Subject: Re: thermal mass

From: [email-masked] (Nick Pine)
Date: 27 Jun 1996 06:45:01 -0400

<[email-masked]> wrote:
>[email-masked] (Nick Pine) wrote:
>> Mike Dickson <[email-masked]> wrote:
>> 
>> >I was wondering what was the best material to make a thermal mass out of,
>> 
>> Water is good. About 3 times more heat capacity (62 Btu/F-ft^3) than rocks
>> or concrete by volume, with less thermal and airflow resistance, in sealed
>> containers. Iron or steel are almost as good, at 54 Btu/F-ft^3, but more 
>> expensive...
>
>Right. Water.

It's nice we agree on that. 

>> >I plan to run pipes through it and heat with hot water from a
>> >solar collector. Any ideas.
>> 
>> Sounds complicated and expensive.
>
>Balderdash!

I'll see your balderdash, and raise one balderdash :-) Does $30/ft^2 seem
cheap to you, not counting roof mounting brackets and installation and
insulated pipes and tanks and antifreeze and heat exchangers and pumps
and the electrical power needed to run the pumps, IF that square foot of
"solar collector" only collects the heat equivalent of a gallon or two
of oil per year, and that's ALL it does, vs a sunspace or a transparent
south roof or solar siding on a house?

>Nick, we keep going over the same material. 

True. You should give up. Or use numbers.

>Air is a pitiful heat transfer medium.

True, compared to water.

>The only thing that is has is fluidity.

No, it also has heat capacity, and it doesn't freeze, which is nice, and
it requires no plumbing or heat exchangers, and sometimes no pumps or fans,
and leaks are not a serious business. It wasn't long ago that one of the
alternative energy experts around here said "air has no mass." :-)

>How umpteen many more times heat capacity has water got than air

About 4000 umpteen times, by volume, 1000 times less density and 1/4 the
specific heat by weight. Is this a problem? Can planes fly? Should we
abandon them all for boats? 

>(the range of air's heat capacity that you're going to give me will
>relate directly to how much water vapor is in that air)?

Wrong again. Why don't YOU come up with that range? Water vapor does
make a small difference. Care to guess which direction? :-)

>Water can be pumped thru 1/2" pipes that are easily insulated, taking up
>much less indoor (read valuable) real estate,

It may surprise you to learn that air may not need pipes, that one can move
air through whole rooms and floors and walls and ceilings sometimes, with
absolutely no loss of floorspace.

>How much more efficient a heat exchange would that be than blowing warm air
>around a room with 55 gal drums in it?

I give up. How much? You tell me. Where are your numbers? Why does this matter?

>Add to that the longevity of copper pipe

Do we also add the longevity of wood or drywall or fiberglass insulation 
or plastic 55 gallon drums? :-) 

>and the ability to take heat off from this storage tank with more
>copper pipe to feed DHW,

I'd use about 20' of fin-tube pipe for that, in a thermosyphon loop.

>or your spa, or your pool, or any one of your space heat zones without
>heating rooms above or adjacent to the storage room or the ducting

Insulation... Another matter of numbers. Where are your numbers, Dan?
  
>and the cost and complexity become minor.

Perhaps, if you are rich as Croesus, or enjoy complexity.
Did you say you were in the copper piping business, Dan? :-)
 
>>>I may just blow air over it instead of running water pipes through it
>>>if this turns out to be much easier or better.
 
>>Good idea. Using free 55 gallon plastic drums or recycled 5 gallon paint
>>pails, with lids? Or $25 waterbed mattresses holding 300 gallons, or big
>>cheap circular swimming pools, or plywood boxes or trenches made with a
>>single 28 cent/ft^2 piece of 20' wide EPDM rubber roofing material folded up
>>like a Chinese restaurant takeout box?
 
>If, like most fluid based systems... the storage temps consistantly approach
>150F plastic drums, $25 waterbed mattresses, and cheap swimming pools are a
>disaster waiting to happen.

So are airplanes, especially lately. Engineers specialize in disasters
waiting to happen. The better ones avert disasters for a very long time.

>Your trench idea will work up to a point. The ground will become a heat
>sink and cool your storage off...

