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Effects of velocity variations in ventilated rooms on comfort, affect and cognitive performance
Univ Gavle, Dept Technol & Built Environm.
Univ Gavle, Dept Technol & Built Environm.
2002 (English)In: Proceedings of Indoor Air 2002 (9th International Conference on Indoor Air Quality and Climate) - June 30 - July 5, 2002 - Monterey, 2002, 635-640 p.Conference paper, Published paper (Refereed)
Abstract [en]

96 human subjects (18 years age students from a Swedish high school) were submitted in an experimental room furnished as a classroom to different air flows issued from different ventilation systems : displacement with constant air flow rate, alternating between displacement (floor diffusers) and mixing ventilation (ceiling diffusers) with constant flow rate, mixing ventilation with varying flow rate, displacement with constant flow rate and with ceiling fans to generate air motions alternatively on and off. Activuty of the subjects was composed of tasks allowing to estimate their intellectual performance. A questionnaire also concerned their perception of comfort. Air velocity variations did not affect thermal comfort but had a positive effect on perceived indoor air quality and on cognitive performance.

Place, publisher, year, edition, pages
2002. 635-640 p.
National Category
Environmental Engineering
Identifiers
URN: urn:nbn:se:kth:diva-53025OAI: oai:DiVA.org:kth-53025DiVA: diva2:468509
Conference
9th International Conference on Indoor Air Quality and Climate
Note
QC 20111221Available from: 2011-12-21 Created: 2011-12-21 Last updated: 2011-12-21Bibliographically approved
In thesis
1. Technique and human perception of intermittent air velocity variation
Open this publication in new window or tab >>Technique and human perception of intermittent air velocity variation
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Objectives. The main objective of the present thesis was to evolve a controlled intermittent velocity field and to examine the impact of this type of dynamic indoor climate on human’s psychology and physiology. The prediction was that intermittent velocity variation could provide occupants with the desired cooling without causing draught and that this intermittent change of the indoor climate would influence peoples’ affect and cognitive performance.

Methods. All experiments were performed in a classroom-like environment where groups of subjects were exposed to a temperature increase and step changes in air velocity. The changes or intermittent variations in air velocity consisted of elevated speed during five minutes, which were repeated three times. To reduce the influence of individual thermal preferences all measures were collected twice and the statistical analyses were based on the change scores in these measures.

Results. The obtained results showed that, intermittent velocity variation may provide occupants with the desired cooling without causing draught. Subjects exposed to velocity variations were significantly less affected by the temperature rise in the room, compared to the control group. Moreover, the method reduced the expected increase of occupants who perceived the temperature condition as uncomfortable. The findings concerning air movements demonstrate that very few perceived the condition as draughty, after being exposed to the three high velocity pulses.

The results concerning affect showed a significant effect on high activation, in the temperature range 21 - 24oC when the velocity variations made the subjects rate the temperature as slightly lowered over time, they kept their level of activation. In the higher temperature interval, 25 - 27oC, unactivated unpleasantness increased and activated pleasantness decreased significantly more in subjects in the constant velocity condition than it did for subjects in the velocity variation condition. In sum, all results concerning affect, the significant ones and tendencies point in the same direction. Subjects exposed to velocity variation report changes, over time, indicating higher activation and more positive feelings.

No differences in cognitive performances were shown between the air velocity conditions. However, a tendency to a significant result (p = 0.10) in an attention task was shown, indicating that subjects in the velocity variation condition increased their speed in a short-term memory search, compared to subjects in the constant velocity condition.

In the temperature range 21- 24oC, where the perception of the room temperature was measured at 0, 5 and 10 minutes respectively after the last high velocity period, the difference in MTV scores between the two groups, did decrease over time. Ten minutes after the last pulse the difference in MTV scores between the two groups was not significant. This suggests that the high velocity period should be repeated every10 to 15 minutes to keep the expected rise in subjects who judged the thermal conditions as uncomfortable down.

The skin temperature was not affected neither by the rise in ambient temperature (from 21 to 24oC over 80 minutes) nor the periods (3 x 5 minutes) of high velocity. A consequence of this result is that the human temperature regulation system permitted an increased heat loss during the high velocity pulse, and hence a reduction of the body’s internal stored heat. For uncovered body parts the increase in heat loss was 20 % during the high velocity pulse. Summarised over the whole exposure time the three pulses produced a total energy loss that was only 2 % higher compared to constant low velocity.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2005
Keyword
indoor climate
National Category
Other Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-423 (URN)91-7178-137-4 (ISBN)
Public defence
2005-09-29, Sal 202, Hus 33, Högskolan i Gävle, Gävle, 10:30
Opponent
Supervisors
Note
QC 20111221Available from: 2005-09-20 Created: 2005-09-20 Last updated: 2011-12-21Bibliographically approved

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