Simple, fully featured boiler loop modelling

The performance of hot water space heating systems for mild to warm temperate climates is dominated by the efficiency of boiler operation at low load (i.e. below 25% of nameplate capacity). This efficiency is influenced by a number of effects that are poorly represented in common modelling approaches, including static thermal losses from the boiler and distribution system, changes in burner efficiency at different firing rates, thermal inertia in the boiler loop and the effects of cyclic operation. In this paper, a simple model that includes these loss mechanisms is developed. An example from an actual project is used to demonstrate that addressing the full range of low-load efficiency effects can increase predicted boiler gas consumption substantially relative to standard simulation approaches.