**4. Discussion**

When the glazing is part of an insulated room, the thermal problem of the glazing is coupled with the thermal problem of the room, and the indoor temperature should be determined. The indoor boundary condition disappears to be part of the solution to the thermal problem. The prototype was a rectangular room with glazing facing south. The dimensions of the room, the near and far-infrared absorption (αNIR, αFIR), and the thermal transmittance of the opaque envelope are defined in Table 4.


**Table 4.** Dimensions of the cabins with thermal and spectral properties of opaque walls.

In these following test cases, outdoor temperature and solar irradiance varied during the day, and thermal performances depended on time. The indoor temperature was unknown, and it should have been obtained at the same time as the glazing temperature profile. Regarding the water flow glazing, the flow rate and the inlet temperature were constant values given by Table 5.

**Table 5.** Parameters of WFG.


Transient behavior occurred when the outdoor temperature and solar irradiance varied during the day. Besides, each wall had a different temperature due to the luminance of the direct beam solar radiation. Since the WFG was facing south, the north indoor wall absorbed solar radiation. The rest of this energy was diffusely reflected and created the indoor diffuse irradiance. Later, this irradiance was absorbed in each indoor surface. Hence, in this test case, the water flow glazing absorbed extra energy from the indoor irradiance. Figure 13 shows the validation of the Software Tool using real data from both cabins. The figure illustrates six days, from 22 July 2018 to 27 July 2018, in which we can see how the measured curves replicate the simulation curves in all the cases.

**Figure 13.** Indoor air temperature. Real results and simulation of the Reference cabin and the WFG cabin. Sample summer days 22 July 2018 to 24 July 2018.

The software tool tested in this article is an open software code written in modern Fortran, with a graphic user interface. The functionalities are grouped visually and logically into thematic units. There are libraries of spectral and absorption properties with different glasses and coatings. These libraries can allow developers to integrate WFG in existing building energy simulators. A thermal simulator of zones with glass and opaque envelopes includes properties such as thermal mass and reflections inside the zone. Some papers on the functionality of this tool have been published to present the design approach [62].
