Winter design conditions
Use Table B-l in the textbook or Table 1A of ASHRAE Fundamental Handbook Chapter26.
The 99.6% and 99% indicate the risk level desired. When 99% is selected, it means the outdoor temperatures have been equaled or exceeded by 99% of the total number of hours in a year (8760 hrs).
99.6% (0.4%) ~ 35 hrs 99.0% (1.0%) ~ 88 hrs
98.0 (2.0%) ~ 175 hrs
95.0 (5.0%)-438 hrs
Design conditions — Column 2 Wind — Column 3
Peak load for infiltration — Columns 4 and 5
ASHRAE Handbook 1997 and the textbook use annual percentiles of 99.6% and 99%.
Design rule of thumb: design outdoor relative humidity in winter 60%
Posted in Fundamentals of Heating. Ventilating, and Air-Conditioning