Mean radiant temperature

The concept of mean radiant temperature (MRT) is used to quantify the exchange of radiant heat between a human and their surrounding environment, with a view to understanding the influence of surface temperatures on personal comfort. Mean radiant temperature has been both qualitatively defined and quantitatively evaluated for both indoor and outdoor environments.^[1]^[2]^[3]

MRT has been defined as the uniform temperature of an imaginary enclosure in which the radiant heat transfer from the human body is equal to the radiant heat transfer in the actual non-uniform enclosure.^[4]

MRT is a useful concept as the net exchange of radiant energy between two objects is approximately proportional to the product of their temperature difference multiplied by their emissivity (ability to emit and absorb heat). The MRT is simply the area weighted mean temperature of all the objects surrounding the body. This is meaningful as long as the temperature differences of the objects are small compared to their absolute temperatures, allowing linearization of the Stefan-Boltzmann Law in the relevant temperature range.^{[citation needed]}

MRT also has a strong influence on thermophysiological comfort indexes such as physiological equivalent temperature (PET) or predicted mean vote (PMV).^[5]

What we experience and feel relating to thermal comfort in a building is related to the influence of both the air temperature and the temperature of surfaces in that space, represented by the mean radiant temperature. The MRT is controlled by enclosure performances.^{[citation needed]}

The operative temperature, which is a more functional measure of thermal comfort in a building, is calculated from air temperature, mean radiant temperature and air speed.^[6] Maintaining a balance between the operative temperature and the mean radiant temperature can create a more comfortable space.^[7] This is done with effective design of the building, interior and with the use of high temperature radiant cooling and low temperature radiant heating.^[8]

In outdoor settings, mean radiant temperature is affected by air temperature but also by the radiation of absorbed heat from the materials used in sidewalks, streets, and buildings. It can be mitigated by tree cover and green space, which act as sources of shade and promote evaporative cooling. The experienced mean radiant temperature outdoors can vary widely depending on local conditions. For example, measurements taken across Chapel Hill, North Carolina to examine urban heat island exposure ranged from 93 to 108 °F (34 to 42 °C).^[9]

^ Guo, Hongshan; Aviv, Dorit; Loyola, Mauricio; Teitelbaum, Eric; Houchois, Nicholas; Meggers, Forrest (1 January 2020). "On the understanding of the mean radiant temperature within both the indoor and outdoor environment, a critical review". Renewable and Sustainable Energy Reviews. 117: 109207. doi:10.1016/j.rser.2019.06.014. ISSN 1364-0321. S2CID 208834605. Retrieved 6 December 2022.
^ Bean, Robert (2010). "Mean Radiant Temperature (MRT) - Part I". Healthy Heating. Retrieved 6 December 2022.
^ Di Napoli, Claudia; Hogan, Robin J.; Pappenberger, Florian (1 July 2020). "Mean radiant temperature from global-scale numerical weather prediction models". International Journal of Biometeorology. 64 (7): 1233–1245. doi:10.1007/s00484-020-01900-5. ISSN 1432-1254. PMC 7295834. PMID 32274575.
^ Cite error: The named reference ISO 7726 was invoked but never defined (see the help page).
^ Fanger, P.O. (1970). Thermal Comfort: Analysis and Applications in Environmental Engineering. New York: McGraw Hill.
^ Reynolds, Mike (8 February 2020). "Designing Homes for Human Comfort". ecoHOME.
^ Matzarakis, Andreas. Estimation and Calculation of the Mean Radiant Temperature within Urban Structures.
^ Mclntyre and Griffiths, D.A. and I.D. (1972). Subject Response to Radiant and Convective Environments.
^ Waldrop, M. Mitchell (19 October 2022). "What can cities do to survive extreme heat?". Knowable Magazine. doi:10.1146/knowable-101922-2. Retrieved 6 December 2022.

[Guo-1] Guo, Hongshan; Aviv, Dorit; Loyola, Mauricio; Teitelbaum, Eric; Houchois, Nicholas; Meggers, Forrest (1 January 2020). "On the understanding of the mean radiant temperature within both the indoor and outdoor environment, a critical review". Renewable and Sustainable Energy Reviews. 117: 109207. doi:10.1016/j.rser.2019.06.014. ISSN 1364-0321. S2CID 208834605. Retrieved 6 December 2022.

[Bean-2] Bean, Robert (2010). "Mean Radiant Temperature (MRT) - Part I". Healthy Heating. Retrieved 6 December 2022.

[Di_Napoli-3] Di Napoli, Claudia; Hogan, Robin J.; Pappenberger, Florian (1 July 2020). "Mean radiant temperature from global-scale numerical weather prediction models". International Journal of Biometeorology. 64 (7): 1233–1245. doi:10.1007/s00484-020-01900-5. ISSN 1432-1254. PMC 7295834. PMID 32274575.

[ISO_7726-4] Cite error: The named reference ISO 7726 was invoked but never defined (see the help page).

[5] Fanger, P.O. (1970). Thermal Comfort: Analysis and Applications in Environmental Engineering. New York: McGraw Hill.

[6] Reynolds, Mike (8 February 2020). "Designing Homes for Human Comfort". ecoHOME.

[7] Matzarakis, Andreas. Estimation and Calculation of the Mean Radiant Temperature within Urban Structures.

[8] Mclntyre and Griffiths, D.A. and I.D. (1972). Subject Response to Radiant and Convective Environments.

[Waldrop-9] Waldrop, M. Mitchell (19 October 2022). "What can cities do to survive extreme heat?". Knowable Magazine. doi:10.1146/knowable-101922-2. Retrieved 6 December 2022.

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