Ralph H. Torborg

Control of overall thermal efficiency of combustion heating systems

A method for analyzing the energy performance of central combustion heating systems has been derived. The method consists of a combination of measuring a minimum number of key system parameters and using them as input for HFLAME, the digital model used to simulate the dynamic performance of the heating system. HFLAME is based on the stack loss method, uses only input that can be obtained during field measurements, and relies on the steady state operation of the burner to calibrate flows and temperatures. This methodology is being applied to the study of a variety of furnace/boiler designs, modes of operation and control options, aimed at reducing the energy consumption for residential space heating. One of the main reasons for the substantial, difference between steady state furnace efficiency and average seasonal system efficiency was found to be caused by the furnace draft flows during the burner off-period. Power burners can reduce the losses, LD, caused by those flows considerably by virtue of functioning like leaky dampers in the off-period. Other reasons for the generally high LD losses are: low average furnace load (oversizing), the use of pilot flame ignition systems, frequent system cycles and high fan/pump control set points. Although typical seasonal efficiency data for gas fired heating systems are about 60%, and 66% for those fired with oil, we estimate that efficiencies of up to 69%, respectively 76%, can be achieved by attending to careful selection, sizing, installation and adjustment.