Hybrid Car – More Fun with Less Gas

Dumping heat or saving heat - Page 2

register ::  Login Password  :: Lost Password?
Posted by SJC on March 3, 2006, 6:46 pm
 


  I was thinking in terms of lower temperatures and higher volumes.
Since you would be using a heat pump, 90F would be a nice store
to draw from. You don't have to store 100 therms, maybe 20-30 would
be ok. It is a matter of what you can afford and build, versus your =
need.
  The original post was for something to do with summer heat collection.
Some would say, just turn off the pump. That might be ok for most of the
summer, but I might want to turn it on again, say in August and =
September
to get ready for October and November, when cloudy days might require
me to use heating oil or natural gas.

Posted by Steve Shantz on March 4, 2006, 3:45 am
 
Storing heat is difficult, as Ecnerwal correctly points out.  However,
I'm not quite so pessimistic.  I'd like to think that a well designed
system can give a good supplement to winter heat, and take care of a
large portion of your domestic hot water needs all at once.

The posts above alude to the issue of storing heat in water, vs. sand /
earth.  Water has a higher specific heat, but is harder to work with,
and presents some significant hazards.  We don't want anybody falling
into a tank of 150F water do we?  I think it was Nick who advocated a
water cistern, but in 6' x 6' compartments, so that the ceiling can
span the short distances with no problems.

Earth systems present some advantages, as they can support a concrete
slab with no structural issues.  But trucking in 5 or 10 truckloads of
sand isn't cheap either.  Also, getting heat into and out of sand is a
bit more complicated than for water.

At the Midwest Renewable Energy Fair, I took a solar tour, and saw two
very nice solar cisterns, where 3 - 4 feet of sand under a slab of
concrete is heated all summer, and slowly gives off it's heat in the
winter by passive conduction.  But who wants a toasty warm floor in
August?
My idea is to put 2" of foam between the sand and the concrete, with an
extra loop of PEX in the sand to pump heat out of the sand and into PEX
embedded in the concrete floor.  You get heat when you want it.  Also,
put in another loop of PEX to pre-heat your hot water.

These ideas work best with new construction.  Renovations of such
magnitude are difficult.  Also, economies of scale exist.  Larger
masses store more heat, but losses get scale up slower as the size of
the system is increased.

Other minor issues... or not so minor...
How much weight can rigid foam board support?  Will 4' of sand cause it
to collapse?  How about 8' of sand?  How about if the sand is quite
HOT???  Also... lots and lots of PEX.  Ecnerwal is correct about the
$$$$ of such systems, (count the number of dollar signs!) but in the
long term, it may not be so bad.  Anybody want to guess on the price of
natural gas 5, 10, or 15 years into the future?

Clearly, some important issues need to be worked out yet before I start
digging for my solar heated addition!

Steve


Posted by SJC on March 4, 2006, 4:46 am
 
Storing heat is difficult, as Ecnerwal correctly points out.  However,
I'm not quite so pessimistic.  I'd like to think that a well designed
system can give a good supplement to winter heat, and take care of a
large portion of your domestic hot water needs all at once.

The posts above alude to the issue of storing heat in water, vs. sand /
earth.  Water has a higher specific heat, but is harder to work with,
and presents some significant hazards.  We don't want anybody falling
into a tank of 150F water do we?  I think it was Nick who advocated a
water cistern, but in 6' x 6' compartments, so that the ceiling can
span the short distances with no problems.

Earth systems present some advantages, as they can support a concrete
slab with no structural issues.  But trucking in 5 or 10 truckloads of
sand isn't cheap either.  Also, getting heat into and out of sand is a
bit more complicated than for water.

At the Midwest Renewable Energy Fair, I took a solar tour, and saw two
very nice solar cisterns, where 3 - 4 feet of sand under a slab of
concrete is heated all summer, and slowly gives off it's heat in the
winter by passive conduction.  But who wants a toasty warm floor in
August?
My idea is to put 2" of foam between the sand and the concrete, with an
extra loop of PEX in the sand to pump heat out of the sand and into PEX
embedded in the concrete floor.  You get heat when you want it.  Also,
put in another loop of PEX to pre-heat your hot water.

These ideas work best with new construction.  Renovations of such
magnitude are difficult.  Also, economies of scale exist.  Larger
masses store more heat, but losses get scale up slower as the size of
the system is increased.

Other minor issues... or not so minor...
How much weight can rigid foam board support?  Will 4' of sand cause it
to collapse?  How about 8' of sand?  How about if the sand is quite
HOT???  Also... lots and lots of PEX.  Ecnerwal is correct about the
$$$$ of such systems, (count the number of dollar signs!) but in the
long term, it may not be so bad.  Anybody want to guess on the price of
natural gas 5, 10, or 15 years into the future?

Clearly, some important issues need to be worked out yet before I start
digging for my solar heated addition!

Steve

  Some good points. I have seen mobile homes that have foundation =
pillars
that are down in a 4 foot deep hole the size of the floor footprint. It =
might
not be that hard to put pipes in that hole and fill it, since it is dug =
all ready.
I would assume that the earth could provide a good foundation for earth
that was once there.


Posted by Solar Flare on March 4, 2006, 5:28 am
 This energy price rise scare was massive in the 70s but our NG prices
have dropped considerably until the last two years.

Who knows what will come but I see no reason to suspect there will be
anything more than normal inflation of energy prices.

With the price of NG for my home being less than 1/2 of my automobile
fuel now I see it as not a worry.

It is all in our minds and completely relative to what we are used to.


  Anybody want to guess on the price of
natural gas 5, 10, or 15 years into the future?

Clearly, some important issues need to be worked out yet before I
start
digging for my solar heated addition!

Steve



Posted by Alan on March 4, 2006, 6:07 pm
 I've been concerned about the heat store issue too (see excessive heat
build-up thread).  I'm skeptical of the idea of summer heat below the
house because I have to imagine that it will contribute to a hotter
house in summer.  If you live in the south or pacific coast, the costs
of electricity for summer a/c are about equal and sometimes greater
than the cost for natural gas to heat the house in winter.  If you are
doing new construction then the geothermal heat pump is certainly the
way to go for heating/cooling, but this is a considerable investment
involving hundreds of feet of tubing in 6ft deep trenches.  The slinky
coil system I considered meant digging ten 100 ft long sections, 6ft
deep by 6ft wide.  That's a lot of backhoe work, and for retrofit, it's
pretty much impossible, unless one has a 1/2 acre or so of extra open
land that's close to the house and not currently used for anything, not
even for landscaping.  If this is a new construction situation (I
suspect it's not), then an extra trench for the solar dump is no big
deal and could be dug parallel to the geothermal trench to swap energy
in winter.  The solar dump should be relatively short, say a 100 foot
loop buried down a couple of feet.  I still wouldn't put it in the
basement or under the crawl space of a house though.  Summer cooling is
equally important to winter heat.  Simply turning off the pump may
result in the pressure release valve opening, and these units don't
have the reputation for working well with repeated and frequent use.
Besides, this would lose water and introduce air into the system.  If
set of shutters can be constructed to shade the solar panel, that would
eliminate the problem.  If someone knows how to automate a canopy or
shutter system that exposes or shades the solar panel according to a
thermostat set for excessive heat, I'd like to know.  It seems to me
that a small motor and track system for selectively drawing a canopy or
shutter over the solar panel should be possible, but I'm not a
mechanical engineer.  Again, this could be tied to a thermostat on the
hot water tank that draws the shade when temperatures rise above, say
200F, or just below the temperature of the release valve.

Solar Flare wrote:


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