Transient human thermophysiological and comfort responses indoors after simulated summer commutes

Zhai, Yongchao; Zhao, Shengkai; Yang, Linlin; Wei, Na; Xu, Qinyun; Zhang, Hui; Arens, Edward

doi:10.1016/j.buildenv.2019.04.023

Cited by 57 publications

(19 citation statements)

References 30 publications

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“…It has also been found that a modest air speed significantly reduces a CO2 bubble that accumulates in a person's breathing zone under still air conditions in workstations [16]. Finally, higher air temperatures and air speeds have also recently been shown to be far more effective (compared to cooler temperatures and still-air) at restoring comfort to occupants who have just entered a space with elevated metabolic rate and stored body heat from walking [17,18]. Note that in each of these above cases the desirable air flows are isothermal, involving only the room air itself.…”

Section: Comfort Zones and Air Quality Effects Under Elevated Air Movmentioning

confidence: 99%

Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

Chen

Zhang

Arens

et al. 2020

Building and Environment

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Ceiling-Fan-Integrated Air Conditioning (CFIAC) is a proposed system that can greatly increase buildings' cooling efficiency. In it, terminal supply ducts and diffusers are replaced by vents/nozzles, jetting supply air toward ceiling fans that serve to mix and distribute it within the room. Because of the fans' air movement, the system provides comfort at higher room temperatures than in conventional commercial/ institutional/retail HVAC. We have experimentally evaluated CFIAC in a test room. This paper covers the distributions of airspeed, temperature, and calculated comfort level throughout the room. Two subsequent papers report tests of human subject comfort and ventilation effectiveness in the same experimental conditions. The room's supply air emerged from a high-sidewall vent directed toward a ceiling fan on the jet centerline; we also tested this same jet on a fan located off to the side of the jet. Primary variables are: ceiling fan flow volumes in downward and upward directions, supply air volume, and room-vs-supply temperature difference. Velocity, turbulence, and temperature distributions are presented for vertical and horizontal transects of the room. The occupied zone is then evaluated for velocity and temperature non-uniformity, and for comfort as predicted by the ASHRAE Standard 55 elevated air speed method. We show that temperatures are well-mixed and uniform across the room for all of the fan-on configurations, for fans both within or out of the supply jet centerline. The ceiling fan flow dominates the CFIAC airflow, and even though non-uniform is capable of providing comfortable conditions throughout the occupied area of the room.

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Section: Comfort Zones and Air Quality Effects Under Elevated Air Movmentioning

confidence: 99%

Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

Chen

Zhang

Arens

et al. 2020

Building and Environment

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“…Our previous study [3] found that although the metabolic level, heart rate, and skin blood flow were able to recover in a few minutes after the exercise and ambient temperature stepdown, the core temperature remained elevated during the entire 60 min. Further measurement of these longer-term heat storage changes after commutes would be useful in projecting occupants' thermal requirements over periods as long as a day.…”

Section: Discussionmentioning

confidence: 91%

“…Especially in warm weather, such increases affect people's thermal comfort well after they have entered cooler air-conditioned indoor spaces and become sedentary. Thermal sensation, comfort, and physiological responses all require time to reach steadystate indoor values [3], primarily due to body heat that was stored during the exercise in the heat [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…However, there have been few studies on investigating the underlying mechanism of human comfort requirement during thermal transitions induced by a metabolic rate down-step, and finding energy efficient way to restore and maintain comfort after it. In a preceding study [3], the authors examined transient human thermophysiological and comfort responses following exercise levels simulating commutes in the heat. The study showed that after the commutes, although metabolic rate dropped to sedentary within about 2-5 min, the body's stored heat (observed by increased core temperatures) continued to be elevated for 60 min.…”

Section: Introductionmentioning

confidence: 99%

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Using personally controlled air movement to improve comfort after simulated summer commute

Zhai

Miao

Yang

et al. 2019

Building and Environment

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People often feel uncomfortably warm and sweaty in their workspace after commuting there by walking or cycling in summer. This is because body heat stored during the commute takes a substantial time to dissipate. People complaining about this uncomfortable transition may cause operators to lower the thermostat setpoint, causing long-term overcooling and wasting energy. In addition, space cooling is slow, requiring minutes to take effect. This study addresses how to improve comfort in the transition by increasing the availability of convective cooling, where the response time is in seconds. Thirty-five subjects (17 men and 18 women) dressed in 0.6 clo entered a test room after exercising at 4.4 met for 15 min in 30 ºC. The exercise emulates the commute activity in summer. The test room was controlled to 24, 26, and 28 ºC, with and without the option of cooling using fan-produced horizontal airflow. Subjects were sedentary for 60 minutes, during which subjective thermal responses and physiological responses were measured. The enhanced convective and evaporative heat loss caused by fans significantly shortened the time needed to reach thermal comfort after the exerciseinduced thermal stress and improved the final comfort level. Compared to a typical indoor condition of 24 ºC and still air, 26 and 28 ºC with fans provided equal or better comfort more quickly, and inherently required much less energy to do so. Our study suggests that personally controlled air movement should be available in spaces where thermal and metabolic down-steps take place.

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“…Surprisingly they are not usually turned on until the period 10:30 to 12 noon (Fig. 7b), rather than around 9am upon arrival, this is probably related to the higher metabolic rate that occupants experience during their commute, and the time required for body heat to dissipate [25]. Like the windows, there are large differences in usage frequency between the different heaters ( Fig.…”

Section: Heatersmentioning

confidence: 97%

Use of adaptive control and its effects on human comfort in a naturally ventilated office in Alameda, California

Zhai

Honnekeri

Pigman

et al. 2019

Energy and Buildings

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Naturally ventilated buildings have been found to be comfortable over a wider range of indoor temperatures than in air-conditioned buildings, while using less energy. The mechanisms underlying this are not well understood. Through a longitudinal field study of a naturally ventilated office in Alameda, CA, we obtained insights into how occupants exercise various adaptive control opportunities to meet their comfort needs in the absence of a mechanical HVAC system. Continuous measurements were made of adaptive behaviors such as window state, ceiling fan usage, heater usage, and indoor and outdoor climate (dry-bulb air temperature, relative humidity, CO2, outdoor temperature). Over 1400 thermal comfort survey responses were collected, which showed that the building provided acceptable thermal conditions for 98% of the survey period, covering an indoor temperature range of 16-28°C. Occupants wore clothing between 0.5 and 0.6 clo in summer, and 0.7-0.8 in winter. Occupants opened windows when the outdoor temperature was above 15°C, with window opening often occurring at the occupant's arrival and proportional to outdoor temperature. Fan use was best explained by indoor temperature, typically being turned on during summer at indoor temperatures above 25°C. Heaters were turned on in winter more than an hour after arrival and commencement of sedentary activity. With these adaptive control behaviors, occupants were thermally neutral and satisfied from 18 to 27°C. Their satisfaction exceeded that predicted by ASHRAE Standard 55 or PMV-based ISO standards. Overall, our findings provide empirical support for adopting adaptive comfort model in office buildings.

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Transient human thermophysiological and comfort responses indoors after simulated summer commutes

Cited by 57 publications

References 30 publications

Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

Using personally controlled air movement to improve comfort after simulated summer commute

Use of adaptive control and its effects on human comfort in a naturally ventilated office in Alameda, California

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