9.1
CHAPTER 9
THERMAL COMFORT
Human Thermoregulation .......................................................... 9.1Energy Balance .......................................................................... 9.2Thermal Exchanges with the Environment ................................. 9.2Engineering Data and Measurements ........................................ 9.6Conditions for Thermal Comfort ............................................. 9.11Thermal Comfort and Task Performance ................................. 9.13
Thermal Nonuniform Conditions and Local Discomfort ......... 9.14Secondary Factors Affecting Comfort ...................................... 9.16Prediction of Thermal Comfort ................................................ 9.16Environmental Indices .............................................................. 9.20Special Environments ............................................................... 9.23Symbols .................................................................................... 9.27
principal purpo of HV AC is to provide conditions for human A
thermal comfort, “that condition of mind that express satis-faction with the thermal environment” (ASHRAE Standard 55).This definition leaves open what is meant by “condition of mind” or “satisfaction,” but it correctly emphasizes that judgment of comfort is a cognitive process involving many inputs influenced by physical,physiological, psychological, and other process. This chapter summarizes the fundamentals of human thermoregulation and com-fort in terms uful to the engineer for operating systems and designing for the comfort and health of building occupants.
The conscious mind appears to reach conclusions about thermal comfort and discomfort from direct temperature and moisture n-sations from the skin, deep body temperatures, and the efforts nec-essary to regulate body temperatures (Berglund 1995; Gagge 1937;Hardy et al. 1971; Henl 1973, 1981). In general, comfort occurs when body temperatures are held within narrow ranges, skin mois-ture is low, and the physiological effort of regulation is minimized.Comfort also depends on behaviors that are initiated consciously or unconsciously and guided by thermal and moisture nsations to reduce discomfort. Some examples are altering clothing, altering activity, changing posture or location, changing the thermostat t-ting, opening a window, complaining, or leaving the space.
Surprisingly, although climates, living conditions, and cultures differ widely throughout the world, the temperature that people choo for comfort under similar conditions of clothing, activity,humidity, and air movement has been found to be very similar (Busch 1992; de Dear et al. 1991; Fanger 1972).
HUMAN THERMOREGULATION
Metabolic activities of the body result almost completely in heat that must be continuously dissipated and regulated to maintain nor-mal body temperatures. Insufficient heat loss leads to overheating (hyperthermia ), and excessive heat loss results in body cooling (hypothermia ). Skin temperature greater than 45°C or less than 18°C caus pain (Hardy et al. 1952). Skin temperatures associated with comfort at dentary activities are 33 to 34°C and decrea with increasing activity (Fanger 1967). In contrast, internal temper-atures ri with activity. The temperature regulatory center in the brain is about 36.8°C at rest in comfort and increas to about 37.4°C when walking and 37.9°C when jogging. An internal tem-perature less than about 28°C can lead to rious cardiac arrhythmia and death, and a temperature greater than 46°C can cau irrevers-ible brain damage. Therefore, careful regulation of body tempera-ture is critical to comfort and health.
A resting adult produces about 100 W of heat. Becau most of this is transferred to the environment
through the skin, it is often convenient to characterize metabolic activity in terms of heat production per unit area of skin. For a resting person, this is about
58W/m 2 and is called 1 met . This is bad on the average male European, with a skin surface area of about 1.8 m 2. For comparison,female Europeans have an average surface area of 1.6 m 2. System-atic differences in this parameter may occur between ethnic and geographical groups. Higher metabolic rates are often described in terms of the resting rate. Thus, a person working at metabolic rate five times the resting rate would have a metabolic rate of 5 met.The hypothalamus , located in the brain, is the central control organ for body temperature. It has hot and cold temperature nsors and is bathed by arterial blood. Becau the recirculation rate of blood is rapid and returning blood is mixed together in the heart before returning to the body, arterial blood is indicative of the aver-age internal body temperature. The hypothalamus also receives thermal information from temperature nsors in the skin and per-haps other locations as well (e.g., spinal cord, gut), as summarized by Henl (1981).
