Shower Scene

[Breaking Wind]

I thought this was a neat idea so I thought I'd pass it along.  I read in article in my local paper up here in Vermont about a couple creating an energy efficient house.  One way they cut down on energy waste was by putting in a heat exchanger in the waste water coming from their shower.  The exchanger is called a Gravity Film eXchanger (GFX) and it replaces a section of vertical drain pipe with an all-copper heat exchanger.  The heat exchanger consists of two and three inch diameter copper pipes (containing the gray water) with 1/2 inch tubing coiled tightly around them.  The 1/2 inch tubing contains the incoming fresh water about to be sprayed into the shower.  Up to 85% of the heat from the waste water can be recouped using this method of preheating the fresh water with the heat from the waste water.

Anyway, just thought it was an interesting article...maybe someone can use the technology.

Mike

[MountainMan]

In keeping with your title for this thread, if the couple showers together, the "extra" heat produced might make the total system more than 100% efficient!

jp

[wooferhound]

A coupla people have done it in this story . . .

http://www.fieldlines.com/story/2003/12/26/17724/816

It's a great idea, But it seems to me that it would be hard to adjust the temperature of your shower since everytime you change the hotness of the waste water, it would change the temperature of your cold water too.

[mikey ny]

I have had another idea about preheating water in a similar way. Make the same type heat exchanger, copper tubing around the pipe for the exhaust of my gas fired hot water heater , but I abandoned that idea since my solar water heater makes most of my hot water now. That could also work with a boiler. Any method to reclaim heat energy from something before it leaves the house is great.

[jimovonz]

Don't get me wrong - I think that every effort to minimize household energy use is great, but I do not think that this type of system would be very effective. I considered such a system myself when I started building my house but gave up the idea pretty quickly when I actually measured the temp of the water going down the drain. The water comming out of your typical shower head has a very large surface area due to the 'spray'. This large surface are means that the water very quickly looses its energy to the surrounding air. You can test this very easily by crouching down in the shower - where you will notice a significant temp drop in the water. You can also easliy notice the rapid air temp rise in the bathroom when you take a shower. The water looses still more energy when it comes in contact with the shower walls/floor. I like a nice hot shower of around 45degC at the shower head. I measured a water temp of approx 20degC entering the waste drain towards the end of my shower. Considering that our ground water is about 14degC year round, the temp difference of only 6degC would require a very substantial heat exchanger to recover any significant portion of tha already small fraction of energy left in the water reaching the waste pipe. Come to think of it, you could probably recover more energy with less effort by putting a heat exchanger on the ventilation fan in the bathroom so that the moisture laden air you pump out of the bathroom heats the incomming air that replaces it.

[Breaking Wind]

Well, I can certainly understand your position but I find it unlikely that the water that comes out of my shower head could drop 50-60 degrees before getting to the drain.  I did a little research and found that these GFX heat exchangers are becoming quite a mainstream technology these days so there must be some validity to their ability to exchange heat and save energy.  Below is quote from a company study from Emerging Technologies.  For more details visit http://www.eere.energy.gov/buildings/emergingtech/printable/page2d.html

"This experiment confirmed that the fraction of energy saved by the GFX does not depend on whether it is installed in a triplex as in this case or in a single family home. With high or low hot water consumption, the relative savings of the GFX were much the same. In terms of absolute energy (and cost) savings, it is important to recognize how the thermal energy contributed by the GFX would have been provided if the GFX had not been there. This requires that the field efficiency of the main water heater be measured and applied to a calculation of the GFX benefit. In this experiment, we determined that the GFX would save between 25 and 30% of the total energy needed for hot water production based on the measured efficiency of the resistance water heater in the triplex. Over the year of this experiment, the GFX saved the equivalent of 2800 kWh of electricity."

Where I live, this is equivalent to at least a couple of hundred dollars a year.

Regards,

Mike

[Norm]

   Considering that using anything more than

5 gallons of water...(of which only half of it is

hot water from the water heater)is a waste of water...1 gallon to wet down and all soaped and

washed ...and 4 gallons to rinse the soapy water

off ....standing under a nice warm shower after

that could easily be accomplished by recirculating a couple of gallons of water...

