The Portuguese Building Thermal Regulations on solar collectors
The new Thermal Regulations are applied to the all new residential and to some office buildings. Some cases of important retrofit work are also enclosed. The regulations are applied separately to each autonomous zone of a building (each zone with an electricity energy meter). It establishes the obligatory use of solar collectors for hot water supply if the building has a sufficient solar exposure . To have sufficient solar exposure means the building roof must not be shadowed during the period that begins two hours after sunshine and ends two hours before sunset, oriented between SE and SW. They also establish the obligatory use of a minimal of 1 m2 of solar collector area (SCA) (aperture area) per each household of an autonomous zone (conventional nr of households = nr of bedrooms +1). This measure, recognised as a government policy effort to increase solar energy use in Portugal and meet strategic goals, immediately create some discussion in project designers about its cost-effectiveness. The law does not provide anything about the system efficiency and the project climate zone. There is only a regulation exception that allows breaking this minimal area. The value can be reduced to 50% of the total south-oriented roof area. Recently, the Portuguese Energy Agency (ADENE), that rules the Portuguese System for Energetic Certification of Buildings (SCE), clarified this situation and has allowed the use of a smaller collector area. Applying the regulations minimal area, the thermal project designer must proof that with less area can produces at least the same energy than a standard system (optical efficiency n0=69% and loss coefficients a1=7,500 W/(m2.K) and a2=0,014 W/(m2.K2)). The thermal regulations methodology uses the Esolar to quantify the energy produced by the solar collector system. The same methodology allows also using other renewable energy systems (Eren). The total energy for heating water using conventional energy (Nac) is calculated by the following equation (1).
Nac = (Q - Esolar - Eren) / Ap (kWh/m2.year) (1)
The Qa value represents the total energy needs during a year for hot water heating and the pa represents the equipment efficiency. The minimum value of pa adopt by these regulations is 65%. The Nac value is later comparable with a maximum value defined by regulations (Na) and contributes also to the final value of total primary energy (Ntc) in kg of petroleum equivalent (2).
Ntc = 0Л(—)Fpui + 0,1(----------------- )Fpuv + NacFpua (kgpe/m .year) (2)
Better values of Esolar, led to more reduced values of conventional energy consumptions therefore conducting to a more easily satisfaction of the requisites imposed by the thermal regulations. One important aspect can be noticed from this analysis, the equipments efficiency (pi, pv and pa), for space heating, cooling and DHW became fundamental to achieve a good building thermal performance. Is not only important to have a strong envelope insulation to meet energy conservation, as the project designers were used to with the previous regulations, but now the efficient use of energy is a crucial aspect. Therefore, choosing the equipments efficiency became one of the mainly concerns that thermal project designers must be prepared for. Also, the selection of the conventional energy is fundamental, being electricity much more penalized than oil or gas (Fp oil/gas =0,086 Kgpe/kWh and Fp electricity = 0,290 Kgpe/kWh).