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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

#211

Post by fomine3 »

socialismisok wrote: post #205
fomine3 wrote: post #179

Earlier quoted context omitted.

It heavily depends how they use bath, and how cold. In Japan, 25-40% (vary depending on research) of energy at home is used for heating water because people prefer bathing. Heating water is expensive.

Japanese houses are more likely to be cooler but have local sources of heat, from what I understand. For example a kotatsu is a warm space. Heating locally is such an interesting idea to me.

The local heating "idea" is now low valued because moving between cold and hot area isn't good for health (called "heat shock"). It is recommended to make house insulated well and heat all rooms, for new houses. https://japantoday.com/category/national/agency-issues-warni...

Re: Re-using the heat in bathwater in Britain

#212

Post by jve »

> 90% of the heat in that water currently goes down the drain.

I think this number is very flawed, at least if we talk about bath and not shower. Kids sometimes play in bath until the water is "cold". Even if they just wash, the resulting water is far cry from what it was when "inputted" into bath.

Moreover, all that temp won't be recovered to heat air. Some energy goes to heat bath itself, some goes to heat space under bath and some goes to heat air. So I suspect the impact numbers to be far less benefit. And the result will be slightly warmer bath, but no effect to overall heating.

But it is true that water is hungry for energy. My avg energy usage is 550kWh and I have electrical water heater. It takes exactly half of total energy usage per month.

Re: Re-using the heat in bathwater in Britain

#213

Post by hkt »

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.

You might have benefited from MVHR, dMVHR, or an EAHP:

* MVHR extracts air from "warm" rooms like kitchens and bathrooms, runs it through a heat exchanger to warm new supply air, and then pushes the supplied air into other rooms in the house. It stands for Mechanical Ventilation with Heat Recovery. These systems can significantly increase the efficiency and comfort of your house, provided you also air tighten.

* dMVHR is similar, supplying fresh air but reclaiming heat, except the "d" is for distributed. They're like extractor fans but they don't waste the lovely heat.

* EAHP is an Exhaust Air Heat Pump. Usually they sit on top of an invented (eg pressurised) hot water cylinder, and they'll take hot, humid air out of whatever rooms you duct them to, heat you water for a quarter of the cost of an immersion heater, then blow cold air out of your house. This is a great option IMO (I have one) but unlike the first two options it depressurises your house and draws cold air in from outside through drafty bits of your house unless you have a corresponding system to warm incoming air at a similar rate to it being expelled.

tl;dr there are options to recover the heat while expelling the moisture!

Re: Re-using the heat in bathwater in Britain

#214

Post by oezi »

roenxi wrote: post #181
vkou wrote: post #157

Earlier quoted context omitted.

> It remains a mystery why everyone was so calm walking in to this while tightening the screws on fossil fuel industries to stop them investing int he future. Because the only half-solutions we got for mitigating climate change were drafted by people who are largely free market types, and they can only envision free market solutions - which require end users figuring out how they are going to deal with more expensive…

The German situation is pretty illustrative of what would have happened to anyone stupid enough to try and build more power plants in Western Europe - nuclear stations would have been shut down, fossil fuels have been staring down the barrel of the burgeoning Green movement for at least 20 years and are somewhere close to being hit with legislation designed to make them unprofitable. Renewable haven't been cost-effec…

On the contrary: everyone who invested in Europe in building any sort of capacity was handsomely rewarded (incl. nuclear).

Energy prices are so high because too many guarantees were given to too many parties to entince investment.

Re: Re-using the heat in bathwater in Britain

#215

Post by robertlagrant »

Retric wrote: post #165
godelski wrote: post #159

Earlier quoted context omitted.

I'm very confused at the lash back you're getting. Have you all never seen the pipes freeze? Or worse: burst? They wouldn't do that if they didn't swing in temperature. I'm not convinced of SEC's 2-3x estimated increase but the claim that water temperature delivered to your taps vary in temperature is an objective fact. Of course different areas have different infrastructure and can be more resistant to freezing and…

I agree water temperature at the tap can vary quite a bit. My parents place has the water go through an unheated crawl space and they would regularly keep the tap on to avoid the pipes freezing when temperatures got unusually cold. Further many municipalities extract water from rivers which experience significant seasonal variation etc. My comment was simply in reference to well water which has very consistent temper…

The original point was that a shower would have to use more energy to heat shower water in winter. Not sure now how any of your comments relate to that - do you agree with it?

