# Dynamic Performance Analysis for an Absorption Chiller under Different Working Conditions
## 1 Introduction  
With the speed-up of urbanization, the energy consumption of air conditioning and refrigeration keeps increasing continuously [1]. The vapor compression chiller is widely applied due to its attractive advantages, such as high efficiency, low costs, quick response time, etc. [2; 3]. But it usually consumes a significant quantity of high-grade electricity, and large-scale application can cause overload of electricity generation and transmission [4]. As a potential solution to the energy and environmental problems, the absorption chiller (AC), which is mainly driven by fossil fuel, renewable energy or low-grade waste heat, is being more and more popular [5; 6]. Moreover, AC has a competitive primary energy efficiency compared to electricity-driven chiller, and can adopt environmentally friendly working fluids, such as H\({}_{2}\)O-LiBr and NH\({}_{3}\)-H\({}_{2}\)O [7]. A number of researchers have studied the steady-state performance of AC by both theoretical simulations [8; 9; 10] and experiments [11; 12; 13; 14]. However, the real-time operation of a commercial AC is governed by continuous transient processes, and the relaxation time required to achieve a new steady-state is rather long compared to the vapor compression chiller with a similar cooling capacity [15; 16]. What's more, the dynamic process of AC is essential for the adjustment of AC and the control of the whole system, of which the stabilization can be affected by the transient process. Under this circumstance, the dynamic performance of AC has been studied, including various working fluids like H\({}_{2}\)O-LiBr [17], NH\({}_{3}\)-H\({}_{2}\)O [18] and CO\({}_{2}\)-[bmim][PF6] [19], different absorption cycles like double-effect AC [20] and diffusion AC [21], as well as alternative method like exergy analysis [22]. [PERSON] and [PERSON] [23] developed a dynamic model of an absorption heat pump, the heat source flow rate had a \(\pm\)20% stepwise change, and the heat sink inlet temperature linearly increases 5 K within 300 s. The accuracy of the model was good as compared with a real machine. [PERSON] et al. [24] carried out the numerical simulations of a steam-driven absorption heat pump recovering waste heat, the storage terms in the model included the thermal capacities of the containers and the solution mass storage in the vessels, but lacked the thermal inertia of the heat exchangers. During the shut-off period of the system, the simulated values of the absorption heat, condensation heat and evaporation heat showed good agreement with the operational data. [PERSON] and [PERSON] [16; 25] established a dynamic model of an absorption chiller, which considered the transport delays of the solution cycle, thermal storage and mass storage. The thermal capacities of all the components were divided into internal and external parts. The work also analyzed the effects of the thermal storage and transport delay on the relaxation time. But the model was a little over-simplified, since the evaporation latent heat, sorption latent heat and weak solution mass flow rate were all considered as constants. [PERSON] et al. [26] presented a dynamic model and its experimental verification for a single-effect absorption chiller, taking into account the thermal inertia of the heat exchangers, containers and solution storage. The largest relative error between the model and experiment was \(\pm\)5%. And a 10 K step change of the driving temperature was investigated. However, the cumulated heat capacities of all components, which should vary with the fluid storage, were considered as constants in this work. [PERSON] et al. [15; 27] completed the dynamic analysis on an absorption chiller, which considered the mass, species and energy balance. The convective coefficients were calculated with the mathematical correlations to determine the variable overall heat transfer coefficients by updating the thermal and physical properties in time.