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Measurement of Heat Stress
Published in Ken Parsons, Human Heat Stress, 2019
Operative temperature is the weighted average of air temperature and mean radiant temperature. The weighting factors are the heat transfer coefficients for convection and radiation, respectively [TO = (hc · TA + hr · TR)/(hc + hr)]. Approximations to operative temperature can be made by measuring the globe temperature of a black sphere of appropriate size. This misses the point, however, and operative temperature should be considered as a calculated temperature that represents the combined effects of air temperature and radiant temperature or convection and radiation. That is, the temperature that represents the driving force for dry heat transfer. As this is a single number that represents the effects of two relevant variables, it is a thermal index.
Performance Analysis
Published in Brian Ford, Rosa Schiano-Phan, Juan A. Vallejo, The Architecture of Natural Cooling, 2019
Brian Ford, Rosa Schiano-Phan, Juan A. Vallejo
The range of acceptable temperatures defined by these standards derive from the prevailing mean outdoor temperature and responds to seasonal temperature variations. This comfort ‘band’ becomes in most cases the criteria for assessing the thermal performance of an indoor environment presenting an operative temperature relative to a particular space heat balance. Operative temperature is a simplified measure of human thermal perception derived from air temperature, mean radiant temperature and air speed. However, when mean radiant temperature may be similar, air temperature alone can be a reasonable indicator of thermal comfort.
The Role of Ventilation
Published in Cristian Ghiaus, Francis Allard, Natural Ventilation in the Urban Environment, 2012
For example, a sitting person wearing a lounge suit would prefer, on average, an operative temperature of 22°C ± 2°C. If this person is more active – for example, when giving a lecture – a temperature of 18°C ± 3°C is preferred. This is why a temperature of about 20°C is preferred in schools and offices. A sitting person wearing shorts and a light shirt will prefer 26°C ± 1.5°C, while an average person naked and at rest is comfortable, on average, at 28°C ±1°C.
Cooling load comparison of rooms conditioned with radiant cooling panels and all-air HVAC systems (ASHRAE RP 1729)
Published in Science and Technology for the Built Environment, 2023
Ardeshir Moftakhari, Stephen Bourne, Atila Novoselac
Both the air and room surface mean radiant temperatures are equally important for operative temperature control. However, the indoor room surface temperatures that define mean radiant temperature (MRT) are slightly lower and closer to the room air temperature, especially with radiant systems. This causes the MRT to vary significantly with respect to sensor locations in the radiantly conditioned space. If an operative temperature control strategy is used, this variation in the MRT temperature may cause the system response and thus cooling load to change. To minimize this effect, a set of 5 full-globe thermometers suspended from the ceiling (at the standing height of 1.75 m) at various random locations were used to find the average operative temperature of the test chamber. These globe thermometers consist of matte grey balls (with diameter of 0.04 m) enclosing temperature sensors (RTD – resistance temperature detector) with the accuracy of +/- 0.2 (C) of readings, and calibrated with respect to the actual operative temperature of the room ():
Life-cycle cost optimization of a solar combisystem for residential buildings in Nepal
Published in Journal of Asian Architecture and Building Engineering, 2022
Bishan Thapa, Weimin Wang, Wesley Williams
The house modeled in this study has its floor area and envelope constructions based on a real design by a professional architectural firm in Kathmandu. The house has two and half stories and a total floor area of 232 m2. Regarding constructions, the external wall is built from 230-mm-thickness brick, plus 12-mm-thickness plaster on both interior and exterior sides. The roof is constructed from 100-mm-thickness reinforced concrete slab with 12-mm cement plaster on the interior side. Following the current construction practice in Nepal, no thermal insulation is used in roof and exterior walls. The window type is single-pane glazing with wooden frame because double-pane glazing is not a common practice (Subedi 2010). Hydronic radiant floor heating is the system used for space heating. Featured with uniform warm surfaces, quiet operation, and no air drafts, radiant floor heating is more favorable for thermal comfort than forced air systems and baseboard heaters. Because of the use of radiant floor heating, the operative temperature, defined as the average of the space air temperature and the mean radiant temperature, is selected for the space thermostat control. The thermostat has its heating set point at 21°C from 7 am to 10 pm (i.e., daytime) and at 18°C from 10 pm to 7 am (i.e., nighttime), with a deadband of 4°C.
Coordination of radiant floor and baseboard heating systems: Sequential and simultaneous MPC schemes
Published in Science and Technology for the Built Environment, 2019
Sayani Seal, Vahid Raissi Dehkordi, Benoît Boulet
For each thermal zone, two temperature outputs are identified: air temperature () and operative temperature (). For radiant heating, the floor temperature differs significantly from the air node temperature in a given space. The operative temperature is defined as a weighted average of the air temperature and the mean radiant temperature (Hutcheon and Handegord 1983; Olesen 2002; ASHRAE 2010). It has been used as a representative measure of thermal comfort in several works in the literature (Mui and Chan 2003; Xu et al. 2004; Jain et al. 2011; Joe et al. 2016, 2018). Here the respective operative temperature of each zone is maintained within a predefined comfort range. The air temperatures are also recorded.