# Multi-Objective Optimization of Hybrid Renewable Tri-Generation System Performance for Buildings
## 3 Simulation Methodology  
An annual simulation was performed for a single house under Incheon, Republic of Korea, weather conditions. Co-simulation between GAMS and TRNSYS has been applied. Figure 2 shows flowchart design system optimization and simulation for Trigeneration System. The hybrid trnsys's component models awhp, PVT and GAHX have been validated using the manufacturers' experimentally generated performance data. The performance for each component of the trigeneration system is fed to GAMS alone with thermal and non-HVAC electrical loads and weather data in addition to capital, installation and maintenance, and operation costs for each unit and energy price cost. To solve the complex optimization problem, a nonlinear programming solver of GAMS was used. The optimum design parameters of the awhp size, GAHX length and PVT surface area are returned to the TRNSYS model for a complete hybrid system annual simulation. TRNSYS output is then used to conduct annual energy and cost analyses.  
Figure 3 presents GAHX outlet temperatures at different pipe lengths and outside air temperatures during summer/winter conditions. The GAHX performance data are based on a constant airflow rate of 2900 kg/h. The results showed that the outlet airflow temperatures from the GAHX range from \(-1\)\({}^{\circ}\)C to 4 \({}^{\circ}\)C when the outside air temperature is below zero degrees, with a GAHX length of 125 m. The outlet temperature from GAHX reaches 17 \({}^{\circ}\)C on the warmest day of 35 \({}^{\circ}\)C. Moreover, for further increases in GAHX length, the outlet airflow temperature from GAHX increases in the winter season and decreases in the summer season. At a GAHX length of 500 m, there is no significant variation in outlet airflow temperature from GAHX in winter and summer seasons, with an average temperature of 7 \({}^{\circ}\)C.  
The AWHP performance data in terms of heat delivery and COP at different water inlet temperatures in the winter and summer seasons are presented in Figure 4. The AWHP  
Figure 3: Outlet air temperature from GAHX at different outside temperatures and GAHX lengths.  
Figure 2: Flowchart design system optimization and simulation for Trigeneration System.  
performance at the inlet water temperature of 40 \({}^{\circ}\)C, 30 \({}^{\circ}\)C and 20 \({}^{\circ}\)C for the winter season and 10 \({}^{\circ}\)C and 15 \({}^{\circ}\)C for the summer season are modeled and presented. The results show that the heat transfer delivery from the AWHP increases with further increases in the outside air temperature during the winter period and decreases with the increase in the outside air temperature during the summer period, as presented in Figure 4a. In the winter period, the heat delivery from the AWHP increases by an average of 3% by decreasing inlet water temperature from 30 \({}^{\circ}\)C to 20 \({}^{\circ}\)C and increasing by an average of 7% for further decreases in inlet water temperature from 40 \({}^{\circ}\)C to 30 \({}^{\circ}\)C. However, the heat delivery increases by an average of 16% by increasing the inlet water temperature from 10 \({}^{\circ}\)C to 15 \({}^{\circ}\)C in the summer period. On the other hand, the COP for AWHP increases by 7% with a further decrease in the inlet water temperature to the AWHP from 30 \({}^{\circ}\)C to 20 \({}^{\circ}\)C and increases by an average of 15% with decreasing the inlet water temperature from 40 \({}^{\circ}\)C to 30 \({}^{\circ}\)C in the winter season, as shown in Figure 4b. Whereas, in the summer season, the COP of the AWHP increases at a high inlet water temperature of 15 \({}^{\circ}\)C by an average of 11% compared to an inlet water temperature of 10 \({}^{\circ}\)C.