Various single stage ammonia-water absorption system configurations result in a confusion of determining a better one with better performance. In this paper, a unified single stage ammonia water absorption system configuration for freezing, air-conditioning, and space heating applications is proposed, and it can produce best thermal efficiencies in terms of internal heat recovery under different application conditions. The model of the unified system is established to investigate the operating parameters and the performance of the system under the representative freezing, air-conditioning, and space heating application conditions. The results verify the feasibility of the unified system, and show that the thermal efficiency is improved by 25%, 34%, and 20% respectively, compared to a conventional single stage absorption system. The calculated results also verify the key points of the system operation, which are making the feed saturated, and adjusting a proper split ratio of the strong solution to the rectifier, respectively. The 3D figures of the system thermal efficiency versus the boundary temperatures show the performance and its improvement of the unified system configuration intuitively. The cycle switching diagram is presented and provides a reference for regulating the cycle operation of the unified system. (C) 2019 Elsevier Ltd. All rights reserved.