The hypothalamus controls various physiological process to regulate body temperature. Its control behavior is primarily propor-tional to deviations from t-point temperatures with some integral and derivative respon aspects. The most important and often-ud physiological process is regulating
blood flow to the skin: when internal temperatures ri above a t point, more blood is directed to the skin. This vasodilation of skin blood vesls can increa skin blood flow by 15 times [from 1.7 mL/(s·m 2) at resting comfort to 25 mL/(s·m 2)] in extreme heat to carry internal heat to the skin for transfer to the environment. When body temperatures fall below the t point, skin blood flow is reduced (vasoconstricted ) to con-rve heat. The effect of maximum vasoconstriction is equivalent to the insulating effect of a heavy sweater. At temperatures less than the t point, muscle tension increas to generate additional heat;where muscle groups are oppod, this may increa to visible shiv-ering, which can increa resting heat production to 4.5 met.
At elevated internal temperatures, sweating occurs. This defen mechanism is a powerful way to cool the skin and increa heat loss from the core. The sweating function of the skin and its control is more advanced in humans than in other animals and is increasingly necessary for comfort at metabolic rates above resting level (Fanger 1967). Sweat glands pump perspiration onto the skin surface for evaporation. If conditions are good for evaporation, the skin can remain relatively dry even at high sweat rates with little perception of sweating. At skin conditions less favorable for evaporation, the sweat must spread on the skin around the sweat gland until the sweat-covered area is sufficient to evaporate the sweat coming to the surface. The fraction of the skin that is covered wit
h water to account for the obrved total evaporation rate is termed skin wet-tedness (Gagge 1937).
Humans are quite good at nsing skin moisture from perspira-tion (Berglund 1994; Berglund and Cunningham 1986), and skin moisture correlates well with warm discomfort and unpleasantness (Winslow et al. 1937). It is rare for a dentary or slightly active per-son to be comfortable with a skin wettedness greater than 25%. In addition to the perception of skin moisture, skin wettedness
The preparation of this chapter is assigned to TC 2.1, Physiology and Human Environment.
9.22009 ASHRAE Handbook—Fundamentals (SI)
increas the friction between skin and fabrics, making clothing feel less pleasant and fabrics feel more coar (Gwosdow et al. 1986). This also occurs with architectural materials and surfaces, particu-larly smooth, nonhygroscopic surfaces.
With repeated intermittent heat exposure, the t point for the ont of sweating decreas and the proportional gain or tempera-ture nsitivity of the sweating system increas (Gonzalez et al. 1978; Henl 1981). However, under long-term exposure to hot con-ditions, the t point increas, perhaps to reduce the physiological effort of sweating. Perspiration as creted has a lower salt con
cen-tration than interstitial body fluid or blood plasma. After prolonged heat exposure, sweat glands further reduce the salt concentration of sweat to conrve salt.
At the surface, the water in sweat evaporates while the dissolved salt and other constituents remain and accumulate. Becau salt lowers the vapor pressure of water and thereby impedes its evapo-ration, the accumulating salt results in incread skin wettedness. Some of the relief and pleasure of washing after a warm day is related to the restoration of a hypotonic sweat film and decread skin wettedness. Other adaptations to heat are incread blood flow and sweating in peripheral regions where heat transfer is better. Such adaptations are examples of integral control.
Role of Thermoregulatory Effort in Comfort. Chatonnet and Cabanac (1965) compared the nsation of placing a subject’s hand in relatively hot or cold water (30 to 38°C) for 30 s with the subject at different thermal states. When the person was overheated (hyper-thermic), the cold water was pleasant and the hot water was very unpleasant, but when the subject was cold (hypothermic), the hand felt pleasant in hot water and unpleasant in cold water. Kuno (1995) describes similar obrvations during transient whole-body expo-sures to hot and cold environment. When a subject is in a state of thermal discomfort, any move away from the thermal stress of the uncomfortable environment is perceived as pleasant during the tran-sition.
