Hybrid Car – More Fun with Less Gas

just an idea - Page 4

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Posted by user on April 21, 2009, 3:44 am
Winston wrote:

LOL, I have a pool in the back yard that holds 10,000 gallons of water.
When fresh filled with city water at the end of May here it heats up to
air temperature in about a week a week. The idea that a mere 40 gallons
wouldn't have a significant rise in temperature between showers after
initial stabilization at 66f is crazy.

Posted by Winston on April 21, 2009, 5:29 am
user@domain.invalid wrote:

Your tank in the basement isn't a solar collector and has very poor

coupling to any heat source.

Neglecting convection, every inch of air between the basement (walls

and floor) and your preheater tank has a conductivity of 0.014 Btu/hr ft F.

Let's say that your 40 gallon preheater has an exposed surface area of

15.5 square feet. Temperature differential is 32 F. Let's say

further that all surfaces of your preheater average about 3

feet from the toasty 66 F basement floor and walls.

I think that means your conductivity between the "warm" basement

and the cold tank contents is about 6.9 Btu/hr ft F per

inch of distance from the preheater to the basement floor

and walls.

So, we are looking at a net conductivity of 0.193 Btu/hr F

because of the 36" air gap between the basement and your tank.

As before, it'll take over 10,600 BTU/hr F to bring

the 40 gallons of 34 water within a few degrees of 66

"earth normal" during the day.

A 1060 BTU/hr F source should take about ten hours to do

that job. (Picture burning about 10.4 cubic feet of natural gas

using a 100% efficient, perfectly insulated 40 gallon water heater.)

That is not too far off in terms of a WAG. This source implies

35 cu ft. of natural gas daily, to power a 40 gallon water heater,

producing ca 130 F water:


Your 0.193 Btu/hr F source would take an impractically long

time to do the same thing, unless it had a much greater

'conductivity path' to a heat source.



Don't *faff*, dear.

Posted by user on April 21, 2009, 11:39 am
 Winston wrote:

Number one, any water tank I've ever had or seen is bang up against a
wall, not three feet out from one. My current tank is three inches from
the wall, the space I have for the tempering tank would be in the
corner, three inches from the wall on each side.

Number two, you are not going to see a complete tank change of water
all the time, incoming water from the mains is going to mix with
existing water within the tempering tank (34F & 66F).

I can see your point though, for best results I'd have to build a flat
rectangular tank mounted on the wall.

Posted by Jim Wilkins on April 21, 2009, 1:33 pm
 On Apr 21, 7:39am, u...@domain.invalid wrote:

I have a 30 Gal tempering tank, of a type not easily available so I
didn't suggest it, and it works quite well. Right now it reads 59F. It
takes less than a day to recover from laundry, which uses about 15
gallons or less with all my mods to the old top-loading Maytag. This
water all comes from the bottom drain of the tempering tank and about
half is heated in kettles on the wood stove, the rest is for rinsing.

The cold water inlet extends to the bottom of the horizontally-mounted
tank so there isn't much mixing with warmer water going out to the
electric water heater. I had to modify plumbing fittings on a lathe to
do this, as I did for the solar water heater.

I don't keep the water heater at 145 all the time, only run it up
there before a storm and possible power outage. Normally it's at the
non-adjustable setting of the upper quick-recovery element, with the
lower one set to max and switched off. The water is 106F at the faucet
right now, about 115F on a thermocouple under the tank insulation the
last time I checked. My sink spray shower head reduces the flow low
enough that the upper element will keep up with long showers. When I
need hotter water I use a teakettle.

I was an industrial electrician and production test engineer among
other jobs and know how to wire heaters and controls for these
modifications but am not going to toss the details out for everyone.
To me, typical home appliance wiring is cheap and scary, I use GM's
machine tool wiring standards and oiltight controls from surplus
stores. These and professional quality solderless terminal crimpers
are unreasonably expensive for home use unless you find them second

HD and Lowes have rigid and flexible conduit and small breaker boxes
that you can modify somewhat with hole saws or Greenlee punches if you
don't have machine tools.

Jim Wilkins

Posted by Winston on April 21, 2009, 5:41 pm
 user@domain.invalid wrote:

For best results, you would want to bury a *lot* of uncoiled 1" copper
tubing as far under the floor of the basement as you could manage.

Second best would be to place the copper in a serpentine pattern on the
floor of the basement underneath an insulated 'false floor', almost
as if you were making a hydronic floor heater, except insulated from
the basement area above. It's a twofer because the insulated floor
would make the basement feel marginally warmer during the winter.


Third best would be to plumb a serpentine pattern under an insulated
false basement floor with galvanized schedule 40 steel pipe.  The pipe
is cheap and you can spot leaks much more readily than if it were buried.

500' of galvanized 1" diameter pipe gets you a 10.5 gallon 'tank' that
is almost sufficiently coupled to the warmth entering the basement from
underneath via its 10.4 square feet of surface area.



Don't *faff*, dear.

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