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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

#31
post #20

Earlier 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?

The UK climate has moderate temperatures and a lot of rain. Excess humidity is a common problem here, and excessive dryness is rare.

Re: Re-using the heat in bathwater in Britain

#32
post #20

Earlier 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?

It tends to often be humid here, even in winter.

Right now, it’s 81% humidity. Our laundry has been taking two days to air dry.

Re: Re-using the heat in bathwater in Britain

#33
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.

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.

Re: Re-using the heat in bathwater in Britain

#35
If you let dirty water fill up your tub while you shower that'll result in a dirty ring around your bathtub which you'll have to clean... with more water (and possibly chemicals)... it'll cost you extra time to clean as well.

All together the total costs of the extra cleaning resulting from this may exceed the cost savings from letting the water heat your home.

Re: Re-using the heat in bathwater in Britain

#36
post #20

Earlier 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?

Cold air can hold much less water (hence why it's relative humidity). This is good if you take in cold air and heat it to 21°C or so because the air you end up with will have very low humidity, but if the outside is a drizzly 10°C and you are only heating to some 18°C, it can be a problem.

Re: Re-using the heat in bathwater in Britain

#37

Energy poverty can be sorted out by better insulation and investment in cheaper and more sustainable sources such as nuclear, wind and solar. Instead of working around this issue with clever hacks this needs to be a national policy. I think all roofs should be mandated to have solar panels installed, as a start, and all new builds should have proper insulation.

I think a step further is required. I really like the idea of using solar panels as an integral part of the roofing structure. There are people in the UK doing this as integrated solar panels which use a plastic tray underneath. I think with some slight adaptions we could even do better.

We had a few of these projects in the Netherlands. It is nice, until it isn’t. The solar panels are more vulnerable than tiles, they will degrade or need repairs/replacing. The mechanism for sealing it up will leak. The format of the panels and or the inverter was proprietary. Or the connection was and you couldn’t retrofit another inverter. It wasn’t a good experience.

Re: Re-using the heat in bathwater in Britain

#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.wikipedia.org/wiki/District_heating.

Usually district heating systems route heat into your building's pipes using a heat exchanger - so the network's fluid never actually intermingles with your building's fluid lines. These systems also use the same heat exchanger to return excess heat back to the network. District heating systems require a large initial investment, but over the long term are very efficient.

Re: Re-using the heat in bathwater in Britain

#39
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.

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?

Re: Re-using the heat in bathwater in Britain

#40

I was actually looking at heat recuperation systems for bathrooms recently and stumbled upon https://ecodrain.com/en/ - if we hadn’t already remodeled our bathrooms I’d have loved to have installed this. For now we make do with a heat pump water heater which is very efficient.

I wonder how different it would be to use an off the shelf heat exchanger, e.g. this one? https://www.ebay.co.uk/itm/263272702860

You'd probably have to filter the shower water before sending it through, but beyond that I wonder how different the principle is. Maybe being easy to clean is a significant factor in drain showers.

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