Function of Data Whose Value Vary Over a Continuous Range Temperature Atmospheric pressure

Distribution of the temperature field in a pavement structure

Lijun Sun , in Structural Behavior of Asphalt Pavements, 2016

2.4.3 Daily Change of Main Environmental Factors and Pavement Temperature

The air temperature and solar radiation have periodical daily variations; consequently, the pavement temperature distribution is also changing periodically. On sunny days, the daily variety of air temperature, solar radiation, and pavement temperature all have certain patterns. The typical variation of daily pavement temperature, air temperature, and solar radiation are shown in Fig. 2.5A. In other weather conditions, the pattern of the daily variety for air temperature, solar radiation, and pavement temperature are very complex. For example, in the scenario of a brief afternoon rainfall, the variation of daily pavement temperature, air temperature, and solar radiation are shown in Fig. 2.5B.

Fig. 2.5. Daily variety of air temperature, solar radiation, and pavement temperature.

In sunny conditions, the highest air temperature normally happens between 12:00 and 14:00. The lowest air temperature normally happens between 04:00 and 06:00. Therefore, the time requirement for air temperature rising from the lowest temperature to highest temperature is less than 10   h, but the time requirement for air temperature going from the highest to the lowest is more than 14   h. In the 2–4   h after the sunrise, the air temperature is rising the fastest. Around 1   h before the sun setting, the air temperature is dropping the fastest. The solar radiation normally reaches its peak value at noon. The increase and decrease process of solar radiation are almost symmetrical, but in other weather conditions, both air temperature and solar radiation will be influenced by many factors and are more complex in their variety.

Generally, the variation of pavement temperature is similar to the variation of air temperature and solar radiation. Those factors would cause the transient effects on the pavement surface temperature so that its variations almost synchronize with that of the air temperature. When the heat energy conducts itself to a depth in a pavement structure, it would take some time and cannot happen at once; therefore, the transient variation of air temperature or other environmental factors can't be reflected immediately at the bottom of the asphalt layer. The lag time between pavement temperatures at certain depth with environmental factors would increase with depth. Therefore, the influence of environmental factors to pavement temperature distribution at a deep layer have significant lagging characteristics, whereas the influence to pavement temperature distribution at any depth has significant accumulation characteristics. In summary, the pavement temperature distribution at a certain time is not only affected by the air temperature and solar radiation at the moment, but it is also reflected by the combined efforts of air temperature and solar radiation during a previous period of time. With the increase of pavement depth, the influence of environmental factors on pavement temperature declined; the variation of daily pavement temperature fluctuations at this depth will be less and less significant.

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Drying, conditioning and industrial space heating

In The Efficient Use of Energy (Second Edition), 1982

Effect of Air Temperature on Drying Rate.

As the air temperature increases, its potential for holding water vapour increases out of all proportion (exponentially). Higher air temperature also increases the rate of heat transfer to the surface water and the material, resulting in higher evaporation rates, and increasing the driving force assisting moisture or vapour to flow to the material surface.

Highest drying rates will therefore be obtained at the maximum practicable air temperature compatible with the tolerance of the material to be dried, and of course limited by the heating medium available. But high air temperatures are only attainable at the expense of high energy input to the drying system. Drying costs will be high unless measures are taken to lower the air temperature at the drier exhaust to the practical minimum, e.g. by causing the spent air to preheat incoming material.

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Impacts of Pavement Strategies on Human Thermal Comfort

Hui Li Ph.D., P.E. , in Pavement Materials for Heat Island Mitigation, 2016

13.6.1 Climate Data in the Three Chosen Regions

The air temperature data across a year for the three regions, namely Sacramento and Los Angeles in California and Phoenix in Arizona, are presented in Figure 13.3. The Sacramento and Phoenix areas have inland climates with large air temperature fluctuations across the seasons, whereas the Los Angeles region has a coastal climate with much smaller air temperature fluctuations across the seasons. Phoenix has a very hot climate during the summer. Los Angeles, with the coastal climate, is cool during summer. Sacramento has a cold winter compared to the other two regions. The typical summer (July) and winter (January) climate data for these three locations are listed in Table 13.3 and were used for assessment.

