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Re-using the heat in bathwater in Britain

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Re: Re-using the heat in bathwater in Britain

#81

Post by kragen »

I've done this. It works surprisingly well, and (as Might points out) humidifies the house in a way that radiators and resistance heaters do not.

The evaporating water does convert (to use the traditional terms) sensible heat into the latent heat of water vapor, and you might think that this heat should be discounted from the heat you're getting out. Sometimes it should, but not other times, because if the water vapor condenses again inside the house (for example, near the surface of the plaster in cold walls) it will release this heat again as sensible heat. In other cases, it's worse — I've had the displeasure of staying in a cold guest room where the blankets were all slightly damp from such condensation and so failed badly at keeping me warm.

In that case, the water vapor had been produced not by evaporating standing water but by burning natural gas. Be careful.

Re: Re-using the heat in bathwater in Britain

#82

Post by sixstringtheory »

In addition to things like heat exchangers or reducing the amount of time/water in a shower, is there any work being done around optimizing the amount of time a hot water heater keeps the water at high temp? I’ve thought about this for extended absences but this could also bring potential benefits if it just doesn’t run for certain portions of the day or middle of the night.

Re: Re-using the heat in bathwater in Britain

#83

Post by pbhjpbhj »

upsidesinclude wrote: post #69

Turning your thermostat down by one or two degrees per week and getting acclamation to cold is a better alternative. 5 degrees on the thermostat would be a far better measure than tub heat. Short showers, or 'sea showers', to conserve water and heating would likewise be a far better option than a 50 gallon bath.

What's a "sea shower". Do you mean when you literally just spray water on yourself, then soap all over, then rinse off?

Re: Re-using the heat in bathwater in Britain

#84

Post by comboy »

wcoenen wrote: post #7

I tried this once on a cold winter day: I let the bath cool down to room temperature (which was <20C) before letting it drain, with the bathroom door open. The result was a lot of condensation on the windows in the surrounding rooms. I figured the high humidity was going to cause more damage than it saved money, so I scrapped the idea.

Simplest use case would just to have a container in the basement / garage through which the water flows, assuming you are heating it at least a little. You likely keep lower temp there so it is much more efficient. Although in practice drain from the shower or bath quickly connects with the one from the toilet so it's not that easy to implement.

In your case efficiency is also slightly lower due to evaporation. If anybody has any idea how significant it is I'd love to learn. I was surprised one day in winter to find that my evaporative humidifier has temp below 10C on it (room temp 23C).

I think ground heat pumps could have an exchanger around the main drain pipe which should work nicely both in winter and during summer.

Re: Re-using the heat in bathwater in Britain

#85

Post by ac29 »

ArmandGrillet wrote: post #53

Tangentially related: has someone found something less energy intensive than taking a bath while bringing the same degree of warmth? I've been looking at heated blankets but they're all made of polyester which is not comfortable due to the moisture being trapped under the blanket. Heated seats in some cars are the closest sense of comfort I've found but that technology doesn't seem to exist for regular seats.

Electric heating pads?

Re: Re-using the heat in bathwater in Britain

#86

Post by luckylion »

ArmandGrillet wrote: post #53

Tangentially related: has someone found something less energy intensive than taking a bath while bringing the same degree of warmth? I've been looking at heated blankets but they're all made of polyester which is not comfortable due to the moisture being trapped under the blanket. Heated seats in some cars are the closest sense of comfort I've found but that technology doesn't seem to exist for regular seats.

Heated blankets never really did the trick for me either. Electric foot-warmers do. They're cheap, don't consume too much energy, and will get your feet nice and toasty in no time.

Re: Re-using the heat in bathwater in Britain

#87

Post by nsteel »

jitl wrote: post #38

I read a lot about district heating systems yesterday after seeing an article on NYC's steam system on HN ( https://news.ycombinator.com/item?id=33388473 ). District heating systems allow you to capture waste heat at the power plant (called co-generation), and use that to heat & cool (via cooling compressors) many, many buildings at once. The wikipedia article about it is very informative as well: https://en.wikipedi…

The problem with district heat schemes in the UK (at least) is they are becoming mandatory for new large housing developments but are 100% unregulated every step of the way. The builders do the cheapest job possible because the efficiency targets they're supposed to hit are never measured or verified post install. And unlike the rest of domestic energy in the UK, pricing is totally unregulated. The residents can (and are) charged high rates because it's impossible for them to change supplier. Any potential savings are undone by these two things. The energy regulator has so far refused to do its job because they supposedly don't want to stifle growth in this new market.

It is a good idea but it's been sabotaged by greed.

Re: Re-using the heat in bathwater in Britain

#88

Post by twic »

ArmandGrillet wrote: post #53

Tangentially related: has someone found something less energy intensive than taking a bath while bringing the same degree of warmth? I've been looking at heated blankets but they're all made of polyester which is not comfortable due to the moisture being trapped under the blanket. Heated seats in some cars are the closest sense of comfort I've found but that technology doesn't seem to exist for regular seats.

I have an electric blanket. The way it works is that you put it underneath the sheet, on top of the mattress. Moisture getting trapped under it isn't really a concern, because i lie on top of it. From the sheet up, the bed works in the normal way.

I turn it on for 30 - 60 minutes or so before getting into bed, to warm the bed up, and turn it off once i get in. I have tried leaving it on all night on the lowest setting, when it is very cold, but i wake up dehydrated.

Re: Re-using the heat in bathwater in Britain

#89

Post by pbhjpbhj »

sixstringtheory wrote: post #79
upsidesinclude wrote: post #69

Turning your thermostat down by one or two degrees per week and getting acclamation to cold is a better alternative. 5 degrees on the thermostat would be a far better measure than tub heat. Short showers, or 'sea showers', to conserve water and heating would likewise be a far better option than a 50 gallon bath.

And not just short showers, but managing the amount of time the water is actually running. Here’s my strategy for an efficient shower: 1. turn on the water, get in, rinse down, soak a wash cloth 2. turn off water 3. lather hair with shampoo 4. lather wash cloth with soap and scrub body 5. turn on water and rinse down The majority of the time we’re standing in the shower, we don’t actually need the water to be running…

It gets really cold without the shower water running. Our indoor temperature in the day is 16-18°C in Winter (UK).

Re: Re-using the heat in bathwater in Britain

#90

Post by ArmandGrillet »

zubspace wrote: post #58
ArmandGrillet wrote: post #53

Tangentially related: has someone found something less energy intensive than taking a bath while bringing the same degree of warmth? I've been looking at heated blankets but they're all made of polyester which is not comfortable due to the moisture being trapped under the blanket. Heated seats in some cars are the closest sense of comfort I've found but that technology doesn't seem to exist for regular seats.

Maybe just one or two hot water bottles? [1] We use them in Winter to warm our feet in bed. But they are very versatile and can also be used to alleviate any kind of tension. I also use one while I code: I put it inside of a small (baby-)sleeping bag wrapped around my feet. Sounds weird, but it's so comfortable! [1] https://www.google.com/search?q=hot+water+bottle&tbm=isch

Went for https://www.yuyubottle.eu/ after a bit of googling due to the cotton fabric + the strap, will test it this winter.
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