## 2 Description of Flow Schemes for HTF  
The schematic of the main components used in the solar absorption cooling system for educational building is shown in Figure 1. Heat transfer fluid (water in the current study) flows between different components of the cooling system to exchange its heat during flow. For analyzing the controlled flow of HTF, three loops are presented between the components of the cooling system in the current study i.e.,  
* Collector-tank loop
* Storage-chiller loop
* Chiller-building loop  
These loops of HTF are indicated by yellow, red and green colors respectively in Figure 2. The current study focused on the loop in which HTF feeding the generator of the chiller (i.e., storage-chiller loop). To the best of our knowledge, HTF can be circulated between the components of a storage-chiller loop by three different ways which are known as three proposed flow schemes of the current study.  
In scheme 1, solar collector receives the radiations from the sun and and heat up the water that flows toward thermal storage which then circulates towards solar collector after increasing the temperature of stored hot water.  
The flow of the collector pump is controlled in such a way that when the hot water inlet to the solar collector exceeds its outlet temperature, it will stop pumping. The minimum required input to the chiller unit is the 109 \({}^{\circ}\)C hot water (neglecting the boiling point as the system is pressurized) either at storage temperature (if it is equal to greater than 109 \({}^{\circ}\)C) or after heated by auxiliary unit fulfilling the requirement of refrigerant evaporation in the chiller's generator and returns to the storage tank.  
A pump is used to control the flow of hot water from the storage tank to the chiller only during the operating hours of the building. During this time period an auxiliary heating unit with the thermostat is used that turns on the pump when the temperature from the hotter side of the storage outlet is less than the required operating temperature to run the chiller.  
In Figure 1, the removal of tee, diverter component and direct links (of storage to pump 2 and chiller to storage) in storage-chiller loop shows conventional flow pattern of heat transfer fluid which is named as scheme 1 of the current study.  
In scheme 2, the conventional flow pattern is modified in such a way that when hot water (\(T_{chiller,out}\)) coming out from absorption chiller, it will divert towards the auxiliary heating unit instead of flowing directly towards the storage tank if storage's outlet is colder compared to the water returning from chiller as shown in Figure 3a. A flow diverter was used for diversion of the chiller's output hot water the to auxiliary heater and a tee piece component to pass the hot water either from storage tank or from diverter. The flow of water in the collector-tank and chiller-building loop is the same as in scheme 1 shown in Figure 2.  
In scheme 3, the flow of heat transfer fluid is modified with one of the most advanced techniques by diverting the flow after coming out from the absorption chiller unit. Figure 3b illustrates the mechanism of scheme 3 in which hot water (\(T_{chiller,out}\)) will continuously divert towards the auxiliary heater unless the temperature of the storage tank's hot side outlet would reach up to the minimum required temperature i.e., 109 \({}^{\circ}\)C for the chiller so that it will operate without consuming auxiliary energy. A controller signal has been introduced to generate the signal for diverter to start or stop the diversion of HTF, the remaining components are the same as scheme 2 as shown in Figure 2 with the only difference in the temperatures values for managing the diversion flow of chiller's hot water outlet.  
Figure 1: Solar absorption cooling system.