Vacuum Insulated Glazing in Energy Efficient Buildings
December 14, 2018
Vacuum glass or more correctly, vacuum insulated glazing is an emerging technology aimed at meeting the severe thermal performance requirements of net-zero energy windows. By creating a vacuum between panes of glass, thermal efficiency and sound insulation is maximized as no gas enters the space.
A smart triple vacuum glazing that can be placed over windows of buildings to reduce the thermal transmittance value (U value) of 0.33 Wm-2K-1 (a decrease of 88.21% of U value if compared with triple-air filled glazing) has been developed by Dr Saim Memon.
The UK domestic housing stock consumes more space-heating energy than any other sector, with 27 million houses in the UK accounting for approximately 66% of total natural-gas consumption.
Despite the retrofitting of a number of housing stock insulation methods and improved heating systems, there is still scope for curtailing space-heating energy loss. Progressive technologies – such as the smart triple vacuum insulated glazing discussed here have a clear role to play in providing energy efficiency that also meets customer expectations.
What is triple vacuum insulated glazing?
Triple vacuum insulated glazing (TVIG) has an ability to reduce thermal heat flow between the warm side and cold side of the window, i.e. to provide high thermal insulation or lower U value. It is said to be smart because it is constructed with three sheets of 4 mm thick glass, with an evacuated cavity of less than 0.1 Pa, separated by 0.13 mm high and 0.3 mm diameter stainless-steel support pillars. The edges are sealed with hermetic glass-alloy seal.
With a U value of ≈ 0.33 Wm-2K-1, TVIG can be retrofitted to existing buildings If we were to compare it with triple air-filled glazing, which has a U value of 2.8 Wm-2K-1, then it would decrease the U value by ≈ 88.21%. It would also allow an increase to the window-to-wall area ratios because of its U value being closer to that of cavity wall insulation for improved day-lighting.
According to research, when compared to conventional glazing types, dwellings retrofitted with triple vacuum glazings show a dramatic decrease of space-heating load and moderate increase of solar gains. The space-heating annual energy cost of a single glazed dwelling was minimised to 15.31% (≈USD 90.7) with the retrofit of triple-vacuum glazings. An influence of total heat-loss through the fabric of a solid-wall dwelling was analysed with steady-state calculations, which indicates a fall of 10.23 % with triple vacuum glazings compared to single glazings.
Challenges of vacuum insulated glazing
However, Dr Saim Memon, a Senior Lecturer in Electrical Engineering at London South Bank University, says it’s one thing having a triple vacuum glazing technology and another thing to persuade the mass market to invest in this technology. The primary concern is the tendency for some gas molecules remaining in the cavity to react when exposed to sunlight and/or under extreme climate conditions for longer time periods due to the production of carbon monoxide inside the cavity that degrades the vacuum layer affecting U value.
It is obvious that triple vacuum glazing is exposed to sunlight and thus must be designed to withstand different climates and temperatures to avoid degradation of the vacuum. Further research is required to investigate and improve the durability and duty cycle of the triple vacuum glazing with the use of non-evaporable getters, that absorb gases outgassed from the internal glass surfaces in the cavity provide long-term stability of vacuum pressure of TVIG, and cost-effective hermetic edge sealing materials.
References
Memon, S., Farukh, F., Kandan, K. 2018. Effect of Cavity Vacuum Pressure Diminution on Thermal Performance of Triple Vacuum Glazing Appl. Sci. 8(9), 1705.
Memon, S and Eames, P. C. 2017. Predicting the solar energy and space-heating energy performance for sold-wall detached house retrofitted with the composite edge-sealed triple vacuum glazing. Energy Procedia (122) 565-570.
Memon, S., Farukh, F., Eames, P. C., Silberschmidt, V. V. 2015. A new low-temperature hermetic composite edge seal for the fabrication of triple vacuum glazing. Vacuum (120) 73-82.
Dr Saim Memon is a Senior lecturer in Electrical Engineering at London South Bank University, UK. He studied BEng(hons) in Electrical Engineering, MSc in Mechatronics (Staffordshire University, UK), PhD (Smart Vacuum Insulated Glazings) (Loughborough University, UK) and PGCert in Teaching Qualification FE (University of Aberdeen, UK). He is a Fellow of Higher Education Academy and has a Qualified Teacher status by General Teaching Council for Scotland (GTCS).
