The laboratory has gained a strong experience in the testing and the modeling of conventional and condensing boilers supplied by fuel or natural gas.

Simplified models to predict boiler performance and pollutant emissions are very useful for HVAC programs. Simulation models of the thermal performance of boilers have been developed and validated.

During the last three years, we have focused on condensing boilers as they offer substantial energy savings because of their high thermal efficiency compared to non condensing boilers. Moreover, nowadays, condensing boiler technology is a standard technology for space heating but it is not always used in the best operating conditions. To ensure continuous condensing operation, heat emitters surfaces must be high enough and, therefore, the return water temperature to the boiler must be well below the flue gas dew point temperature. That means that the heating system must be designed so that its return temperature is low enough in order to have the highest condensing rate. In other words, the heat emitters in the house must be designed to lower the temperature of the leaving water from the boiler.

There has been few published work over the condensing behaviour of domestic boilers. The aim of this work is to show the influence of boiler parameters variation (as water temperature, heat input, excess air) on thermal performance of the boiler and develop a simplified model that well predicts these performance variations.

Test rig

There are three test benches equipped with boilers. There is one semi-industrial conventional boiler with a power output of 400kW that can be set with gas fired or oil fired burner. We also have two condensing boilers that are 24kW household appliances: a natural gas and a fuel oil fired boiler. Each condensing boiler is placed in a loop with a plate heat exchanger that simulates the emitters of a house and regulates the return temperature to the condensing boiler. Flue gas from all boilers are continuously analyzed with gas analyzers ([O2], [CO2], [NO], [CO]).



Danielle Makaire
Département d'aérospatiale et mécanique / Thermotechnique
Adress: ULg - Bât. B49 Thermotechnique
chemin des Chevreuils 7
4000 Liège 1 Belgique
Tel. : +32 4 3664821
Fax : +32 4 3664812


This project is performed in the frame of IEA implementing agreement with the financial support of the SPW-DGO4.

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