## 4 Results
### Energy Demand According to the Energy Simulation
Figures 12 and 13 show computational fluid dynamics (CFD) results for the  
Based on the conditions set out in Section 3.5 to perform the simulations, we obtained for the flat--in particular for the main bedroom, and for the MUA, in the Sempere Exhibition Hall--cooling and heating energy demand; overall thermal load values of each building; and the specific thermal loads of each simulated roof. Table 15 lists these values. We can first observe that the energy demands of the Sempere Hall are almost double those of the apartment. This is mainly due to five factors: the glazing of the south and west facades is 100%; the ventilation or renewal air flow is much higher, i.e., 1.95 acH instead of 0.77 acH; the infiltration air ratio value is double; the set temperature degree in summer for the Sempere Hall is lower; high occupancy of the hall, with high internal loads. When calculating the annual-total of thermal loads, loss or gain of heat through the roof is high. It represents a load percentage between 12% and 19% of the total for the loft flat bedroom and between 18% and 19% for the MUA's Sempere Exhibition Hall, with the greatest thermal loads corresponding to the water-covered roofs. The highest percentages of thermal loads relative to the roof, with respect to the total thermal loads, correspond to the paved walkable roofs, Q\({}_{R}\)_1, Q\({}_{R}\)_2 and Q\({}_{M}\)_2. The latter were 18.98%, 19.01% and 18.52%, respectively. The table also shows that based on the particular conditions of use defined, activity deployed, location, climate data and associated thermal loads, the cooling energy demand is between 68% to 81% greater than heating demand. This coincides with similar previous research [34]. With regard to the value of annual energy demand, the conclusions we can draw are significant. In the case of the building block roof, the action of the 15-cm-thick water sheet visibly generates substantial energy savings. Energy demand is reduced from a value of 60.06 kWh/m\({}^{2}\)year to 54.213 kWh/m\({}^{2}\)year, or 9%. This reduction is lower than that obtained in other studies that take advantage of the accumulation of solar energy in water tanks on the facade, with values ranging from 14% to 32% [72]. In these systems, water is stored in tanks. Its energy model is like a Trombe wall and cannot transfer heat by evaporation to the outdoor environment. Furthermore, convection heat transfer in sunspace is much lower than the water-covered roof with outside air. So, water heat build-up capacity increases and it uses to heat night-time states. In the case of the roof of the MUA Sempere Hall, with a useful surface area of 366 m\({}^{2}\), the consumption came down from 117,760 to 104,335 kWh/m\({}^{2}\)year, i.e., a reduction of 8.9%. These are significant values that, in the case of the MUA, could lead to substantial energy savings due to the building's high level of consumption. Annual consumption values drop by approximately 4914 kWh, equating to an annual energy bill reduction of around 700 euros, with an energy cost of 0.142 \(\upxi\) per kWh of electricity given by IDAE [1]. In the case of the flat, annual consumption was reduced by 725 kWh, corresponding to a reduction in the annual energy bill by 103 euros. This means that if an inverted flat roof had been set up on the MUA, instead of the adopted water-covered roof solution, in the 20 years of the building's existence, an additional 14,000 euros would have had to have been paid. If we extrapolate this to the entire surface of the MUA that is currently under the water sheet, i.e., 746 m\({}^{2}\), a total of 28,500 euros would have been saved. Future studies will examine whether investments made with the construction of the water-covered roof could or not be paid back within a reasonable period of time. We must remember that the costs of