This is a matter of degree, of course. Numbers again, and design. Looked at
figure 6 on page 22.13 of your ASHRAE HOF lately? It shows fine grain soils
eg clay (there's a lot of that where I live) have a thermal conductivity
that approaches 0 as they become very dry, in the region with less than 5%
moisture. At 8%, Fig 6 shows their thermal conductivity as 5 Btu-in/h-ft^2-F,
and the clear exponential curve extrapolates along a line to 0 from there,
so one might well expect that such a soil at 1% moisture would have a thermal
conductivity of 5/8 Btu-in/h-ft^2-F, ie about R20 for a foot of soil. Not bad,
I'd say. How do we keep the soil dry? Put a vapor barrier all around it, with
a few air holes at the top, and something warm in the middle. I suppose they
do this with underground district heating pipes in Sweden and Siberia. 

>Paint cans aren't even worth discussing.

OK. Let's not discuss them. Except, I might add, I just filled up a 5 gallon 
plastic paint pail with 150 F water and stood on top of it. Even bounced a bit,
in the interest of science. Perhaps you will try this with a plastic 55 gallon
drum. I wouldn't expect temps much over 130 F without a selective surface.

>I would suggest the largest electric water heaters that you can find, or unused
>oil tanks, or strong fiberglass tanks, or reinforced block walls forming a
>tank that then is lined with edpm, or recycled milk tanks (stainless, of
>200-300gal size, from farm supply), even steel 55 gal drums.

I would suggest that that will work, but it's a waste of money. Perhaps a
plywood box with some 2x4's around it, lined with EPDM rubber, as widely used
for off-peak electric heat storage.

Thanks for making my morning, Dan! This is like shooting fish in a barrel.

May you remain ever ignorant. 

And silent.

Cheers,

Nick

---

From: [email-masked]
Date: Sun, 30 Jun 1996 16:30:19 -0400

In article <[email-masked]>, [email-masked]
(Nick Pine) wrote:

> and the electrical power needed to run the pumps, ...

Cheap is something that you spend time and/or money on (no matter how
much) that falls apart before it's time. I'm not aiming for cheap.
Inexpensive? Certainly not. Valuable? Cost effective? A bargain? Your
decision.

Do you read what others post or do you just spout off? Where does $30/ft^2
come from? I've told you before (why do I think that you might listen this
time?), a complete dhw system (including electric back up) with all new
materials using 2 4x10s, installed correctly and completely wll cost about
$43.75 per sq ft. - $3500. Do you want these panels delivered to your
door? $1000 each. $25 per sq ft.

OK, my system is installed and operating at $43.75 per sq ft. Your "heat
equivalent of oil" nonsense means nothing until you have purchased and
installed the necessary equipment to process that oil into a useable form.
It might also be the heat equivalent of a truckload of elephant turds. If
those turds are delivered to your front door, they do you no good until
you bring them inside and find a way to use them. 2 gallons of oil
delivered to your front porch times 50 year minimum life cycle times 80 sq
ft = 8000 gallons of oil seeping thru the cracks of your porch (at today's
oil price, of course).

How many gallons of oil (maybe you've scooped it up now and put it in your
paint cans) does your sunspace replace per foot? Remember, getting it into
the sunspace doesn't count. It's getting it into a place where it can be
used that matters.

> True. You should give up. Or use numbers.
I used numbers last time. In fact, I gave you a ten year warranty on all
pumps, controls, and sensors, inspected the system every year, changed the
glycol, and factored in ongoing operating costs. You didn't respond. I
still want to know where I can get my free 100% efficient oil burner,
tank, flue, piping, filters and control system warrantied for 10 years.

> No, it also has heat capacity,

Not much.

> and it doesn't freeze,

Good point.

> which is nice, and
> it requires no plumbing or heat exchangers,

Maybe that explains why your storage doesnt get up to 90 degrees in the winter.

> and sometimes no pumps or fans,
> and leaks are not a serious business.

Or maybe that has something to do with it.

