## 3 TRNSYS Modelling  
TRNSYS is employed for the modeling and simulating all schemes of the heat transfer fluid flow between storage tank to the chiller in SACS. The monthly averaged solar radiations of hot climate cities of Pakistan (Lahore, Islamabad, Multan, Peshawar and Karachi) are compared as shown in Figure 4 and a cooling system in an educational building of Peshawar (highest radiations city of Pakistan) is chosen for modeling of the solar absorption cooling system, having 108 kW peak cooling load during the summer season and daily operating schedule from 9 a.m. to 5 p.m. TRNSYS model for modified flow schemes exhibited in Figure 2. Thick red lines shown in Figure 2 depict hot water loop from the storage to the chiller unit, yellow lines depict the collector-tank loop while green lines indicated loop of chilled water from the chiller to building. Scheme 2 and Scheme 3 are having the same components except for the temperature range for the diverter. Meteororm weather data available with the TRNSYS v17 was used in the current model of SACS.  
To accomplish the objective of comparing the performance of three proposed flow schemes of the study, the following assumptions are considered with the design of cooling system used:  
* Heat losses from pipes are neglected.
* Energy balance technique is used for cooling tower specifications.
* Boiling effects of the heat transfer fluid are ignored.
* Electricity consumption of pumps is not included as the auxiliary energy consumption record.  
Figure 3: Mechanism of modified flow schemes. (**a**) Scheme 2. (**b**) Scheme 3.  
Figure 2: TRNSYS model of solar absorption cooling system (SACS) for modified flow schemes.  
Connections shown in Figure 2 are just logical connections and not represents pipes. For simplicity of the model, pipes or valves connections are not included in the current model by which heat losses from pipes can be measured as it can be assumed that they are perfectly insulated. The second assumption of the study reflects theoretical calculations of cooling water energy by energy balance equation i.e., Equation (6) which tells us energy from absorber and condenser rejected by cooling water by keeping the temperature difference of 5 \({}^{\circ}\)C between the inlet and outlet cooling water for design consideration in Equation (6) of the current study and no separate TRNSYS component of the cooling tower is used. The third assumption depicts the pressurized water system by which the normal boiling point of water can be varied, however, pressure calculations are not included in the study. All flow schemes of the current study use two flow pumps and would consume considerable but same amount of electricity as the designed flow rates are the same in all schemes, so that this electricity consumption of the pumps is not included as auxiliary energy consumption calculation.  
With the aforementioned assumptions, it is suggested that this simulation study provides a somewhat higher evaluation of performance indicators than practically installed system but still, our sole purpose from this study of analyzing the effects on the performance of the solar cooling system due to modified flow schemes can be fulfilled with these assumptions.