## 1 Introduction  
As a result of the improvement in human life standards, the demand for heating, ventilation and air conditioning (HVAC) has increased and consequently, the electrical consumption. The adsorption chiller is a promising candidate to utilize solar or waste heat at situations near environmental temperatures. Adsorption chillers were widely studied by many researchers due to many advantages over compression and absorption chillers. Some advantages were a lower grade heat source, silence, possibility for storage, simple control and maintenance and finally environment friendly chillers with zero ozone depletion potential and low potential for global warming. However, adsorption chillers had some disadvantages such as low Coefficient of Performance (COP), larger volume and weight and more expense when compared with vapor compression chillers. Most available adsorption chillers use a one stage non-regenerative cycle that operates at temperatures higher than 90 \({}^{\circ}\)C, which requires either a high temperature fossil fuel collector, a vacuum tube solar system or large-scale concentrated solar power (SCP) [1]. This equipment contributes to the high initial cost of the cooling systems and the problems associated with steam. A two-stage adsorption chiller was patented by Al-Maaitah in USA, built and tested for small scale capacity around two tons (7 kW) with promising results [2]. The chiller uses two-stage (desorption/adsorption) beds that make it possible to run the chiller at a hot water temperature as low as 60 \({}^{\circ}\)C and high ambient temperature ranges up to 50 \({}^{\circ}\)C to produce chilled water as low as 7 \({}^{\circ}\)C. This high ambient application is important since no water consuming cooling towers are needed. This application is essential for locations that are poor in water (such as Jordan) or for humid climates where wet cooling towers will not work properly (humid Gulf areas). However, to design for larger capacity and to conduct a pre-operation detailed test, a simulation of such chillers had to be conducted for this patented chiller at various weather conditions. Two of the pioneer researchers were [PERSON] and [PERSON], who carried out many fundamental experiments on adsorption cooling systems [3]. A simple model which takes into account both adsorption properties and apparatus characteristics was used to interpret experimental results. The mass and heat transfer were also interpreted using this model. They quantitatively studied the regeneration temperature on the cooling performance [4; 5; 6; 7; 8; 9]. Bed and heat exchanger configurations to reduce heat transfer resistance and improve performance were reviewed for single stage and multistage adsorption chillers [10; 11; 12]. Basic equations necessary for developing a novel empirical lumped analytical simulation model to predict chiller performance within acceptable tolerances were presented [13]. Genetic algorithm and adaptive neuro-fuzzy optimization tools were used to determine the optimum cycle time corresponding to maximum cooling capacity and unit performance [14]. Researchers have applied mathematical simplification to improve the performance prediction for single- and multi-stage adsorption chillers for low grade waste heat; the drawback was low COP and cooling capacity [15; 16; 17; 18; 19; 20; 21; 22; 23]. Many experimental studies were conducted on two-stage freezing machines, ice makers and chillers operated at temperatures less than 100 \({}^{\circ}\)C. The cooling capacity and COP increase with source temperature and decrease with decreasing evaporating temperature. The influence of evaporating temperature was not as significant as that of regeneration temperature [24; 25; 26]. For cycle time optimization, the transient behavior of a two-bed silica gel-water adsorption chiller and cycle time allocation to enhance performance for maximum cooling capacities and reduce chilled water fluctuations were fully discussed [27; 28].