How much energy can I save with WFG?

Whilst exact savings will depend on the project and location, WFG can save 60-75% of associated energy costs (heating and cooling) compared to standard double glazing.

How does WFG save energy?

Water is not only a good absorber, but it is also a very efficient material for energy transfer. Moving energy for example with a water pump is much more efficient than heating or cooling the same space, which WFG uses to its advantage.

In summer WFG absorbs incoming radiant heat (for example solar heat) from the outside and pumps it away before entering the room which lowers the demand for cooling. Since radiant heat represents 66% of the typical energy exchange through a window and is not blocked by insulation, this is why WFG has a significant advantage over standard double and triple glazed panels glass panels.

In winter the water behind the insulation layer can absorb the radiant heat escaping through the window and circulate it back. The absorbed energy can be reused for example for heating and hot water, which becomes the third and final tier of energy savings.

Does WFG only work effectively in hot climates?

Because WFG absorbs heat both entering and leaving a building, not only can it prevent excessive solar gain in hot climates, but I can also act as a more effective barrier than a simple insulating window panel. WFG is a solution for different seasons and climates and we can optimise the particular solution to the relevant climate (triple glass WFG is better suited to colder climates whereas double glass may be sufficient in hot climates).

Can you calculate the amount of energy I would save for my particular project?

Our team has developed a specific energy simulation method that enables us to calculate energy savings with water-filled glass (WFG) in any location. Our aim is currently to develop a web application which will show the savings to any visitor, but we can also currently supply estimates for any project you approach us with.

How is WFG different to other energy saving windows?

Unlike other technologies WFG does not save energy through insulation (U-value) or reflection (SHGC, shading), but through absorption. Since our innovation idea originates in Japan, we often refer to this approach with the philosophy of aikido: Our goal is not to resist or block an opponent but to use its momentum to our advantage. The same happens with WFG, the more radiant heat there is, the more absorption can occur, leading to further energy savings. This approach is not something that works against existing energy mitigating strategies. On the contrary, the absorption-based approach of WFG can complement existing systems, which is a great help not just for new builds but also retrofits.

Does Water-Filled Glass manufacture glass panels itself?

We are not glass manufacturers but rather license the use of our Intellectual Property to well established construction firms and glass manufacturers. Although the glass is novel, standard manufacturing techniques, frames and mechanical systems are used which enables us to have a straightforward supply process.

Is WFG expensive to install?

Although WFG is a new technology it uses many of the same components as traditional glazing (glass and frames) and uses mechanical systems which are already in use (for heat pumps and underfloor heating). This means that we are not much more expensive than existing triple glazing solutions while also being much more energy efficient. This gives us a lower payback period compared to other technologies as well as providing additional benefits.

What makes your retrofit solution so compelling for improving energy performance versus the alternatives?

Retrofitting buildings by improving (replacing) windows is difficult in the construction industry. Such projects require outside access as the window needs to be taken out from outside. This needs scaffolding and building permits for many projects. If there is a big proportion of glass on the façade, the building also has to be vacated for the retrofit to take place. These issues bring a lot of additional cost to the project that diminish the economic viability for such improvements. Water-filled Glass effectively mitigates all of these concerns by introducing a WFG retrofit solution that is installed behind the existing façade from the inside.

Standard glass technologies cannot do this because installation from inside would lead only to minimal energy savings. Current glass solutions save energy through insulation and reflection and adding another double glass panel to an existing one would not make a significant difference because the insulation is already there. WFG on the other hand saves energy through absorption and is therefore able to bring a significant incremental benefit.

What other benefits does WFG have apart from energy efficiency?

Unlike other energy saving solutions such as shading or tinted glass, WFG allows windows to bring in lots of natural light (which is proven to beneficial for people’s comfort, health and mood).

By preventing excessive solar gain and heat loss, WFG improves a buildings thermal comfort allowing a more pleasant and productive environment in which to live and work.

WFG reduces the impact of noise pollution. The principal of soundproofing is to use surfaces of different densities to break the sound waves. The triple glazed WFG panels are perfect examples of that.

WFG is an environmentally friendly choice. As well as having low embodied carbon and avoiding unnecessary wastage for retrofit, WFG saves 66kg of carbon saved per year per m2 installed (versus double glazing) through energy efficiency. This means a carbon payback as low as 1.5 years.

Is WFG complicated to install and maintain?

The installation of WFG has deliberately been kept as simple as possible using off the shelf components as well as standard glass and piping.


The water in the panel runs on a special closed circuit that is secured by our environmentally friendly water treatment technology. WFG uses inspected joint systems that meet the highest industrial standards and quality and are also used for special drinking water treatment technologies. WFG has more than a decade of experience in water tightness. This is the essence of our technology and that makes us unique.

Is there any risk that the water layer will freeze in cold weather and crack the glass?

The water layer is behind the insulating layer, so technically it is inside the building. The temperature indoors must be well below freezing for a long period of time for freezing to occur in case the facility is out of operation, which does not normally happen with inhabited buildings. Water-filled glass (WFG) technology is designed to use and circulate renewable energy sources to provide better comfort than a normal window and supply the building with optimal thermal energy in low temperatures in cold climates. On top of that we use special environmentally friendly water treatment technology, that prevents freezing on special climates. In case of vis major, the system can be drained and refilled any time.