# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 3 Newly Developed Commercial Absorption Chillers
### Air-Cooled Small Capacity Chiller  
The solar absorption cooling system benefits if dry cooling towers are used because less maintenance is required and operational costs are lower, especially in a small capacity range. An air-cooled small capacity water/LiBr chiller (ASC) was developed for small-scale applications [19; 20] which introduced a new concept in solar space cooling. It consisted of three main components--flat plate solar thermal collectors, an ASC, and several types of indoor cooling devices--and made it possible to replace the most typical space cooling systems used in residential and small commercial buildings (i.e., split air conditioner systems which were often designed with mounted indoor cooling devices and outdoor electricity-driven vapor compression chillers). The solar space cooling that uses ASC (depicted in Figure 2) is a stand-alone system based on a modular design that replaces electricity-driven split air conditioner systems, of which there were about 145 million units worldwide in 2018. Additionally, the solar cooling system connected to a backup central heating system (e.g., central boiler and district heating (DH) networks) to ensure a continuous supply of space cooling to the end-user throughout the year despite intermittent solar radiation. The modular features of this system provide long-term operational reliability and facilitate installation. Moreover, the flexibility of the design enables various indoor cooling devices to be incorporated to adapt to the interior design and architectural needs of existing buildings as well as new ones. These indoor cooling devices include wall-mounted fan coil units, cassettes, radiant ceiling panels, and suspended/integrated chilled beams (Figure 2) and can be used in single or multi-split arrangements depending on the design requirements. The ASC, type A25s, has a nominal cooling capacity of 2.5 kW at an ambient temperature of 35 \({}^{\circ}\)C with chilled water supply/return temperatures of 13/18 \({}^{\circ}\)C and a thermal COP of \(\sim\)0.81 [20]. The chiller is driven by hot water, \(>\)70 \({}^{\circ}\)C, produced by two flat-plate collectors (total aperture area of 4.8 m\({}^{2}\), 2\(\times\)2.39 m\({}^{2}\), and/or backup central heating systems (with 3.1 kW heat supply capacity)). It has a compact size of approximately 0.39 m\({}^{3}\) and a weight of 75 kg which can connect up to three indoor cooling units. This chiller needs minimal electricity (\(<\)0.15 kW\({}_{\text{el}}\)) for its solution circulation pump and parasitic electrical power consumption. Besides, the electricity consumption of the indoor cooling unit depends on whether the unit used in the air conditioning system is, for example, a wall-mounted fan coil unit (\(<\)0.05 kW\({}_{\text{el}}\)), a cassette unit (\(<\)0.11 kW\({}_{\text{el}}\)), or a floor/ceiling unit (\(<\)0.08 kW\({}_{\text{el}}\)). The system is relatively silent with a noise level of less than 45 dB(A) for outdoor units (i.e., ASC) and 48 dB(A) for indoor cooling devices (i.e., wall-mounted, cassette, and floor/ceiling fan coils) [20]. The cooling capacity of the system can be extended to 160 kW by using a cascade control unit to manage the absorption chiller and up to 256 fan coil units [21]. Figure 2: A modular stand-alone, small-scale solar space cooling system developed and commercialized by PURIX ApS (type A25s). (**a**) Outdoor unit: ASC and two flat-plate solar collectors; (**b**) Indoor unit: fan coil types. Adapted from References [19; 20]. Note: ASC = air-cooled small capacity water/LiBr chiller. The system can be implemented as a stand-alone or in combination with other air conditioner systems using chilled water as a secondary fluid for cold distribution. A system such as this one has economic and environmental benefits: it saves up to 85% on the electricity bill and reduces CO\({}_{2}\) emissions by 64% (compared to an energy class A+ air conditioning system) [22].