Abstract
Natural ventilation associated with a mechanical fan is a feasible strategy to enhance thermal acceptability in warm weather. The ASHRAE-55 provides the increase for operative temperature proportional to the increase in air speed while maintaining thermal comfort. Conversely, the range of informed values is limited and little guidance for mechanical fans is provided. This work explores the relationship between operative temperature and air speed produced by ceiling fans, and the effectiveness to deliver thermal comfort for a wider range of values. The research method comprises transient computer fluid dynamics simulations coupled with a thermal sensation model and is divided into two stages: a calibration exercise and a parametrical investigation. Three matrices are presented for a range of operative temperatures (21.0–36.0 °C) and air speeds (0–2.5 m/s) for: Dynamic Thermal Sensation (DTS) (a computer-based seven-point index), Predicted Percentage of Dissatisfied, and potential Cooling Effect. When compared to the Predicted Mean Vote, the DTS overestimates thermal comfort for temperatures under 28.0 °C with increased air speed and overestimates discomfort for temperatures above 31.0 °C, even with increased air speed. Agreement is found between both scales for 28.0–31.0 °C, defining a range for the effective use of ceiling fans to provide thermal comfort under warm weather conditions.
Highlights
The unprecedented growth in the number of room air conditioning (RAC) units in buildings located in hot-dry and warm-humid regions has the potential to cause a substantial increase in energy demand, worsening the effects of global climate change [1,2]
The research method comprises transient computer fluid dynamics (CFD) simulations coupled with a model to predict thermal sensation and reproduce the airflow field environment of a mechanical ceiling fan
The matrices are presented for Dynamic Thermal Sensation (DTS) (Figure 9), Predicted Percentage of Dissatisfied (PPD) (Figure 10), and Cooling Effect (CE) of the air speed on the Buildings 2022, 12, x FOR PEER REVIEmWean skin temperature (Skm) (Figure 11), with this last matrix based on the compar1i3soonf o19f Skm obtained with still air
Summary
The unprecedented growth in the number of room air conditioning (RAC) units in buildings located in hot-dry and warm-humid regions has the potential to cause a substantial increase in energy demand, worsening the effects of global climate change [1,2]. Adaptive behavior increases thermal acceptability in free-run buildings under wider hot climatic conditions, as opposed to RAC environments [13,14], along with changing clothing, reducing activity performed, opening/closing openings for natural ventilation, and switching on/off mechanical fans [15,16,17]. The proportionality provided is valid for a range of operative temperatures (20.0–31.0 ◦C), air speeds (0–1.6 m/s or more, if individuals have control over mechanical devices or ventilation openings), and humidity ratios (0.010 kg of H2O/kg of dry air), plus is applicable for given parameters of clothing insulating values (0.5 and 1.0 clo), a specific metabolic rate (1.1 met), and subject to the possibility that individuals perform adaptive behavior [15,17]. Until now, no previous studies were found utilizing transient CFD simulations coupled with the dynamic thermal sensation model to analyze the impact of a wide range of operative temperature values and air speed produced by virtual ceiling fans beyond the range of values presented by ASHRAE Standard 55 [6] on the human thermal sensation
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