RayMan (radiation on the human body)

RayMan stands for "radiation on the human body". It can estimate and calculate the mean radiant temperature within urban structures.

Radiationmicroclimateurban

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Contributor(s)

Initial contribute: 2019-11-03

Authorship

:  
Research Center Human Biometeorology, German Meteorological Service (DWD)
:  
andreas.matzarakis@meteo.uni-freiburg.de
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Method-focused categoriesData-perspectiveGeoinformation analysis

Detailed Description

English {{currentDetailLanguage}} English

Quoted from: https://www.urbanclimate.net/rayman/index.htm 

INTRODUCTION

The mean radiant temperature Tmrt is the most important meteorological input parameter for the human energy balance during sunny weather in summer. Therefore, Tmrt has the strongest influence on thermophysiologically significant indexes like PET (Physiological Equivalent Temperature) or PMV (Predicted Mean Vote) which are derived from models for the human energy balance (1, 2).

Tmrt is defined as „the uniform temperature of a surrounding surface giving of blackbody radiation (emission coefficient e = 1) which results in the same radiation energy gain of a human body as the prevailing radiation fluxes which are usually very varied under open space conditions". Tmrt can be either obtained by direct measurement of all relevant radiation fluxes or by calculations of the short-wave and long-wave radiation fluxes (1, 2).

The objective of this presentation is to present a simple method on how to calculate Tmrt.

Calculation of Tmrt

To calculate Tmrt, the relevant properties and dimensions of the radiating surfaces and the sky view factor as well as the posture of the human body (e.g. seated or standing) must be known. The entire surroundings of the human body are divided into n thermal surfaces with the temperatures Ti (i = 1, n) and emission coefficients ei, to which the solid angle proportions („angle factors") Fi are to be allocated as weighting factors. Long-wave radiation (Ei = ei * s * TSi4, with s the Stefan-Boltzmann constant (5.67 * 10 –8 W/m2K4) and TSi the temperature of the ith surface), diffuse short-wave radiation Di are emitted from each of the n surfaces of the surroundings. This results in a value for Tmrt as (see details in (3)):

 (1)

ep is the emission coefficient of the human body (standard value 0.97). Di is the total of diffuse solar radiation and diffusely reflected global radiation. ak is the absorption coefficient of the irradiated body surface for short-wave radiation (standard value 0.7).

Tmrt is replaced by T*mrt, if there is also direct solar radiation (3):

 (2)

I* is the radiation intensity of the sun on a surface perpendicular to the incident radiation direction and the surface projection factor fp is a function of the incident radiation direction and the body posture. For practical application in human-biometeorology, is it generally sufficient to determine fp for a rotationally symmetric person standing up or walking. fp ranges from 0.308 for 0° of the angle of the solar altitude and 0.082 for 90° (4).

The problems associated with determining the angle factors Fi are discussed in detail in (3, 4, 5, 6, 7) In the case of large flat surfaces without any restrictions of the horizon, the problem of determining Fi is reduced to an upper and a lower hemisphere with angle factors of 0.5 for both situations.

 

Determination of Tmrt by use of an integral measuring procedure

Several procedures which can be used to determine Tmrt by means of integral radiation measurements are known from the technical literature, e.g. (5). A simple procedure which can be applied by use of a pyranometer and a pyrgeometer, which are standard meteorological measuring instruments, is presented below (6). The pyranometer is used to measure the short-wave radiation fluxes from the whole surroundings, while all long-wave radiation fluxes can be recorded with the pyrgeometer. A radiation measuring system was constructed with the pyranometer at one side and the pyrgeometer at the opposite side. This system can rotate around a vertical and a horizontal axis. Therefore, the short- and long-wave radiation fluxes from all directions can be measured which give information of the three-dimensional short- and long-wave radiation field affecting human beings. In practice, short- and long-wave radiation fluxes from the four cardinal points as well as from the upper and lower hemisphere are measured. The measurement height is 1.1 m above the ground, which corresponds approximately to the level of the centre of gravity of a standing person in Central Europe (1, 2).

In order to calculate the radiant fluxes on the surface of a standing or seated person from the six individual measurements of the short- and long-wave radiation fluxes, they have to be multiplied by weighting factors Wi (i=1, 6) which can be derived from the projection factors fp (3). The weighting factors Wi for a (rotationally symmetric) standing or walking person are (8):

radiation fluxes from the east, south, west and north direction: 0.22 in each case

radiation fluxes from above and below: 0.06 in each case

The mean radiation flux density Sstr of the human body can be calculated as follows (6):

 (3)

 

with Ki being he short-wave and Li being the long-wave radiation fluxes. ak and al are the absorption coefficients for short-wave and long-wave radiation. Following from its definition, Tmrt (in °C) can be calculated from the Stefan-Boltzmann radiation law:

 (4)

For a standing man the radiation fluxes from the cardinal points are more important than the upward and downward radiation fluxes. An answer to the question how Tmrt is influenced by the selected positions for the radiation fluxes is given in Figure 1 which illustrates the Tmrt-differences induced by a addition 45 ° rotation of the measurement systems round the vertical axis. The results show no differences in the absence of short-wave radiation and no significant difference during the day when short-wave radiation is present (9 and 10).

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: Differences of mean radiant temperature DTmrt in the human-biometeorologically significant height of 1.1 m above ground for the measurement of the radiation fluxes from the four cardinal points and from the points rotated by 45 ° from those (three urban structures in Freiburg, Southwest Germany, on a summer day (9)

 

Modelling the radiation fluxes BY THE MODEL RAYMAN

In the procedure explained in detail in (4 and 6), the radiation fluxes are calculated by model approaches which include air temperature and air humidity, degree of cloud cover, air transparency and time of the day of the year. The albedo of the surrounding surfaces and their solid angle proportions must also be specified. The radiation fluxes from meteorological and astronomical data are often calculated by use of well-known formulas. The major problem associated with this method for application in urban and regional planning lies in quantifying the shading of direct and diffuse radiation by building structures. Fisheye-photos are one experimental possibility for determining the sky view factor.

