What is a Condensing Boiler?
A condensing boiler is a water heating device designed to recover energy normally discharged to the atmosphere through the flue. it does this through the use of a secondary heat exchanger which most commonly uses residual heat in the flue gas to heat the cooler returning water stream.
How it work
A conventional non-condensing boiler works by burning fuel and the hot combustion gases heat water contained in a heat exchanger. The waste gases are still quite hot (180°C - 200°C) and these are discharged to the atmosphere using convection of the hot gases.
In a condensing boiler working at peak efficiency the water vapour produced by the burning fuel in the boiler is condensed back into liquid water using a second heat exchanger which heats the cool water returning to the boiler. Provided the returning water is sufficiently cool, the steam condenses to water vapour and to liquid water - hence the name " condensing boiler". Some of the extra efficiency of the condensing boiler is due to the cooling of the exhaust gases, but the majority of the energy recovered is from the condensation of the water vapour in the exhaust gases. This releases the latent heat of vaporisation of the water - 2260kJ/kg (970btu/pound) of condensate into the heat exchanger.
The actual operating efficiency of a condensing boiler depends on the temperature of the return water stream - if it is too warm then little condensation takes place and there is little extra energy extracted.
Efficiency
Condensing boiler manufacturers claim that up to 98% thermal efficiency can be achieved, compared to 70%-80% with conventional designs (based on the higher heating value of fuels). Typical models offer efficiencies around 90%, which brings most brands of condensing gas boiler in to the highest available categories for energy efficiency.
|
Not happy with your current Heating Boiler? Want to reduce your Gas Bill? 
