According to the features of protective engineering

an index for energy efficiency evaluation of an air-conditioning system is proposed

which is named as operating-demand energy efficiency ratio. Its definition and calculation method are provided in this paper. The energy efficiency evaluation strategy of an air-conditioning system is established from the whole system and its components

and the limiting values of the energy efficiency are provided. By taking a small underground engineering in hot summer and cold winter zones as an example

the energy efficiency evaluation of the air-conditioning system was carried out. The evaluation result shows that the system exhibited a daily low level of energy efficiency. On the basis of the result

the original project was retrofitted

and the energy efficiency of the system was improved by 18.9%

which verifies the feasibility and rationale of the proposed evaluation method.