Electric Immersion usage query

[alert]

Hi guys,

At present I have the immersion element in my insulated 300 litre hot water cylinder coming on for 6 hours a night, (using the night rate), in addition to this I have moderate temperature water from the geo-thermal heat-pump heating one of the coils all day, (geo-thermal on all day, set to heat return temperature of house floors to 32 degrees).

Now my question is this: Would it be more efficient to have the immersion element on 24 hours a day depending on said element's thermostat to direct the electric element to heat up when hot water is drawn off and the tank's internal insulation to keep the temperature steady? I think this would mean less water would be heated using the nightrate, however, would this be offset by the smaller heating increments during the day as opposed to one big heating session of a "cold" hot-water tank in said 6 hours overnight?

Hope I'm making sense.
ALERT.

 

[ClubMan]

Maybe the easiest way to find out is to do this for a week or two and monitor your meter usage (day and night meters) and compare it to a similar period when you do not leave it on all of the time? Obviously things like other electricity usage and environmental temperature will affect results but it might give you an idea of the comparative costs?

 

[Hoagy]

I'm not quite sure about the physics of this, but it seems to me that the immersion will end up doing all the work if the cylinder temperature is raised above the temperature of the water in the geothermal coil.

I suppose it depends where the immersion is located in the cylinder, if it's in the top it might be ok, in that the coil would heat the whole cylinder to a certain temp and the immersion would bring up just the upper section to a higher temp.
If the immersion is in the side then I think it's not going to work.

As to running costs, monitoring as CM suggests is the way to go.

 

[jrewing]

I have heard this question about leaving the immersion on 24 hours debated many times. Until 3 months ago, my parents left it on 24 hrs as they were told this would use the least electricity. I finally convinced them to put it on a timer for about 4-6 hrs per day. Their ESB bill has dropped by 16% straight away.