| 41. |
- Kabanshi, Alan
(författare)
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Experimental study of an intermittent ventilation system in high occupancy spaces
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spaces with high occupancy density like classrooms are challenging to ventilate and use a lot of energy to maintain comfort. Usually, a compromise is made between low energy use and good Indoor Environmental Quality (IEQ), of which poor IEQ has consequences for occupants’ health, productivity and comfort. Alternative strategies that incorporate elevated air speeds can reduce cooling energy demand and provide occupant’s comfort and productivity at higher operative temperatures. A ventilation strategy, Intermittent Air Jet Strategy (IAJS), which optimizes controlled intermittent airflow and creates non-uniform airflow and non-isothermal conditions, critical for sedentary operations at elevated temperatures, is proposed herein.The primary aim of the work was to investigate the potential of IAJS as a ventilation system in high occupancy spaces. Ventilation parameters such as air distribution, thermal comfort and indoor air quality are evaluated and the system is compared with a traditional system, specifically, mixing ventilation (MV). A 3-part research process was used: (1) Technical (objective) evaluation of IAJS in-comparison to MV and displacement ventilation (DV) systems. (2) An occupant response study to IAJS. (3) Estimation of the cooling effect under IAJS and its implications on energy use. All studies were conducted in controlled chambers.The results show that while MV and DV creates steady airflow conditions, IAJS has cyclic airflow profiles which results in a sinusoidal temperature profile around occupants. Air distribution capability of IAJS is similar to MV, both having a generic local air quality index in the occupied zone. On the other hand, the systems overall air change rate was higher than a MV. Thermal comfort results suggest that IAJS generates comfortable thermal climate at higher operative temperatures compared to MV. Occupant responses to IAJS show an improved thermal sensation, air quality perception and acceptability of indoor environment at higher temperatures as compared to MV. A comparative study to estimate the cooling effect of IAJS shows that upper HVAC setpoint can be increased from 2.3 – 4.5 oC for a neutral thermal sensation compared to a MV. This implies a substantial energy saving potential on the ventilation system. In general, IAJS showed a potential for use as a ventilation system in classrooms while promising energy savings.
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| 42. |
- Kabanshi, Alan, et al.
(författare)
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Human perception of room temperature and intermittent air jet cooling in a classroom
- 2017
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Ingår i: Indoor + Built Environment. - 1420-326X .- 1423-0070. ; 26:4, s. 528-537
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Tidskriftsartikel (refereegranskat)abstract
- Environments with high temperatures and under steady conditions are perceived poor. The introduction of airflow variations in such environments improves the perception. However the risk of draught is high and to avoid this, variations in high velocity supply is used. This method is far more energy efficient than cooling the entire space as only the occupants are cooled. This paper discusses two studies on occupant cooling conducted at the University of Gävle. The experiments were performed in a full scale mockup classroom and a total of 85 students participated. In Study 1, students sat in a classroom for about 60 minutes in one of two heat conditions: 20 and 25 º C. In Study 2, the indoor parameters of 25 º C were maintained but airflow variation in the sitting zone was manipulated. In both studies, the participants performed various tasks and answered questionnaires on their perception of the indoor climate. As shown here, higher room temperature deteriorates human perception of the indoor climate in classrooms, and the use of intermittent air jet cooling improves the perception of indoor climate just like cooling by reducing the room air temperature. This study contributes to further knowledge of how convective cooling can be used as a method of cooling in school environments so as to improve on building energy use.
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| 43. |
- Kabanshi, Alan, et al.
(författare)
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Occupants’ perception of air movements and air quality in a simulated classroom with an intermittent air supply system
- 2019
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Ingår i: Indoor + Built Environment. - : Sage Publications. - 1420-326X .- 1423-0070. ; 28:1, s. 63-76
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Tidskriftsartikel (refereegranskat)abstract
- The study reported herein builds on occupant response to an intermittent air jet strategy (IAJS), which creates periodic airflow and non-isothermal conditions in the occupied zone. Previous research has highlighted the benefits of IAJS on thermal climate and supports energy saving potential in view of human thermal perception of the indoor environment. In this study, the goal was to explore occupant acceptability of air movements and perceived indoor air quality, and to determine a way of assessing acceptable air movement conditions under IAJS. Thirty-six participants were exposed to twelve conditions: three room air temperatures (nominal: 22.5, 25.5 and 28.5 oC), each with varied air speeds (nominal: <0.15 m/s under mixing ventilation (MV), and 0.4, 0.6 and 0.8 m/s under IAJS) measured at the breathing height (1.1 m). The results show that participants preferred low air movements at lower temperatures and high air movements at higher temperatures. A model to predict percentage satisfied with intermittent air movements was developed, and predicts that about 87% of the occupants within a thermal sensation range of slightly cool (-0.5) to slightly warm (+0.5), in compliance with ASHRAE standard 55, will find intermittent air movements acceptable between 23.7 oC and 29.1 oC within a velocity range of 0.4 – 0.8 m/s. IAJS also improved participants’ perception of air quality in conditions deemed poor under MV. The findings support the potential of IAJS as a primary ventilation system in high occupant spaces such as classrooms.
