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

What ?? I was going to say google a DHW setup diagram, but most of the results on duckduck are equally garbled. Maybe google is messing with the duck.

NT

It's still a minor possibility, so no. There are a handful of issues inherent in current CH/HW setups that can be solved by a ground-up redesign.

NT

NT is fond of making this kind of statement. He still thinks it makes him sound impressive, when in reality we've noticed that he's rather better at sounding impressive than he is at delivering actual expertise.

--
Bill Sloman, Sydney

given up to evaporation. latent heat of vaporization...

the water going down the drain is warm but not hot.

m

e:

ote:

ank.

can't see what's unclear.

t. You need a pressure difference to make it flow.

ater through

ifference

ank. The

...

eds that heat to

g.

Right, I'm pretty sure it's a big deal to get the cold water to return to t he hot water tank. There are systems available, mostly commercial for hotel s and similar, that continuously recirculate the hot water feed to the fixt ures, under thermostatic control, to maintain the instantaneous availabilit y of, usually scalding, hot water at the tap. And they're a big deal. Here's the last word on the subject:

So, the British seized Ireland so they could control the sheep that made the yarn for all the wooly sweaters that they needed to survive in un-heatable stone castles.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

You gonna post your measurements or whistle Dixie?

Cheers

--
Clive

or heat

dies often with

ck to the

llows - and

from the

pper pipes

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

er in one

and then

run of

into the

that into a 5' run along the bath and a 5' run back can solve both issues. Also deal with differential expansion.

There

llion

ve

t 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 buying or remodelling a house is the worst time to invest in nonessentials .

er

rding & less easy.

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

ttle & daub inside, lime render mostly outside. Filling the cavity with foa m causes structural rot.

& usually not done. Some cavity walls have random or rough surfaces inside , especially stone, cavity insulating those tends to lead to damp problems, ie mould, rot, plaster cement & masonry decay.

n fillable due to resulting damp problems.

outside, so external insulation isn't a realistic option, and highly decora ted inside, making interior insulation too expensive or unworkable.

rot, mould, decay etc. Cavity wall insulation (glued polystyrene bead, fib re or foam) is popular for cavity wall houses, but has had its share of pro blems.

chitectural interest. Insulating those is mostly not an option as the featu res must be preserved. Some have leaded windows or Crittall steel windows, both of which are energy disasters. Decorative leaded windows are typically 1 or more centuries old, too expensive to replace and many have holes wher e glass has broken. Repairing them is no cheaper than replacement.

It's not so much that stone castles are unheatable as that they fall to pie ces if kept warm. I once ran into a Canadian doctor who kept up the family castle in Scotland (while I was keeping company with a bizarre bunch of Sco ttish academics) and installing central heating wasn't an option. Water wou ld have condensed inside the outer walls and frozen, and ripped the walls a part.

You can create pockets of warmth, but you have to put insulation and imperm eable membranes inside the structural walls, and windows are tricky.

--
Bill Sloman, Sydney

Just for completeness, using a domestic alcohol in glass thermometer, water at the shower rose measured 38'C. With the thermometer lying by the drain, the waste measured 33'C and I didn't even piss on it. It's not a precision device, but I'm sure the interval would be about right.

I don't see a heat exchanger as being worthwhile for energy saving, I guess each shower use is about 1kWh. We have a pressurised HW system and plenty of water, but used to have an 'instant heat' electric shower, as do a lot of people. These are usually between about 7kW and 10kW. In the winter, 7kW is barely adequate but 10kW requires better wiring and may be at the limit of the mains supply. This is where a heat exchanger could help, boosting the flow rate from an underpowered electric shower. The flow control valve would need to be replaced with something thermostatic to cope with the incoming temperature fluctuations.

Cheers

--
Clive

ter runs

eat up.

those figures are about right. With incoming water at 5C, that's 85% of the heat energy still present in the drain water.

show us your calculations.

guesses. Mmkay.

. 40A is the limit of the mains supply on a minority of places, most are 60A or more. As you've begun to notice there are side benefits. A DHE does not require t he addition of a thermostatic shower if none were needed before.

NT

t the water leaving our homes and offices?specifically, warm and ho t wastewater?is an astoundingly powerful source of energy. One esti mate is that Americans flush 350 billion kilowatt-hours of energy into the sewers each year?roughly enough to power 30 million U.S. homes. Cit ies are taking notice, and taking steps to install sewage heat recovery sys tems to get a piece of that energy resource.

heat exchangers might get tricky dealing with raw sewage though.

t-recovery/

The waste treatment digesters don't need external heating even during winte r to keep from freezing, the biological activity is enough to keep them war m.

