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merlyn (47)

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Journal of merlyn (47)

Wednesday November 16, 2005
05:03 AM

When less is more

[ #27590 ]
For the past eight days, I've had the pleasure of kicking back in a rented apartment one block from Copacabana Beach in Rio De Janeiro, Brazil, mostly because my last assignment was two weeks ago in Sao Paulo, and my next assignment is tonight in downtown Rio.

The apartment has a tiny "just-in-time" hot water heater that seems prevalent in Brazil: a gas water heater with no apparent storage tank, and a flame that comes on (loudly!) whenever any hot water is drawn. This is in sharp contrast with the 30-ish gallon water storage tanks we have in the US, which keep a supply of hot water warm enough for a long shower or a load of clothes or dishes, but not continuously (it must have time to recycle). The difference between inline heat and stored heat led me to an interesting series of observations.

When I ran the hot water for the sink to wash my hands, the water was too hot, requiring me to add cold water to bring it to a safe temperature. But when I took a shower, it was never that hot! I couldn't get it as hot as the sink, which baffled me.

On a whim, I reduced the water flow in the shower, and waited 15 seconds, wondering if I was exceeding the capacity of the inline water heater. Sure enough, the water was too hot to touch. After a few more "change volume, wait 20 seconds, test temperature" cycles, I found that my preferred water temperature resulted from having only the hot water tap open, and about 70% of the way.

However, this now leads to counter-intuitive behavior during the shower. If the water is too cold, I reduce the hot water volume. If the water is too hot, I increase the hot water volume, and then stand aside for a moment until it cools.

I suspect I will be burned a few times when I return to my home this weekend, trying to unlearn my new habits.

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  • FWIW, it's probably not a Brazilian vs USian thing, it's a small vs large thing. Your hot water tank is in a house, which has enough space for such a beastie to be big enough to be efficient. Shrink the hot water tank so that it doesn't take up too much space in an apartment and it will become less efficient because the ratio of surface area to volume will be much bigger. I would expect that small apartments in the US would use on-demand heat for the same reason. That's certainly the case here in the UK
    • unfortunately, is probably not feasible in 120V-land, because it would require *very* high current.

      that's why in the US we normally have a 2-phase main domestic service feed to the household circuit breaker panel. In addition to running mulitiple 110v single-phase circuits off each phase, we run a few discrete 2-phase, 220-V circuits with monster plugs for electric ranges (stoves) and electric clothes driers (and ham radio kW amplifiers).

      We have instant-hot water devices available here that either are pa

      # I had a sig when sigs were cool
      use Sig;
  • The other main benefit of them is that heating the water on demand is a much more efficient system. At least in the context of domestic water usage.
  • In Germany, two systems are common: continuous-flow heaters, where the water runs through a very pipe helix heated by electricity, or district heating, where hot water is delivered from afar.

    In both cases, you get hot water as soon as you run it, and for as long as you run it. And no funky “less is more” business – if you run it faster, it’s hotter.