Immersion gismos with PV

osolemio

I am very happy with my 4KW system PV running now almost 5 months and am looking now to perhaps extend it with one of the many gismos that connect to the immersion heater. I always read carefully into a subject before committing myself and am fairly sure I understand what they are about except for one thing that I just can't figure out. Given that it is the temperature of the water in the tank falling below the thermostat setting that kicks things into action, how does my oil boiler "know" that the water is going to be heated by the PV system (when there is a "surplus") and hence not fire up as it would usually do?
That looks a pretty stupid question and perhaps I haven't explained it very well but I'm sure there is someone out there who knows what I mean!

Cardew

Your oil boiler 'doesn't know' that the tank is going to be heated by the Immersion(powered by the PV Gizmo)

You will need to have the boiler on timed operation(not 24/7) or off altogether.

You attempt to balance your consumption requirements against the likely output from the PV gizmo. On a dull day with little PV output you may need to switch on the boiler 'manually'.

You can also set the immersion thermostat higher(say 70C) than the oil boiler hot water output.

Edit.
Some older CH systems do not allow 'heating only' i.e. if heat to radiators is on, so is Hot water.

Also other systems do not have a tank thermostat - so the temperature of the hot water tank is the same as that in the radiators.

If that is the case you have a problem.

EricMears

Cardew wrote: »

You can also set the immersion thermostat higher(say 70C) than the oil boiler hot water output.

Not really a 'disagreement', just a change of emphasis.

At this time of the year you can deliberately set your tank setpoint for the oil (or gas, solid fuel, whatever . . . ) boiler rather lower than normal and push your immersion heater setpoint up as far as possible (or safe !).

N.B. If you are setting a very high immersion heater setpoint you need to be very careful that you don't scald users ! A blending valve on the DHW circuit would be ideal although providing you're absolutely sure that no young children or other non-readers are likely to use the taps, warning notices might be sufficient.

pwllbwdr

Or you could change your on/off times for your oil boiler to come on at (say) 5pm for an hour. Then if you've had a good day of solar, the tank will be hot. If not, the oil boiler will heat it up in the evening.

Depends when you use your hot water of course.

osolemio

Thank you both, you have confirmed what I had suspected would be the way of working the 2 (oil and electricity) together. Need to think about it more in the light of your thoughts/advice.

osolemio

Thanks also pwllbwdr, that way of operating had occurred to me, out main hot water use is evening and early morning so it looks as if that might be the way to go.