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| 44. |
- Kabanshi, Alan, et al.
(författare)
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Perception of intermittent air velocities in classrooms
- 2014
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Ingår i: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate. ; , s. 189-191
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Konferensbidrag (refereegranskat)abstract
- Classrooms normally host a large number of people and the heat generated provides a challenge cool. Traditional cooling methods by increased low temperature supply airflow rate or use of heat sinks are expensive and mostly inefficient. The strategy of controlled air movements in the occupied zone may prove cheaper and desirable. This research investigates recirculation of room air to provide intermittent velocity cooling in classrooms. The objective of this experiment was to assess how occupants perceive the recirculated intermittent air velocity conditions in classrooms and when the variations should be introduced in the room for optimal results. This was done with a between participant design, accessing how they perceived indoor air quality (IAQ) and the thermal comfort in two velocity conditions: constant low air velocity condition (< 0.15 m/s) and intermittent air velocity condition (0.4 m/s). As shown here; intermittent air velocity has a positive effect on the perceived thermal comfort (p < 0.04) and perception of air quality: less draughty and improved humid perception. The participants perceived the conditions with intermittent velocity to give comfortable feelings and better air quality. The variations also showed better performance if they were provided at the start of occupancy as opposed to during or after a temperature build up. This strategy can be used in environments where it is rather uneconomical to provide cooling like spaces hosting a group of people: movie theatres, auditoriums, classrooms and perhaps in restaurants.
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| 45. |
- Kabanshi, Alan, et al.
(författare)
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The effect of heat stress on writing performance in a classroom
- 2014
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Ingår i: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate. ; , s. 183-188
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Konferensbidrag (refereegranskat)abstract
- Studies have shown that heat stress impairs performance. This depends on the mental loading capacity of the task performed and the exposure time. This is a study of a common task in schools and offices: writing task. It also analyses the occupants’ perceived thermal comfort. The experiment was done in two heat conditions: 20 and 25 centigrade. The between participant design was used. ScriptLog was used to perform the writing task, while questionnaires and a Sudoku task were paper based tasks. The results show that the predicted mean vote (PMV) between conditions was significant (p<0.02) and participants perceived the 20 º C condition to be draughty. They however preferred a little more air movements in both conditions. Writing performance only showed a significant difference (p = 0.03) on deleted characters but the other variables considered did not show any significant differences but showed a strong tendency that with a long exposure time it would eventually be impaired. This shows that writing despite being a complex task is not a high mental loading task and is not quickly impaired by heat stress.
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| 46. |
- Kabanshi, Alan, et al.
(författare)
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The influence of heat, air jet cooling and noise on performance in classrooms
- 2015
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Ingår i: The International Journal of Ventilation. - : Informa UK Limited. - 1473-3315 .- 2044-4044. ; 14:3, s. 321-332
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Tidskriftsartikel (refereegranskat)abstract
- The quality of indoor environments influences satisfaction, health, and work performance of the occupants. Additional understanding of the theoretical and practical value of individual indoor parameters in relation to health and performance aids indoor climate designers to obtain desired outcomes. This also results in expenditure savings and increased revenue: health care and improved productivity. Here, we report two experiments that investigated how heat, cooling strategy and background noise influence performance in a full-scale classroom mockup setting. The results show that heat and background noise are detrimental to logic-based tasks and to writing, whilst cooling manipulations can protect performance. Implications for indoor environment design are discussed.
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| 47. |
- Keus van de Poll, Marijke, et al.
