CLIMATIC DESIGN INFORMATION
Revised outdoor climatic conditions published by the American Society of Heating,
Refrigerating and Air-Conditioning Engineers (ASHRAE).
The recently published 1997 ASHRAE Handbook of "Fundamentals" shows revised
climatic conditions for various cities in the United States. This affects VA Design criteria
for sizing equipment which is based on previously published climatic conditions by
For consistency in design, VA HVAC Design Manuals list specific climatic conditions to
be followed on VA projects, and are tabulated under columns 1% and 2.5% for summer
and 99% and 97.5% for winter in attachment 6 of the manuals. These percentages
reflect annual cumulative frequency of occurrence of outdoor weather conditions.
These percentages have changed in the 1997 manual to 0.4% and 1% for summer and
99.6% and 99% for winter.
According to ASHRAE, for summer conditions, the new 0.4% annual value is about the
same as the old 1% summer design temperature, and the new 1% annual value is
about 1 degree F lower than the old 2.5% summer design temperature. The new 99.6%
and 99% winter conditions are slightly colder than the old 99% and 97.5% conditions.
1. The latest climatic design information is contained in chapter 26 of 1997 ASHRAE
Handbook of Fundamentals and should be followed on future projects.
2. VA design manual attachment 6 has been revised to conform to latest 1997 ASHRAE
FOR ADDITIONAL INFOR MATION:
Contact Satish Sehgal at 202-565-5032, Kurt Knight at 202-565-4980, or Sat Gupta at
August 4 1997