> It wasn't long ago that one of the

Compared to water, it doesn't. By the way, I know the guy, he's not so
presumptive as to call himself an expert. Just a mechanic with a working
knowledge of the realities involved.
> abandon them all for boats? 

There's an intelligent argument. Should we abandon all toasters for blenders?

Lets see,  if I buy a $100 Grudfos 15-42F circulator at 120v and 85 watts
and my closed loop has the equivalent resistance of 5 ft of head then I
can pump 15 gallons per minute. divided by 7.5 gallons per cu ft = 2 cu ft
per minute. Times 4000 umpteen = 8000 cu ft per minute. So, for every ETT
(elephand turd truckload) of heat that I can move in one minute using 85
watts, you need to move 8000 cu ft of air. You like Grainger's stuff,
here's a floor fan that can move from 6810 cfm to 10300 cfm on page 2898
of the 1995 catalog. It only costs $562 and only uses 930 watts. It may
cost you something to have delivered. Shipping weight 148 lbs. My pump
costs about $5 to ship. Of course, this being a fan, it will only deliver
that cfm where it has deliverable free air, in other words, low static
pressure, in other words, a big open room. If you need to duct it there's
a 22" blower on page 2929 for $1035 for a 230/460v 3hp motor. Or, there's
a 36" whole house fan on page 2993 for $319 at 690 watts, it too needs low
s.p. to do the job.

> absolutely no loss of floorspace.

AT 8000 CFM ? Oh yeah, that's right, you're doing everthing with
conduction, convection, and radiation, which of course, don't apply to
water, glycol, OR copper.
> I give up. How much? You tell me. Where are your numbers? Why does this
matter?

Why does this matter? WHY DOES THIS MATTER? Nick, it's time to wake up.
This is the entirety of the argument. Your sunspace gets hot. Very little
of this heat gets into the livable area. Even less gets into storage. Any
house in the Northern Hemisphere with south facing windows gets a direct
heat gain when the sun shines. Any more heat gain than what you can use
right now is waste. Just like your sunspace. Insulate those windows at
night and forget about your plastic greenhouse. 
 
> or plastic 55 gallon drums? :-) 

Of course you do. Dont forget to factor in rot. If your system worked, the
wood, drywall, or fiberglass that is the surface between hot and cold will
condense  if given a high enough delta T. By the way, if it leaks air, it
can leak rainwater and bugs. Plastic drums wont rot, they'll just get soft
and weak with repeated thermal cycling. But, of course, that's only if the
system works.

> Insulation... Another matter of numbers. Where are your numbers, Dan?

No, Nick, it's not a matter of numbers. It's a matter of common sense. It
doesn't take an engineer to realize that any number of ETTs going thru
finned copper pipes immersed in water (or air, or floor, or boot warmers)
will put more ETTs into where it's needed than the same number of ETTs
blown around some plactic drums, even at 8000 cfms. Nor does it take an
architect to look at a sheet of 80% shade cloth (called that because 20%
of its surface area is holes -you can see thru it) and decide if it will
be a better absorber sheet for IR light than copper treated with a
selective surface.

An automobile mechanic that knows his ass from a hole in the ground doesnt
need a book of formulas to recognize that his car wont get far on the gas
produced by the taco he had for lunch. I work with these things every day.
I get my hands in up to the elbows. I know what a heat exchanger is for
and how to use it.

When I give you numbers, you chose to ignore me. Pick a number, Nick.
Spend that number on your plastic sunspace. Give yourself a livable wage
for your time. I'll spend the same amount on a copper system. My system
will outperform yours from day one.
 
> Did you say you were in the copper piping business, Dan? :-)

No, but I think I know where to go for shade cloth if I ever need it.
 
> waiting to happen. The better ones avert disasters for a very long time.

Better still, if you build nothing, you can avert disaster forever.

> for off-peak electric heat storage.

Time is money. Unless your time is worth nothing, of course. My time, on
the other hand is worth many times what I've gleaned from you. You were
right from the start. It's time that I give up.

Do the job right or don't bother.

> Thanks for making my morning, Dan! This is like shooting fish in a barrel.

It's more like talking to my dog. She wags her tail and looks at me, but
all she ever really comprehends is the sound of her own name. 