The model RayMan which is presented here is well-suited for the calculation of the radiation fluxes especially within urban structures, because it takes into consideration various complex horizons. Working with RayMan at a PC, an input window for urban structures (buildings, deciduous and coniferous trees) (Fig. 2, left) and the possibility of free drawing and output of the horizon (natural or non-natural) are included (Fig. 2, right) for the estimation of the sky view factors. Fig. 2 (right) shows the sky view factors for an urban area in Freiburg and the sun paths for the 19. July 1999, a day where measurements have been done for comparison reason with the calculated results with RayMan. The amount of clouds covering the sky can also be included by free drawing while their impact on the radiation fluxes can also be estimated. In the field of urban climatology and human-biometeorology the most important question is, if the object of interest is in shadow or not. Hence in the presented model the shadow by urban and natural obstacles is included.

 

 

 

 

 

 

 

 

 

 

 

Figure 2: Window for the input of urban structures (buildings, deciduous trees and conifers) (left side) and output of the resulting horizon in urban structures and the sun paths for 2. July 1999 in Freiburg (right side) for the calculation of the sky view factors in Rayman

 

Figure 3 shows a comparison of measured and estimated data from Rayman for the 2. July 1999 in Freiburg, a sunny day with no clouds, where the differences between the calculated and the measured results for the global radiation on the top of a 51 m building are not big.

The final result of the model is the calculation of the mean radiation temperature in urban areas (Fig. 4) which is required for the energy balance model for humans for the assessment of urban bioclimate. The model is developed according to the German VDI-Guideline 3786, Part 2 "Methods for the human-biometeorological evaluation of climate and air quality for urban and regional planning at regional level, Part I: Climate" (3).

Fig. 4 shows a comparison measured parameters for the 19. July 1999 with computed parameters for the same day by RayMan. The values between the measured and calculated surface temperatures and mean radiant temperatures vary but this is an effect of the complex radiation fluxes like the multiple short wave radiation reflexion that were not included at that time in Rayman. Also the additional long wave radiation from vertical orientated surfaces and the complex situation of shadow in urban areas that is not correctly represented in RayMan yet produces differences in the results between measurements and calculations.

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3: Output of measured global radiation and computed global radiation computed by Rayman for the 2. July 1999 in Freiburg


























Figure 4: Output of measured mean radiant temperature Tmrt, computed mean radiation temperature for different cloud conditions (0 and 1 octas) clouds Tmrt (0/8, 1/8), calculated surface temperature Ts model and air temperature Ta computed by Rayman for the 19. July 1999.

 

CONCLUSIONS

For the evaluation of the thermal component of urban and regional climate precise and high resolution radiation data from the whole surrounding is necessary. This data can be either measured or calculated by use of a suited radiation model. RayMan is one of these models. Another advantage of RayMAN is that it is available for general use.

 

REFERENCES

Mayer, H., 1993. Urban bioclimatology. Experientia 49, 957-963.

Höppe, P., 1993. Heat balance modelling. Experientia 49, 741-746.

VDI, 1998. VDI 3787, Part I: Environmental meteorology, Methods for the human biometeorological evaluation of climate and air quality for the urban and regional planning at regional level. Part I: Climate. VDI/DIN-Handbuch Reinhaltung der Luft, Band 1b, Düsseldorf.

Jendritzky, G., Menz, H., Schmidt-Kessen, W., Schirmer, H., 1990. Methodik zur räumlichen Bewertung der thermischen Komponente im Bioklima des Menschen. ARL Beiträge Nr. 114.

Fanger, P. O., 1972. Thermal Comfort, Analysis and application in Environment Engineering. New York. McGraw Hill.

VDI, 1994. VDI 3789, Part 2: Environmental Meteorology, Interactions between Atmosphere and Surfaces; Calculation of the short- and long wave radiation.. VDI/DIN-Handbuch Reinhaltung der Luft, Band 1b, Düsseldorf.

Krys, S. A., Brown, R. D., 1990. Radiation absorbed by a vertical Cylinder in Complex Outdoor Environments Under Clear Sky Conditions. Int. J. Biometeorology 34, 69-75.

Höppe, P., 1992. Ein neues Verfahren zur Bestimmung der mittleren Strahlungstemperatur im Freien. Wetter und Leben 44, 147-151.

Matzarakis, A., Mayer, H., 1998. Investigations of urban climate’s thermal component in Freiburg, Germany. Preprints Second Urban Environment Symposium - 13th Conference on Biometeorology and Aerobiology. November 2.-6. 1998, Albuquerque, USA, American Meteorological Society. 140-143.

 

Mayer, H., Matzarakis, A., 1998. Human-biometeorological assessment of urban microclimates` thermal component. Proc. Of the second Japanese-German meeting "Klimaanalyse in der Stadtplanung" - Toward Reconstruction in Kobe -. Report of research center for urban safety and security, Kobe University. Special Report Nr. 1, 109-122.

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Andreas Matzarakis (2019). RayMan (radiation on the human body), Model Item, OpenGMS, https://geomodeling.njnu.edu.cn/modelItem/033be299-02f9-45ec-b65b-29a5095b403e
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Contributor(s)

Initial contribute : 2019-11-03

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Authorship

:  
Research Center Human Biometeorology, German Meteorological Service (DWD)
:  
andreas.matzarakis@meteo.uni-freiburg.de
Is authorship not correct? Feed back

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