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Preheating water

Post in 'DIY and General non-hearth advice' started by JRP3, Feb 23, 2008.

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  1. JRP3

    JRP3 Member

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    I've been thinking about running a pipe from the basement up to the peak of my A frame to preheat water before it enters the water heater. Instead of having to heat up 40-45 degree well water it would be 70-80 degree water since the loft is usually 75-85 degrees. I figure a 1 inch pipe up, along the peak, and back down should hold around 5 gallons or so. Maybe go up to a 2 inch pipe along the peak to hold more water. What do you think?

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  2. Mr.M2

    Mr.M2 Member

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    Is the well pump powerful enough to pump water as high as you want?
    Also, a large demand of hot water would flow too quickly to gain any heat.

    Good luck, I'm always in favor of making something work better.
  3. JRP3

    JRP3 Member

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    I think it is but I can test it with a garden hose. I would like to calculate how much extra electricity it would take to pump the water up. I'd imagine not that much though I am a little concerned with pressure loss due to friction as it would probably end up being close to a 60ft loop.
    As for flowing too quickly to gain heat, the idea is that it would sit in the pipe overnight and hold enough for a shower in the morning, then do the same during the day.
  4. Mr.M2

    Mr.M2 Member

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    If possible, you could always place a small storage tank up there too.

    You can make use of check-valves, a back flow preventer, and the storage tank to eliminate
    the back pressure of water working against your well pump.

    I have fun trying to invent better ways of doing things too.
  5. JustWood

    JustWood Minister of Fire

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    The actual cost of electric has more than doubled here in the last 2 years(electric hot water heater). I thought about rigging a storage tank from the ceiling directly above plenum of my wood furnace to preheat water .It's 90 - 110 on the surface of the plenum. I think your idea would work might want to insulate line coming down to your hot water tank.
  6. Gooserider

    Gooserider Mod Emeritus

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    As long as you don't have gas bubbles in the line, head loss isn't a big deal - what you lose on the way up you get back on the way down, so the only number that really matters is the net difference between the inlet and outlet points - i.e. what is the net difference between the pump and the faucets. Water friction in the pipe is a concern, but not a very big one as long as your pipes are properly sized to begin with.

    However I would expect that unless you did something pretty significant to increase the heat exchange area that you would not get enough of a pre-heat effect to do you much good. (However what might be worth considering is a drain-back solar panel system hooked up to pre-heat your DHW tank, and a thermostatic mixing valve to keep the water temps steady.)

    Gooserider
  7. Sandor

    Sandor Minister of Fire

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    Per size, inches Volume in gallons per foot of pipe
    1 0.04
    1 ¼ 0.07
    1 ½ 0.10
    2 0.17
    2 ½ 0.24
    3 0.38
    4 0.65


    Can't format this properly, but the above table shows volume in gallons per foot of pipe size.

    50 feet of 1 inch pipe holds 2 gallons of water! Was going to do what you want to do, and after I figured this out, came to the conclusion that it wasn't worth it.
  8. JRP3

    JRP3 Member

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    Do you think I could get away with smaller than 1 inch on the way up to reduce load on the pump? At what point does it get too small and create friction?
    I was thinking of doing some sort of manifold along the peak. Looking at the chart I could do 2 10 foot sections of 3inch pipe which would give me 7.6 gallons, plus whatever is in the feed and drain pipes. 12 hours overnight should heat that up, don't you think?
    I live in the woods and don't get much solar, not to mention the nights can be freezing from Sept. to May around here.
  9. Gooserider

    Gooserider Mod Emeritus

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    Not sure, there are charts on pipe friction vs/ flow rates in the plumbing books, however pipe diameter as I understand it isn't a head load factor - pipe friction is. As a general rule the longer the distance or the higher the flow rate, the larger the pipe diameter should be (though not sure how much) in order to keep the pipe friction to a reasonable value. Excess friction increases the load on the pump, and can also lead to erosion of the pipes if the flow rate past a given point is to high.
    It might heat up some, but not sure how much, or how much good it would do you. The water in that pipe section would not be the water that you showered with, only the make-up water that would go into your water heater tank as you shower. The largest part of a typical tank heater's energy consumption isn't in heating the incoming water initially, but rather in keeping it at temp while you aren't using it. Also the heat energy to bring water up from 40-80* is pretty negligible, so I don't think that even at the best theoretical transfer rate you'd gain all that much. What I've heard of that MIGHT work is a "Grey Water Heat Recovery" system - this is a heat exchanger that connects between your higher temperature grey water drains (shower, sink, dishwasher, etc) on one side and the DHW input line on the other, so that your hot water going down the drain would pre-heat the input water. I don't know how well these work in practice, or how easy it would be to retrofit them to an existing structure who's plumbing wasn't layed out with doing this in mind.

    Lack of sun is a problem with solar - freezing weather isn't, or so the solar advocates claim... There seems to be two methods of doing freeze-proof solar, each has it's advantages and disadvantages. I prefer a "drain-back" system, where the panels are designed to self drain into a resevoir in the heated space when there isn't enough heating and the pump shuts off - you then don't care how cold the panel gets, and don't have to worry about glycol and it's hassles. The other approach is to fill the solar system with a glycol mix (there is a special blend for solar apps) so that you don't have to worry about freezing, but do have to do more with heat exchangers. Either way, the panels are equipped with sensors to only circulate if the net result is heating gain. (IMHO the best route would be to have a solar panel that powered the pump, so you have a natural throttling effect, and truly "free" heating) however neither approach would do you much good if you don't have any sunshine to begin with.

    Gooserider
  10. JRP3

    JRP3 Member

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    Well my water heater is set at around 120, so raising it 40 degrees from 40-80 is about half of the heating that I need overall. The heater is setup on a night rate timer, so adding 40 degree warmer water to it while using it should help keep it warmer longer. However you maybe correct that it wouldn't be enough to make all this worthwhile.
    I've been considering this as well.
  11. JRP3

    JRP3 Member

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    I think I'll stick a small jug of water up there overnight and measure the temp in the morning just to see what happens.
  12. drizler

    drizler Minister of Fire

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    My neighbor has just that suspended above his barrel stove in the basement. Its a 30 gallon old scrap water tank painted black and it feeds his super cell that common feeds to the oil boiler. He says its usually around 130* or so during the winter. Neat rig. Dirt cheap to boot.
  13. sleepie

    sleepie New Member

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    think about the pipe sweating in the summer--you would not want your ceilings wet---just a thought
    but you should check into this---pat
  14. drizler

    drizler Minister of Fire

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    That is the simple beauty of an unfinished basement. No ceiling and concrete, let her drip no problem. His are like mine right out in the open where you can see and get at them. Function over beauty.
  15. JRP3

    JRP3 Member

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    Results so far: One gallon of water in a plastic jug, 44 degrees start, 56 degrees after 1.5 hrs, 78 degrees when I just got home, about 7 hours later. The water was sitting on a shelf about 6 feet below the peak, so it may have gotten even hotter up there. The gallon jug doesn't have much in the way of exposed surface area for heat exchange so I'd think it would heat up even faster stretched out in pipes.
  16. JRP3

    JRP3 Member

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    Yeah I've been thinking of some ways to deal with that if it becomes a problem. This morning the water was still at 76 though the upstairs had cooled down to 70.
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