Stop pouring hot water down the drain

http://green.yahoo.com/blog/ecogeek/1010/stop-pouring-hot-water-down-the-drain.html

by chaostheory • 17 years ago

125 49 17 years ago

green.yahoo.com

mhb• 17 years ago

Doesn't it make more sense to use the hot, gray shower water to heat the water going in to the hot water heater?

Doesn't it make more fun to wedge a peltier device between the outgoing warm and the incoming cold and use the generated power to light some LEDs in the shower?

froo• 17 years ago

I love peltiers, I used one as a heat exchanger on my brother's 944 Turbo on the induction system and transferred the heat to the fuel rail, creating a fuel warmer.

Result was he set the engine management system (motec) to run the fuel system richer, as the fuel that was more ready to combust (as a result of the heat) and given the air going into the turbocharger was colder (more dense) there was more air to react.

That being said - we never got the opportunity to test if there was any actual horsepower gain, but he used to suggest that there was.

Now as for LED's in the shower, that might not be as silly as it sounds. Imagine if the tiles on the floor were semi transparent (I'd suggest some kind of translucent polycarbonate) and lit up like a disco floor for those people who love to sing in the shower.

_pius• 17 years ago

On first blush that sounds like the way to go, but for most existing homes it would probably be suboptimal.

To reduce costs, a device like this should be localized to a room rather than force you to route the water from your shower all the way back down to a water heater. The latter would necessitate a major plumbing addition.

jwilliams4• 17 years ago

Agree - and given the locality (i.e. there is someone using heat/hotwater right there), it would make sense to use it as soon as possible.

If you didn't have locality, the water heater approach probably make more sense -- i.e. Your washing machine, dishwasher, which tend to hold on to hot water and then dump it at the end of the cycle.

mikeyur2• 17 years ago

I'd actually prefer the gray water be used to heat the floor in the bathroom. If you've ever stepped out of a shower onto a tile floor you know how cold it can be sometimes. And if you've ever stepped onto a (electrically) heated floor, you'll know how awesome it is.

Running the warm water through a series of pipes below the bathroom floor would seem like a pretty good use of it to me, when compared to just dumping it into the sewer as-is.

Then of course, in a green house, the gray water would be collected and used to flush the toilets.

matthavener• 17 years ago

there is a similar idea for high insulation homes where you heat exchange the outgoing air (recirculated for freshness) with the incoming air to avoid having to cool/heat the incoming air as much

imo, heat exchangers are a good way to reduce consumption because they're usually passive and don't require much maintenance

pingswept6• 17 years ago

That's a great idea. Modern gas boilers and tankless water heaters often run their exhaust and intake in concentric pipes, so that the outgoing hot air warms the incoming cold air.

abthomson• 17 years ago

Furthermore, the flow in the two pipes is usually in opposite directions because it's more efficient that way.

jwilliams4• 17 years ago

The one that's always confused me is having a Fridge in a cold climate.

Always wondered if there was a technology that could simply couple the fridge to the outside temperature.

pingswept6• 17 years ago

This does exist. For industrial applications, there's http://www.freeaire.com/. There are also small fans designed for use with RV fridges that could do the same thing.

Unfortunately, in a cold climate, you need to heat your house anyway. Electric heat is more expensive than natural gas or oil heat, so you might save some money, but from a greenhouse gas perspective, the savings are small at best.

jwilliams4• 17 years ago

Yeah, good point.

furyg3• 17 years ago

"but from a greenhouse gas perspective, the savings are small at best"

Taking that argument down to an even more micro-level: most of the light in my apartment comes from overhead halogen lights (hot), and sometimes I'm inclined to switch them for energy efficient fixtures, but...

I live in a cold place anyway, so I'm not sure that switching makes a lot of sense. I know it's more efficient for the central heating system to be doing the heating (and not light bulbs, refrigerators, or laptops), but I need the heat, I need the light, and my energy bill isn't that big, so why switch?

parenthesis• 17 years ago

I remember staying in a Youth Hostel in Scotland in cold weather, and people keeping their cartons of milk on the outside windowsill 'in' the kitchen. (Presumably there was no fridge.)

The point being: if you are in a cold climate, you can just keep food outside (suitably protected, etc., etc.).

jwilliams4• 17 years ago

Yeah I used to live in Zurich. Great for parties. Just put the beer on the balcony :-)

kqr2• 17 years ago

During the winter, I kept my sodas outside my window sill, but sometimes it would get too cold and they would burst!

