Electro-chromic windows: For the use in buildings GESIMAT gives a possible energy saving of about 40% of average energy demand for air-conditioning (this number was derived for the very hot Californian climate). The electric energy needed for window switching is about 20-150 Ws/m2 and can therefore be neglected.
The corresponding effect for an application in railways is difficult to assess. The following estimate gives a rough potential.
As an annual average, cooling to make up for sunlight induced coach heating will in most cases be less than 10 % of climatisation energy.
Assuming that smart windows reduce incident light by some 50%, they may save about 5 % of the climatisation energy.
This yields a saving potential for total energy consumption of about 1 % (taking into account that climatisation energy comes to 20% of total energy consumption). |