Based on performance test results

characteristics of cooling capacity (CC) and energy efficiency ratio (EER) change with indoor dry-bulb and wet-bulb temperatures (D&WBT) are examined. By applying corrected Akaike information criterion

best fit 3D surface equations of CC and EER are determined to obtain their variation gradients and corresponding intervals of gradient extrema. Based on the classification principle of keeping the maximum (minimum) EER variation rates between neighboring classes equal

D&WBT allowances in national standard are classified into three classes by using nonlinear classification

with the corresponding range of D&WBT in the union set of the intervals of gradient extrema of CC and EER as Class A

and the current D&WBT allowances set in the national standard as Class C. As an illustration of this new method

indoor D&WBT allowances under the cooling working condition are classified into Class A

B and C. The results show that the EER variation rate in Class A is as low as 1.04%

while that in Class C is 5.19%. It can be concluded that classified D&WBT allowances are more effective in evaluating the performance of a unit and valuable as a reference for revision of the national standard.