# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 3 Newly Developed Commercial Absorption Chillers
### Single-Effect Double-Lift (Half-Effect) Absorption Chiller  
A new absorption cycle that combines the typical single-lift (i.e., single-effect) and a double-lift (i.e., half-effect) absorption cycle was proposed and studied by [PERSON] et al. [33; 34] for solar energy, industrial use, and application in DH networks. It extracts unused low-temperature heat sources and uses excess heat from DH networks in summer. This cycle can use driving heat at return temperatures of about 55 \({}^{\circ}\)C and permits temperature glides in desorption of more than 30 K. Therefore, the return (i.e., outlet) temperature of the hot water was lower with this cycle configuration, and it increased heat intake. Thus, the cooling capacity produced from the same heat source can be larger than that of a single-effect chiller run at the same heat carrier supply temperature and mass flow. On the basis of this cycle configuration, since 2017, the company Hitachi Johnson Controls Air Conditioning Co., Ltd. has been developing and commercializing a single-effect double-lift water/LiBr absorption chiller (product type DXS) [16; 35]. This product was developed under the commissioned research of the New Energy and Industrial Technology Development Organization (NEDO), Japan. The company has been conducting a research project of for NEDO on technology for the innovative use of unused thermal energy since 2015. The single-effect double-lift absorption chiller (see Figure 6) can be operated as both a double-lift and a single-effect double-lift operation absorption chiller. Switching between these two modes of operations, half-effect and single-effect double-lift, is done using the hot water and solution valves to switch the flow directions. This absorption chiller adopts a two-stage structure for the evaporator and absorber, denoted as two-step EVA-ABS, which is applied in high-performance chillers [16]. Since the temperature of the chilled water in the first evaporator (EVA1) is lower than that of the second evaporator (EVA2), the refrigerant pressure in the EVA1 (P\({}_{\text{low1}}\)) is also lower than EVA2 (P\({}_{\text{low2}}\)). Consequently, this chiller design has four pressure levels (i.e., high-pressure (P\({}_{\text{high}}\)), mid-pressure (P\({}_{\text{mid}}\)), and two low-pressure levels (P\({}_{\text{low2}}\)\(>\) P\({}_{\text{low1}}\)). Hence, the chiller operates at four pressure levels by dividing the evaporator and absorber into two-step instead of three pressure levels as in the basic single-effect double-lift cycle. The driving hot water stream first enters the high-temperature desorber (HDES) and then the low-temperature desorber (LDES) and auxiliary desorber (ADES). The cooling water is connected in a series flow arrangement entering first the ABS and then the auxiliary absorber (AABS) and condenser (CON). The hot water and cooling water circulating patterns, shown in Figure 6a, were chosen to maximize the chiller's cooling capacity. It is useful for applications of this kind of heat-driven chiller because it maximizes the specific cooling capacity per unit of hot water mass flow. The single-effect double-lift water/LiBr chiller (Figure 6b) has a nominal cooling capacity between 176 kW and 4395 kW with chilled water supply/return temperatures of 7/12 \({}^{\circ}\)C for the European market and 8/13 \({}^{\circ}\)C for the Asian market (e.g., Japan). The inlet/outlet temperatures of the hot water and cooling water in the nominal condition are 95/51 \({}^{\circ}\)C and 27/33 \({}^{\circ}\)C, respectively, for the European market and 95/55 \({}^{\circ}\)C and 31/36.5 \({}^{\circ}\)C for the Asian market. The corresponding thermal COP of the absorption chiller is 0.72 and 0.70, respectively, for the European and Asian chiller market. This chiller product (type DXS) can extend the usable temperature of hot water (obtained from a solar thermal collector installation or DH network) to the low-temperature range and extract about twice as much heat (~200%) as the temperature difference of the single-effect absorption chiller machines.