Figure 13.3. Comparison of the climate data in three regions: Sacramento and Los Angeles in California and Phoenix in Arizona. (a) Average high air temperature. (b) Average low air temperature.

Table 13.3. Typical summer and winter climate data for three regions

Season	Daily peak air temperature $T_a^{\mathbf{max}}$ (°C) a	Daily low air temperature $T_a^{\mathbf{min}}$ (°C) a	Daily total solar radiation volume Q (MJ/m2) b	Daily effective sunlight hour c (h) b	Daily average wind velocity v w (m/s) c
Sacramento, California
Summer (July)	34	16	28.3	11	4.0
Winter (January)	13	5	6.3	8	3.2
Los Angeles, California
Summer (July)	29	18	22.6	10	2.8
Winter (January)	20	9	9.7	8	2.2
Phoenix, Arizona
Summer (July)	40	25	27.4	11	3.2
Winter (January)	19	4	11.4	9	2.4

Note: data obtained from:

a

http://www.weather.com/weather/wxclimatology.

b

http://rredc.nrel.gov/solar/old_data/nsrdb.

c

http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/hourly/list_by_state.html#C.

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Calculation and analysis procedures

Peter D. Osborn BScEng (Hons), C Eng, FIEE Engineering Consultant , in Handbook of Energy Data and Calculations, 1985

B10 Environmental temperature and thermal comfort

The concept of environmental temperature is used principally to compensate for radiation from internal surfaces in a building where the temperature of these surfaces is lower than the air temperature within the building. Clearly these lower surface temperatures are likely to occur on external walls particularly those with a high degree of exposure.

The environmental temperature is calculated by taking two-thirds of the mean radiant temperature and adding it to one-third of the air temperature. To illustrate the calculation the data quoted in B11.7 and summarized in Table B10.1, covering a small machine shop may be used.

B10.1. Data for environmental temperature calculation

Region	Temperature (°C)	Area (m2)
Floor	17	690
External walls	18	210
Wall glazing	10	25
Roof	12	600
Roof glazing	10	230
Internal air	19	—

Mean radiant temperature:

$\frac{(690\times 17)+(210\times 18)+(25\times 10)+(600\times 12)+(230\times 10)}{690+210+25+600+230}=14.39°\text{C}$

Environmental temperature:

$(\raisebox{1ex}{$2$}\!\left/ \!\raisebox{-1ex}{$3$}\right.\times 14.39)+(\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right.\times 19.00)=15.9°\text{C}$

Work by Professor P. O. Fanger in the Laboratory of Heating and Air Conditioning at the University of Denmark has introduced further concepts into the study of temperature and comfort conditions. This work co-ordinates six factors affecting both physiological and psychological reactions to comfort conditions; these factors are

air temperature, mean radiant temperature, air velocity, water vapour pressure (humidity), metabolic rate of the individual and the thermal insulation of his clothing.

Professor Fangar's approach is to demonstrate that when a person feels comfortable in his environment these six factors are in equilibrium. The first four can be measured by well established techniques and Professor Fangar ^* has postulated scales of measurement for the last two, i.e. MET factor and CLO factor.

Table A4 gives empirical values for the metabolic heat generated by people varying for an average person from 100 w at rest to 400 w when doing heavy work. Corresponding MET factors are 1.0 to 4.0.

CLO factors run from zero (no clothing) to 3.0 (full winter outdoor clothing).

A further approach to comfort conditions uses the Effective Temperature which is intended to compensate for the degree of humidity; this assumes that people will feel comfortable provided conditions fall short of the point where they are perspiring continuously (conversely it must also ensure that they feel warm enough!). This approach results in an effective temperature scale and a zone of comfort conditions for a person engaged in sedentary activity.

