In Finland, majority of energy costs comes from heating, and majority of that from water heaters. And majority of hot water is used by the shower. So when water from the mains comes in at between +1 and +8 degrees and used water leaves at +37 degrees, recovering some of that heat ought to mean massive savings in energy bills.
I found this video about how to make such a heat exchanger yourself, so I'd like to know PrepHole's opinions on this: https://youtu.be/I4wO3tjoQpw?si=hK0rpD0h3Cc53POY
How long would the exchanger need to be? Should I do it myself or are there better commercial versions already? Any other thoughts or recommendations?
Not worth the trouble
>Not worth the trouble
The average heating bills from January have been on average 400 euros. If you managed to somehow cut down just a quarter of that, it'll be an extra 100 euros per winter month every year. Very worth it if you ask me.
>This is moronic penny pinching savings. Why dont you get insulated triple plane windows instead.
That's a lot of money. Also, insulated windows have been a standard in Finland for decades.
>The hot shower water is already cooled by mixing cold water with it. The cold water flowing thru the heat exchanger will cool it even further.
The idea is to recapture heat from the used shower water before it flows out of the house, and using that to preheat the replacement water coming into the water heater.
Thanks! This and a shower version would be perfect. It's good to know they're already available, although ordering them from America would cost a fortune in shipping.
>that wouldnt work and it would also be unsanitary...how very finnish of you
How so? Waste water flows in its own straight pipe out the house, and the incoming clean water in its own pipe around it.
>kek everyone too moronic to see its drain waste water heat recovery.
in theory it works, but in practice you will save maybe 1 cent in a year. And have fun cleaning that shit up.
That's exactly what I'm looking for. You'd think it saves more than that considering the heat difference between incoming water (in Finnish winter) and waste water. And why would it need more cleaning than a straight pipe without another pipe around it?
Pure speculation with regards to savings
Lets see some data b***h that likes to argue
Fairly easy to calculate; we know the specific heat capacity of water, and we know how many liter-degrees we're going to save per minute, so now you'll just need to plug in the electricity prices (4-250 cents/kWh depending on day)
< The idea is to recapture heat from the used shower water before it flows out of the house, and using that to preheat the replacement water coming into the water heater.
No shit Sherlock. The drain water from shower will be cooled by the cold water in the exchanger. Its a trade off. Not to mention the used water from shower wont be that hot to begin with derp derp
Exactly. I just had to explain it because
didn't seem to get it.
And lukewarm water is still easily 15-30 degrees warmer than the 1-8 degree warm water coming in.
Again, how is it any different from a plain straight pipe? Only the clean water twists around while the waste pipe goes straight through the exchanger.
Finn, let me give you some advice. It seems to me your problem is with finding cheap energy. You see, nature has provided the answer for that. Go outside. What do you see?
Trees. Plenty of them. Chop one down, set it on fire. What do you have?
Heat. See what I'm getting at? Now you just need a way to apply that heat to water. Yep, there's your hot water. How much did it cost?
Nothing.
You're welcome.
Firewood is economical only if you own forest. If you have to buy wood, it'll generally be cheaper to buy electricity instead.
Solar collectors are good for most of the year, but there's hardly any sunlight over the four coldest months when the heating is most needed. Solar panels do good job reducing the electricity bill over the year, but in the cold and dark winter there's no light to power them either.
> Solar-heated water systems to boost inlet temp to the gas/electric water heater tank "are not as useful {or, I'll take your 'not useful at all'} for four months out of the year."
Bro, can you math? Useful for, with your proposal, 8 months (or 9, if 13 month calendar) with all the hot water needs being taken care of for ~4 of those.
You calculate savings averaged across the entire year. Solar water systems can be DIY'd. Although they'd be more effective with well established vendors, OP sounds like a penny-pincher. Circulation pump, coil of proper poly pipe, and some reservoir. I'm sure tons of diy guides exist.
> He's not in the woods
He should be. Are you not OP, and don't know anything about Finland's woods?
nailed it.
Reburning water boiler stove combo.
Cut wood. Finland has a lot.
Sorry that being a eurobro is expensive. I have natural gas on the property and springwater, and am completely offgrid.
