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The time that an absorption chiller needs to reach the designed working condition is called start-up. During this time, energy is consumed through the system while efficient refrigeration is not available. So, it's too important to consider the influencing parameters on this period of time so that reduction in energy consumption is achieved. Also, dynamic analysis is used to reduce the startup time and increase system performance in addition to strategic control purposes. Optimizing an absorption cycle during transient operations, such as start up or shut down is very important. The aim of this study is to investigate and compare the effect of employing refrigerant and solution heat exchangers (RHX and SHX) on dynamic performance of both NH 3-H 2 O and H 2 O-LiBr absorption chillers (ACs). Also, the effect of solution heat exchanger's efficiency on the start-up time of the key parameters of both ACs is investigated. To diminish the effect of approximate relations on the results, thermodynamic properties of NH 3-H 2 O and H 2 O-LiBr solutions are extracted from the EES software. By making a link between MATLAB and EES software, a set of differential equations is solved in MATLAB software. The fourth order Runge-Kutta method is employed to solve the differential equations system. This process is continued until convergence criteria are satisfied. The results show that removing SHX from the cycle increases the start-up time of both NH 3-H 2 O and H 2 O-LiBr AC's COPs by 11.76% and 45.16% respectively. The start-up time of the COP of H 2 O-LiBr absorption chiller is highly affected in comparison with the NH 3-H 2 O absorption cycle, by removing SHX or increasing the SHX efficiency. Also, utilizing the RHX does not affect the dynamic response of the key parameters of the both absorption chillers.

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