Hybrid Car – More Fun with Less Gas

An air-soil solar sub-basement heat battery

register ::  Login Password  :: Lost Password?
Posted by nicksanspam on January 31, 2005, 7:45 pm
 
"C Johnson, Physicist, Univ of Chicago" writes at

http://mb-soft.com/solar/subbase.html


Then again, some houses have no basements. I seem to recall that simple
concrete slabs cost about $/ft^2, installed.


A window unit might handle dehumidification, for an "airtight" house.


The phrase "kind contractor" seems oxymoronic :-)


Pay no attention to all the empty dynamite cases in the yard :-) But how
big a blower, and how many pipes, and will they collect water and dust
and mold and mildew and varmints?


With significant thermal resistance, which limits the rate of heat storage
and withdrawal...


How long would that take?


Assuming perfect heat exchange...


NREL says Chicago has 752 cooling degree days. Not much. A modest house with
a 400 Btu/h-F thermal conductance might need 24hx752x400 = 7.2 million Btu/yr
of cooling, or more, with some internal electrical use and unshaded windows.


How do we get the sun into the basement? :-)


Mirrors?


That works for Kachadorian "solar slabs" and Adirondack "solar houses."


NREL says Chicago has 6536 cooling degree days. Our 400 Btu/h-F house would
need 24hx6536x400 = 63 million Btu/yr, or less, with some internal electrical
use and sun into windows.


Is Chicago north of the arctic circle, with no sun for months at a time?


Like this?

  The Lyckebo [Sweden] system is a cavern of 100,000 m^3 capacity, cut out of
  bedrock using standard mining methods, of cylindrical shape, with a central
  column of rock left to support the overhead rock. The cavern is about 30 m
  high and its top is about 30 m below ground level. It is water filled, and
  inlet and outlet pipes can be moved up and down to inject and remove water
  from controlled levels. The water is highly stratified with top to bottom
  temperatures of about 80 to 30 C. Figure 8.7.2 shows temperature profiles
  in the store at various dates in the second year of operation... No thermal
  insulation is used, and there is a degree of coupling with surrounding rock
  which adds some effective capacity to the system. Losses occur to a semi-
  infinite solid and can be estimated by standard methods. Observed losses
  from this system are higher than those calculated; this is attributed to
  small but significant thermal circulation of water through the tunnel used
  in cavern construction and back through fissures in the rock. It takes
  several years of cycling through the annual weather variations for a storage
  several years of cycling through the annual weather variations for a storage
  system of this size to reach a "steady periodic" operation. In the second
  year of its operation, while it was still in a "warm-up" stage, 74% of the
  energy added to the store was recovered.

         from p 404 of section 8.7, "seasonal storage," of _Solar Engineering
     of Thermal Processes_, by John A Duffie and William A Beckman, 2nd
     edition, 1991, Wiley-Interscience ISBN 0-471-51056-4

But why do we need seasonal storage in Chicago?

And soil is not a good heat conductor and stores about 3X less heat by volume
than water, and it's easier to transfer heat from water to water than soil
to air, or move the warm air around very far. We might line a sub-basement
with concrete block partitions to make tubs and line the tubs with single
pieces of EPDM rubber folded up like Chinese takeout boxes (a 20'x20' piece
of rubber could line a 12'x12'x4' deep tub) and fill the tubs with water,
with a vapor barrier (eg foamboard) and a removable wood floor on top... 4
12'x12'x4' deep tubs would hold about 143.6K lb of water. With a 120 F temp
on an average day and 80 F min temp, they could store 6 million Btu, enough
to heat a modest house for 29 cloudy days in a row. But who would need that?


A water system might collect and distribute heat with some fin-tube pipes
below a ceiling, with the help of a ceiling fan and a room temp thermostat
and some simple solar air heaters and a low-e coating under the ceiling to
avoid overheating the room.


This would be the second $50, or more?


As you say, we could use more details. More engineering than physics.