I think you would be better off having a heating loop circulating coolant that goes through conventional solar (not electric) radiators on the roof. It's an unpressurized system. Very safe. That will get you the additional heat you're looking for, without the risk of mixing sewer with freshwater, which, is, for sure, the reason why your suggested solution is not done. 100%: a ton of disease was solved by basic indoor plumbing, and keeping those two lines separate.
Keep the poopchute separate from the drinking water.
>The average heating bills from January have been on average 400 euros
What the frick. If you're spending 400 euros a month on heat you need insulation not whatever shit you're trying to do with hot wastewater.
Indeed, Pekka is living in his 1910s 300sqm wooden house with 5cm sawdust insulation and one glass windows.
Should rebuild with 30cm insulation on qalls and 60cm on ceiling.
Or invest 20k on geothermal and 5k on underfloor heating pipes
>If you managed to somehow cut down just a quarter of that
The idea of reclaiming enough heat from shower water to heat your house 25% of the time is laughable. Assuming you live in the fricking shower and run it constantly, you might get a 5% saving. Assuming a family of 4 taking showers every day, you're looking at sub 1%.
The cost of your hot water tank isn't from the water being lost to showers. It's from the HEAT being lost to radiators. Turn off the heating, marvel as your heating bills drop to summer levels!
Saving a quarter of water heating costs, not total heating costs.
Yes, but warm showers feel better, and warm water cleans better. It's worth using money on, but having to pay less for the same luxury is obviously better.
>Saving a quarter of water heating costs
I don't know what your heating system is like, but I assume it's just running the hot water out to radiators to heat the house. That loses heat, which means you need to re-heat the water even without showers.
If you want to make showers more efficient, have cold ones, or use a timer. Quick rinse, turn the shower off, lather up. Turn it back on, remove the suds, turn it off. You don't need a 10 minute shower, 2-3 minutes will do.
In Finland at least, the water that goes around the radiators heating the house is a closed loop, while the water that goes to showers and faucets is an entirely separate system. The latter is the water that goes down the drain and out of the house, taking its heat energy with it.
That's like telling >>>PrepHole to go ride a bus to make their car more efficient
FPBP
I did the calculations on this a few years ago for my own home while I was studying energy management. It's really, honestly not worth it. If you have electric instantaneous hot water and pay variable rates for electricity, install a water storage heater and program the element to only come on at cheap times. That's the $2k solution that will pay for itself over a few years. I don't personally recommend a hot water heat pump, that's a $5k solution that may not pay for itself over its lifetime due to increased maintenance costs and low efficiency in Finland's climate.
The problem with it is that shower water is full of soap and hair. The heat exchanger getting clogged would be a nightmare. See
yes this is my concern as well. i asked myself how to design this properly in a way you have both the needed surface contact and doesn't clog immmediately, more difficult than i thought. if you want to squeeze the last bit out of your zero energy home then maybe but not everyone has an infinite budget and there are probably better ways to spend your money like on extra insulation or a heat pump
The hot shower water is already cooled by mixing cold water with it. The cold water flowing thru the heat exchanger will cool it even further.
>The hot shower water is already cooled by mixing cold water with it.
Are you stupid? Some hot water is MIXED with some cold water.
>The cold water flowing thru the heat exchanger will cool it even further.
Cold? It will be lukewarm and it's meant to preheat the water supply of the water heater. Am I just responding to bait?
Oh look honey we saved .37 cents on gas last month.
Wah b***h
At least I can comprehend what a fricking water mixer is.
Still whining
Must be nice to heat water with energy dense cheap gas. Let me tell you resistive heating just ain't worth it.
https://www.energy.gov/energysaver/drain-water-heat-recovery
there are commercial products that exist for this
In short, this is impossible and cannot be done.
As said there are solutions.
The problem is they must be part of the plan when doing construction/remodeling, and aren't really a quick "DIY" project.
There are many ways to more efficiently heat water than taking in pipeline water and having your heater heat that from cold to hot but this is something that benefits from having lots of area, not something you can fit in most homes if it wasn't part of the plan.
