The previous section has shown that it is possible to comply with the energy requirements of the RCCTE even without solar thermal collectors for domestic water heating. Yet, two important questions remain.

One is whether the use of solar thermal collectors, mandatory by the RCCTE, can be discarded for historical areas based on a criteria of “justified esthetical incompatibility”. According to the law, it is up to the licensing authorities (generally the municipalities) to judge this justification. The authors will take no definitive position here, although they admit that in some cases the relief from compliance may be justified.

The second question is, regardless of the answer to the previous paragraph, what is the energy relevance of the collectors if they are indeed applied, and its consequences in terms of energetic classification — especially its relevance to achieve class A+. This assessment was made by analysing a case with the same envelope and constructive solutions of table 8, but now adding solar collectors of medium performance (n0=0.73; ai=5.0 W/m2K; a2=0.05 W/m2K) for heating of the domestic hot water, maintaining the gas boiler as auxiliary system. As prescribed by the regulation a collector area of at least 1 m2 per person was considered. Table 9 shows the results of this exercise, which shows that by adding the solar thermal collectors the buildings now fall within class A. This strong effect is easily understood if we recall eq. 1 which shows that the primary energy consumption Ntc strongly values the energy consumption for domestic hot water when compared with the consumption for heating and for cooling.

4. Conclusions

Portuguese thermal regulation for residential buildings, the RCCTE is applicable to all new or significantly retrofitted buildings. It foresees the possibility that for buildings in historical areas certain requirements of the regulation may be discarded if an incompatibility with the architectural

frame are found and duly justified. An analysis to 6 apartments undergoing a retrofitting process in the downtown area of Porto (the “Ribeira”- classified by UNESCO as human heritage patrimony) allowed the identification of some important findings.

The first major finding was of a process nature and showed a possible trend towards trying to exempt the buildings from compliance with the RCCTE even before making any calculation and therefore without proving any incompatibility. The licensing authorities (generally the municipalities) and ADENE shall thus pay particular attention to this point in order to ensure proper compliance and ultimately a better energy performance of their built environment, with the known benefits in terms of comfort, economy and environment.

The second major finding was that, even if the requirement of installing solar collectors is hypothetically discarded, it is possible to comply with the energy requirements of the regulation (Nic, Nvc, Nac and Ntc) without interfering with the appearance of the buildings. The major features to take into account for seem to be:

• — The use of about 3 to 8 cm of thermal insulation (depends of the specific case) at an internal position relatively to the traditional stone walls. More than complying with the direct minimum requirements, this is needed to ensure compliance with the maximum heating needs.

• — Avoidance of an internal envelope using extensively thick gypsum layers as internal finishing, since it may lead to low thermal inertia. This is because the solar factors of traditional internal shading devices are compatible with medium or high thermal inertia but not with low inertia ones.

The third major finding was that, despite the fact that being at an historical area may in some cases be a justified reason to discard the installation of thermal solar collectors for water heating; its installation seems to be crucial to achieve buildings with energy class A.

5. References

[1] AdePorto — Energy Agency of Porto: Energy Matrix of Porto, Porto, 2008 (in Portuguese).

[2 ] INE — Institute Nacional de Estatistica, www. ine. pt [3 ] www. portovivosru. pt/

[4 www. adeporto. eu/

[5 DL80/2006 de 4 de Abril de 2006 — RCCTE — Regulamento das Caracteristicas de Comportamento Termico dos Edificios

[6] European Comission: 2002/91/EC — Energy Performance of Buildings Directive,

Acknowldegments

The authors thank the cooperation of Porto Vivo SRU, in the person of Eng. Antonio Baptista, and of SOPSEC S. A., in the person of Eng. Pedro Pinto, which provided free access to the retrofitting design data for the analysed buildings, as well as to AdEPorto for the financial support to the internship of Eng. Francisco Craveiro.