Problem description:
Better be specific.
Analysis:
1. Influencing factors of human thermal comfort
2. How to combine the requirements of human thermal comfort when designing the HVAC scheme?
3. The human body's response to the dynamic environment
5- 1 Physiological and psychological basis of human body's response to hot and humid environment
First, the thermal balance of human body.
(a) the basic physiological requirements of the human body:
1, metabolic rate:
The rate at which the human body releases energy in chemical reactions. Different parts of the human body have different temperatures.
Organs with high metabolic rate have higher temperatures.
2. Thermal balance equation of human body
M-W - C - R - E = S
Where: m-human energy metabolic rate, w/㎡;
W-mechanical work done by human body, w/㎡;
C—— heat emitted by the external surface of human body through convection to the surrounding environment, w/㎡;
R—— the heat radiated from the outer surface of human body to the surrounding environment, w/㎡;
E—— heat taken away by sweat evaporation and exhaled steam, w/㎡;
S—— heat storage rate of human body, W/㎡.
(In the formula, all items are expressed in terms of calorific value and heat dissipation per unit surface area of human body.)
3, bare human skin surface area calculation:
AD=0.202mb0.425H0.725
Where: AD-human skin surface area, m2;
H-height, m;
Mb-weight, kg;
4. The maximum physiological change range of human body is 35 ~ 40℃;
S = 0, indicating that the human body is normal;
S>0, indicating that the body temperature rises and the human body is uncomfortable;
When the body temperature is ≥45℃, people die.
S<0 shows that the heat dissipation of human body increases in cold environment.
When the body temperature
When the body temperature
When the body temperature
5. Average skin temperature:
Four-point model method:
The core temperature of the human body: it is determined by the exercise intensity of the human body, that is, the metabolic rate. The higher the metabolic rate, the higher the core temperature of human body. However, the core temperature of the human body must be maintained in a fairly narrow range to ensure its normal function.
Human skin temperature: it changes with the change of external temperature, and there are certain differences in different parts, just like the core temperature of human body.
In order to determine the average skin temperature, Ramanathan( 1964) proposed a four-point model.
That is, by testing the temperature of human chest, upper arm, thigh, calf and skin, the weighted average is carried out according to the weight coefficients of 0.3, 0.3, 0.2 and 0.2. The average skin temperature thus obtained is suitable for most applications.
(2) heat exchange between human body and the outside world
Heat exchange forms: convection, radiation and evaporation. These different types of heat exchange methods are all influenced by human clothing.
Convection: The temperature of ambient air determines the convective heat transfer between the human body surface and the environment, and the temperature difference thus affects the convective heat transfer. The ambient air velocity affects the convective heat transfer coefficient. When the air velocity is high, the convective heat of human body increases, so it will increase the cold feeling of human body.
Radiation: the surface temperature of the surrounding objects determines the intensity of radiation heat dissipation of the human body. For example, under the condition of the same indoor air parameters, the high temperature on the inner surface of the envelope will increase the thermal feeling of the human body, and vice versa.
Evaporation: latent heat exchange. It mainly takes away body heat through skin evaporation and breathing. It depends on the relative humidity of the air and the air speed.
Skin evaporation: including sweat evaporation and wet diffusion through the skin;
Air velocity: not only affects the sensible heat and latent heat exchange rate between human body and environment, but also affects the touch of human skin.
"through flow": It is an unpleasant feeling caused by the increase of air flow, which leads to the increase of evaporation of skin and mucosa and the impact of air flow.
(3) Several environmental factors that affect the sensible heat exchange between human body and the outside world.
1. Average radiation temperature:
Where:-average radiation temperature,℃
Fn —— the visible area of each surface of the surrounding environment, m2.
TN-temperature of all surfaces in the surrounding environment,℃.
Physical meaning: the surface temperature of the imaginary isothermal enclosure is equal to the radiation heat exchange between the actual non-isothermal enclosure around the human body and the human body.
Black ball thermometer: It consists of a thin-walled copper ball coated with black, and a thermometer is installed inside. The bulb of the thermometer is wrapped in the center of the copper ball.