This is why commie blocks (large apartment buildings) are so efficient. When trying to min-max things for personal homes it becomes more difficult unless you're creating your own floor plan and can dedicate the square footage to such a thing.
This is moronic penny pinching savings. Why dont you get insulated triple plane windows instead.
that wouldnt work and it would also be unsanitary...how very finnish of you
kek everyone too moronic to see its drain waste water heat recovery.
in theory it works, but in practice you will save maybe 1 cent in a year. And have fun cleaning that shit up.
>in theory it works, but in practice you will save maybe 1 cent in a year.
Waste water treatment plants do it for profit on commercial scale. There's lots of energy in hot water
Not only this, but there's enough heat to make a profit out of it even after it has traveled from houses miles and miles away. There's even more heat to be recaptured if you do it at the source.
>which i'm not going to do
Translation: I have no idea how to do it.
>it's on wikipedia
Translation: I know it's possible but have no idea where to even find out how.
Black person i'm more than capable and i can look up the books in question from of the shelves in the attic, or if i don't and to just ignore the radial heat transfer math because a flat surface is easier, and pretend you have a nice turbulent flow with an even radial temperature without a thermal boundary layer so you can ignore the fluid conduction mostly and it's just a question of looking up and plugging in some numbers and other gay shit such as logarithmic temperature but the reason i don't is because i'm not entirely convinced about the project so why should i. what do you expect, a full report with first estimations and then over 9000 billion cells in CFD or just basic info and jargon to steer someone in the right direction so he can learn and know what's going on and if the idea is really worth it
frick me i literally had multiple courses on this subject in a rabbit hole that goes deeper and deeper so yes you managed to offend me wtih your shitpost, good job
and fouling and clogging is an obvious problem here so good luck with that as well maintaining it
kys
>it's just a question of looking up and plugging in some numbers and other gay shit
Black person pretending to know what he's talking about confirmed.
For an actual answer:
Assuming a copper pipe with 4mm inner and 6mm outer diameter (assuming you'd use multiple pipes like in
), waste water temperature of 30 degrees, incoming water temperature of 8 degrees and a target temperature of 20 degrees, the answer would be
P=350w/K/m2A∆K
P=0.25kg/s4200j/kg/K∆T
350W/m2A(10)=1050j/s(13)
A=(105013)/(3500)m2=3.9m2
A=πdL
d*L=1.25m2
meaning the incoming water would have to flow through combined length of 200 meters of uniformly warm waste water. But because half the amount of water used goes into the heater, the efficiency is about three times better than that, meaning the system would require 66 meters of pipes. That isn't as crazy length as I'd have expected, and with a more realistic shower temperature of 37 degrees the pipe would only have to be about 122 meters, or about 40 with the amount of incoming water accounted for.
You need less pipe if you send the 20C water to the cold inlet.
I wouldn't call the shorter ones more efficient. They need less length because they save less energy. When you reduce the flow, the approach temperature difference at the cold inlet is higher, and from that you rightly calculate that they need less length to reach 20C. If you instead were to put all the water through the 8C inlet, you recover the same energy with a target of 14C. Your 13C LMTD increases to 16C, and your length can be reduced to ~80%.
Your setup needs less temperature adjustments. Mine needs a thermostatic valve.
>uniformly warm waste water
bruh
can you be a bit more elaborate with your numbers?
the exergy of hot water is approximately 0
Okay, let the big companies have their profits to themselves then
you're an idiot
Well if an anon says so it must be true
That heat exhangern is gonna foul like a motherfricker. Hair, dirt, soap, cum....
If your shower is also a bathtub, just plug the drain while showering, and then let the water sit till it reaches room temperature.
The air temperature is about 20 degrees, while the water from the underground mains is less than ten. Even room temperature water holds plenty of energy compared to the water coming in.
Your indoor wet bulb temperature might be 10C. The tub won't drop to that but a direct contact heat exchanger might achieve that. Shower water has hair and grease to clog pumps and nozzles. Direct contact won't help in the summer unless you take cold showers.
Quesition: won't the lukewarm mixed water near heat exchangers make for prime habitat for legionella?