...you could even use the gray water to water your plants...vegetable garden etc....

    Not saying I do the 5 gallon bit all the time

...but it is a lot more do able than crawling

down in the crawl space with a heat exchange that

would cost me time and money on a project such

as this....

                  ( :>) Norm.

[ghurd]

There was a prototype posted here a year or 2 ago.

Connected to a electric water heater, the "main" heating element never turned on. Only the lower power element was needed to maintain the temperature in the tank.

(Wish someone would post the link to that old story)

I notice neither of the ones I saw (that one and this one) had any insulation on the drain or the preheater line.  Insulation would have to help.

After insulating the hot supply lines at my parents home, they reduced the thermostat by 10~15'F with no noticable change at the faucets.

G-

[steak2k1]

25 - 30% of the total hot water use in the household..??  Interesting.  but as previously noted, water temp at the drain is not the same as at the nozzle. Given a typical shower is only 7 -10 min on avg...just how much savings can there be at that one particular shower head.?  I guess the question is, is the cost outlay/hassle VS actual savings worth it.?

I think I would rather do the Cu coil over the nat. gas exhaust line.  Something I have been thinking about for a while...next weekekend methinks.! pics to come.

My feeling is that an exhaust line is typically exposed and easy to access, as opposed to a drain line inside a mechanical wall. A good sized coil around an exhaust line could have the potential to preheat all of the potential hot water use in the home...as long as the furnace/hot water tank is running & consuming Nat gas.

Just some thoughts and I'm glad I read this thread.  Another little project that will help.  Nat Gas here is booked at $14.40 gJ (CAD), Nov delivery so every little bit helps.

rgds,

stk

[ChrisR]

I saw this device a couple of days ago, and thought it was an awesome idea.  Then I started doing some calulations.

Average shower time: 6 minutes @ 2 showers per day

Flow rate of the shower head: 2.5 gallons per minute

Hot water temperature: 55 decrees celcius

Cold water temperature: 10 degrees celcius

For a 40 degree shower, we will use 1.22 gpm of hot water.  So, the total hot water usage per year is 5343 gallons.

Assume that the water loses 25% of its heat to the air and the bathtub, the drain water is 30 decrees celcius.

Also assume that the heat exchanger is 75% efficient, so that we transfer 75% of the heat from the drain water to the incoming water.  The temperature different between the two is 20 degrees, so we will increase the incoming water from 10 degrees to 25 degrees (10 + .75*20).  I might be wrong in how I am calculating this heat transfer.

Now, the energy required to heat 5343 gallons of hot water from 10 degrees to 55 degrees is 1054 kWh.  The energy required to heat this same water from 25 degrees to 55 degrees is 703 kWh.  So, over the course of a year, we will save about 350 kWh, or $35 on a grid connected system.

The model of heat exchanger I looked at was between $300 and $400 dollars.  At that price, and assuming my other assumptions are right, it will take about 10 years to recover this cost.

Now, on an RE system, a savings of 1 kWh per day might be very significant.  However, it seems unlikely that users of an RE system would be taking 2 6-minute showers per day, using electric heated hot water at 40 degrees.  So the savings might be far less than 1 kWh per day.

Am I thinking correctly here?  Am I missing something?

Chris

[Gagster]

I have had another idea about preheating water in a similar way. Make the same type heat exchanger, copper tubing around the pipe for the exhaust of my gas fired hot water heater...



This seems like it would actually be kind of a bad idea.  If your water heater is a high efficiency model, it is power vented because the exhaust is too cool to draft up a chiminey stack.  If it is not high efficeincy, you would have heat to harvest, but doing so would cool the exhaust to the point that it would not draft.  Water heater exhausts are typically not sealed systems, so you would likely fill your living space with CO in realatively short order.



As for this preheating making it hard to adjust your shower water temp, don't worry about it.  Your water heater pulls from the top and feeds to the bottom.  You should always be pulling water from the top at whatever temperature your thermostat is set to.  The only thing this changes is how hard your heater has to work to keep up with your useage.