Overheating Assessment of a Passive House Case Study in Spain

In response to the European Energy Performance Buildings Directive 2010/31/EU and the Energy Efficiency Directive 2012/27/EU, buildings have increasingly become more insulated in order to reduce the heating losses to a minimum. However, this could also lead to the problem of indoor high temperatures during warm and transition seasons. Furthermore, the Intergovernmental Panel on Climate Change (IPCC) warns about increases in temperature of more than 4 ºC by the end of the century. Taking into account the different thermal comfort indices, this research analyses the overheating risk in a single family house built in Spain according to the Passivhaus standard. For the purpose of this research, we selected the following models: the Fanger Predicted Mean Vote (PMV) model defined in the ISO 7730:2005, the adaptive model defined in the EN 15251:2007, the criteria for overheating prevention defined in CIBSE TM52 in 2013 and the PH limitation about warmer temperatures. Moreover, we have analysed the influence of dwelling occupancy and the periods of verification over the results of each methodology. The studied building has a high level of thermal insulation and air-tight envelope, reducing heat losses until a heating demand of 14 kWh/m2 per year. It is equipped with a convective heating system and a mechanical ventilation system with heat recovery, without any cooling system apart from the bypass configuration of the heat recovery unit and the window openings. The monitoring lasted more than a year, from January of 2013 until April of 2014, and includes both indoor environment and outdoor weather parameters.  The different criteria result in different outputs: According to the ISO 7730 standard, the discomfort caused by warm temperatures represents the 9.8 % of the non-heated season, which reaches up to 13.6 % when taking into account only the day-time rooms; this result is obtained through the weighted average of the temperatures in the kitchen, the living room and the dining room. On the other hand, the adaptive model EN 15251 leads to an outcome of only the 0.2% in the whole house and 1.7% in the weighted average temperature of the day-time rooms. The TM52 criteria for avoiding overheating risk shows that the building is not overheated because it meets the three criteria. The house doesn’t meet the Passivhaus requirement, because the period over 25ºC exceeds 11.8 %. Finally, we have analysed some guidelines about overheating risk assessment and proposed some improvements, such as including transition months of fall and spring, considering full time occupancy instead of specific timetables or splitting the building into different zones to detect local discomfort conditions.