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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

#161

Post by syockit »

chihuahua wrote: post #116
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.

What, all my life I thought that was the normal way of showering. So how do you people actually shower? You leave the tap on while soaping?

Re: Re-using the heat in bathwater in Britain

#162

Post by hedora »

twic wrote: post #96
maherbeg wrote: post #11

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.

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.

Re: Re-using the heat in bathwater in Britain

#163

Post by BurningFrog »

I've noticed that people wildly overestimate the environmental impact of things they personally touch.

This, I theorize, is why sub-rounding error things like plastic straws, plastic bags, cups, etc get such disproportionate attention.

Bathwater that heats every pore of our naked bodies is probably even more susceptible to this bias.

Re: Re-using the heat in bathwater in Britain

#165

Post by Retric »

godelski wrote: post #159
SECProto wrote: post #119

Earlier quoted context omitted.

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 hom…

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 temperature and will warm or cool the soil surrounding pipes at any reasonable depth if you are using water regularly.

Re: Re-using the heat in bathwater in Britain

#166

Post by bemmu »

In Japan at our place we always do this. After the last person has used the bath water, we let it sit there overnight, and then use the water for the first wash cycles of the washing machine.

The less efficient part of this story is that everyone showers before entering, and that does go down the drain.

Re: Re-using the heat in bathwater in Britain

#167

Post by mistercow »

kragen wrote: post #81

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 vapo…

On the latent heat problem, I wonder how the math works out if you put a dehumidifier in the bathroom to counteract the effect of leaving warm water standing around.

What's interesting about that is that you'd effectively be using the dehumidifier as a heat pump, indirectly pumping the heat out of the water and into your home, leaving you with cold water in the heat pump's reservoir. You're adding energy, but that energy also ends up as heat, so you'd still certainly end up ahead compared to using electroresistive heating (but not necessarily compared to a traditional heat pump).

My guess is that it would be a lot more effective to _directly_ pump the heat out of the waste water, but you can't do that with off the shelf appliances.

Re: Re-using the heat in bathwater in Britain

#168

Post by russellbeattie »

Years ago I was renting a house with a small in-law building in the back which was rented separately. I'd get the electric bill and then split it 75/25 with the guy who lived there. Over time the electric bill kept getting higher and higher, until it was like $500+ a month. I talked to the landlord and the other renter about it and none of us could figure out what was drawing so much electricity. I called the electric company several times, and they'd asked if I had shut off my pool, which I didn't have, or if I had been using the jacuzzi a lot, which I also didn't own. Then they asked about power tools, welders, and all sorts of other things, and when I finally convinced them something was wrong they sent someone out.

The electric guy did the obvious thing: He started flipping breakers to see which circuit was drawing so much electricity. I had done that as well, but had no idea what to do from there. He was able to follow it out to the in-law house, which was in complete darkness as it had zero electricity inside - except for a tiny water heater installed out back. It had somehow gotten filled with sediment, so the heating element was basically trying to keep a barrel full of sand warm. (The guy who lived there just assumed the hot water tank was small and took fast showers as a result). The landlord replaced it and suddenly the bill went down to less than $100. Crazy.

The point to this story is that there's probably a lot more that could be done before worrying about recouping the heat from your bath water.

Re: Re-using the heat in bathwater in Britain

#169

Post by hedora »

cameronh90 wrote: post #56
newaccount74 wrote: post #44

Earlier quoted context omitted.

Ventilation with heat recovery sounds like it could work in those conditions, but just barely. 80% @ 15C would turn into 55% @ 21C.

Unfortunately, very few homes in the UK have any air ducting. I'm looking at installing a MHRV system at the moment, but planning the ducts is a nightmare. Brick walls, lintels and structural joists everywhere with no headroom between floor and ceiling. We absolutely should be doing it in new builds though, and we're not.

That sounds rough. Consider putting in air to air mini-splits instead, and leaving window cracked open, etc. As a bonus, each room will get its own thermostat, and cooling / heating.

The mini-split will only require coolant lines, and will have a sufficiently high coefficient of power that this + whatever ventilation exists might use less energy than heating with natural gas (or resistive electric), even with the loss of efficiency from not using heat exchangers.

(Doing both things would be much better, of course. Retrofitting is hard.)

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