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Natural Ventilation and Air Infiltration in Large Single‑Zone Buildings: Measurements and Modelling with Reference to Historical Churches
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Natural ventilation is the dominating ventilation process in ancient buildings like churches, and also in most domestic buildings in Sweden and in the rest of the world. These buildings are naturally ventilated via air infiltration and airing. Air infiltration is the airflow through adventitious leakages in the building envelope, while airing is the intentional air exchange through large openings like windows and doors. Airing can in turn be performed either as single-sided (one opening) or as cross flow ventilation (two or more openings located on different walls). The total air exchange affects heating energy and indoor air quality. In churches, deposition of airborne particles causes gradual soiling of indoor surfaces, including paintings and other pieces of art. Significant amounts of particles are emitted from visitors and from candles, incense, etc. Temporary airing is likely to reduce this problem, and it can also be used to adjust the indoor temperature. The present study investigates mechanisms and prediction models regarding air infiltration and open-door airing by means of field measurements, experiments in wind tunnel and computer modelling.

In natural ventilation, both air infiltration and airing share the same driving forces, i.e. wind and buoyancy (indoor-outdoor temperature differences). Both forces turn out to be difficult to predict, especially wind induced flows and the combination of buoyancy and wind. In the first part of the present study, two of the most established models for predicting air infiltration rate in buildings were evaluated against measurements in three historical stone churches in Sweden. A correction factor of 0.8 is introduced to adjust one of the studied models (which yielded better predictions) for fitting the large single zones like churches. Based on field investigation and IR-thermography inspections, a detailed numerical model was developed for prediction of air infiltration, where input data included assessed level of the neutral pressure level (NPL). The model functionality was validated against measurements in one of the case studies, indicating reasonable prediction capability. It is suggested that this model is further developed by including a more systematic calibration system for more building types and with different weather conditions.

Regarding airing, both single-sided and cross flow rates through the porches of various church buildings were measured with tracer gas method, as well as through direct measurements of the air velocity in a porch opening. Measurement results were compared with predictions attained from four previously developed models for single‑sided ventilation. Models that include terms for wind turbulence were found to yield somewhat better predictions. According to the performed measurements, the magnitude of one hour single-sided open-door airing in a church typically yields around 50% air exchange, indicating that this is a workable ventilation method, also for such large building volumes. A practical kind of diagram to facilitate estimation of suitable airing period is presented.

The ability of the IDA Indoor Climate and Energy (IDA-ICE) computer program to predict airing rates was examined by comparing with field measurements in a church. The programs’ predictions of single-sided airflows through an open door of the church were of the same magnitude as the measured ones; however, the effect of wind direction was not well captured by the program, indicating a development potential.

Finally, wind driven air flows through porch type openings of a church model were studied in a wind tunnel, where the airing rates were measured by tracer gas. At single-sided airing, a higher flow rate was observed at higher wind turbulence and when the opening was on the windward side of the building, in agreement with field measurements. Further, the airing rate was on the order of 15 times higher at cross flow than at single-sided airing. Realization of cross flow thus seems highly recommendable for enhanced airing. Calibration constants for a simple equation for wind driven flow through porches are presented. The measurements also indicate that advection through turbulence is a more important airing mechanism than pumping.

 

The present work adds knowledge particularly to the issues of air infiltration and airing through doors, in large single zones. The results can be applicable also to other kinds of large single-zone buildings, like industry halls, atriums and sports halls.

