Energy Codes and Glass

Reducing energy consumption in every aspect of our lives is high on the national agenda. Buildings in which we live and work consume approximately 50% of energy with correlating greenhouse gas emissions. In response to this, government has developed mandatory minimum Energy Efficiency Measures. These regulations cover both residential and commercial construction types.

Energy use modelling has shown that the selection and placement of glazing is one of the most critical elements in designing for energy efficiency. In large commercial and apartment buildings where the roof is a smaller proportion of the building envelope, treatment of glazing is the most important design consideration. Selecting the right glass allows designers to maximise light, while insulating against heat loss and selectively shielding unwanted heat gain. Choosing the right balance of these factors during the design phase will provide a comfortable, healthy and energy efficient environment for the life of the building.

The code is performance based, offering a number of paths to compliance and sets out the performance that a building has to achieve. In terms of glazing, the key focus is on minimising the rate of summertime heat gain and winter heat loss (the emphasis will shift depending on the climate). The requirements will also vary depending on the nature and type of heating and cooling systems employed, if at all.

Glazing performance is measured in terms of U Value (for conduction) and solar heat gain coefficient (SHGC), and is based on National Fenestration Rating Council (NFRC100-2001) conditions. All Viridian glass performance data presented in this catalogue is assessed under NFRC 100-2001 environmental conditions. Care should be exercised when selecting performance data to ensure that it meets these criteria.

The code also allows for a dual approach to calculating glazing system performance – either by reference to published ‘window system’ (glass plus frame) data, or by aggregation of the glass performance data and a frame adjustment (for conductance). The performance data presented in this guide is glass only.

The deem to satisfy provisions of the code are aimed at allowing unlimited mixing of glazing sizes, glass and frame types. Glazing requirements in each climate zone are a function of floor area, conductance and solar radiation of the glazing system, orientation, shading devices and window area. The code recognises high performance glazing through maximising allowable window sizes.

Generally, southern locations will often require products with high performance thermal insulation (lower U Values), while in a northern location, solar radiation (lower SHGC value) will usually be the critical component. In the more temperate locations, a combination of U Value and or SHGC could be the critical component. Viridian offers a range of products that can meet these various requirements. A simple chart reference indicating the relative performance by product for daylight transmission, thermal insulation (conductance) and solar control is shown in the glass performance data tables.

The performance data for Viridian glass is derived using the International Glass data base and software developed by Lawrence Berkley University. The international standard of measurement used is NFRC 100–2001 conditions.

The combination of the SHGC and U Value determines the performance of the glass and its energy contribution. The building structure, glass framing system and orientation will all contribute to determining the overall environmental performance of the facade and the building. It should be noted that performance data presented in this guide is for glass only and a window rating or assessment is required.

Not all manufacturers’ data is calculated using NFRC 100–2001 conditions, in particular some countries have different conditions that will impact on the glass performance.