2. Operating temperature to (operating temperature)
It reflects the comprehensive effect of environmental temperature ta and average radiation temperature tr;
Where: HR-radiation heat transfer coefficient, w/(㎡℃)
Hc—— Convective heat transfer coefficient, w/(㎡℃)
3. Convective heat transfer coefficient hc
Natural convection:
Forced convection: related to wind speed;
4. Fluid exchange coefficient
(i.e. evaporation heat transfer coefficient) LR= he/hc
LR is called "Lewis coefficient", and the general indoor air environment is LR= 16.5.
(4) the role of clothing:
Heat preservation; Obstruct wet diffusion.
1, clothing thermal resistance Icl: refers to sensible thermal resistance Iclo.
Commonly used units are ㎡ k/w and clo.
1clo=0. 155 ㎡ K/W
1clo is defined as * * * the thermal resistance of clothes that people need to feel comfortable in the environment where the air temperature is 2 1℃, the wind speed is less than 0.05m/s and the relative humidity is less than 50%.
For example, summer clothes are generally 0.5clo (0.08m2 k/w/w).
General work clothes are: 0.7clo (0. 1 1m2 k/w).
Winter clothes normally worn outdoors:1.5 ~ 2.0clo.
Arctic clothes: 4.0 grams
2. Influencing factors of clothing thermal resistance
(1) Influence of Chair on Thermal Resistance
It depends on the contact area between the chair and the human body.
The increase in thermal resistance of the seat can be estimated.
△Icl = 7.48× 10-5a-0. 1
(2) The influence of walking on thermal resistance
△Icl = 0.504 Icl+0.0028 1 vwalk-0.24
If a person is at rest, the thermal resistance of clothing is 1clo, and if the walking speed is 90 steps/minute (about 3.7km/h), then △ ICL = 0.504 ICL+0.0028 1 V walking -0.24.
=0.504 +0.0028 1×90-0.24=0.52
(3) Moisture permeability of clothing
On the one hand, clothing has extra resistance to the diffusion of water vapor on the skin surface;
On the other hand, clothing absorbs a part of sweat, leaving only a part of sweat to evaporate, making the skin cool;
Clothes will cool people down after absorbing sweat.
(4) the surface area of clothing
Clothing area coefficient: fcl=Acl/AD
Estimated value: fcl= 1.0+0.3Icl
(5) Energy metabolism of human body
1. Human energy metabolic rate:
Basal metabolic rate
Basal metabolism and basal metabolic rate
(1) basal metabolism: the energy metabolism of the human body in the basic state.
Basal metabolic rate: basal metabolism per unit time.
(2) Basic state:
1) Wake up in the morning and lie quietly for half an hour.
2) Fasting for more than 12 hours.
3) the room temperature is 18 ~ 25℃
4) Spiritual peace and tranquility
In the above state, the body only maintains the most basic metabolic state (blood circulation, breathing), and the heat produced by the body per unit time is the basal metabolic rate.
(3) Factors affecting energy metabolism
Muscle activity, mental activity, special dynamic function of food, age, sex and environmental temperature are the factors that affect energy metabolism.
1) Brain activity: Because the energy source of the brain mainly depends on the oxidation of sugar to release energy, it has little effect when thinking quietly, but it increases heat production and energy metabolism rate when nervous.
2) Special dynamic effect of food: After eating for a period of time, extra heat can be generated in the body, which is called special dynamic effect of food. Among them, protein is the strongest, followed by fat and sugar.
3) Ambient temperature: People are most stable when they are in a quiet state at 22.5 ~ 35℃, and low ambient temperature can increase muscle tension and energy metabolism. If the ambient temperature is too high, the substance metabolism in the body will be strengthened and the energy metabolism will also increase.
4) Gender and age
5) Muscle activity: It has the most significant influence on energy metabolism. Mainly to increase muscle oxygen consumption and do work, so that the energy metabolism rate increases.
2. Mechanical efficiency of human body
η = Watt/meter
In the calculation of air conditioning load, the mechanical efficiency of human body is often considered as 0.
