The annual heating energy demand of the Passivhaus proposed for Portugal has been estimated as 16.9 kWh/m2, of which 11 kWh/m2 are supplied by the solar system (in this analysis priority of the solar system is given to heating and the solar fraction for domestic hot water is 48%). The annual cooling energy demand is 3.7 kWh/m2. The sum of net heating and cooling demand is

9.6 kWh/m2/yr. According to the thermal regulation, the limits of heating and cooling for this house built in Lisbon are 73.5 and 32 kWh/m2/yr, respectively. See fig. 2.

80 70 60 50 40 30 20 10 0

The analysis of the thermal comfort is based on the resultant (or operative) temperature, which is the average between air and radiant temperature. The comfort criteria adopted during the summer analysis were based on the calculation of comfort indexes. [6]

This prototype, with an active cooling, has a Fanger Comfort Index of 811 (the house is penalized by the influence of the high glazed area on the radiant temperature). If no active cooling is present, the Adaptive Comfort Index (AI2) applies and is 16. The resultant temperature is kept below 25°C for 71% of the occupied time, and below 28 °C during 98% of the occupied time. To reduce overheating the size of the windows and the thermal insulation should be reduced (though this increases the heating demand). See fig. 3 for the simulated distribution of the indoor and outdoor temperatures in a hot summer week with the Lisbon’s weather file. In winter, the low-power heating system of 10 W/m2 is in use, resulting in only 8% of time with a resultant temperature below 19.5°C (the lower temperature achieved is 18°C). Indoor temperatures show a reduce variation especially in comparison to the outdoor temperature fluctuation.

4. Acknowledgements

The two Portuguese partners would like to acknowledge the remaining partners and subcontractors of the project and the EC financial support for the work developed within the project Passive-On (‘Marketable Passive Homes for Winter and Summer Comfort’ EIE/04/091/S07.38644, 2004-‘07).

5. Conclusion

Clearly, there is a trend to move towards low energy buildings with comfortable indoor conditions and the Passivhaus standard may be an economically feasible solution to achieve those aims. A discussion is raised whether there is the necessity to create airtight buildings with heat recovery mechanical ventilation. In relatively mild climates of Europe where many people still routinely sleep with their windows open, the adoption of a mechanical enforced ventilation system may be compromised. Strategies that combine natural ventilation, solar control and high thermal inertia have been accepted as possible solutions to implement in places with climate conditions similar to those studied within this project. A set of preferred passive/hybrid systems which allow the energy limit and the quality requirement to be met cost-effectively were also defined. An effective solar control and a night ventilation strategy, which dissipates solar and internal gains, can reduce the power of the active cooling system or make its installation unnecessary.

Previous analysis shows how the strategies adopted for the design of a Passivhaus for the heating and cooling climate of Lisbon can be successful, both regarding the energy demand limits and the comfort levels requirements. Although the specific design may be very different from the simple layout presented, the applied strategies have proven effective in reducing energy consumption.

References

[1] Directive 2002/91/CE of the European Parliament and of the Council of December 16 2002 on the energy performance of buildings, Official Journal L 001 of 04/01/2003 p 0065-0071;

[2] Action Plan for Energy Efficiency: Realising the Potential, INI/2007/2106: 31/01/2008 — EP: non-legislative resolution;

[3] Code for Sustainable Homes: Technical Guide, Department for Communities and Local Government, April 2008;

[4] Nicol, F. and McCartney, K. (2001) Smart Controls and Thermal Comfort (SCATs), final report to the European Commission (Contract JOE3-CT97-0066) Oxford Brookes University.

[5] Humphreys, M. A. and Nicol, J. F. (1998) Understanding the Adaptive Approach to Thermal Comfort, ASHRAE Technical Data Bulletin Vol. 14 (1) Field studies of thermal comfort and adaptation (ed. Geschwiler M et al) American Society of Heating Refrigeration and Air­Conditioning Engineers, Atlanta, USA 1998

[6] The Passivhaus standard in European Warm Climates: Design Guidelines for Comfortable Low Energy Homes: Part 2. National proposals in detail: Passivhaus Portugal and Part 3. Comfort, climate and passive strategies, both Edited and compiled by: Brian Ford, Rosa Schiano-Phan and Duan Zhongcheng, School of the Built Environment, University of Nottingham. Download at: http://www. passive-on. org/en/cd. php (accessed Aug 2008).