The strategy

Solar availability is quite high in Portugal, even during the heating season. This makes the direct capture of solar radiation (windows), the indirect collection for domestic hot water and space heating (thermal solar system) and eventually energy production (photovoltaics) advised. Large windows are mainly oriented south, increasing the useful solar gain during winter. Smaller areas are oriented east and west and minimal areas to north. Overhangs on south windows and exterior venetian blinds on all provide solar protection during summer.

High thermal inertia allows control over the inside temperature and combined with night ventilation, prevents overheating. In the bedrooms ventilation should take place in the evenings to avoid drafts during the sleeping period. In all other spaces, all night cooling can be used. High thermal inertia can be achieved by exposing the heavy concrete slab, using brick internal partitions

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and preferably applying external insulation to the roof and walls. However, there is still some scepticism among Portuguese builders to the mechanical performance of exterior insulation. Therefore, this proposal uses the traditional double brick wall with cavity insulation.

Insulation levels proposed for the roof (150mm) and exterior walls (100mm) with U-values of 0.23 W/m2.K and 0.32 W/m2.K, respectively, are well below the current regulation requirements. Only a 1m stripe of the perimeter of the floor slab is insulated to allow the core of the house to release heat to the soil during summer. Windows facing south correspond to around 60% of the total glazed area and about 20% of glazed area faces east and another 20% west. Low-emission double glazing can be very effective in colder regions of Portugal, but in most situations standard double glazing is more cost-effective (U-values of 2.9 W/m2.K for standard double glazing and 1.9 W/m2.K for low-emission glazing are considered).

The utilization of solar panels for domestic hot water in new or refurbished buildings (a few exemptions apply) is compulsory under the new thermal regulation. The current proposal extends the solar installation to also cover a significant portion of the heating demand, by increasing the solar panels area and using a low-temperature hydraulic heat distribution (for instance radiant floor). The solar panels are installed facing south, tilted 50° from the horizontal plane, to increase the efficiency during winter. In accordance with the Passivhaus proposal, the active heating and cooling capacity is limited to 10 W/m2. The extra costs of the proposed Passivhaus for Portugal is 57 €/m2 with a payback period of 12 years.

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