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Showers are a relatively simple concept, essentially a flow of pleasantly warm water to wash in. The preferable water temperature varies from person to person, but tends to hover around body temperature, 37°C. Commonly this is made of a mix of hot (~60°C) and cold water, which in my house, changes from
about 7-13°C winter/summer. That means that the shower water is a mix of hot and cold, in summer between 50-55% cold water and winter 40-45% cold to make ~37°C water.
We could substantially reduce the hot water, and therefore cost, if we were to warm up the cold water specifically. Especially since this water is way below room temperature. What difference would room-temp cold feed have? Well, room temperature between 20-25°C winter/summer would mean about 50-65% cold contribution, around 10% of the mix or 20% in terms of the hot water savings. How do we heat up this cold feed? Well, just use the ambient room temperature.
To do this, we have a box, this box is full of a wax that melts at ~19-25°C. The cold feed pipes split into 2-6 copper lines that run through the wax. Cold water runs in, wax solidifies, supplies phase-change heat energy to warm the water. After the shower, the wax slowly re-melts in the ambient temperature. In the winter, this energy would come from the heating (gas in my case, vs electric water) and in summer, this energy would essentially be free/reduce the AC load.
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//phase-change heat energy// [+] |
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If you had a higher temp wax, say 30°C, and kept it melted with a small Peltier heat pump. Winter hot water flow would go from 1.5GPH to 0.9GPH. That's substantial, and if the device were under the bath for example, the Peltier would be harvesting heat from the warm water waste. Plus it would avoid any condensation issues you may have to think about with the passive system. |
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I like it. This kind of "passive" optimization of our HVAC, water service etc with various forms of thermal transfer is a great thing to explore. A bit of thought into ideas like this and you've got a system that pays for itself in reasonably short order. [+] |
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//various forms of thermal transfer is a great thing to explore.// |
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Actually, put one on the front end of the hot water heater while we're at it. 20°C vs 13°C (summer) intake for the water heater is 40 vs 47°C delta. Assuming a California (ha!) kWhr price of $0.3, that's $0.71 per typical 80 gallon water heater volume. Which is a ball-park per day use/house. $26/year. not too shabby for a passive system. Place it outside in warm parts of the world and it gets a lot better. |
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Actually, Hawaii is the obvious candidate, $0.35 electricity, 25°C average temp. ~$90/year. Although the water is probably not as cold to be fair. |
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A friend of mine built a heat exchanger for the cold water feed & the shower drain. No fancy wax etc, just some pipes (not sure what his precise design is; probably just a concentric pipe counter-flow). |
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I'd thought of that, didn't think it was original enough for a HB idea, and it would lead to constant re-adjustment of the temp I think. I think the wax is a cheap and good way of harnessing energy all day. |
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//A friend of mine built a heat exchanger// |
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I forgot! I built one for my dryer. I found it particularly galling that running the dryer in summer meant that I was paying money to heat and eject roughly half a ton of air per hour. Air that I'd paid to cool/dehumidify in the first place via the AC. Then of course, that ejected air is replaced by warm/humid air from outside, that I then paid to re-cool/dehumidify. |
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The design was simple, one of those big plastic storage boxes, baffles made of that disposable corrugated plastic stuff that politicians like to advertise with, and then I needed some thin wall aluminum tubing. In a triumph of redneck engineering, I found I could cut the top and bottom off Coors Light cans with a standard can opener. Silicone sealant glued everything together and I had a cross-flow air-air heat exchanger, cut electricity use by the dryer by 20-40% and noticeably sped up the initial warm up time. I have a gas dryer now, or I'd have made a Mk2, there was room for improvement regarding management of the condensate/lint. |
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