Abstract [sv]

Naturlig ventilation är den dominerande ventilationsprocessen i äldre byggnader såsom kyrkor, och även i de flesta småhus i Sverige och övriga delar av världen. Luftinfiltration och vädring utgör viktiga komponenter i naturlig ventilation, där luftinfiltration är luftflöde genom oavsiktliga läckage i byggnadsskalet, medan vädring är avsiktligt luftutbyte genom stora öppningar såsom fönster och dörrar/portar. Vädring kan i sin tur ske ensidigt (genom en öppning) eller som tvärdrag (genom två eller flera öppningar belägna på olika ytterväggar). Det totala luftutbytet påverkar värmeförluster och inomhusluftens kvalité. I kyrkor orsakar avsättning av luftpartiklar en gradvis nedsmutsning av invändiga ytor, inklusive väggmålningar och andra konstföremål. Betydande mängder partiklar avges från besökare, tända ljus, rökelse, o.d. Tillfällig vädring kan minska detta problem, men även användas för att justera innetemperaturen. Föreliggande studie analyserar mekanismer och predikteringsmodeller gällande luftinfiltration och dörrvädring genom fältmätningar, vindtunnelförsök och datorsimuleringar.

Luftinfiltration och vädring har samma drivkrafter, d.v.s. vind och termik (inne‑ute temperaturskillnader). Båda dessa drivkrafter är svåra att predicera, särskilt vindinducerade flöden och kombinationen av termik och vind. Två av de mest etablerade modellerna för luftinfiltrationsprediktering i byggnader har utvärderats via mätningar i tre kulturhistoriska stenkyrkor i Sverige. En korrigeringsfaktor av 0,8 föreslås för bättre prediktion av den ena modellen (som gav bäst resultat) gällande höga en-zonsbyggnader såsom kyrkor. En detaljerad numerisk modell är utvecklad för luftinfiltrationsprediktering, där indata baseras på fältundersökningar, inkl. IR-termografering och uppmätt av neutrala tryckplanet (NPL). Modellens funktionalitet har validerats via mätningar i en av fallstudierna och pekar på tämligen god prediktionsprestanda. Vidare utveckling av modellen föreslås, inkl. ett mer systematiskt kalibreringssystem, för olika typer av byggnader och väderförhållanden.

Gällande vädring mättes både ensidigt flöde och tvärdrag genom portar i olika kyrkobyggnader med hjälp av spårgas samt direkta lufthastighetsmätningar i portöppning. Mätresultaten jämfördes med erhållna prediktioner från fyra tidigare utvecklade modeller för ensidig ventilation. De modeller som tog hänsyn till vindturbulens gav något bättre resultat. Enligt utförda mätningar medför en timmes ensidig portvädring i en kyrka cirka 50 % luftutbyte, vilket indikerar att detta är en tillämpbar ventilationsmetod, även för så pass stora byggnadsvolymer. Ett särskilt vädringsdiagram presenteras, som syftar till att underlätta uppskattning av erforderlig vädringsperiod.

Vidare studerades predikteringsprestanda hos IDA Indoor Climate and Energy (IDA-ICE) simuleringsprogram avseende vädring, där simuleringsdata jämfördes med fältmätningar i en kyrka. Programmets prediktion av ensidigt luftflöde genom en öppen kyrkport var av samma storlekordning som det uppmäta; dock klarade programmet inte av att hantera inverkan av vindriktning så väl, vilket pekar på en utvecklingspotential.

Avslutningsvis undersöktes vinddrivet flöde igenom portöppningar i en kyrkmodell i vindtunnel, där luftomsättningen mättes med hjälp av spårgasmetoden. Vid ensidig vädring observerades högre flöde vid högre vindturbulens och när öppningen var på vindsidan av byggnaden, i överensstämmelse med fältmätningarna. Dessutom var vädringsflödet vid tvärdrag i storleksordningen 15 högre än det vid ensidig vädring. Det verkar alltså som att man kan öka vädringstakten avsevärt om man kan åstadkomma tvärdrag. Kalibreringskonstanter presenteras också för en enkel ekvation för vinddrivet flöde genom portar. Vindtunnelstudien indikerar vidare att advektion genom turbulens är en viktigare vädringsmekanism än pumpning.

Föreliggande arbete bidrar med kunskap speciellt kring luftinfiltration och vädring genom portar i höga en-zonsbyggnader. Resultaten kan även vara tillämpliga på andra typer av höga en-zonsbyggnader såsom industrihallar, atrier/ljusgårdar och idrottshallar.

