The latest forms of advanced window films could be amongst the best means for improving building energy efficiency during retrofits, permitting the ingress of large amounts of visible light while blocking heat.
Low-e window films have the potential to dramatically reduce building energy consumption for a far lower cost compared to other window-related efficiency solutions.
The indoor cooling of built environments comprises a significant percentage of their energy needs, especially in Australia where much of the country is beset by torrid weather for large parts of the year.
According to data from the Australian government’s Energy Efficiency Exchange, electricity usage related to heating, ventilation and air-conditioning (HVAC) typically accounts for approximately 40 per cent of total building energy consumption and 70 per cent of base building (landlord) energy consumption.
HVAC also plays a leading role in peak building electricity demand, and thus has a pivotal role regarding the billing of a given premise at peak demand rates.
This problem is further compounded in Australia by fast rising electricity costs. According to figures from the ABS Electricity Price Index, during the period from 2000 to 2014, household electricity prices in Australia surged by 174 per cent.
Given the predominant role that HVAC energy consumption plays in building utilities bills, any convenient and low-cost means of raising temperature efficiency is a definite boon for owners and occupants.
One of the most convenient means of improving building efficiency is the retrofitting or adjustment of window materials, as they are are invariably one of the lowest-rated components of the building envelope when it comes to insulating properties.
According to data from the US Department of Energy, inefficient windows account for anywhere between 25 to 35 per cent of the energy wasted by commercial buildings – a deficit which alone adds up to 10 per cent of total annual carbon emissions in the country.
While a broad variety of solutions exist for improving window efficiency, from double-glazing to the latest smart-window technologies, these measures can be quite costly when it comes to retrofits.
Depending on the nature of the window solution, the materials involved can be expensive, while the installation procedures themselves can be costly and entail extensive alteration of the building envelope.
Low-e films (the “e” stands for emissivity) could be the ideal solution for raising the energy efficiency of pre-existing windows, given their ease of installation and strong insulating qualities.
The films improve energy efficiency by means of their low levels of emissivity – the ability of a material to emit radiant energy. Because the materials emit less infrared electro-magnetic energy, their installation reduces the amount of heat that either enters or exits buildings via their windows.
According to figures from Hanita Pacific, solar heat gains in summer can be reduced by as much as 72 per cent, while during the winter months the materials can prevent as much as 24 per cent of interior heat from escaping.
As a film, the installation process for the materials during retrofits is comparatively easy and uncomplicated, necessitating little more than their placement and fixing upon the glass of pre-existing windows.
The total installed cost for window films is low, estimated by the US Department of Energy to be between $5 and $15 per square foot, depending upon the brand or type of product employed.
Because the window films are installed on the interior of the window, they do not entail complex or potentially hazardous construction set-ups, as would be the case for the construction of fixtures or structures on the outside of the building envelope.
Installation simply requires the temporary removal of occupants and furniture, the cleaning and preparation of the glass using a special mounting solution, and the application of the film, followed by a curing process that can take only a few days.
Another advantage of the latest and most advanced forms of low-e films is that they are capable of reducing the ingress or escape of heat without causing an attendant loss in visible light transmission.
This is because the material primarily targets the infrared radiation which we feel as heat without necessary affecting other forms of electromagnetic energy that are responsible for illumination. In some of the latest and more advanced forms of low-e films, visible light transmission levels can be as high as 70 per cent.
This means that windows can continue to fulfill their original function – allowing the entry of natural light from outside without severely compromising building efficiency and adding needlessly to utilities costs. Low-e films are so specific in their targeting of infrared radiation that they do not impede the plant growth in rooms where they've been installed.