Waste Wattage: Cities Aim to Flush Heat Energy Out of Sewers

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becomes a common drain. I just don't see it in a single family residence, e specially when these heat exchangers sell for $450 apiece, and you would ne ed a lot of them.

by 8 to get a realistic diy construction cost.

gy star appliances, clothes washers and dishwashers, which also minimize wa ter usage, flow limiters on shower heads I think are 2.5 GPM, which is plen ty, they should come out ahead. I think the commonly available and cheap 99 % efficiency electric water heater, at my $0.11 rate, estimates at $400 for an entire year for a family of four.

the shower & hot water heater you'd save $100 a year. If it's there for 20-

30 years that's 2-3k saved. Not bad for under $100.

You now need to run the cold water-> heat exchanger->shower mixing valve. I don't see running a second cold water feed all the way back to the hot wa ter feed cold water inlet.

at, so it warmed the cold feed into the shower. If you wanted to recover he at from other things you'd run the incoming cold feed via your heat exchang er to the HW cylinder/boiler. Whether that would add no or lots of pipe dep ends on house layout.

be at lower pressure and therefore will not enter the tank. The return pip ing would need a one way flow valve, and then you would either need to shut down the cold water street feed to the tank via another valve or use a boo ster pump of some kind to overcome street pressure to get the water into th e tank. Those kinds of components are not cheap.

wer duration is 5 minutes, making for just 5 gallons of water total, of whi ch maybe 3 gallons may come out of the hot water heater. It just doesn't se em like all that trouble is worth it.

That's confused. The heat is returned to the HW cylinder, when that option is used, simply by running the cold feed to the cylinder through the drain heat exchanger first. That cold feed stays at mains pressure.

NT

Reply to
tabbypurr
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t bad if someone has time on their hands. And plenty aren't capable of anyt hing better. Of course if bought as steeply priced commercial systems it's not going to pay well. Solarthermal collectors are one of the easiest techs to make pay back.

s are falling. I suspect one day kit with good ROI will be widespread - but we're not there yet.

C, only run a limited percentage of the time, and are gas not water, with c orrespondingly less heat density. If you wanted to eke the last of the heat out, an exchanger that sends warmed water from that bottom end to the bott om of the hot water cylinder, or for instant systems to a radiator would wo rk. At current prices the payback - well I've not calculated it, but am not especially optimistic. I'd expect more at lower cost from a 'hot harry' so lar preheater.

y and it needs to have very rugged construction to withstand hail and const ant beating from UV. The panel itself will contain a phase change medium th at is valved through a heat exchanger through which your potable water is p umped.

There are many designs of solarthermal collector. Some use vacuum tubes, so me use flat plate, some use concentrators, and there are other types. Some use phase change in the collector, some water, some just metal or air. Some heat water, some heat air. Some are expensive, some are cheap, some are ma de from scrap.

as temperatures approach freezing,

Again there are a few ways to deal with freezing in water heating systems. The usual approaches are drain back, drain down & antifreeze. You're descri bing drain down.

h large thermal heat storage mass, usually stone.

Stone is one option, many don't use it.

small system is $4000, which is a decade payback time. This is why you don' t see a whole lot of them.

It's why you don't see a whole lot of systems of that cost & design in use. There are many a small fraction of that price. It's a challenge to get goo d payback but some have done a good job of that. If you go to a solar heati ng company & buy what you describe, you lose.

NT

Reply to
tabbypurr

They're already doing that effectively.

In the UK, condensing boilers are meandatory (more or less). And I've recently heard of another evolution where there will be secondary heat recovery from the flue.

But to be honest, the gas and vapour that comes out of mine is on the hot side of warm rather than "burn the paint off the wall" like old fashioned boilers.

Given there is still a vapour plume on a cold day, there's some potential for further latent heat and absolute heat recovery, but I wonder how much?

I guess, for a combination boiler, they could route the incoming cold water via a flue heat exchanger.

But for central heating, the return temperature on a reasonably designed system is still 45-50C so that's less easy.

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Reply to
Tim Watts

That sounds like materials cost. It would cost kilobucks here to have a plumber do it.

We dump a lot of heat out the exhaust from our gas-fired space and tank-type water heaters, but that would be hard to recover; the water is not necessarily flowing when the hot gas is.