And they can extract enough energy from burning organics and toilet paper, once it's been run through centrifuges to drive out most of the water, to k eep the whole waste treatment operation going. It needs NG to start it.

Seems like they could combine that with district heating plants.

--Spehro Pefhany

I bought a ready-made heat exchanger for a shower here:

these are intended for the Australian / New Zealand market. I don't think they are very common because few people know or understand the possible benefits.

When I get around to having mine installed I intend to add some temperature sensors so that I can quantify the benefit.

You'll need flow sensors too.

Wouldn't it be better to just turn down the water heater temperature?

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Please do quantify the benefit. Hard figures beat handwaving!

That's what I do. It is a no-brainer in my situation.

There is a dependency on how much hot water is required relative to the tank capacity. If there is only a small tank then a higher water temperature would mean that less volume has to be drawn.

with

n

d

The picture shows the spiratech or whatever it was has a single wall betwee n waste & cold water, which is not legal in the UK. One pinhole and you get all sorts of nasty contamination in your drinking water.

NT

n with

In

and

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e

All you need is temp readings, something very simple can do that. No need f or permanent sensors.

Just time how long it takes for the shower head to fill a jug. You can work ut the rest if you know the temps.

It would in most cases result in a legionnaire's disease risk, and is not l egal here (UK).

NT

I wonder whether a single wall of double the usual thickness is legal, or if there needs to be a path for the water to escape into the air in the event of a hole.

I see it as only a theoretical risk anyway, as the mains water pressure is very high here, so any leak would cause clean water to spray into the drain pipe at high velocity. Perhaps if the water supply to the property were to fail for a long period then it could become a risk, though I always flush out the pipes after any outage, before drinking the water. I would install a non-return valve in the cold water feed anyway as they are cheap.

I see the low-pressure bathroom plumbing common in the UK as being a much bigger risk, due to the unsealed tank in the ceiling that premits vermin etc. to contaminate the bathroom tap water. A colleague of mine got sick in the UK, he believes from drinking from the tap in the bathroom.

Yes, I think that I could calculate the percentage energy saving with just all of the temperatures. For the absolute measurement, as you suggest, I could just measure the flow out of the shower head with a bucket etc.

Finding flowmeters that are legal for installation here might be expensive, due to a requirement that plumbing fittings be certified and marked, in exchange for some sort of "licencing fee" (a legal form of bribe, as I understand it). I have found that cheap mechanical flowmeters often jam up fairly quickly, so an investment in flowmeters might not be very attractive.

Nor here (Australia). I think 60 degrees C is the minimum allowed. As a consequence, tempering valves are also mandatory for the bath and shower to avoid scalding.

Also, assuming I still keep the water temperature at the shower head how I like it, then turning down the water heater temperature does not recover or reduce the heat that goes down the plughole, and to a first order it does not affect the amount of heat required to achieve the temperature and flow rate that I desire at the shower head. It only reduces the losses through the insulation of the tank, which are already small.

Having a large tank with the water at a moderately high initial temperature allows me to run the heat pump only every 2 - 3 days if I wish, and the water remains quite stratified in the tank whilst the heat pump is off. This has the potential advantage that it would permit me to for example preferentially run the heat pump during sunny days, which would be ueful if I had photovoltaic solar panels installed. The export price of solar electricity is only about a quarter of the price at which I buy electricity, so self-consumption is more worthwhile than selling and re-buying the power from the utility company, and a water tank is cheaper than a battery of the same energy capacity. Even without using PV, I have a tank big enough that I never need to run the heat pump during cold nights, I can run it at the warmest time during the day, so I can get a better coefficient of performance from the heat pump than I would if it were sometimes required to run at night.

tween waste & cold water, which is not legal in the UK. One pinhole and you get all sorts of nasty contamination in your drinking water.

I don't believe so

I don't think that's legally required either. It was years ago I looked int o it all though.

Usually it goes as you say, but water feeds do get times of negative pressu re. That can suck some nasty stuff into your drinking water.

that's a plus. You can get double nonreturn valves for better reliability, they're often used.

m.

Header tanks only supply the hot normally. There are still a few ancient in stalls where the header also supplies the bathroom cold tap, in which case the cold tap should not be considered potable. Header tanks should have a c lose fitting lid, but installs a century or so old can be in poor condition .

NT