Reducing Climate-Change-Induced Heat Strain and HVAC Performance Loss With Circulating Fans

With the rate of climate change accelerating and predicted outcomes growing more dire, the authors examine the potential of air-circulating fans to mitigate increased occupant heat strain in heated-and-ventilated-only warehouses and improve the resilience of mechanical systems and maintain occupant thermal comfort in conditioned commercial buildings.

In 1990, the Intergovernmental Panel on Climate Change (IPCC), the United Nations (U.N.) body for assessing the science related to climate change, released its First Assessment Report,1 detailing the impacts human activities were having on atmospheric greenhouse-gas concentrations and tropospheric air temperature. The report predicted global mean air temperature would rise by an average of 0.54°F (0.3°C) per decade in the 21st century, or 5.4°F (3.0°C) by the year 2100, an outcome that would be devastating for the environment and many of the world’s most vulnerable populations, which would suffer the effects of more frequent severe-weather events, sea-level rise of up to 3.3 ft (1 m), and food insecurity.

Flash forward to 2021 and the release of IPCC Working Group I’s contribution to the Sixth Assessment Report, which the U.N. secretary-general called a “code red for humanity.”2 While international treaties such as the Kyoto Protocol and the Paris Agreement were designed to cap mean-temperature increase at 2.7°F (1.5°C), the most likely greenhouse-gas-concentration trajectory adopted by the IPCC, the intermediate representative concentration pathway (RCP) of 4.5, sees a mean-temperature increase of up to 6.3°F (3.5°C) by the end of the century.3 In short, it is becoming increasingly clear that the 2.7°F (1.5°C) target will be exceeded, and it could happen as soon as 2050.3

This article will examine the predicted performance of buildings at significant risk from climate change and illustrate how the use of circulating fans can reduce cooling demand in conditioned buildings and heat strain in unconditioned ones under increasingly demanding climatic conditions.

Contextualizing Global Impacts and Existing Works

One of the greatest communication challenges in climate science is “consensus gap,” or the dissonance between analytical, scientific, and numerical effects of climate change (e.g., rise in mean temperature) and more human, contextual, and observational impacts of climate change (e.g., seasonal temperature, drought). Researchers at ETH Zurich leveraged connections between what populations subjectively know about and associate with their current climates to underscore the dramatic changes that will occur under the RCP-4.5 scenario by 2050, selecting 520 cities around the world and applying statistical models to 19 independent bioclimatic variables to determine the cities’ best future climatic analog.4

Distilling the results of the ETH Zurich study, Table 1 shows the future climatic analog of cities in 15 climate zones (CZ) used in U.S. Department of Energy (DOE) reference-model simulations and in ANSI/ASHRAE Standard 169-2021, Climatic Data for Building Design Standards.5 For context, 2017 annual heating degree-days based on 65°F (HDD65) and 2017 annual cooling degree-days based on 50°F (CDD50) from the ASHRAE Climatic Design Conditions database are given.

David Rose

Will Conner

Representative City CZ HDD65 CDD50
Miami, Fla. 1A 113 9,942
Houston, Texas 2A 1,167 7,630
Phoenix. Ariz. 2B 912 9,229
Atlanta, Ga. 2,640 5,391
Las Vegas, Nev. 3B 1,975 7,249
San Francisco, Calif. 3C 3,779 1,835
Baltimore, Md. 4A 4,491 3,936
Albuquerque, N.M. 4B 3,956 4,271
Seattle, Wash. 4C 4,705 2.068
Chicago, Ill. 5A 6,190 3,122
Boulder, Colo. 5B 10,865 369
Minneapolis, Minn. 6A 7,477 2,882
Helena, Mont. 6B 7,504 2,092
Duluth, Minn. 7 9,286 1,674
Fairbanks, Alaska 8 13,577 1,087

TABLE 1. Representative cities in continental-U.S. climate zones and their future climatic analogs.

Future Climatic Analog Future CZ HDD65 CDD50
Rio de Janeiro, Brazil 1A -106 -391
Jacksonville, Fla. 2A 136 -670
Kuwait City, Kuwait 1B -201 1,808
Memphis, Tenn. 244 325
Phoenix, Ariz. 2B -1,063 1,980
Lisbon, Portugal 3C -2,083 3,165
Nashville, Tenn. 3A -1,000 946
El Paso, Texas 3B -1,656 1,874
San Francisco, Calif. 3C -926 -233
St. Louis, Mo. 4A -1,518 1,017
Amarillo, Texas 4B -6,822 3,981
Kansas City, Mo. 4A -2,450 1,166
Salt Lake City, Utah 5B -2,038 1,474
Toledo, Ohio 5A -3,381 1,587
Winnipeg, Canada 7 -3,212 728
Portland. Ore. Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec.
2% DB (°F) 54.9 57.3 64.6 71.7 81.2 84.5 91.3 90.2 86.6 72.2 59.8 53.6
2% MCWB (°F) 50.7 49.5 52.5 57 61.9 64.6 68.4 67.6 63.9 58 55.2 50.5
2% DB (°C) 12.7 14.1 18.1 22.1 27.3 29.2 32.9 32.3 30.3 22.3 15.4 12.0
2% MCWB (°C) 10.4 9.7 11.4 13.9 16.6 18.1 20.2 19.8 17.7 14.4 12.9 10.3