In practice a relative humidity of between 40% and 70% satisifies most people and this is the normal criterion for air conditioning calculation; in winter time people will tolerate a dry bulb temperature two or three °C below the summer level.

There is no ideal: people vary, activity varies and clothing worn varies.

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Factors affecting comfort: human physiology and the role of clothing

A.K. Roy Choudhury , ... C. Datta , in Improving Comfort in Clothing, 2011

Air (dry-bulb) temperature

Air temperature affects the rate of heat loss from the body by convection and evaporation. It is perhaps the most important determinant of thermal comfort, since a narrow range of comfortable temperatures can be established almost independently of the other variables. A fairly wide range of temperature, with properly combined relative humidity, MRT, and air flow, can provide comfort. With variation of the above conditions, the surrounding air temperature must be adjusted in order to maintain comfort conditions.

Temperature drifts and ramps are passive and actively controlled gradual temperature changes over time, respectively. People may feel comfortable with temperatures that rise or fall like a ramp over the course of time, even though they would be uncomfortable if some of the temperatures were held constant. Ideal comfort standards call for a change of no more than 1   °F/hr (0.6   °C/hr) during occupancy, provided that the temperature excursion doesn't extend far beyond the specified comfort conditions, and for very long.

Air temperature in an enclosed space generally increases from floor to ceiling. If this variation is sufficiently large, discomfort could result from the temperature being overly warm at the head and/or overly cold at the feet, even though the body as a whole is thermally neutral. Therefore, to prevent local discomfort, the vertical air temperature difference within the occupied zone should not exceed 5   °F (3   °C). The occupied zone within a space is the region normally occupied by people. It is generally considered to be the first 6 feet (1.8   m) above the floor and 2 feet (0.6   m) or more away from walls or fixed air conditioning equipment. The floor temperature should be between 65 and 84   °F (18 and 29   °C) to minimie discomfort for people wearing appropriate indoor footwear.

The hot or cold objects can be quickly identified just by touching, but one may mislead while describing how hot or cold the objects are. The touching sensation depends more on the rate of conduction of heat to or from the body than the actual temperature of the objects. Even if steel and wood are at the same temperature, the former will be felt cooler or hotter, if touched, depending on whether both being cooler or hotter than the body, respectively. This is because steel conducts heat away from or to fingers or other touching body parts very quickly. In other words, the sensors on our skin are poor judges of temperature, but are designed to sense the degree of heat flow.

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Plant Factory and Space Development, "Space Farm"

Yoshiaki Kitaya , in Plant Factory Using Artificial Light, 2019

9.4.2.2 Temperature

Air temperature is generally used as the temperature when discussing the influence of temperature on plant photosynthesis or respiration. However, plant body temperature (or leaf temperature) has a direct effect on the biochemical reactions necessary for plant physiology. For example, the leaf temperature at which the maximum net photosynthetic rate is reached falls in the range of 20–30°C. Leaf temperature increases due to the increase in radiant energy absorbed by the leaves and decreases due to the increase in sensible and latent heat energy transported from the leaves to the air. Therefore, environmental factors (light intensity, temperature, humidity, airflow velocity, etc.) associated with this energy balance influence leaf temperature and eventually influence photosynthesis and growth.

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Conduction of Heat in Mass Concrete, Boundary Conditions, and Methods of Solution

Zhu Bofang , in Thermal Stresses and Temperature Control of Mass Concrete, 2014

2.3 Air Temperature

2.3.1 Annual Variation of Air Temperature

The variation of air temperature in 1 year or 1 day generally can be expressed by the following cosine series:

(2.26) $T_{\mathrm{a}}(\tau )=T_{\mathrm{am}}+\sum _{i=1}^n{A}_i\cos \left[\frac{2i\pi }{P}(\tau -{\tau }_0)\right]$

(2.27) $A_i=\frac{2}{P}{\int }_0^P{T}_{\mathrm{a}}(\tau )\cos \left[\frac{2i\pi }{P}(\tau -{\tau }_0)\right]\mathrm{d}\tau$

where

T _a(τ)—the air temperature

T _am—the mean air temperature

P—the period of variation, P is equal to 1 year or 1 day

τ—time

τ ₀—the time for the maximum air temperature

n—the number of terms, generally n=1 or 2.

