Heat transfer coefficient


Source: Schott Solar AG
The "U" thermal transmittance coefficient is the measurement unit for determining the loss of heat in a building element.
It expresses the quantity of heat which crosses a square metre of a building element per second for a temperature difference of 1°C between internal and external air.
The lower the value, the higher the thermal insulation. Typical values vary between 6W/m2K for a simple glass window to 1W/m2K for a double glazed low emission window.


Photovoltaic product from Ertex Solar with information on the "U" value

Source: Ertex Solar

Comparison of the heat transmittance coefficient for different glazing configurations and a double glazed photovoltaic module (a-Si)

  U-value (EN673)
[W/m2K]
   Single glass pane or laminated glass 5.6
   Double glazed unit without low-e coating 2.7
   Double glazed unit with low-e coating 1.2
   ASI THRU double glazed unit 1.2
   sc-Si photovoltaic module with insulated glazing 1.1
   a-Si/a-Si photovoltaic module with insulated glazing 1.1
   a-Si photovoltaic module with insulated glazing 1.2
   Micromorph photovoltaic module with insulated glazing 1.2

Source: Schott Solar AG & ISAAC-SUPSI

Examples of thermal transmittance values as a function of the specific characteristics of an integrated photovoltaic module fro transparent roofs and facades

Source: Ertex Solar