The International Glazing Database

Click here to link to my first data viz of 2016 - the latest in a series of data visualisations and infographic blog posts on sustainable buildings that I started last year. 

This month I have begun to analyse the International Glazing Database (IGDB). The IGDB has been published by the Lawrence Berkeley National Laboratory in California for several years and now includes optical data for more than 4000 items. It is an excellent resource as it is contributed to globally, carefully scrutinised and widely referenced.

Solar vs Light Transmittance

The raw data reveals an interesting relationship between the solar and visual light transmittance properties of the glazing in the database (please note the solar transmittance is not the SHGC or g-value but a major component of these commonly referenced window properties).

Typically for buildings in temperate or hot climates we seek to limit the degree to which a building's glazing permits the transfer of solar energy in summer as this can reduce the demand for air conditioning. However we are also trying to simultaneously enable high levels of daylight to access the space. These opposing requirements can result in a challenging glazing specification.

The data reveals that the glazing manufacturing industry has impressively produced a high number of products that have a relatively high visible light transmittance whilst also offering a relatively low solar energy transmittance as shown by the curving distribution of the data.

The filters included in my analysis provided can be manipulated to reveal that there are over 700 products with a solar energy transmittance less than 0.3 (less than 30% of the sun's energy will pass through the glass) and with a visible light transmittance of more than 0.4 (more than 40% of the daylight will pass through the glass).

Who Makes This Glass?

The manufacturers (as listed in the IGDB) who produce glazing products that meet this specification are also filtered in my data viz, the top 10 are shown below.

How do Manufacturers Compare?

The difference in glazing specification from different manufacturers follows the general overall trend but the range available can differ considerably as demonstrated with a sample of glass manufacturer IGDB data below.

Is Lower Solar Energy Transmittance Always Better?

It is important to note that if a building has an effective shading strategy, glazing with such a low solar energy transmittance may not be required, given the direct solar energy would have already been blocked before it reaches the glazing.

A major advantage of limiting the summer's solar gains with external shading opposed to using these specialist glazing products is that potentially beneficial solar gains in the winter months may still be able to enter the building and reduce the demand for heating given the sun's lower trajectory in the winter. This is important to consider when specifying glazing with low solar transmittance as this glass will limit solar gains into the building all year round and potentially result in an increased heating demand.

Global Glass Giants

The glazing database also reveals the largest contributing manufacturers to the database overall which is a handy glimpse into the industry.

On this basis, the 10 largest glass manufacturers make up ~75% of the International Glazing Database.

The IGDB data includes numerous other attributes including colour, conductivity, emissivity, thickness etc and perhaps in future posts I will present further findings...