The Ecodrain: How a simple, non-moving part can reduce hot water consumption by 40% | Hacker News Reader

The Ecodrain: How a simple, non-moving part can reduce hot water consumption by 40%

inhabitat.com

64 pointsjskopek24 comments

It doesn't reduce water consumption, it reduces energy consumption required to heat water.

Now, of course, the missing calculation is how much energy is required to make a stainless steel heat exchanger, install it, and perform maintenance. If that is more than 40% of the energy I spend on showers over the useful life of the device, then I'm not buying either a cost savings or an environmental improvement, I'm buying an image of myself as "environmentally conscious".

I'll have to admit, though, if I were the manager of the gym (which has 25 hot showers in the men's room kept between 34 and 40 degrees Celsius running for probably in excess of 1 hour per day each), this might be pretty interesting to me for economic reasons.

chances are the useful life time of a chunk of steel with a couple holes in it is as long as the rest of your plumbing

Being a heat exchanger I assume it uses small tubes with tight turns. Probably not great for hair.

That's what I think too. But look at how often car radiators and air conditioner coils have to be replaced. Hopefully since this doesn't have to hold pressure, or work at very high temperatures, it should last longer than the house.

I'm skeptical. To get meaningful energy transfer in a heat exchanger, you need time for the two material streams to be in thermal contact with each other. This is done by either increasing the surface areas using some porous or tortuitous channel, or just making the channels really long. In either case, it means you have significant pressure drop.

Now, a significant pressure drop in the incoming flow is bad enough, as I like a strong shower. But more concerning, is the pressure drop in the drain, which is already only at atmospheric pressure.

I predict lots of plugged drains and showers that you're wading ankle deep in water. Or... more likely, they found all this out, reduced their pressure-drop, and ended up with a device that doesn't really save that much energy.

This doesn't warm up the water to the heater, but rather the water going to the cold side of the mixing valve in the shower.

If it takes me 5 minutes to get the stupid thing at the right temperature now, imagine what will happen when the temperature of the incoming cold water depends on the temperature of the drain water - and it's a positive feedback - the hotter the water, the hotter the incoming cold water, making the output even hotter, etc.

This has the potential for using more water rather than less. Although I assume not all faucets are as sensitive as mine - in less than a degree or so of turning I go from freezing to boiling.

According to their actual website, you can set it up so that it feeds the warmed water back into the water heater, rather than straight back into the shower. Apparently there are thermostatic mixing valves that would probably help with your problem as well (although I just read that in their FAQ and really don't actually know what that even means).

I have a thermostatic mixing valve in my shower. You have two knobs: One for volume and one for temperature. That's all you need to know to use it.

The valve keeps adjusting the mixture of hot and cold water until the desired temperature is achieved. (Alas it can only achieve convex combinations.)

Thermostatic mixing valves use a thermostat to control the ratio of hot and cold water to output a selected temperature. Basically you select a desired temperature and the system attempts to provide you with it. This let's you use the shower while the hot water pipes are still heating up even though the hot water's temperature is changing.

Of course you can feed it that way, but the plumbing would be very convoluted - up to the shower, through the machine, and back down to the heater. The loss in water pressure would be bad, and can you imagine having two showers? The plumbing would be nuts.

I know about thermostatic mixing valves, but I'd have to break the wall of the shower, and redo all the tile. But I guess if I'm putting in this device I could do it at the same time.

But all the thermostatic mixing values I know of actually work on water pressure - so if someone turns on a faucet it automatically adjusts to keep the temperature correct.

I don't know of any that actually measure the temperature of the water, which is what is needed to help this device.

If you want to do this properly you install a heat exchanger on your main sewer stack, and then route the incoming water line through it. They do exist, this concept is not new.

Try living somewhere where there's a drought! We're asked to limit our showers to under 4 minutes (including getting the temp right!)

