Comparison of different methods of estimating the mean radiant temperature in outdoor thermal comfort studies

Correlations between outdoor thermal indices and the calculated or measured mean radiant temperature T_mrt are in general of high importance because of the combined effect on human energy balance in outdoor spaces. The most accurate way to determine T_mrt is by means of integral radiation measurements, i.e. measuring the short- and long-wave radiation from six directions using pyranometers and pyrgeometers, an expensive and not always an easily available procedure. Some studies use globe thermometers combined with air temperature and wind speed sensors. An alternative way to determine T_mrt is based on output from the RayMan model from measured data of incoming global radiation and morphological features of the monitoring site in particular sky view factor (SVF) data. The purpose of this paper is to compare different methods to assess the mean radiant temperature T_mrt in terms of differences to a reference condition (T_mrt calculated from field measurements) and to resulting outdoor comfort levels expressed as PET and UTCI values. The T_mrt obtained from field measurements is a combination of air temperature, wind speed and globe temperature data according to the forced ventilation formula of ISO 7726 for data collected in Glasgow, UK. Four different methods were used in the RayMan model for T_mrt calculations: input data consisting exclusively of data measured at urban sites; urban data excluding solar radiation, estimated SVF data and solar radiation data measured at a rural site; urban data excluding solar radiation with SVF data for each site; urban data excluding solar radiation and including solar radiation at the rural site taking no account of SVF information. Results show that all methods overestimate T_mrt when compared to ISO calculations. Correlations were found to be significant for the first method and lower for the other three. Results in terms of comfort (PET, UTCI) suggest that reasonable estimates could be made based on global radiation data measured at the urban site or as a surrogate of missing SR data or globe temperature data recorded at the urban area on global radiation data measured at a rural location.     

Modelling radiation fluxes in simple and complex environments—application of the RayMan model

The most important meteorological parameter affecting the human energy balance during sunny weather conditions is the mean radiant temperature T_mrt. It considers the uniform temperature of a surrounding surface giving off blackbody radiation, which results in the same energy gain of a human body given the prevailing radiation fluxes. This energy gain usually varies considerably in open space conditions. In this paper, the model ‘RayMan’, used for the calculation of short- and long-wave radiation fluxes on the human body, is presented. The model, which takes complex urban structures into account, is suitable for several applications in urban areas such as urban planning and street design. The final output of the model is, however, the calculated T_mrt, which is required in the human energy balance model, and thus also for the assessment of the urban bioclimate, with the use of thermal indices such as predicted mean vote (PMV), physiologically equivalent temperature (PET) and standard effective temperature (SET*). The model has been developed based on the German VDI-Guidelines 3789, Part II (environmental meteorology, interactions between atmosphere and surfaces; calculation of short- and long-wave radiation) and VDI-3787 (environmental meteorology, methods for the human-biometeorological evaluation of climate and air quality for urban and regional planning. Part I: climate). The validation of the results of the RayMan model agrees with similar results obtained from experimental studies.     

Mean radiant temperature in idealised urban canyons—examples from Freiburg, Germany

Studies on the thermal comfort of humans in urban areas require meteorological data such as air temperature, air humidity, wind speed, and short- and long-wave fluxes. In such studies radiation fluxes can be expressed by the mean radiant temperature—a parameter with high variability in urban areas due to variability in global radiation. Wind speed in urban areas is influenced by urban obstacles and their orientation. Both mean radiant temperature and wind speed can be modified or changed by different height-to-width ratios or orientation of urban structures. Modifications to these parameters by typical urban structures (represented by the height-to-width ratio) can result in variation of mean radiant temperature over a range of more than 30°C, which can correspond to three levels of thermal stress. The results presented here provide a possible means of comparing different urban configurations in different climate regions.     

