###### Abstract  
The solar absorption-subcooled compression hybrid cooling system (SASCHCS) is tech-economically feasible for high-rise buildings. Since such a system operates with no auxiliary heat source, the performance coupling of its absorption subsystem and solar collectors is sensitive to the variation of hot water flow rate. In this regard, the relationship of system performance and hot water flow rate is required to be clarified exactly. Therefore, this paper aims to illustrate the effect mechanism of hot water flow rate and to propose the corresponding decision criterion. The case study is based on a typical high-rise office building in subtropical Guangzhou. The daily working process of this system with different hot water flow rates is simulated and analyzed. Subsequently, the useful heat of collectors and cooling capacity of the absorption subsystem with the hot water flow rate is discussed in detail. The results show that the SASCHCS operates with hot water temperatures ranging from 60 \({}^{\circ}\)C to 90 \({}^{\circ}\)C. The energy saving increases with the rise of hot water flow rate, but such variation tends to be flat for the excessively high flow rate. As the collector flow rate increases from 1 m\({}^{3}\)/h to 10 m\({}^{3}\)/h, the daily energy saving improves by 21% in August. Similarly, the daily energy saving increases by 37.5% as generator hot water flow rate increases from 1 m\({}^{3}\)/h to 10 m\({}^{3}\)/h. In addition, the collector flow rate of 3.6 m\({}^{3}\)/h (13.33 (kg/m\({}^{2}\) h)) and the generator flow rate of 5.2 m\({}^{3}\)/h (19.26 (kg/m\({}^{2}\) h)) are optimal for the annual operation, with considering power consumption of water pumps. This paper is helpful for the improvement of SASCHCS operating performance. Keywords:hot water flow rate; solar cooling; absorption chiller; subcooled compression; hybrid system +
Footnote †: journal: Applied  
to insufficient collector installation areas and rather high cooling demand in these buildings. In this case, given that the specific collector area is as high as 4 m\({}^{2}\)/kW for single effect LiBr/H\({}_{2}\)O absorption chillers [4], it is inferred that an auxiliary thermal source (e.g., gas-fired heaters) is necessary to provide supplementary heat. The resultant high fossil fuel consumption leads to the extremely high operation costs and poor economic profitability of such a solution [5]. Therefore, it is essential to propose an economically feasible solution for solar cooling in high-rise buildings. To this point, different absorption-compression hybrid cooling systems, which employ conventional vapor compression chillers as their backup cooling devices, are proposed as alternatives. In the so-called parallel hybrid systems, chilled water is successively cooled in the evaporators of absorption and compression chillers [6]. It was found that, for such configurations, the payback period achieved 36.2 years without subsidies, which is 61.3% less than that of conventional solar cooling with a backup heat source [7]. In order to further enhance the economic feasibility of solar absorption-compression hybrid refrigeration for high-rise buildings, the solar absorption-subcooled compression hybrid cooling system (SASCHCS) was investigated by [PERSON] [8]. The notable characteristic of SASCHCS lies in the fact that the cooling capacity of the absorption subsystem serves as subcooling power for the compression subsystem [9]. Consequently, the performance of absorption chillers is enhanced, and more solar cooling power is produced. It is measured by an experiment in which 22.2% of compressor work is saved as compared to vapour compression chiller without subcooling on summer sunny days [10]. It was indicated that the payback period of SASCHCS is close to that of solar photovoltaic cooling (the most economical solution of solar cooling recently) [11]. Moreover, it was obtained that the absorption subsystem with a smaller size is appropriate for the thermo-economic design if the hot water temperature is less than 75 \({}^{\circ}\)C [12].