Let's compare the different systems
With a classic boiler of atmospheric type, a non-negligible part of this latent heat is evacuated by the fumes, which implies a very high temperature of the combustion products of the order of 150°C. The use of a condensing boiler allows to recover a very large part of that latent heat and this recovery of the energy considerably reduces the temperature of the flue gases to return values of the order of 65 ° C thus limiting the emissions of polluting gas.
Lower Calorific Value (PCI) and Higher Calorific Value (PCS)
The lower calorific value (PCI) indicates the amount of heat that can be produced with a certain amount of fuel (solid, liquid or gaseous). With this reference value combustion products are available in a gaseous state.
The higher calorific value (PCS) contains in comparison with the lower calorific value a percentage of energy added in the form of heat by condensation of water vapor, the so-called "latent heat".
We will use as an example a cubic meter of gas.
Boiler efficiency greater than 100 %
The condensing boiler owes its name to the fact that, in order to produce heat, it uses not only the lower PCI calorific value of a fuel but also its higher PCS calorific value. For all performance calculations, European standards retained as referenced the ICP. Using PCI to describe a condensing gas boiler, we achieve yields above 100 thanks to the restitution of latent heat that represents 11%. This method represents the only means of comparison between classical boilers and condensing boilers. In relation to modern boilers at low temperature, it is possible to obtain yields higher than 15%. Compared to old installations, energy savings can reach 40%. If we compare the energy use of current boilers with low temperature with that of condensing gas boilers, we obtain the following balance as an example:
Heat by condensation (latent heat)
With natural gas, the share of heat by condensation is 11% in relation to the PCI. This value is rendered useless on boilers at low temperature. The condensing gas boiler allows the continuous use of this heat potential, thanks to the condensation of water vapor.
Losses from vapours (sensitive heat)
Steam comes out of low-temperature boilers at relatively high temperatures between 150 and 180ºC, resulting in a heat loss of around 6 to 7%.
The significant decrease in the temperature of the steam on the gas condensing boilers (temperatures that can drop to 30º) allows the use of the sensitive heat part of the flue gas and significantly reduces steam losses.
TRUTHS AND LIES ABOUT CONDENSING BOILERS
Due to lack of custom or ignorance, Spain continues to lag behind in the installation of condensing boilers compared to other European countries such as England or Germany. On many occasions this lack of decision on the part of users to install a condensing boiler is due to the fact that around this type of boilers, a series of myths circulate that in most cases are unfounded.
Let's look at some of the most common:
· Condensing boilers are too expensive
False. The price of condensing boilers has been reduced considerably in recent years. Today we can buy a condensing boiler at the same price as a conventional boiler. In addition, the investment is really worth it if we take into account the fuel savings that this type of boiler guarantees in the medium to long term.
· Not compatible with already installed systems
False. Condensing boilers can be installed without any problem replacing a previous installation and are perfectly compatible with radiators and underfloor heating. Only a good cleaning of the old heating system should be carried out.
· Its installation is very complicated
The only difference between a condensing boiler and a conventional one is that the former need a drain for the remains of condensation, consisting of a simple PVC had. On the other hand, its location does not have to be different from that of conventional boilers. The only thing to keep in mind is that the steam that arises from condensation can be visible on certain occasions, so it is advisable to place the gas outlet in a place where this vapor does not disturb.
· They only get good performance when they condense
It's not true. A condensing boiler gets a performance efficiency of between 84 and 92 percent, compared to a traditional boiler, which gets 78 percent and an old boiler that gets 55 to 65 percent.
· Condensing boilers require larger radiators
Nothing could be further from the truth. In the vast majority of installations, the radiators are already large. There is a marginal advantage of approximately 3% that can be gained by increasing the size of the radiators for a new system, which would slightly facilitate the return of cooled water to the boiler and maximize the time spent on condensation, but this is usually unprofitable and impractical.
· They are less reliable
False. In the United States this type of boiler has been used since the 80s. In our country they are not yet widely used, but current technology and years of experience in other European countries show that this type of boilers work just as well as traditional boilers. · They are difficult to maintain and repair
It's not true. The only difference with conventional boilers is that you have to make sure that the extraction tube is clean while it is active.
· If so many boilers of this type are not installed, it is because there is not much supply
False. That of condensing boilers is a growing market in our country. There are a wide variety of brands that offer condensing boilers of different characteristics and qualities. Always consult your trusted installer who will recommend the model that best suits your needs.
INSTALLATION TYPES
Heating and Domestic Hot Water heating installation with condensing boiler
The condensing boiler is a product indicated for any type of installation for heating and / or domestic hot water, regardless of the working temperature, type of emitters, etc. In any case, the comfort obtained thanks to the regulation margins, the energy savings (performance above 99%) will always be much higher than those of boilers with a traditional combustion generator and, of course, the emission of polluting elements into the atmosphere much lower.