Our house is townhouse style, so we don't lose heat on the sides, which are most of the surface area. The best way to save energy for most people is insulation and good windows.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

Running the incoming cold through the flue is not quite as easy as it sounds. Exposed to outdoor temps it would a) be prone to freeze b) lose heat much of the time.

With 3 electrically actuated valves one could a) run the water through there when there is overall gain b) open the 3rd valve to drain the flue loop when temp gets low.

There is a more effective & cheaper approach, but I'm not going to get into that here.

NT

Reply to
tabbypurr

e:

te:

heat

ten with

. In some

to the

t becomes a common drain. I just don't see it in a single family residence, especially when these heat exchangers sell for $450 apiece, and you would need a lot of them.

t by 8 to get a realistic diy construction cost.

ergy star appliances, clothes washers and dishwashers, which also minimize water usage, flow limiters on shower heads I think are 2.5 GPM, which is pl enty, they should come out ahead. I think the commonly available and cheap

99% efficiency electric water heater, at my $0.11 rate, estimates at $400 f or an entire year for a family of four.

o the shower & hot water heater you'd save $100 a year. If it's there for 2

0-30 years that's 2-3k saved. Not bad for under $100.

e. You now need to run the cold water-> heat exchanger->shower mixing valve . I don't see running a second cold water feed all the way back to the hot water feed cold water inlet.

heat, so it warmed the cold feed into the shower. If you wanted to recover heat from other things you'd run the incoming cold feed via your heat excha nger to the HW cylinder/boiler. Whether that would add no or lots of pipe d epends on house layout.

ll be at lower pressure and therefore will not enter the tank. The return p iping would need a one way flow valve, and then you would either need to sh ut down the cold water street feed to the tank via another valve or use a b ooster pump of some kind to overcome street pressure to get the water into the tank. Those kinds of components are not cheap.

hower duration is 5 minutes, making for just 5 gallons of water total, of w hich maybe 3 gallons may come out of the hot water heater. It just doesn't seem like all that trouble is worth it.

n is used, simply by running the cold feed to the cylinder through the drai n heat exchanger first. That cold feed stays at mains pressure.

Not following that at all. What do you mean by hot water cylinder?

Reply to
bloggs.fredbloggs.fred

t

ften with

? In some

the

- and

the

ipes

ipe is universal indoors here. Either way replacing a bit is part of the pl an

one

en

f

he

nto a 5' run along the bath and a 5' run back can solve both issues. Also d eal with differential expansion.

Materials cost yes. Greenies, keen diyers, self builders etc would not mind doing it themselves. It would cost 100s for a plumber to do it here, which would not help ROI any but it would still get 10% pa. Of course when buyin g or remodelling a house is the worst time to invest in nonessentials.

Condensing heaters get 90 something % out, that last bit is less rewarding & less easy.

yep. Those have been mandatory for years here. But we also have millions of houses from the 1800s & earlier with no insulation of any kind.

NT

Reply to
tabbypurr

e:

ote:

rote:

or heat

often with

er. In some

ck to the

hat becomes a common drain. I just don't see it in a single family residenc e, especially when these heat exchangers sell for $450 apiece, and you woul d need a lot of them.

ost by 8 to get a realistic diy construction cost.

energy star appliances, clothes washers and dishwashers, which also minimiz e water usage, flow limiters on shower heads I think are 2.5 GPM, which is plenty, they should come out ahead. I think the commonly available and chea p 99% efficiency electric water heater, at my $0.11 rate, estimates at $400 for an entire year for a family of four.

to the shower & hot water heater you'd save $100 a year. If it's there for 20-30 years that's 2-3k saved. Not bad for under $100.

ure. You now need to run the cold water-> heat exchanger->shower mixing val ve. I don't see running a second cold water feed all the way back to the ho t water feed cold water inlet.

r heat, so it warmed the cold feed into the shower. If you wanted to recove r heat from other things you'd run the incoming cold feed via your heat exc hanger to the HW cylinder/boiler. Whether that would add no or lots of pipe depends on house layout.

will be at lower pressure and therefore will not enter the tank. The return piping would need a one way flow valve, and then you would either need to shut down the cold water street feed to the tank via another valve or use a booster pump of some kind to overcome street pressure to get the water int o the tank. Those kinds of components are not cheap.

shower duration is 5 minutes, making for just 5 gallons of water total, of which maybe 3 gallons may come out of the hot water heater. It just doesn' t seem like all that trouble is worth it.

ion is used, simply by running the cold feed to the cylinder through the dr ain heat exchanger first. That cold feed stays at mains pressure.