Solar heat load on man

Different methods have been compared for the estimation of solar heat load on man. The comparison comprised several methods based on the calculation of absorbed solar radiation and one method for calculation of mean radiant temperature (Mrt). Regression analysis was carried out for predicted values and values calculated for a vertical cylinder, assumed as an analog model of a standing man. Regression of mean skin temperature, measured in 10 subjects exposed to solar radiation under a variety of climatic conditions, on predicted radiant heat load was also analysed. Mean skin temperature correlated best withMrt, accounting for more than 50% of the variance. The results indicated that three methods provide a realistic estimation of the radiation heat load, whereas some methods show deviations of several hundred per cent.     

Daytime relapse of the mean radiant temperature based on the six-directional method under unobstructed solar radiation

This study contributes to the knowledge about the capabilities of the popular “six-directional method” describing the radiation fields outdoors. In Taiwan, measurements were carried out with three orthogonally placed net radiometers to determine the mean radiant temperature (T _mrt). The short- and long-wave radiation flux densities from the six perpendicular directions were recorded in the daylight hours of 12 days. During unobstructed direct irradiation, a specific daytime relapse was found in the temporal course of the T _mrt values referring to the reference shapes of a standing man and also of a sphere. This relapse can be related to the short-wave fluxes reaching the body from the lateral directions. Through deeper analysis, an instrumental shortcoming of the six-directional technique was discovered. The pyranometer pairs of the same net radiometer have a 10–15-min long “blind spot” when the sun beams are nearly perpendicular to them. The blind-spot period is supposed to be shorter with steeper solar azimuth curve on the daylight period. This means that the locations with lower geographical latitude, and the summertime measurements, are affected less by this instrumental problem. A methodological shortcoming of the six-directional technique was also demonstrated. Namely, the sum of the short-wave flux densities from the lateral directions is sensitive to the orientation of the radiometers, and therefore by deviating from the original directions, the T _mrt decrease on clear sunny days will occur in different times and will be different in extent.     

Case study of skin temperature and thermal perception in a hot outdoor environment

Focusing on the understanding and the estimation of the biometeorological conditions during summer in outdoor places, a field study was conducted in July 2010 in Athens, Greece over 6 days at three different sites: Syntagma Square, Ermou Street and Flisvos coast. Thermo-physiological measurements of five subjects were carried out from morning to evening for each site, simultaneously with meteorological measurements and subjective assessments of thermal sensation reported by questionnaires. The thermo-physiological variables measured were skin temperature, heat flux and metabolic heat production, while meteorological measurements included air temperature, relative humidity, wind speed, globe temperature, ground surface temperature and global radiation. The possible relation of skin temperature with the meteorological parameters was examined. Theoretical values of mean skin temperature and mean radiant temperature were estimated applying the MENEX model and were compared with the measured values. Two biometeorological indices, thermal sensation (TS) and heat load (HL)—were calculated in order to compare the predicted thermal sensation with the actual thermal vote. The theoretically estimated values of skin temperature were underestimated in relation to the measured values, while the theoretical model of mean radiant temperature was more sensitive to variations of solar radiation compared to the experimental values. TS index underestimated the thermal sensation of the five subjects when their thermal vote was ‘hot’ or ‘very hot’ and overestimated thermal sensation in the case of ‘neutral’. The HL index predicted with greater accuracy thermal sensation tending to overestimate the thermal sensation of the subjects.     

夏季绿洲生态环境对荒漠背景地表能量过程的扰动

利用观测试验资料,对比分析了夏季典型晴天敦煌绿洲与周围荒漠戈壁背景地表过程的差异,揭示了绿洲生态系统对干旱区荒漠背景地表过程的扰动特征。结果表明:绿洲地表净辐射日平均要高出周围荒漠戈壁背景60 W/m2以上,约占绿洲净辐射的1/4以上。对绿洲高出的净辐射贡献最大的是绿洲相对低的地表长波辐射,其次是较高的太阳总辐射。而绿洲相对较低的大气长波辐射对高出的净辐射有较大的负贡献,特别是地表反射辐射也有很小的负贡献。绿洲高出的地表净辐射主要贡献于加强潜热和地热流量,还有一部分被绿洲地表能量不平衡差额所占,它实际上可能由一般地表热量平衡所不考虑的垂直热量平流来输送。而绿洲明显低于荒漠背景的感热通量则节省了一部分净辐射能量。     

