Investigation of Humidity Effects on the Thermal Comfort and Heat Balance of the Body

Abstract

Humidity, one of the most confusing of all climatic parameters in assessing the indoor climate, affects comfort in a number of ways both directly and indirectly, and the avenues by which humidity affects comfort are not completely known. The aim of this study is to comprehend the effects of humidity on thermal interaction between the human body and its environment, and thermal sensation. In this chapter, the effect of humidity on heat and water balance of human body, and in turn on body temperatures and thermal sensation, is investigated. A mathematical model of heat and mass interaction between the human body and the surrounding environment has been established, and the effect of air humidity has been examined under various relative humidity levels by means of using the empirical relations that express thermoregulatory control mechanisms. In the numerical model, human body has been separated into 16 sedentary segments, and possible local discomforts have been taken into consideration. Using the model, changes in the sensible and latent heat losses, body temperatures, skin wettedness, and thermal comfort indices have been calculated and results have been discussed explicitly.

Nomenclature

A _b :

Body surface area, m²

c _p,b :

Specific heat of body, kJ/(kg K)

DISC :

Discomfort

f _cl :

Clothing area factor

h _cv :

Convective heat transfer coefficient, W/(m² K)

h _rd :

Radiative heat transfer coefficient, W/(m² K)

i :

Segment number

i _cl :

Vapor permission efficiency of clothing

j :

Air or fabric layers number

K :

Effective conductance between core and skin, W/(m² K)

LR :

Lewis Ratio, °C/kPa

m :

Body mass, kg

M :

Rate of metabolic heat production, W/m²

M _act :

Rate of metabolic heat production due to activity, W/m²

${\dot{m}}_{bl}$ :

Mass flow rate of blood, kg/(s m²)

${\dot{m}}_{res}$ :

Mass flow rate of air inhaled, kg/s

${\dot{m}}_{rsw}$ :

Mass flow rate of regulatory sweat generation, kg/(s m²)

nl :

Number of layers covering segment

p _a :

Water vapor pressure in the ambient air, kPa

p _a,s :

Saturated water vapor pressure in the ambient air, kPa

p _atm :

Atmosphere pressure, kPa

p _sk,s :

Saturated water vapor pressure at the skin temperature, kPa

Q _cd :

Heat flow rate due to conduction, W/m²

Q _cr,sk :

Heat flow rate between core and skin, W/m²

Q _cv :

Heat flow rate due to convection, W/m²

Q _rd :

Heat flow rate due to radiation, W/m²

Q _res :

Total heat flow rate due to respiration, W/m²

Q _e,dif :

Latent heat flow rate due to diffusion, W/m²

Q _e,max :

Maximum latent heat flow rate due to evaporation, W/m²

Q _e,res :

Latent heat flow rate due to respiration, W/m²

Q _e,rsw :

Latent heat flow rate due to regulatory sweat generation, W/m²

Q _e,rsw,req :

Required latent heat flow rate due to regulatory sweat generation, W/m²

Q _e,sk :

Total latent heat flow rate from skin, W/m²

Q _s,res :

Sensible heat flow rate due to respiration, W/m²

r :

Outer radius of fabric layer, m

R _a :

Thermal resistance of outer air, (m² K)/W

R _al :

Thermal resistance of air layer, (m² K)/W

R _cl :

Thermal resistance of clothing, (m² K)/W

R _f :

Thermal resistance of fabric, (m² K)/W

R _t :

Total thermal resistance of clothing, (m² K)/W

R _e,a :

Evaporative resistance of outer air, (m² kPa)/W

R _e,al :

Evaporative resistance of air layer, (m² kPa)/W

R _e,cl :

Evaporative resistance of clothing, (m² kPa)/W

R _e,f :

Evaporative resistance of fabric, (m² kPa)/W

R _e,t :

Total evaporative resistance of clothing, (m² kPa)/W

${\overline{R}}_a$ :

Gas constant of air, kJ/(kg K)

${\overline{R}}_v$ :

Gas constant of vapor, kJ/(kg K)

RH :

Relative humidity

S _cr :

Rate of heat storage in the core, W/m²

S _sk :

Rate of heat storage in the skin, W/m²

t _a :

Air temperature, °C

t _b :

Body temperature, °C

t _b,c :

Lower limit temperature of evaporative regulation zone, °C

t _b,h :

Upper limit temperature of evaporative regulation zone, °C

t _cr :

Core temperature, °C

t _ex :

Exhaled air temperature, °C

t _o :

Operative temperature, °C

t _rd :

Mean radiant temperature, °C

t _sk :

Skin temperature, °C

TSENS :

Thermal sensation

w :

Total skin wettedness

w _dif :

Skin wettedness due to diffusion

w _rsw :

Skin wettedness due to regulatory sweating

W _a :

Humidity ratio of ambient air, kg H₂O/kg dry air

W _ex :

Humidity ratio of exhaled air, kg H₂O/kg dry air

W :

Rate of external work accomplished, W/m²

WSIG _b :

Warm signal from body

WSIG _cr :

Warm signal from core

WSIG _sk :

Warm signal from skin

α :

Fraction of total body mass concentrated in skin compartment

θ :

Time, s

η_e :

Evaporative efficiency