This line didn't add up for me: "likely your most energy-intensive daily household activity". I think overall temperature control for my house is vastly more expensive than this, given that my gas bill drops to $45 in the summer but touches $300 in the winter. I also run the dishwasher every day and do an average of one load of laundry per day (kids!).

Not a bad idea for new construction, but dialing back your hot water heater to 120F from the 140F they list probably saves more energy overall.

While I pretty much agree with you, and the water heater advice is great, I suspect that a decent part of that $300 jump in the winter is because the temperature of the water entering your home during the winter is much colder than it is in the summer (a.k.a. it costs significantly more to heat the same amount of water in the winter than it does in the summer).

Probably not. Water entering the house comes in below the frost line so the pipes don't freeze in winter and the ground temperature below the frost line is pretty constant year-round. There is a small change, but the water coming out of my cold faucets is almost the same temperature whether is 100F or -25F outside.

I've seen an even simpler non-moving device to reduce electricity use in supermarket freezers. Because the air in the freezer gains heat more quickly than the produce, the freezer switches on too often. A simple sleeve for the thermometer made in a material with heat capacity comparable to the produce makes the thermometer measure something closer to the temperature of the food. It got tested by the standards agency in the UK and is getting used in some supermarket chains (I'd post a link if I could find one!).

I'm not sure whether I like this particular design but the idea is very good aand basic.

It is one of those things that are

- rather orthogonal to the existing system (plumbing) - helps a bit in each installation - but cumulates large gains when scaled up over a threshold number of installations.

So far, such ideas for energy consumption haven't typically thriven largely because energy has been cheap but this will probably change. It would be a good idea for the government to subside installation of such devices.

In Finland (and other Nordic countries, I guess, and probably in any country with subzero seasons) we do the same in machinated ventilation systems in homes and buildings. The thermal energy of the warm indoors air (that is exiting the system) is transferred to the air intake where it's used to heat the cold outdoors air (that is entering the system).

When I saw the title, I was expecting basically a low flow drain. I'd imagine you would take a shorter shower if the water was pooling up around your feet as you did it.

As a previous commenter pointed out, the device purportedly saves up to 40% in hot water energy, not consumption. My bad on the incorrect title

Wastewater heat exchange is not a new concept. Here's a 1986 paper on it. http://www.gfxtechnology.com/Pravda.pdf

The GFX "falling-film counterflow" system is mounted vertically, in-line with the plumbing drain, and has a wide-bore drain pipe. It seems to me that this is inherently less prone to clogging than the horizontally mounted Ecodrain would be.

Clever device, I'm not convinced it would save a lot of money for one person taking a quick shower every morning, but I do think it could benefit those households with three or four people all wanting a shower in the morning: by recovering part of the heat from the first showers, the last person has a better chance of getting a hot shower instead of a lukewarm or cold one.

Pretty brilliant in it's simplicity. I'm not sure how it'll deal with all the crap that always works it way down the drain, though.

This is from the FAQ on the EcoDrain website:

    When my drain clogs, I use chemical and/or bacterial
    cleaners to unclog it. Is it safe to use these with the
    EcoDrain?

    The EcoDrain is corrosion resistant and it is as safe to
    use chemical and bacterial cleaners with the EcoDrain
    as it is for the rest of the piping.

The FAQ also says there is a non-stick coating to help prevent buildup inside the unit.

This doesn't add up. The drain water is, by definition, cooler than the boiler water. Looking at the diagram, cold water is heat exchanged with the drain water which means it will be heated but to less than what a boiler does.

This heated stream is then pumped directly to the shower to be mixed with the boiler water, which should cool it a bit. Anyone else find this odd?

Personally I'd redesign the system to put the exchanger upstream of the boiler water inlet which means that the boiler would need to expend less energy to heat the water going to the shower head.

The idea is that, instead of using cold water to mix with your boiler water, you use cold water that has been slightly heated by the heat-exchanger. This allows you to use less water from your boiler.

Reply on news.ycombinator.com