Water-filled glass can ‘revolutionise building design’ and performance when used as part of a wider heating system.
This is the claim of Loughborough University’s Dr Matyas Gutai who has been researching the concept for over a decade. The latest research – published in Energy and Buildings – has been conducted in collaboration with Dr Abolfazl Kheybari from the University of Kaiserslautern.
Water-filled glass involves a sheet of water being trapped between a panel of glass. The research reveals that WFG systems perform well in any inhabited climate – keeping buildings in hot climates cool, and buildings in cool settings warm – without requiring an additional energy supply.
Dr Gutai developed the concept while studying for a PhD at the University of Tokyo after being inspired by rotenburo, which are Japanese outdoor hot spring baths. He developed the idea into a working design and then created two prototype buildings in Hungary and Taiwan that use WFG as part of a larger mechanical system.
The water-filled glass system involves connecting the water-filled window panels to a storage tank using pipes embedded in the walls, so fluid can circulate between the two. This system allows the ‘Water Houses’ to cool and reheat themselves, without needing an additional energy supply for most of the year.
When it is warm, the buildings stay cool as the water absorbs external and internal heat; this warm water is then circulated to the storage tank.
According to Loughborough University, the heat is stored in the tank and, if the temperature drops, it can be brought back to the walls to reheat the building using a monitoring system similar to central heating. Alternatively, the stored heat can be used for hot water supply.
The reason why this process saves energy is because water absorption and pumping take much less energy than HVAC systems. The technology is also claimed to have other benefits, including acoustics, less need of ‘shading’ (methods used to avoid overheating and the greenhouse effect), and there is no need to colour the glass to improve energy efficiency.
Dr Gutai has developed a more sophisticated version of the system by adding a heat pump, which can heat and cool the water depending on the season, which is examined in the latest research paper. He joined Loughborough University in 2017 and has used data gathered on the two Water Houses to develop a simulation system that can evaluate the energy performance of such structures.
His latest paper uses simulations to compare the performance of the WFG system (with heat pump) against a typical building heating system (i.e. windows paired with gas heating and air conditioning).
For the study, Dr Gutai focused on the annual energy consumption for a typical office space (17.5m2) with one glazed façade of equilateral orientation (south in the northern hemisphere). He used the simulation to explore how this office with a WFG system would fair in 13 cities from all major climate regions – tropical, dry, temperate, continental and polar.
For the traditional systems, Dr Gutai looked at the performance of double glass window with low-e (a type of radiation coating), and triple glass – which are filled with argon.
The main findings of the study are that the WFG system uses the absorption of the water effectively to improve the energy performance of glass, and that the water layer lowers the load for heating and cooling effectively, minimising daily and seasonal peaks.
Simulations also highlighted that current glass technologies could lead to bigger energy savings if more focus was put on improving solar absorption as opposed to insulation.
In a statement, Dr Gutai said: “Glass is currently a liability in buildings as it compromises energy consumption, thermal comfort, acoustics and other aspects. WFG changes this paradigm and turns glass into an opportunity for sustainable construction.
“It shows us that thinking holistically about buildings and building components leads to a more efficient and sustainable built environment.
“In case of a window for example, if we see it as an isolated system, solar overheating is a challenge that needs to be remedied with cooling. If we approach this holistically, the heat surplus is an opportunity because the same heat is missing from somewhere else [a colder part of the building or hot water supply].”
Dr Gutai is now looking to develop this technology into a product and is working with colleagues in academia and enterprise to achieve this goal.