ENERGY BALANCE
Figure 1 shows the thermal interaction of the human body with its environment. The total metabolic rate M within the body is the metabolic rate required for the person’s activity M act plus the meta-bolic level required for shivering M shiv (should shivering occur). A portion of the body’s energy production may be expended as exter-nal work W; the net heat production M – W is transferred to the envi-ronment through the skin surface (q sk) and respiratory tract (q res) with any surplus or deficit stored (S), causing the body’s tempera-ture to ri or fall.
M – W = q sk + q res + S
= (C + R + E sk) + (C res + E res) + (S sk + S cr)(1) where
M=rate of metabolic heat production, W/m2
W=rate of mechanical work accomplished, W/m2
q sk=total rate of heat loss from skin, W/m2
q res=total rate of heat loss through respiration, W/m2
C + R=nsible heat loss from skin, W/m2
E sk=total rate of evaporative heat loss from skin, W/m2
C res=rate of convective heat loss from respiration, W/m2
E res=rate of evaporative heat loss from respiration, W/m2
S sk=rate of heat storage in skin compartment, W/m2
S cr=rate of heat storage in core compartment, W/m2
Heat dissipates from the body to the immediate surroundings by veral modes of heat exchange: nsible heat flow C + R from the skin; latent heat flow from sweat evaporation E rsw and from evapo-ration of moisture diffud through the skin E dif; nsible heat flow during respiration C res; and latent heat flow from evaporation of moisture during respiration E res. Sensible heat flow from the skin may be a complex mixture of conduction, convection, and radiation for a clothed person; however, it is equal to the sum of the convec-tion C and radiation R heat transfer at the outer clothing surface (or expod skin).
Sensible and latent heat loss from the skin are typically expresd in terms of environmental factors, skin temperature t sk, and skin wettedness w. Factors also account for the thermal insula-tion and moisture permeability of clothing. The independent envi-ronmental variables can be summarized as air temperature t a, mean radiant temperature , relative air velocity V, and ambient water vapor pressure p a. The independent personal variables that influ-ence thermal comfort are activity and clothing.
The rate of heat storage in the body equals the rate of increa in internal energy. The body can be considered as two thermal com-partments: the skin and the core (e the ction on Two-Node Model under Prediction of Thermal Comfort). The storage rate can be written parately for each compartment in terms of thermal capacity and time rate of change of temperature in each compart-ment:
(2)
(3) where
αsk=fraction of body mass concentrated in skin compartment
m=body mass, kg
c p,b=specific heat capacity of body = 3490 J/(kg·K)
A D=DuBois surface area, m2
t cr=temperature of core compartment, °C
t sk=temperature of skin compartment, °C
θ=time, s
The fractional skin mass αsk depends on the rate of blood flow-ing to the skin surface.
THERMAL EXCHANGES WITH
THE ENVIRONMENT
Fanger (1967, 1970), Gagge and Hardy (1967), Hardy (1949), and Rapp and Gagge (1967) give quantitative information on calcu-lating heat exchange between people and the environment. This c-tion summarizes the mathematical statements for various terms of heat exchange ud in the heat balance equations (C, R, E sk, C res, E res). Terms describing the heat exchanges associated with the ther-moregulatory control mechanisms (q cr,sk, M shiv, E rsw), values for
Fig. 1Thermal Interaction of Human Body and Environment
t r
S cr
1αsk
–
()mc p b,
A D
------------------------------------
dt cr
国家重点实验室dθ
--------
×
=
S sk
αsk mc p b,
A D
----------------------
dt sk
dθ
--------
×
=
m·bl
Thermal Comfort
9.3
the coefficients, and appropriate equations for M act and A D are pre-nted in later ctions.
Mathematical description of the energy balance of the human body combines rational and empirical approaches to describing thermal exchanges with the environment. Fundamental heat transfer theory is ud to describe the various mechanisms of nsible and latent heat exchange, and empirical expressions are ud to deter-mine the values of coefficients describing the rates of heat exchange. Empirical equations are also ud to describe the thermo-physiological control mechanisms as a function of skin and core temperatures in the body.
