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Heat Exchange Between Human Skin Surface and Thermal Environment

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Abstract

The sections in this article are:

1 Body Heat Balance Equations
2 Independent Variables in Human Thermal Environment
2.1 Ambient Temperature
2.2 Dew‐point Temperature and Ambient Vapor Pressure
2.3 Air (and Fluid) Movement
2.4 Mean Radiant Temperature or Effective Radiant Field
2.5 Clothing Insulation
2.6 Barometric Pressure
2.7 Time of Exposure
3 Dependent Physiological Variables in Body Heat Balance Equation
3.1 Mean Skin Temperature
3.2 Skin Wettedness
3.3 Body Heat Storage and Rate Change of Mean Body Temperature
3.4 Metabolic Energy
4 Sensible Heat Exchange by Radiation and Convection
4.1 Operative Temperature
4.2 Clothing in Sensible Heat Exchange
5 Radiation Exchange
5.1 Mean Radiant Temperature and Effective Radiant Field
5.2 Direct Evaluation of Effective Radiant Field
5.3 Solar Radiation
5.4 Measurement of Radiation Exchange
6 Convective Heat Exchange
6.1 Heat Transfer Theory
6.2 Free and Forced Convection
6.3 Measurement of Convective Heat Transfer Coefficient
6.4 Effect of Barometric Pressure
7 Evaporative Heat Exchange
7.1 Direct Measurement of Evaporative Heat Loss
7.2 Maximum Evaporative Heat Loss from Skin Surface
7.3 The Lewis Relation Between Heat and Mass Transfer Coefficients
7.4 Skin Wettedness vs. Efficiency of Evaporative Regulation
8 Special Environments
8.1 Water Immersion
8.2 Hyperbaric Helium‐Oxygen Atmospheres
9 Rational Temperature Indices of Thermal Environment
9.1 Operative Temperature
9.2 Humid Operative Temperature
9.3 Standard Operative Temperature
9.4 Standard Humid Operative Temperature
9.5 Standard Effective Temperature
9.6 A New Effective Temperature Index
10 Summary
Figure 1. Figure 1.

Variation of absorptance (α) of human skin as a function of the radiating temperature of the source. Total surface reflection and absorption of human skin for blackbody radiators.

Data from Gagge et al.
Figure 2. Figure 2.

Family Tree of rational environmental temperature indices. The physical properties of the skin are temperature (Msk) and wettedness (w). Basic environmental temperatures are mean radiant (Mr), ambient air (To), and dew‐point (Tdp) temperatures. Barometric pressure (Pb) and air movement affect the convection coefficient (hc). Clothing insulation (Iclo) affects the efficiency factors (Fcl and Fpcl) for transfer of heat and water vapor through clothing. The standard of reference environment, used for comparison in standard operative (Tso) and standard humid operative (Tsok) temperatures, describes usually one which is familiar for our daily living conditions. The indices for new effective temperature (ET*) and new standard effective temperature (SET*) refer to environments at 50% relative humidity (rh).

Figure 3. Figure 3.

Graphic representation of a typical environment for a sedentary clothed subject. All loci of constant wettedness pass through a common point (CP) whose coordinates are . The dotted loci represent the classic Effective Temperature (ET). The abscissa at the intersection of all solid loci with the 50% rh curve is the new Effective Temperature (ET*) of the American Society of Heating, Refrigerating and Air‐Conditioning Engineers (ASHRAE). Shaded zone represents the ASHRAE Comfort Standard for environmental design. Tsk, skin temperature; rh, relative humidity.

Figure 4. Figure 4.

Psychrometric chart which relates a prescriptive condition (PP), described by a humid operative temperature (Toh) of 27.5° for a man working at about 3 mets and wearing 0.3 clo to an equivalent temperature at 50% and for a desert environment at 5 Torr vapor pressure. The values for wettedness (w), operative temperature To, and Toh, at operating conditions OP‐1 and 2 for a man working in front of a radiant heat source at ambient vapor pressure (Pa) of 9 Torr and at OP‐3 and OP‐4 for 20 Torr are also indicated graphically. CP, common point; Msk, net rate of metabolic heat to skin surface; hc, convective heat transfer coefficient; hr, linear radiation exchange coefficient; Iclo, clothing insulation; Tsk, skin temperature; ET*, new effective temperature; rh, relative humidity; ERF, effective radiant field.

Figure 5. Figure 5.

