Passivhaus proposal to include the Mediterranean conditions

Milder winter and hotter summer climates suggested a set of modified conditions where limits to winter and summer demands are defined minimising life-cycle costs and considering local construction. Also comfort requirements needed to be met as defined by EN 15251 (2007). Lastly, country or climate specific low energy solutions proposed require to meet the energy and comfort requirements in many, if not all situations. Other solution sets, if not explicitly identified by the standard, would comply with the standard as long as the comfort and energy limits were achieved. A thorough energetic analysis under these climatic conditions demonstrated a much less necessity to promote reduced air infiltration rates or pre-heat air intake. Then the revised Passivhaus definition proposed under the Passive-On project must verify the following guidelines:

• Heating criterion: The useful energy demand for space heating does not exceed 15 kWh per m2 net habitable floor area per annum.

• Cooling criterion: The useful, sensible energy demand for space cooling does not exceed 15 kWh per m2 net habitable floor area per annum.

• Primary energy criterion: The primary energy demand for all energy services, including heating, domestic hot water, auxiliary and household electricity, does not exceed 120 kWh per m2 net habitable floor area per annum.

• Air tightness: If good indoor air quality and high thermal comfort are achieved by means of a mechanical ventilation system, the building envelope should have a pressurization test (50 Pa) result according to EN 13829 of no more than 0.6 ach-1. For locations with winter design ambient temperatures above 0 °C, a pressurization test result of 1.0 ach-1 is usually sufficient to achieve the heating criterion.

• Comfort criterion room temperature winter: The operative room temperatures can be kept above 20 °C in winter, using the above mentioned amount of energy.

• Comfort criterion room temperature summer: In warm and hot seasons, operative room temperatures remain within the comfort range defined in EN 15251. Furthermore, if an active cooling system is installed, it should be possible to keep the room temperature below 26 °C.

As the Passivhaus has a reduced amount of energy consumption for heating and cooling, it is quite often neither practical nor economical to introduce an active system, in particular for cooling. On this assumption the proposed standard adopts the adaptive comfort theory against the more constrained Fanger approach appropriate for climatised spaces. Unlike the former, method the adaptive theory claims that upon discomfort people will react in order to restore the previously comfortable condition. In practical terms an immediate energy reduction is expected as the cooling set point is set to a higher temperature and the range of comfort temperatures is wider. Several surveys showed that people’s degree of satisfaction is strongly correlated with the outside temperature and the memory of recent temperatures. The adaptive comfort method applies to non air-conditioned or naturally ventilated buildings. [4, 5]

Traditional Mediterranean architecture often makes use of its strong building inertia, coupled with night-time natural ventilation to reduce the swing and the peak of indoor temperatures. The generalised scepticism among builders around the highly airtight buildings also promotes a variation of the German standard to combine a strong inertia with naturally ventilated buildings.

2. Passive strategies