Central air-conditioning energy consumption accounts for a large proportion of the buildings. And cold and heat source energy consumption accounts for about two-thirds of central air-conditioning system. For a research and development center in Shanghai, because cold and heat source capacity largely surpasses the actual demand, we propose to combine with cold sources of the two buildings. We call it "two-in-one" reconstruction. When cooling load is small, we use cold source in one building to support the two buildings. After implementation, by return on investment analysis, the average electric energy-saving rate is 9.6%. Investment can be recovered within one year.