Passive Houses in South West Europe


Heating and cooling demands of the same building in different locations (simulation results). The example building has the typical concrete skeleton construction of the region (with U-values around 2 W/(m²K) due to the severe thermal bridges), no insulation in the basement, ordinary double glazing, poor airtightness, exterior Persian shutters. Heating is required everywhere, the annual cooling demand is usually lower than the respective heating demand.

The locations considered in the study and a view of the sample building used for the simulations


Summer temperatures in a Passive House in Seville, with good insulation (8 cm wall, 20 cm roof) and supply air cooling: The design indoor temperature of 26 ° is hardly exceeded, thermal comfort can be provided.


The same building following a purely passive cooling approach, with white exterior surfaces, strong night ventilation and without heat recovery: sometimes not fully comfortable, up to 30 °C (in a later period not shown here)


A poorly insulated existing building, also with exterior blinds and full night ventilation: unbearable conditions

Most experience with Passive Houses is available from Central Europe. Can Passive Houses also be built in warmer climates, where hot and possibly humid conditions prevail in summer? A theoretical study dating from 2009 has considered this question in great detail for the warmer climates of south-west Europe. The major finding is that indeed buildings which can provide high thermal comfort in both winter and summer by solely heating, cooling and/or dehumidifying the supply air required for good indoor air quality can be realised here. Some key results from the study are given on this page.

First, it is important to note that, like in central Europe, space heating is the dominant energy demand in most climates of the Mediterranean.

On a European level, the annual energy demand for residential space cooling is still relatively small, but major problems are expected due to the strongly growing market for air conditioning devices. High peak loads, which are bound to occur simultaneously in all households of a larger region, tend to cause blackouts already today. Therefore, addressing both heating and cooling demands is essential.


Given the milder climate of the Mediterranean, the heating task can easily be solved using components which can be of a somewhat lower efficiency than in central Europe. Some interesting issues concerning the winter arise:
In Southern Europe with its higher level of solar radiation, single glazing is already sufficient to achieve net solar gains on a south façade during the heating period in many locations, provided there is no significant shading. Nevertheless, for the sake of thermal comfort double low-e glazing appears to be the appropriate choice. Triple glazing is not recommended south of the Alps: its energy balance is usually worse because of the lower solar gains.

Proper orientation can make things easier to a much greater extent than in more northern climates. The influence of orientation on the heating demand is typically twice as high in the Mediterranean as in central Europe. For the heating load, this factor may even rise to 3 or 4. Additional south-facing glazing areas can reduce the heating demand and heating load significantly (provided that the building site has good solar access, of course).

For Passive Houses in central Europe, it has long been known that the influence of thermal mass on heating demand is negligible. In the sunnier Mediterranean climates this influence becomes notable: The effect on heating demand may reach as much as 5 kWh/(m²a). The influence is most significant in lightweight buildings. In heavier structures additional thermal mass has no considerable effects any more; other factors such as hygrothermal interaction may even outweigh the thermal storage effects.
Insulation between the heated envelope and the ground can be omitted in climates with annual average temperatures between approximately 15 and 20 °C, such as lower regions of southern Spain and Italy. It would not save any significant amounts of energy, and the surface temperatures on top of the basement ceiling are sufficiently high even without insulation. In both hotter or colder climates, the building should also be insulated to the ground.


Cooling by means of the small amounts of supply air that are required for good indoor air quality, i.e. 30 m³ per hour per person, is indeed possible throughout the Mediterranean climate zone. Some aspects deserve special attention.

Contrary to some publications, good thermal protection also helps to provide high thermal comfort in summer (particularly if applied in the roof) and to reduce temperature fluctuations. A compact building shape is beneficial, too. The double low-e glazing recommended for winter comfort simultaneously protects against heat transfer from the window blinds in summer.

A good, movable exterior shading is indispensable. Fixed shadings or solar control glass become equivalent to movable shading only in extreme cases, but result in very high additional heat demand in winter. Without movable shading the cooling load can increase by 5 W/m² even in the study's comparatively robust reference situation, having moderate window areas and all windows facing north or south. With east or west oriented windows the influence is even bigger.

