At last: a practical Energy Harvesting proposal?

In summary, there are several options for utilizing waste warm water from plumbing systems, such as shower heat recovery and whole house systems. These systems require regular maintenance and may involve separate drainage for foul water. However, they can provide more usable heat per electrical kWh than air source heat pumps in the winter and could be a cheaper alternative. There are also existing systems for this purpose, such as greywater heat recovery systems and balanced ventilation systems with heat recovery.
  • #1
sophiecentaur
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TL;DR Summary
Use the waste warm water from your plumbing system.
I was enjoying my (very short) hot shower this morning and realized that the lovely warm water was flowing over my body (sorry - too much information) only once and then disappearing down the drain.

This water - and what comes out of the washing machine, dishwasher etc. could be at a seriously 'useful' temperature for a heat pump. There must be many kWh lost over a day. You can find systems for shower heat recovery, advertised but they seem to be passive and are low hanging fruit, afaics. A whole house system would be better and would involve a hot water storage tank (which I have).

Obviously the heat exchanger plumbing would need to be maintained (cleaned out) on a regular basis and I would imagine that separate drainage would be needed for foul water. Also, the discharge water temperature would need to be well above freezing but the usable heat would be a lot more, per electrical kWh, than what can be obtained from an air source heat pump in winter. An installation could be a lot cheaper than heat pumps that are being considered today.

Many years ago I heard of a scheme to recycle heat from a house via a ventilation system where outgoing air is passed through a heat exchanger to warm up incoming air. That's a similar principle.

I ask myself why there aren't dozens of these alternative systems to be found working in houses all ov er the country.
 
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  • #2
sophiecentaur said:
I ask myself why there aren't dozens of these alternative systems to be found working in houses all ov er the country.
Ah yes, something else that needs regular maintenance and can break or leak all over my house...
Honestly they probably just don't save very much money for their added cost and complexity.
 
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  • #3
Before the water becomes waste, heat is lost to the air, and to your body.
Hot water evaporates to steam, then condenses on the ceiling and the mirror.
Hot air, and saturated air rise, so the heat moves to the top of the room, not to the drain.
 
  • #4
sophiecentaur said:
Many years ago I heard of a scheme to recycle heat from a house via a ventilation system where outgoing air is passed through a heat exchanger to warm up incoming air.
By the way, that works both for recovering heat and: cold too :wink:

sophiecentaur said:
I ask myself why there aren't dozens of these alternative systems to be found working in houses all over the country.
Unless you have a really beefy heat pump to do the job 'on the fly', like that Zypho thing does, you need to store the wastewater for a time. Not impossible, but also not really convenient since it may mean a m3 class insulated tank somewhere (below shower level, likely).

The more thorough the design, the more problems and costs pops up. So far just wasting that heat was not really painful.
 
  • #5
Rive said:
So far just wasting that heat was not really painful.
So far. I agree but things are changing and Energy will be increasingly relevant - that's both for heating and for building things.
As for the quantity of hot water that would need to be stored, in a house with a hot tank (and that will soon have to be the norm because Combi Boilers will die out) we'd need' only something like that volume. 'On tap' heat will not be a sustainable method and heat storage will be necessary in any case.

I like the cooler idea . btw.
 
  • #6
sophiecentaur said:
Summary:: Use the waste warm water from your plumbing system.

I was enjoying my (very short) hot shower this morning and realized that the lovely warm water was flowing over my body (sorry - too much information) only once and then disappearing down the drain.

This water - and what comes out of the washing machine, dishwasher etc. could be at a seriously 'useful' temperature for a heat pump. There must be many kWh lost over a day. You can find systems for shower heat recovery, advertised but they seem to be passive and are low hanging fruit, afaics. A whole house system would be better and would involve a hot water storage tank (which I have).

Obviously the heat exchanger plumbing would need to be maintained (cleaned out) on a regular basis and I would imagine that separate drainage would be needed for foul water. Also, the discharge water temperature would need to be well above freezing but the usable heat would be a lot more, per electrical kWh, than what can be obtained from an air source heat pump in winter. An installation could be a lot cheaper than heat pumps that are being considered today.

Many years ago I heard of a scheme to recycle heat from a house via a ventilation system where outgoing air is passed through a heat exchanger to warm up incoming air. That's a similar principle.

I ask myself why there aren't dozens of these alternative systems to be found working in houses all ov er the country.

There is already many systems for this on the market.