(författare)
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Disruption of writing by background speech: The role of speech transmission index
- 2014
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Ingår i: Applied Acoustics. - : Elsevier. - 0003-682X .- 1872-910X. ; 81, s. 15-18
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Tidskriftsartikel (refereegranskat)abstract
- Speech transmission index (STI) is an objective measure of the acoustic properties of office environments and is used to specify norms for acceptable acoustic work conditions. Yet, the tasks used to evaluate the effects of varying STIs on work performance have often been focusing on memory (as memory of visually presented words) and reading tasks and may not give a complete view of the severity even of low STI values (i.e., when speech intelligibility is low). Against this background, we used a more typical office-work task in the present study. The participants were asked to write short essays (5 min per essay) in 5 different STI conditions (0.08; 0.23; 0.34; 0.50; and 0.71). Writing fluency dropped drastically and the number of pauses longer than 5 s increased at STI values above 0.23. This study shows that realistic work-related performance drops even at low STI values and has implications for how to evaluate acoustic conditions in school and office environments.
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| 48. |
- Keus van de Poll, Marijke, 1984-
(författare)
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Disruption of writing in noisy office environments
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of the four experimental studies included in this dissertation was to investigate the influence of background speech on writing performance. In Paper I, a manipulation of speech intelligibility of background speech, by using the Speech Transmission Index (STI), revealed disruptive effects at lower STI values (i.e. with relative low speech intelligibility) than expected, based on an earlier developed model. This showed that writing is more sensitive to disruption from background speech than previously thought.Experiment 1 in Paper II addressed the question whether the sound of babble, sound of water waves, or pink noise is the most effective and appreciated way of masking background speech to reduce its intelligibility and thereby its disruptiveness. Masking with babble was best. Experiment 2 in Paper II followed this finding up by showing that the disruption of writing by background speech is a function of the number of voices talking in the background—less voices, more disruption.Paper III investigated the combined impact of background speech and task interruptions on writing performance. Background speech (which was played during the whole condition) after an interruption was expected to prolong the time it took to resume the same writing speed as before the interruption. This hypothesis was not confirmed, but participants’ self-reports showed that the combination of task interruptions and background speech convey a particularly high workload.Paper IV explored what role sound source location and individual differences (inattention, noise sensitivity and working memory capacity) play in the disruption of writing by background speech. Self-reports showed that speech in front of the individual was perceived as more distracting compared to speech from behind. Other results in the same study showed that high inattentive individuals profit more from less intelligible speech located behind them than attentive individuals and high noise-sensitive individuals were more distracted by highly intelligible background speech than by less intelligible background speech.The most important and replicable finding in this dissertation is that writing fluency is very sensitive to disruption from background speech; a finding relevant for the design of open work environments. In work areas where writing is a common task, the aim should be to create quiet work areas.
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| 49. |
- Keus van de Poll, Marijke, 1984-, et al.
(författare)
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Effects of speech on writing : Is there a right-ear disadvantage?
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has been shown, with tasks specifically designed for well-controlled laboratory research, that task-irrelevant speech is more distracting when it is presented to the right ear (as right-ear presentation has privileged access to the left hemisphere that plays a dominant role in language processing). This is called the right-ear disadvantage. The purpose of this study was to investigate whether the right-ear disadvantage generalizes to more applied, less well-controlled, tasks. Students were asked to write short stories while they were hearing task-irrelevant sound, either normal or spectrally-rotated speech, which they were to ignore. The sound was either presented to the right or to the left ear. The participants produced less written text when they were exposed to normal speech in comparison with rotated speech. However, this difference was just as large when the sound was presented to the right as to the left ear. In all, the semanticity of speech seems to disrupt output writing processes, but there was no evidence of a right-ear disadvantage with this task, probably because writing is not an experimentally controlled task. This study shows that the applied consequences of right-ear disadvantage are limited.
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| 50. |
- Keus van de Poll, Marijke, et al.
(författare)
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Effects of task interruption and background speech on word processed writing
- 2016
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Ingår i: Applied Cognitive Psychology. - : Wiley. - 0888-4080 .- 1099-0720. ; 30:3, s. 430-439
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Tidskriftsartikel (refereegranskat)abstract
- Task interruptions and background speech, both part of the everyday situation in office environments, impair cognitive performance. The current experiments explored the combined effects of background speech and task interruptions on word processed writing-arguably, a task representative of office work. Participants wrote stories, in silence or in the presence of background speech (monologues, halfalogues and dialogues), and were occasionally interrupted by a secondary task. Writing speed was comparably low during the immediate period after the interruption (Experiments 1 and 2); it took 10-15s to regain full writing speed. Background speech had only a small effect on performance (Experiment 1), but a dialogue was more disruptive than a halfalogue (Experiment 2). Background speech did not add to the cost caused by task interruptions. However, subjective measures suggested that speech, just as interruptions, contributed to perceived workload. The findings are discussed in view of attentional capture and interference-by-process mechanisms.
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