Cooler buildings and lower bills in summer thanks to green walls and roofs

Sourced from Modern Diplomacy

A 15% cut in the energy bill with a 40% reduction of the direct solar radiation in dwellings and a lower indoor temperature by up to 3 degrees thanks to plants grown on roofs, balconies and external walls. These are part of the outcomes of the Italian pilot project ENEA is conducting at its research center near Rome.

“We developed a green wall based on an extensive roof-garden system and a self-supporting structure positioned at 50cm from the wall of the School of Energies building, where we conduct training courses”, Carlo Alberto Campiotti at the Department Unit for Energy Efficiency, said. “Successively – Campiotti went on – we’ve begun to study the interactions among green coverings, energy flows, the microclimate and indoor comfort, diversifying the species”.

The “plant system” installed on walls, roofs and balconies, has proved capable of creating an actual insulating pad enveloping houses and condos; in this way vegetation can mitigate temperature peaks during summer, capturing most of solar energy, which doesn’t directly hit the building surface, dissipating through evapotranspiration of plants a large amount of thermal energy (up to 1 liter of water daily per square meter) which would otherwise be absorbed by the building and released as heat inside the house.

“In summer this vegetation system allows to reduce up to 15% of energy for cooling- Campiotti pointed out- while in winter savings for heating reach 10% thanks to the chimney effect between the wall and the vegetable blanket; in practice, a natural ventilation system removing moisture from walls and reducing the thermal dispersion of the building”. Each plant has its own type of leaf given by color, thickness, shape, arrangement on the stems and biological cycle, which determines the amount of solar radiation it captures instead of hitting the walls of the building.

The parameter defining the energy and bio-agronomic traits of plants is called green factor (kv) and it varies from a minum of 0 to a maximum of 1. In practice, if kv is 1, it means the green mantle doesn’t exert any shielding towards solar radiation and, in summer conditions, the temperature of the external wall is superior to both that of the air and that inside the building; but if the value is zero, it means that vegetation exerts a total shield and the temperature of the wall is equal to that of the air.

Click here to read the full article