(1) The efficiency of most office labor machines is 0;
(2) There are errors in the estimation of human metabolic rate;
(3) partial to safety considerations.
3. Evaporation and heat dissipation of human body
(1) human skin evaporative heat dissipation Esk
Emax=( Psk-Pa)/[ i.e. Cl+1/(fclhe)] = He' (PSK-PA)
(This formula is the latent heat dissipation of human body completely soaked by sweat)
Where: he '- Convective mass exchange coefficient of clothing surface.
Pa-partial pressure of water vapor in ambient air, kPa.
PSK-partial pressure of saturated water vapor on skin surface, kPa；; Psk =0.254tsk-3.335
Cl-the latent heat transfer thermal resistance of clothing.
Actual evaporation heat dissipation of human skin;
Esk=Ersw+Edif=wEmax
Where: Ersw———— heat dissipation by sweat evaporation;
Edif-skin moisture diffusion and heat dissipation;
W- skin humidity; w = Esk /Emax
Among them, skin wet diffusion dissipates heat Edif.
A) If the ambient humidity increases, if the skin does not sweat; Edif =0.06Emax
B) If there is normal perspiration; Edif =0.06(Emax-Ersw)
The evaporation of skin sweat is controlled by the thermoregulation system.
When the human body is in a lukewarm state;
Tsk=35.7-0.0275 (m-w)
Ersw=0.42 (male-female -58.2)
W =(M-W-58.2)/46he[5.733-0.007(M-W)-Pa]+0.06
(2) The amount of heat dissipation and moisture dissipation of human body.
Sensible heat dissipation: Cres=0.00 14M(34-ta) W/㎡.
Latent heat dissipation: eres = 0.0173m (5.867pa) w/㎡.
4, the human body and the outside radiation heat exchange.
R=efclfeff s (T4cl-T4r)
Where: e refers to the emissivity of the human body surface.
s—5.67× 10-8W/㎡K4
Feff- correction coefficient of human posture affecting effective surface area.
Tcl-human body surface temperature, k
Tr-the average radiation temperature of the environment, k
5. Under different environmental conditions and activity intensity, the human body dissipates heat and moisture.
Second, the human body's temperature sensing system.
(1) There are cold spots and hot spots on human skin, but their positions are different. There are more cold spots than hot spots.
1, there are temperature receptors in human skin.
2. There are also temperature receptors in some mucous membranes and abdominal organs of human body.
3. There are also neurons in the reticular structure of spinal cord and brain stem.
(two) according to the characteristics of the reaction, classification:
1, classification:
(1) Thermoreceptor:
Only impulse to hot * * *, restraint to cold * * *.
(2) cold receptors:
Can only impulse to cold * * *, be hot * *, restraint.
There are more cold receptors than heat receptors.
Third, the human body's temperature regulation system.
The difference between the thermal change process of human body and non-living body is that the temperature and heat dissipation of human body are not completely determined by environmental factors, because the temperature regulation system of human body has the ability to actively adjust these parameters within a certain range of environmental parameters. Warm-blooded animals, including humans, have a perfect thermoregulation mechanism (thermoregulation mainly depends on nerve regulation and body fluid regulation) compared with inanimate objects. When the external environment temperature changes, the body temperature can be kept relatively stable by adjusting the heat generation process and heat dissipation process.
The most important inputs of thermoregulation system are: core temperature; Average skin temperature. When the core temperature deviates from the set value, the temperature regulation system starts to work. However, the set point of human body temperature is not constant, but depends on the intensity of work, and the set point will rise at a higher metabolic rate.
(1) Surface body temperature and deep body temperature
1. Surface temperature
The temperature of human peripheral tissues, that is, the surface layer, including skin, subcutaneous tissue and muscle, is called the surface temperature.
The surface temperature is unstable. For example, when the ambient temperature is 23℃, see table.
Skin temperature of feet and hands trunk℃ forehead℃
27 30 32 33—34
When the temperature is above 32℃, the temperature difference in different parts of the skin will become smaller. In a cold environment, with the temperature drop, the skin temperature of hands and feet will drop most significantly, while the skin temperature of the head will change relatively little.