The large tank in which cold water is heated to become hot water.

When instant heating is used, the obvious place to return warmed cold water to is the shower cold inlet.

NT

Reply to
tabbypurr

of

not bad if someone has time on their hands. And plenty aren't capable of an ything better. Of course if bought as steeply priced commercial systems it' s not going to pay well. Solarthermal collectors are one of the easiest tec hs to make pay back.

sts are falling. I suspect one day kit with good ROI will be widespread - b ut we're not there yet.

80C, only run a limited percentage of the time, and are gas not water, with correspondingly less heat density. If you wanted to eke the last of the he at out, an exchanger that sends warmed water from that bottom end to the bo ttom of the hot water cylinder, or for instant systems to a radiator would work. At current prices the payback - well I've not calculated it, but am n ot especially optimistic. I'd expect more at lower cost from a 'hot harry' solar preheater.

ogy and it needs to have very rugged construction to withstand hail and con stant beating from UV. The panel itself will contain a phase change medium that is valved through a heat exchanger through which your potable water is pumped.

some use flat plate, some use concentrators, and there are other types. Som e use phase change in the collector, some water, some just metal or air. So me heat water, some heat air. Some are expensive, some are cheap, some are made from scrap.

The durable manufactured units use vacuum technology with heat power circul ation of a phase change fluid to exchange heat with the water. All this hom espun stuff using beer cans and what not are total junk. For the far north, like Canada to U.S., they do use parabolic dish systems, BIG dishes, with water circulated through insulated tubing through focal point.

ng as temperatures approach freezing,

. The usual approaches are drain back, drain down & antifreeze. You're desc ribing drain down.

Anyone can figure out how to make it freeze proof, including electric heate r traces, but is the efficiency any good.

ith large thermal heat storage mass, usually stone.

I'm pretty sure stone is the tank of choice in U.S. systems.

a small system is $4000, which is a decade payback time. This is why you do n't see a whole lot of them.

e. There are many a small fraction of that price. It's a challenge to get g ood payback but some have done a good job of that. If you go to a solar hea ting company & buy what you describe, you lose.

True- but I think they may be losing out to heat pump hot water heating.

There are systems, GE has one, with a hot water tank with mini heat pump at tached that heats the water with the indoors ambient heat. There are others where the heat pump conditions the whole house in addition to being switch ed into an additional exchanger to heat the water as needed.

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The 80 gal version lists for $1100 on Amazon. That's not too bad for a fami ly of four situation, and it looks to outdo the solar.

Reply to
bloggs.fredbloggs.fred

ote:

for heat

s often with

ater. In some

back to the

what becomes a common drain. I just don't see it in a single family reside nce, especially when these heat exchangers sell for $450 apiece, and you wo uld need a lot of them.

cost by 8 to get a realistic diy construction cost.

e energy star appliances, clothes washers and dishwashers, which also minim ize water usage, flow limiters on shower heads I think are 2.5 GPM, which i s plenty, they should come out ahead. I think the commonly available and ch eap 99% efficiency electric water heater, at my $0.11 rate, estimates at $4

00 for an entire year for a family of four.

ly to the shower & hot water heater you'd save $100 a year. If it's there f or 20-30 years that's 2-3k saved. Not bad for under $100.

xture. You now need to run the cold water-> heat exchanger->shower mixing v alve. I don't see running a second cold water feed all the way back to the hot water feed cold water inlet.

wer heat, so it warmed the cold feed into the shower. If you wanted to reco ver heat from other things you'd run the incoming cold feed via your heat e xchanger to the HW cylinder/boiler. Whether that would add no or lots of pi pe depends on house layout.

r will be at lower pressure and therefore will not enter the tank. The retu rn piping would need a one way flow valve, and then you would either need t o shut down the cold water street feed to the tank via another valve or use a booster pump of some kind to overcome street pressure to get the water i nto the tank. Those kinds of components are not cheap.

ge shower duration is 5 minutes, making for just 5 gallons of water total, of which maybe 3 gallons may come out of the hot water heater. It just does n't seem like all that trouble is worth it.

ption is used, simply by running the cold feed to the cylinder through the drain heat exchanger first. That cold feed stays at mains pressure.

er to is the shower cold inlet.

You might draw a diagram to show how you return the water to that tank.