Thermal equilibrium of goats

The effects of air temperature and relative humidity on thermal equilibrium of goats in a tropical region was evaluated. Nine non-pregnant Anglo Nubian nanny goats were used in the study. An indirect calorimeter was designed and developed to measure oxygen consumption, carbon dioxide production, methane production and water vapour pressure of the air exhaled from goats. Physiological parameters: rectal temperature, skin temperature, hair-coat temperature, expired air temperature and respiratory rate and volume as well as environmental parameters: air temperature, relative humidity and mean radiant temperature were measured. The results show that respiratory and volume rates and latent heat loss did not change significantly for air temperature between 22 and 26 °C. In this temperature range, metabolic heat was lost mainly by convection and long-wave radiation. For temperature greater than 30 °C, the goats maintained thermal equilibrium mainly by evaporative heat loss. At the higher air temperature, the respiratory and ventilation rates as well as body temperatures were significantly elevated. It can be concluded that for Anglo Nubian goats, the upper limit of air temperature for comfort is around 26 °C when the goats are protected from direct solar radiation.     

Radiation absorbed by a vertical cylinder in complex outdoor environments under clear sky conditions

Research was conducted into the estimation of radiation absorbed by a vertical cylinder in complex outdoor environments under clear sky conditions. Two methods of estimation were employed: a cylindrical radiation thermometer (CRT) and model developed by Brown and Gillespie (1986), and the weather station model. The CRT produced an integrated temperature reading from which the radiant environment could be estimated successfully given simultaneous measurements of air temperature and wind speed. The CRT estimates compared to the measured radiation gave a correlation coefficient of 0.9499, SE=19.8 W/m², =99.9%. The physically-based equations (weather station model)require the inputs of data from a near by weather station and site characteristics to estimate radiation absorbed by a vertical cylinder. The correlation coefficient for the weather station model is 0.9529, SE=16.8 W/m², =99.9%. This model estimates short wave and long wave radiation separately; hence, this allowed further comparison to measured values. The short wave radiation was very successfully estimated:R=0.9865, SE=10.0 W/m², =99.9%. The long wave radiation estimates were also successful:R=0.8654, SE=15.7 W/m², and =99.9%. Though the correlation coefficient and standard error may suggest inaccuracy to the micrometeorologist, these estimation techniques would be extremely useful as predictors of human thermal comfort which is not a precise measure buut defined by a range. The reported methods require little specialized knowledge of micrometeorology and are vehicles for the designers of outdoor spaces to measure accurately the inherent radiant environment of outdoor spaces and provide a measurement technique to simulate or model the effect of various landscape elements on planned environments.     

The effect of Sub-MAC anesthesia and the radiation setting on repeated tail flick testing in rats.

The tail flick (TF) response is regarded as a spinal reflex that is influenced by supraspinal structures. The TF test using radiant heat is the most common way to assess pain perception; however, there are few reports dealing with the heat source's properties and score consistency. This study examined the usefulness of light anesthesia for suppressing supraspinal signals and the effects of radiant heat on skin temperature during TF testing. The fluctuations of TF latency over one hour were evaluated while the rats were given oxygen and 0%, 0.5%, 1.0%, or 1.5% isoflurane. The stimulator's infrared radiant (IR) power flux was measured over time, and the tail skin surface temperature was predicted using a non-linear regression equation. TF latencies were measured at various heat source intensities, and response temperatures were estimated. Inhalation anesthesia suppressed the TF reflex according to the inspiratory concentration of the volatile anesthetic. IR power fluxes reached constant power 2.5 s after the stimulator was turned on, and the predicted skin temperature depended on the maximum IR power flux of the IR intensity and the radiation time. One percent isoflurane inhalation and an IR20 heat intensity (which was 161.5 mW/cm(2) and resulted in a skin temperature of 65 degrees C after 10 s of radiation) provided reliable TF latencies on repeated TF testing. Given these results, it can be concluded that the stimulator setting influenced TF latency, and that the inhalation of light anesthesia provided consistent scores on repeated TF testing.     