Place, publisher, year, edition, pages
Gävle: Gävle University Press , 2017.
Series
Studies in the Research Profile Built Environment. Doctoral thesis, 4
Keyword [en]
Natural ventilation, Airing, Air infiltration, Single-sided ventilation, Cross flow, Large single zones, Historical Churches, Model evaluation/optimization, Field measurements, Wind tunnel, Indoor climate and Energy simulation, IDA-ICE, Tracer gas technique, Pressurization test.
Keyword [sv]
Naturlig ventilation, Vädring, Luftinfiltration, Ensidig ventilation, Tvärdrag, Höga en-zonsbyggnader, Kulturhistoriska kyrkor, Modellutvärdering/optimering, Fältmätningar, Vindtunnel, Inomhusklimat och energisimulering, IDA-ICE, Spårgas teknik, Trycksättningstest.
National Category
Building Technologies
Identifiers
URN: urn:nbn:se:hig:diva-24612ISBN: 978-91-88145-17-8 (print)ISBN: 978-91-88145-18-5 (electronic)OAI: oai:DiVA.org:hig-24612DiVA: diva2:1117979
Public defence
2017-09-29, Lilla Jadwigasalen (12:108), Kungsbäcksvägen 47, Gävle, 10:00 (English)
Opponent
Supervisors
Projects
Church project
Funder
Swedish Energy Agency, 2011-002440
Available from: 2017-08-28 Created: 2017-06-29 Last updated: 2017-08-29
List of papers
1. Evaluation of the LBL and AIM-2 air infiltration models on large single zones: three historical churches
Open this publication in new window or tab >>Evaluation of the LBL and AIM-2 air infiltration models on large single zones: three historical churches
2014 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 81, 365-379 p.Article in journal (Refereed) Published
Abstract [en]

Air infiltration in ancient churches and other historical and monumental buildings is of great importance considering moisture transfer, energy consumption, thermal comfort and air pollutants that induce surface soiling. Two of the most established models for predicting air infiltration rate in buildings are the Lawrence Berkeley Laboratory (LBL) model and the Alberta air Infiltration Model (AIM-2). Being originally developed mainly for dwellings, their applicability to large single zone buildings is evaluated in this study by comparing model predictions with field measurements in three historical stone churches that are naturally ventilated only through infiltration. The somewhat more developed AIM-2 model yielded slightly better predictions than the LBL model. However, an LBL version that allows inclusion of the Neutral Pressure Level (NPL) of the building envelope produced even better predictions and also proved less sensitive to assumptions on air leakage distribution at the building envelopes. All models yielded however significant overpredictions of the air infiltration rate. Since NPL may be difficult to attain in practice, the AIM-2 model was chosen for model modification to improve predictions. Tuning of this model by varying its original coefficients yielded however unrealistic model behaviors and the eventually suggested modification implied introducing a correction factor of 0.8. This reduced the median absolute prediction error from 25% to 11%. Thus, especially when the NPL is not at hand, this modification of the AIM-2 model may suit better for air infiltration assessment of churches and other buildings similar to the tested kind.

Keyword
Air infiltration, LBL model, AIM-2 model, Large single zones, Churches, Model optimization
National Category
Building Technologies
Identifiers
urn:nbn:se:hig:diva-17371 (URN)10.1016/j.buildenv.2014.07.013 (DOI)000342532200035 ()2-s2.0-84907334554 (Scopus ID)
Projects
Church project
Funder
Swedish Energy Agency, 2011-002440
Available from: 2014-08-18 Created: 2014-08-18 Last updated: 2017-06-29Bibliographically approved
2. Development of a Numerical Air Infiltration Model Based On Pressurization Test Applied On a Church
Open this publication in new window or tab >>Development of a Numerical Air Infiltration Model Based On Pressurization Test Applied On a Church
2016 (English)In: ASHRAE and AIVC IAQ 2016 — Defining Indoor Air Quality: Policy, Standards and Best Practices, 2016, ASHRAE, 2016, 224-231 p., C030Conference paper, Published paper (Refereed)
Abstract [en]