They are perfect for the home since they are very quiet, with sound levels lower than the acoustic regulations.
Equipped with a burner that modulates its heating power, it adapts to your needs. With heating only service, that is, simple service, they occupy a minimum space and can be installed in any room (kitchen, water room, cabinets, etc.) Heating + A.C.S with microaccumulation (example 6 liters
Example 1:
Taking as an example a boiler with a tank of 6 liters, and a heating power of 30 kW, will consume a domestic hot water power of 24 kW with an DHW production of 12 to 16 liters / minute (delta T of 30 ° C, that is, a temperature difference between the cold water inlet, example 15°C, and output 45°C - Control by the European standard EN 625).
Heating + A.C.S with integrated storage tank (example 46 liters)
Example 2:
Taking as an example a boiler with a tank of 46 liters, and a heating power of 20 kW will consume a domestic hot water power of 25 kW with an DHW production of 17 to 21 liters / minute (delta T of 30 ° C or a temperature difference between the cold water inlet, example 15 ° C and the output 45 ° C - EN 625).
A.C.S SUPPLY CAPACITY IS IMPROVED DUE TO THE 46-LITRE TANK
Underfloor heating installation
There are applications in which the benefits of this boiler are further enhanced. They are those where for reasons of comfort the emitters work at a lower temperature or, simply, where low-polluting systems with ecological objectives are needed. In addition, working at a lower temperature improves performance and therefore decreases consumption.
The use of a condensing boiler in underfloor heating installations is therefore an ideal application, since when working at low temperature the performance will be the maximum and the boiler will not suffer problems of uncontrolled condensation.
Integration of renewable energies
Also interesting is the combination of solar installation - condensing boiler. Since it will always be necessary to use an alternative energy to solar, the less polluting it is, the greater the contribution towards sustainable development. And what is clear is that the boilers that pollute the least are those of condensation.
Different types of condensing boilers
In order to exploit the latent heat of the water vapor contained in the flue gases, the latter must be cooled to a temperature below the dew point. The increase in the exchange surface allows the combustion products to cool down considerably, thus allowing the recovery of this latent heat.
The cooling system of the combustion products (the condenser) can be, integrated into the boiler or separated from it.
Examples of integrated capacitor:
Example of condenser not integrated into the boiler. This condenser is placed on the place of exit of the combustion gases of the boiler: Figure 3. Example of a separate capacitorAn example of the operating economy:
THE VIRTUES OF CONDENSATION
The main virtue of condensing boilers is that they produce hot water at low temperature (40-60°C), with high performance.
As we have explained in the section Basic Principles of Condensation, the performance of these boilers turns out to be higher than 100% (measured in traditional conditions, on the lower calorific value), which can be shocking, but that is true. On the higher calorific value (taking into account the latent heat of the water) is, of course, a yield of less than 100%.
The lower calorific value, which does not take into account the heat of condensation of the water, was defined as the maximum heat that could be obtained in a rational combustion without endangering the boiler.
As a consequence of the lower temperature of the prepared water, the final heat emitters must have a larger exchange area (larger radiators) or be low temperature (underfloor heating or air heating).
In short, it allows to obtain a greater amount of heat to equality of fuel burned, with an evident saving.
The environmental aspect and the reduction of pollutants
Condensing boilers emit a lower amount of pollutants than a conventional boiler: consumption can be reduced by up to 30%, and NOx and CO emissions by up to 70%, making it an environmentally friendly product.
In response to international awareness of the harmful effects on the environment linked to human activity, the various representatives of industrial and developing countries met in Kyoto in 1997 to define an action plan to limit greenhouse gas emissions, that contribute to the process of global warming.
Europe has committed to reducing greenhouse gas emissions by 8% by 2010. Spain's commitment is not to increase emissions by more than 15% over the 1990 level.
Statistically, the environmental impact of energy use in the domestic sector is responsible for more than 25% of CO2 emissions into the atmosphere. With condensing boilers, the pollutant emissions that contribute to the greenhouse effect are 3 times lower than the current European standards, in respect of the Kyoto agreements.
In addition, together with the use of solar energy, they constitute a much less polluting and more economical solution, since solar energy is a free energy, beyond the cost of installation.
Condensing boilers in Europe
Countries such as the Netherlands, Germany or the United Kingdom have promoted the use of condensing boilers, whose consumption statistics reflect percentages of 90, 70 and 71 percent, respectively. Meanwhile, in France, Italy and Spain, these percentages are 9, 6 and 0.4 percent, respectively.