A model of heat flow in the sheep exposed to high levels of solar radiation.

The fleece is an important component in thermoregulation of sheep exposed to high levels of solar radiation. A model written in CSMP has been developed which represents the flow of energy between the sheep and its environment. This model is based on a set of differential equations which describe the flux of heat between the components of the system--fleece, tip, skin, body and environment. It requires as input parameters location, date, time of day, temperature, relative humidity, cloud cover, wind movement, animal weight and linear measurements and fleece length. At each integration interval incoming solar radiation and its components, the heat arising from the animal's metabolism and the heat exchange by long-wave radiation, convection, conduction and evaporative cooling are computed. Temperatures at the fleece tip, skin and body core are monitored.     

Analysis of Environmental Effects on Leaf Temperature under Sunlight,High Pressure Sodium and Light Emitting Diodes

The use of LED technology is commonly assumed to result in significantly cooler leaf temperatures than high pressure sodium technology. To evaluate the magnitude of this effect, we measured radiation incident to and absorbed by a leaf under four radiation sources: clear sky sunlight in the field, sunlight in a glass greenhouse, and indoor plants under either high pressure sodium or light emitting diodes. We then applied a common mechanistic energy-balance model to compare leaf to air temperature difference among the radiation sources and environments. At equal photosynthetic photon flux, our results indicate that the effect of plant water status and leaf evaporative cooling is much larger than the effect of radiation source. If plants are not water stressed, leaves in all four radiation sources were typically within 2°C of air temperature. Under clear sky conditions, cool sky temperatures mean that leaves in the field are always cooler than greenhouse or indoor plants-when photosynthetic photon flux, stomatal conductance, wind speed, vapor pressure deficit, and leaf size are equivalent. As water stress increases and cooling via transpiration decreases, leaf temperatures can increase well above air temperature. In a near-worst case scenario of water stress and low wind, our model indicates that leaves would increase 6°, 8°, 10°, and 12°C above air temperature under field, LED, greenhouse, and HPS scenarios, respectively. Because LED fixtures emit much of their heat through convection rather than radiative cooling, they result in slightly cooler leaf temperatures than leaves in greenhouses and under HPS fixtures, but the effect of LED technology on leaf temperature is smaller than is often assumed. Quantifying the thermodynamic outputs of these lamps, and their physiological consequences, will allow both researchers and the horticulture industry to make informed decisions when employing these technologies.     

北方典型农牧交错带草地开垦对地表辐射收支与水热平衡的影响

以北方典型农牧交错带草原和农田生态系统的涡度相关数据为基础,对比分析了生长季两种不同土地利用类型的辐射和水热通量之异同,揭示了草地开垦影响地表辐射收支与水热平衡的机制。结果表明:在植被生长季(5月—9月),草地开垦引起太阳总辐射增加了10.74%,短波反射辐射减少了14.20%,净辐射增加了35.16%;在水热通量方面,草地开垦引起潜热通量日积分平均值增加了0.20MJ/m~2,同时显热通量减少了0.09 MJ/m~2;生长季内地表反照率减小,表征地表吸收太阳辐射增加,有升高气温的趋势;非生长季内地表反照率增加,有降低气温趋势,此外地表反照率与土壤湿度存在负指数关系;波文比在植被生长早期和末期增加,生长旺期减小,说明草地开垦与影响着近地表大气状态,从而改变了区域气候。     

Air and soil temperature differences in controlled environments,as a consequence of high radiant flux densities and of day/night temperature changes

Summary Soil/air temperature differences were measured in 15 cm diameter plastic pots and in 30-cm diameter fibre pots under high radiant flux densities in a controlled environment cabinet. When there was no surface insulation or shading on the sides of the plastic pots, soil temperatures at –1 cm equilibrated at 7.5°C above air temperature. Reflective surface covering and shading on the sides of the pot reduced this difference to 2.4°C. In the fibre pots with reflective surface covering and side shading, soil equilibrium temperature was 1°C below air temperature, but equilibration time was 8 to 9 hours following day/night temperature changes.     

