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Experimental study of an intermittent ventilation system in high occupancy spaces
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.ORCID iD: 0000-0002-2171-3013
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
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 [en]
Intermittent airflow, Indoor air quality, Perceived air quality, Thermal sensation, thermal comfort, Air movement acceptability, Convective cooling, Cooling effect.
Keyword [sv]
Intermittent luftflöde, Luftstrålar, Upplevd luftkvalitet, Termisk komfort, Acceptans av luftrörelser, Konvektiv kylning, Kyleffekt.
National Category
Energy Systems
Identifiers
URN: urn:nbn:se:hig:diva-23754ISBN: 978-91-88145-11-6 (print)ISBN: 978-91-88145-12-3 (electronic)OAI: oai:DiVA.org:hig-23754DiVA: diva2:1082049
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
List of papers
1. Experimental evaluation of an intermittent air supply system: Part 1: Thermal comfort and ventilation efficiency
Open this publication in new window or tab >>Experimental evaluation of an intermittent air supply system: Part 1: Thermal comfort and ventilation efficiency
2016 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 95, 240-250 p., 4263Article in journal (Refereed) Published
Abstract [en]

Spaces with high occupancy density e.g.; classrooms, auditoriums and restaurants, provide challenges to ventilate at a lower energy use due to elevated temperatures. To meet occupants’ thermal comfort requirements traditional systems use a lot of energy. Alternative ventilation strategies that optimize high air movements in the occupied zone allow human activities at elevated temperatures while attaining improve occupants’ perception and acceptance of the indoor climate at a low energy use. This paper presents an experimental evaluation of a novel ventilation strategy for high occupancy spaces that provides fresh air and thermal comfort in the sitting zone through a controlled intermittent air jet system. The strategy uses ceiling mounted high momentum air jet diffusers (AJD) made from ventilation duct fitted with nozzles that generate confluent jets. The jets coalesce into a single two-dimensional jet which is directed downwards in the sitting zone. This paper presents an experimental evaluation/analysis of the proposed system with regard to ventilation efficiency and thermal comfort measurements in a classroom mockup. Results show that the system qualifies to be used as a primary ventilation system and has local air change index > 1 inside the jet, and a ventilation efficiency > 50%. The system also provides better thermal climate than mixing and displacement ventilation at elevated temperatures.

Keyword
Air jet diffuser, Ventilation strategy, Tracer gas, Ventilation efficiency, Thermal comfort, Occupancy density
National Category
Civil Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:hig:diva-20212 (URN)10.1016/j.buildenv.2015.09.025 (DOI)000367699800022 ()2-s2.0-84943329317 (Scopus ID)
Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-03-15Bibliographically approved
2. Experimental evaluation of an intermittent air supply system – Part 2: Occupant perception of thermal climate
Open this publication in new window or tab >>Experimental evaluation of an intermittent air supply system – Part 2: Occupant perception of thermal climate
2016 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 108, 99-109 p.Article in journal (Refereed) Published
Abstract [en]

A newly proposed intermittent air jet strategy (IAJS) provides satisfactory indoor climate while promising a substantial energy saving potential, as shown in technical (objective) measurements. The strategy creates non-uniform airflow and non-isothermal conditions critical for sedentary operations at elevated temperatures. The current study explored human perception of thermal environment under an IAJS. Assessment of thermal sensation, thermal comfort, and thermal acceptability were collected based on responses from 36 participants. Participants sat in a classroom setup and performed sedentary work. Their clothing had an insulation of 0.51 clo (T-shirt on upper body). Participants were exposed to homogeneous (v < 0.15 m/s) and nonhomogeneous (0.4 m/s < v < 0.8 m/s) velocity conditions across three temperature conditions: 22.5 °C, 25.5 °C and 28.5 °C. The participants found air speeds to be undesirable at lower temperatures, but reported an improved thermal sensation, comfort and acceptability at higher temperatures. As shown here, IAJS generated neutral operable conditions between 24.8 °C and 27.8 °C, within an air speed range of 0.4 m/s to 0.8 m/s. Additionally, air movements induced thermal alliethesia resulting in improved comfort and acceptance of the thermal climate even at lower air speeds in warm temperature conditions. Hence, the current study supports the energy saving potential with IAJS in view of the human perception of the indoor environment.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Intermittent air jets, Convective cooling, Thermal comfort, Thermal acceptability, Thermal preference, Thermal satisfaction
National Category
Energy Engineering
Identifiers
urn:nbn:se:hig:diva-22336 (URN)10.1016/j.buildenv.2016.08.025 (DOI)000385324300009 ()2-s2.0-84984810423 (Scopus ID)
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2017-03-15Bibliographically approved
3. Occupants’ perception of air movements and air quality in a simulated classroom with an intermittent air supply system
Open this publication in new window or tab >>Occupants’ perception of air movements and air quality in a simulated classroom with an intermittent air supply system
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. 

Keyword
Intermittent air jets, Air movement acceptability, Perceived air quality, High occupant density
National Category
Energy Engineering
Identifiers
urn:nbn:se:hig:diva-23753 (URN)10.1177/1420326X17732613 (DOI)
Available from: 2017-03-15 Created: 2017-03-15 Last updated: 2017-09-21Bibliographically approved
4. Human perception of room temperature and intermittent air jet cooling in a classroom
Open this publication in new window or tab >>Human perception of room temperature and intermittent air jet cooling in a classroom
2017 (English)In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 26, no 4, 528-537 p.Article in journal (Refereed) Published
Abstract [en]

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. 

Keyword
Heat, air jet cooling, Air velocity variations, Human perception, Indoor air quality, thermal sensation
National Category
Psychology (excluding Applied Psychology) Building Technologies
Identifiers
urn:nbn:se:hig:diva-20211 (URN)10.1177/1420326X16628931 (DOI)000400158700008 ()2-s2.0-85019000704 (Scopus ID)
Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-06-16Bibliographically approved
5. Experimental Evaluation of Intermittent Air Jet Ventilation Strategy: Cooling effect and the associated energy saving
Open this publication in new window or tab >>Experimental Evaluation of Intermittent Air Jet Ventilation Strategy: Cooling effect and the associated energy saving
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The potential to reduce building energy demand is high especially on building services like ventilation and air conditioning. This potential lies in identifying ventilation strategies that can provide both the required indoor climate and lower the energy use. One of the strategies is optimizing elevated air movements to enhance human convective and evaporative cooling which, as shown in literature, results in reduced energy use on cooling. This paper evaluates the cooling potential and the resulting energy saving of a novel air supply system called intermittent air jet strategy (IAJS). As shown in this study, IAJS with velocities of 0.4 m/s at the breathing height provides a cooling effect equivalent to reducing the ambient temperature in a mixing ventilation system by up to 1.5 oC to achieve a neutral sensation. This translates to a 13% reduction on the cooling demand. The strategy is also shown to have an energy saving potential of up to 50% on the supply fan. 

Keyword
Convective cooling, Equivalent temperature, Cooling power, Thermal manikin, Energy saving, High occupant density
National Category
Energy Engineering
Identifiers
urn:nbn:se:hig:diva-22179 (URN)
Conference
Indoor Air 2016, The 14th International Conference on Indoor Air Quality and Climate, Ghent, Belgium, July 2-9, 2016
Available from: 2016-07-28 Created: 2016-07-28 Last updated: 2017-03-15Bibliographically approved

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