Condensing Gas Boilers - The Process

The Condensing Process within one of our Gas Boilers

One of the elements in both Natural Gas and Propane is hydrogen. A gas burning condensing boiler 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 1kg of hydrogen burned, 9kg of water vapour is produced. The temperature in the heat exchanger of a boiler can reach 1400°C. 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 or steel and cools the gases to between 250°C and 350°C.

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. As a measure of how efficient eco hometec condensing boilers are they use stainless steel for the heat exchangers and plastic for the flue systems. A condensing boiler is operating in its most efficient mode when flue gas temperatures are at their lowest.

In an eco hometec condensing boiler, superheated steam, normally lost up the flue, is cooled to its dew point, typically around 55°C. At this temperature the flue gases change from steam to water. During this change they give up their latent heat to the boiler and condense out. To aid the change from superheated steam to condensing mode the critical factor that ensures maximum efficiency, from a condensing boiler, is the return water temperature. Advantages of a Condensing Gas Boiler:

More efficient by approximately 15% compared to a non condensing gas boiler
Produced less CO₂
More cost effective over time

The return water is used to cool the heat exchanger which in turn cools the flue gases. If the return water temperature is to hot then the cooling effect will be impaired resulting in less condensing and lower efficiencies. To sum up, with water return temperature of 55°C or less, the latent heat is condensed out of the flue gases. For more information on how eco hometec can help you to incorporate a solar panel swimming pool heating system please submit your Building plans here.

The Traditional Non-Condensing Gas Boilers Process

At eco-hometec we specialise in the latest technology focusing on efficient and low energy usage hot water & heating applications. The data provided in this section is to provide general information on older hot water & heating systems which are not provided by eco hometec. A typical, non-condensing, traditional central heating system is designed with a water flow temperature of 80°C and a return water temperature of 70°C. This 10°C design differential is critical. System designs had to incorporate high return temperatures (typically 70°C) to stop any unwanted condensing of the flue gases. The flue gases leaving a conventional boiler have to be discharged very hot for the following reasons:

To propel the flue gases up a chimney or through a flue they have to be discharged hot to give them buoyancy and enough thermal lift to overcome the flues natural resistance.
If the flue gases are not hot enough the effectiveness of the flue system is reduced and harmful by products of combustion could enter the building via the condensing boiler or its flue.
A conventional boiler has to discharge the flue gases hot to prevent any unwanted condensing.

If the flue gases are not kept hot enough they will condense allowing water to run back down the flue and into the boiler. Clearly this has to be avoided. Heat exchangers made of cast iron, or boiler designs not equipped to discharge this water would suffer imminent failure. To sum up the flue gas discharge from conventional boilers has to be maintained at high temperatures. The disadvantages of a traditional gas fuelled hot water and heating system are:

Requires higher flue gas temperatures
Produce more CO₂ (compared against a gas condensing boiler)
Use more gas and cost more to operate

Please browse our website for more information about eco hometec and our range of Eco Heating products including Condensing Gas Boilers then click here to submit your plans or contact us on Freephone 0800 8620278 to speak to one of our team or e-mail us on sales@eco-hometec.co.uk.