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Technique and human perception of intermittent air velocity variation
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
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 [en]
indoor climate
National Category
Other Environmental Engineering
Identifiers
URN: urn:nbn:se:kth:diva-423ISBN: 91-7178-137-4 (print)OAI: oai:DiVA.org:kth-423DiVA: diva2:11362
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
List of papers
1. Velocity variations in ventilated rooms as a method for creating comfort
Open this publication in new window or tab >>Velocity variations in ventilated rooms as a method for creating comfort
2001 (English)In: Market Opportunities for Advanced Ventilation Technology: AIVC 22nd Conference Belgium, 2001Conference paper, Published paper (Refereed)
Abstract [en]

The aim is to develop a new method for comfort in settings with high thermal load in buildings that do not require continuous cooling but cooling only during shorter periods. Example of such buildings is schools. The present ventilation and control systems are designed for supply of air at a constant flowrate or to respond to relatively slow variations in load or step changes in load. The slow variations in load are mainly governed by the diurnal cycle and sudden step changes in load are mainly due to people entering or leaving a room. Systems of today are monotonous in the sense that the indoor climate is kept almost constant over long periods. However, there are indications that intermittent variations in velocities can be beneficial to people's perceived comfort. For example when people feel too warm the introduction of a short "breeze" of "high velocity" air may make them feel more comfortable. One example is window airing. The use of (non-turbulent) variations as a stimulus for creating comfort has not as yet been explored systematically or been technically implemented. The idea is to create velocity variations in the head region on people. Both momentum (mixing ventilation) and pure buoyancy driven (displacement system) ventilation are used for creating velocity variations. In addition to using the ventilation system for introducing velocity variations, stirring generated by propellers (ceiling fans) are used. The paper reports on the velocity field obtained in the occupied zone.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6602 (URN)
Conference
AIVC 22nd Conference Belgium, Brussels, INIVE EEIG, 2001, 'Market Opportunities for Advanced Ventilation Technology'. held at Hilton Bath City Hotel, Bath, United Kingdom, 11th - 14th September 2001
Note

QC 20111220

Available from: 2005-09-20 Created: 2005-09-20 Last updated: 2012-10-23Bibliographically approved
2. Effects of velocity variations in ventilated rooms on comfort, affect and cognitive performance
Open this publication in new window or tab >>Effects of velocity variations in ventilated rooms on comfort, affect and cognitive performance
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.

National Category
Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-53025 (URN)
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
3. Creating velocity variations in a whole room
Open this publication in new window or tab >>Creating velocity variations in a whole room
2002 (English)In: Proceedings of Room Vent 2002: 8th International Conference on Air Distribution in Rooms, 2002, Vol. 4, 635-640 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper investigates the possibilities to create velocity variations of that type : (change from "low" to "high" velocity and then back "low" velocity again) in a whole room using standard velocity components. The results show large differences at individual points, but the mean value of all 8 positions in the room shows an expected behaviour.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6603 (URN)
Conference
Proceedings of Room Vent 2002 (8th International Conference on Air Distribution in Rooms) - 8-11 september 2002 - Moltke's palace, Copenhagen - Denmark
Note
QC 20111221Available from: 2005-09-20 Created: 2005-09-20 Last updated: 2011-12-21Bibliographically approved
4. Psychological impact of air velocity variations in ventilated room
Open this publication in new window or tab >>Psychological impact of air velocity variations in ventilated room
2005 (English)In: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847, Vol. 48, no 9, 1086-1096 p.Article in journal (Refereed) Published
Abstract [en]

