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I made the calculation for 250 showers of 3 minutes a day (1642500 l - 51566,33 kWh).

Although a sun collector will have almost no contribution in winter (nov, dec, jan, feb) I believe even a small installation can be a good support.
An underdimensioned system will have the benefit of a higher delta T which means more solar energy can be harvested.

As such a sun collector can mean a reduction of the labour needed to heat the water:
5 m2 - 4%
10 m2 - 8%
25 m2 - 20%

The difficulty would be:
- water must go to top of building to get heated
- insulation of downward hot water/losses

Part of the solutions could be:
- only use the sun heated water on the highest shower floor
- the potential energy of the waste water from the showers (0 - 60 l/minute per shower floor) can be recuperated with a micro water turbine. The rain water from the roof can be connected with this system to harvest more energy.


Even the water from the sinks in the student rooms could be connected to the micro water turbine(s)

Human Power Plant

Great idea, Jens !


Hot shower - use the sun to heat coils of pipe.


In the general thread i read that small solar panels will be mounted on the exterior of the rooms on the south side of the building.

Maybe there is a possibility of mounting the sun collectors on the exterior of the shower floor?
This would eliminate the need to pump the water to the top floor and the hot water would be used where it is heated.

Why didn't I think about this option from the start! :p


yeah heat is a often forgotten energy elephant! great idea this blog! in winter my thermal solar works fine. you can even mount it on the window sill or facade, because sun is so low in winter. made a kwh to heat calculator also many more energy related calculators for educational purposes... http://www.pv4.eu/kwh-to-heat/ ...currently i am searching for a practical albedo formula how much cooling energy could be saved with white roofs ...


The showers can be made more efficient by requiring a button push for every ten seconds of water, and having pre-set water temps (cold, barely-warm, very warm).


When I was a kid, like 50 years ago, my YMCA had turn-dial water timers on the showers that only allowed 3 or 5 minutes before the water turned off. Of course you could turn it back on, but ... why can't I find these things on the internet? The best would be a push button (as are on some sinks) that only give 10 seconds of shower water at a time. There's no reason to run the water for the entire time that you're soaping up. This could be something mechanical that does not need any electricity to operate. I'm reading various websites and they all seem to think that it's reasonable to spend 5 to 8 minutes standing under hot running water. If you need hot water to relax, a communal spa-bath (after a quick shower rinse-off) would probably be much more efficient.


Maybe a shower head with pullchain?



One addition to the idea of harvesting the potential energy of the waste water and rain water:
the rain water and waste water can not be mixed to generate the energy. The rain water can be used as shower water, which will lower the energy needed to pump water to higher shower levels but will also lower the flow of water to generate energy from.
The surplus of rain water that can't be stored to use as shower water may have a flow rate that is too low for sustainable use of a micro water turbine.

Human Power Plant

Thanks for all the ideas. We start improving the design once we have documented all floors.


Why not adapt to a different method of showering? The Japanese use just enough water to get wet, then lather up without running water. Finally, they rinse off, and then there's a communal bath to soak in. This method can save a lot of water and thus a lot of heat.


I read "the temperature is lowered to 37°C." Is that also the temperature of the water in the boiler? Any fear of legionalla? It is an optimal temperature for the bacteria to multiply... Normally they advise to heat it at least once a week to 60°C. At our home I only heat the boiler to 48°C and hadn't had any problem with legionella... so far.

Do you use rain water for washing clothes ánd for personal hygiene? Do you take measures to eliminate bacteria? Do you have enough rainwater? How do you get water for cooking and drinking?

Lots of questions, but it is an interesting experiment you are doing. Good luck!!

Nikolay Ivankov

Perhaps one could save water and yet give students a decent opportunity to clean themselves by offering hot wet towels. A pair of such towels may be enough to clean whole body, while the amount of water needed them is substantially smaller, hence allowing higher temperatures, thus avoiding the risk of contamination.

Jan Fabry

A radically different option might be the way of David Whitlock, who hasn't showered in many years, and uses bacterial spray to prevent smells. There are quite a few stories about him and his company (AOBiome), some more sensational than the other, but this one seems decent: https://motherboard.vice.com/en_us/article/pga7xk/the-chemist-who-hasnt-showered-in-12-years-explain-why-he-doesnt-stink

Nikolay Ivankov

@Jan Fabry

The people in many traditional societies live without ever washing, just sometimes smearing themselves with fat or similar procedures. By the times my parents were kids, human smell was not considered as offensive. By the time my grandparents were kids, not having any skin and gut parasites was still considered unusual. So a real paradigm change will be to simply go back to the roots and admit dirt and smell and parasites as normal. Oh, and those who don't want to wash their hair may just shave their heads entirely - this is what many ancient civilizations, including ancient Egyptians, actually did.

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