One of the priorities in the development of Russian Federation is the policy of reducing energy consumption and implementation of energy efficient technologies. The article shows the example of the solution aimed at increasing the energy efficiency of systems which maintain optimal microclimate parameters in the office buildings. The solution is based on usage of WLHPS (Water Loop Heat Pump System). Consolidation into a united system makes it possible to utilize heat of the exhaust air heat and of other low-grade heat sources. The article shows the method of estimation the economic efficiency of these systems. The method is demonstrated on the example of office building. Comparison of various investment projects and selection the best solution was made by using economic indicators such as net present value (NPV) or the integrated effect and profitability index.