# A Sustainable Polygeneration System for a Residential Building
## 2 Materials and Methods
### System Layouts  
The main integrated scheme starts with a solar loop consisting of PVTs, a storage tank (ST), and a heat sink to avoid overheating (AE). Additional electricity generation to cover the demands of the building is provided by a PV field and supported by the installation of TEGs on 50% of the solar aperture of the resulting PVT field. The facility will have the corresponding inverter according to the absolute power, buying and selling energy to the grid depending on the demand (ED) and instantaneous production. The DHW demand is covered by a mixture of the secondary tank (HWDT) and cold freshwater to serve the required flow rate at 45 \({}^{\circ}\)C. The heating demand (HD) is covered in \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Zone** & **1** & **2** & **3** \\ \hline Location & Almeria & Valencia & Zaragoza \\ Climate zone & A4 & B3 & D3 \\ Latitude & 36\({}^{\circ}\)50\({}^{\prime}\) N & 39\({}^{\circ}\)28\({}^{\prime}\) N & 41\({}^{\circ}\)39\({}^{\prime}\) N \\ Altitude above sea level (m) & 0 & 8 & 207 \\ Annual average outdoor temperature (\({}^{\circ}\)C) & 18.4 & 17.6 & 15.2 \\ Horizontal global solar radiation (kWh/y) & 1829 & 1615 & 1656 \\ Average annual wind speed (m/s) & 4.1 & 3.1 & 4.5 \\ Average annual temperature of tap water (\({}^{\circ}\)C) & 15.7 & 14.6 & 13.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Description of the main climate conditions of the selected cities. Source: [28; 29; 30]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Location** & **Almeria** & **Valencia** & **Zaragoza** \\ \hline Heating demand (HD, kWh/y) & 21,449.7 & 59,572.9 & 101,297.2 \\ per dwelling (kWh/y-dwelling) & 268.1 & 744.7 & 1265.0 \\ Cooling demand (CD, kWh/y) & 75,691.8 & 46,907.0 & 48,271.0 \\ per dwelling (kWh/dwelling) & 946.1 & 587.3 & 603.4 \\ Electricity demand (ED, kWh/y) & 151,905.3 & 151,905.3 & 236,655.1 \\ per dwelling (kWh/dwelling) & 1888.7 & 1888.7 & 2958.2 \\ Freshwater demand (FWD, m\({}^{3}\)/y) & 8555.1 & 8555.1 & 8555.1 \\ per dwelling (m\({}^{3}\)/y-dwelling) & 106.95 & 106.95 & 106.95 \\ Domestic hot water demand (DHWD, kWh/y) & 93,887.0 & 93,887.0 & 150,101.0 \\ per dwelling (kWh/y-dwelling) & 1173.6 & 1173.6 & 1876.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Annual energy and water consumption for the same building in the three selected cities. the same way as DHW, but in this case, it is done at 35 \({}^{\circ}\)C and returned at 25 \({}^{\circ}\)C, considering there is underfloor heating in the building. The fundamental difference between the configurations analyzed for the three sites with the same base building is the production of cooling and desalinated water. They may require either heat, which will come from the secondary tank, or electricity. For cooling (CD), a single-effect lithium bromide absorption cycle (SEAC) or a high-efficiency heat pump (HP) connected to an aquifer with a stable temperature (15 \({}^{\circ}\)C) can be chosen. A membrane technique (RO) or distillation (MED) is proposed for seawater desalination. The biomass boiler (BB) allows the secondary tank to maintain a setpoint temperature according to the cooling and desalinated water demands since they operate at the highest temperatures. TEGs were also incorporated at its top to produce more electricity for the system. Finally, a 50 m\({}^{3}\) tank (FWT) has been foreseen to regulate desalinated water production concerning consumption (FWD). The selected cooling technology has a third storage tank to avoid system start-ups and shutdowns while meeting demand. Thus, the four combinations analyzed for the polygeneration system differ in selecting technology for cooling and desalination (whose flows are marked as dashed lines in Figure 3 depending on the chosen technology), as shown in the attached Table 4. In any case, the final design of each option will be different in terms of the number of PV/PVTs, biomass boiler power, HP/SEAC capacity, and size of the hot and cold water storage tanks.