Measuring the performance of a condensing boiler

Until the entry of the Ecodesign Directive, for all boiler performance calculations, European and Spanish standards have used the PCI as a reference. Since the entry of the ErP Directive, the criterion for defining performance has changed, using the PCS as a reference for the calculation (now including the latent heat available due to the phase change when the condensation of the water vapor contained in the combustion fumes occurs).[3]​.

With the ErP, two performances are defined, one for heating service and the other for DHW. (in case a mixed double service team is considered).

Similarly, the heating efficiency is expressed as a seasonal efficiency for boilers below 70 kW (through a weighted average of instantaneous efficiency at 30% and 100%), while that of DHW. It is defined from a declared load profile.

This means that from September 26, 2015, no boiler on the market will have an efficiency greater than 100% (due to the fact that it refers to the PCS in which the latent heat recovered in condensation is already taken into account). The above is coherent since practically all the boilers on the market will be condensing, and therefore, they will already take advantage of the latent heat present in the fumes and included in the PCS of the fuel.

Performance

The apparent efficiency of these boilers is greater than 100% (measured under traditional conditions, based on the lower heating value), compared to 70-90% for conventional ones. The fact that it is possible to obtain a performance greater than 100% is due to the fact that the lower calorific value was defined as the maximum heat that could rationally be obtained in combustion, so the loss of the latent heat of vaporization of water is not taken into account, since it was necessary to evacuate the gases at temperatures above 140 °C so as not to damage the boiler (with fuels containing sulfur). At these temperatures, water was expelled in the form of steam. If measured on the upper heating value (which takes into account the latent heat of vaporization of water) the efficiency of these boilers is, of course, less than 100%. But, to compare its performance with that of other boilers, the same standard must be used, and the usual thing is to measure the performance based on the lower heating value.

As a consequence of the lower temperature of the prepared water, the final heat emitters must have a larger exchange surface (larger radiators) or use low temperature emission systems (underfloor heating or air heating).

There are also boilers that, from a certain temperature required by the installation (see proportional regulation), stop operating in condensation, to function as normal boilers, with lower performance during these periods of time. With this device it is possible to use existing installations, with emission systems with smaller exchange surfaces.

Measuring the performance of a condensing boiler

Until the entry of the Ecodesign Directive, for all boiler performance calculations, European and Spanish standards have used the PCI as a reference. Since the entry of the ErP Directive, the criterion for defining performance has changed, using the PCS as a reference for the calculation (now including the latent heat available due to the phase change when the condensation of the water vapor contained in the combustion fumes occurs).[3]​.

With the ErP, two performances are defined, one for heating service and the other for DHW. (in case a mixed double service team is considered).

Similarly, the heating efficiency is expressed as a seasonal efficiency for boilers below 70 kW (through a weighted average of instantaneous efficiency at 30% and 100%), while that of DHW. It is defined from a declared load profile.

This means that from September 26, 2015, no boiler on the market will have an efficiency greater than 100% (due to the fact that it refers to the PCS in which the latent heat recovered in condensation is already taken into account). The above is coherent since practically all the boilers on the market will be condensing, and therefore, they will already take advantage of the latent heat present in the fumes and included in the PCS of the fuel.