# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 3 Newly Developed Commercial Absorption Chillers
### Compact Absorption Chiller: Asymmetric Plate Heat Exchanger  
Typically, horizontal tube bundle heat exchangers are used as the main components of water/LiBr absorption chillers (i.e., absorber, condenser, desorber, and evaporator). Besides, designing a compact water/LiBr absorption chiller has been a challenge because of the high specific volume of water vapor which requires a relatively large heat exchanger surface area. The use of conventional plate heat exchangers (PHEs) (i.e., the same channel heights in both fluid flow sides) for water/LiBr absorption chiller technology is hampered by the high specific volume of water vapor and the low-pressure drops allowed in the heat exchanger's vapor channels. In contrast, on the external heat carrier sides of the chiller (i.e., driving hot water, cooling water, and chilled water), small dimensions are required for better heat transfer [30]. Hence, conventional PHEs cannot be used in water/LiBr chillers because channel heights need to be different. Different channel heights create optimum heat transfer conditions on both sides of the heat exchanger (i.e., optimum heat transfer on both the vapor and the liquid sides). Accordingly, a new asymmetric PHE was designed exclusively for use in water/LiBr absorption technology by EAW Energieanalagenbau GmbH and ILK Dresden (Germany) [30,31]. This asymmetric PHE has engraved patterns that improve plate wettability and flow conditions [30]. The asymmetric PHEs developed with optimized channel heights under the operating conditions of the components of water/LiBr chillers, particularly for the absorber and evaporator, are the low-pressure side of the chiller. These PHEs can be used to manufacture absorption machines with cooling capacities up to 400 kW.  
By using the newly developed asymmetric PHEs, a new generation of single-effect water/LiBr absorption chillers, shown in Figure 5, was developed and commercialized by the company EAW [32]. The company's current product series, model WEGRACAL(r) Maral, includes chillers with a nominal capacity of 15 kW (Maral 1), 30 kW (Maral 2), and 65 kW (Maral 3) with thermal COP of 0.75 at chilled water supply/return temperatures of 9/15 \({}^{\circ}\)C [32]. In nominal conditions, the inlet/outlet temperatures of the driving hot water and heat rejection medium (water/ethylene glycol mixture (66%/34%) or water) are 86/71 \({}^{\circ}\)C and 27/32 \({}^{\circ}\)C, respectively. These chillers are activated using low-temperature hot water between 75 and 95 \({}^{\circ}\)C [32]. The specific chiller volume and transport weight (and operating weight) are approximately in the range 0.062-0.101 m\({}^{3}\)/kW\({}_{\text{cold}}\) and 20.9-30.0 kg/kW\({}_{\text{cold}}\) (28.3-36.7 kg/kW\({}_{\text{cold}}\)) [32]. The volume of this chiller is, on average, 40% less than the same capacity chiller using tube bundle heat exchangers.  
Figure 5: A 30 kW single-effect water/LiBr absorption chiller machine using an asymmetric plate heat exchanger technology from EAW Energieanalagenbau GmbH [30]. (**a**) Internal view of WEGRACAL® Maral 2; (**b**) External view of WEGRACAL® Maral 2. Reproduced with the permission of the International Institute of Refrigeration ([[https://iiifir.org](https://iiifir.org)]([https://iiifir.org](https://iiifir.org))) + [PERSON] et al. [30].