Definition

• Building America criteria: over 20 in. annual precipitation, plus a wet-bulb temperature of 67 F or higher for 3,000 or more hours, or 73 F or higher for 1,500 or more hours, during the warmest 6 consecutive months
• Maps to the moist (A) portions of IECC zones 1, 2, and 3 below the warm-humid line
• Representative cities: Miami, FL (1A) and Houston, TX (2A)

Design implications

• Latent load: air conditioning removes moisture less effectively than it removes heat; a thermostat set low is a poor fix
• Dehumidification: provide it separate from sensible cooling, such as a whole-house dehumidifier
• Oversizing: short run cycles from oversized equipment leave indoor moisture uncontrolled; size to the load
• Air leakage: reducing building and duct leakage, or placing ducts inside the conditioned space, cuts both latent and sensible cooling load
• Ventilation: running outside air ventilation well below the design rate has been linked to high indoor humidity in field studies
• Controls: coordinating cooling, dehumidification, and ventilation in central ducted systems through control settings and lower airflows has held indoor humidity within goals using conventional equipment

Example locations

Zones are from ANSI/ASHRAE Standard 169-2020, Addendum a (October 29, 2021), Tables A-3 to A-6.

• North America: Miami, FL (1A); Houston, TX (2A); San Juan, Puerto Rico (0A)
• South America: Belem, Brazil (0A); Rio de Janeiro, Brazil (1A)
• Asia: Singapore (0A); Kuala Lumpur, Malaysia (0A); Mumbai, India (0A); Hong Kong (1A); Guangzhou, China (2A)
• Africa: Lagos, Nigeria (0A); Abidjan, Cote d'Ivoire (0A); Dar es Salaam, Tanzania (0A)
• Oceania: Port Moresby, Papua New Guinea (0A); Brisbane, Australia (2A)
• Europe: no station among the cities checked falls in zones 0A to 2A; the nearest are zone 3A cities such as Barcelona, Spain, Rome, Italy, and Sochi, Russia

Flora and fauna

• Southeastern coastal plain: longleaf, slash, and loblolly pine; southern live oak; pond and bald cypress in wetlands
• Understory: wiregrass and scrub oaks in sandhills; saw palmetto and gallberry in flatwoods
• Wildlife: red-cockaded woodpecker and gopher tortoise in mature longleaf forest
• Climate: humid subtropical, with rainfall peaking in the warmest months
• Building pests: Formosan subterranean termite colonies can hold several million workers and forage widely around a structure; in a Charleston survey of 50 infested structures, about 94 percent were infested from ground-based colonies; control methods match those for native subterranean termites

Sources

• Wikipedia: Tropical rainforest climate, https://en.wikipedia.org/wiki/Tropical_rainforest_climate
• 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: ANSI/ASHRAE Addendum a to Standard 169-2020, Climatic Data for Building Design Standards (October 29, 2021), Tables A-3 to A-6
• U.S. Department of Energy: Advanced HVAC humidity control for hot-humid climates, https://www.energy.gov/cmei/buildings/advanced-hvac-humidity-control-hot-humid-climates-0
• U.S. Department of Energy: whole-house dehumidifier case study, https://www.energy.gov/sites/prod/files/2013/11/f5/case_study_wholehouse_dehumidifier.pdf
• Wikipedia: Southeastern conifer forests, https://en.wikipedia.org/wiki/Southeastern_conifer_forests
• Clemson Cooperative Extension: Formosan subterranean termites, https://hgic.clemson.edu/factsheet/formosan-subterranean-termites/
• Wikimedia Commons: Our Conch House - Front porch - Key West Florida November 2023.jpg, by Cayobo (CC BY 2.0), https://commons.wikimedia.org/wiki/File:Our_Conch_House_-_Front_porch_-_Key_West_Florida_November_2023.jpg