RogerS wrote:Doesn't time fly.
I went round yesterday to the originator of using the heat store with an oil boiler to look at his controls etc. He uses a Laddomat (which I don't have or intend to get) and that does his controlling. But essentially there is a sensor (A) at the top of the tank and one at the bottom (B).
While the setpoint at A has not been reached, the boiler is fired up. It stays fired up until setpoint B has been reached whereupon the boiler stops. Of course, while this has been going on, the temperature at the top of the tank has gone past its setpoint (A).
As heat is drawn out of the heat store, the temperature at the top will gradually drop until it goes below setpoint A when the cycle repeats.
I asked him why bother with the top setpoint and after some thought he came to the conclusion that i would work just as well with only the bottom setpoint as the controlling mechanism.
I'm not sure. The whole aim of using the heat store is to have very few but long condensing burn cycles from the oil boiler. My gut feel suggests that if there is little hysteresis in the bottom sensor then it will be demanding heat on/off quite frequently. Having the top sensor as part of the controlling mechanism means that there is a very large hysteresis inherent in the system.
What does the team think ?
Assuming that both sensors are needed then any suggestions for a simple interim solution using relays ?
I'd consider using the top sensor to start the boiler run on cooling below setting and the bottom one to stop it on rising above setting.
To make best use of the stored heat at the end of the heating day, arrange to stop the boiler a predetermined time before system shut down. Remember that storing hot water is very inefficient over periods when you don't need it.
Our heating switches off about 9pm and we then open the lounge door (thermostat is in the lounge) to let some heat go upstairs to the bedrooms
At start up in the morning, you could arrange for the store to be bypassed until the first occurrence of the demand in the house being met.
It just depends on how far you want to go with economy measures.
You could also scale the store settings back according to inside/outside temperature differential.