Publication: HVAC & R Research
Publication Date: 01-JUL-07
Delivery: Immediate Online Access
Author: Melikov, A.K. ; Knudsen, G.L.
Article Excerpt
Received January 21, 2006; accepted April 30, 2006
The response of 48 subjects to an individually controlled microenvironment was studied at room air temperatures of 20[degrees]C, 22[degrees]C, and 26[degrees]C. An individually controlled system (ICS) comprising personalized ventilation, an under-desk air terminal device supplying cool air, a chair with convectively heated backrest, an under-desk radiant heating panel, and a floor-heating panel were used. The temperature of the air supplied from the personalized ventilation and the under-desk device was 20[degrees]C. The subjects were provided with control of the flow rate and direction of the personalized air, the under-desk airflow rate, the temperature of the convection flow from the chair, and the surface temperature of the heating panels. The results reveal that the thermal and air quality acceptability was significantly higher with the ICS at all room temperatures compared to the reference condition at a room temperature of 22[degrees]C without ICS. Thus, ICS will increase the number of satisfied occupants when applied in practice. The design and control of the ICS, as well as the background air distribution in a room, should be carefully considered in order to obtain the maximum number of occupants who are comfortable with their microenvironment.
INTRODUCTION
The engineering goal has been to maintain a temperature in spaces with many occupants close to the optimal level recommended in the standards and to create uniform indoor environmental conditions. However, under these conditions not all occupants will be satisfied because of individual differences in preferred temperature, air movement, and air quality perception (Melikov 2004).
In traditional open landscape offices with total-volume air-conditioning, where many workers occupy the same space, the means of compensating for the above-mentioned individual differences are very limited. The solution may be to provide each occupant with the means of controlling individually the microenvironment at his/her workplace. Wyon (1996) has estimated that individual control of the temperature at each workplace in the range [+ or -]2.3 K around the group average neutral temperature would be necessary for 95% of office workers in their preferred clothing to achieve thermal neutrality. However, these predictions need validation in order to justify the use of individual control of the local thermal environment in practice.
Often, the temperature in rooms changes during the day. The changes can affect occupants' comfort and performance. An individually controlled microenvironment may compensate for these changes and may provide occupants with a preferred environment without substantially increasing the initial and running costs of the HVAC system. This, however, needs to be studied.
Providing occupants with individual control has a psychological impact resulting in increased satisfaction with the indoor environment. A field study reported by Bauman et al. (1998) revealed that it is more important for occupants to be able to control their local environment than it is to actually make a large number of adjustments.
The CEN Report CR 1752 (CEN 1998) describes three categories of indoor environment. The requirements for a category A environment are that less than 6% of occupants should be dissatisfied due to the whole-body thermal environment, 15% due to draft, and 15% due to air quality. It is stated in the report that it is advantageous to use some form of individual control of the local environment. Maybe the only way of achieving the category A environment is to provide workers with individual control of their microenvironment?
The effect of individually controlled local heating on occupants' thermal comfort has been studied by Madsen and Saxhof (1979), Jones (1988), Nelson and Langness (1992), and S[empty set]rlie et al. (1993), and Melikov et al. (1998). The effect of individually controlled personalized ventilation on inhaled air quality and thermal comfort has been reported as well (Kaczmarczyk et al. 2004; Melikov 2004). Local heating and ventilation, when used simultaneously, will increase nonuniformity of the microenvironment. Human response and the potential of an individually controlled microenvironment for improving both occupants' thermal comfort and inhaled air quality has not been reported in the literature.
The objective of this study was to identify the potential of an individually controlled environment for increasing the number of occupants satisfied with both the thermal environment and the air quality. An important aim was to study people's response to the system and to identify design characteristics important for its proper performance in practice.
RESEARCH METHOD
Experimental Facilities
The experiment was performed in a climate chamber 4.7 X 5.4 X 2.6 m (W X L X H) in size. The air temperature in the chamber was kept constant by mixing ventilation with a ceiling swirl diffuser. The surface temperature of the walls in the chamber was kept equal to the room air temperature. Two workstations provided with ICSs were set up in the chamber. The ICS consisted of a personalized ventilation system (PVS) with an air terminal device (ATD) called a round movable panel (RMP). The RMP, described in the following paragraph, aimed at providing clean and cool air to the breathing zone, an under-desk air terminal device (UD ATD) supplying cool air toward the front of the body, and a chair with convectively heated backrest (Heating Chair), an under-desk radiant heating panel (UD RHP), and a floor radiant heating panel (Floor RHP), all designed to provide local heating of the occupant's body. Figure 1 shows a sketch of the ICS.
[FIGURE 1 OMITTED]
The air terminal device used for the PVS was the RMP described by Bolashikov et al. (2003). It has a round front panel with a diameter of 215 mm. The air was discharged from an area with diameter of 0.185 m. The initial velocity profile was rather uniform. At a distance of up to 0.4 m from the outlet, the centerline velocity was above 90% of its initial value and the turbulence intensity did not exceed 10%. The RMP is mounted on a movable arm-duct attached to the desktop, allowing for change of its distance and of positioning in regard to the occupant. Up to 100% personalized air (not mixed with the polluted room air) in inhalation can be achieved when the RMP is used. The UD ATD attached below the desktop...
NOTE: All illustrations and photos have been removed from this article.
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