ASHRAE Journal - December 2019 - 48

ASHRAE - CELEBRATING 125 YEARS

reasonable operating and ﬁrst cost. At the same time,
the engineering community was deeply focused on the
importance of humidity control on human thermal
comfort but found it hard to reconcile how operators
wanted to run systems, versus what evolving comfort
research was showing. Carrier noted, "art never achieves
its full possibilities, regardless of the market, until the
basic principles of its operation are thoroughly investigated and understood."2
In the early 20th century, tension rose among
those who were proponents of mechanical ventilation versus air conditioning versus natural ventilation. Experimental data largely came from the ASHVE
Research Laboratory, established in 1919 at the U.S.
Bureau of Mines in Pittsburgh, Penn. and led by F.
Paul Anderson. This laboratory was ﬁrst discussed by
President Harry M. Hart at the 1917 ASHVE annual meeting. In 1922, the laboratory published its ﬁrst ﬁndings,
including a comfort chart, consisting of a graph of the
combinations of temperature and humidity at which
most people would ﬁnd thermal comfort.
The historical record on July 4, 1919 for the Riviera
Theater, a sister to the Central Park Theater, indicated
an outdoor temperature of 94°F (34°C), while the
inside condition was between 74°F and 78°F (23°C and
26°C) with 70% relative humidity.2 At this time, comfort
was considered qualitatively rather than quantitively.
Wittenmeier was a proponent of an element of adaptive
thermal comfort we see today, where the indoor temperature should be set to 15°F (-9°C) lower than the outdoor
temperature.2 Wittenmeier disregarded relative humidity compared to Carrier and thought an RH of 75% was
acceptable, noting that while air could be sub-cooled
to 50°F (10°C) and reheated, this required additional
equipment and operating cost. Carrier's experience with
humidity control in industrial settings gave him valuable insights and a perspective that precision control of
the indoor environment was important.
In 1919, Balaban and Katz turned to the Carrier
Engineering Corporation (CEC) to address the "cold and
clammy" environment of Wittenmeier's system in an
economical manner. A major challenge was Chicago's
ventilation requirement of 25 cfm (12 L/s) per person,
lower than the 30 cfm (14 L/s) per person seen in New
York City but still signiﬁcantly higher than today's
requirement of 5 cfm (2 L/s) per person and 0.06 cfm/
ft2 (0.31 L/s/m2). A tension continued to exist between
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D E C E M B E R 2 0 19

Figure 5 Return Air Bypass. This diagram from 1928 showed a return air bypass
strategy that became dominant in providing cost-effective humidity control in 90% of
theaters during that era. Source: Air-Conditioning America / Refrigeration Engineering,
15, May 1928

proponents of mechanical ventilation alone versus air
conditioning. CEC considered three options:2
* Option 1: Reheat chilled water downstream of an air
washer. This was common to industrial systems but too
expensive for comfort air conditioning.
* Option 2: Reduce airﬂow to 10 to 15 cfm
(5 to 7 L/s) per person, but still at 100% outdoor air fraction, to better align with the temperature rise associated
with occupant heat gain. This would require a variance
from the Chicago Health Department.
Option 3: Provide 25 cfm (12 L/s) per person, but as a
mixed air system, with 50% recirculated air. This was
technically not compliant with the Chicago standards,
which called for 25 cfm (12 L/s) of outdoor air.²
The relationship between health and ventilation was a
signiﬁcant topic of focus in the late 1910s through 1920s,
driven by work at the ASHVE laboratory as well as the
Harvard School of Public Health. At the 1923 ASHVE
annual meeting, members voted to delete the term
"fresh air" from its proposed ventilation standard, noting its imprecision and support of a perception that only
non-recirculated air delivery systems were acceptable.
Carrier's team focused heavily on providing humidity control efﬁciently and developed what we still know
today as a return air bypass system (Figure 5). The early
version of this system called for 75% of the return air
to bypass an air washer while allowing the remaining
25% of outdoor air to enter the air washer. In 1921, the
Metropolitan Theater in Los Angeles became the ﬁrst to
use a bypass arrangement. The air-conditioning system
was estimated to cost $115,000. The system cost $500 per
month to run during the winter and $2,200 per month
during the summer. The bypass system allowed for an

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ASHRAE Journal - December 2019

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