Blah,Blah,Blah,Blah,Nick,Blah,Blah,Blah...

> May you remain ever ignorant. 

Go soak your head.

Goodbye,
 
Dan

---

From: [email-masked] (Nick Pine)
Date: 2 Jul 1996 08:07:44 -0400

>...a complete dhw system (including electric back up)... wll cost about
>$43.75 per sq ft. - $3500..

So, that's 80 ft^2... Or 7.4 m^2. Where I live near Philadelphia, the average
yearly sun that falls on a surface tilted at the latitude is 4.6 kWh/m^2/day,
ie 365 x 4.6 x 12,483 kWh fall on that collector. The average yearly temp
is 54 F. Say we collecting heat at 120 F, average? Is the panel losing about
8hr(120-54)80/R2 = 21K Btu/day, or 365 x 21K/3410 = 2250 kWh/year for an
annual average collection efficiency of 82%? Is the heat store infinite? If
not, how often does we run out of solar hot water? What's the annual solar
fraction for a system like this?

>installed the necessary equipment to process that oil into a useable form.

I don't know what an oil burning water heater costs, and yes, you'd need a
tank and a chimney. Perhaps I should have said electricity, at 0.08 cents/kWh,
Or a third of that, using a heat pump that cools the basement air a bit? Or
natural gas? Let's say we just use electric resistance heat. Then this $3500
investment, less $300 for the electric water heater, assuming the solar heat
store is infinite, saves 10,233 kWh/year, ie about $800/year. Good :-) Like a
25% tax-free bond. Worth doing, but are there better alternatives?

>How many gallons of oil... does your sunspace replace per foot?

1-2 gallons of oil per year per square foot of glazing. But the sunspace
doesn't heat water, just the house. The solar closet would heat water. 

>Remember, getting it into the sunspace doesn't count. It's getting it into
>a place where it can be used that matters.

Sure. Getting warm air into the house with a motorized damper or window fan,
and getting sun into the solar closet through the inner glazing, with another
motorized damper or low power fan, then getting the heat into an electric
water heater on the floor above using, say 20' of fin-tube pipe near the solar
closet ceiling, in a thermosyphon loop, a la Big Fin sunspace collectors.

Now there's another more economical alternative than all these rooftop solar
panels and pipes and tanks and pumps and so on, no? Something like Big Fins in
a sunspace. Might even glue some PV solar shingles on them, and add 2:1
reflectors, a la Richard Komp. Electricity, hot water and heat for the house,
as well as more daytime floorspace...
 
>> >Air is a pitiful heat transfer medium.
 
A cfm of water with a temperature difference of 1 F moves about 3720 Btu/hr.
A cfm of air with a temperature difference of 1 F moves about 1 Btu/hr. So? 

>Good point.
 
Norman Saunders, PE, often makes this point.

>Compared to water, it doesn't.

But it's a matter of degree, no?

>There's an intelligent argument. Should we abandon all toasters for blenders?

I don't follow your logic here, Dan. Can you explain further?

>watts, you need to move 8000 cu ft of air.

Yup. You can move lots of heat. But what's your point?

>You like Grainger's stuff, here's a floor fan that can move from 6810 cfm
>to 10300 cfm on page 2898 of the 1995 catalog. It only costs $562 and only
>uses 930 watts. It may cost you something to have delivered. Shipping weight
>148 lbs.

I wouldn't buy one of those. But I might buy a $12 Holmes 20" window fan, or
a $60 4C588 36 Watt 560 cfm 149 F max cooling fan, or a $168 4C721 130 Watt
5' diameter 43,700 cfm ceiling fan, with a $15 speed controller. It weighs
34 pounds. Or I might try to make the whole shebang work by natural convection,
as Steve Baer has been successfully doing for 30 years. I'd probably cheat
a bit and use a $50 2 Watt damper motor and thermostat.

>My pump costs about $5 to ship. Of course, this being a fan, it will only
>deliver that cfm where it has deliverable free air, in other words, low static

Hey Dan, you might like Grainger's 7F916 25 _Horsepower_ 3 phase blower! :-)
Page 2930, 23,000 cfm at 2" of static pressure, $2139, 325 pounds. Our solar
closet has 0.05" static pressure at 500 cfm. We haven't tried to streamline it.

