The Homeothermic Imperative

The pitfalls of nineteenth century determinist versus twentieth century free will semantics were sidestepped by biologists who traced the evolutionary distribution of the human organism on the earth's surface in response to the demands of thermoregulatory processes (Burton and Edholm 1955; Dubos 1980; Newman 1956; Sargent 1963; Scholander 1955, 1956). While large scale determinism and questions of survival of civilizations are of interest in themselves, examination of the smaller scale level of the individual enables identification of the actual mechanisms involved, both biological and technological.

First order (direct environmental effect) studies of the homeothermic imperative came from several fields including medical biometeorology (e.g. classical works of Mills 1946; Petersen 1947; Tromp 1963), applied psychology (e.g. Mackworth 1950; Pepler and Warner 1968), and especially thermophysiology (Yaglou 1926; Gagge 1936; Gagge et al. (138); Winslow and Herrington 1949; Burton and Edholm 1955; Hensel 1959; Hardy 1961) and heating, cooling and ventilating practice and theory (e.g. Houghten and Yagloglou 1923 a, b; Bedford 1936; Fanger 1967 and many others).The model for these studies was largely one that envisaged a linear cascade:

thermal _ thermoregulatory_ physiological_discomfort_► Performance stimulus response stress _______decrement

Although there were seemingly anomalous observations of seasonality and regional differences (e.g. Yaglou and Drinker 1928; Hickish 1955), until the late 1960s of the last century there was very little dissent from Gagge's (1936) renowned formulation that human responses could be well estimated from the thermal energy budget equation+/-S = M+/- R+/- C - E where S is storage or stress, M is metabolism,

R is radiation, C is convection and E is evaporation. Each of the environmental terms could be measured instrumentally and metabolic rates could be approximated from empirically derived tables for work categories. Minimum stress occurs when metabolism is balanced by heat losses which maintains homeostasis at a constant core temperature, or homeothermy, at near 37°C. This particular core temperature is reached when environmental temperature is near 25°C. Following a series of controlled laboratory experiments with healthy young males, it was strongly argued by Fanger (1970) that this was a universal optimum for people engaged in tasks at near 100 Wm2 metabolic rate, when at 25.5°C his "predicted mean vote" PMV (Fanger 1967) and S = 0. Any deviation from this could be simply explained through either metabolic variability or clothing insulation (ASHRAE laboratory based standards prescribed 24°C for summer and 22°C for winter clothing). Second order or higher level cultural adaptations were dismissed as being of little relevance.

As with Huntington's search for a universal optimum temperature, Fanger's insistence upon a simple deterministic explanation fails when different peoples and cultures are examined. Thermal comfort and real life preference surveys, using the 7 point ASHRAE or Bedford scales of subjective thermal sensations, have shown that there is no single "neutral" temperature. Rather thermal neutrality migrates with exposure towards ambient temperature. Empirically, such far reaching adaptation has been observed in repeated and comparable studies into differences of warmth perception in regression of group mean neutralities on monthly outdoor and prevailing indoor temperatures (Auliciems 1969, 72, 83; Humphreys 1975, 1976; Howell and Kennedy 1979; Berglund 1979; Auliciems and de Dear 1997; Nichol 1974; de Dear et al. 1997; Schiller et al. 1988; Humphreys and Nicol 2000a, b; Heidari and Sharples 2002; de Dear and Brager 2001; Soebarto et al. 2004; van der Linden et al. 2006).

The neutrality shift cannot be explained by clothing or other personal parameters, but rather by the "thermopreferendum", or more simply preference (or choice) resulting from thermal expectations elicited by current and past thermal experiences, and cultural and technical practices (Auliciems 1981). This "adaptive comfort model" is shown schematically in Fig. 11.1. Within air conditioned buildings with constant equable levels of warmth, however, seasonality and regional adaptability tends to fail (de Dear et al. 1997). This provides serious argument in favor of reducing air conditioner usage, which happily in turn would reduce energy consumption. At this time, the adaptive model is being espoused in amendments in ASHRAE Standards 55, ASHRAE database RP884, European directive EN 15,251 and various national standards publications.

