Cost-benefit evaluation for building intelligent systems with special consideration on intangible benefits and energy consumption

Building intelligent system has become one of the standard configurations in a public building even in a residential building. Intelligent buildings are expected to provide high-efficient, convenient, comfortable and energy-saving built environment so as to bring additional benefits. However, problems like sensor faults and control strategy flaws may result in low performance and high energy consumptions and maintenance costs are needed as well. Thus it is needed to synthetically evaluate the costs and benefits of intelligent systems to help building investors to make decisions. This paper proposes a cost-benefit evaluation method for building intelligent systems. Life cycle net present value (NPV) of all the costs and benefits, including tangible and intangible, is used as an index to evaluate the performance of the building intelligent systems. The proposed method puts emphases on the quantitative evaluation of intangible benefits using Analytical Hierarchy Process (AHP) method to determine the weights of each aspects of intangible benefit. The building energy consumptions are taken as an another emphasis as well. The proposed method is applied to evaluate three actual buildings to check its feasibility and effectiveness. Sensitivity analysis of NPV to energy consumption of the case study buildings shows that the energy consumption increase or decrease caused by different performances of intelligent systems can influence the positive or negative of NPV, which implies the building intelligent systems are worth of investment or not.