# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 4 Prototypes of Absorption Chillers
### Single-Stage Absorption Chillers  
#### 4.1.1 Ammonia-Based Working Pairs  
It is a common practice to use plate heat exchangers (PHEs) in vapor compression chillers because of their compactness, lower system refrigerant charge, and reduced cost. Consequently, absorption chillers built with PHEs can be smaller and cheaper than conventional absorption chillers. Besides, PHE-based chillers have a dynamic behavior quite unlike that of other absorption chillers, especially water/LiBr chillers which require larger heat exchangers with higher thermal inertia [48]. Therefore, the use of PHEs to build absorption chillers has been one the main advances in the last two decades, particularly for _refrigerant_ ammonia-based absorption chillers. To date, the use of PHEs to reduce the size (i.e., volume) of ammonia/water-based absorption chillers is limited. A few laboratory prototypes have been built using PHEs as the main components of the ammonia/water absorption chiller [49; 50]. The prototype of a 5 kW single-effect ammonia/water chiller was developed using brazed PHEs for solar cooling applications [50]. The PHEs were used as the desorber, rectifier, and absorber in which the falling film absorption process occurs. Under experimental test conditions, this prototype delivered 4.2 kW of cold with a thermal COP of approximately 0.65 when the heat source, heat sink (for absorber and condenser), and chilled fluid inlet temperatures were 80 \({}^{\circ}\)C, 27 \({}^{\circ}\)C, and 18 \({}^{\circ}\)C, respectively. Another prototype of a single-effect ammonia/water chiller was built using commercially available _Alfa Laval(tm)_ PHEs with its main components in vertical alignment [49]. The two types of stainless-steel plate heat exchangers used in this prototype were Alfanova 52 (40 plates) and Alfanova 27 (20 plates). The Alfanova 52 model was used for the absorber, desorber, and solution heat exchanger, whereas Alfanova 27 was used for the condenser and evaporator. All the other parts of the prototype, including the 1/2 inch nominal diameter and 0.4 m long finned tube rectifier, were built using stainless steel to avoid corrosion due to the presence of ammonia. The overall volume of the prototype was approximately 0.8 m\({}^{3}\). Its performance was investigated at driving hot water and cooling water inlet temperatures between 85 \({}^{\circ}\)C and 105 \({}^{\circ}\)C and 20 \({}^{\circ}\)C and 32 \({}^{\circ}\)C. The corresponding maximum cooling capacity and thermal COP attained in these operating conditions were \(\sim\)2.6 kW and 0.61. Both of these values were calculated using internal measured variables [49]. An evaporation temperature of approximately \(-\)19 \({}^{\circ}\)C was reached so that the compact chiller prototype could operate to serve a range of applications including air conditioning and refrigeration. It has been suggested in the literature that the ammonia/LiNO\({}_{3}\) mixture could be used as an alternative to alleviate some of the drawbacks associated with the conventional working pairs (i.e., ammonia/water and water/LiBr), especially in solar cooling applications [51]. The thermophysical properties of ammonia/LiNO\({}_{3}\) that are useful for performance analysis and designing absorption chillers can be found elsewhere [52; 53; 54; 55; 56]: vapor pressure, density, heat capacity, and viscosity in [PERSON] et al. [52; 53]; thermal conductivity in [PERSON] et al. [55]; and enthalpy and entropy with absorption chiller's energy and exergy analysis of single-effect ammonia/LiNO\({}_{3}\) absorption cycle in [PERSON] et al. [56]. The ammonia/LiNO\({}_{3}\) absorption chiller has performed better than the water/LiBr absorption chiller at high heat rejection temperatures, and it does not present the risk of crystallization in the range of working temperatures for space cooling applications. Moreover, low-temperature heat from flat-plate solar collectors, between 80 and 90 \({}^{\circ}\)C, can activate the chiller [51].