I have just replaced my hot water tank with a 210 litre one that is heated by indirect wood burner and a direct pumped oil fired condensing boiler. (ie it has two coils) My calculations show that its cheaper to heat the hot water overnight with off peak electricity (2p a unit!) and the tank has space for an emersion heater in it and I'm on the off peak tariff. So I am trying to work out how long the emersion needs to be on or what size emersion heater to heat 210 litres of water to 60degrees. Where are the calculations?
emersion heater sizing
- Thread starter Robalan
- Start date
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All immersion heaters are 3 kW rating. The length will depend on the arrangement of your cylinder and immersion heater boss. Just time it to stay on for whole off-peak period - it will switch off when water gets to temp (60C).
I was trying to avoid the maths...but since you insist .....
To raise 1 litre (= 1 Kilogram) of water by 1 degree Celsius requires 4.18 kilojoules.
The joule is a measurement of the quantity (amount) of energy (heat).
The Watt is a measurement of the flow of energy (heat).
1 joule/sec = 1 Watt. 1 joule/min = 60 Watts. 1 joule/hour = 3,600 Watts.
The kWh (kiloWatt hour), also a measurement of the quantity of energy (heat), is 1,000 Watts flowing for 1 hour or 1,000 joules/sec x 60 x 60 = 3,600,000 joules. 1 kWh = 3,600 kilojoules = 3.6 Megajoules.
Examples.
To raise say 100 litres through 50 degrees Celsius requires (50 x 100) 5,000 x 4.18 kilojoules = 20,900 kJ = 20.9 MJ = 5.8 kWh. Approx. 2 hrs of a standard 3 kW immersion heater.
to raise 210 litres through 50C requires 43,890 kJ = 43.9 MJ = 12.2 kWh Approx 4 hrs of 3 kW immersion heater.
To raise 1 litre (= 1 Kilogram) of water by 1 degree Celsius requires 4.18 kilojoules.
The joule is a measurement of the quantity (amount) of energy (heat).
The Watt is a measurement of the flow of energy (heat).
1 joule/sec = 1 Watt. 1 joule/min = 60 Watts. 1 joule/hour = 3,600 Watts.
The kWh (kiloWatt hour), also a measurement of the quantity of energy (heat), is 1,000 Watts flowing for 1 hour or 1,000 joules/sec x 60 x 60 = 3,600,000 joules. 1 kWh = 3,600 kilojoules = 3.6 Megajoules.
Examples.
To raise say 100 litres through 50 degrees Celsius requires (50 x 100) 5,000 x 4.18 kilojoules = 20,900 kJ = 20.9 MJ = 5.8 kWh. Approx. 2 hrs of a standard 3 kW immersion heater.
to raise 210 litres through 50C requires 43,890 kJ = 43.9 MJ = 12.2 kWh Approx 4 hrs of 3 kW immersion heater.
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