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Heating water from room temp up to 60C using 9V battery

  1. Dec 17, 2015 #1
    On average it takes about 30 seconds for hot water to reach the shower, so for 30 secs water is being wasted. I know running water for 30 seconds doesn't seem that bad but there are a lot of water shortages and droughts going on all around the world. I know its possible to heat water with 9v battery. Question is How does it work ? What are the process involved ? I want to heat the water during those 30 second until the hot water kicks in.
     
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  3. Dec 17, 2015 #2

    SteamKing

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    You might heat enough water to 60° C with a 9V battery to give a gnat a shower, but otherwise, it would take a lot of 9V batteries to heat any significant quantities of water sufficient to give a person a shower.

    It takes time for the shower plumbing to purge itself of colder water, and if metal pipes are being used in the plumbing system, some time for the hotter water to heat the metal in the pipes.

    There are systems which supposedly save energy and water for showers (like the so-called tankless hot water heaters), and you can always plan your home such that the water heater is located close to the shower facilities, which reduces water wastage and the time it takes to get a hot shower.
     
  4. Dec 17, 2015 #3

    meBigGuy

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    It takes 1 calorie to heat 1cc of water by 1C. 1 calorie is .001163 watt hours. Assuming a 9V battery you can turn watt hours to amp hours. Choosing a volume of water and playing will all those you can determine how many amp hours in a 9V battery you would need for a 100% efficient system.
     
  5. Dec 17, 2015 #4

    anorlunda

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    A typical 9V battery can deliver 440 milliamp-hours. 9*0.44 = 3.96 watt hours = 14256 joules.

    The specific heat of water is 4181 J / kg °C. You want to raise the temperature from 20 to 60 C, a change of 40 C.

    So, one 9 volt battery can heat 14256/(4181*40)=0.08 kg of water. To do that in 30 seconds, the water flow rate should be 0.028 kg/sec, or 0.17 liters/minute.

    That is not very much. You will need many 9V batteries to match the flow rate of a kitchen faucet or a shower. If the flow rate is 5 liters/minute, you would need thirty 9 volt batteries. But at the end of 30 seconds, the batteries will be dead, so you'll need a new set of 30 9V batteries the next time you turn on the faucet.

    Note: 440 mah is optimistic because it does not de-rate the battery based on discharge rate. In real life, you might need 2 or 3 times as many 9V batteries as this calculation suggests. The real message is that you over-estimated the energy available from a 9V battery.
     
  6. Dec 17, 2015 #5
    Thanks for the speedy answer. would a 9v pp9 do the trick.
    What if i use a lithium ion battery about 1800 mah will that do ?
     
  7. Dec 17, 2015 #6

    SteamKing

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    I think you're missing the point.

    Normal household voltage is considerably more than 9V, which voltage is what runs most appliances like electric water heaters and such.

    This is a small electric tankless water heater which fits under a sink:

    http://www.globalindustrial.com/p/h...mpaignId=T9F&gclid=CPqUrLXa48kCFdgYgQod6aEO5g

    Note, it requires 277 V and 11 A of current to work. This is about 3 kW of power consumed when heating the water.

    It would take a lot of 9V batteries of any kind to produce that sort of power.

    And no, lithium ion batteries would not be an alternative. These batteries are designed to discharge slowly over time, because the devices they typically power, like laptop computers, consume only a couple hundred watts at most, not 3000 watts like the water heater. Laptops use a mix of 12V and 5V to operate, and newer ones typically use lower voltages for things like the CPU.
     
  8. Dec 17, 2015 #7

    CWatters

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    The normal solution is to install secondary loop. At least that's what it's called I the UK. They are common in hotels but I have one in my house. I have a boiler/furnace that heats a thermal store. The thermal store is basically a tank of water. The thermal store delivers hot water to the taps/faucets. The secondary loop comprises a small bore pipe and a pump that circulates water from the taps back to the store keeping the water in the pipe hot. So you get hot water the moment you turn on the taps. The pipes are insulated to minimise heat loss and the pump is on a timer so its off at night.
     
  9. Dec 17, 2015 #8

    meBigGuy

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    You are going to have to learn how to do the math. Check this math for me. 1800mah 3.6V lithium battery is 0.5 watt-hours = 429 calories meaning you can heat 429 cc (less than 2 cups) of water by 1 degree Celsius assuming 100% efficiency and no heat loss during heating. Study that and figure out exactly how I got those numbers.

    So make some assumptions about amount of water,and temperature rise needed. Then determine how many calories (watt-hours) that would require, and then, based on battery voltage (3.6v, 9V or 12V) how many thousands of ampere hours you will require at each voltage.

    Please don't ask us to do your basic math. Study what is here and use it creatively. You will achieve a much better understanding of what is really going on.
     
    Last edited: Dec 17, 2015
  10. Dec 18, 2015 #9

    CWatters

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    The problem is that water has a high specific heat capacity. Its why any instant water heater like an electric shower needs so much power.
     
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