Minimum neutrality values have been observed below 15°C for highly acclimatized British schoolchildren (Auliciems 1969) and also the elderly at 17°C (Fox 1973), and maximum preferred temperatures at 34°C and higher in hot countries (Nicol 1974). In brief, the shift of preferred indoor comfort temperatures at a monthly resolution (see Fig. 11.2) is at 0.31°C/1°C in the direction of prevailing outdoor (and indoor) temperature according to a generalized regression

T^=0.31T M + 17.6 where T^ is the preferred group temperature, and TM is mean monthly temperature outdoors (Auliciems 1981). Despite earlier criticism of this

Fig. 11.1 The Adaptive Comfort Model (from Auliciems 1981, 1983)

seemingly simple relationship (de Dear et al. 1997), de Dear and Brager (2001) have revalidated the equation and the Auliciems (1981) adaptive model as the best predictor of indoor comfort for naturally ventilated buildings.

Table 11.1 attempts to generalize main characteristics or principles of human adaptations to atmospheric variability. In summary, since biologically humans are homeotherms, their life processes and infrastructures are ultimately centered to the maintenance of a constant core temperature. To do so, the core is protected (cocooned, enveloped) by a combination of thermoregulatory processes as listed in bold fonts, together with empirically observable impacts in Table 11.2. All are linked to thermoregulatory responses, and except for the adverse impacts and the involuntary physiological responses (item i), are controlled to some degree by cognitive and affective evaluations of thermal signals, with respect to their intensity, and to their subjectively evaluated desirability as determined by past experiences (Fig. 11.1). The processes in Table 11.2 are arranged in an approximate ascending time sequence and total impacts on a society, but probably any

Fig. 11.2 Regression of Thermal Neutralities On Indoor and Outdoor Temperatures (from Auliciems 1981, 1983)

adaptation, or impact, can trigger those either above or below. The duration of any cascade would depend upon the strength of the signal and thresholds for impacts, the readiness and capacity of the particular mechanism, the fitness and vulnerability of individuals or groups being affected. Since all of the eight hazard categories in Table 11.2 are essentially the same but magnified physical avenues for metabolic heat dissipation, it is not surprising to see them impacting upon all human systems and their manifestations linked to thermoregulatory processes.

Where individuals are free to make decisions and respond, depending upon the signal strength, thermoregulatory processes may be triggered individually or as a system. The initial and reinforcing signals may be real or perceived,

Table 11.1 Principles of Human Adaptation to Atmospheric Variability

Atmospheric variability, at all temporal and spatial scales, provides stimulus that requires response, either spontaneous or voluntary.

A precondition to the well being of the homeothermic human, is a successful maintenance of a constant core temperature near 37°C. This requires continuous physiological and behavioural adjustments to balance energy exchanges between the body and the environment.

Most atmospheric stimuli may be thought as occurring on a continuum where "absence" or extremes of thermal or hydrometeor phenomena deviate from a biologically neutral intermediate state, or a subjectively perceived comfort zone. Within limits, deviations above and below induce increasing levels of response.

Repeated exposure to a particular stimulus promotes habituation that enables a reduction of response to that stimulus, but at the cost of narrowing the tolerance band or coping range.

In contrast, repeated and cyclical exposure to stimulating climatic variation and variability leads to acclimatization that promotes increased broadening of the tolerance band, both physiological and psychological1.

Biological fitness results from a sustained ability to adapt to a changing resource base and an individual's or group's initial psycho-physiological condition (physiological fitness, mental health, including capacity for acclimatization and habituation)2.

The relative position of any "optimum" is not constant, but shifts in the direction of the exposure3, 4.

There is a limit to adaptation capacity over time. Overexposure to atmospheric stimulus becomes hazardous: the resulting physiological and psychological impairment leads to reduced capacity in bodily and decision-making responses5.

Involuntary exposure to atmospheric stimulus is particularly stressful6.

Failure to adapt or exceeding adaptation energy results in individual and group dysfunction (ability to concentrate, vigilance, motor coordination and dexterity, moods, prison order, street riots, sexual aggression, domestic violence etc), morbidity and mortality7, 8.

Some human responses may over time prove to be unsustainable maladaptation.