Pressurization (blower door) test is a well-established standardized method, performed in order to quantify the total leakage in a building envelope. However, blower door results are not adequate to use when air leakage through the building envelope during natural conditions (non-pressurized) is to be estimated. A common assumption made when estimating air leakage during natural conditions, is that air leakage paths are evenly distributed in the areas of the building envelope. This assumption gives quite poor calculation results since different leakage configurations are often situated unevenly in the envelope. In order to improve the correspondence between Blower door and air leakage model results, more information on the types and locations of the leakage paths are required as input to simulation models. 

This paper investigates if additional information from visual inspection and IR-thermography observations at site can increase the precision when simulating air change rates due to air leakage in natural conditions.  A numerical model is developed in this study by allocating leakage in various parts of the building envelope. The leakage allocation is based on visual inspection and IR-thermography observations at the site during the blower door test.

This procedure is tested in the case study of a large single zone church. Blower door, neutral pressure level measurement and leakage allocation results are used as input in the numerical model. Model results are compared with tracer gas measurements and result accuracy is compared with results from the Lawrence Berkeley Laboratory model (LBL) and the Alberta Air Infiltration Model (AIM-2) for the same church. 

Place, publisher, year, edition, pages
ASHRAE, 2016
Keyword
Air infiltration, Air leakage, Modeling, Churches.
National Category
Building Technologies
Identifiers
urn:nbn:se:hig:diva-22734 (URN)978-1-939200-48-8 (ISBN)
Conference
ASHRAE and AIVC IAQ 2016 — Defining Indoor Air Quality: Policy, Standards and Best Practices, 12–14 September 2016, Alexandria, Virginia
Projects
Church project
Funder
Swedish Energy Agency, 2011-002440
Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2017-06-29Bibliographically approved
3. Viewpoints on wind and air infiltration phenomena at buildings illustrated by field and model studies
Open this publication in new window or tab >>Viewpoints on wind and air infiltration phenomena at buildings illustrated by field and model studies
Show others...
2015 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, 504-517 p.Article in journal (Refereed) Published
Abstract [en]

Ventilation and infiltration caused by wind are difficult to predict because they are non-local phenomena: driving factors depend on the surrounding terrain and neighbouring buildings and on the building orientation with respect to the wind direction. Wind-driven flow through an opening is complex because wind can flow through the opening or around the building, in contrast to buoyancy driven flow. We explored wind and air infiltration phenomena in terms of pressure distributions on and around buildings, stagnation points, flow along façades, drag forces, and air flow through openings. Field trials were conducted at a 19th-century church, and wind tunnel tests were conducted using a 1:200 scale model of the church and other models with openings.

 

The locations of stagnation points on the church model were determined using particle image velocimetry measurements. Multiple stagnation points occurred. The forces exerted on the church model by winds in various directions were measured using a load cell. The projected areas affected by winds in various directions were calculated using a CAD model of the church. The area-averaged pressure difference across the church was assessed. A fairly large region of influence on the ground, caused by blockage of the wind, was revealed by testing the scale model in the wind tunnel and recording the static pressure on the ground at many points. The findings of this study are summarized as a number of steps that we suggest to be taken to improve analysis and predictions of wind driven flow in buildings.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Infiltration, Wind, Particle Image Velocimetry, Openings, Stagnation points, Drag force
National Category
Building Technologies
Identifiers
urn:nbn:se:hig:diva-19278 (URN)10.1016/j.buildenv.2015.05.001 (DOI)000358807800046 ()2-s2.0-84930645066 (Scopus ID)
Projects
Church project
Funder
Swedish Energy Agency, 34964-1
Available from: 2015-05-04 Created: 2015-05-04 Last updated: 2017-06-29Bibliographically approved
4. Single-sided ventilation through external doors: measurements and model evaluation in five historical churches
Open this publication in new window or tab >>Single-sided ventilation through external doors: measurements and model evaluation in five historical churches
2017 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 141, 114-124 p.Article in journal (Refereed) Published
Abstract [en]

