The importance of the modulation ratio in the boilers installed inrefurbished buildings

The refurbishment of a building with better insulation particularly in the walls and in the roof with thewindows replacement gives rise to a relevant reduction of the heating load. Then the existing boiler issurely oversized and it must be replaced. The selection of the model is connected to the new design load,but it is also bound to the nominal capacity of the equipment on sale, that is never below about 10 kW.Then it is of paramount importance the modulating ratio that is till which capacity the boiler can operatecontinuously without working in the inefficient ON–OFF control.For a typical detached building, first of all the load reductions with common refurbishment is consideredfor three climates: cold, temperate and mild in Italy. Condensing boiler seasonal performances are thencompared with modulating ratio that from the simple ON–OFF arrives till 1:10 for two different nominalcapacity.Finally a further performance improvement can be obtained with variable flow rate pumps, operat-ing with a temperature drop relatively constant between supply and return. Whereas the already highboiler efficiency is not appreciably increased, the electricity saving to drive the pumps can be reallyoutstanding.