>AT 8000 CFM ?

Now where did the 8000 cfm come from? Oh yes, you were moving 2 cfm of water.
I wonder why? Oh, you don't have any natural way to make the hot water go
downhill... I wonder if you do Copper Crickets.

>of this heat gets into the livable area. Even less gets into storage.

We've seen the the sunspace heat the little room in our outdoor structure
comfortably and controllably using only natural convection, with a motorized
damper between them, while our measurements indicated the solar closet was
capturing 55% of the incoming sun. 

>Any house in the Northern Hemisphere with south facing windows gets a direct
>right now is waste.

That's the usual arrangement... Were we talking about water heating?

>Just like your sunspace. Insulate those windows at

Ah yes, the ritual curtains. That will work, but it's a bit expensive,
and not automatic, and there's no heat stored at a higher temp than the
house, for future cloudy days, and no hot water. We were talking about
water heating here? 

>condense if given a high enough delta T.

Can you be more specific, Dan?

>By the way, if it leaks air, it can leak rainwater and bugs.

Who says "it" leaks air? And what is the "it"? Bugs are our friends.

>Plastic drums wont rot, they'll just get soft and weak with repeated thermal
>cycling.

Have you ever seen that? These drums should mostly just stay hot, in this 
trickle-charged heat battery, which is a collector with an instantaneous
solar collection efficiency of zero, unlike a rooftop collector.

>> Insulation... Where are your numbers, Dan?
 
>blown around some plactic drums, even at 8000 cfms.

I don't quite follow your logic here, Dan. You can move about 75K Btu/hour
with 2 cfm of water. That is impressive, but an R20 4'x 8'x 10' solar closet
only needs about 22K Btu/day to stay warm, eg 360 cfm of air for 6 hours a
day with a 10 F temp difference. If it makes hot water, it may need a fan to
collect sun, or larger motorized dampers, or a motorized insulating and
reflecting cover, hinged at ground level, that folds down from the glazing
to a horizontal position in the sunspace to let sun and reflected sun shine
directly onto the thermal mass during the day. These things work best when
lightly loaded.

>Nor does it take an architect to look at a sheet of 80% shade cloth (called
>that because 20% of its surface area is holes -you can see thru it) and
>decide if it will be a better absorber sheet for IR light than copper treated
>with a selective surface.

Engineers are typically more interested in those things than architects, eg
Norman Saunders, PE, who has been using transpired collectors like this since
about 1944 in his 100% solar New England houses. He likes them because they
are 50 times less expensive than selective surfaces, and they have little
thermal mass to wake up in the morning, and they store and waste little heat
at dusk. There is more surface area to absorb the sun than with a simple dark
surface, so the average surface temperature is less, since heat loss to air
is proportional to area, and the lower temperature of the absorber surface
REradiates less IR heat back out at the glazing. Glass and polycarbonate
plastic block UV and IR in both directions. Norman also says that transpired
absorbers are more efficient because some of the sun shines through the holes
and hits the dark surface to the north, which heats up that surface, which
reradiates heat to the south, and the transpired absorber intercepts that
reradiation trying to heat up the glazing. He also likes them because we can
end up with relatively cool air next to the relatively cold glazing, with
sun-warmed air next to the house wall, away from the cold glazing. 

>An automobile mechanic... doesnt need a book of formulas to recognize that
>his car wont get far on the gas produced by the taco he had for lunch.

Perhaps you are saying this is a matter of proportion.

>I know what a heat exchanger is for and how to use it.

Heat exchangers make pretty good scrap metal...

>>>disaster waiting to happen.

Recall we've tested the plastic paint pails now. Care to try the drums? 

>Better still, if you build nothing, you can avert disaster forever.

Yes, but that won't make the world a better place. Or maybe it will...
Bertrand Russell used to say "All that is necessary for goodness to
triumph in the world is for enough good men to do nothing."

>You were right from the start.

Ahh, I like to hear that :-)

>It's time that I give up.

Agreed.

Nick