## 3 System Configurations and Modelling
### Performance Indicators  
In this paper, we used some parameters and performance indicators to evaluate the individual performance of the SUS and SDS units in each configuration presented in Figure 5, and also to evaluate the overall performance of the whole configuration (SUS + SDS). To evaluate and compare the performance of the SUS of each configuration, the following parameters and indicators were used:  
* Heat transport line's supply temperature (\(T_{t,s}\)). * Temperature lift defined as: \(\Delta T_{lift}=T_{s}-T_{WH}\). * High and low internal pressures: \(p_{h}\) and \(p_{l}\), respectively. * Mass flow rates of the waste heat stream (\(m_{WH}\)) and water stream in the cooling tower circuit (\(m_{CT}\)). * LiBr concentration difference between stronger and weaker solution streams (\(\Delta x\)). * Coefficient of performance of the absorption heat transformer: \(COP=Q_{A}/(Q_{G}+Q_{E})\). To evaluate and compare the performance of the absorption heat pumps installed at the SDS, we used the following parameters and indicators:  
* Heat transport line's return temperature (\(T_{t,R}\)). * High and low internal pressures: \(p_{h}\) and \(p_{l}\), respectively. * Mass flow rates of the distribution district heating and cooling network (\(m_{DH}\) and \(m_{DC}\), respectively) and water in the cooling tower circuit (\(m_{CT}\)). * LiBr concentration difference between strong and weak solution streams (\(\Delta x\)). * Coefficient of performance for heating (\(\text{COP}_{\text{H}}\)) defined as: \(COP_{H}=\frac{Q_{H}}{(Q_{G}+Q_{WHE})}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Component**} & \multicolumn{2}{c}{**Absorption Heat Transformer (SUS)**} & \multicolumn{2}{c}{**Absorption Heat Pump (SDS)**} \\ \cline{2-6}  & **Single-Effect** & **Double AHT Type 3** & **Single-Effect** & **Double-Lift** & **Double-Effect** \\  & **[Figure 4a]** & **[Figure 4b]** & **[Figure 5a]** & **[Figure 5b]** & **[Figure 5c]** \\ \hline \multirow{5}{*}{Evaporator(s)} & \multirow{5}{*}{\(T_{16}/T_{15}=\frac{m}{25}\ ^{\circ}\)C} & \multirow{5}{*}{\(T_{25}-T_{25}=\frac{m}{25}\ ^{\circ}\)C} & \(T_{18}/T_{17}=\frac{m}{6}\ ^{\circ}\)C & \\  & & & \(T_{16}/T_{15}=\frac{m}{25}\ ^{\circ}\)C & \(T_{25}-T_{25}=\frac{m}{25}\ ^{\circ}\)C & \(T_{18}/T_{17}=\frac{m}{25}\ ^{\circ}\)C & \(T_{28}/T_{27}=\frac{m}{6}\ ^{\circ}\)C & \(T_{18}/T_{17}=\frac{m}{25}\ ^{\circ}\)C \\  & & & \(T_{3}-T_{25}=5\ ^{\circ}\)C & \(T_{10}=19\ ^{\circ}\)C & \(T_{10}=19\ ^{\circ}\)C & \\  & & & & \(\text{[O-448]/M]}\) & \\ \hline \hline \end{tabular} _Superscripts nomenclature_ [N/Y-(x)/M]: E: Except for; O: Only for; (x): configuration; M: Machine number (only for configuration (d) 2 xse/H&C).  
\end{table} 
Table 2: _Cont._* Coefficient of performance for cooling (COP\({}_{\text{C}}\)) defined as: \(COP_{\text{C}}=Q_{C}/Q_{G}\). Besides, to evaluate the overall performance of the proposed system configurations, the following parameters and performance indicators were selected to compare the simulated system configurations:  
* Total amount of waste heat as input in the step-up thermal station (\(Q_{WH}\)). * Heat capacity (\(Q_{H}\)) (see Table 3), heat delivered by the step-down station to the local district heating. * Cooling capacity (\(Q_{\text{C}}\)) (see Table 3), cooling delivered by the step-down station to the local district cooling. * Overall coefficient of performance for heating (\(COP_{H,tot}\)). Defined as the ratio between the heat input from the waste heat source at the step-up station to the heating delivered at the step-down station: \(COP_{H,tot}=Q_{H}/Q_{WH}\). * Overall coefficient of performance for cooling (\(COP_{C,tot}\)). Defined as the ratio between the heat input from the waste heat source at the step-up station to the cooling produced at the step-down station: \(COP_{C,tot}=Q_{C}/Q_{WH}\). * Equivalent electricity saving (\(EqES\)). Defined as the ratio between the heating and cooling produced converted into electric terms (W of electricity) and the waste heat required.