What is Uw,corr – Uw,rb?
Recently, there has been a lot of talk about what Uw,corr – Uw,rb is. As we saw in our article how to reduce the cold entering through frames, the thermal insulation of a frame (balcony door or window) depends on whether the external covering (roller shutter or blind) is closed. We have different thermal losses if our roller shutters or blinds are open and different if they are closed (see the article for a comparison on the same frames).
What is Uw,rb?
But what is Uw,rb? Uw shows us the thermal transmittance – thermal insulation coefficient of the frame (aluminum profile + glazing) while Uw,rb shows us the thermal insulation coefficient of the entire frame (aluminum profile + glazing + closed external covering, roller shutter or blind)
with the external covering (roller shutter or blind) when it is closed. In short, it shows us the thermal insulation of the frames when the blinds or roller shutters are closed. Uw.rb. is derived from the formula:
Uw,rb = 1 / (1 / Uw) + Rrb
Where:
- Uw,rb[W/(m²·K)] : the thermal transmittance coefficient of the frame with external protective coverings in the closed position,
- Uw[W/(m²·K)] : the thermal transmittance coefficient of the frame,
- Rrb[W/(m²·K)]-1 : the thermal resistance provided by the use of the external protective covering.
What is Uw,corr?
The Uw,corr. of a frame is the thermal transmittance – thermal insulation coefficient, which shows us the overall performance of a frame with both open and closed external coverings. As mentioned above, the frame has different thermal behavior with the external coverings (blinds or roller shutters) closed and different with the external coverings open. The Uw,corr. shows us the overall performance of the frame (an average throughout the day) based on standard TOTEE 20701 – 2/2017. Uw.corr. is derived from the formula:
Uw,corr. = Uw x (1 – frb) + Uw,rb x frb
Where:
- UW,corr.[W/(m²·K)] : the corrected thermal transmittance coefficient of the frame with the use of a roller shutter or external covering
- UW,rb[ W/(m2K) ] : the thermal transmittance coefficient of the frame with the roller shutter or external covering in the closed position
- UW[ W/(m2K) ] : the thermal transmittance coefficient of the frame
- frb[ – ] : the usage coefficient of the roller shutter or external covering (in percentage terms), which is taken as 0.5.
What is the Urb of the roller shutter box?
Urb in W/(m²·K) expresses the thermal transmittance (thermal insulation) coefficient of a roller shutter box
