As electricity costs soar and ever-higher comfort levels are expected by building users, the replacement of old glazing systems with superior modern products makes more sense than ever. JOHN POWER explores the issues surrounding glass and glazing retrofits.
Retrofitting glass windows and façade systems used to be considered a discretionary element of any major refurbishment. Today, the replacement of inefficient, poorly functioning glazing is seen as an essential component of any serious building upgrade.
There are powerful arguments for undertaking glazing upgrades as a first priority, given that the enhanced performance of improved glazing will establish the minimum requirements for all subsequent heating, cooling and shading systems.
In this article we will examine some typical signs that glazing may be in need of an upgrade, and consider the main design and material options (and costs) of new systems. We will conclude with some practical advice about how to make sure you get what you pay for, and whether the glazing system installed is fit for purpose, fully compliant and installed by an accredited glazing professional. We will also present an overview of some of the latest architectural glass and glazing products to hit the Australian market.
IS THERE A PROBLEM?
One of the difficulties facing facilities managers is uncertainty about the state of the existing glass and glazing in a building: is it adequate and is it fully compliant?
According to façade engineering expert, Stefan Brey, an environmental design consultant at BG&E Facades in Melbourne, there are two obvious signs that existing glass and glazing systems are performing poorly. First, users complain about poor comfort and amenity due to excessive heat or cold, wide temperature fluctuations and glare, among other factors; and, second, energy costs appear high compared to other buildings or other sections of the building.
“Basic thermal performance of the window might be one driver for action,” Brey says. “There might be reports about people being uncomfortable; for instance, on certain days a room is just unusable even when the blinds are pulled. That might be one starting point.
“On the other hand, you have the energy efficiency and heat gain conditions to consider. In order to measure these you could get an energy audit done, or undertake some sub-metering of air-conditioning systems to work out how much power a specific component consumes in terms of chillers, fans and pumps.”
SIGNIFICANT SAVINGS ACHIEVABLE
According to Brey, it is possible to achieve clear financial and energy savings by replacing poorly performing glass and glazing systems with high performance options.
“Where there is a lot of glass facing east, west or north, the opportunity to achieve energy savings by upgrading the glass is the greatest. If the building is old, say 20 or 30 years old, and fitted with the most basic 6 millimetre clear glass with an aluminium-framed window system, then, generally speaking, you should be looking at 25 to 30 percent savings in electricity consumption as a minimum for air-conditioning for any system that’s dedicated to the perimeter of the building, say 5 metres in from the façade. Significantly higher savings in electricity cost could be achieved where the old glass can be replaced with the latest performance glazing,” Brey notes.
“Specification of performance glazing could also facilitate a reduction in HVAC system size and capacity, providing an immediate gain on the cost of the project. Usually savings in capital and ongoing costs lead to very short payback periods for any investment in an advanced glazing system,” he adds.
PINPOINTING PERFORMANCE REQUIREMENTS
“If implemented properly, the design process should generate minimum performance specifications for glass that are compatible with architectural intent or vice versa. Performance requirements should be specified to satisfy the needs of heating and cooling loads, aesthetics, thermal comfort and access to natural daylight,” says Brey.
“Low-emissivity (low-E) coatings on glass now play an important role. Low-E soft coatings can be incorporated with a clear double-glazing to reduce solar heat gain through glass, typically by 40 to 60 percent relative to clear single glazing, without significantly compromising clarity and transparency. However, depending on the type of air-conditioning system or orientation and exposure of the façade, this is often not enough,” he adds.
“The next step would be to include a tint as well as the low-E coating. A reduction of solar heat gain through the glass of 75 percent is now possible. Different types of tint can provide a similar degree of solar heat gain control, but significantly different levels of daylight transmission. High performing laminates with good thermal properties can also be used, providing a solution where there is a requirement for single glazing.”
Brey notes that understanding the multitude of configurations and variations of glazing systems to meet and exceed performance targets requires skill and knowledge, and that the answers are often prescriptive and unique to a project. “Whatever framing and glazing system you choose, ensuring that your combined system is operating as intended and fully compliant with Australian Standards is essential,” Brey states.
VERIFYING COMPLIANCE
Quality assurance is another matter of great importance when commissioning projects or verifying the integrity of products. Quality refers to professional and appropriate installation practices as well as the assurance that glass products conform to labelled specifications and comply with all current Australian Standards.
“The first step is to confirm whether the measured spectral data, the measured properties, are available in the International Glazing Database (http://windows.lbl.gov/g/IGDB/default.htm), which is a database managed by the National Fenestration Rating Council (NFRC) in the US,” says Brey. “A lot of our local Australian processed glass is in that database. And that’s always the first check that anyone should do.”
According to Brey, if the data and the performance are not verified in the International Glazing Database, it is advisable to send off a glass sample to get it measured. He notes that this can be done at the University of Technology Sydney (UTS). “The cost may be around $2000 and it can be done within a few days. Taking these extra steps to ensure compliance with Australian Standards is essential,” he states.
Brey also suggests that facilities managers contact the Australian Glass and Glazing Association (AGGA) for guidance regarding compliant products and reputable installers. While there is no single independent certification scheme in Australia referencing all glass products, Australian Standards and Building Code requirements must be followed at all times.
Even the most skilfully prepared specifications are meaningless if products and installation practices do not comply with designated performance and rating requirements. The AGGA is leading a renewed focus of attention on non-compliance, urging all builders, developers and specifiers to avoid risks by choosing only reputable AGGA member companies as their preferred manufacturing partners, suppliers and installers.
AGGA’s executive director, Nigel Carpenter, states, “Retrofits involving glass and glazing can enhance energy efficiency, add significant value to a building, and make it more appealing and comfortable for tenants and users. The AGGA website provides advice on how to source appropriate products that are compliant, fit for purpose and from a reputable supplier. We can also provide details of AGGA-accredited professional, skilled local installers.”
Carpenter adds that the certification of glazing products is another contentious issue, and that the building and construction industry needs to be extremely cautious. “Ensure supporting certification is legitimate and, most importantly, from a reputable certifier – one that knows and works to the Australian Standard.”
NEW GENERATION PRODUCTS
Some fascinating new products have reached Australia recently, including dimmable glass products that allow users to manually or automatically change the tinting levels of glass.
“We can now specify a dimmable electrochromic glass that goes from very clear to quite dark with excellent solar heat gain performance,” Brey notes. “The tint can be controlled by an external sensor that reads the level of solar radiation, or manually controlled with a switch, or both.”
Another interesting development is thermochromic glass, says Brey, which involves a similar idea, except that instead of the glass being switched by electric current, it responds to temperature. “As the glass heats up in the sun, it will develop a tint to improve its performance in terms of heat gain control,” he explains.
Brey also commends the new generation of triple silver low-E coatings. “These coatings, which are designed for double-glazing applications, offer a very good balance between daylight transmission through the glass and solar heat gain control. All the major suppliers have a version of a triple silver low-E,” says Brey.
“Selecting the right glazing product involves far more than taking the cheapest option. Be excited and embrace new glazing technologies, but we urge you to be cautious, do your research and demand proof of compliance,” Carpenter concludes.
