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One of the critical factors affecting the efficiency of heat engine-derived power is the difference between the hot and cold sides of the turbine. This is the reason why power stations often have large cooling towers. A large amount of low-grade heat is released to the environment.
During the cold
seasons here in the UK, (perhaps 6 months or so of the year) I (and I expect most people) find the water supply to be undesirably cold for most purposes.
I propose that one could drain the waste heat from power stations into the domestic water supply, during the cold season. The water would not end up hot, just not quite as freezing cold. This would both increase the efficiency of power generation and improve water user experience (either warmer water or more cheaply heated water).
There are only two drawbacks to this.
One is that people who actually want cold water will need to cool the water down before use. This is probably not much of an issue in practice - apart from masochistic cold-water bathers only a small amount is needed, and so easily obtained by refrigeration. This drawback is of course massively outweighed by the general benefit of warmer water.
The other issue is that the water supply would need to be routed via the powerstation.
Rather than attempting to retrofit this process to existing power-stations, I suggest that this could be a factor taken into account in the siting and design of new installations.
With current thinking being that efficiency savings are gained by converting most heating to electrical methods, there will be a much higher demand for power in cold periods anyway. It therefore seems to me to be an ideal fit for new plant intended to primarily serve this seasonal demand.
From a quick online search, mains water temperature can be 16 degrees Celcius in Summer, and in Winter can be 6 degrees (and perhaps less).
The legal maximum temperature for cold water supply is 20 degrees Celcius.
Therefore there is scope for heating the water by 10 degrees C or so, without leaving the normal range.
So we could both create electricity more efficiently, and save heating energy (or have a more pleasant non-heated experience)!
Rather a common practice really
http://en.wikipedia...ined_heat_and_power
[FlyingToaster, Apr 15 2012]
What is the average temperature of potable mains water?
http://uk.answers.y...080229032239AAEqIDA
Built-in defence against link rot: Summer temp. 16 degrees C, recent Winter temp. 6 degrees C. [Loris, Apr 15 2012]
Hot beverage district heating
Hot_20beverage_20district_20heating
You want biscuits with that ,,, ? [8th of 7, Apr 15 2012]
GB summer and winter power demand graph
http://www.national...2/images/fig2-2.gif
winter electricity demand is approx. 10 GW higher. [Loris, Apr 18 2012]
[link]
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[+] but as you say //the water supply would need to be routed via the powerstation// |
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//Rather a common practice really// |
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Actually, no. Sure, cogeneration exists already, but not in the form I'm proposing.
The distinction is that I'm talking about heating the standard water supply, not putting in an extra hot-water pipe. |
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District heating systems necessarily limit the efficiency of the power-plant (since they effectively raise the temperature of the cold side of the engine). |
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Also, with this idea, the power-plant doesn't need to be near the housing district, merely on the water supply main. |
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//the power-plant doesn't need to be near the
housing district, merely on the water supply main.//
You'd need well-insulated pipes. |
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Water mains are buried, so the heat loss would be limited to the heating capacity of the adjacent substrate. This heat would be recovered when the system is switched off. This is actually a benefit, since it means the temperature is buffered and will only change gradually; it won't be disconcerting to the public. |
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Would this system necessitate the need for more chlorine in the water supply to supress bacterial growth? |
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I was thinking of a similar use for the constant methane fire at our local landfill and waste treatment facility. It seems like a huge squandering of rescources to me. |
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Adding things to the water supply is very popular in some circles. Chlorine, fluoride, even statins have been suggested, so why not the waste heat from atomic reactors? And why not make it boiling hot, so that it won't take so much heat to boil your eggs, and so you can run it right through radiators in your house. To cool it sufficiently for drinking and bathing, you could have a cooling tower in your backyard, which would emit a warm fog in the mornings, keeping your lawn green and your orange trees from freezing. Eventually, with every home hooked up to this boiling supply main, the rare cold-water flat will become not only nostalgic, but quite desirable. |
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//Would this system necessitate the need // |
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It would almost certainly demand the requirement
to necessitate the need. |
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//Would this system necessitate the need for more chlorine in the water supply to supress bacterial growth?// |
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Good question. I don't know the answer.
