In order to improve the energy efficiency, energy certification plays an essential role allowing us to evaluate and compare buildings and their features related to demand, consumption and emissions. The aim of this work is to analyse the methodology used by current regulation to estimate the energy consumption from domestic hot water systems and its subsequent energy rating. The relationship of the results obtained with the different types of homes is studied according to their area and number of bedrooms, justifying how the area of the house has an excessive influence on the qualification obtained in the sanitary hot water parameter, favouring a better certification to larger homes.

Nowadays, one of the most significant technological challenges is the decreasing dependence of carbon-based fuels and the polluting emissions into the atmosphere. In pursuit of that objective, the Directive 2010/31/UE from the European Commission, provided that all new buildings must be low energy consumption, nearly zero-energy. This Directive is being transposed into national law through the modification of CTE, Technical Building Code and RITE, Regulation of Thermal Installations in Buildings, both are pending to publish along this year 2018. According to the data from both the European Commission recommendations about net primary energy consumption at kWh/(m2/year) and the Development Ministry communicated in the EECN Congress, celebrated last December 2017, the outer skin, solar protection and ventilation of new buildings going to reach a very high level of efficiency, so energy consumption by domestic hot water will become very important. This change in residential buildings energy consumption profile, requires a detailed study of this system. This work studies, statistically, the materials more used in domestic hot water distribution systems, thanks to the data from last years gathered by Spanish Professional Associations both new and refurbishment Works. In a first step of this study, it is concluded that the metallic materials use has been reduced considerably, but nowadays these materials are used about in 20% of building works, despite their worst thermal transmission coefficient. We also know that the material more used is Cross-Linked Polyethylene, however, there are important differences over all the Spanish regions.