Requirements of Sustainable Building Envelope Marco Citterio Enea – ENE SIST th June

Aim of presentation To help Decision Makers in expressing their requirements to designers in early design phase of sustainable buildings

Comparison of EU countries energy consumption in building sector

European Directive about Energy Building Performance 91/2002 Aspects: Building envelope thermal and permeability characteristics; HVAC and DHW plants; Efficient Lighting (specially in NR buildings); Building location and orientation, climate characterization included; Passive solar systems; Solar shading systems; Daylighting; Natural Ventilation; Indoor Environment Quality.

“These (buildings) are properly designed, when due regard is had to the country and climate in which they are erected. For the method of building which is suited to Egypt would be very improper in Spain, and that in use in Pontus would be absurd at Rome: so in other parts of the world a style suitable to one climate, would be very unsuitable to another: for one part of the world is under the sun's course, another is distant from it, and another, between the two, is temperate.” “In the north, buildings should be arched, enclosed as much as possible, and not exposed, and it seems proper that they should face the warmer aspects. Those under the sun's course in southern countries where the heat is oppressive, should be exposed and turned towards the north and east. Thus the injury which nature would effect, is evaded by means of art.” Marcus Vitruvius Pollio: de Architectura, Book VI,1,1-2 I st century B.C.

Could you tell where these buildings are located?

Indoor microclimate control can be obtained by means of interaction of passive measures (mainly involving architectural, morphological and building technology related variables) active measures (related to technological plants) Active and passive measures should be balanced in order to obtain indoor comfort conditions by means of right amount of energy and resources

Building envelope and thermal inertia Each envelope and building structure element has thermal capacity: capability of storing thermal energy and delaying heat transfer.

Heavy structures have longer time response and limited thermal excursions in comparison to “lighter” structures. This fact helps to limit indoor temperature fluctuations due to seasonal and daily outdoor temperature variation.

Energy consumption of buildings with high thermal inertia in cold or warm climates can be considerably lower than energy consumption of lighter buildings. Thermal energy storage in building mass sometimes allowes to shift the time of max cooling energy demand to time when building is not in use.

The time lag φ represents the temporal delay of peak heat flow of actual wall compared to instantaneous heat flow of a wall with zero capacity; Decrement factor µ represents the ratio between max heat flow of actual wall and max heat flow of zero capacity wall.

Φ and μ in function of mass and Uvalue

Effectiveness of thermal inertia increases accordingly to day-night thermal excursion. In warm climates, walls store heat during the day and release it during the night: that is particularly effective in the case of building used during the day only. Thermal mass can also cooled by way of night ventilation (natural or mechanic) In cold climates, thermal mass helps in storing solar energy during the day, and mitigates indoor climate during the evening and the night.

Influence of positioning thermal insulation on walls thermal inertia Wall typeInsulation positioning  [h] Supporting walls with concentrate insulation Internal0,2811 Intermediate0,2211 External0,2011 Non Supporting walls with concentrate insulation Internal0,488 Intermediate0,448 External0,448 Multilayered envelope walls Insulation thickness: 6 cm 0,754 Windows10

Building shape and orientation The right building orientation; The appropriate building shape; Rational spatial and functional organization of internal environments; can allow, with no extra costs: significant energy saving (30 – 40%) better indoor comfort

Building shape Building should have the lower possible ratio between losing envelope surface and enclosed volume

Take into account effects of prevailing winds due to building shape and boundary condition.

Building orientation The best solution is to orient the main building axis on east-west direction; South façades receive more solar radiation during winter (when the sun height is lower) than in summer.

Amount of solar radiation on different oriented surfaces for different latitudes

Example of good internal layout of a residential building

Solar shading control Transparent envelope and solar shading control can be obtained by means of: dimensioning and placing the right amount of glazed surfaces on different orientations choosing the right glass characteristics (even accordingly to facade orientation) Adopting solar shading systems (preferably external)

Glazed surfaces on North, East and West orientations should be dimensioned with the purpose of providing the right amount of daylighting. On North orientation, rarely reached by beam solar radiation, it is important –to provide excellent thermal insulation –to limit glazed surface dimensions

Dimensioning glazed surfaces on South orientation, the right amount of daylight is not the matter: –Windows can be enlarged in order to improve solar gains in winter. –Solar shading adoption is anyway a must in order to limit and control solar gains during summer. –Good Uvalue should be adviceable, in order to limit thermal losses in winter.

Type of glasses The choice of glass typology is an important issue: –Different kind of glasses available on the market, with variable optical characteristics, can fit with needs of different climate conditions (Selective glasses)

Influence on PPD per different glass types during a sunny winter day Glass typeΔPPV Radiant asymmetry ΔPPV Direct radiation ΔPPV Convection ΔPPV Total Light 3 mm Light 3 mm + Air 13 mm + Light 3 mm Light 3 mm + Argon 13 mm + Low Emissivity 3 mm Selective 3 mm + Argon 13 mm + Light 3 mm

Solar shading External solar shading systems should be preferred: they shade solar radiation before it comes into the building.

On SOUTH orientation shading systems have to be horizontal: they are effective in order to limit solar gain during summer and allow solar gain in winter

On EAST and WEST orientations vertical shading device have to be adopted. They shade solar radiation during early morning and late afternoon during summer.

Thanks for your attention Acknowledgment: Simone Ferrari: “Progettazione Eco-sostenibile dell’involucro dell’edificio” - Progetto SICENEA JRC – Directorate General for Energy (DG-XII): “Passive Solar Architecture for mediterranean area” THERMIE PROGRAM Commission of the European Communities, Brussels 1994