"Greywater heat recovery system" is the water heat recovery you are talking about. And there is both systems that is just a box you put under a shower cabinet, and systems that you put in the drainpipes that demands more installation work. The nice thing about the box under the shower cabinet solution is that it is really cheap and does not demand any installation work (just connect the drain pipe to it, and reroute the cold water intake to the shower), and it is the biggest water heat waste source in the house. And it is easy to clean out because the drain water usually just run in a open gutter with the clean water going in a copper pipe in that gutter.
1fcc198f621e21387f0d4bd74852fe2849a1dd50.jpg


And balanced ventilation systems with heat recovery via a Enthalpy Wheel or other forms of heat exchangers has been a rule that every new building has to have in Norway for many years now, and that is probably the same in other countries as well.
 
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  • #7
Stormer said:
just connect the drain pipe to it, and reroute the cold water intake to the shower
Does it increase the time the water runs before you "get" hot water at the shower head? Where I live (desert) the cost of the water far exceeds the cost of heating it up.

EDIT -- oops, just realized you said the cold water line runs thru the drain. OK, never mind...
 
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  • #8
Drakkith said:
Ah yes, something else that needs regular maintenance and can break or leak all over my house...
If the use of energy becomes as big an issue as 'they' predict then a bit of complexity may be the only way to maintain the comfortable life style. Our lives will change and sooner than we might have hoped, I think.
Stormer said:
that is just a box you put under a shower cabinet,
The simple version uses no heat pump so I'd assume it would only work to heat incoming cold water to a electric shower, perhaps. Or it could go in the cold feed to a thermostat which would then just 'top up' from the hot feed. The advertising blurb seems to imply that people use 50% of their hot water for showers. I would argue that the way to cut down on their bills would be to take
Stormer said:
And balanced ventilation systems with heat recovery via a Enthalpy Wheel has been a rule that every new building has to have in Norway for many years now, and that is probably the same on other countries as well.
Ah yes; that's the term for it. It's not a thing that the UK have introduced in any quantity. Even a neighbour with a 'built from scratch' green home didn't have one of them.
fewer showers.
Baluncore said:
Before the water becomes waste, heat is lost to the air, and to your body.
Hot water evaporates to steam, then condenses on the ceiling and the mirror.
I'm not in the habit of laying in my bath until the water is room temperature. By the time I rise up from it (too much info again) the water is still comfortably warm and the bubbles will reduce the evaporation significantly so I don't think that's a valid objection / comment. Perhaps a lid could be put on top of the bath until it has actually cooled down to near room temperature.

Energy can be saved by multiple use of the same bath water. Not impossible. When I was a small boy, staying with my grandparents, Grannie got first go in the galvanised bathtub, followed by me and then Grandad. The water was hand drawn and heated up in a 'copper' - then emptied out into a ditch at the rear of the cottage. (Once a week.) Ahh, the simple life.

gmax137 said:
Where I live (desert) the cost of the water far exceeds the cost of heating it up.
Yet more factors at work. There are parts of the world where the water supply is being over-stretched and the populations will need to address that situation much more than they appear to be doing. It's just the same as with use of Energy. Life will need to change.
 
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  • #9
sophiecentaur said:
I was enjoying my (very short) hot shower this morning and realized that the lovely warm water was flowing over my body (sorry - too much information) only once and then disappearing down the drain.
sophiecentaur said:
I'm not in the habit of laying in my bath until the water is room temperature.
I am sorry, I thought you were having a shower.
 
  • #10
I suggest that it would take less money, save more energy, and be more fun to do a DIY rooftop solar hot water project. Even at latitude 65, it can be very effective.

1638980502619.png
 
  • #11
Baluncore said:
I am sorry, I thought you were having a shower.
I started off in the shower but you were suggesting that all the heat was lost into the room and not down the drain. The only possible way that could happen would be if a bath were allowed to cool down so I assumed we were now in the bath.
There are many paths for heat to be lost but the drain is the main one when having a shower. (And also for anything but a stone cold bath.)
 
  • #12
anorlunda said:
I suggest that it would take less money, save more energy, and be more fun to do a DIY rooftop solar hot water project. Even at latitude 65, it can be very effective.

View attachment 293785
Definitely but hot water from any source has heat in it that's worth 'harvesting'. And a harvesting system would work at night. :wink:
 
  • #13
OK then. Many of you have told me about existing possible systems. BUT how many PFers actually have any heat recovery working in their homes? How many such systems are operating in places you know of?
Why hasn't our government taken notice of any possibilities, other than ground or air sourced heat pumps? (Daft question , I know - but that would take us into politics.)
 