Body Surface Area
The terms in Equation (1) have units of power per unit area and refer to the surface area of the nude body. The most uful measure of nude body surface area, originally propod by DuBois and DuBois (1916), is described by
A D = 0.202m 0.425l 0.725
(4)
where
A D =DuBois surface area, m 2m =mass, kg l =height, m
A correction factor f cl = A cl /A D must be applied to the heat transfer terms from the skin (C , R , and E sk ) to account for the actual surface area A cl of the clothed body. Table 7 prents f cl values for various clothing enmbles. For a 1.73 m tall, 70 kg man, A D = 1.8m 2. All terms in the basic heat balance equations are expresd per unit DuBois surface area.
Sensible Heat Loss from Skin
Sensible heat exchange from the skin must pass through clothing to the surrounding environment. The paths are treated in ries and can be described in terms of heat transfer (1) from the skin sur-face, through the clothing insulation, to the outer clothing surface,and (2) from the outer clothing surface to the environment.
Both convective C and radiative R heat loss from the outer sur-face of a clothed body can be expresd in terms of a heat transfer coefficient and the difference between the mean temperature t
cl of the outer surface of the clothed body and the appropriate environ-mental temperature:
C = f cl h c (t cl – t a )(5)(6)
where
h c =convective heat transfer coefficient, W/(m 2·K)h r =linear radiative heat transfer coefficient, W/(m 2·K)f cl =clothing area factor A cl /A D , dimensionless
The coefficients h c and h r are both evaluated at the clothing surface.
Equations (5) and (6) are commonly combined to describe the total nsible heat exchange by the two mechanisms in terms of an operative temperature t o and a combined heat transfer coefficient h :
C + R = f cl h (t cl – t o )
(7)
where
(8)h = h r + h c
(9)
Bad on Equation (8), operative temperature t o can be defined as the average of the mean radiant and ambient air temperatures,weighted by their respective heat transfer coefficients.
The actual transport of nsible heat through clothing involves conduction, convection, and radiation. It is usually most conve-nient to combine the into a single thermal resistance value R cl ,defined by
C + R = (t sk – t cl )/R cl
(10)
where R cl is the thermal resistance of clothing in (m 2·K)/W.
Becau it is often inconvenient to include the clothing surface temperature in calculations, Equations (7) and (10) can be com-bined to eliminate t cl :
(11)
where t o is defined in Equation (8).
Evaporative Heat Loss from Skin
Evaporative heat loss E sk from skin depends on the amount of moisture on the skin and the difference between the water vapor pressure at the skin and in the ambient environment:
(12)
where
w =skin wettedness, dimensionless
p sk,s =water vapor pressure at skin, normally assumed to be that of
saturated water vapor at t sk , kPa
p a =water vapor pressure in ambient air, kPa
R e,cl =evaporative heat transfer resistance of clothing layer (analogous
to R cl ), (m 2·kPa)/W
h e =evaporative heat transfer coefficient (analogous to h c ),
W/(m 2·kPa)
Procedures for calculating R e,cl and h e are given in the ction on Engineering Data and Measurements. Skin wettedness is the ratio of the actual evaporative heat loss to the maximum possible evapora-tive heat loss E max with the same conditions and a completely wet skin (w = 1). Skin wettedness is important in determining evapora-tive heat loss. Maximum evaporative potential E max occurs when w =1.