美国黑核桃实生苗生态生理过程对环境因素响应的数值模拟(Ⅱ):气象要素日变化进程的数理模型

在建立植物生态生理模型（如光合作用、蒸腾作用数理模型）的过程中,气温、太阳辐射、相对湿度等气象要素的日变化及瞬时资料是必不可少的．本文根据常规台站的日常观测资料,建立了气温、太阳辐射、风速、相对湿度等气象要素日变化的数理模型．并应用实测资料对所建模型进行了验证．实践表明：（1）描述气温日变化的正弦一指数模型通常其模拟结果不甚理想,但通过引用最高温度的时间延迟参数及惯性系数,可增加模拟结果的准确性．（2）根据测量的太阳辐射日总量值以及太阳高度的日变化值等,可准确地模拟太阳辐射的日变化;（3）根据实际水汽压的日均值和气温常规资料可准确模拟相对湿度的日变化．如果区域参数已知或被正确估计。上述方法可得到较为理想的气象要素日变化的模拟结果．     

The rapid determination in controlled environments of parameters for predicting seedling growth rates in natural conditions

Parameters which characterise the response of seedling growth rate to temperature and mean daily radiant exposure were determined for cultivars of eight vegetable species and two ornamental bedding plant species using controlled environments. All species were grown for approximately four weeks in a series of four controlled environments consisting of factorial combinations of 20°C or 15°C with 7.78 or 0.98 MJ m^-2 radiant exposure per day to photosynthetically active radiation. Four of the vegetable cultivars had been used previously in a study of growth in the glasshouse at different seasons. The parameters derived from controlled environments were used, with temperature and light measurements from the glasshouse, to predict seedling shoot growth in the glasshouse. These predictions accounted for 92% of the observed variance in log shoot dry weight in a series of glasshouse experiments involving thirteen combinations of species and sowing date, each grown at four plant densities and sampled on four occasions. Equivalent parameters derived previously from the glasshouse data themselves accounted for 92% of the variance in the same predictive exercise. Differences in base temperature for growth, the responsiveness of relative growth rate to daily radiant exposure (light), and the potential relative growth rate were apparent between species and were quantitatively characterised by the parameters. To determine these parameters for a cultivar requires the equivalent of one square metre of controlled environment growing area for approximately sixteen days. Such parameters could be applied for scheduling and management in crop production, particularly in transplant production.     

An apparatus for measuring photosynthetic quantum yields and quanta absorption spectra of intact plants

Abstract An apparatus is described which consists of an assimilation chamber mounted in the centre of a light-integrating Ulbricht sphere, irradiated through two fibreoptic light pipes. This arrangement provides totally diffuse radiation in the sphere. The quantum flux density in die sphere is measured by an integrating quantaspectrometer connected to the sphere by eight fibreoptic light pipes. The quantaspectrometer gives the spectral and the total quantum flux density in the sphere. By measuring the quantum flux density in the sphere before and after the insertion of a plant the number of absorbed quanta per unit time and plant area can be determined. In addition, the spectral distribution of the absorbed quantum flux density is obtained. CO₂-assimilation per unit time and plant area is determined in the same apparatus. The totally diffuse radiation within the sphere minimizes mutual shading between branches and leaves. Hence, well-defined light-responsecurves of photosynthesis can be obtained by plotting the flux density of C0₂-assimilation as a function of the absorbed quantum flux density, and the quantum yields of intact plants can be calculated. Examples of photosynthetic quantum yield determinations and quanta absorption spectra are given for some plant species.     

