**5. Conclusions**

The design of new light envelopes for zero-energy buildings must integrate different disciplines such as architectural design, building simulation, HVAC systems, and the curtain wall industry. This article developed a methodology for selecting WFG solutions for different facades and tested its performance using real data. Case 1 was a triple glazing with the water chamber facing outdoors. Case 2 was made of triple glazing with water chamber indoors and Low-E coating. Case 3 had a high reflective coating on face 2 and a water chamber indoors.


This article showed an industrialized water flow glazing unitized facade ready to be used in the architecture, engineering, and construction industries. The authors developed a simulation tool to be used at the first stage of the design process. The outputs were validated with an actual test facility placed in Sofia, Bulgaria. The difficulties identified were related to the limitations of the software for simulating the dynamic properties of WFG. The high initial cost and the need for an energy management system integrated with the rest of the equipment conditioned the WFG system. After the first year of monitoring, there are uncertainties and system issues that must be addressed. Firstly, the control unit must integrate the ventilation system to reduce condensation risks. Secondly, the presented simulation tool must be integrated into commercial building performance simulation software. Finally, further research on the deployment is needed to bring down payback periods.

With economies of scale a price comparable to triple-pane glazing systems equipped with automated exterior shading can be achieved.

**Author Contributions:** Conceptualization, B.M.S., F.d.A.G., J.A.H.R.; methodology, B.M.S., F.d.A.G.; software, J.A.H.R.; formal analysis, B.M.S., F.d.A.G.; data curation, J.A.H.R.; writing—original draft preparation, B.M.S., F.d.A.G., J.A.H.R.; writing—review and editing, F.d.A.G., D.P.; visualization, B.M.S., F.d.A.G., B.L.A.; supervision, J.A.H.R., B.L.A.; project administration, B.M.S.; funding acquisition, F.d.A.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This article has been funded by a KSC Faculty Development Grant (Keene State College, New Hampshire, USA).

**Acknowledgments:** This work was supported by program Horizon 2020-EU.3.3.1: Reducing energy consumption and carbon footprint by smart and sustainable use, project Ref. 680441 (InDeWaG: Industrialized Development of Water Flow Glazing Systems). Special thanks to the Central Laboratory of Solar Energy and New Energy Sources of the Bulgarian Academy of Science (CL SENES–BAS) for providing measured data of the solar radiation on the different facades of the test facility in Sofia, Bulgaria.

**Conflicts of Interest:** The authors declare that they have no conflict of interest.