The lukewarm mixed water flows out of the house, dissipating heat as it passes through the heat exchanger. Cold, fresh water flows in, preheats in the heat exchanger, and then goes into the water heater to be heated up to full temperature.
I mean the cold water is in the loop, and if it's not flowing, it'll stay in the loop until more water comes in
That same water stays in straight pipes too. And because it goes into the water heater, it will be heated hot enough to kill legionella before being used anyway.
It could be, depending on your heater size and setup, but it could also be used before it gets time to cook
At least in Finland, water heaters fill up from the bottom and drain from the top, to make sure only the hot water gets used. If so much water is taken out that the temperature starts to drop too much, there is another electric coil at the top to heat the water as it exits the tank too.
Is this bait? Are you getting off to this? Just chomp down on a mouthful of winter air and a mouthful of snow and tell me which takes longer to heat to body temperature.
The air in your mouth isn't moving, like the air around the fins of a CPU cooler.
But more importantly, you are saying but are just to dumb to realize it.
>there is another electric coil at the top to heat the water as it exits the tank too
They aren't both activated at once, but the top one switches on instead of bottom one to cope and give a couple minutes more until you're completely out of warm water.
>Just chomp down on a mouthful of winter air and a mouthful of snow and tell me which takes longer to heat to body temperature.
And which one takes longer to cool back down? There aren't any free rides out there. If you got a closed loop the only real matter is how you're going to exchange heat. The absorbing material is just there as a filler.
>If you got a closed loop
what part of taking cold water from the mains, heating it, and putting it down the drain warm sounds like a closed loop to you?
That doesen't make water any better at cooling, you're just externalizing the process to somewhere else.
sorry can you say that again?
bump
>finland, a country with more geothermal than most of the world but are so leftist they need a 2nd mortgage to afford electricity.
If youre so crazy about it why not apply the same garbage tech thats mostly suited for your coastal country and use a heat pump as an exchanger? Then you can really virtue signal as you save a couple of cents of heat for even more expensive electricity. Awww shit stick a peltier device and feed back a couple of watt-seconds into the grid.
, a country with more geothermal than most
...that's Greenland.
We did try geothermal on commercial scale, but after drilling a hole for about 4 miles the water was still lukewarm. Couple hundred million down the drain.
did you consider putting some type of water heater at the bottom to warm it? just a thought..
>hurr durr we suck at geothermal
Yeah. The 4 mile deep hole was one of those so called 'great potential' sites. You can make educated guesses on paper, that's cheap, but once you have to invest hundreds of millions into realizing a dud, not many are willing.
One or two 30 minute showers a day equates to pennies in btu energy. If that.
An inline-heated shower can take 15kW of power. If you combine it with some unfortunate prices (like 2,5€/kWh two weeks ago) you'll be taking 30€ showers a day.
Wrong.
The heat exchanger goes on the side of the tank. The circulating water enters the bottom of the side arm and flows up.
Buy your side arm according to the measurement between the blow off valve and the tank drain. If the heat exchanger is too long, the length needs to be added at the bottom by lowerign the tank drain, not by lifting the pop off.
Your basic premise is wrong - if the water is coming into your house at 1 C, this means your ground temp is 1C and your average air temp is 1C aka you have cold winters and you are spending most of your energy on heating, not showers.
>Your basic premise is wrong - if the water is coming into your house at 1 C, this means your ground temp is 1C and your average air temp is 1C aka you have cold winters and you are spending most of your energy on heating, not showers.
Water has four times the heat capacity of air, which is why it takes much more energy to heat it. It's why liquid cooling is so much more powerful than air cooling, and in this case it would be cooling the house instead of a motor or a computer.
I'm sorry, but is PrepHole experiencing some kind of moron season? I've never had to explain so many, so basic things in one thread before.
>It's why liquid cooling is so much more powerful than air cooling
It's not any more powerful than the other side dissipating the heat somewhere else. You can have several better air-cooled PC setups simply because thet all eventually cool down the same way. Water just works like a heat capacitor to smooth out bumps
you'll never recover the cost of setup
you're better off investing in heat pumps and on-demand water heaters
Nobody mentioned that it'd be more efficient if the cold water entered the heat exchanger from the right...