In the environment, with the decrease of temperature, the skin temperature of hands and feet decreases most significantly, while the skin temperature of head changes relatively little.
2. Deep temperature
The temperature of the deep body (heart, lungs, brain, abdominal organs, etc.). ) is called the core temperature. The deep temperature is higher than the surface temperature, and it is relatively stable, and the difference between different parts is also small.
(1) In different environments, the distribution of deep temperature and surface temperature will change relatively.
(2) In the cold environment, the temperature distribution in the deep part is narrow, mainly concentrated in the head, chest and abdomen, and there is an obvious temperature gradient between the surface and the deep part.
(3) In a hot environment, the deep temperature can extend to the limbs.
Human body temperature regulation method:
Under the control of hypothalamic thermoregulation center, thermoregulation randomly changes the information of internal and external environment, and regulates the release and production of body temperature by increasing or decreasing physiological reactions such as skin blood flow, sweating and chills.
(2) the center for regulating body temperature:
The hypothalamus is a part of the brain.
1, anterior hypothalamus: promoting heat dissipation.
2. Posterior hypothalamus: promoting thermogenesis; Resist the cold.
The regulating method of human body temperature includes:
Regulate the blood flow on the surface of skin;
Adjust the amount of perspiration;
Improve heat production.
Fourth, thermal sensation.
1. Definition:
Thermal sensation is a subjective description of whether the surrounding environment is "cold" or "hot".
Thermal sensation cannot be measured by any direct method. People often evaluate the "cold" and "warm" of a room. In fact, people can't directly feel the temperature of the environment, only feel the temperature of nerve endings under the surface of their skin.
The discipline that studies the relationship between feeling and * * * is called psychophysics, which is one of the earliest branches of psychology.
"neutral" state: that is, the state in which people feel neither hot nor cold.
2. Factors affecting thermal sensation:
(1) The existence of cold and hot * * *
(II) Duration * * *
(3) the original thermal state of human body
The cold and hot receptors of human body have obvious adaptability to the environment.
3. The influence of human skin temperature on thermal sensation
In the neutral zone, the skin thermal sensation is related to the temperature change rate.
4. The influence of human core temperature on thermal sensation.
Conclusion: Thermal sensation depends first on skin temperature and then on core temperature.
When the ambient temperature changes rapidly, the thermal sensation changes faster than the body temperature.
Therefore, temperature is often used to predict thermal sensation.
6. Description of thermal sensation
Questionnaire survey method
Figure 5-8 Sensory and adaptive temperature caused by skin temperature change
And the relationship between variables.
Verb (abbreviation for verb) is warm and comfortable.
Definition of thermal comfort: the state of being satisfied with the environment.
There are two views: (1) the neutral thermal feeling of "neither cold nor hot"
(2) Make people happy, happy and satisfied.
Influencing factors of thermal comfort:
(1) Air humidity: The adhesion of human body increases, and the discomfort is enhanced.
(2) Vertical temperature difference: If the temperature around the head is higher than that around the ankle, the more uncomfortable it is.
For example, radiant floor heating is more comfortable than ordinary radiators.
(3) Blowing sensation
(4) Other factors: such as differences in age, living background and personal hobbies.
5-2 Description of Human Body's Response to Stable Thermal Environment
I. thermal comfort equation
Prerequisites for thermal comfort equation of steady-state energy balance of human body;
The human body must be in a state of thermal balance;
The average temperature of human skin should have a suitable and comfortable level;
The human body should have the best perspiration rate.
In the thermal balance equation of human body, when the thermal storage rate of human body S=0, the thermal comfort equation of human body is obtained:
M-W-C-R-E=0
By bringing the calculation formulas of the variables in the heat balance equation into the equation, we can get:
Quantitative relationship among six variables that affect human thermal comfort: m, Pa, ta, tr, Icl and va.
2. Forecast average voting (PMV)
If the human body can satisfy the comfort equation through convection and radiation, the human body is in a comfortable state.
On the other hand, if the human body cannot satisfy the comfort equation through convection and radiation in a certain thermal environment, the human body will produce a "load" TL.