Fox example, the air temperature at Three Gorges dam is given by (n=1):

(2.28) $T_{\mathrm{a}}=17.30+11.35\cos \left[\frac{\pi }{6}(\tau -6.50)\right](°\mathrm{C})$

and the air temperature at Baise dam is expressed by (n=2):

(2.29) $T_{\mathrm{a}}=22.1+7.57\cos \left[\frac{\pi }{6}(\tau -6.50)\right]-1.22\cos \left[\frac{\pi }{3}(\tau -6.50)\right](°\mathrm{C})$

2.3.2 Cold Wave

The cold wave, a rapid drop of air temperature in 2–6 days, is an important cause for cracking of mass concrete. The variation of the air temperature during a cold wave may be expressed as follows ( Figure 2.5):

Figure 2.5. Variation of air temperature in a cold wave.

(2.30) $T_{\mathrm{a}}=T_0-A_{\mathrm{c}}\sin \left[\frac{\pi (\tau -{\tau }_1)}{2Q}\right]$

where

T ₀—the initial air temperature

A _c—the maxima drop of air temperature

Q—the duration of drop of air temperature in the cold wave.

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The thermal management and fuel consumption effect of future engine technology

J. Miller , ... R. Dingelstadt , in Vehicle Thermal Management Systems Conference Proceedings (VTMS11), 2013

4.1 Cascaded Charge Air Cooling

Charge air temperature plays an important role in determining the performance of a turbocharged gasoline downsized engine, as increasing charge air temperature increases

the engine's propensity to knock. As a result combustion phasing is not optimum and more retarded leading to higher turbine inlet temperatures and thus increasing the over-fuelling requirement for a given engine operating point.

The amount of heat that can be absorbed from the inlet air is a function of the type of charge-air-cooler that can be packaged with the engine in the vehicle. Traditionally, a direct (air-to-air) charge air cooler has been used for this purpose, however the trend for in-direct (water-to-air) charge air cooling [11–15] especially with an integrated intake manifold cooler is becoming state of the art. An Integrated Indirect Charge Air Cooler (i²CAC, figure 2) has the added benefits, amongst others, of having smaller packaging requirements, thus eliminating the need for long charge air pipe lengths around the engine bay associated with a direct charge air cooler, as well as offering improved transient response due to lower plenum temperatures as a result of the higher specific heat capacity of coolant compared to air [14]. In order to achieve lower plenum temperatures the LT radiator (figure 2) size can be increased, however due to vehicle packaging requirements, this can only be increased so far and thus places a limit on the potential reduction in charge air temperature.

MAHLE Powertrain and BEHR have addressed this issue whilst taking the i²CAC concept a step further with Cascaded Charge Air Cooling (CCAC = HTCAC + i²CAC) [18]. In this arrangement, two heat exchangers are installed in the intake manifold, a conventional i²CAC plus a High Temperature Charge Air Cooler (HTCAC, figure 2). The CCAC concept uses the excess cooling capacity in the HT circuit to further reduce the charge air temperature. To achieve this the HTCAC is fed with engine coolant exiting the block at around 90°C and therefore can be used to reduce the air temperature upstream of the i²CAC and hence lower the plenum air temperature. In order to prove this concept, simulation runs with the different cooling pack hardware were carried out in BISS using a MAHLE demonstrator vehicle model, table 2. This shows the improvement in plenum air temperature offered by an i²CAC and CCAC system over the direct charge air cooler at peak power.

