The study presented in this paper comprised the following steps: Build a model that represents an optimized single family house in a mild southern European climate (Lisbon was taken as reference); Predict the energy demand profiles for ambient heating, cooling, domestic hot water (DHW), heat needed for domestic appliances, electrical needs for lighting and appliances; Size renewable energy systems such that, on an annual basis, the house presents a zero energy demand and Perform a financial analysis.

2. Heating, cooling and DHW energy demands

This analysis builds on previous work performed for the Passive-On project [4][5]. This 110 m2 single family detached house with four occupants is a passive house with low heating and cooling needs. The house will be comfortable through all year with reduced contribution from active systems for thermal environmental control. The model house was developed using building thermal simulation (the software used is EnergyPlus [6]), optimizing several variables: building orientation, window layout and size, glazing systems and shading devices, insulation, thermal mass and natural ventilation (including nighttime cooling).

In the approach followed in this work all energy demand is converted into electricity. Since space heating, cooling and DHW are going to be supplied by the solar thermal system or a heat pump that runs on electricity.