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  • #14
sophiecentaur said:
As for the quantity of hot water that would need to be stored
Regarding water storage: I don't know how this works in other countries, but we still has these electric boiler things and (here) 2-300l storage for hot water is enough for an usual household (parents & kids).

The m3 class tank I mentioned would be needed to store the wastewater till the heat pump can do its work.
sophiecentaur said:
... Energy will be increasingly relevant - that's both for heating and for building things.
... heat storage will be necessary in any case.
I think it'll be a bit more complex than that on long run. My bet is, that while energy as we know it right now will be on shorter supply, there will be significant amount of intermittent energy available - if you have adequate amount of heat storage, yes.
 
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  • #15
Rive said:
I think it'll be a bit more complex than that on long run.
That's right. Thing is, a lot of waste water is 'cold' in any case and wouldn't be the best to get heat from for hot applications. If we are really interested in kWh per buck then hot waste would be best value. It's not unthinkable to use selective storage of waste, on the basis of its temperature and the circumstances. A m3 tank may be bigger than needed but, compared with all the other systems, it's not a lot. We may have to deal with a lot of changes.

In a heat pump world, domestic radiators will need to be very large as the water will not be at 60C. Any system will need to be smart and flexible.

Sorry @Drakkith but you may well have a lot more pipes in your home if you want the comforts of a 2020s home.
 
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  • #16
sophiecentaur said:
Sorry @Drakkith but you may well have a lot more pipes in your home if you want the comforts of a 2020s home.
My house was built in the 1950's and I pay about $25 a month for gas for the water heater, and much of that is probably just a flat connection fee. Would any alternative system save me significant amounts of money?
 
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  • #17
Drakkith said:
My house was built in the 1950's and I pay about $25 a month for gas for the water heater, and much of that is probably just a flat connection fee. Would any alternative system save me significant amounts of money?
Do you just have a thick overcoat or a big dog to keep you warm? I'm impressed.

But can that be the whole story? Whatever energy source you use, things are bound to hit you (ore someone else) at more than £25 pm. Even if you are off grid, there must be some possible harvesting of wasted heat.
 
  • #18
sophiecentaur said:
Do you just have a thick overcoat or a big dog to keep you warm? I'm impressed.
I live in Louisiana. It's currently 67 F in my house without turning the heat on. :wink:
Besides, we're just talking about the hot water heater, not the heating system.

sophiecentaur said:
But can that be the whole story? Whatever energy source you use, things are bound to hit you (ore someone else) at more than £25 pm.
But realistically how much of an impact could recovering warm wastewater make? I haven't seen any numbers in this thread yet in that regard.
 
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  • #19
sophiecentaur said:
OK then. Many of you have told me about existing possible systems. BUT how many PFers actually have any heat recovery working in their homes? How many such systems are operating in places you know of?
Why hasn't our government taken notice of any possibilities, other than ground or air sourced heat pumps? (Daft question , I know - but that would take us into politics.)
Yes i do. I live in Norway in a apartment from 2018 so it's got a balanced ventilation system with heat recovery of the exhaust air just like all newer houses and apartments is required to have in Norway. But I'm not impressed by the efficiency of the system because i use more electricity now than i did in my previous appartement of approximately the same size that was from the 50's that had bad isolation. But the passive air exchange in the old apartment was probably pretty bad to. I have the fans on my current system set to medium speed because there is a lot of radon where i live so i want a good air exchange to not accumulate to much of it inside.

And after Norway has sold all of its hydro power to the EU because they decided to shut down their gas, coal and nuclear power plants and drained our water magazines so we suddenly got really high electricity prices i am considering to add a graywater recovery system to the shower to. Sadly I'm not allowed to install a air to air heat pump by the housing association, but that would have made the biggest impact on the electric bill. Because it is not normal to use gas for heating in Norway, and newer buildings almost never have chimneys so i can not install a wood burning stove either. And the EU even want to ban wood burning stoves...
 
  • #20
Stormer said:
And the EU even want to ban wood burning stoves...
Norwexit. :smile:
 
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  • #21
Drakkith said:
I live in Louisiana. It's currently 67 F in my house without turning the heat on. :wink:
Besides, we're just talking about the hot water heater, not the heating system.But realistically how much of an impact could recovering warm wastewater make? I haven't seen any numbers in this thread yet in that regard.
Fair comment about the figures. I based my idea on the advertised figure of 50% for hot water use in the link I posted. That would be a lot of money in our house.
The UK government doesn't help here and I hesitate to go for any significant scheme because there are no incentives, despite the statements that are made about the climate situation etc.. But that's no excuse, I guess.
 