Table 2. BISS simulated plenum air temperature of the MAHLE demonstrator vehicle at 180km/h and 24°C ambient temperature

Charge Air Cooling Configuration	Plenum Air Temperature [°C]
Direct	47
i2CAC	35
CCAC	30

The CCAC concept was then applied and tested on the MAHLE downsized engine on a dynamometer to assess the potential benefits of reduced charge air temperature. Typical plenum temperatures (50-60°C) for a gasoline turbocharged engine with a direct charge air cooler are approximately 25°C above ambient temperature. Figure 3 shows the results of a charge air temperature sweep, with up to 10% improvement in BSFC for a reduction in plenum temperature from 60 – 30°C. This is predominantly due to more advanced combustion phasing arising from a lower knock propensity with reduced plenum temperatures and hence a reduction in the amount of over-fuelling required for component protection. Further tests carried out by Taylor et. al [18] have shown additional performance improvements on the run up line through lowering charge air temperature. At the 1400rpm full load operating condition, engine torque could be increased by 17.4% for a plenum temperature reduction from 60 – 30°C. The implication of increased run up line performance is to increase the downsizing factor. That is being able to install the engine in a heavier vehicle and shifting the operating point to a higher load, further improving part load fuel consumption.

Figure 3. Relative BSFC improvement as a function of plenum temperature (reference = 60°C) at5000rpm 120kW

Table 3 shows the measured heat rejection to the HT and LT circuits at different plenum temperatures. As expected the total heat rejected by the i²CAC and HTCAC increases with reducing plenum temperature. Breakdown of the heat rejection by charge air cooler shows that the HTCAC absorbs the majority of the rejected heat at higher plenum temperatures, whilst conversely the i²CAC absorbs the majority of the heat with reducing temperature. This effect is as a result of improving combustion efficiency with lower plenum temperatures, thus lowering the boost pressure requirement for constant engine load and hence reducing the air temperature upstream of the HTCAC.

Table 3. Experimentally measured heat rejection to coolant circuits, 5000rpm 120kW, for lower target plenum temperatures

	60°C plenum temperature	30°C plenum temperature
Engine Coolant [kW]	36	36
HTCAC – HT coolant [kW]	6	4
i2CAC – LT coolant [kW]	2.4	6
Total	44.4	46

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Environmental ergonomics

E.J. Skilling , C. Munro , in Human Factors in the Chemical and Process Industries, 2016

Thermal Comfort

Thermoregulation is the physiological process within the human body, which regulates and maintains the internal core temperature at approximately 37°C (Wilson and Corlett, 2005). Deviation from 37°C can cause ill health and any deviation of 2°C can cause death.

Thermal comfort describes an individual's perception of their immediate environment, ranging from feeling too hot, moderate or too cold. Thermal comfort is defined as "that condition of mind which expresses satisfaction with the thermal environment" (Wilson and Corlett, 2005 ). It becomes apparent to the individual that they are uncomfortable if there are changes in the environment or extremes of thermal conditions. Thermal comfort is not simply related to temperature alone; it is a combination of six environmental and personal factors; air temperature, radiant temperature, humidity, air flow, metabolic rate, and the clothing worn by individuals. The combination of these factors can be complicated, and due to the nature of individuals experiencing and expressing their own perceptions of thermal comfort, there can be a wide range of opinions and levels of satisfaction within a group of users sharing the same work environment. Establishing the ideal thermal environment to suit everyone can be difficult. Using room temperature as an example, it is unlikely that it will be considered "ideal or comfortable" by more than 60% of people (McKeown and Twiss, 2004). Despite the difficulties in satisfying individuals, it is important to assess the thermal environment and thermal comfort factors.

Air Temperature

Air temperature is the temperature of the air surrounding an individual and is typically measured in degrees Celsius (°C) or degrees Fahrenheit (°F). It is traditionally measured using mercury in glass thermometer, with thermocouples and thermistors being used more recently ( Wilson and Corlett, 2005).

