One of the most important factors for measuring the performance of building glass is the U-Value, U or U-Factor, which actually indicates the degree of insulation of the glass, or in other words, the amount of heat loss through the glass wall due to the temperature difference between the outside and the inside of the building. be

The U-Value number shows us how a double-glazed unit or IGU maintains the cold or heat of the indoor environment and whether it works effectively or not. The smaller the U-Value number and the closer to zero, it indicates this. is that glass works better in terms of insulation.

U-Factor is usually in the range of 0.1 (very little heat loss) to 1 (high heat loss), which in BTU (British Heat Measurement System) system is equal to the amount of heat that comes from one square foot of glass per The degree of heat loss inside and outside the building is measured.
But what is the difference between U-Value and R-Value factors? And how do we use each one?

Usually, we use U-Value to measure double or multi-walled units, but R-Value is mostly used to measure other materials and materials used in the building, such as walls, floors, ceilings, etc.

There is a mathematical relationship between U-Value and R-Value. In fact, these two factors are inverse of each other, so if the lower U-Value indicates more effective thermal insulation, in this case, the higher the R-Value indicates thermal resistance. Above it is material.

To calculate R-Value, we must divide 1 by U-Value. For example, 0.10 in U-Value is equivalent to 1 (01/1). The same relationship is used to calculate U-Value.

Solutions to reduce U-Value and improve thermal insulation

U-Factor index in summer days and winter nights are two common and widely used factors. U-Value measures the hot environmental conditions outside the building under direct sunlight on summer days. The lower the U-Factor number in this case, it shows that the glass works better in preventing the heat-generating rays of sunlight inside. and has actually increased the efficiency of air conditioning systems as well as energy efficiency.

U-Value measures the cold conditions outside the building without sunlight during winter nights. The lower this number is, it means that the glass is more successful in keeping heat inside the building and has increased energy efficiency.
Some of the ways to improve U-Value are:

     Using double or multi-wall units instead of using single-layer glass
     Using an inert gas between two glass walls, such as argon
     Using warm-edge spacers instead of aluminum spacers to prevent the creation of thermal bridges
     Optimum considering the distance between two glasses, the distance of 20 mm is the most common size, which is effective in both cases when the cavity is filled with air or with argon gas.
     Using glass with Low-e coating

This note is based on an article on the website https://www.vitroglazings.com.