Mixed Climates
Summary
Mixed climates have roughly 5,400 or fewer heating degree days and winter monthly means below 45 F, with mixed-humid above 20 in. of annual precipitation and mixed-dry below it. Both seasons load the envelope, so assemblies must handle winter condensation and summer solar and humidity without favoring one season.
Cols
Definition
- Mixed-humid: over 20 in. annual precipitation, about 5,400 or fewer HDD65, monthly means falling below 45 F in winter
- Mixed-dry: under 20 in. annual precipitation, about 5,400 or fewer HDD65, monthly means falling below 45 F in winter; corresponds to IECC zone 4B
- By degree days, mixed climates fall in IECC zones 3 and 4 (zone 3 is 3,600 HDD65 or less; zone 4 is above 3,600 to 5,400)
- Representative cities: Atlanta, GA (3A), Baltimore, MD (4A), Albuquerque, NM (4B)
Design implications
- Heating and cooling loads are both significant, so insulation, glazing, and shading choices trade between seasons
- Moist (A) locations carry summer humidity and winter condensation risk; dry (B) locations carry large daily swings and solar gain
- Use the Hot-Humid and Cold notes for the moisture practice that applies at each end of the range
Example locations
Zones are from ANSI/ASHRAE Standard 169-2020, Addendum a (October 29, 2021), Tables A-3 to A-6. Mixed-dry cities are 3B or 4B; the rest are moist (A).
- North America: Atlanta, GA (3A); Baltimore, MD (4A); New York, NY (4A); Washington, DC (4A); Albuquerque, NM (4B); Mexico City, Mexico (3A)
- South America: Buenos Aires, Argentina (3A); Montevideo, Uruguay (3A)
- Europe: Lisbon, Portugal (3A); Rome, Italy (3A); Paris, France (4A); London, UK (4A); Budapest, Hungary (4A)
- Asia: Tokyo, Japan (3A); Shanghai, China (3A); Seoul, South Korea (4A); Beijing, China (4A)
- Africa: Johannesburg, South Africa (3A); Addis Ababa, Ethiopia (3A)
- Oceania: Sydney, Australia (3A); Melbourne, Australia (3A); Canberra, Australia (4A)
Flora and fauna
- Great Plains side of the dry boundary: the 20 in. annual rainfall line runs roughly along the 100th meridian, separating moister prairies to the east from semi-arid steppe to the west
- Plants: tallgrass, mixed-grass, and shortgrass prairie by decreasing moisture
- Wildlife: American bison, pronghorn, black-tailed prairie dog, swift fox, prairie rattlesnake, greater and lesser prairie-chicken
- Hazards: drought and dust storms in the semi-arid west; strong winds, especially in winter
Sources
- Wikipedia: Humid subtropical climate, https://en.wikipedia.org/wiki/Humid_subtropical_climate
- U.S. Department of Energy: Climate zones, https://www.energy.gov/eere/buildings/climate-zones
- ASHRAE Meteo: climate zone definitions for IECC and ASHRAE, https://ashrae-meteo.info/v2.0/help_IECC.php
- ASHRAE: ANSI/ASHRAE Addendum a to Standard 169-2020, Climatic Data for Building Design Standards (October 29, 2021), Tables A-3 to A-6
- Wikipedia: Great Plains, https://en.wikipedia.org/wiki/Great_Plains