Radiant Temperature

Radiant temperature is the heat radiated by a heat source such as a furnace, a fire, or the sun. The temperature is measured with a black globe thermometer and recorded in Celsius (°C) or degrees Fahrenheit (°F). The impact of radiant temperature is larger than that of air temperature, when considering the heat absorbed or lost by an individual to their environment.

Humidity

Humidity is the amount of moisture in the air and is expressed as a percentage of Relative Humidity (%RH). Hygrometers containing wet and dry bulbs are used to calculate humidity; alternative methods include hair hygrometers and capacitance devices.

Air Velocity

Air velocity describes the speed at which air is moving over an individual and is measured in meters per second (m/s). Kata thermometers or hot wire anemometers are used to measure air velocity.

Metabolic Rate

The type of work undertaken has an impact on the perception of temperature. Tasks that are more physical in nature raise the metabolic rate, the body produces heat, and the individual feels hotter. Tasks that are less physically demanding are associated with a lower metabolic rate, less body heat is produced, and individuals feel cooler than someone performing more physical tasks. Metabolic rate is measured in kilocalories. Figures for common work tasks have been established using laboratory and mobile data collection.

Clothing

The clothing worn by individuals has a significant effect on the thermal comfort; too many items of clothing may lead to the individual becoming too hot or to be too cold if they are not wearing adequate layers of insulation. Clothing can be used to self-regulate thermal comfort, with individuals adding or removing layers of clothing to adapt to their immediate environment. Personal Protective Equipment (PPE) can be a source of thermal discomfort for individuals, especially if it is not carefully selected as it can lead to the individual being too hot or too cold and affects their ability to conduct their tasks. Measurements of clothing and insulation are measured in CLO and TOG respectively and used to calculate thermal comfort (Wilson and Corlett, 2005).

Psychological and Physical Effects of Thermal Comfort

Thermal discomfort caused by the internal or external environment being too hot or too cold may lead to a variety of psychological or physical effects.

Mild thermal discomfort in hot environment can affect cognitive capability and concentration, and can lead to irritability and exhaustion. The physical effects associated with mild "hot" thermal discomfort include sweating and dehydration.

Extremely hot environments may lead to heat stress and cause heat stroke, delirium, and an inability to process information or communicate coherently. The physical symptoms range from fainting, progressive dehydration to systemic organ failure, and eventually death.

Mild thermal discomfort in cold environments may lead to reduced motivation and reduced ability to process information. Cold environments can cause physical reactions, including shivering and reduced blood flow peripherally to the hands and feet; causing issues with dexterity. Subsequently, this can have an effect on the ability to manipulate controls. Cold environments, including cold draughts can cause an increased risk of musculoskeletal injury.

Extreme cold environments can cause individuals to experience a loss of situational awareness and cause irrational behavior, as well as cardiac and respiratory failure, and eventually death.

The physiological, physical, and psychological impacts affect work capability and productivity. Thermal discomfort can cause staff to be less efficient and more prone to error, which increases the risk of injury or accidents.

Assessment of Thermal Comfort

Thermal comfort is assessed using different approaches including thermal indices, thermal scales, and comfort surveys.

Thermal Indices

Wet Bulb Globe Temperature (WBGT) can be used to calculate a composite temperature figure which accounts for the measured air temperature, radiant temperature, and humidity. The formula is presented in Box 16.1.

Box 16.1

Wet Bulb Globe Equation

Taken from Wilson and Corlett (2005)

Indoor environments or outdoors with minimal sun exposure (solar load):

$\text{WBGT}=0\text{.7tnw}\text{+}\text{0}\text{.3tg}$

Outdoor environments, including sun exposure (solar load):

$\text{WBGT}=0.7\text{tnw}\text{+}0.2\text{tg}\text{+}0.1\text{ta}$

where

t _nw = natural wet bulb temperature,

t _g = 150   mm diameter black globe temperature,

t _a = air temperature.

