CH-85-02-2 -- Research of a Good Boiler Model for HVAC Energy Simulation PDF

A large amount of information is already available for the prediction of boiler seasonal efficiency. Due to the very low average load ratio to which this sort of equipment is submitted, the seasonal efficiency is generally much lower than the efficiency in nominal conditions, i.e., when running continuously at the maximal power.

The most well-known method in Europe to establish the boiler energy balance corresponds to a purely steady-state evaluation with account of the load ratio, the nominal efficiency, and the “stop losses”. The main simplification of this approach is to neglect the variations of exhaust gas temperature in transient conditions, i.e., according to the durations of the on-and off-periods.

In the present paper, a simplified dynamic model of a water boiler has been developed. Its results are analyzed and compared to the information gained through the use of a steady-state model in two very different operating conditions: laboratory standardized test and working in a real building studied within the framework of I.E.A. (International Energy Agency) Annex 10.

As far as energy calculations are concerned, it appears that the steady-state evaluation of the boiler performance over a long period is already very satisfactory. Actually, the use of the dynamic model doesn't allow more accurate energy calculations, but it is necessary in specific problems such as control or integration of the boiler in a complete building and system modelization.