stupid plumbing question
09 June 2004, 12:53 PM
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stupid plumbing question
300 litre hot water tank has an 11" 3kw immersion heater in it.
Stat is set to 65c, but water is only getting to 40c
Is the immersion heater rating too small for the job ?
Stat is set to 65c, but water is only getting to 40c
Is the immersion heater rating too small for the job ?
09 June 2004, 01:05 PM
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Originally Posted by russell hayward
300 litre hot water tank has an 11" 3kw immersion heater in it.
Stat is set to 65c, but water is only getting to 40c
Is the immersion heater rating too small for the job ?
Stat is set to 65c, but water is only getting to 40c
Is the immersion heater rating too small for the job ?
too small?? 11 inches!! the immersion element should go down to at least 2/3rds of the tank 
09 June 2004, 01:25 PM
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Originally Posted by russell hayward
it goes in the bottom, and its brand new
no seriously it may just scaled up as posted above, try taking it out and inspecting for scale or heavy pitting
09 June 2004, 01:37 PM
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Originally Posted by andypugh2000
Sounds painfull
no seriously it may just scaled up as posted above, try taking it out and inspecting for scale or heavy pitting
no seriously it may just scaled up as posted above, try taking it out and inspecting for scale or heavy pitting
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09 June 2004, 01:42 PM
#9
Well, if my old "O" level Physics suffices, the specific heat capacity of water is 4200J/kg, and you have 300kg of water, so you need 1,260,000 Joules of energy to heat that amount of water by 1 degee Celsius.
Now assuming the water comes in at 20 degrees, and you want it to be at 65 degrees, that's a 45 degree rise, making your power input requirement now 56,700,000 Joules
Since a Watt is a rate of working of 1 Joule per second, and knowing the power output of your immersion, should allow you to work out how long to heat up that much water.
Remember, however, that those figures are based on no heat losses, so figure in about 75% efficient to allow for losses, and you should be able to see a time.
If it's a very long time, perhaps your tank is losing the heat faster than the heater can supply it?
Alcazar
Now assuming the water comes in at 20 degrees, and you want it to be at 65 degrees, that's a 45 degree rise, making your power input requirement now 56,700,000 Joules
Since a Watt is a rate of working of 1 Joule per second, and knowing the power output of your immersion, should allow you to work out how long to heat up that much water.
Remember, however, that those figures are based on no heat losses, so figure in about 75% efficient to allow for losses, and you should be able to see a time.
If it's a very long time, perhaps your tank is losing the heat faster than the heater can supply it?
Alcazar
09 June 2004, 01:59 PM
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Well, if my old "O" level Physics suffices, the specific heat capacity of water is 4200J/kg, and you have 300kg of water, so you need 1,260,000 Joules of energy to heat that amount of water by 1 degee Celsius.
Now assuming the water comes in at 20 degrees, and you want it to be at 65 degrees, that's a 45 degree rise, making your power input requirement now 56,700,000 Joules
Since a Watt is a rate of working of 1 Joule per second, and knowing the power output of your immersion, should allow you to work out how long to heat up that much water.
Remember, however, that those figures are based on no heat losses, so figure in about 75% efficient to allow for losses, and you should be able to see a time.
If it's a very long time, perhaps your tank is losing the heat faster than the heater can supply it?
Now assuming the water comes in at 20 degrees, and you want it to be at 65 degrees, that's a 45 degree rise, making your power input requirement now 56,700,000 Joules
Since a Watt is a rate of working of 1 Joule per second, and knowing the power output of your immersion, should allow you to work out how long to heat up that much water.
Remember, however, that those figures are based on no heat losses, so figure in about 75% efficient to allow for losses, and you should be able to see a time.
If it's a very long time, perhaps your tank is losing the heat faster than the heater can supply it?
dave
09 June 2004, 02:03 PM
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OK, so a 3Kw heater produces 3000 J per second.
56,700,000 J to get up to temp
so that's 18900 seconds or 315 minutes or 5.25 hours at 100% efficiency. So it looks like it going to take about 6 or 7 hours to get up to temperature, but may never make it if the lagging is a bit on the thin side
56,700,000 J to get up to temp
so that's 18900 seconds or 315 minutes or 5.25 hours at 100% efficiency. So it looks like it going to take about 6 or 7 hours to get up to temperature, but may never make it if the lagging is a bit on the thin side
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