Waste heat as heat source [was Re: Energy 101 [was Re: OT Hydrogen economy, not?]} - Page 2

 
It might make more sense to split the condenser and circulate only the
hotter water from the first stage.

Around here taking a narrow strip of land for a sidewalk is frequently
too contentious and disruptive; the buildings went up when the road
was much narrower and losing any setback makes the lots non-
compliant.

If we could install separate European-style paths for bicycles and
small personal electric vehicles like the Segway and power wheel
chairs, the pipe could be under it.  At the university I attended the
heating pipes ran through tunnels under the sidewalks and incidentally
melted the ice on them. Of course those roads could never be widened.

 

There would also be the problem of everyone becoming dependent on the one source
of heat. If the plant is shut down for maintainence, can everyone still get the
necessary heat?

 


source

Ahh, finally someone addresses a directly related issue instead of going off
on tangents.

The answer is "it depends but probably yes".  A couple of different
situations.  One, the plant is built with numerous smaller units instead of
one or two very large ones.  That's a fairly common practice with coal-fired
plants.  TVA's Widow's Creek, for example has around 13 units (I'm unsure of
the number because they were talking about decommissioning the oldest one(s))
units on one site.  One or more are always down for maintenance but the plant
always makes power and thus warm condenser water.

Routine outages can be planned for mild weather.  Emergency outages are not
likely to affect both/all units on a site.

In the event all units are down, river water can still be diverted into the
canal system.  39 degree water (where water is the densest and thus the
typical temperature underneath ice) still contains a LOT more heat than, say,
20 degree air.  Or -20 deg air where a heat pump would not function at all.

Ultimately, everyone would fall back to their resistance heating that is built
into every heat pump.  Or use an alternative heat source for the duration of
the outage.  Propane, wood stove or whatever.

In any event, I don't think that this would be a show-stopper.

That does bring up an interesting question.  What do large cities do when the
district heating plant has an un-planned outage?  Is there sufficient excess
capacity and plumbing to pipe heat from another district?

John



--
John De Armond
See my website for my current email address
http://www.neon-john.com
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Tellico Plains, Occupied TN
There is much pleasure in useless knowledge. —Bertrand Russell

 |
|>
|
|>> I guess that I could spend a few hours calculating this out using some
typical
|>> numbers but I thought that I'd instead toss out the idea and see what others
|>> have to say.
|>
|>There would also be the problem of everyone becoming dependent on the one
source
|>of heat. If the plant is shut down for maintainence, can everyone still get
the
|>necessary heat?
|
| Ahh, finally someone addresses a directly related issue instead of going off
| on tangents.

Tangents are way too common on Usenet.  Sometimes they are useful, but most of
the time not.


| The answer is "it depends but probably yes".  A couple of different
| situations.  One, the plant is built with numerous smaller units instead of
| one or two very large ones.  That's a fairly common practice with coal-fired
| plants.  TVA's Widow's Creek, for example has around 13 units (I'm unsure of
| the number because they were talking about decommissioning the oldest one(s))
| units on one site.  One or more are always down for maintenance but the plant
| always makes power and thus warm condenser water.
|
| Routine outages can be planned for mild weather.  Emergency outages are not
| likely to affect both/all units on a site.

Are there any aspects of "single point of failure" that would take the plants
entirely down?  How about their connection to the grid?  In a local plant I
was looking at, although there were 6 transmission lines leaving the plant,
it all came out of one single largish switchyard.  I did not note how many
transformers were there as I was also doing the driving at the time and had
to have my eyes on the road for at least part of the time.


| In the event all units are down, river water can still be diverted into the
| canal system.  39 degree water (where water is the densest and thus the
| typical temperature underneath ice) still contains a LOT more heat than, say,
| 20 degree air.  Or -20 deg air where a heat pump would not function at all.

That would then be the likely worst case.  But you'd have to have a lot of
water flow if there is a lot of heat extraction, to keep it above 32.


| Ultimately, everyone would fall back to their resistance heating that is built
| into every heat pump.  Or use an alternative heat source for the duration of
| the outage.  Propane, wood stove or whatever.

If a community were built with central distribution heating would they have
this already?

Still, I like the idea of extracting heat from 39F through 50F water as opposed
to -20F air.  I also like the idea of warming water instead of air in summer.


| In any event, I don't think that this would be a show-stopper.

It is likely to be the infrastructure that would be a show-stopper.  That and
acquiring all the right of ways.


| That does bring up an interesting question.  What do large cities do when the
| district heating plant has an un-planned outage?  Is there sufficient excess
| capacity and plumbing to pipe heat from another district?

When I was working in Pittsburgh, my parking area was near a steam release
pipe.  The parking attendant told me there used to be a building where the
parking lot is, and that was its steam pipeline to heat it.  It was always
releasing steam.  Apparently is it non-trivial to shut it off.  I'm guessing
that non-flowing branches pose a condensation issue.

Maybe that's an issue with steam heat.  If the system were based on just a
flow of hot water, I wonder how they might do that.

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Some fish aren't so happy with it, however.