In a previous life, I was an engineer at Boeing. One of the projects I worked on in connection with the ultra long range version of the 777 was giving bored passengers something to do on 20+ hour flights. We looked at many things -- for example, bunks or casinos in the lower lobe... But, one thing that kept coming up from the passengers is that they would really like to be able to take a shower during the flight. As you can imagine, this turns out to be a tough thing to offer. If you have 50 passengers who want to take a 10 minute shower each, that's a thousand gallons of water to carry and heat. Flying around 8000+ lbs of extra water is not something you really want to do -- especially if you can just barely carry enough fuel to get to your destination.
I came up with the thought (I'm sure I'm not the first) of a shower that recirculates water. That is, a passenger would get a fresh charge of heated water at the start of the shower -- maybe a couple gallons. This water would just be recirculated again and again with some heat added as needed to keep the temperature up. This makes the whole idea a lot more practical -- it reduces the water needed by a factor of 10 or so, and also greatly reduces the heating requirement. There is a certain "yuk" factor to re-circulated water, but the water can be filtered during recirculation. Its better than taking a tub bath where you are sitting in "recirculated" water the whole time without any filtering. Anyway, while this never "got off the ground", it was considered practical by many (well, at least by some), and there was some real interest in it.
So, why not use the same sort of scheme for household showers? The saving in both energy and water would be very large, and it could be a very quality shower with features that are not practical in conventional showers:
For a "normal" 10 minute, 20 gallon shower, it takes about 10,000 BTU (3KWH) to heat the water.
For a reticulating shower with a 2 gallon initial charge, the initial energy would be about 1/10th.
There would be some additional energy for keep the water hot, but even this reheat energy can reduced with good shower design...
You might save about 2.5 KWH per shower with good design? This is about an 85% saving -- as good as many solar water heating systems achieve.
If a "normal" shower is 10 minutes with a 2 gpm showerhead, then the saving for a recirculating shower with an initial charge of 2 gallons is 18 gallons. For longer shower and higher flow shower heads the savings go up.
With the recirculation of water, you can stay in the shower all day, and not really use much energy. There is a little bit of reheat energy and a bit of pumping energy, but nothing like the energy needed to heat new water the whole time. There is no penalty at all in water usage for staying in a long time.
You can also have a shower with high flow shower heads -- several of them if you like. This increases pumping energy a little bit, but not much.
You could have truly outstanding showers with no guilt.
So, is this worth building a prototype??? -- Gary...
|It turns out Kenneth has already built a somewhat
similar shower with recirculation of water.
Kenneth's goal was to achieve lots of flow (6 shower heads!) and long showers without incurring a huge energy cost.
Gary March 26, 2010