## 3 Materials and Methods
### On-Site Energy Generation  
The building under study has a nearby total area of more than 2000 m\({}^{2}\), free of obstacles, where PV modules could be installed without any inconvenience in case of implementation. For the purpose of the present work, we proposed to use between 20% to 25% of the total available area. Taking into account the size and power of the selected PV module and the target area, we considered a grid connected solar PV system (SPVS) of 50 kWp for on-site energy generation.  
The SPVS aims to reduce the use of the building's electrical energy from the electric power grid. In the implementation of a SPVS, its investment costs could be much higher than the execution of the other energy saving measures in the building, depending mainly on its size [33]. In the simulation it is assumed that the surfaces of the PV modules are facing north with a tilt angle similar to the latitude of the site. These last conditions are ideal for extracting the most significant PV energy in SPVSs, located in the southern hemisphere [53]. DC/AC power converters sends the power generated by the PV panels to the electric power grid, which can operate in parallel to the grid without any inconvenience.  
The simulations of this system were carried out in the HOMER Pro software [54], taking into consideration the electrical load modeled in EnergyPlus. The governing equation to calculate the output power of each system is the following:  
\[P_{out,PVysst}=Y_{PVysst}\times f_{PVysst}\bigg{(}\frac{G_{T}}{G_{T,PVysst}} \bigg{)}\big{(}1+\alpha_{p}\big{(}T_{c}-T_{c,PVysst}\big{)}\big{)}, \tag{1}\]  
where \(Y_{PVysst}\) is the nominal capacity of the PV system, \(f_{PVysst}\) is the derating factor of the PV system, \(G_{T}\) is the incident radiation on the PV system [kW/m\({}^{2}\)], \(G_{T,PVysst}\) is the irradiation under standard test conditions [1 kW/m\({}^{2}\)], \(\alpha_{p}\) is the temperature coefficient of the power [%/\({}^{\circ}\)C], \(T_{c}\) is the cell temperature of the PV system [\({}^{\circ}\)C], and \(T_{c,PVysst}\) is the temperature of the PV system under standard test conditions [25 \({}^{\circ}\)C].  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Cooling Capacity [BTU/h]** & **COP** \\ \hline \textless{}65,000 & 3.45 (SEER 14) \\ \(\geq\)65,000 and \textless{}135,000 & 3.55 (SEER 14.6) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Cooling capacity ranges and DOE minimum energy efficiency requirements for air conditioners (extracted from [52]).  
The PV module considered for the calculations was 360 Wp, monocrystalline type, with a surface area of 1.77 m\({}^{2}\)[55]. The cost for this module in the Ecuadorian market is around USD$220.00 per unit with a lifetime of 25 years [56]. In addition, we considered a derating factor of 90%, where 10% represents the losses such as dust on the surface of the panels, wiring, shading, and others [57]. Likewise, the cost of the 6 kW DC/AC power converter was USD$5,000.00, with an efficiency of 95%. The replacement costs of these two equipment are not considered in this simulation.  
Figure 8 shows the configuration of SPVS, which was simulated in Homer Pro. It is composed of PV panels, DC/AC power converters, electric power grid and the electrical load of the building.