The composite temperature can then be reviewed in conjunction with measurements for likely metabolic work rate (based on tasks and rest) and the clothing being worn. This is used to define an exposure limit for users and judge the suitability of the environment using the guidance in Table 16.2 and the WBGT correction values in Table 16.3.

Table 16.2. WBGT Exposure Limits for Various Levels of Work and Workload

Work/Rest cycle: allocation of work	United States Department for Labor Occupational Health and Safety Administration (OSHA, 2015)			Canadian Centre for Occupational Health and Safety (CCOHS, 2011)			Work/Rest cycle: allocation of work
	Physical workload			Physical workload
	Light	Moderate	Heavy	Light	Moderate	Heavy
Continuous work	30.0°C (86°F)	26.7°C (80°F)	25.0°C (77°F)	31.0°C	28.0°C	Not specified	75–100% work
75% work (25% rest) each hour	30.6°C (87°F)	28.0°C (82°F)	25.9°C (78°F)	31.0°C	29.0°C	27.5°C	50–75% work
50% work (50% rest) each hour	31.4°C (89°F)	29.4°C (85°F)	27.9°C (82°F)	32.0°C	30.0°C	29.0°C	25–50% work
25% work (75% rest) each hour	32.2°C (90°F)	31.1°C (88°F)	30.0°C (86°F)	32.5°C	31.5°C	30.5°C	0–25% work

Table 16.3. Clothing Worn and WBGT Correction Values

Clothing Type	CLO Value	WBGT Correction Value (°C)
Cotton trousers and shirt (Hanson and Graveling, 1999)	Not specified	+3.6
Lightweight clothing, appropriate for summer (OSHA, 2015)	0.6	0
Light work clothing (Mital et al., 2000)	Not specified	0
Cotton overalls (OSHA, 2015)	1.0	−2
Cotton overall, jacket (Mital et al., 2000)	Not specified	−2
Work clothing, appropriate for winter (OSHA, 2015)	1.4	−4
Winter work clothing, double cloth coveralls, water barrier (Mital et al., 2000)	Not specified	−4
Permeable, water barrier (OSHA, 2015)	1.2	−6
Light weight vapor barrier suits (Mital et al., 2000)	Not specified	−6
Vapor-barrier suit, hood, gloves, boots (Hanson and Graveling, 1999)	Not specified	−7
Fully enclosed suit with hood and gloves (Mital et al., 2000)	Not specified	−10

PMV and PPD

The Predicted Mean Vote (PMV) is the most established thermal comfort scale, shown in Fig. 16.1 (adapted from ANSI/ASHRAE Standard 55, 2004). The scale can be used to survey a group within a working population and be used in conjunction with the six environmental and personal factors as previously discussed by applying equations. The result provides a measure of PMV for that population within that environment. In an internal environment, an acceptable range should be from −0.5   PMV to +0.5   PMV with a zero PMV being the ideal result.

Figure 16.1. PMV scale.

The "Predicted Percentage of Dissatisfied" people (PPD) is related to the PMV (ANSI/ASHRAE Standard 55, 2004). As the PMV score moves away from zero, either towards −3 or +3, the PPD increases as more people are dissatisfied in an environment where they feel colder or hotter than they would prefer.

Comfort Surveys

Comfort surveys are used to subjectively measure the work environment. The results summarize the subjective perception of thermal comfort in a specific work environment, and are used to derive control measures or interventions. It is recognized that it is difficult to satisfy all users sharing a work environment.

Control Measures

A sample of acceptable work area temperature limits is presented in Table 16.4, taken from NORSOK (2004). These limits can be used to assess and monitor the environment. If temperatures fall out with these limits, control measures should be implemented by an organization.

