h a l f b a k e r yMay contain nuts.
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A conventional household hot-water supply relies on water being heated up in a boiler and then piped to where it will be used - e.g. your shower. This is, of course, inefficient. Instead I propose a cold-water shower, fitted with a device to monitor and track every droplet of water leaving the shower
head, and to heat each drop with a highly-targeted microwave beam to the precise temperature you desire (taking into account the predicted amount of cooling of the water between the heating zone and it hitting you). This device will also monitor your position under the shower and save energy by not heating any droplets that are not going to hit you. The luxury model will also heat droplets to different temperatures, based on your preferences - e.g. slightly cooler water for your head and warmer for your shoulders.
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Can a moving drop of water be heated that quickly? We're talking about maybe a fraction of a second of airborne travel time. |
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Interesting question. The 'airborne time' doesn't matter; what's important is the continuous power output, which will either deliver high power over a short period to a droplet or lower power over a longer period, equating to the same total energy. Let's suppose that 250g of water drops from the shower every second, and needs its temperature raising by 20°C. The specific heat capacity of water is approximately 4.2 J/g°C so we need a system that's going to put out 4.2 x 250 x 20, or 21,000 Joules per second, or 21kW (lower if not all the drops are predicted to fall on you). That's higher than I thought (suggesting I've made a mistake with the maths) but just within the range of what's possible with a domestic electrical supply. |
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Is there an advantage to this model over existing in-faucet heaters? |
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[21 Quest] You've been here nearly 20 years and *now* you want Halfbakery idea to have some advantage over existing technology?! :-)
I guess by only heating up the water that's going to hit you it should* save energy.
[* no guarantee of energy-saving is implied or intended by this statement] |
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If you heated a droplet for an infinite amount of time it would flash to steam so of course it wouldn't hit you even if you waited until the infinite amount of time had finished. |
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Perhaps you need to halve the microwave intensity or frequency every so often. |
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What happens at the heat death of the universe? |
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I suppose there's only one way to find out. |
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There aren't all that many drops that can be predicted not to hit you. Most people stand fairly close to the shower and people move around a lot, meaning a wide range of predicted movement would need to be incorporated. Power loss due to range would exceed efficiencies even assuming free computing power. [+] |
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If the drops that miss me aren't heated, won't my feet get cold in the cold water puddling around them? I guess the obvious solution to that is to have the entire shower floor be a grating (possibly heated for comfort). |
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Would it be simpler to save energy (and water) by just designing a shower head that carefully aims each drop so it doesn't miss? [+] anyway. |
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[21 Quest], I'll take it one step further. I will carry your outlook to other ideas for the foreseeable future. |
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