i did hear about some shower drains that reuse the heat like this one:
https://www.youtube.com/watch?v=s5bJ61fCA2E
Re-using the heat in bathwater in Britain
41–50 of 257 posts
Re: Re-using the heat in bathwater in Britain
#42Not discussed: hot water in houses increases humidity. In modern well sealed houses, that can result in unfortunate mold growth.
Why do you say "not discussed"? That's point #4 in the article.
Re: Re-using the heat in bathwater in Britain
#43Not discussed: hot water in houses increases humidity. In modern well sealed houses, that can result in unfortunate mold growth.
From the article:
> Extra moisture in the air might cause problems with things like mold. Use your judgment. It’s probably fine as long as things don’t stay damp all the time. For many, extra humidity in the air would be welcome. (Maybe you can stop using that ultrasonic humidifier.)
Re: Re-using the heat in bathwater in Britain
#44Earlier quoted context omitted.
I've always experienced extremely low humidity in winter months, so I would think the net effect might be a reasonable positive if this saves me needing to run a humidifier. Am I missing some detail? Or is that just unusual?
It depends massively on your climate and how air in your house is managed. If you live somewhere which is significantly colder outside than in (e.g. 0-5C out, 21C inside) heating outside air to comfortable temperatures will greatly decrease humidity. Couple this with a system which circulates air, or even exchanges inside&outside air and you will have incredibly low humidity inside. I live somewhere which often sees…
Ventilation with heat recovery sounds like it could work in those conditions, but just barely. 80% @ 15C would turn into 55% @ 21C.
Re: Re-using the heat in bathwater in Britain
#45As the article points out, only some 9% of domestic energy goes towards heating water for showers and baths. Instead of trying to force yourself to do cold showers, you could save much more just turning down the thermostat.
Exactly. Space heating is the most energy-intensive an expensive item on the list of things you can save on in a detached house - especially that you only really need the heat to be where you are.
Re: Re-using the heat in bathwater in Britain
#46Earlier quoted context omitted.
Although higher humidity should make it feel warmer given the same ambient temperature. So if you're increasing the temperature mildly using this method AND increasing humidity, it may compound one another positively. Although, it is a minor efficiency gain either way.
I thought high humidity made it feel colder, when the temperature was relatively low? Hot damp air feels hotter than hot dry air, but I've had the idea that cold damp air feels colder than cold dry air. Is that a misconception?
I agree with you. Water facilitates heat transfer, and the surface of skin is about 95f, so it seems that below that temperature, and assuming you aren't already sweating for the evaporative cooling effect, humid air should move heat out of your body more effectively than dry air.
Re: Re-using the heat in bathwater in Britain
#47This is so much more reasonable than that …other… Modest Proposal.
What other proposal?
That would be A Modest Proposal For preventing the Children of Poor People From being a Burthen to Their Parents or Country, and For making them Beneficial to the Publick by Jonathan Swift: https://en.wikipedia.org/wiki/A_Modest_Proposal
Re: Re-using the heat in bathwater in Britain
#48I 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.
It could also be that your windows are not insulated enough. For 20C and 40RH the windows need to be colder then 6C to get condensation.
The relative humidity of a bathroom after a shower must be much higher than 40% - I would imagine getting towards 100% (hence room temperature mirrors steaming up). Where I live (UK) I don't think I've ever seen an indoor humidity as low as 40% - it's typically in the 60-70% range.
Re: Re-using the heat in bathwater in Britain
#49Earlier quoted context omitted.
You’re in the uk?
No, but I was given to understand that winter => cold => dry air was driven by the basic physical properties, so I would be very curious if it was different there. Is it different in the UK, and if so, why?
someone else can explain better than me, but.. humidity is lower when it's cold but relative humidity is higher.
Being outside in the uk when it's cold is often like being inside a cloud, with 100% relative humidity levels.
Combine this with the old, badly insulated, difficult to heat housing stock, and you can guarantee that there is one part of the house (a north facing wall, say) that is at or dangerously close to the dew point for some part of the day/night.
You wouldn't want to leave a steaming bath for longer than necessary.
Re: Re-using the heat in bathwater in Britain
#50I 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 mirror image of this is combined heat and power (CHP). That is, instead of burning fuel to heat the home, use the fuel to power a generator of some sort, and using the electricity to power the home. The waste heat (most of the energy from the fuel ends up as waste heat) is then captured to heat the home It's basically free electricity, if you were already heating the home by means of combustion anyway (e.g. oil, natural gas, propane).