ASHRAE CLIMATIC DESIGN CONDITIONS 2009/2013/2017

2021 International Energy Conservation Code (IECC)

SECTIONC301 CLIMATE ZONES

Climate zones from Figure C301.1 or Table C301.1 shall be used for determining the applicable requirements from Chapter 4. Locations not indicated in Table C301.1 shall be assigned a climate zone in accordance with Section C301.3.

a. Key: A ‒ Moist, B ‒ Dry, C ‒ Marine. Absence of moisture designation indicates moisture regime is irrelevant. Asterisk (*) indicates a Warm Humid location.

C301.3Climate zone definitions.

To determine the climate zones for locations not listed in this code, use the following information to determine climate zone numbers and letters in accordance with Items 1 through 5.

To determine the climate zones for locations not listed in this code, use the following information to determine climate zone numbers and letters in accordance with Items 1 through 5. 

1. 1.Determine the thermal climate zone, 0 through 8, from Table C301.3  using the heating (HDD) and cooling degree-days (CDD) for the location.

2. 2.Determine the moisture zone (Marine, Dry or Humid) in accordance with Items 2.1 through 2.3.

   1. 2.1.If monthly average temperature and precipitation data are available, use the Marine, Dry and Humid definitions to determine the moisture zone (C, B or A).

   2. 2.2.If annual average temperature information (including degree-days) and annual precipitation (i.e., annual mean) are available, use Items 2.2.1 through 2.2.3 to determine the moisture zone. If the moisture zone is not Marine, then use the Dry definition to determine whether Dry or Humid.

      1. 2.2.1.If thermal climate zone is 3 and CDD50°F ≤ 4,500 (CDD10°C ≤ 2500), climate zone is Marine (3C).

      2. 2.2.2.If thermal climate zone is 4 and CDD50°F ≤ 2,700 (CDD10°C ≤ 1500), climate zone is Marine (4C).

      3. 2.2.3.If thermal climate zone is 5 and CDD50°F ≤ 1,800 (CDD10°C ≤ 1000), climate zone is Marine (5C).

   3. 2.3.If only degree-day information is available, use Items 2.3.1 through 2.3.3 to determine the moisture zone. If the moisture zone is not Marine, then it is not possible to assign Humid or Dry moisture zone for this location.

      1. 2.3.1.If thermal climate zone is 3 and CDD50°F ≤ 4,500 (CDD10°C ≤ 2500), climate zone is Marine (3C).

      2. 2.3.2.If thermal climate zone is 4 and CDD50°F ≤ 2,700 (CDD10°C ≤ 1500), climate zone is Marine (4C).

      3. 2.3.3.If thermal climate zone is 5 and CDD50°F ≤ 1,800 (CDD10°C ≤ 1000), climate zone is Marine (5C).

3. 3.Marine (C) Zone definition: Locations meeting all the criteria in Items 3.1 through 3.4.

   1. 3.1.Mean temperature of coldest month between 27°F (-3°C) and 65°F (18°C).

   2. 3.2.Warmest month mean < 72°F (22°C).

   3. 3.3.Not fewer than four months with mean temperatures over 50°F (10°C).

   4. 3.4.Dry season in summer. The month with the heaviest precipitation in the cold season has at least three times as much precipitation as the month with the least precipitation in the rest of the year. The cold season is October through March in the Northern Hemisphere and April through September in the Southern Hemisphere.

4. 4.Dry (B) definition: Locations meeting the criteria in Items 4.1 through 4.4.

   1. 4.1.Not Marine (C).

   2. 4.2.If 70 percent or more of the precipitation, P, occurs during the high sun period, defined as April through September in the Northern Hemisphere and October through March in the Southern Hemisphere, then the dry/humid threshold is in accordance with Equation 3-1.

      

      (Equation 3-1)

      where:

      P = Annual precipitation, inches (mm).

      T = Annual mean temperature, °F (°C).

   3. 4.3.If between 30 and 70 percent of the precipitation, P, occurs during the high sun period, defined as April through September in the Northern Hemisphere and October through March in the Southern Hemisphere, then the dry/humid threshold is in accordance with Equation 3-2.

      

      (Equation 3-2)

      where:

      P = Annual precipitation, inches (mm).

      T = Annual mean temperature, °F (°C).

   4. 4.4.If 30 percent or less of the precipitation, P, occurs during the high sun period, defined as April through September in the Northern Hemisphere and October through March in the Southern Hemisphere, then the dry/humid threshold is in accordance with Equation 3-3.

      

      (Equation 3-3)

      where:

      P = Annual precipitation, inches (mm).

      T = Annual mean temperature, °F (°C).

5. 5.Humid (A) definition: Locations that are not Marine (C) or Dry (B).

ZONE NUMBER	THERMAL CRITERIA
	IP Units	SI Units
0	10,800 < CDD50°F	6000 < CDD10°C
1	9,000 < CDD50°F < 10,800	5000 < CDD10°C < 6000
2	6,300 < CDD50°F ≤ 9,000	3500 < CDD10°C ≤ 5000
3	CDD50°F ≤ 6,300 and HDD65°F ≤ 3,600	CDD10°C < 3500 and HDD18°C ≤ 2000
4	CDD50°F ≤ 6,300 and 3600 < HDD65°F ≤ 5,400	CDD10°C < 3500 and 2000 < HDD18°C ≤ 3000
5	CDD50°F < 6,300 and 5,400 < HDD65°F ≤ 7,200	CDD10°C < 3500 and 3000 < HDD18°C ≤ 4000
6	7,200 < HDD65°F ≤ 9,000	4000 < HDD18°C ≤ 5000
7	9,000 < HDD65°F ≤ 12,600	5000 < HDD18°C ≤ 7000
8	12,600 < HDD65°F	7000 < HDD18°C

For SI: °C = [(°F) – 32]/1.8.