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Occupants’ perception of air movements and air quality in a simulated classroom with an intermittent air supply system
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. (Energy Systems)ORCID iD: 0000-0002-2171-3013
Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental psychology.ORCID iD: 0000-0002-7584-2275
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. (Indoor environment)
2017 (English)In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070Article in journal (Refereed) Epub ahead of print
Abstract [en]

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. 

Place, publisher, year, edition, pages
2017.
Keyword [en]
Intermittent air jets, Air movement acceptability, Perceived air quality, High occupant density
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:hig:diva-23753DOI: 10.1177/1420326X17732613OAI: oai:DiVA.org:hig-23753DiVA: diva2:1082031
Available from: 2017-03-15 Created: 2017-03-15 Last updated: 2017-09-21Bibliographically approved
In thesis
1. Experimental study of an intermittent ventilation system in high occupancy spaces
Open this publication in new window or tab >>Experimental study of an intermittent ventilation system in high occupancy spaces
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.  

Abstract [sv]

Lokaler där många människor vistas, som t.ex. klassrum, är ofta svåra att ventilera. Att upprätthålla en bra termisk komfort kräver en hög energianvändning. Vanligtvis blir det en kompromiss mellan låg energianvändning och bra kvalitet på inomhusmiljön (IEQ). Dålig IEQ får konsekvenser för människors hälsa, produktivitet och komfort. Alternativa ventilationsstrategier, som använder förhöjda lufthastigheter, kan minska kylbehovet och därmed energianvändningen. I denna avhandling utvärderas en ny ventilationsstrategi, Intermittenta luftstrålar (IAJS), där korta perioder med hög lufthastighet genererar en svalkande effekt, när rummets temperatur upplevs som för hög.

Det primära syftet med arbetet var att undersöka potentialen hos IAJS som ett ventilationssystem för klassrum, där den termiska lasten ofta är hög. Strategin jämförs mot traditionella ventilationsprinciper som omblandande ventilation (MV) och deplacerande ventilation (DV). Parametrar som luftdistributionsindex, termisk komfort, luftkvalitet och energibesparing har utvärderats. Alla studier utfördes i klimatkammare.

Resultaten visar att medan MV och DV skapar konstanta luftflödesförhållanden genererar IAJS cykliska hastighetsprofiler samt en sinusformad temperaturvariation i vistelsezonen. IAJS klarar att bibehålla ett bra termiskt klimat vid högre operativa temperaturer jämfört med MV. I en jämförelse med ett traditionellt HVAC-system visar beräkningar  att dess börvärde kan höjas från 2.3 till 4.5 °C med bibehållen termisk komfort. Detta indikerar en avsevärd energibesparingspotential vid användande av IAJS.

Place, publisher, year, edition, pages
Gävle: Gävle University Press, 2017. 74 p.
Series
Studies in the Research Profile Built Environment. Doctoral thesis, 3
Keyword
Intermittent airflow, Indoor air quality, Perceived air quality, Thermal sensation, thermal comfort, Air movement acceptability, Convective cooling, Cooling effect., Intermittent luftflöde, Luftstrålar, Upplevd luftkvalitet, Termisk komfort, Acceptans av luftrörelser, Konvektiv kylning, Kyleffekt.
National Category
Energy Systems
Identifiers
urn:nbn:se:hig:diva-23754 (URN)978-91-88145-11-6 (ISBN)978-91-88145-12-3 (ISBN)
Public defence
2017-05-18, 12:108, Kungsbäcksvägen 47, Gävle, 10:00 (English)
Opponent
Supervisors
Available from: 2017-04-26 Created: 2017-03-15 Last updated: 2017-04-26Bibliographically approved

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