TL definition: the difference between the heat generated by human body and the average skin temperature under the condition of keeping human body comfortable, and the heat released to the outside when the latent heat generated by sweating dissipates heat.
TL=M-W-C-R-E
When TL is positive, the human body produces thermal sensation; If TL is negative, it will produce a cold feeling.
Checkbox investigated 1396 subjects.
Conditions: four different activity intensities, the same amount of clothes (all 0.6clo), the human body's reaction when the wind speed changes;
Conclusion: People's reaction is a function of activity and "load"
Draw (a conclusion)
PMV =[0.303 exp(-0.036m)+0.0275]TL
The 7-level division of PMV index is shown in the following table:
The PMV index represents the comfortable feeling of most people in the same environment.
PPD (Percent of Predicted Dissatisfaction) index, which indicates the percentage of dissatisfaction with the thermal environment.
PPD = 100-95 exp[-(0.03353 PMV 4+0.2 179 PMV 2)]
As can be seen from the figure, when PMV=0, PPD=5%. It means that 5% people are still dissatisfied when they are in the best thermal comfort state indoors. Therefore, the recommended value of PPV-PPD index in ISO7730 is between -0.5 and +0.5, which is equivalent to making 10% people in the crowd feel dissatisfied.
Thirdly, the effective temperature ET and the comfort zone of ASHRAE.
The definition of effective temperature ET: the influence of dry bulb temperature, humidity and wind speed on human body's warm feeling or cold feeling is integrated into a single arbitrary index.
Numerically equal to the temperature of static saturated air that produces the same feeling.
New effective temperature ET *: The estimation of the influence of excessive effective temperature and humidity on cool and comfortable state at low temperature has been changed, and the concept of skin wetness has been introduced.
The standard effective temperature set * *: (the most common index considering different activity levels and thermal resistance of clothes) is the equivalent dry-bulb temperature. That is, set * normalizes the air temperature, relative humidity and average radiation temperature in the real environment into a temperature parameter, so that environments with different air temperature, relative humidity and average radiation temperature can be compared with each other with a set * value.
Specifically, if the ambient temperature is set to *; The average radiation temperature is the same as the ambient temperature; In an isothermal imaginary thermal environment with a relative ambient temperature of 50%; The humidity of human skin and the heat exchanged through the skin are the same as the real environment; Then, SET* * can be used to represent the temperature of this real environment.
As shown in Figure 5- 12, a set of dashed lines drawn obliquely are equivalent effective temperature lines, and their values are the corresponding temperature values marked on the relative humidity line with φ = 50%. If t = 25℃, φ = 50%, and the dotted line at the intersection of the two lines is 25℃, the effective temperature line is measured with indoor wind speed of 0. 15m/s and clothing thermal resistance of 0.6clo.
The rhombic area obtained by experiments at Kansas State University, USA.
Applicable conditions: people who wear clothes with thermal resistance of 0.6 ~ 0.8 clo, * * *.
Comfort standard recommended by ASHRAE 55-74 comfort zone, parallelogram area.
Applicable conditions: the thermal resistance of clothing is 0.8 ~ 1.0 clo, and the sitting person has a large amount of activities.
The overlap of two comfort zones is the recommended indoor air design condition.
5-3 Human Body's Response to Dynamic Thermal Environment
The above indexes and evaluations about thermal comfort are all obtained under the condition of stable thermal balance. In fact, most human beings are in a changeable dynamic thermal environment. It is necessary to study the reaction of human body under unstable temperature or wind speed.
Gagge et al. found that there is a transition process between skin and thermal sensation when the temperature changes step by step.
Experiments show that:
1. When the human body suddenly changes from a neutral environment to a cold or hot environment, the change of thermal sensation has a "lag".
2. When suddenly changing from a cold or hot environment to a neutral environment, there will be a short-term "advance" of thermal sensation, that is, the perceived cold and hot sensation index is lower than the stable environment.
First, the human body's response to step temperature changes.
