# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 3 Newly Developed Commercial Absorption Chillers
### Single/Double-Effect Absorption Chiller: Solar-Gas Fired  
In the conventional solar space cooling system, illustrated in Figure 1, single-effect absorption chillers are driven by low-temperature solar thermal collectors (i.e., evacuated tube and flat-plate solar collectors are mostly used). In this system, a gas-fired heater was used as a backup to supply hot water to the low-efficiency single-effect chiller (i.e., thermal COP of about 0.7-0.8 [10]). Additionally, the solar cooling system uses a complicated control system to regulate the hot water supply of the chiller per end-user cooling load and solar heat variations [37; 38]. Hence, it is difficult to establish an optimum control system. To avoid these shortcomings, a new absorption chiller was exclusively designed and developed to efficiently use low-temperature solar thermal collectors for air-conditioning applications by Kawasaki Thermal Engineering Co., Ltd. in 2010 [37]. The main features of the solar cooling system concept, depicted in Figure 9, are no external backup heater; direct gas-fired desorber; and continuous priority for the efficient use of the solar resources available. This system is particularly relevant to buildings with high cooling loads and a limited area for installing solar collectors. The crucial part of this improved solar absorption cooling system (Figure 9) is the solar-gas-fired single/double-effect water/LiBr chiller developed and commercialized by Kawasaki Thermal Engineering Co., Ltd. [39; 40]. This chiller, depicted in Figure 10, functions as a single-effect chiller, a double-effect chiller, or a single/double-effect hybrid depending on the intensity of the solar irradiation  
Figure 8: Single-effect double-lift water/LiBr absorption chiller developed by the World Energy Co., Ltd. Adapted from Reference [36]. and the cooling load of the end-user (e.g., buildings). It has three desorbers (shown in Figure 10a): the high-temperature desorber (HDES); low-temperature desorber (LDES); and a single-effect desorber (SDES). The chiller also operates at four pressure levels. The SDES is driven by hot water between 75 and 90 \({}^{\circ}\)C produced using solar heat in the nominal condition (i.e., cooling water inlet temperature at 32 \({}^{\circ}\)C and 100% cooling capacity). The HDES is _a direct-fired-type desorber_ using natural gas as a fuel, the primary function of which is to support/provide backup when there is not enough solar irradiation and/or the cooling demand is high. The cooling water first enters the single-effect condenser (SCON) coupled to the SDES, then the low-temperature condenser (LCON), and finally the absorber (ABS) to collect heat rejected from the corresponding condensation and absorption processes. This series flow arrangement of the cooling water stream, from the cooling tower, enables maximum use of the solar energy available by allowing the SDES to operate at a relatively lower pressure (and, consequently, driven by a lower temperature heat). The absorption chiller has a nominal cooling capacity of 281-1055 kW at chilled water supply/return temperatures of 7/15 \({}^{\circ}\)C and cooling water inlet/outlet temperatures of 32/37.6 \({}^{\circ}\)C. The driving hot water inlet/outlet temperatures at the SDES are 90/79.5 \({}^{\circ}\)C for the nominal operating condition [37]. Figure 10: Solar-gas-fired single/double-effect absorption chiller from Kawasaki Thermal Engineering Co. Ltd. Adapted from Reference [41]. (**a**) Absorption cycle schematic; (**b**) Absorption chiller external view. Note: ABS = absorber; EVA = evaporator; HDES = high-temperature desorber; HSHX = high-temperature solution heat exchanger; LCON = low-temperature condenser; LDES = low-temperature desorber; LSHX = low-temperature solution heat exchanger; SCON = single-effect condenser; SDES = single-effect desorber. Figure 9: Solar absorption cooling system based on solar-gas-fired single/double effect absorption chiller [37; 38].