water heating

[Jambo]

 

This is exactly what I'm going to do. How long does it take to heat up the water to lets say 50'C? (more or less) with 500W immersion?

 

Difficult to say in terms of practical experience as I don't have a way of measuring the water temp and tend to just leave it on whenever I'm on board and it's sunny enough (although I'm now considering getting an SMS activated socket to allow me to switch it on and off remotely).

 

But if you want to know how the theoretical calculations they work like this:

 

Energy required = (Specific heat capacity of water x mass of water x change in temperature) - standing losses

 

The specific heat capacity of water = 4184J/kg°C i.e. it takes 4184 Joules of energy to heat 1 kg of water 1 degree C.

 

1kg of water is very close to 1 litre of water.

 

To convert from Joules to kWh you need to divide by 3,600,000.

 

So taking Alan's example we have:

 

4184J/kg°C x 55kg x 43°C = 9,895,160J = 2.75kWh. Divide that by the power of the immersion heater (0.5kW) and you get 5.5h (neglecting losses).

 

The losses are unknown and are significant but are also relatively small in comparison to the energy required to heat the water. I think I'll add a load of extra insulation to our calorifier when we move it from the engine room to the bathroom when we fit a back boiler to our stove - at least any standing losses will be put to better use there rather than heating the engine room!

 

ETA: I should note that the calculation should also take into account the efficiency of the heat source but in the case of an immersion heater the efficiency is 100% so can be neglected. If you were doing the same calculation for the OP's Webasto then you would need to divide the result by the efficiency of the Webasto to get the actual energy consumed.

Edited June 16, 2014 by Jambo

[Staarek]

 

Difficult to say in terms of practical experience as I don't have a way of measuring the water temp and tend to just leave it on whenever I'm on board and it's sunny enough (although I'm now considering getting an SMS activated socket to allow me to switch it on and off remotely).

 

But if you want to know how the theoretical calculations they work like this:

 

Energy required = (Specific heat capacity of water x mass of water x change in temperature) - standing losses

 

The specific heat capacity of water = 4184J/kg°C i.e. it takes 4184 Joules of energy to heat 1 kg of water 1 degree C.

 

1kg of water is very close to 1 litre of water.

 

To convert from Joules to kWh you need to divide by 3,600,000.

 

So taking Alan's example we have:

 

4184J/kg°C x 55kg x 43°C = 9,895,160J = 2.75kWh. Divide that by the power of the immersion heater (0.5kW) and you get 5.5h (neglecting losses).

 

The losses are unknown and are significant but are also relatively small in comparison to the energy required to heat the water. I think I'll add a load of extra insulation to our calorifier when we move it from the engine room to the bathroom when we fit a back boiler to our stove - at least any standing losses will be put to better use there rather than heating the engine room!

 

ETA: I should note that the calculation should also take into account the efficiency of the heat source but in the case of an immersion heater the efficiency is 100% so can be neglected. If you were doing the same calculation for the OP's Webasto then you would need to divide the result by the efficiency of the Webasto to get the actual energy consumed.

 

Thanks for that Jumbo. Loads of interesting info!

 

I found that earlier just to have an idea of time needed etc.

 

http://elementsofheating.wordpress.com/2012/09/26/how-to-calculate-the-kw-required-to-heat-a-volume-of-water-in-a-particular-time/

 

 

I bought SIM socket as well but first I would like to play with the setup over the weekend to see exactly if the solar will be able to cope. (it should as I've seen readings of 70 amps and more before)

[Grace and Favour]

 

How do you calculate this? Is there a formula? Thanks

Rounding up the formula, a 1Kw heater will heat 1litre of water by 1C in four seconds

Thus, as others have said, a 500w heater would take eight seconds to lift the temperature by 1C.

 

Either way, the same amount of energy is required, of course. Though the slower the heating, the greater the risk of losing your stored heat through imperfect heat insulation losses round one's calorifier

[Bodkin]

The valve was just in the pipe running to the radiators. Turning off your radiators would be just as good -- that's all we do with our Eberspacher.

Great thanks, we've had a poke around and think we have located said valve - there are 2 that we have turned off (there were 4 in total) and have then tried running the Webasto - the radiators didn't come on and the water appeared to be getting warmer although it's hard to tell for certain as it's still warm from a trip out yesterday (but the OH had a shower and wasn't complaining it was cold for once!).

 

The true test will be tomorrow when we've let the water cool completely and then fire up the Webasto - fingers crossed it works - if it does, it'll be a revelation for us! Only been boating 4 years you always learn something new