## 3 TRNSYS Modelling
### Absorption Chiller  
Single effect hot water fired absorption chiller (type107) is used to encounter the cooling load of the building. This component uses a catalog data lookup approach to predict the performance and gives the correct output by interpolation if given input are in the range of performance catalog file. In TRNSYS v17 catalog data file of type107, the operating range of inlet hot water temperature for the chiller's generator is between 108 \({}^{\circ}\)C to 116 \({}^{\circ}\)C. Therefore, in current design, the minimum operating temperature of 109 \({}^{\circ}\)C is chosen to operate the absorption chiller to encounter the peak cooling load of 108 kW (31 TR). The inputs of this section is crucial for designing of the cooling system as the chiller's capacity decides the amount of cooling demand that it can withstand. TRNSYS referenced formulation [21] is used for designing the parameters:  
\[Q_{hw}=\frac{Capacity_{rated}}{COP_{rated}}f_{Designedenergyinput}. \tag{3}\]  
In Equation (3), \(Q_{hw}\) is hot water energy that must be available for the chiller operation, rated capacity and COP are given in Table 2 while \(f_{Designedenergyinput}\) is taken from performance catalogue data file of type107 at designed conditions.  
\[Q_{coolingcapacity}=m_{chw}Cp_{chw}(T_{chw,in}-T_{chw,set}). \tag{4}\]  
In Equation (4) \(Q_{coolingcapacity}\) is the energy rate which must be removed by chiller (sometimes denoted by \(Q_{remove}\) or \(Q_{chilled}\)) that must be removed by chiller, \(m_{chw}\) is the flow rate of water from the chiller, \(m_{chw}\) is flow rate of water out from the chiller, \(C_{pchw}\) is the fluid's heat capacity from the chiller and (\(T_{chw,in}-T_{chw,set}\)) is the difference between the temperature of the chilled fluid entering and leaving at the chiller which is taken by considering default values of inputs of type107 i.e., default values of \(T_{clw,in}\) and \(T_{clw,set}\) are 12.22 \({}^{\circ}\)C and 6.667 \({}^{\circ}\)C respectively, in current study.  
\[Q_{hw}=m_{hw}Cp_{hw}(T_{hw,in}-T_{hw,out}). \tag{5}\]  
Figure 5: Hot water storage tank.  
In Equation (5) \(Q_{hw}\) is hot water energy that must be available for the chiller operation, \(m_{hw}\) is the flow rate of hot water and is calculated from this equation by choosing the difference of hot water inlet and hot water outlet (\(T_{hw,in}-T_{hw,out}\)) value as 10 \({}^{\circ}\)C while \(C_{phtw}\) is the heat capacity of hot water. \(Qcw\) is cooling water energy rate is found out by the energy balance approach in the current study i.e.,  
\[Q_{cw}=Q_{chw}+Q_{hw}+Q_{aux}. \tag{6}\]  
In Equation (6), \(Q_{aux}\) is the auxiliary electricity consumed by the chiller for solution pumps and refrigerant pump etc. Equation (6) is used to balance the total energy of the chiller. This is the total energy rejected from chiller to environment and is used to find \(Q_{cw}\). The \(Q_{cw}\) will be further used in Equation (7) for design consideration. The design parameters are already tabulated in Table 2.  
\[T_{cw,out}=T_{cw,in}+\frac{Q_{cw}}{m_{cw}C_{pcw}}. \tag{7}\]  
where, \(Q_{cw}\) is the energy required by the cooling water, \(m_{cw}\) is the flow rate of cooling water and is found from the Equation (7) by fixing the temperature difference of cooling water outlet and cooling water inlet (\(T_{cw,out}-T_{cw,in}\)) as 5 \({}^{\circ}\)C while \(C_{pcw}\) is the heat capacity of cooling water.