Nick
 

Posted by Steve Shantz on February 3, 2005, 4:14 am
 
Nick,

I've been lurking for too long now, and your comments here are related
to an active interest of mine.  The idea of using earth or water for
heat storage is very interesting, but as your comments accurately
indicate... it isn't all that easy.  I have rolled my own numbers on a
system such as this.  My design would  use parallel PEX loops to
deposit and extract the heat.  One loop for glycol, one loop for
domestic hot water.  Maybe a third loop for radiant floor heating.
Unfortunately, when one adds up all of the costs, it gets very
expensive.

One needs to insulate the sub-basement very well.  My design uses lots
and lots of PEX ($$$ - must be spaced quite close because of poor
thermal conductivity of the ground).  If you have sand, great.  Easy to
work with.  Clay.... haul it away and truck in sand ($$$ - which is my
situation).  Also, the writer seems to ignore heat losses.  More
insulation helps, but more $$$.  I understand that water flowing
through the earth around the sub-basement might carry away a
significant amount of heat.

I thought about placing some radiant subfloor aluminum heat plates in
contact with the PEX to help distribute and collect the heat from the
ground.  This would give the system more 'power' by increasing the
effective surface area of the PEX, but... $$$ - nobody gives these
panels away for free.

Larger systems hold more heat for a given surface area.  It seems that
this system might work better for a large house.  What about for larger
buildings yet... or a community based project.  There have been some
designs along this line done in northern Europe. I think they used
enormous tanks of water.  I haven't seen any good evaluations on their
performance.

One could make the sub-basement deeper than the standard 8' to help
reduce the mass / surface area ratio.  Now you have a big deep hole...
more $$$$  How much mass can dense foam board hold before it
compresses?

The use of water for heat storage has several big advantages, one being
it's much higher heat capacity per cubic foot, but now the basement
floor must span the pool in the sub-basement.  Would the basement floor
have to be concrete to resist the water just below? More $$$$.  What
about when you get a leak?  You aren't going to send a diver into 120
F water to patch it!  My current thinking is that sand has some
advantages here in spite of it's lower specific heat.  Does a large bed
of sand expand when heated?

Near the end of 2002, there was a long thread at alt.solar.thermal on
the solar cistern that Alan Stankavitz installed in his home.
(www.daycreek.com)
Alan's design is not at all like what you have dug up, but it is a
related idea  that has some merrit. The storage potential in Alan's
system is much more short term, and the design is very different.
Performance expectantions are very different too, subsequently, his
cost is much less. I wonder what Alan does with the heat from all of
those panels in the summer?  Did he install a dump load?

A lot of the discussion in that thread was related to trying arrive at
an understanding on how heat flows through Alan's system, (and trying
to convert Mr. Pine).  This is a very important point to consider.
Failure to understand how heat flows in soil will likely doom a
project, or at least make it a serious under-performer.  Has there been
any good research on this topic of heat flow in solar cisterns?

I have toured two buildings that use the solar cistern concept at the
Midwest Regional Engery Fair 'Solar Tour'.  Both systems were well
thought out, and seem to be working very well.  However, neither system
design is full of the hype which you have correctly pointed out below,
and both buildings use good passive design concepts.

I would like to point out some serious flaws in the assumption that one
can heat and cool with the same mass.  If one shuts off the heat in
April, what will be the source of cooling for this insulated mass so
that it is 55 F come the 4th of July?  Sounds like horse feathers to
me.

OK, so I've rambled long enough.  I guess what I want to really say is
that you are absolutely right to be highly sceptical of the claims
made.  However, I still think the  idea has lots of merrit if correctly
designed.  Maybe one's house construction budget would be much better
allocated to an extra 4-8" of insulation in the walls and ceiling, and
good passive design.  Under these conditions, a solar cistern wouldn't
have to be so large... or expensive.

Steve




nicksanspam@ece.villanova.edu wrote:

thousand

concrete.

without

anything new or

that they

complications

actually be

entirely

buried in

properly

and the

feet by

then have

cubic feet

materials.

storage is

storage

Chicago's,

temperature,

beginning of

76F, that

million

Chicago's,

at 30,000

house with

million Btu/yr

windows.

sources

noticed that

summer day.

several

equipment.

similar.

houses."

million

winter.

reasonably

electrical

furnace

representing

for every

would be

cut out of

central

about 30 m

filled, and

remove water

profiles

thermal

surrounding rock

attributed to

tunnel used

a storage

a storage

Engineering

by volume

sub-basement

top... 4

need that?

surfaces,

inward or

must be

economy

efficient

thermostat

ceiling to

this page,

of this

variables can

performance...

version of

might as

greatest

(2) the

areas, we


Posted by nicksanspam on February 3, 2005, 3:09 pm
 

From sand. Water seems better.


