Technology Assessment of Electrochromic Glazing for Energy Efficiency, Thermal and Visual Comfort

Project Key Words:
Electrochromic Glazing for Energy Efficiency, Thermal and Visual Comfort
Prof. Man Pun WAN
Organization:School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore
Designation:Associate Professor
Project Period:
12/07/2019 To 04/06/2020
Project Description:

Buildings and construction together account for global energy use of 36% .Thermal properties of building facade have significant impact on the cooling and heating loads as well as the lighting loads. Facade, accounts for almost 50% of the thermal loads in buildings in the tropics. Electrochromic glazing (EC) can dynamically modulate the solar energy entering a building by adjusting its tinting state, which influences the visible transmittance and solar heat gain coefficient (SHGC). Due to this adjustability, EC provides the potential for optimisation of solar heat gain and visual comfort. This research project hence aims to further understand the performance of EC glazing facade against an advance spectrally selective low-emissivity double glazing unit (DGU).

The objective of this controlled laboratory evaluation was to analyse the EC glazing operational characteristics and energy savings potentials in the tropical context. The study focuses on the investigation of facade performance of EC glazing in terms of heat gain and its impact on thermal and visual comfort. The impacts of EC glazing on lighting and air-conditioning energy consumption is also analysed.

EC glazing’s ability to modulate the solar heat gain through the window, reduces stress on HVAC and other equipment. EC window require low-voltage power to modulate between it clear and dark state. In the clear state, more solar radiation is transmitted in to the interior. A high transmission is desirable for admitting daylight during the time of the day when sun is not shining directly into the space and during overcast periods. In the tinted state solar radiation is absorbed, to reduce heat transfer to the interior.

Following are the advantages of EC glazing system-

a. EC glass reduces heat gain by tinting the glass instead of covering the window with opaque shading elements like blinds do. This provides advantage in maintaining the exterior view.

b. Provides energy saving potential.

c. Better thermal comfort by enabling zonal control of occupant temperature.

d. Better visual comfort by tint modulation to control glare at occupant viewing position.

The EC glazing was evaluated against the reference technology, DGU along with blinds, through a controlled laboratory monitoring at BCA SkyLab, Singapore. The SkyLab facility consists of two test compartments designed to replicate a typical office interior environment. The testing was performed for two different window orientations (North and West) to represent the majority of the buildings in Singapore. Monitored data related to energy consumption, heat gain, weather, comfort was collected to conduct an exhaustive study of the EC glazing performance in tropical climate.

Compared to traditional double glazing with indoor solar protection, Halio was able to:

-   eliminate 100% of the of glare experienced with double glazing and retracted blinds;

-   save 17%-25% on lighting energy compared to double glazing with closed blinds;

-   deliver good thermal comfort (PMV in category B per ISO 7730) for 95% of the time, compared to 75%-78% for double glazing.

Lead Organization:
Nanyang Technological University, Singapore
Project Impact
The EC glazing is a prospective facade solution for Singapore tropical climate since it exhibits higher energy saving potential when compared to DGU+CB without compromising on visual and thermal comfort of the occupants. Daylight glare is one of the critical issues in highly glazed office buildings in Singapore. Conventional technologies like manual blinds hinders the daylight harvesting and related energy savings potential while eliminating glare discomfort. This deficit can be tackled optimally by employing EC glazing which does not compromise on the exterior connectivity while eliminating glare successfully. EC glazing performance is highly dependent on local weather and orientation of window. The control mechanism of EC glazing should be fine-tuned according to these factors to achieve acceptable performance. The current provision in the ETTV calculation as per “BCA code on Envelope thermal performance in buildings” underestimates the thermal transfer through envelope and has no allowance for dynamic glazing like EC glass. It is therefore, more prudent to consider the annual average SHGC in case of EC glazing instead of static SHGC of the clearest tint, in order to account its advantage in ETTV calculation and to represent a more realistic scenario. Lower SHGC reduces heat gain and high VLT enhances daylight ability; the lower the SHGC (eg. tinting of glass), higher is the reduction of VLT. A proper combination of these two properties is thus required for balancing both heat gain reduction and daylight transmission. The theoretical limit is VLT 60% and SHGC 0.25. Hence, the performance benefit of EC glazing depends on the control with respect to combination of these properties. EC glazing should be programmed to optimise both thermal, visual comfort with as minimal energy consumption as possible. Splitting the EC glazed facade into multiple sections is one of the ways that allow better flexibility to control daylight, outdoor view and thermal comfort.
Project Website
Project status:
On-Going Completed Terminated
Project Outcomes:

This study shows that EC glazing facades could effectively utilise daylighting and reduce heat gain to provide energy benefits without compromising on visual and thermal comfort. EC glazing facade could also maintain good visual comfort (DGP below 0.35) without the need for internal shades, which is beneficial for good exterior visual connectivity. The results of this study provide performance evaluation data of EC glazing in tropical environment to support decision making for industry adoption.

Corresponding Author

Mr David Yim, Manager of AGC Asia Pacific Pte Ltd, E-mail:

Disclaimer of Building and Construction Authority

This content was prepared by the project team. While this document is believed to contain correct information, neither Building and Construction Authority (BCA), nor any of its employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favoring by BCA. The views and opinions of authors expressed herein do not necessarily state or reflect those of BCA.