Re: Re-using the heat in bathwater in Britain

#216

Post by spike021 »

SnaggyJoker wrote: post #70
georgeg23 wrote: post #28

Earlier quoted context omitted.

You could place a plastic mat on top to limit evaporation.

You could also switch to a water conserving mist shower and reduce the amount of heated water used for the shower. You could also reclaim the water from the shower for use in the toilet by turning the supply to the toilet off and manually transferring it to the toilet tank. There are lots of things you could do to save resources but most things are not done and are not going to be done because it is inconvenient and…

On one of my visits to japan my hotel had a toilet with a sink on top of the tank. Really loved the idea of flushing and washing my hands at the same time. The water used to wash your hands ends up being used for toilet water anyway. So you're not really wasting water at a completely separate sink.

Re: Re-using the heat in bathwater in Britain

#217

Post by hkt »

Maxion wrote: post #207
bombcar wrote: post #91

Earlier quoted context omitted.

Moisture has to go somewhere even if you don't see it visibly condensing on windows. Either it's being absorbed or you have something removing moisture from the system (venting, etc).

House code in Finland requires mechanical ventilation with vents in the bathroom. I only see brief condensation on my bathroom windows when I leave the sauna door open in the winter (approx. 100 celsius, 80%RH). With good building codes, you won't have condensation issues.

Alas, the UK has the twin problems of poor building codes and lots of old housing stock that nobody puts much thought into maintaining. In the latter case, people will take single skin brick buildings and apply "vapour control" materials outside the building, thus ensuring moisture is locked into the bricks. Then they wonder why they have damp, etc.

Alas, we are a very silly country.

Re: Re-using the heat in bathwater in Britain

#218

Post by hkt »

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…

It is worth pointing out that a more modern approach to district heating will use ground source heat pumps on-premise in people's homes, and will circulate fairly low grade heat (20C or less). Top-ups in system temperature can come from refrigerated warehouses inputting into the system, or solar photovoltaic-thermal setups that cool PV with circulating water, or just the ambient heat of the ground (10C most of the year far enough down).

See: https://www.cibsejournal.com/technical/take-it-down-low/

These networks are advantageous because the heat pumps using them can still produce enough heat even if the system temperature drops - they just do so less efficiently.

Re: Re-using the heat in bathwater in Britain

#219

Post by hkt »

sokoloff wrote: post #104
nsteel wrote: post #87

Earlier quoted context omitted.

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…

It seems sabotaged by incompetence on the part of regulators. You can’t make something both 100% mandatory and unregulated and then go shocked-Pikachu when the monopoly grantee takes advantage.

Charitable of you to assume it is incompetence rather than malice :/

Re: Re-using the heat in bathwater in Britain

#220

Post by hkt »

hedora wrote: post #162
twic wrote: post #96

Earlier quoted context omitted.

There are numerous manufacturers of these things, eg: https://powerpipehr.co.uk/ https://showersave.com/vertical-wwhrs/ https://recoupwwhrs.co.uk/ Ultimately they're just cleverly arranged copper pipes, so the barrier to entry for new manufacturers is low! I am keen to get one - my shower sits directly above a cupboard on the floor below, where it would be simplicity itself to fit. This article suggests the energy sa…

Note the manufacturer of the GP's device claims a 33% energy savings. You can get a hybrid heat pump hot water heater with a coefficient of power of 4, for a 75% savings. If your water heater is in a garage, it is likely a simple retrofit. (If it is in a small closet, it will require a duct). Ignoring installation, the heat pump water heater costs more than those devices. With installation, I imagine it is cheaper.

Given the coefficient of performance of heat pumps is a function of the difference in temperature between the two mediums, if you can use heat recovery on the shower water you can boost your COP further by having both. I'm in the midst of this exact system being installed: it'll be extracting hot, humid air from the bathroom and receiving pre-heated mains water via a reclamation unit.

The main thing with EAHPs is finding a plumber who is cognitively flexible enough to fit one. I'm on number six and it is finally going in next week.

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