Just buy a hybrid heat pump water heater you dumb gay. That'll cut energy usage by 60% right there.
https://www.jlconline.com/how-to/plumbing/wastewater-heat-recovery-systems_o
Thanks, this is exactly what I've been talking about.
I even found a shop selling these in Finland, and a square model that goes directly under the shower seems ridiculously easy to install. The pipe-shaped ones appear to be even better, but they all seem to require a vertical installation. Considering I've never seen a non-apartment building with shower on the second floor in Finland, I wonder how much efficiency the pipe version would lose if installed horizontally?
Most residential waste water heat recovery systems will never pay for themselves or recoup the energy + CO3 needed to manufacture them at any reasonable time scale. A system that actually is efficient as claimed will cost you more. The most common systems installed in Ontario are based on idealized if not outright falsified testing data. The government was lobbied to make them mandatory in new homes, pocketing the family that owns the manufacturing rights a lot of money.
how many carbonate anions do you expect such a project to require
>In Finland, majority of energy costs comes from heating, and majority of that from water heaters.
Same problem here. Someone made what you propose, and also provides measurements:
https://sondred.info/varmegjenvinner.htm
I hope gorilla moron israelite OP homosexual builds his penny pincher constraption and posts results or fricks off already.
This is a vertical model. Probably more efficient.
That definitely seems to be the most common model, they seem entirely unusable in Finland because no house has a shower high enough up to install a vertical pipe like that under it.
Pic related is a new idea I've been thinking of, using a tank of standing water that gets replaced with warm water as the shower is used. The downside is that the tank will be full of legionella and need to be manually emptied of any debris every few years, but the upside is that because just the top curve of the emptying pipe needs to be above the sewer pipe, the rest of the tank could extend much deeper into the floor.
If you place the tank so it can be easily cleaned outside perhaps it could work, right?
Yes, the human waste of grey water.
Maybe if you use black water the fermentation process actually warms up the water. Besides you might be able to catch off methane for your very own bio-gas.
>Ah yes, and this is my scum tank, beware it's warmth!
i don't know how saturated the tube is that the water from the shower flows down. i don't think there would be all that much thermal contact. also the residence time isn't going to be great.
probably you'd want to have it at an angle, like OP's pic but at a slight angle. vertical model is going to be less efficient due to less residence time and less thermal contact.
things which are important to keep in mind: plastic is an insulator, the pipes are going to need to be something like aluminum or copper. corrosion concerns? can't put strong bases down the drain any more (lye drain cleaner, etc).
how difficult will it be to maintain? if something goes wrong, how devastating will that be? will you be able to tell if a leak happens? what if your graywater ends up in your water tank?
Why do so many heat exchangers have the incoming water pipe spiraling around the outgoing pipe instead of going in one thick pipe like in OP's video? It has less metal between the two water flows, and I'd assume it's cheaper to use one thick outer pipe instead of loads and loads of thinner pipe that won't even be in full contact with the inner pipe from all points.
Could someone explain this in pain English?
seems to me like the temperature profiles in a heat exchanger with and without counter flow but i don't really get why that's relevant to what he responded to
>incoming water pipe spiraling around the outgoing pipe instead of going in one thick pipe like in OP's video
There isn't that much surface area on the outside of a plain pipe. A pipe-in-pipe heat exchanger would work okay, but not as well as it could. Imagine if you added a sort of sleeve that had fins to the inner pipe before covering it, increasing surface area to aid heat transfer. Look up what the inside of a water cooling block looks like for an idea of what that looks like.
The walls of the spiral square pipe are those fins. It's just easier to wrap and solder some small tubes around a larger one than it is to make a whole other part with a bunch of thin walls.
this was actually mentioned in thermo class so it's definitely a thing, but as others have said it's a question if it's really worth it. btw you can use a similar setup for regular heating where the outgoing air heats up the incoming fresh outside air, but that is next level
>How long would the exchanger need to be
if it's just two concentric pipes then it's pretty much the most basic heat exchanger you can imagine which is fairly easy to calculate
which i'm not going to do, frick you. it's on wikipedia. useful knowledge though so you can now design your own stills as well to save even more money
I mean if you don't mind paying for all that copper and are pretty skilled with a torch it might be a fun project.