Evaporative heat loss from the skin is a combination of the evap-oration of sweat creted becau of thermoregulatory control mech-anisms E rsw and the natural diffusion of water through the skin E dif :
E sk = E rsw + E dif
(13)
Evaporative heat loss by regulatory sweating is directly propor-tional to the rate of regulatory sweat generation:
(14)
where
h fg =heat of vaporization of water = 2.43 × 106 J/kg at 30°C
=rate at which regulatory sweat is generated, kg/(s·m 2)
The portion w rsw of a body that must be wetted to evaporate the reg-ulatory sweat is
w rsw = E rsw /E max
(15)
With no regulatory sweating, skin wettedness caud by diffusion is approximately 0.06 for normal conditions. For large values of E max or long exposures to low humidities, the value may drop to as low as
R f cl h r t cl t r –()
=t o h r t r h c t a +h r h c
+-------------------------=C R +t sk t o
–R cl 1 f cl h ()
⁄+------------------------------------=E sk w p sk s ,p a –()
R e cl ,1f cl h e ()
⁄+-------------------------------------------=E rsw m ·rsw h fg
=m ·rsw
9.4
2009 ASHRAE Handbook—Fundamentals (SI)
0.02, becau dehydration of the outer skin layers alters its diffusive characteristics. With regulatory sweating, the 0.06 value applies only to the portion of skin not covered with sweat (1 − w rsw ); the dif-fusion evaporative heat loss is
E dif = (1 – w rsw )0.06E max
(16)
The equations can be solved for w , given the maximum evapora-tive potential E max and the regulatory sweat generation E rsw :
w = w rsw + 0.06(1 – w rsw ) = 0.06 + 0.94E rsw /E max
(17)
Once skin wettedness is determined, evaporative heat loss from the skin is calculated from Equation (12), or by主题班会教案
E sk = wE max
(18)
To summarize, the following calculations determine w and E sk :
E max Equation (12), with w = 1.0E rsw Equation (14)w Equation (17)
E sk
Equation (18) or (12)
Although evaporation from the skin E sk as described in Equation
(12) depends on w , the body does not directly regulate skin wetted-ness but, rather, regulates sweat rate [Equation (14)]. Skin
wettedness is then an indirect result of the relative activity of the sweat glands and the evaporative potential of the environment. Skin wettedness of 1.0 is the upper theoretical limit. If the aforemen-tioned calculations yield a wettedness of more than 1.0, then Equa-tion (14) is no longer valid becau not all the sweat is evaporated.In this ca, E sk = E max .
Skin wettedness is strongly correlated with warm discomfort and is also a good measure of thermal stress. Theoretically, skin wetted-ness can approach 1.0 while the body still maintains thermoregula-tory control. In most situations, it is difficult to exceed 0.8(Berglund and Gonzalez 1977). Azer (1982) recommends 0.5 as a practical upper limit for sustained activity for a healthy, acclima-tized person.
Respiratory Loss
During respiration, the body los both nsible and latent heat by convection and evaporation of he
at and water vapor from the respiratory tract to the inhaled air. A significant amount of heat can be associated with respiration becau air is inspired at ambient con-ditions and expired nearly saturated at a temperature only slightly cooler than t cr .
The total heat and moisture loss through respiration are
(19)
(20)
where
=pulmonary ventilation rate, kg/s h ex =enthalpy of exhaled air, J/kg (dry air)
h a =enthalpy of inspired (ambient) air, J/kg (dry air)=pulmonary water loss rate, kg/s
W ex =humidity ratio of exhaled air, kg (water vapor)/kg (dry air)W a =humidity ratio of inspired (ambient) air,
kg (water vapor)/kg (dry air)
恭喜买车的祝福语
Under normal circumstances, pulmonary ventilation rate is primar-ily a function of metabolic rate (Fanger 1970):
(21)
where
M =metabolic rate, W/m 2
K res =proportionality constant (1.43 × 10–6 kg/J)
周口店北京猿人遗址
For typical indoor environments (McCutchan and Taylor 1951),the exhaled temperature and humidity ratio are given in terms of ambient conditions:
t ex = 32.6 + 0.066t a + 32W a (22)W ex = 0.0277 + 0.000065t a + 0.2W a
(23)
where ambient t a and exhaled t ex air temperatures are in °C. For extreme conditions, such as outdoor winter environments, different relationships may be required (Holmer 1984).
