The number of householders in buildings
In Portugal 1/5 of buildings are occupied during only a part of the year [4]. Many cases of emigrant people and second house for holidays are example of this. In these cases, there are not regular consumptions and applying the regulations can originate a potential for excessive energy production. In some summer occupied homes the solar collector mounting tilt angle should be lower, above 35°, to maximize gains, maintaining the minimal area required [7]. Even another problem can be faced. The number of householders can vary widely. On this case, the system is over dimensioned and the equipment can not be cost-effective solution.
5.3 The integration on building architecture and construction
The collector’s building integration is a new challenge for architects. It known that the recommendable optimal panel tilt angle is the local latitude angle plus ± 5 °C [7]. Portuguese continental territory has latitude angles between 36° and 42°. In horizontal roofs this angle it should be guaranteed by an independent structure. On pitched roofs the better choice was to follow the roof tilt angle but it should be south oriented and not always is like that. If this is the case, is necessary to mount an independent structure for the panels using the calculations tilt angle and
south-orientation. The result is a strong and negative visual impact on building architecture. In large panel areas, this solution even can result in more mounting panel area because some panels can more easily obstruct others. Some facade elements near the roof can make a good role on disguising this type of installation. If the roof is E and/or W oriented, the panels tilt angle need to be reduced to 25°C to guarantee not more than 5% of decrease in energy captured [7]. On this case, it could be difficult to use the roof tilt angle. But if the roof is south-oriented the decrease of energy captured by not using the optimal angle is insignificant comparing with the benefits in cost, panel safety to wind and building aesthetic [7]. The most current tilt angle roofs in Portuguese buildings vary between 20° and 50°. Are these angles proper to be adopted and still get solar collector energy? It were made simulations using the software Solterm (version 5.0) for a three bedrooms autonomous zone (4 householders/4m2 of minimal SCA by regulations) and using a range of tilt angles between 20°-50° . Nine different Portuguese localities representing the nine continental climatic zones (locality - climatic zone) were selected: Agueda - I1V1, Albufeira - I1V2, Alandroal - I1V3, Alcobaqa - I2V1, Alcanena - I2V2, Castelo de Vide - I2V3, Celorico da Beira - I3V1, Braganqa - I3V2 e Mirandela - I3V3. The other fixed parameters were:, a south oriented panel; a water storage tank with 200 l of capacity, a gas boiler and the solar collector standard defined by ADENE (chapter 3). It was observed from the Esolar values that for a same autonomous zone: the south localities are better to capture solar energy; even using a distant tilt angle from the optimal angle the south zones are still better then some north zones using the optimal angle; the best panels tilt angles are the latitude angle ± 5 °C; the maximal AEsolar between the optimal tilt angle and the lower angle (20°) is of 92 kWh/year that represents a not problematic value. Then, it seems acceptable for a pitched roof south orientated (including also SW and SE) to mount the collectors close to the tilt roof angle. But it would be even better that architects designed the roof tilt angles to mach with the optimal panel tilt angle previous calculated. Finally, it must not forget that some additional cares must also be in weatherproof all penetrations through the roof covering with suitable flashings and purpose-made tiles.