Reply to
bloggs.fredbloggs.fred

The standard US construction is wood with drywall inside, studs, and something ourside. It's not hard to pump in foam or something. I'd imagine a stone cottage would be harder to insulate.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
 Click to see the full signature
Reply to
John Larkin

e:

st of

- not bad if someone has time on their hands. And plenty aren't capable of anything better. Of course if bought as steeply priced commercial systems i t's not going to pay well. Solarthermal collectors are one of the easiest t echs to make pay back.

costs are falling. I suspect one day kit with good ROI will be widespread - but we're not there yet.

0-80C, only run a limited percentage of the time, and are gas not water, wi th correspondingly less heat density. If you wanted to eke the last of the heat out, an exchanger that sends warmed water from that bottom end to the bottom of the hot water cylinder, or for instant systems to a radiator woul d work. At current prices the payback - well I've not calculated it, but am not especially optimistic. I'd expect more at lower cost from a 'hot harry ' solar preheater.

ology and it needs to have very rugged construction to withstand hail and c onstant beating from UV. The panel itself will contain a phase change mediu m that is valved through a heat exchanger through which your potable water is pumped.

, some use flat plate, some use concentrators, and there are other types. S ome use phase change in the collector, some water, some just metal or air. Some heat water, some heat air. Some are expensive, some are cheap, some ar e made from scrap.

ulation of a phase change fluid to exchange heat with the water. All this h omespun stuff using beer cans and what not are total junk. For the far nort h, like Canada to U.S., they do use parabolic dish systems, BIG dishes, wit h water circulated through insulated tubing through focal point.

ping as temperatures approach freezing,

ms. The usual approaches are drain back, drain down & antifreeze. You're de scribing drain down.

ter traces, but is the efficiency any good.

with large thermal heat storage mass, usually stone.

n a small system is $4000, which is a decade payback time. This is why you don't see a whole lot of them.

use. There are many a small fraction of that price. It's a challenge to get good payback but some have done a good job of that. If you go to a solar h eating company & buy what you describe, you lose.

attached that heats the water with the indoors ambient heat. There are othe rs where the heat pump conditions the whole house in addition to being swit ched into an additional exchanger to heat the water as needed.

mily of four situation, and it looks to outdo the solar.

I can only conclude you're not upto speed on this stuff. There are systems using all sorts of collectors other than vac tubes that give far better ROI . Go explore the subject.

NT

Reply to
tabbypurr

e:

te for heat

ies often with

water. In some

n back to the

ng what becomes a common drain. I just don't see it in a single family resi dence, especially when these heat exchangers sell for $450 apiece, and you would need a lot of them.

at cost by 8 to get a realistic diy construction cost.

use energy star appliances, clothes washers and dishwashers, which also min imize water usage, flow limiters on shower heads I think are 2.5 GPM, which is plenty, they should come out ahead. I think the commonly available and cheap 99% efficiency electric water heater, at my $0.11 rate, estimates at $400 for an entire year for a family of four.

pply to the shower & hot water heater you'd save $100 a year. If it's there for 20-30 years that's 2-3k saved. Not bad for under $100.

fixture. You now need to run the cold water-> heat exchanger->shower mixing valve. I don't see running a second cold water feed all the way back to th e hot water feed cold water inlet.

hower heat, so it warmed the cold feed into the shower. If you wanted to re cover heat from other things you'd run the incoming cold feed via your heat exchanger to the HW cylinder/boiler. Whether that would add no or lots of pipe depends on house layout.

ter will be at lower pressure and therefore will not enter the tank. The re turn piping would need a one way flow valve, and then you would either need to shut down the cold water street feed to the tank via another valve or u se a booster pump of some kind to overcome street pressure to get the water into the tank. Those kinds of components are not cheap.

rage shower duration is 5 minutes, making for just 5 gallons of water total , of which maybe 3 gallons may come out of the hot water heater. It just do esn't seem like all that trouble is worth it.

option is used, simply by running the cold feed to the cylinder through th e drain heat exchanger first. That cold feed stays at mains pressure.

ater to is the shower cold inlet.

Incoming cold water -> drain heat exchanger -> hot water cylinder. I can't see what's unclear.