  • #22
Stormer said:
Because it is not normal to use gas for heating in Norway, and newer buildings almost never have chimneys so i can not install a wood burning stove either. And the EU even want to ban wood burning stoves...
sophiecentaur said:
The UK government doesn't help here and I hesitate to go for any significant scheme because there are no incentives, despite the statements that are made about the climate situation etc.. But that's no excuse, I guess.
If a nation or an economy does not manage energy wisely, it's currency will be devalued by inflation. All economies are in competition, to preserve their buying power in the international marketplace. The United States of Europe's € is an interesting case to watch, as the component nations have different resources and philosophies.
 
  • #23
sophiecentaur said:
Why hasn't our government taken notice of any possibilities, other than ground or air sourced heat pumps? (Daft question , I know - but that would take us into politics.)
It’s not politics, it’s economics. The low-hanging fruit is harvested first; the residual heat from single-family residential water usage is higher in the tree.
 
  • #24
sophiecentaur said:
In a heat pump world
It may worth to consider that every solution mentioned here has its own footprint and cost. And complicated systems tends to have both at the 'terrible' range.

It's like the well known paradox around insulation and heating. Once you invest into insulation, you cut the energy need: the more you invest, the lower. So the calculated return of an investment on a complicated high efficiency heating system will become further and further away in the future.

From financial standpoint, to install anything else but the most basic climatization or low efficiency (cheap) gas convector in an almost-passive house is just madness. It has no return point at all.
This stands for the footprint too.

Hot water is a bit different, of course, but hot water alone is again, a tricky matter.
 
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  • #25
Rive said:
From financial standpoint, to install anything else but the most basic climatization or low efficiency (cheap) gas convector in an almost-passive house is just madness. It has no return point at all.
This stands for the footprint too.
Yes. With enough insulation (plus smart windows etc.) less and less energy input is needed. Retro-fitting adds factors to that but there are many 'passive' solutions, even for old housing. The UK government doesn't seem to be aware of this. High Tech solutions seems to appeal more.
And yes - footprint equates to energy consumption.
 
  • #26
anorlunda said:
Norwexit. :smile:
The funny thing is we are not a member of the EU. We voted no two times. But still we are following more EU rules and regulations than most EU member countries because the politicians made us members of the EEA with no peoples vote. So now we are draining our hydropower magazines to supply Germany's power shortage because they closed all of their stable powerplants to go for solar and wind and end up with massive power shortages. Plus China buyed up all of the gas from EU so their gas prices went up and the energy prices is tied to the gas prices. And we are setting our energy prices according to the EU countries prices even if our production cost for the hydro power is really low.
 
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  • #27
Stormer said:
And we are setting our energy prices according to the EU countries prices even if our production cost for the hydro power is really low.
OMG Norway used to be called "the blue eyed Arabs of the north." Norway's hydro resources were enough for 100% sufficient and clean electric energy. On top of that, they discovered the huge North Sea oil and gas resources.

But it sounds like in the long term, Norway decided to export their energy and import everyone else's angst. I can't think of good words to express my surprise.
 
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  • #28
sophiecentaur said:
I based my idea on the advertised figure of 50% for hot water use in the link I posted. That would be a lot of money in our house.
You're being inconsistent. If you are motivated by money, then you would not have pushed aside the less expensive solar hot water idea to favor energy harvesting. I think you're being human like the rest of us, motivated by the cleverness of the harvesting idea, not its economics.
 
  • #29
anorlunda said:
OMG Norway used to be called "the blue eyed Arabs of the north." Norway's hydro resources were enough for 100% sufficient and clean electric energy. On top of that, they discovered the huge North Sea oil and gas resources.

But it sounds like in the long term, Norway decided to export their energy and import everyone else's angst. I can't think of good words to express my surprise.
Yes we produce around 110% of what we use per year just from hydro power. And then the wind turbines, gas power and solar comes on top of that. And that is including all of our energy intensive industries like aluminium and fertilizer production.

And it is only the Norwegian people that have to suffer. Because the counties and the government still rake inn the money they make from using 0.10 NOK per kw/h to produce the hydropower and selling it to EU and the Norwegian consumer for 4.0 NOK per kw/h. So they drain out the water magazines so they have something to blame the high prices on, and use the profit to finance their pet projects that they promised before the election... And the consumer is left with the bill for it... And they say they have to export the energy because of EU agreements (that we voted to not be a member of), and the same goes for why they can not differentiate the prices to the Norwegian consumer and to the export market. If we just cut the export cables we would have like 3-5 times lower energy bills.
 
