ASHRAE Journal Supplement - AMCA InMotion - November 2024 - 19

and heat stroke to organ failure and even death.
American Medical Association (AMA) data show heat
exposure was the underlying cause or a contributing
cause in more than 2,300 deaths in the United States
from 2019 to 2023, an increase in number of deaths per
million people of approximately 50 percent compared
with the previous 40 years.2 Given there is no federal law
requiring heat-related illnesses to be reported to public
health agencies and the fact symptoms often go unrecognized
or are misidentifi ed, the actual number of deaths
likely is much higher.
To provide a more complete picture of heat-related
illness in the United States, the U.S. Department of Health
& Human Services (HHS) Offi ce of Climate Change and
Health Equity (OCCHE) in 2023 launched the Heat-Related
EMS Activation Surveillance Dashboard (https://bit
.ly/NEMSIS_Dashboard).
Updated weekly, the tool
tracks emergency-medicalservices
(EMS) responses
to people experiencing
heat-related emergencies
in pre-hospital settings.
The fact the dashboard
was modeled after a tool
designed to t rack and
prevent opioid overdoses
is a clear signal extreme
heat offi cially has become
a national health crisis.
Th i s a r t i c l e wi l l
100
120
20
40
60
80
Heat
Generation
Respiration
Heat Loss
AC
Basal metabolism Posture
Evaporation
discuss t he g rowing
prevalence of heat stress,
the role of buildings in
providing protection, and heat mitigation through the
frameworks of resilience, refuge, regulations, and redundancy,
the use of large-diameter (greater than 7 ft [2.1 m])
ceiling fans (LDCF), also known as high-volume, lowspeed
(HVLS) fans, in particular.
Heat Loss
AC+ Fans
Activity
Convection
Radiation
FIGURE 1. Heat balance at 1.1 Met and various
indoor-air conditions.
and core body temperature rises. Heat stroke occurs when
core body temperature reaches 104°F (40°C).
The following equation shows heat generation as three
separate factors: basal metabolism (Mb), posture (Mp), and
activity (Ma):4
M = Mb + Mp + Ma
Figure 1 shows the heat-generation breakdown for
a seated occupant doing light work, which equates to
approximately 1.1 Met, or 6 W/ft2 (65 W/m2). Also shown
is balancing heat loss for two scenarios:
■
Heat Loss 1: 75°F (23.9°C) air dry bulb, mean radiant
temperature equal to air dry bulb, 50-percent relative
humidity, 30-fpm (0.15 m/s) air speed, 0.6 clothing
insulation (Clo)
■
Heat Loss 2: 80°F
(25.7°C) air dry bulb, mean
radiant temperature equal to
air dry bulb, 50-percent relative
humidity, 120-fpm (0.61
m/s) air speed, 0.6 Clo
While the amount of heat
loss from the body is the same
for both scenarios, the body
utilizes different modes of heat
transfer to achieve thermal
equilibrium/comfort.
Under more extreme environmental
condit ions, the
body may not be able to maintain
a balance between heat
generation and heat loss. With
100-percent relative humidity
Heat Balance
Normal core body temperature is approximately 98.6°F
(37°C).3 Heat illness occurs when the body is unable to
maintain a balance between heat generation and heat loss
www.amca.org
and still air, body temperature may begin to rise at an
air temperature as low as 94°F (34°C).3 With low relative
humidity and the movement of air, body temperature
can be maintained at air temperatures above 125°F
(52°C). The World Health Organization (W.H.O.) suggests
air movement is benefi cial only when air temperature is
below 104°F (40°C).5 This, however, neglects the impact
of humidity, which is accounted for in the Center for the
Built Environment (CBE) Thermal Comfort Tool (https://
comfort.cbe.berkeley.edu).
2023 AMCA inmot ion
19
Body Heat (Watts)
https://bit.ly/NEMSIS_Dashboard https://bit.ly/NEMSIS_Dashboard https://comfort.cbe.berkeley.edu https://comfort.cbe.berkeley.edu http://www.amca.org
ASHRAE Journal Supplement - AMCA InMotion - November 2024

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