HeyLaughingBoy• 17 years ago

That works well for stuff you want frozen rock solid (around here it drops to -25F in winter) and it makes it easy to run out to the grocery at lunch time and safely leave meat in the car. But for things like milk, eggs, etc. that you don't want to freeze, not so much.

david927• 17 years ago

In the Czech Republic people used to have two windows -- an inner and an outer. Not only is it great for insulation but you can keep things between the two windows and it stays cold without freezing.

lsb• 17 years ago

Carlin mused about a fridge with a butter warmer.

lutorm4• 17 years ago

Amory Lovins talks about this in "factor four" (great book). They go through how the refrigerator is a textbook example of loads of small design decisions ending up with something really suboptimal. In a cold climate, what you do is put the radiator coils on the outside of the house. Every kitchen would have two pipe hookups where the fridge goes, leading to the coils on the outside. Then you get the fridge and plug it in just like you do with washers. (Or you could plug it into your heat pump, which you should use to heat your house anyway.)

quizbiz• 17 years ago

Now this is value added. The key would be for housing developers to adopt this.

ars2• 17 years ago

Dup: http://news.ycombinator.com/item?id=529552

And the messages there indicate this device probably isn't practical, it has too many caveats. And if you want to do this, you attach one to the main sewer stack of the whole house - it's been available for about 20 years.

noonespecial2• 17 years ago

If your house is older and has copper sewer piping, it does an excellent job of radiating that heat back into your house. What you save heating water might not be too far off the heat you don't have to use your furnace to make.

lutorm4• 17 years ago

Pipes generally don't go in your living spaces, they might heat your basement but that's not really where you want the heat.

lutorm4• 17 years ago

The trouble with that is that by mixing the hot drain water with cold water you spend the energy heating the cold water and lose efficiency. You want to avoid the cold toilet flush water and whatever and just get the "hot stuff".

ars2• 17 years ago

Don't warm the entire cold water supply - just what goes to the water heater. But do it in the basement, where all the pipes already are, not under the shower, and not with a small device that is likely to get clogged.

phugoid• 17 years ago

I usually wait a little while for the water temperature to stabilize, before getting in. That transient period will be much longer with this gadget.

- time it takes for the heat exchanger (gadget) to warm up due to shower drain water. - now the shower water temperature has changed (increased), so you need to adjust the valves. - another transient time for the heat exchanger to warm up, etc.

Depending on the design, you might find yourself wasting a lot more water, or jumping around in the shower as the temperature keeps changing in this slow control loop.

eggnet• 17 years ago

There are shower control systems, purely mechanical, that regulate the temperature themselves. Those systems would automatically adjust to the changing temperature of the "cold" water.

savrajsingh• 17 years ago

this is super cool.

blahblahblah2• 17 years ago

The diagram shown in the article doesn't make a whole lot of sense to me. They've got the output of the heat exchanger going directly to the supply of the shower where it mixes with the output of the water heater. This actually reduces the temperature of the shower and, as phugoid already noted, introduces undesirable temperature transients. It seems to me that it makes more sense to use the heat exchanger to preheat the feed to the water heater. This has the added advantage of making the energy exchange mechanism generally applicable to any hot water that exits via the drain which supplies the heat exchanger, not just shower water. Also, when you finish your shower and shut off the water, there is still heat in the drain and still water refilling the water heater, but the design as shown does nothing productive with that energy.

Of course, one would hope that the heat exchanger itself is made of highly corrosion-resistant material. It would be quite nasty to have a leaky drain introducing gray water into your potable water supply.

extension• 17 years ago

It only reduces the temperature of your shower if you would otherwise be standing under 100% hot water, which would literally be lethal with a typical hot water system (I'm guessing you don't have a typical hot water system?). It's more likely you are using a mix of, say, 70% hot, 30% cold. If you use this thingy to heat the cold water, you could get the same temperature with maybe 60%/40% mix, thus using less hot water and getting a cheaper and/or longer shower.

blahblahblah2• 17 years ago

Perhaps most people have the thermostat on their water heater set higher than it really needs to be? On the other hand, as a bachelor, I concede that my hot water usage pattern is not the same as an average household with a family of 3 to 5 people. I typically do use 100% hot water for my showers. The only exception to this is if I run the dishwasher or the washing machine a few hours before taking a shower, which will result in 100% hot water being too hot.

ryanvm• 17 years ago

My cheaper version: Stand in my own filthy gray water and then leave it overnight. Problem solved. Of course now I have to solve this jock itch on my feet...

rsheridan6• 17 years ago

The purported savings are comparable to what you would save by switching to tankless water heaters: http://apps1.eere.energy.gov/consumer/your_home/water_heatin...

The tankless heater also doesn't have the energy cost of building this grey-water heat exchange device. It does have the energy cost of being built itself, but that's probably comparable to the cost of building a standard heater with a tank.

Your best bet energy-wise would probably be to go with a tankless heater as near as possible to the shower, maybe combined with a hypothetical system like the one in the article, except it would warm the water going into the tankless heater. Or you could not drain your bathtub until the water cools, if you need to heat your house anyway.

gills• 17 years ago

This would work well in my house, but not for the stated purpose.

We have a hydronic heating system (hot water circulates through pipes to toasters...kind of like old radiators but more efficient). A heat exchanger from graywater to our heating system would help our winter gas bill quite a bit.

Tying it to the dishwasher and washing machine would help out a lot too.

Stop pouring hot water down the drain

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