# Regional Adaptability Analysis of Solar Roof Utilization Technologies in China
## 2 Methodology
### The Solar Utilization Systems
#### 2.4.1 The Solar Heating System  
For multi-story buildings in urban cities, due to the limitation of available solar energy on rooftops, the solar heating system is typically used to provide domestic hot water. Therefore, the solar heating system is designed to cover the demand of hot water  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Types** & **Lighting Load** & **Occupant Density** & **Activity Intensity** & **Equipment Load** & **Fresh Air** \\  & **(W/m2)** & **(m2/Person)** & **(W/Person)** & **(W/m2)** & **Volume (m3/p \(\cdot\)h)** \\ \hline Residential & 7 & 20 & 72 & 7 & 30 \\ building & 11 & 20 & 120 & 13 & 30 \\ Office building & 19 & 4 & 88 & 13 & 30 \\ Hotel building & 15 & 20 & 72 & 20 & 30 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Parameters of heat loads for different building types.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Building Type** & **Time** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** & **12** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Office \\ buildings \\ \end{tabular} } & Workdays in & \multirow{4}{*}{\begin{tabular}{c} Cold supply \\ Winter \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{c} Cold supply \\ Heat supply \\ \end{tabular} } & - & - & - & - & - & - & 28 & 26 & 26 & 26 & 26 & 26 \\  & & & - & - & - & - & - & 18 & 20 & 20 & 20 & 20 & 20 \\  & & Cold supply & - & - & - & - & - & - & - & - & - & - & - \\  & & Heat supply & - & - & - & - & - & - & - & - & - & - & - \\ \hline Commercial & \multirow{2}{*}{\begin{tabular}{c} Summer \\ buildings \\ \end{tabular} } & Summer & \multirow{2}{*}{\begin{tabular}{c} Cold supply \\ Heat supply \\ \end{tabular} } & - & - & - & - & - & - & - & - & 28 & 25 & 25 & 25 \\  & & & - & - & - & - & - & - & 16 & 18 & 18 & 18 \\ \hline \multirow{4}{*}{\begin{tabular}{c} Office \\ buildings \\ \end{tabular} } & Workdays in & \multirow{4}{*}{\begin{tabular}{c} Heat supply \\ Heat supply \\ \end{tabular} } & \multirow{4}{*}{\
\begin{tabular}{c} Cold supply \\ Heat supply \\ \end{tabular} } & \multirow{4}{*}{
\begin{tab  
of the building. Determining the solar collector area is the important step to analyze the adaptability of solar thermal technology on a building roof.  
In the relevant code on hot water supply [41], daily hot water usage per capita is given depending on the function of the building. For example, the hot water temperature is typically 60 \({}^{\circ}\)C. The maximum daily hot water consumption is about 60-100 L per capita for a residential building equipped with a central hot water supply system. The hot water consumption is quite different for an office building. Based on the daily hot water consumption per capita and the number of occupants, the total hot water consumption and the heat needed can be calculated, and then, the gross area of the solar collectors can be obtained [42]:  
\[A_{\rm c}=L_{\rm w}\,{\rm c}\,\,p\,(t_{\rm h}-t_{\rm c})f/[J_{\rm t}\,\,\eta_{ \rm c}\,(1-\eta_{\rm l})] \tag{1}\]  
In the equation, \(A_{\rm c}\) is the solar collector area, m\({}^{2}\); \(L_{\rm w}\) is the total hot water usage, L; \(t_{\rm h}\) is the temperature of hot water, \({}^{\circ}\)C; \(t_{\rm c}\) is the mains water temperature, \({}^{\circ}\)C; \(c\) is the specific heat of water, kJ/(kg \({}^{\circ}\)C); \(\rho\) is the density of water, kg/L; \(f\) is the solar fraction,%; \(J_{\rm t}\) is the annual average solar radiation, W/m\({}^{2}\); \(\eta_{\rm c}\) is the average solar collector efficiency, %; \(\eta_{\rm l}\) is the loss of efficiency due to the heat loss of pipes and tanks, %.  
Based on Equation (1), the solar fraction\(f\) could be calculated. The maximum solar collector area is proportional to the rooftop area depending on row distance, collector tilt, and the location of the buildings, therefore, the maximum solar fraction could be determined.