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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

#111

Post by tempestn »

nicd wrote: post #107

This reminds me of a "re-circulating shower" concept I was looking into recently. By filtering and re-using shower water, it saves both water and heating energy. There is a company in Sweden doing this: https://orbital-systems.com/ . There's a bit of an ick factor, but with filtration, it seems this should be more hygienic than bathing? My family remains unconvinced though ;)

Most people are fine with hot tubs aka spas, which are essentially this. (In fact most spa designs don't even filter all the water on each re-circulation, as there are returns both at the bottom and in the skimmer, and only the latter is filtered.) Re-circulating shower sounds like a great idea to me.

Re: Re-using the heat in bathwater in Britain

#112

Post by twic »

mgaunard wrote: post #68
lkramer wrote: post #67

In my experience, there a many lower hanging fruits in British houses to save energy than this. Uninsulated and draughty old houses seems to be the norm here (at least if you're renting). I'm surprised the government is not pursuing this more aggressively.

Even if you're buying, the most popular houses are ancient Victorian ones which, in spite of their charm, are very badly insulated. They're often listed and require fitted wooden windows, so it's not exactly easy to fix.

Vanishingly few houses are actually listed. Some are in conservation areas, which have similar but less strict restrictions on what changes you can make. These are the areas in my borough - almost half the built-up area, but i would guess proportionally less of the homes, because they are lower-density old buildings:

https://www.haringey.gov.uk/sites/haringeygovuk/files/haring...

You can coax a London-wide map of conservation areas out of this, and see that most of the suburbs aren't covered by them:

https://apps.london.gov.uk/planning/

It probably is true that the most desirable houses are in those areas, but being in a conservation area helps preserve them and keep them desirable.

Anyway, even within those conservation areas, there is plenty you can do to improve insulation. I had internal wall and ceiling insulation fitted, and replaced the window sashes with double-glazed ones.

Re: Re-using the heat in bathwater in Britain

#113

Post by tempestn »

afandian wrote: post #110
shellfishgene wrote: post #76

Earlier quoted context omitted.

There may also be problems with sanitation rules, only a minimum of water should sit in the pipes, and then ideally hot our cold but not luke warm.

Got a link (or explanation) for that temperature stipulation?

Temperature window for bacterial growth. Above about 120F harmful bacteria commonly found in water won't proliferate, but will survive. As you get hotter from there, they're killed off increasingly rapidly. Above 135 or 140 or so they don't survive long. In cold water they won't die off but also won't multiply quickly. The dangerous range is in the middle.

Re: Re-using the heat in bathwater in Britain

#114

Post by Retric »

SECProto wrote: post #63
skrause wrote: post #55

Earlier quoted context omitted.

Living in Germany and getting both my heating and hot water from natural gas I regulary track my gas consumption throughout the different seasons. With 1-2 showers per day in the household my daily natural gas consumption in winter is about 20x higher than in summer, so compared to heating the house the energy in the hot water is a drop in the bucket.

Note that a portion of that increase in gas consumption is still due to the hot water usage, even if the number and duration of showers stays the same - tap water varies in temperature through the year, getting colder in winter and warmer in summer. In my case, it varies between ~5 and ~22C. Germany has milder winter temperatures so likely not as much variation, but still a significant fraction of the temperature inc…

Well water stays very consistent year round in most areas.

Some municipal systems vary more depending on where they get it and how they store it. Water towers used to smooth out water demand for example can noticeably impact water temperatures.

Re: Re-using the heat in bathwater in Britain

#115

Post by mvhvv »

Gigachad wrote: post #102
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…

Why not feed that heat back in to the power plant to squeeze more electricity from it?

I'm no power-plant engineer, but vaguely remembering back to thermodynamics 101, in a perfect heat-engine efficiency is relative to the temperature delta.

You can't just turn heat to electricity, so below a certain threshold it's only good for warming spaces.

Re: Re-using the heat in bathwater in Britain

#116

Post by chihuahua »

tempestn wrote: post #109

Problem is you're not just adding heat, but humidity. Normally while having a shower you're going to run an exhaust fan in the bathroom. So if you want to conserve heat, the better approach is just to make the shower as short as possible.

That seems like a more realistic suggestion to me. If you want to take this further, switch to taking Navy showers: get wet, turn off shower, apply soap, turn on shower to rinse off.

Re: Re-using the heat in bathwater in Britain

#117

Post by frankus »

louison11 wrote: post #66

Where we live in Portugal humidity is a big problem, and we actually spend 1kW 24/7 running dehumidifier throughout the house. If we didn’t, mold would grow and we would get severe allergies. So… this seems like a very bad idea even for the UK, considering it’s very rainy there in the winter.

A house with plenty of air exchange (either mechanical or because of a leaky air barrier) in a cold climate will tend to suffer from too low of humidity (cold air enters, and as it gets heated to room temperature the relative humidity drops).

Re: Re-using the heat in bathwater in Britain

#118

Post by frankus »

oliwarner wrote: post #108

Having read this, I'm strongly considering routing my bath and shower wastes through a poorly insulated hot water cylinder in reverse (new [warm] waste in at the top, old cold waste out the bottom). Hot water will float in there. Cold will be displaced first. It only has to hold the volume of "a shower" and we'd keep that energy within the envelope of the house, without added humidity or state-change heat loss. The o…

Something like this could be interesting with active heat transfer, for example using it as the source side of a heat pump water heater. As long as the outgoing water remains above freezing, of course.

Re: Re-using the heat in bathwater in Britain

#119

Post by SECProto »

Retric wrote: post #114
SECProto wrote: post #63

Earlier quoted context omitted.

Note that a portion of that increase in gas consumption is still due to the hot water usage, even if the number and duration of showers stays the same - tap water varies in temperature through the year, getting colder in winter and warmer in summer. In my case, it varies between ~5 and ~22C. Germany has milder winter temperatures so likely not as much variation, but still a significant fraction of the temperature inc…

Well water stays very consistent year round in most areas. Some municipal systems vary more depending on where they get it and how they store it. Water towers used to smooth out water demand for example can noticeably impact water temperatures.

Temperature at the well stays consistent, but it can vary at the tap. At a family member's secondary property, tap water will vary from 2 deg in winter up to 15 in summer (because the line between the well and the house is only ~3-4 feet deep, and surface temperature changes a lot). If we were drawing more or less/line was different length/different depth, the variation would change.

(I know all these values from homebrewing, where water temperature plays a big role in how long it takes to cool)

Re: Re-using the heat in bathwater in Britain

#120

Post by alkonaut »

SECProto wrote: post #63
skrause wrote: post #55

Earlier quoted context omitted.

Living in Germany and getting both my heating and hot water from natural gas I regulary track my gas consumption throughout the different seasons. With 1-2 showers per day in the household my daily natural gas consumption in winter is about 20x higher than in summer, so compared to heating the house the energy in the hot water is a drop in the bucket.

Note that a portion of that increase in gas consumption is still due to the hot water usage, even if the number and duration of showers stays the same - tap water varies in temperature through the year, getting colder in winter and warmer in summer. In my case, it varies between ~5 and ~22C. Germany has milder winter temperatures so likely not as much variation, but still a significant fraction of the temperature inc…

22 degrees is the coldest tap water? That means you basically need ice cubes or fridge storage before you can drink it in the summer?
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