A lot... 30 psi?


That's one reason I suggested 12'x12'x4' tubs. You might fill a sub-basement
with sand, then add some water for greater heat capacity and easier transfer
(just pump water in an out, with no heat exchanger), leaving a layer of sand
on top which could support a floor, but 12' isn't a large floor span. Water
could increase fire safety.


I think it just needs a good vapor barrier. Plastic film and/or foamboard.
Putting the tank in the ground removes the need to build strong sidewalls.


A tub shouldn't leak, if carefully lined with a single 20'x20' piece of EPDM
rubber folded up like a Chinese takeout box. In the rare event that it does,
it might be pumped out for repair, which might just consist of adding another
layer of rubber. We could make 4'x19'x3' tubs with 10'x25' pieces of rubber.


Trickle water over a north roof at night, or through a pond, under some rocks
for safety and shading. Or keep the tub hot to make DHW.

Nick


Posted by News on March 14, 2005, 11:12 pm
 


Or use a heat pump to extract heat from it for DHW.  But that defeats the
object.

The Germans spiral a 6" plastic pipe around the outside of the foundations
and use this as the inlet to a heat recovery and vent system.  Pre-heats in
winter and cools in winter.  They don't need a/c in their climate.



Posted by News on March 14, 2005, 4:33 pm
 



but it is a
related idea  that has some merrit. The storage potential in Alan's
system is much more short term, and the design is very different.
Performance expectantions are very different too, subsequently, his
cost is much less. I wonder what Alan does with the heat from all of
those panels in the summer?  Did he install a dump load?

A lot of the discussion in that thread was related to trying arrive at
an understanding on how heat flows through Alan's system, (and trying
to convert Mr. Pine).  This is a very important point to consider.
Failure to understand how heat flows in soil will likely doom a
project, or at least make it a serious under-performer.  Has there been
any good research on this topic of heat flow in solar cisterns?

I have toured two buildings that use the solar cistern concept at the
Midwest Regional Engery Fair 'Solar Tour'.  Both systems were well
thought out, and seem to be working very well.  However, neither system
design is full of the hype which you have correctly pointed out below,
and both buildings use good passive design concepts.

I would like to point out some serious flaws in the assumption that one
can heat and cool with the same mass.  If one shuts off the heat in
April, what will be the source of cooling for this insulated mass so
that it is 55 F come the 4th of July?  Sounds like horse feathers to
me.

OK, so I've rambled long enough.  I guess what I want to really say is
that you are absolutely right to be highly sceptical of the claims
made.  However, I still think the  idea has lots of merrit if correctly
designed.  Maybe one's house construction budget would be much better
allocated to an extra 4-8" of insulation in the walls and ceiling, and
good passive design.  Under these conditions, a solar cistern wouldn't
have to be so large... or expensive.

Steve




nicksanspam@ece.villanova.edu wrote:

thousand

concrete.

without

anything new or

that they

complications

actually be

entirely

buried in

properly

and the

feet by

then have

cubic feet

materials.

storage is

storage

Chicago's,

temperature,

beginning of

76F, that

million

Chicago's,

at 30,000

house with

million Btu/yr

windows.

sources

noticed that

summer day.

several

equipment.

similar.

houses."

million

winter.

reasonably

electrical

furnace

representing

for every

would be

cut out of

central

about 30 m

filled, and

remove water

profiles

thermal

surrounding rock

attributed to

tunnel used

a storage

a storage

Engineering

by volume

sub-basement

top... 4

need that?

surfaces,

inward or

must be

economy

efficient

thermostat

ceiling to

this page,

of this

variables can

performance...

version of

might as

greatest

(2) the

areas, we


This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread