You have failed to provide truly coherent questions...

That's a two way street, Will. 

>A little knowledge is a dangerous thing, indeed.

I agree.

>     he would have time to indulge in as many "discussions"."

True.

>     background to support his raves."

Untrue.

>     to think he's really a kid, out to impress himself."

Sometimes :-)

>    "If you're like me, you'll probably either toy with him

Perhaps you are toying. Or posturing. Or something.

I try not to quote email in newsgroups, even anonymously, but someone
just sent me some email mentioning you... He said something like "I hope
Will's idiocy isn't getting to you. We are all learning." That was nice
to hear. I'm trying to be very patient and civil, lately :-)

>You might reconsider your attitude towards others in the energy field.

I might. But a lot of them seem to be opportunists or shortsighted criminals.

Was it Disraeli who said "When a man is wrong, and he fails to admit it,
he almost always gets angry"?

Here's a quote from Tom Smith, the inventor of the envelope house:

  I do not forsee any of the systems we now have surviving past the next few
  years. We have created a bit of a Frankenstein with my house here because it
  launched the field of envelope homes and is seen in competition with other
  systems. Nothing could have been further from my intentions...

  I would feel most proud if my house is remembered for being a step in the
  evolution toward mass energy-efficient design, rather than for introducing
  the "most efficient system."

  After working on, literally, hundreds of passive designs, and living in
  this house over the past three years, I am convinced that energy efficiency
  will become considerably less exotic in the future. It is my belief that
  if we just study closely what is going on inside a house, we'll come up with
  some very simple, if prosaic, solutions. If you have ever spent any time
  living in other parts of the world you'd realize that a lot of our energy
  problems stem from just plain doing it wrong. It's a snap to save energy
  in this country. As soon as more people become involved in the basic math
  of heat transfer and get a gut-level, as well as intellectual, grasp on
  how a house works, solution after solution will appear.

Let me quote the last part again.

It's a snap to save energy in this country. As soon as more people become
involved in the basic math of heat transfer and get a gut-level, as well as
intellectual, grasp on how a house works, solution after solution will appear.

Tom Smith said that in 1980. 

It hasn't happened yet.

Nick