How a condensing boiler works

A condensing boiler it allows to obtain a higher efficiency than a traditional boiler. How is it possible? The answer is in the particular technology used.

A condensing boiler it is designed to exploit a large part of the latent heat of condensation of the water vapor contained in the exhaust fumes. This steam is generated by the combustion process of methane gas, generally in the amount of 1.6 kg per cubic meter of gas, and in a normal boiler it is dispersed at temperatures ranging from 140-150 ° C in high-efficiency boilers to 200-250 ° C of traditional boilers.

In practice, the condensation it is an efficient technology because it allows you to recover the heat contained in the fumes, which makes up about 11% of the energy consumed, instead of dispersing it into the atmosphere.

Technically, here it is how a condensing boiler works. In this type of boiler, the fumes give their heat to the feed water, cooling down to a liquid state. Their temperature is lowered up to 40 ° C, well below the release temperature of the fumes of both traditional and high-performance generators.

The performance of a condensing boiler they are evaluated in terms of efficiency considering the higher calorific value, which takes into account the quantity of energy extractable from methane gas and latent heat. Today the yields of available condensing technologies range from 105% to 109%. Those of traditional boilers are around 90% -93%.

Question: How is it possible to have a return greater than 100%?

Answer: of fossil fuels, (methane gas, coal, oil) a lower calorific value and a higher calorific value are identified. The lower calorific value corresponds to the quantity of usable heat without condensation of the exhaust gases; the upper one refers to all the theoretically usable heat, therefore also the part contained in the water vapor of combustion.

By convention, in traditional boilers the lower calorific value is used as a reference and, in order to be able to compare them, the same criterion is maintained for the condensing boilers. This is why we hear about condensing boiler efficiency exceeding 100%, which is theoretically impossible.

The technology of heat recovery from the fumes costs one condensing boiler much more than the traditional one. This is because it must be resistant to corrosion and have a heat exchange surface that is not only smooth and without fins, but also arranged in such a way that the condensate can flow to the neutralizer or to the waste water.

Furthermore, since auxiliary ventilation is possible and in some cases necessary, the flue system requires special calculations for the draft. But the savings you get with one condensing boiler are of the order of 15-20% for the supply of hot water at 80 ° C and 20-30% for the supply of hot water at 60 ° C. The maximum benefits, around 40% but even more, occur when the condensing boiler it is used in systems that operate at low temperatures (30-50 ° C), such as radiant systems (ceiling panels, underfloor heating or wall-to-wall heating).

Since September 2015, the condensing boiler is mandatory for new installations

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