Two experiments investigated the psychological impact of two velocity conditions (constant low velocity (V1) and variations of low and high velocity (V2)) in two temperature conditions (Experiment 1: an air temperature increase from 21 degrees C to 24 degrees C; Experiment 2: an air temperature increase from 25 degrees C to 27 degrees C) in females and males, aged 16 to 18 years, under realistic classroom conditions during an exposure period of 80 min. It was predicted that the V2 room condition compared to the V 1 room condition would be more beneficial for subjects' perceived room temperature and air quality, self-reported affect and cognitive performance. The results obtained showed no significant effects on cognitive performance. However and as predicted, in Experiment 1, the subjects in the V2 compared to those in the V1 room condition felt that the air temperature decreased (while it de facto increased) and reported a constant level of high activation. In Experiment 2, the subjects in the V2 room condition felt that the air temperature increased less and reported that their unactivated unpleasantness increased less and activated pleasantness decreased less than it did for subjects in the V 1 room condition. All this indicates, as was suggested by Wigo et al. (2002), that a cooling effect, induced by air velocity variations, might be beneficial for subjects in a ventilated room and that their perceived pleasantness of the indoor climate could be met at a higher room temperature than otherwise.

Keyword
velocity variation, perceived temperature, draught, self-reported affect, transient temperature
National Category
Environmental Analysis and Construction Information Technology
Identifiers
urn:nbn:se:kth:diva-6605 (URN)10.1080/00140130500197294 (DOI)000232780800002 ()
Note
Updated from in press to published. QC 20111216Available from: 2005-09-20 Created: 2005-09-20 Last updated: 2017-12-14Bibliographically approved
5. Application of a thermal manikin to evaluate heat loss rates from people caused by variations in air velocity and air temperature
Open this publication in new window or tab >>Application of a thermal manikin to evaluate heat loss rates from people caused by variations in air velocity and air temperature
2004 (English)In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 3, no 3Article in journal (Refereed) Published
Abstract [en]

Heat loss monitoring from a thermal manikin was undertaken representing an occupant in a classroom during a lesson period of 80 minutes in which the room temperature was increased from 21 to 24°C for various airflow velocity configurations. A group of subjects was exposed to various conditions of temperature and airflow rate so that the impact of these variations on their surface/skin temperature could be determined. It was found that skin temperature remained stable and close to 34°C for all conditions of exposure. Thus, over the temperature and air velocity range considered, these new findings verified the suitability of using a thermal manikin, set to steady uniform surface temperature, to determine the heat loss characteristics from occupants subjected to intermittent velocity       variation. When the manikin was exposed to a high velocity pulse, the heat loss from the       whole body increased by 10% while the heat loss from exposed areas (hands and face) increased by 20 % (when compared to no velocity pulse). After the 80 minutes monitoring period, the total energy loss from a manikin exposed to velocity variations was 2% higher than when exposed to constant low velocity.

Keyword
School ventilation, thermal comfort, adaptive comfort, occupant monitoring, thermal manikin
National Category
Environmental Analysis and Construction Information Technology
Identifiers
urn:nbn:se:kth:diva-6606 (URN)
Note
QC 20111006Available from: 2005-09-20 Created: 2005-09-20 Last updated: 2017-12-14Bibliographically approved
6. Effects of intermittent air velocity on thermal and draught perception during transient temperature conditions
Open this publication in new window or tab >>Effects of intermittent air velocity on thermal and draught perception during transient temperature conditions
2008 (English)In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 7, no 1, 59-66 p.Article in journal (Refereed) Published
Abstract [en]

: Previous research has shown that air movement has a significant influence on humans' thermal comfort. For persons feeling cool, air movement tends to be perceived as draught, whilst when feeling warm air movements may provide a desired cooling effect. In the transition zone it therefore seems difficult to use constant air velocity as a tool for cooling without creating draught problems. Nevertheless, from an energy saving perspective it appears to be far more efficient to use enhanced convective cooling, induced by the air movement, to cool only the occupants instead of the entire building. One possible way to use air movement as a method to improve thermal comfort without resultant draught problems could be to use intermittent air velocity instead of constant velocity. The present paper reports results from three experiments where subjects have been exposed to velocity variations, showing support for the hypothesis that it is possible to cool humans and reduce the percentage of occupants who are dissatisfied with the room temperature, without creating draught problems, through intermittent cooling.

Keyword
thermal comfort, human cooling, draught perception, velocity variations, intermittent air movement, convective cooling
National Category
Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-6607 (URN)000207586500006 ()
Note
QC 20111219. Updated from submitted to publishedAvailable from: 2005-09-20 Created: 2005-09-20 Last updated: 2017-12-14Bibliographically approved

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