Psychrometric chart indicating limits for comfort and heat stroke found in a hyperbaric atmosphere for men working at 3 mets and with light clothing (0.3). This chart illustrates how, by using the concept of a standard humid operative temperature, prescriptive conditions for heat stroke, observed by Wyndham , and for thermal comfort by McNall et al. , both at same level of exercise, may be reinterpreted graphically in terms of ambient vapor pressure and operative temperature values in a hyperbaric environment, used as the standard or common reference. □, environments observed by Wyndham and McNall et al. ; ○, 4 ATA environment; sk, skin temperature; ET*, new effective temperature; Iclo, clothing insulation; CP, common point; PP, prescriptive point; ATA, atmosphere absolute; hc, convective heat transfer coefficient.

Figure 6. Figure 6.

A chart relating standard effective temperature (SET*) with ambient vapor pressure in torr, dew‐point temperature (Tdp) or linear dew temperature (Tdew) and with standard operative temperature (Tso). For a standard environment at uniform ambient temperature, this chart is equivalent to an expanded comfort chart of the American Society of Heating, Refrigerating and Air‐Conditioning Engineers.

Adapted from Gonzalez & Gagge


Figure 1.

Variation of absorptance (α) of human skin as a function of the radiating temperature of the source. Total surface reflection and absorption of human skin for blackbody radiators.

Data from Gagge et al.


Figure 2.

Family Tree of rational environmental temperature indices. The physical properties of the skin are temperature (Msk) and wettedness (w). Basic environmental temperatures are mean radiant (Mr), ambient air (To), and dew‐point (Tdp) temperatures. Barometric pressure (Pb) and air movement affect the convection coefficient (hc). Clothing insulation (Iclo) affects the efficiency factors (Fcl and Fpcl) for transfer of heat and water vapor through clothing. The standard of reference environment, used for comparison in standard operative (Tso) and standard humid operative (Tsok) temperatures, describes usually one which is familiar for our daily living conditions. The indices for new effective temperature (ET*) and new standard effective temperature (SET*) refer to environments at 50% relative humidity (rh).



Figure 3.

Graphic representation of a typical environment for a sedentary clothed subject. All loci of constant wettedness pass through a common point (CP) whose coordinates are . The dotted loci represent the classic Effective Temperature (ET). The abscissa at the intersection of all solid loci with the 50% rh curve is the new Effective Temperature (ET*) of the American Society of Heating, Refrigerating and Air‐Conditioning Engineers (ASHRAE). Shaded zone represents the ASHRAE Comfort Standard for environmental design. Tsk, skin temperature; rh, relative humidity.



Figure 4.

Psychrometric chart which relates a prescriptive condition (PP), described by a humid operative temperature (Toh) of 27.5° for a man working at about 3 mets and wearing 0.3 clo to an equivalent temperature at 50% and for a desert environment at 5 Torr vapor pressure. The values for wettedness (w), operative temperature To, and Toh, at operating conditions OP‐1 and 2 for a man working in front of a radiant heat source at ambient vapor pressure (Pa) of 9 Torr and at OP‐3 and OP‐4 for 20 Torr are also indicated graphically. CP, common point; Msk, net rate of metabolic heat to skin surface; hc, convective heat transfer coefficient; hr, linear radiation exchange coefficient; Iclo, clothing insulation; Tsk, skin temperature; ET*, new effective temperature; rh, relative humidity; ERF, effective radiant field.



Figure 5.

Psychrometric chart indicating limits for comfort and heat stroke found in a hyperbaric atmosphere for men working at 3 mets and with light clothing (0.3). This chart illustrates how, by using the concept of a standard humid operative temperature, prescriptive conditions for heat stroke, observed by Wyndham , and for thermal comfort by McNall et al. , both at same level of exercise, may be reinterpreted graphically in terms of ambient vapor pressure and operative temperature values in a hyperbaric environment, used as the standard or common reference. □, environments observed by Wyndham and McNall et al. ; ○, 4 ATA environment; sk, skin temperature; ET*, new effective temperature; Iclo, clothing insulation; CP, common point; PP, prescriptive point; ATA, atmosphere absolute; hc, convective heat transfer coefficient.



Figure 6.

A chart relating standard effective temperature (SET*) with ambient vapor pressure in torr, dew‐point temperature (Tdp) or linear dew temperature (Tdew) and with standard operative temperature (Tso). For a standard environment at uniform ambient temperature, this chart is equivalent to an expanded comfort chart of the American Society of Heating, Refrigerating and Air‐Conditioning Engineers.

Adapted from Gonzalez & Gagge
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How to Cite

A. Pharo Gagge, Yasunobu Nishi. Heat Exchange Between Human Skin Surface and Thermal Environment. Compr Physiol 2011, Supplement 26: Handbook of Physiology, Reactions to Environmental Agents: 69-92. First published in print 1977. doi: 10.1002/cphy.cp090105