The humidity ratio of ambient air can be expresd in terms of total or barometric pressure p t and ambient water vapor pressure p a :
(24)
Respiratory heat loss is often expresd in terms of nsible C res and latent E res heat loss. Two approximations are commonly ud to simplify Equations (22) and (23) for that purpo. First, becau dry respiratory heat loss is relatively small compared to the other terms in the heat balance, an average value for t ex is determined by evaluating Equation (22) at standard conditions of 20°C, 50% rh,a level. Second, noting in Equation (23) that there is only a weak dependence on t a , the cond term in Equation (23) and the denom-inator in Equation (24) are evaluated at standard conditions. Using the approximations and substituting latent heat h fg and specific heat of air c p,a at standard conditions, C res and E res can be deter-mined by
C res = 0.0014M (34 – t a )(25)E res = 0.0173M (5.87 – p a )
(26)
where p a is expresd in kPa and t a is in °C.
Alternative Formulations
Equations (11) and (12) describe heat loss from skin for clothed people in terms of clothing parameters R cl , R e,cl , and f cl ; parameters h and h e describe outer surface resistances. Other parameters and definitions are also ud. Although the alternative parameters and definitions may be confusing, note that information prented in one form can be converted to another form. Table 1 prents common parameters and their qualitative descriptions. Table 2 prents equa-tions showing their relationship to each other. Generally, parameters related to dry or evaporative heat flows are not independent becau they both rely, in part, on the same physical process. The Lewis relation describes the relationship between convective heat transfer and mass transfer coefficients for a surface [e Equation (39) in Chapter 6]. The Lewis relation can be ud to relate convective and evaporative heat transfer coefficients defined in Equations (5) and (12) according to
LR = h e /h c
(27)感恩书信
where LR is the Lewis ratio and, at typical indoor conditions,equals approximately 16.5 K/kPa. The Lewis relation applies to sur-face convection coefficients. Heat transfer coefficients that include the e
ffects of insulation layers and/or radiation are still coupled, but the relationship may deviate significantly from that for a surface.The i terms in Tables 1 and 2 describe how the actual ratios of the
m ·rsw q res C res E res
+=m ·res h ex
h a –()A D ----------------------------------=m ·w res ,m ·res W ex W a –()A D
甲鱼是乌龟吗--------------------------------------=m ·res
m ·w res ,m ·res
K res MA D =W a 0.622p a p t p a
–-------------------=
Thermal Comfort9.5
parameters deviate from the ideal Lewis ratio (Oohori et al. 1984; Woodcock 1962).
Depending on the combination of parameters ud, heat transfer from the skin can be calculated using veral different formulations (e Tables 2 and 3). If the parameters are ud correctly, the end result will be the same regardless of the formulation ud.
Total Skin Heat Loss
Total skin heat loss (nsible heat plus evaporative heat) can be calculated from any combination of the equations prented in Table 3. Total skin heat loss is ud as a measure of the thermal environ-ment; two combinations of parameters that yield the same total heat loss for a given t of body conditions (t sk and w) are considered to be approximately equivalent. The fully expanded skin heat loss equation, showing each parameter that must be known or specified, is as follows:
(28) where t o is the operative temperature and reprents the temperature of a uniform environment (t a – t r) that transfers dry heat at the same rate as in the actual environment [t o = (t r h r + t a h c)/(h c + h r)]. After rearranging, Equation (28) becomes
q sk = F cl f cl h(t sk – t o) + w LR F pcl h c(p sk,s – p a)(29)
This equation allows the tradeoff between any two or more parameters to be evaluated under given
conditions. If the tradeoff between two specific variables (e.g., between operative temperature and humidity) is to be examined, then a simplified form of the equa-tion suffices (Fobelets and Gagge 1988):
q sk = h′[(t sk + wi m LR p sk,s) – (t o + wi m LR p a)](30) Equation (30) can be ud to define a combined temperature t com, which reflects the combined effect of operative temperature and humidity for an actual environment:
t com + wi m LR p t
com
– t o + wi m LR p a
or
t com = t o + wi m LR p a – wi m LR p t
com
(31)
where p t
com
is a vapor pressure related in some fixed way to t com and is analogous to p wb,s for t wb. The term wi m LR p t com is constant to the
Table 1Parameters Ud to Describe Clothing Sensible Heat Flow Evaporative Heat Flow
R cl=intrinsic clothing insulation: thermal resistance of a uniform layer of insulation covering entire body that has same effect on nsible heat flow as actual clothing.