Air heat exchangers have been a thing for apartment complexes for a while now, but whether they'll be worth the price in a small house is still questionable. Weirdly enough I've never heard anything of water heat exchangers before, considering how much more thermal energy water carries and how much simpler something like that would be compared to building all the ductwork for an air system.
a heat pump is something else entirely anon
your sewage generates heat...so does compost. why not store it all in the crawlspace to heat the house!
You can! In fact if you already have a bioreactor installer for biomethane you could recycle the waste heat for more efficiency. These systems are usually more expensive to install than traditional gas lines however, so they're mostly reserved for rural areas
Most reasonable posts, there are some dirt cheap methane digesters designs depending on how much of an animal you are, and unless you pressurize i gas i don't think you can have a nice day that easily, I think it burns clean aswell so start saving those poops, and buy a shovel and some pvc glue, also get some horse poop, I think there are bacteria in it you need to get started
Bioreactors are great for farms with livestock, but a single human could never crap enough for the system to be worth it. Especially when most of sewage is just water from flushing the toilet.
For people who are still talking about fouling and clogging, the heat exchanger does literally nothing to the inside of the pipe. It is just as smooth and empty as it is without a heat exchanger. Here's a picture to explain it, but it really shouldn't be this hard, should it?
how are you going to heat up the pipe when the water just falls through it. you need to find a way to get a decent wet surface and here's where the clogging comes in
like the other anon has said it's soapy water and hair with waffle stomping left and right which isn't ideal. in theory it makes total sense and i could easily nig rig basic dimensions but it's not as trivial as it seems to not make it a pain to deal with
like $2000 in installation costs, $200 on monthly plumber visits to save $20 on the heating bill. there are better ways to spend your money
on an industrial scale it would make more sense
also your drawing is dumb, you're dealing with even mass flow rates so your pipe windings seem like a waste of copper. your incoming water won't come out hotter with more copper when the outgoing water doesn't cool down. see where i'm going? perhaps use windings pipes on both sides then? gl with your shower that is now also a foot bath
https://www.supplyhouse.com/ThermoDrain-Drain-Water-Heat-Recovery-29682000
with a good heat exhanger you can reduce the power consumption on each shower by up to 85%
btw the exhanger must be cross flow for that to happend, yours isnt. then the water will leave the exchanger at the same temp as drainwater enters in and the drainwater will leave at the same temp as water enters it, getting close to 100% efficency.
its just a b***h to do in reality because the shower drain probably dumps straight into the main sewage pipe somewhere in your floor so there is no way to physicly do it without ripping up the floor.
in an ideal scenario where the fluids are pure and are driven by a pump with nothing real life to worry about then yeah but this really isn't the case here. i thought about using somethink like an S-waterlock like in your toilet to create a small amount of hydrostatic back pressure and a small hole at the bottom with a flow rate lower than your shower to drain the exchanger after you're done so the waste water doesn't settle but that hole is going to clogh eventually
another solution could be to just simply recirculate the waste water but perhaps that doesn't sound too appealing to most people. no more peeing in the shower
perhaps it wouldn't be that much of a maintenance nightmare if you have easy access to the piping under the shower but presumably that isn't usually the case
Have you considered just taking cold showers? You get used to it.
Why have a house at all? A heated 10sqft box is more than enough to keep humans alive. Imagine all the money you'll save.
Nah, a decent kitchen pays dividends to your lifestyle. Hot showers don't.
Have you considered just eating oatmeal? You get used to it.
>Heat regenerator of waste water
Very interesting. It certainly could work. The regenerator needs to heat the water before it goes into the water heater. Also you would want to split the cold water before the regenerator.
BLACKED
by far the easiest and cheapest way to save on the heating bill is getting a water saving shower head
Best you can do is have the fresh water line and the drain line next to each other and wrapped up in an insulating sleeve. Anything you do to increase surface area for thermal transfer is just going to clog up. Fancy heat exchangers won't do shit if there's not enough time for the heat transfer. Not enough consistency for any of it to matter much unless the shower is running for hours a day and you're living with the fookin Brady bunch ahahahaha