Condensing Boilers For Under Floor Heating
Condensing Boilers are ideal for Under floor Heating systems. One of the elements in both Natural Gas and Propane is hydrogen. A gas burning appliance mixes the gas with air and during the combustion process hydrogen and oxygen combine together and produce heat (143,100kJ/kg) and water vapour (H2O).
For every kg of hydrogen burned 9kg of water vapour is produced. The temperature in the heat exchanger of a boiler can reach 14000C. The water vapour produced is so hot it turns into superheated steam.
This superheated steam contains both sensible (available heat) and latent heat (heat locked up in the flue gases). A conventional boiler will recover some of the sensible heat by passing these hot gases over a heat exchanger.
The heat exchanger in non condensing boilers is generally made of cast iron and cools the gases to between 2500C and 3500C. A conventional boiler does not recover any of the latent heat and this energy is simply lost to the atmosphere through a metal flue. These flue gases are extremely hot and the lost energy wasted can equate to up to half of the annual running costs.
A simple condensing boiler will however extract more of the sensible heat and some of the latent heat by cooling the flue gases down to below 1000C.
When a condensing boiler is operating in its most efficient manner flue gas temperatures of less than 500C will be achieved and the boiler will now start to condense the flue gases. The superheated steam is cooled to its dew point, typically around 550C, the flue gases give up their latent heat to the boiler and condense out.
The critical factor that ensures maximum efficiency from a condensing boiler is the water return temperature. The water return temperature determines whether the boiler operates in condensing mode, which in turn controls the boilers efficiency.
To sum up, with water return temperature of 550C or less, the latent heat is condensed out of the flue gases.
By using less gas condensing boilers reduce carbon dioxide emissions, to help combat global warming, and improve household efficiency thus reducing fuel bills.
Condensing boilers work on the principle of recovering as much as possible of the waste heat which is normally rejected to the atmosphere from the flue of a conventional (non-condensing) boiler.
This is accomplished by using an extra-large heat exchanger or sometimes two heat exchangers within the boiler which maximises heat transfer from the burner as well as recovering useful heat which would normally be lost with the flue gases.
The publication, "Domestic Condensing Boilers - The Benefits and the Myths", produced by Energy Efficiency Best Practice in Housing provides concise information about condensing boilers.
Underfloor Heating1 systems are ideally suited to gas condensing boilers.
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