# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 4 Prototypes of Absorption Chillers
### Advanced Absorption Chillers  
#### 4.2.1 Double-Lift Absorption Chillers  
As previously mentioned in Section 3.2., some of the recent developments in single-effect water/LiBr technologies have extended the heat source temperature glide by about 18 K (e.g., 90 to 72 \({}^{\circ}\)C) in nominal operating conditions. Additionally, using a single-effect water/LiBr chiller driven by hot water at 95 \({}^{\circ}\)C makes it possible to extract heat up to 75 \({}^{\circ}\)C (i.e., a 20 K temperature glide) to deliver chilled water with supply/return temperatures of 7/12 \({}^{\circ}\)C at cooling water inlet/outlet temperatures of 27/33 \({}^{\circ}\)C [16; 35]. To be able to use heat sources at temperature levels that cannot activate a single-effect chiller, it is often necessary to use a double-lift absorption chiller to produce chilled water [73]. Typically, hot water at 70 \({}^{\circ}\)C is compatible with double-lift water/LiBr chillers. Also, an ammonia/water double-lift refrigerator was built and successfully operated in Alaska (United States) in the 1990s, driven by the diesel engine jacket cooling water at 75 \({}^{\circ}\)C to deliver \(\sim\)9071.8 kg per day of flake ice for a remote community [74]. The prototype of a double-lift ammonia/water absorption chiller system based on a direct air-cooled absorber and condenser has also been developed and experimentally studied [75; 76]. In this prototype, a vertical shell-and-tube falling-film heat exchanger was used as a desorber and the vapor generated was passed through a rectifier made of a pall ring packed bed with a solution cooled coil. A shell-and-tube vertical flow countercurrent heat exchanger was used as an evaporator. The absorber and condenser were made of steel tube coils with vertical aluminum fins in which the tubes were horizontal and arranged in one row, all of which was cooled by a 500 mm axial fan. The prototype was tested at chilled water inlet/outlet temperatures of 12/7 \({}^{\circ}\)C, a driving hot water temperature between 80-90 \({}^{\circ}\)C and an air temperature between 22 and 38 \({}^{\circ}\)C. The cooling capacity of the prototype was 2.5 kW at air and inlet hot water temperatures of 30 \({}^{\circ}\)C and 90 \({}^{\circ}\)C. The corresponding thermal and electrical COPs were 0.3 and 10, respectively. The chiller responds quickly to any variation in operating conditions. With this design, the chiller prototype is well-suited to recovering waste heat from internal combustion engines because of its limited temperature glide (e.g., 5 \({}^{\circ}\)C) in the driving heat source. However, for solar cooling applications, the heat transfer in the desorber could be optimized to allow a low flow strategy for the driving circuit. This could be advantageous for the overall electrical COP of the system. The new concept of a single-/double-lift (i.e., single-/half-effect) ammonia/water absorption chiller was built by adapting the commercial product PinkChiller PC 19 [77; 78]. The Pink PC 19 commercial chiller had been developed using tube bundle heat exchangers for the absorber, desorber, and condenser, whereas the falling film-type heat exchanger was used for the evaporator. Thereby, it limits the size of the chiller and incurs high production costs because of the limitations on the assembly and welding of the heat exchangers. Hence, the single-/double-lift chiller is based on redesigning the Pink PC19 chiller and using flat PHEs for its main components (i.e., absorber, condenser, desorber, and evaporator). The absorber design was optimized using a new type of injector nozzle, balancing the water flow between the two solution loops and adapting the internal control strategy (i.e., solution pump control). This new absorption chiller is switchable between single-lift (single-effect), double-lift (half-effect), and single-/double-lift modes with a cooling capacity of 20 kW in the single-effect mode.