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  • #30
What a difference geography makes. Where I live (US-FL), some folks heat their water with waste heat from the air conditioner. Even my cold water is lukewarm by most standards. I recently had to size a water-water heat exchanger for a newly acquired water-jet cutter - the 'City' water is too warm to use without some pre-cooling.

Solar water heat is very common. In fact, it was very common 100+ years ago - until the ice company which was to become the dominant power utility started paying people to remove solar systems and install electric water heaters.
 
  • #31
anorlunda said:
You're being inconsistent.
I was not actually rejecting the home DIY solar heating project, just not discussing it. The two are not mutually exclusive.
One thing about thermal solar energy is the actual details. Pipes up on the roof need to be protected from the frost unless you have an indirect system (with anti freeze fluid) or you drain down the system in frosty weather. You have to choose an operating pressure. Would it be at mains pressure? If so, a coil of rubber tube would not be suitable and the next step it has other refinements and turns into a complicated system with fancy reflectors and double glazed panels etc etc.
People have all sorts of versions but few are cheap. We could have another thread just about thermal solar, which is very attractive because there are few difficulties interfacing with other services.
anorlunda said:
I think you're being human like the rest of us
I'll take that as a compliment. But we all have heat pumps in our homes and they do their job exceptionally well. So using them for other purposes is really not that exotic, is it?
 
  • #32
Dullard said:
Solar water heat is very common. In fact, it was very common 100+ years ago - until the ice company which was to become the dominant power utility started paying people to remove solar systems and install electric water heaters.
An interesting bit of history there. Our lives are always subjected to other interests and it's even worse when the public are not in a position to vote those perps out of office. (But many voting systems don't in fact give us that power in practice.)
 
  • #33
Stormer said:
And it is only the Norwegian people that have to suffer.
I thought of the idiom now. "Snatching defeat from the jaws of victory." (An ironic reversal of the more common "snatch victory from the jaws of defeat.")

I would feel sorry for Norwegians, but actually many countries today are having the similar difficulties with very bad government. [I hope that wasn't too political. I didn't mention names.]If you like irony, the electric power disaster in the Canadian Province of Ontario, sounds very similar to your story about Norway. Ontario also had abundant hydro resources plus nuclear. They too snatched defeat from the jaws of victory thanks to government decisions.

https://www.fraserinstitute.org/art...ice-crisis-how-did-it-happen-and-who-got-hurt
https://www.spiked-online.com/2020/09/17/ontarios-green-energy-catastrophe/
https://ep.probeinternational.org/2...tricity-liberalization-promise-crisis-part-1/@sophiecentaur , here's a UK source's advice on solar hot water.

https://energysavingtrust.org.uk/advice/solar-water-heating/
 
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  • #34
I lived in the Florida Keys at one time and solar hot water was not uncommon. These seemed to be mostly home-built systems cobbled together in the 1970s. I remember the water got so hot in the summer, the relief valve on the roof tank would lift, sending a plume of steam into the air.
 
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  • #35
sophiecentaur said:
Summary:: Use the waste warm water from your plumbing system.

I was enjoying my (very short) hot shower this morning and realized that the lovely warm water was flowing over my body (sorry - too much information) only once and then disappearing down the drain.

This water - and what comes out of the washing machine, dishwasher etc. could be at a seriously 'useful' temperature for a heat pump. There must be many kWh lost over a day. You can find systems for shower heat recovery, advertised but they seem to be passive and are low hanging fruit, afaics. A whole house system would be better and would involve a hot water storage tank (which I have).

Obviously the heat exchanger plumbing would need to be maintained (cleaned out) on a regular basis and I would imagine that separate drainage would be needed for foul water. Also, the discharge water temperature would need to be well above freezing but the usable heat would be a lot more, per electrical kWh, than what can be obtained from an air source heat pump in winter. An installation could be a lot cheaper than heat pumps that are being considered today.

Many years ago I heard of a scheme to recycle heat from a house via a ventilation system where outgoing air is passed through a heat exchanger to warm up incoming air. That's a similar principle.

I ask myself why there aren't dozens of these alternative systems to be found working in houses all ov er the country.
If it is that time of year when you heat your house, there is a very simple way to recover that heat.

Just put the plug in your shower and let it fill up, as you shower.

You'll have to paddle around in a couple of inches of slightly soapy water, but assuming it is at a higher temperature than the rest of your house, then simply leaving it there to find temperature equilibrium with your house, that heat will find its way to displacing heat you have to otherwise generate with input power by heating equipment.
 

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