An important distinction must be made between places which experience relatively low summer humidities, such as most of Spain and Portugal, and locations with higher humidities like the Italian coastal locations and the Po valley. The semi-arid climates of the Iberian peninsula do not require dehumidification, whereas to the south and east of Nice dehumidification can become the major task in summer. Palermo, as an extreme example, has typical summer temperatures between 25 and 30 °C throughout the day and dew point temperatures which hardly drop below 20 °C for longer periods.

The potential for night ventilation may become zero in such humid situations, in spite of sufficiently low ambient temperatures, because any additional ventilation air would bring excess humidity into the building. The latent heat ratio of any combined cooling and dehumidification device also needs be chosen according to the local climatic conditions. Separating cooling and dehumidification is not essential in European climates. Some general remarks should be added:

The installation of a supply and exhaust air ventilation system (to be combined with an airtight envelope) must be recommended in most locations, for different reasons. Either ventilation heat recovery is preferable to excessive insulation thicknesses for the winter case, or active cooling/dehumidification is required in summer, such that heating and cooling via the supply air appears advantageous to installing a multi-split unit, particularly since it also improves indoor air quality and thermal comfort. Any heat recovery should have an automatically controlled bypass to make use of low ambient temperatures during summer nights.

The Mediterranean Passive Houses with, as compared to central Europe, lower insulation levels and higher solar fractions, are more sensitive to changing boundary conditions such as different indoor or ambient temperatures or changes in user behaviour. Greater safety margins than in Central Europe would be a good idea.

Although the Mediterranean climate prevails only in a relatively restricted area of the earth's surface, the incongruent variations in winter and summer temperatures, daily temperature variations, solar radiation and relative humidity require different solutions for different locations. A specific calculation of the energy balance and the space conditioning loads will be required for every Passive House to be built. A PHPP calculation will usually be sufficient.

An interesting option is the use of so-called cool colours, i.e. colours with low solar absorption, for the exterior surfaces to reduce the solar load during summer. Even for well-insulated buildings exterior colours can change the cooling demand by up to 5 kWh/(m²a) and the peak cooling load by as much as 3 W/m². Unfortunately, reduced solar gains in winter may compensate for the advantages in summer.

Mechanical systems

Central European Passive Houses frequently use compact heat pump systems. These devices integrate all mechanical systems required in a dwelling: a heat pump is added to a ventilation unit with heat recovery, using the sensible and latent heat of the exhaust air as a heat source for producing both supply air heating and domestic hot water in an integrated storage tank. One great advantage of these systems is that they are factory-made, including all controls, and the different components can be expected to cooperate smoothly. In addition there is a potential for a mass-production similar to white goods, with the respective cost reduction.

Such systems could in principle easily be supplemented by a cooling function, without impeding the above advantages. Apart from several technical details which need to be solved, the exhaust air cannot be used as a heat sink because its temperature rise would be excessive under full cooling load. Other solutions, such as ground condensers, mixing with ambient air, or outside units from conventional cooling systems, can resolve this issue.

Unfortunately, compact heat pump systems which are appropriate for Mediterranean conditions are not available on the market yet. Current demo projects will probably have to fall back on multi-split units or other conventional technologies. Alternatively, space heating and cooling via large radiant areas, such as floor heating or active structural mass, appears to be an option (but probably a more costly one) because of lower temperature differences and the corresponding higher COPs of a heat pump. Panel cooling in humid locations will require an additional dehumidification system to prevent condensation, rendering the system more susceptible to problems.

Download: contents and sample pages (pdf 464 kB)

Details and further reading can be found in the following publication, to be ordered from

Schnieders, Jürgen: Passive Houses in South West Europe. A quantitative investigation of some passive and active space conditioning techniques for highly energy efficient dwellings in the South West European region. 2nd, corrected edition. Darmstadt, Passivhaus Institut, 2009.

Author: Jürgen Schnieders 2009, PHI

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