The heat transfer coefficient, referred to as the U-value or U-factor, measures the amount of heat transferred through parts of a building. If we look at a picture of a house from a thermal camera, you will notice that the brightest red lines, or where the heat is transferred most from, are the frames of the windows, yes, even more than the glass. Energy finds the weakest point between the walls, frames, and glass to pass from. Therefore, we talk about the frame value and glass value which combine to make the overall window value. Lower U-values mean more energy saved, lower monthly bills and a more comfortable and constant interior temperature.
The R-value is the measure of thermal resistance. This means the ability of energy to move from hot areas to cold areas via materials such as insulation, walls, windows and doors. The higher the R-value is the better that material prevents heat transfer. So in this case ,we recommend you to use thermal break windows with the lowest U-value combine with triple glazed in order to have more energy saving in our building.