R t=total insulation: total equivalent uniform thermal resistance between body and environment: clothing and boundary resistance.
R cle=effective clothing insulation: incread body insulation due to clothing as compared to nude state.
R a=boundary insulation: thermal resistance at skin boundary for nude body. R a,cl=outer boundary insulation: thermal resistance at outer boundary (skin or clothing).
R te=total effective insulation.
h′=overall nsible heat transfer coefficient: overall equivalent uniform con-ductance between body (including clothing) and environment.
h′c l=clothing conductance: thermal conductance of uniform layer of insulation covering entire body that has same effect on nsible heat flow as actual clothing.
F cle=effective clothing thermal efficiency: ratio of actual nsible heat loss to
that of nude body at same conditions.
F cl=intrinsic clothing thermal efficiency: ratio of actual nsible heat loss to
that of nude body at same conditions including adjustment for increa in surface area due to clothing.R e,cl=evaporative heat transfer resistance of clothing: impedance to transport of water vapor of uniform layer of insulation cover-
ing entire body that has same effect on evaporative heat flow
as actual clothing.
R e,t=total evaporative resistance: total equivalent uniform imped-ance to transport of water vapor from skin to environment.
F pcl=permeation efficiency: ratio of actual evaporative heat loss to
that of nude body at same conditions, including adjustment for
increa in surface area due to clothing.
Parameters Relating Sensible and Evaporative Heat Flows
i cl=clothing vapor permeation efficiency: ratio of actual evapora-
tive heat flow capability through clothing to nsible heat flow
capability as compared to Lewis ratio.
i m=total vapor permeation efficiency: ratio of actual evaporative
heat flow capability between skin and environment to nsible
heat flow capability as compared to Lewis ratio.
i a=air layer vapor permeation efficiency: ratio of actual evapora-
tive heat flow capability through outer air layer to nsible
heat flow capability as compared to Lewis ratio.
Table 2Relationships Between Clothing Parameters Sensible Heat Flow
R t=R cl+ 1/(hf cl) = R cl + R a/f cl
R te=R cle+ 1/h = R cle + R a
h′cl=1/R cl
h′=1/R t
h=1/R a
R a,cl=R a/f cl
F cl=h′/(hf cl) = 1/(1 + f cl hR cl)
F cle=h′/h = f cl/(1 + f cl hR cl) = f cl F cl
Evaporative Heat Flow
R e,t=R e,cl + 1/(h e f cl) = R e,cl + R e,a/f cl
h e=1/R e,a
h′e,cl=1/R e,cl
h′e=1/R e,t = f cl F pcl h e
F pcl=1/(1+f cl h e R e,cl)
Parameters Relating Sensible and Evaporative Heat Flows
i cl LR=h′e,cl/h′c l = R cl/R e,cl
i m LR=h′e/h′ = R t/R e,t
山根痣的准确位置图
i m=(R cl + R a,cl)/[(R cl/i cl) + (R a,cl/i a)]
i a LR=h e/h
i a=h c/(h c + h r)
Table 3Skin Heat Loss Equations Sensible Heat Loss
C + R=(t sk−t o)/[R cl + 1/(f cl h)]
C + R=(t sk−t o)/R t
C + R=F cle h(t sk−t o)
C + R=F cl f cl h(t sk−t o)
C + R=h′(t sk−t o)
打屁股3
Evaporative Heat Loss
E sk=w(p sk,s−p a)/[R e,cl + 1/(f cl h e)]
E sk=w(p sk,s−p a)/R e,t
E sk=w
F pcl f cl h e (p sk,s−p a)
E sk=h′e w(p sk,s−p a)
E sk=h′ wi m LR(p sk,s−p a)
q sk
t sk t o
–
R cl R a cl,
+
-------------------------
w p sk s,p a
–
()
R e cl,1LR h c f cl
()
⁄
+
--------------------------------------------------
+
=
