Improving the Energy Rating
Manufacturers of BFRC Rated windows using the BFRC label and A-G rating scheme often want to improve their rating to improve consumer choice.
There are a range of competing technologies available to improve Energy Rating and this page attempts to give guidance on the relative benefits of each technology.
The incremental performances are relative to those of a current domestic style `Part L window' achieving a U-value of 2.0, which is taken to be a 3-chamber PVC-U window, with a 4/16/4 air-filled DGU comprising hard coat low E.
It is important to realise that the improvements suggested are not necessarily cumulative. Using two technologies together will not necessarily result in the sum of the improvements suggested.
In some cases the technologies are mutually exclusive and using one technology will prevent the use of another technology.

Current technologies

Argon fill
Argon filling cannot be carried out through some warm edge spacers but gives good thermal performance improvements.There is a need for the DGU manufacturer to buy and install filling equipment.

Warm edge DGU spacers
These are a simple method for gaining an increase in the BFRC Rating but they can reduce the mechanical strength (and hence wind resistance) of the DGU. Some types of spacer do not enable Georgian bars to be used or are not compatible with textured glass.

Very low emissivity (e0.02-0.04) glass
This is a soft coat glass and will have a major impact on DGU and safety glass manufacturing processes.The material has a limited shelf-life prior to making into DGU, manufacturers will need to install edge-deletion equipment, there is increased process wastage and it is currently uncertain that all products can be satisfactorily toughened.

Low iron glass
This is not currently manufactured in UK and current UK glass plants would require modification, which can only be done at the time of a major tank rebuild.The glass also has a longer cycle time for toughening.

Krypton fill
Krypton filling gives full performance in narrower than normal cavities but a 100% fill is essential, otherwise there is a rapid fall-off in effectiveness.There is a long lead time for krypton supply to meet the market needs.
Triple glazing units for current framing systems
(eg 4/8/4/8/4)
The weight of DGU increases by 50% resulting in window size limitations, more substantial window hardware being needed and Health & Safety implications when lifting.The larger units would effectively double the cycle time unit manufacture and halve the rate of throughput.

Frame technology
There is potential for small improvements in all frame systems. However, due to Building Regulations and current standards for safety, durability, security and wind loading, these are unlikely to offer any improvement greater than 0.1 to 0.2 of a U value for the frame (and therefore less impact on the whole-window U value).
Many of the improvements that can be made are not obvious and thermal simulation is needed to determine the best design for energy efficiency.
Combinations of materials could also increase this benefit but recycling issues would tend to prevent their development. Most available technology developments within the current range of sealed unit widths have already been adopted or are rapidly being adopted.

Air leakage improvements
Air leakage improvements can be made by improving the sealing of the opening lights to the frame. Improved gasket design and improved materials are already possible but need wider application.