Example: put one hand in the warm water basin and the other hand in the cold water basin. After a period of time, put your hands in the third basin at a moderate temperature. Then, the first hand feels cold, and the other hand feels warm, even though it is in water at the same temperature.
Analysis: When the temperature of human body changes step by step, the changes of skin temperature and thermal sensation have a transitional process, and the skin temperature lags behind due to the existence of thermal inertia.
Conclusion:
1. The physiological adjustment of human body to environmental mutation is very rapid, which will not have adverse consequences on human body;
2. In the physiological adjustment cycle of environmental mutation, skin temperature can not be used as an independent evaluation scale of thermal sensation, because the human body is undergoing intense heat exchange with the surrounding thermal environment at this time, and the change of skin temperature is lagging due to the existence of thermal inertia.
Second, the human body's response to changes in wind speed.
The most comfortable environmental conditions determined by wind speed, temperature and humidity are also called thermal neutrality, that is, PPD < 10% and PMV= 0.5. Among them, the decisive factor is wind speed (quantity). If people feel different in seaside, grassland and forest, the most important factor is the difference of wind speed (quantity).
Example: comparison of human thermal comfort between fixed fan and rocking fan
Conclusion: 1 The acceptance of oscillating fan is better than that of fixed fan, and the frequency of airflow pulsation has a significant impact on human thermal sensation.
2. In warmer environment, dynamic wind has stronger cooling effect on human body than stable airflow.
Application: 1. In air conditioning design, when the air flow pulsation frequency is 0.7- 1.0Hz, the refrigeration effect is better and more comfortable.
2. The frequency and wind speed of air conditioner should be closer to the natural wind and more comfortable.
Third, the thermal comfort index in the state of overactivity
For example, some people need to stay for a short time, such as subway stations, station halls and train air conditioners, connecting two spaces with different thermal environment parameters such as temperature and humidity.
The thermal comfort index of human body in transition space environment proposed by the US Department of Transportation;
RWI (relative warmth index): Suitable for warmer environment.
HDR (Heat Loss Rate): Suitable for cold environment.
Its consideration of dynamic process is reflected in:
1. It takes 6m 6 minutes for people to transition from one active state to another, and the metabolic rate m can reach the stable metabolic rate in the final active state.
2. People's activities can lead to sweating and wet clothes. At the same time, human activities will disturb the surrounding airflow, leading to changes in the thermal resistance of clothes.
5-4 Physical measurement of other hot and humid environments
The various evaluation indexes of the hot and humid environment introduced earlier are all used to predict thermal sensation or subjective thermal comfort. However, in the environment with the risk of thermal imbalance, such as high temperature workshop or field work, feeling is not enough as an indicator of physiological strain, and new indicators are needed to evaluate it.
Thermal stress: a potential danger and discomfort
The environment will form a strong * * *, called thermal stress.
Thermal stress: due to thermal stress.
The amount of perspiration is determined by the presence of, and
Changes in heart rate and core temperature of human body,
Call it overwork.
I. Thermal Stress Index (HIS)
1. Concept: temperature and humidity in environmental variables are integrated into a single index, which is used to quantitatively express the pressure of thermal environment on human body.
2. Application: In high temperature, low humidity, low temperature and high humidity environment, if the thermal stress index is the same, the thermal overload is the same.
3. Significance: It is used to evaluate the environment with thermal stress and measure the thermal overload in the environment with thermal imbalance danger.
4. Determination conditions of thermal stress index:
Assume that the skin temperature is constant at 35℃;
In the heat of vaporization regulation area;
Breathing and cooling are not counted;
It is considered that the required perspiration Ereq is equal to the metabolic quantity MINUS the convection and radiation heat dissipation;
The thermal stress index is HSI= Ereq/ Emax× 100.
Second, the wind cooling index WCI(Wind Chill Index)
1. In high and cold areas, the main factors affecting the heat loss of human body are: air velocity and air temperature.
2. Concept: wind speed and temperature are integrated into one index.
3. Meaning: indicates the cooling rate of a certain skin surface when the skin temperature is 33℃.
Wci = (10.45+10 √ va-va) (33-ta) kcal/m2 hour.