# Evaluating the Energy-Saving Potential of Solar Dedicated Ventilation Systems Based on ADRC
## 5 Results and Discussion
### Energy-Saving Potential  
Fresh air is cooled and dehumidified only by direct expansion before providing it to the indoor space in the conventional system. The cooling load of fresh air can be expressed as:  
\[Q_{\text{FAC}}(j)=\rho\cdot v_{\text{FA}}\cdot(h_{2}(j)\ -\ h_{\text{Room}}) \tag{17}\]  
where  
\(Q_{\text{FAC}}(j)\) is the cooling load of fresh air at time \(j\) for the conventional system (kW);  
\(\rho\) is air density (kg/m\({}^{3}\));  
\(v_{\text{FA}}\) is the airflow rate of fresh air (m\({}^{3}\)/s);  
\(h_{2}(j)\) is air enthalpy of test point 2 at time \(j\) for the conventional system (kJ/kg); and  
\(h_{\text{Room}}\) is air enthalpy of the indoor space (kJ/kg).  
Fresh air was cooled and dehumidified by the heat pipe heat exchanger combined with the dedicated ventilation system before being provided to the indoor space in the former study [14]. The cooling load of fresh air can be expressed as:  
\[Q_{\text{FAH}}(j)=\rho\cdot v_{\text{FA}}\cdot(h_{\text{3H}}(j)\ -\ h_{\text{Room}}) \tag{18}\]  
where  
\(Q_{\text{FAH}}(j)\) is the cooling load of fresh air at time \(j\) for the former study (kW); and  
\(h_{\text{3H}}(j)\) is air enthalpy of test point 3 at time \(j\) for the former study (kJ/kg).  
Fresh air is cooled and dehumidified by the proposed solar dedicated ventilation system before being provided to the indoor space in this study. The cooling load of fresh air can be expressed as:  
\[Q_{\text{FAS}}(j)=\rho\cdot v_{\text{FA}}\cdot(h_{\text{3S}}(j)\ -\ h_{\text{Room}}) \tag{19}\]  
where  
\(Q_{\text{FAS}}(j)\) is the cooling load of fresh air at time \(j\) for this study (kW); and  
\(h_{\text{3S}}(j)\) is air enthalpy of test point 3 at time \(j\) for this study (kJ/kg).  
\(Q_{\text{AHU}}(j)\), \(Q_{\text{DX}}(j)\), and \(Q_{\text{SH}}(j)\) are tested and saved for calculation and analysis in the experimental system automatically. \(Q_{\text{FAS}}(j)\) can be calculated by the thermal energy balance Equation (14). As the power of \(Q_{\text{AHU}}(j)\), \(Q_{\text{DX}}(j)\), and \(Q_{\text{SH}}(j)\) is supplied by the photovoltaic and solar thermal system, the power of \(Q_{\text{FAS}}(j)\) is also supplied by solar energy in the proposed system compared with the former system. The proposed system will only use solar energy, not including extreme conditions. Extreme situations that need a standby power supply for the proposed solar dedicated ventilation system rarely occur in southern China and in summer in most parts of China. Solar energy has replaced traditional energy, and the energy-saving potential of the proposed system equals the power consumption of traditional systems, excluding extreme conditions. Therefore, it can be concluded that the proposed solar dedicated ventilation system could gain the most energy-saving potential compared with the conventional and previous systems [12; 13; 14].  
However, there are some shortcomings of the proposed system. In the first place, the proposed system is affected by weather conditions and geographical location and its efficiency is quite different in different regions. In the second place, an adequate energy storage system is significant for the proposed system. Finally, the initial investment for the proposed system is larger and the payback period is longer than for the former systems. Therefore, the actual operation of the proposed solar dedicated ventilation system will be evaluated in the next section.