Table 16.4. Recommendations for Work Area and Temperatures

Work Area	Temperature Min/Max (°C)
Utility and general process areas	Outdoor temperature or 5–35
Meeting rooms and offices	20–24
Stores (storage of large parts)	16–26
Machinery room (unmanned)	5–35

Control measures to improve thermal comfort include administrative controls, engineering controls, acclimatization, and PPE/clothing:

●

administrative controls include: rest periods and breaks, limits of exposure to an uncomfortable environment;

●

engineering controls include: heaters and air conditioning;

●

acclimatization controls relate to planning and monitoring acclimatization programs;

●

PPE controls include: selecting clothing that is suitable for the thermal environment and using specialist PPE for extreme environments, such as gloves, hats, shoes, and jackets.

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Physiological Processes during Winter Dormancy and Their Ecological Significance

Wilhelm M. Havranek , Walter Tranquillini , in Ecophysiology of Coniferous Forests, 1995

B Decrease of Stomatal Conductance and Gas Exchange in the Fall

Decreasing air temperatures and light intensities in autumn also result in decreased gas exchange rates. During mild and clear days, however, photosynthetic rates similar to summer rates are still possible as long as needles do not freeze. At that time, trees are already dormant and most of the cellular changes that increase frost resistance to about − 30°C have been completed. According to the decreased osmotic potential, freezing of needles occurs at temperatures below − 3 to − 5°C. On clear autumn nights, such needle temperatures may often be approached even if air temperatures near 0°C are recorded ( Jordan and Smith, 1994a). Night frost occurs early in autumn at high altitudes and causes a stepwise decrease of photosynthesis and stomatal conductance, depending on its frequency and intensity (Cartellieri, 1935; Tranquillini, 1957; Smith et al., 1984; Smith, 1985). The impact of minimum air temperatures on seasonal gas exchange was demonstrated for six conifer species of the Central Rocky Mountains. Smith et al. (1984) found a significant linear relationship between the daily maximum leaf conductance and the mean of the minimum air temperatures of three preceding nights, conductance becoming zero at − 9°C. Körner and Perterer (1988) found a similar relationship for the gas exchange of P. abies and P. sylvestris near Innsbruck, Austria, if the minimum air temperatures were higher than − 4°C, which is the freezing point of the needles. These researchers also found a close relationship between stomatal conductance and photosynthesis from November to March. Apparently, needle freezing is not required to initiate the strong decline in leaf conductance and transpiration that is typical of cold-hardened conifers. Continuously low but above-freezing temperatures (without intermittent warm periods) have also been observed to decrease stomatal conductance and photosynthesis substantially (Christersson, 1972; Andersson, 1980; Öquist et al., 1980; Teskey et al., 1984b, Bahn, 1988; Strand and Öquist, 1988).

The specific physiological mechanisms that may be responsible for the observed decrease in stomatal conductance in response to near-freezing temperatures are unknown at this time. During the transition to winter dormancy, water potentials at predawn are often remarkably negative but increase during the day, the converse of their daily course in summer (Benecke and Havranek, 1980; Smith et al., 1984). Soil temperatures during this period, although decreasing, are still high enough that serious interference with water uptake can be excluded as a limiting factor (Havranek, 1972; Day et al., 1990). A more probable explanation may be that xylem freezing of thin twigs, needles, or branches generates a low water potential. Rapid declines in the xylem flow (Teskey et al., 1983), as a result of freezing, could also influence the release of abscisic acid (ABA), a known influencer of stomatal behavior. ABA may be a dominant factor in the conversion of environmental signals into the changes in gene expression involved in frost hardening (Qamaruddin et al., 1993, and references therein), and in the acceleration of the transition into true winter dormancy. ABA was shown to increase stomatal sensitivity, both by promoting transpiration in unstressed seedlings and by some contribution to the decrease in transpiration and photosynthesis in water-stressed seedlings (Blake et al., 1990). Thus, the role of ABA in the common down-regulation of stomatal conductance and photosynthesis observed during winter hardening must be investigated further.

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