Apologies for the grand-sounding title but this refers to the high-level design of the heating solution for the property – especially in the context of the full site with both a large house and a substantial range of outbuildings.
The initial plan was to develop the outbuildings at the same time as the main house, to provide garage and storage space as well as a workshop and utility area. At the time when a biomass boiler was under consideration the only possible location for this (and the accompanying fuel store) would have been the outbuildings, with a “heat main” connecting to the main house.
One of the main decisions was therefore whether to link the two buildings from a heating and hot water standpoint or to keep them separate. Both buildings would need some sort of heating and hot water solution, albeit relatively crude in the outbuildings given their planned usage pattern (intermittent – especially in the winter – and not to the same level of comfort as the main house).
Initially a log-fired boiler was looking promising, feeding a thermal store in the outbuildings. Unfortunately the characteristics of high-efficiency log boilers are poorly matched to the heat requirements of Passivhaus buildings since they’re designed to burn “hot and hard”, dumping their heat in a relatively short period of time. If this heat can be stored-long term that’s fine, but the levels of insulation required to store hot water for a week or more are very significant.
Even before it became apparent that cost constraints would require the outbuildings to be developed later than the main house it was seeming more sensible to implement separate heating and hot water systems for the two buildings:
- The outbuildings could have a wood-fired stove with a back-boiler supplying underfloor heating in the workshop, with instantaneous electric heaters for hot water
- The main house could have a more conventional (but small-scale) heating and hot water system