However, provided we don't raise the water temperature above whatever the maximum is in Summer we can safely not add any more than is added then, which is clearly within tolerances.
If the sterilisation protocol is currently held constant throughout the year then no additional treatment would be necessary. |
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Since the higher temperature promotes bacterial
growth, why why fight it? Instead of extra chlorine,
innoculate the water supply with "good" bacteria,
which will out-compete the pathogens, in a manner
analogous to normal colonic flora. |
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If it's boiling hot, you can dispense with the chlorine and just add tea. |
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The legal maximum for cold water is 20degC? That's
it, then. I'm off, to sue the local council for
delivering illegal temperature tapwater all this past
summer. The bastards! |
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//The legal maximum for cold water is 20degC?// |
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Apparently, yes.
Although apparently it's *also* 25 degrees C, which I can't quite reconcile. I just took the lower limit to be on the safe side. |
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and I should have said - in the UK. YMMV, E&OE, IANAL |
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Ah... **in the UK**... that's all better, then. For it
doesn't drop much below 25C (77F) at any time of
the year here, let alone 20C (68F). |
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Incidentally, in places like Blackall and further to
the southwest into South Australia, the water
comes out of the tap at temperatures between
68C and 100C. It's pumped up from the depths of
the Great Artesian Basin, and needs to stand for a
day or so, in cooling tanks, before it can be used
for bathing and normal household water
applications. |
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Siberian cities often had central district water heating systems which were notoriously useless due to downtime for frequent repair. Because of the permafrost, they usually piped it all above ground, as well, which made for some bizarre cityscapes and road intersections. |
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/the water comes out of the tap at temperatures between 68C and 100C/ |
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That is amazing. I would like to learn more. To get water this hot from underground it must be geothermally heated. Water like this would be very tough on pipes as I am sure there must be lots of dissolved minerals that precipitate on cooling. |
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My googles turned up lots of interest in preventing scald injuries in australia but no luck as regards naturally boiling water. Help? |
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wikipedia: great artesian basin: "30C to 100C", world's biggest water table; amazing; doesn't say why it's so hot though. |
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Got to be geothermal. That's what they said on "Australia: a time traveller's guide". Also, what else could it possibly be? Also also, it's hot stuff what comes out of the ground, so by definition it's geothermal. Basically, it's hot down there. |
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The water comes up from depths as great as
10,000 feet, so it gets pretty warm, from
geothermal heating. |
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Yes, it's hard on plumbing infrastructure, as there's
a lot of dissolved minerals in the water table. It
tastes bloody terrible. (Jokes about bacon for
breakfast, pork for lunch, ham for dinner and tea
made with "boar water" are popular in regions
where the water is used for human consumption.) |
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So far, a lot of the water taken from it has been
wasted, as it's been allowed to flow uncapped in
many of the older bores. That is being resolved,
gradually. |
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I couldn't resist some back-of-the-envelope calculations. |
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Apparently domestic water use in the UK averages 150 liters per person per day. Therefore a town with a population of 100,000 draws about 15,000 cubic meters per day (or 15,000 tons/day if you prefer).
Using the aformentioned 10 degree water temperature rise, we can sink 4.2 * 10^6 * 15000 = 6.3*10^10 Joules, or 63000 megaJoules of heat per day.
This corresponds to an average power of 63000000000/24/60/60=730000 Watts, or 730 kilowatts. |
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Let us assume that the associated power station is 33%, or one-third efficient at turning energy into electricity. Power stations are described by wattage of their output electricity. So for every Watt produced, we need to sink two Watts of heat. Therefore the above town's water supply can act as a total sink for a 360kWe (0.36MWe) power station. |
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Certainly, that isn't a large power station, although these values obviously scale with the size of the town or city, and may be increased further if there are significant heat losses, or if this were only a partial sink.
I think it might be a good fit with a biofuel plantation. There are significant diseconomies of scale for those, and it is in any case more efficient to generate power close to where it is needed. |
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