|
...body as a static heat source (Fanger 1973; ISO 1994; Gagge et al. 1971; ASHRAE 1992). However, when people are located in an uncomfortable thermal environment, they can adapt to the surrounding environment to restore comfort. Since a person constantly and actively adjusts the heat exchange with his or her surroundings, he or she provides an active existence to the environment. Therefore, Richard de Dear proposed a new thermal comfort model termed the "adaptive model," which was based on statistical analysis of the results of field experiments performed in over 20,000 office buildings (Dear and Brager 1998; Brager and de Dear 1998). Results of their analysis clarified that people working in a building provided with natural ventilation feel comfort in environments with a wider temperature range than the results calculated using the PMV index. It is possible to reduce the environmental load by decreasing the energy consumption for air-conditioning, which can be assessed using the adaptive model to give looser environmental control than that due to the heat balance models. On the other hand, research on the development of a task-ambient air-conditioning system with a personal airconditioner (PAC) has increased in recent years to aid energy conservation (Yang et al. 2004; Cermak et al. 2006). When a worker is in a task region air-conditioned by a spot PAC, his/ her thermal adaptive behaviors, such as the adjustments of posture and position, etc., which are frequently done in daily life, may contribute greatly to thermal comfort because of the prominent nonuniform velocity and temperature distributions formed by the cooled spot airflow. Therefore, to ensure that energy conservation and thermal comfort are maintained simultaneously, it is necessary to adapt the current adaptive model to incorporate the influence of a person's thermal adaptive behaviors on thermal comfort.
In this study, we examined the thermal effects of postural and positional adjustments of a seated human body exposed to a cooled high-speed spot airflow by simulating personal thermal characteristics in various postures and positions. First, the velocity distribution characteristics were examined in the working space of a seated office worker, which was covered by spot airflow. Then, experiments using an experimental thermal manikin were conducted to measure the local skin temperature and sensible heat transfer rate when changing the leaning posture of the manikin. Also, the coupled simulation of convection, radiation, moisture transport, and Fanger's neutral model was adopted to simulate heat exchange between a seated human body and the surrounding environment, by changing the body's orientation and position relative to the spot airflow. The examination was based on the results of the experiment and simulation.
EXAMINATION OF VELOCITY DISTRIBUTION CHARACTERISTICS IN TASK REGION COVERED BY SPOT AIRFLOW
Outline of Measurement
The experiment was conducted in a climate chamber as shown in Figure 1a. A desk equipped with the spot PAC was placed at the chamber's center, with a styrene board (1.2 m high) to form the surroundings. The ambient air-conditioning system used in the room supplied fresh air of 28[degrees]C from the whole floor surface at a speed of 0.05 m/s; air was exhausted through the whole ceiling surface. The PAC supplied a spot airflow of 28[degrees]C at a speed of 2.5 m/s. The velocities at the positions shown in Figure 1b were measured using an ultrasonic anemometer (KAJIO). During the experiment, the velocities at the positions in section a-a' were measured first, to confirm if the velocities were distributed symmetrically in the flow field. The velocities at the positions enclosed by the dotted line in section b-b' and c-c' were measured subsequently.
[FIGURE 1 OMITTED]
As shown in Figure 1c, the spot PAC is intended for use on a desk. It has two supply openings in the frontal panel, which have an effective diameter of 7 cm (actual size of openings is 8 x 5 cm) and can have grilles to allow adjustment of the airflow's direction. In the experiment, the spot airflow supplied by a spot cooler (Daikin) was spouted out after its airflow rate and temperature were successively adjusted by a branch chamber and a proportional/integral/differential (PID) controller (ASWAN).
Experimental Results
As shown in Figure 2, the velocities were distributed symmetrically left and right in the horizontal sections at each height, with the maximum value at the center of the Y dimension. At the positions within a distance of 15 cm from the center of the Y dimension, the velocities were obviously larger than the ambient velocity of 0.05 m/s. Moreover, for the positions with the same distance to the center of the Y dimension, the velocities became weaker at positions farther away from the desk at X dimension. At the positions over 20 cm away from the center of the Y dimension, the velocities were very small, as the spot airflow exerted little influence. Therefore, the velocities were predominantly influenced by the airflow supplied from the floor. In addition, at the positions at a height of 25 cm and within a distance of 5 cm from the center of the Y dimension, the velocities were larger than at the corresponding position at a height of 15 cm.
[FIGURE 2 OMITTED]
Discussion
According to the results described above, the spot airflow decreased with a steep velocity gradient from its center to the periphery...
NOTE: All illustrations and photos
have been removed from this article.
More articles from ASHRAE Transactions
Impact of control on operating costs for cool storage systems with dyn..., July 01, 2007
Optimized pump speed control using pump water flow station for HVAC sy..., July 01, 2007
Reentrainment of building exhaust air by packaged HVAC economizers.(He..., July 01, 2007
Simulation of the impact of commercial building envelope airtightness ..., July 01, 2007
Static pressure losses in nonmetallic flexible duct.(Technical report), July 01, 2007
Looking for additional articles?
Search our database of over 3 million articles.
Looking for more in-depth information on this industry?
Search our complete database of Industry & Market reports by text, subject, publication
name or publication date.
About Goliath
Whether you're looking for sales prospects, competitive information, company
analysis or best practices in managing your organization,
Goliath can help you meet your business needs.
Our extensive business information databases empower business
professionals with both the breadth and depth of credible,
authoritative information they need to support their business
goals. Whether it be strategic planning, sales prospecting,
company research or defining management best practices -
Goliath is your leading source for accurate information.
|
