Question from Steve Edmondson, via email:
I’m installing a heat store system heated by a Worcester Bosch Greenstar 15i with underfloor heating from the store. The store needs to be at a temperature high enough to heat the tap water (via the internal coil) to an acceptable level.
Will weather compensation be advantageous with this arrangement?
Answer from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
Generally, thermal stores operate at temperatures around 80°C, with a typical differential between the flow and return of 20°C, which would result in the condensing boiler rarely condensing. Some more modern thermal stores operate at lower temperatures and via a combination of two cylinder thermostats set at different temperatures will try and optimise the boiler firing periods and prolong the condensing operation.
A weather compensator will try and reduce the boiler flow temperature according to the external weather temperature, whereby the higher the external temperature the lower the boiler flow temperature. I would therefore see this as being in conflict with the thermal store controls. I feel that if you are going to use a thermal store, you should follow the manufacturer’s instructions when it comes to the controlling of both the boiler and the system. If they allow weather compensation then fine, however, I am not personally aware of a thermal store that operates this way.