Page 214 - Industrial Ventilation Design Guidebook

5.! THERMAL COMFORT I 75
amount of discomfort can sometimes enhance concentration and productivity
by heightening arousal but too much discomfort is clearly detrimental.
Thus, thermal comfort is clearly desirable and important to the well-being
and productivity, and thereby the financial health, of industry. An understand-
ing of the principles of thermal comfort and discomfort can help guide a de-
signer's efforts in creating and operating industrial environments that are both
energy-efficient and thermally acceptable to the occupants.
5
A commonly expressed definition is: "Thermal Comfort is that condition
of mind that expresses satisfaction with the thermal environment." The defini-
tion implies that the judgment of comfort is a mental process that results from
physical, physiological, and psychological factors and processes. Dissatisfac-
tion can lead to complaints and other undesirable side effects.
Manufacturing engineers, operators, and owners, of course, want to mini-
mize complaints. A goal in the design process should be to recognize this ob-
jective and work to minimize discomfort from the outset. In general, designs
that provide satisfying or acceptable environments will be financially more
successful for the designer. That is, individual productivity will not be im-
paired by the environment, resulting in fewer accidents and lost time, fewer
complaints, reduced employee turnover, and lower insurance costs.
Why Is One Comfortable? What Affects Our Comfort?
Both primary factors and lesser secondary factors affect our sense of satisfac-
tion with the thermal environment. The primary factors have significant reproduc-
ible effects and directly affect heat transfer and the occupant's thermal state,
Secondary factors that may affect one's sense of satisfaction with a space are condi-
tions such as color and ambiance, local climate, age, physical fitness, sound, food,
and illness. These secondary factors have smaller to negligible effects on one's ther-
mal state and will not be discussed here, but such information is available. 6

5.1.2 Primary Factors
Humans and the other warm-blooded animals have developed thermoregulatory
systems to carefully control body temperature to levels that enable them to func-
tion and survive effectively. In general, thermal comfort occurs when the physio-
logical effort to control body temperature is minimized for the activity. Table 5.1

m TABLE 5.1 Thermal Environment and Physiological Responses
of Thermoregulation

Thermal
environment Physiological responses

HOT f blood flow to skin (vasodilation), heart rate T, sweating T,
skin moisture T, body temperatures T, metabolism T
NEUTRAL comfort, minimized effort, T mh (mean body temperature)
~36.2°C
COLD -tblood flow to skin (vasoconstriction), muscle tension and
shivering T, body temperatures •I, metabolism T