Thermal comfort has two components:
- Control of sun heat over the summer months.
- Reduction of heat loss over the winter months.
Control of solar heat in the summer is determined by the total solar factor of the window gtot (glazing + level of solar control).
This accounts for the transmission, reflection and absorption factors at play. These factors are assigned an index indicating whether they relate to visual properties (light) (index factor = v(isual)) or solar properties (energy) (index factor = e(nergy)).
For calculating the total solar factor, we employ the calculation method set out in EN 13363 - 1. The solar factor, also known as g factor, measures the flux of energy transmitted through the glazing. The value is a coefficient measured between 0 and 1. The total solar factor therefore measures the effect of the overall system (window + curtains or blinds) in heating the room.
The lower the total solar factor, the lower the amount of solar heat.
In the case of a single-glazed window setup with a Montecarlo-type curtain, the gtot = 0.37.
A room's temperature is influenced by a number of factors, such as its surface area, the outside temperature, the number of people present, the walls and the floor’s respective insulation factors and the presence or absence of heat emitters.
A rough estimation - taking the above into account - is that if the temperature were to rise from 20°C to 30°C in a room with single-glazing or curtains (g = 0.59), installing a Montecarlo-type curtain, for example, could limit the temperature rise to 20°C + (0.38/0.59)*10 = 26.4°C. By reducing the gtot from 0.59 to 0.37 , the temperature increase is limited to +/- 35%.