Discussion on outdoor air design parameters in American URD standard

There are some differences in the definition of outdoor air design parameters in different standards based on the URD standard in China. To clarify the connotation of these outdoor air design parameters in the URD standard, the non-guarantee rate and the coincident wet-bulb temperature in the URD standard are studied in this paper, and the following points are made clear: 1% non-guarantee rate in the URD standard is defined as seasonal non-guarantee rate, and the annual non-guarantee rate in the ASHRAE standard can be equivalent to the annual average non-guarantee hour number per year in GB 50019-2015 standard. The coincident wet-bulb temperature in the URD standard is essentially the maximum of all coincident wet-bulb temperatures.