A single Weil McLain Ultra 310 condensing natural gas boiler replaced an aging cast-iron sectional oil-fired boiler at the Mt. Royal United Church in Moncton NB. The condensing gas boiler was installed in an existing high temperature system with no changes to the maximum operating temperature or the radiation. The following brief case study was performed by Charlie Munroe P.Eng, formerly of Public Works Canada.
A summation of the actual oil consumption for the years 2002, 2003 and 2004 was made from invoices. Environment Canada degree day data was collected and adjusted to closely match the fill dates on a calendar year basis.
The oil consumption matching the 30 year mean degree day value was calculated and found to be 539.4 gigajoules.
The same process was a carried out for the natural gas usage in calendar 2007. The gas consumption for a mean degree day year was found to be 432.6 gigajoules.
The relative AFUE (Annual Fuel Utilization Efficiency) of the old oil plant the new gas one is:
AFUE Ratio Oil/Gas = 539.4 GJ/432.6 GJ = 1.247
By these calculations, the oil plant used 24.7% more energy to heat the same building. If we assume approximately 90% AFUE for the new unit then 90%-24% = 66% efficiency for the oil plant, easily considered unacceptable by today’s standards.