NT

Reply to
tabbypurr

heat

s often with

to the

ws - and

om the

r pipes

e pipe is universal indoors here. Either way replacing a bit is part of the plan

in one

then

n of

o the

t into a 5' run along the bath and a 5' run back can solve both issues. Als o deal with differential expansion.

ere

on

ind doing it themselves. It would cost 100s for a plumber to do it here, wh ich would not help ROI any but it would still get 10% pa. Of course when bu ying or remodelling a house is the worst time to invest in nonessentials.

ng & less easy.

of houses from the 1800s & earlier with no insulation of any kind.

Our 1300s - 1600s houses are mostly fairly like that, with oak frame, wattl e & daub inside, lime render mostly outside. Filling the cavity with foam c auses structural rot.

1800s houses are mostly brick with no cavity. Insulating those is costly & usually not done. Some cavity walls have random or rough surfaces inside, e specially stone, cavity insulating those tends to lead to damp problems, ie mould, rot, plaster cement & masonry decay.

Rat-trap bond is another brickwork type that is cavity but not insulation f illable due to resulting damp problems.

Some large houses are 2' thick stone, no cavity. Many are pretty on the out side, so external insulation isn't a realistic option, and highly decorated inside, making interior insulation too expensive or unworkable.

The big issues with retrofit insulation are cost & damp problems such as ro t, mould, decay etc. Cavity wall insulation (glued polystyrene bead, fibre or foam) is popular for cavity wall houses, but has had its share of proble ms.

There's also a great number of listed properties, buidings of special archi tectural interest. Insulating those is mostly not an option as the features must be preserved. Some have leaded windows or Crittall steel windows, bot h of which are energy disasters. Decorative leaded windows are typically 1 or more centuries old, too expensive to replace and many have holes where g lass has broken. Repairing them is no cheaper than replacement.

Insulation would be a lot easier if our climate were drier.

NT

Reply to
tabbypurr

ote:

date for heat

odies often with

ot water. In some

in back to the

ring what becomes a common drain. I just don't see it in a single family re sidence, especially when these heat exchangers sell for $450 apiece, and yo u would need a lot of them.

that cost by 8 to get a realistic diy construction cost.

d use energy star appliances, clothes washers and dishwashers, which also m inimize water usage, flow limiters on shower heads I think are 2.5 GPM, whi ch is plenty, they should come out ahead. I think the commonly available an d cheap 99% efficiency electric water heater, at my $0.11 rate, estimates a t $400 for an entire year for a family of four.

supply to the shower & hot water heater you'd save $100 a year. If it's the re for 20-30 years that's 2-3k saved. Not bad for under $100.

r fixture. You now need to run the cold water-> heat exchanger->shower mixi ng valve. I don't see running a second cold water feed all the way back to the hot water feed cold water inlet.

shower heat, so it warmed the cold feed into the shower. If you wanted to recover heat from other things you'd run the incoming cold feed via your he at exchanger to the HW cylinder/boiler. Whether that would add no or lots o f pipe depends on house layout.

water will be at lower pressure and therefore will not enter the tank. The return piping would need a one way flow valve, and then you would either ne ed to shut down the cold water street feed to the tank via another valve or use a booster pump of some kind to overcome street pressure to get the wat er into the tank. Those kinds of components are not cheap.

verage shower duration is 5 minutes, making for just 5 gallons of water tot al, of which maybe 3 gallons may come out of the hot water heater. It just doesn't seem like all that trouble is worth it.

at option is used, simply by running the cold feed to the cylinder through the drain heat exchanger first. That cold feed stays at mains pressure.

water to is the shower cold inlet.

t see what's unclear.

Bernoulli's Law. The HW cylinder is at same pressure as cold water inlet. Y ou need a pressure difference to make it flow.

Reply to
bloggs.fredbloggs.fred

I think you are missing that the cold water inlet *always* goes through the heat exchanger.

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Reply to
Rodney Pont

Someone is leaving out too many words. The pressure that forces cold water through the heat exchanger is from the municipal water system, and the pressure difference is created when hot water is drawn (for your shower) from the hot water tank. The tank pressure drops because the hot valve is cracked in your shower stall...

After the shower, a bit of hot water is still in the exchanger, so it bleeds that heat to the air as well as preheating the slender hot-water-tank cold inlet piping.

Reply to
whit3rd

Steam genny would be useful...

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Reply to
David Lesher

Okay- I missed that part. So he has a second heat exchanger at the hot water tank. He uses a lot of pipe or lives in a small house.

Reply to
bloggs.fredbloggs.fred

Well don't leave us hanging, unless it will impinge on the profits you stand to make from this device.

Reply to
Riley Angel

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