Re: Hydrogen economy will never exist
From: william mook (william.mook_at_mokindustries.com)
Date: 07/16/04
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Date: 16 Jul 2004 09:14:15 -0700
"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message news:<1mkJc.44557$yd5.40124@twister.nyroc.rr.com>...
> "william mook" <william.mook@mokindustries.com> wrote in message
> news:407c5321.0407130525.49ebbbbd@posting.google.com...
> > Fred Kasner <fkasner@sdf.lonestar.org> wrote in message
> news:<ccv183$8ii$4@chessie.cirr.com>...
> > > In sci.energy.hydrogen william mook <william.mook@mokindustries.com>
> wrote:
> > > > Fred,
>
> > > > Your objections are utter rot designed to let you make dismissive
> > > > statements with no real analysis whatever.
>
> > > > Check it out.
> > >
> > > ... snip ...
> > >
> > > >> >>
> > > >> >> daestrom
> > > >>
> > > >> Common error is to assume the feed water for a heating system is what
> you
> > > >> claimed as 22 deg C.
>
> > > > Its only an error if its wrong. In cases where the inlet temperature
> > > > is 22 C - its not wrong. In cases where the inlet temperature is
> > > > different, my method of calculation is shown, and easily adjusted to
> > > > account for it.
> > >
> > > Then adjust it and stop generalizing so broadly.
> > > FK
> >
> > Are you talking to me or daestrom? I agree if you're talking to
> > daestrom - since that's exactly what I've said above.
> >
>
> Well, since you guys seem to keep attaching my name to each others
> arguments, I guess I'll just have to jump in here and repeat what I said
> before.
>
> Since Mr. Mook's design has to be forcefully cooled, I merely suggested that
> diverting the rejected heat to a home for some domestic use could be
> worthwhile.
I agree with this, especially in climates where energy costs are high.
I even gave an example where we're doing this - Raytheon Polar
Services at McMurdo Station at the South Pole, where any heat is
highly valued, where energy storage is not a problem (6 months of
sun),and where fuel costs are high ($16 per gallon of diesel) This of
course is an extreme, and other system will certainly benefit from
this application.
> There are a few uses for 'low-grade' heat in the average home
> (space and water heating are two examples).
Yep.
> Mr Mook countered with the
> costs of hot-water heaters and such tanks, saying the cost of the equipment
> outweighs the cost of the energy replaced.
Yes.
> Fine. But since most homes in
> the US already *have* a hot-water storage tank, there may be situations
> where the PV 'coolant' can be used to heat an existing tank of water.
For hot water heating you need a pretty pure source of water, so you
must do this with some sort of heat exchanger. This means you have a
tank for your pure water, and a tank for circulating water, which
means an added tank. The water is necessarily impure from your heat
exchanger because you don't want the stuff to boil away or freeze - so
you put anti-freeze in it, just like in your auto. You wouldn't want
to bathe with radiator water, so you need an extra tank anyway.
> Using
> the existing tank and just some additional fittings *may* lower the capital
> cost to a point where the future value of the rejected heat over the life of
> the equipment is positive.
That won't be possible because doing so makes the heat exchanger in
the PV unit too inefficient and costly.
> Without knowing more details of his current
> cooling system design, it is difficult to make any further analysis.
Right. We're using an auxilarly transmission cooler that we got from
an autoparts store and adapted at our machine shop. It runs on 12
volts, is nicely regulated and costs only $200 - not included machine
shop charges. I wouldn't want to bath in what circulates in that
either.
If I wanted to make use of the heat, I'd have to replace the radiator
with some sort of heat exchanger, and put the whole think in another
tank with fresh water I wanted to heat. This is what we're doing for
McMurdo, except here we're using snow as the water source - and yes,
the inlet temperature is less than zero! (but the cost per watt is
about the same as what I calculated earlier - in fact its less if you
want cold drinking water from snow!)
> As far as 22C, *if* you use a closed loop system to cool the PV and
> circulate the heat into the home for space heating, the return temperature
> from the house could easily be in this range.
Yep.
> Simply circulating the
> 'coolant' through the cold-air return of a forced air system would warm the
> air in the home and provide such a 'return' temperature to the PV cooler.
Yes.
> If you are using open-loop, such as domestic hot-water supply, then of
> course the inlet temperature would most likely be different.
Yes, but not by much.
> But the specific heat capacity of water does *not* vary by much in the
> temperature range we're talking about.
The specific heat stays about the same. What does change is the total
energy needed - but the range of values with different inlet
temperatures doesn't vary by much, which was my point.
> So the exact inlet temperature
> doesn't matter unless you want to completely replace the existing hot water
> heating system.
Well, there's an issue of capacity. It takes a far bigger tank of
water to store enough heat to heat a home during times when the sun
isn't shining than it does to store enough heat to heat water for hot
water purposes (or merely melt snow for fresh water). At McMurdo the
sun's up all the time when the unit is running, so storage is a
minimum, you have a constant flow of hot fluid. Setup for 6 months
of darkness though is a bitch. You've got to drain everything dry, and
switch over to the old diesel powered system- or merely run the diesel
setup 12 months at a reduced capacity (everyone but a skeleton crew
leaves the South Pole when the sun sets).
> If the waste heat is merely used to augment the existing
> system, then a colder inlet water will merely demand more of the existing
> water heater (the pre-heater outlet temperature will be correspondingly
> lower).
Yes and this makes about a 20% difference in the total energy
required.
> The PV rejected heat will provide nearly the same temperature rise
> (22C to 82C, or 10C to 70C for Mr. Mook's example).
That's true - but the outlet temperature on the PV is a function of
the junction temperature which is pretty constant. What happens with
cooler water is that you reduce the flow rate - since the heat source
is pretty constant. Even this changes though when a cloud passes by,
or when the sun sets. Then you cut the circulation to zip, and make
sure your lines don't freeze in the dark (depending on external
temps).
> So its economic benefit
> in replacing some of the energy needed to heat the incoming water is not
> changed.
Yep.
> I'm thinking of the waste heat being used in a preheater for domestic
> hot-water.
This could certainly work well.
> In such a role, it would *not* matter what the inlet temperature
> is over a wide range.
Yep, and you're storage of heat is reduced to a minimum. If you use
solar electricity to run the balance (whether space heating or water
heating) you've made a system that's the most capital efficient -
which is what you're after with a system that doesn't use fuel.
> If the pre-heater outlet temperature is below the
> main water heater's set-point, then the energy savings of the pre-heater
> section would be about the same if the inlet is 22C or 5C.
Yep.
> daestrom
Thanks for your kind comments - they're on target as far as I can
tell.
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