Photosynthetic efficiency of Betula pendula acclimated to different quantum flux densities

Abstract. Seedlings of Betula pendula were grown in a controlled environment chamber at quantum flux densities of 50, 250 and 600 μmol m⁻² s⁻¹. The relationship between the flux densities of absorbed CC₂ and quanta was determined for shoots of whole seedlings. Rates of both light-saturated and in situ (measured under the growing conditions) net photosynthesis were determined and the pholosynthetic quantum yields under light-limiting conditions were calculated. Anatomical leaf characteristics, chlorophyll contents and sizes and densities of the photosynthetic units (chlorophyll/P700) were determined. Chloroplasts were isolated and their rates of 2,6-dichlorophenol indophenol photoreduction were measured together with their pool sizes of the electron transport carriers plastoquinone and cylochrome ƒ.
Although acclimated to different quantum flux densities, the three birch populations showed the same quantum yield of net photosynthesis. This was approximately 0.028 in normal air (21.2 kPa oxygen) and about 0.040 when photorespiration was largely inhibited in 2.0 kPa oxygen. In addition, the in situ net photosynthesis rates were limited by the absorbed quantum flux density for low, intermediate and high light grown seedlings. It was concluded that birch acclimated to the three light regimes at different levels of organization (metabolic and anatomical). Thus, the quanta which were absorbed in situ could be transferred into chemical equivalents at an optimal and constant efficiency. The use of different reference bases for expressing rates of net photosynthesis are also discussed.     

三温模型——基于表面温度测算蒸散和评价环境质量的方法Ⅰ．土壤蒸发

 三温模型是近年提出的测算蒸散量和评价环境质量的一种方法,因为该模型的核心是表面温度、参考表面温度、气温,所以被称为“三温模型”。该文通过理论分析结合实验的方法, 讨论了用三温模型测算土壤蒸发量的方法及其验证。通过引入没有蒸发的参考土壤的概念, 三温模型中用下式计算土壤蒸发量：LE=Rn-G-(Rnd-Gd)(Ts-Ta)/Tsd-Ta 式中,E为土壤蒸发量,L为水汽的汽化潜热,Rn和Rnd为蒸发土壤面和参考土壤面的净辐射, G和Gd为蒸发土壤和参考土壤热通量,Ts、Tsd、Ta分别为蒸发土壤的表面温度、参考土壤表面温度、气温。试验结果表明,在参考土壤和蒸发土壤中,能量通量存在明显差异,参考土壤中的土壤热通量和净辐射通量均小于蒸发土壤,而显热通量则大于蒸发土壤;在一般情况下,参考土壤的表面温度最高,蒸发土壤表面温度次之,大气温度最低,在土壤湿润时,这些差异更为显著。 经过与大型称重式蒸渗仪的实测值比较,三温模型能较好地计算土壤蒸发量,在22 d的实验期间内,绝对平均误差仅为0.17 mm•d^-1,相关系数达r²=0.88。与热电偶测温结果相比较 ,采用红外温度计测温的结果更为精确,和实测值的绝对平均误差仅为每天0.15 mm•d ^-1,相关系数达r²=0.94,表明三温模型有较好的精度。另外,三温模型在计算土壤蒸发量时, 所需要的参数种类少（净辐射、土壤热通量、温度）,不含经验系数,不需要空气动力学阻抗和表面阻抗等参数,因此简便实用,具有较好的应用前景。     

敦煌绿洲夏季典型晴天地表辐射和能量平衡及小气候特征

 利用“我国西北干旱区陆-气相互作用试验”加强期(IOP)在甘肃省敦煌绿洲观测的资料,系统地分析了夏季典型晴天敦煌地表辐射收支和地表能量平衡特征及小气候特征,结果发现：敦煌绿洲总辐射特别大,其峰值高达1 038.1 w·m-2;地表净辐射也高于其它地区,白天能超过600 w·m-2;在地表能量分配中,感热、潜热和地热流量的日积分值的量级相当,白天地热流量比潜热要大,几乎与感热相当;地表反照率除中午比较接近荒漠戈壁的值外,其它时候均明显比荒漠戈壁的值小;Bowen比在白天1～2之间,比一般灌溉地区要大。地表能量不平衡差额较大,这可能与水平热通量的影响有很大关系。另外,还首次发现了比较可观的下沉气流,部分证实了绿洲与荒漠之间存在的热力环流。