Survivability is greater amongst the adaptable than the adapted9 111

Particularly relevant discussions can be found in: 1 Sargent (1963), 2 Medwar (1957), 3 Helson

(1964), 4 Wohlwill (1974), 5 Selye (1957), 6 Starr (1969), examples of meteoroaversisms have been extensively reported in the International Journal of Biometeorology as well as specialist journals and outstanding medical reviews including 7 Petersen (1947) "Patient and Weather", and 8 Tromp

(1963) "Medical Biometeorology"); 9 Dobzhansky (1962), 10 Sargent and Tromp (1964).

instantaneous or seasonal, deliberate or spontaneous. They also may reset new thresholds, such as perceptible cold or neutrality temperature. For example, with the advent of autumn, hearing an inclement weather forecast, a person may deliberately decide to wear a pullover, and perhaps in anticipation of the coming cold, light the fireplace. This voluntary action may lessen subsequent discomfort, or desire to carry out certain tasks, but at the same time initiate an involuntary alteration to seasonal acclimatization. The same complicated combination of processes may have been initiated simply by an unnoticed spontaneous increase in vasoconstriction without the benefit of the weather forecast, and the act of putting on of the pullover may have been quite involuntary. In other words, thermoregulation in an individual is a complex integrated biological and techno-cultural system that may be variously triggered at first, second or higher levels of impacts.

Table 11.2 Atmospheric Hazards Impacts and Adaptations

Impacts in bold involve thermoregulatory processes, asterisks denote likely lowest impact order Observed impacts of weather and climate hazards: 1 hot temperatures, 2 cold temperatures, 3 solar radiation, 4 wind, 5 rain, 6 snow, 7 moisture, 8 "weather", "climate". D / F Deterministic (involuntary) and / or Free-will (voluntary) responses hazard D/F impact or adaptation hazard D/F impact or adaptation

Table 11.2 Atmospheric Hazards Impacts and Adaptations

Impacts in bold involve thermoregulatory processes, asterisks denote likely lowest impact order Observed impacts of weather and climate hazards: 1 hot temperatures, 2 cold temperatures, 3 solar radiation, 4 wind, 5 rain, 6 snow, 7 moisture, 8 "weather", "climate". D / F Deterministic (involuntary) and / or Free-will (voluntary) responses

i

1-

2

D

involuntary physiological adjustments+

ii

1-

5

D -

F

postural adjustment*

iii

1-

6

D -

F

seeking shelter*

iv

1-

7

D -

F

subjective expressions of levels of discomfort*

v

1,

4-

5

D

increased nervousness, irritability, aggressiveness*

vi

1-

2,

7

D

reduced mental performance*

vii

2,

6,

8

F

avoidance of stimulus - hot baths, sauna, heated swimming pools**

viii

1,

3,

8

F

avoidance of stimulus - cold showers, swimming**

ix

1-

7

F -

D

interposition of insulating clothing**

x

1-

8

F -

D

construction of buildings**

xi

1-

2

D -

F

acclimation (acclimatization / incidental habituation)*

xii

2-

8

F

space heating**

xiii

2

F -

D

increasing metabolic/activity rate*

xiv

1,

3

F -

D

decreasing metabolic/activity rate*

xv

1,

3,

7

D -

F

consumption of cold food, drink*

xvi

2,

8

F -

D

consumption of hot food, drink*

xvii

1,

7

F -

D

air-conditioning, cooling**

xviii

1-

2,

8

F

deliberate fitness programs***

xix

1-

3

F -

D

use drugs, alcohol**

xx

1,

7

F -

D

antisocial behavior**

xxi

1,

4,

8

F -

D

increased violence*

xxii

1-

6

F

metabolic alterations by rescheduling work/activities***

xxiii

1-

2,

6

D

elevated morbidity*

xxiv

1-

2

D

increased mortality*

xxv

1-

2,

8

F -

D

temporary migration, holidaying***

xxvi

1-

2,

8

F -

D

permanent avoidance of particular climate, emigration***

xxviii

1-

2

F -

D

changed diet***

xxix

1-

8

F

climatic design, economic resource and infrastructure planning***

xxx

1-

8

F -

D

cultural practices and patterns, philosophies***

+biological first order involuntary mechanisms- vasodilatation and vasoconstriction, perspiration, active sweating, thermogenesis - shivering * biological "first order" largely involuntary responses, ** integrated first and second order responses and behavior *** third and higher order largely voluntary responses excluded from list: extreme thermoregulatory behaviors (e.g. ice swimming) and obvious maladaptation (e.g. leaving open refrigerator door to cool house)

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