Ventilation through open doors is a simple way to temporarily enhance ventilation of indoor spaces, with the purpose to evacuate indoor air pollutants or to adjust the indoor temperature. In churches and other historical buildings, which otherwise are ventilated only through air infiltration, temporarily enhanced ventilation through open doors or windows may be a prudent deed after e.g. services involving large congregations and burning of candles or incense. In the present study, the air exchange occurring at single-sided ventilation through the external doors of five historical churches is measured by tracer gas decay method. Further, air velocity measurements and smoke visualization in a doorway are performed. Measurement results are compared with predictions attained from four previously developed models for single‐sided ventilation. Models that include terms for wind turbulence yielded somewhat better predictions. According to the performed measurements, the magnitude of one hour single-sided open-door airing in a church is typically around 50% air exchange, indicating that this is a workable ventilation method, also for such large building volumes. A practical diagram to facilitate estimation of a suitable airing period is also presented. The study adds particularly knowledge to the issue of airing through doors, in large single zones.

Keyword
Natural ventilation, Single-sided ventilation, Historical buildings, Tracer gas field measurements, Model evaluation, Airing
National Category
Building Technologies
Identifiers
urn:nbn:se:hig:diva-23675 (URN)10.1016/j.enbuild.2017.02.034 (DOI)000400212400009 ()2-s2.0-85013648580 (Scopus ID)
Projects
Church project
Funder
Swedish Energy Agency, 2011-002440
Available from: 2017-02-24 Created: 2017-02-24 Last updated: 2017-06-29Bibliographically approved
5. A Study on Airing Through the Porches of a Historical Church – Measurements and IDA-ICE Modelling
Open this publication in new window or tab >>A Study on Airing Through the Porches of a Historical Church – Measurements and IDA-ICE Modelling
2016 (English)In: ASHRAE and AIVC IAQ 2016 - Defining Indoor Air Quality: Policy, Standards and Best Practices, 2016, ASHRAE, 2016, 216-223 p., C029Conference paper, Published paper (Refereed)
Abstract [en]

In churches, intentional airing may be a measure to evacuate temporarily high levels of contaminants that are emitted during services and other occasions. Crucial contaminants include moisture and other emissions that may deteriorate and/or soil painted surfaces and other precious artefacts. Most old churches do not have any mechanical ventilation system or any purpose provided openings for natural ventilation, but the ventilation is governed by air infiltration. Enhanced airing may be achieved by opening external windows or doors. Thus, models provided in energy simulation programs should predict this kind of air flows correctly, also in order to get a proper estimation of the total energy use. IDA-ICE is examined here and the model for air flow through a large vertical opening used in the program is investigated. In the present study, field measurements were performed for airing rate in a historical church. In comparison with measured air flow rates, the simulated results were of the same magnitude, but the effect of wind direction was less considered by the simulation program.

Place, publisher, year, edition, pages
ASHRAE, 2016
Keyword
Airing, Single-sided ventiltion, Simulation, IDA-ICE, Churches.
National Category
Building Technologies
Identifiers
urn:nbn:se:hig:diva-22747 (URN)978-1-939200-48-8 (ISBN)
Conference
ASHRAE and AIVC IAQ 2016 — Defining Indoor Air Quality: Policy, Standards and Best Practices, 12–14 September 2016, Alexandria, Virginia, USA
Projects
Church project
Funder
Swedish Energy Agency, 2011-002440
Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2017-06-29Bibliographically approved
6. A wind tunnel study of wind driven airing through doors
Open this publication in new window or tab >>A wind tunnel study of wind driven airing through doors
2017 (English)In: Article in journal (Other academic) Submitted
National Category
Building Technologies
Identifiers
urn:nbn:se:hig:diva-25112 (URN)
Available from: 2017-08-28 Created: 2017-08-28 Last updated: 2017-08-28Bibliographically approved

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