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Air gap method: measurements of airflow inside air gaps of walls
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.ORCID iD: 0000-0001-7073-2600
2008 (English)In: Structural Survey, ISSN 0263-080X, Vol. 26, no 4, 343-363 p.Article in journal (Refereed) Published
Abstract [en]

Purpose - Water damage is a severe problem in modern construction, causing economic loss and health implications. By using the patented Air Gap Method inside building constructions, harmful water in the construction can be dried out. The method drains and ventilates air gaps inside walls and floors with an airflow driven by thermal buoyancy caused by a heating cable in vertical air gaps. This paper aims to investigate this method and measurements of airflow inside air gaps of walls. Design/methodology/approach - This study investigates the measured correlation between the power of the heating cable, the difference of temperature inside and outside the air gap, and the airflow. Data are collected by experimentation with a full-scale constructed wall. Findings - The study finds that airflow increases with raised temperature difference between the air gap and room and with raised power of the heating cable. The measured airflow reaches values up to 140 m3/metre wall and day for one cable. A small increase in temperature, between 0.2 and 0.3 oC inside the vertical air gap results in an air flow of approximately 60 m3/metre wall and day. The air change rate per hour for the air inside the wall construction varies between 15 times for a 6 W/m cable and 37 times for a 16 W/m cable. Practical implications - The method provides the means to build houses in a more robust way, minimising the negative effects of water damage. This investigation provides an understanding of how temperature and ventilation are related in this method of construction. Originality/value - The issue of ventilated construction is rarely investigated in scientific research.

Place, publisher, year, edition, pages
2008. Vol. 26, no 4, 343-363 p.
Keyword [en]
Air diffusion; Buildings; Humidity; Temperature measurement; Water
National Category
Building Technologies
Identifiers
URN: urn:nbn:se:kth:diva-9488DOI: 10.1108/02630800810906584Scopus ID: 2-s2.0-51849151932OAI: oai:DiVA.org:kth-9488DiVA: diva2:114181
Note

QC 20100622

Available from: 2008-11-07 Created: 2008-11-07 Last updated: 2012-09-28Bibliographically approved
In thesis
1. Heated air gaps: a possibility to dry out dampness from building constructions
Open this publication in new window or tab >>Heated air gaps: a possibility to dry out dampness from building constructions
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The air gap method is a modification of the common way of building indoor walls and floors. The aim of the method is to make a construction, less fragile to water damage, with air gaps where moisture can be removed with a thermally driven air flow, caused by a heating cable. The thesis includes a number of experimental studies of this method.

Temperature and convective air flow in a vertical air gap was studied and it was noted how air flow increased with raised power of the heating cable. The air flow for one meter of wall varied between 50 m3/day (13 air changes per hour) and 140 m3/day (36 air changes per hour). The lower value was caused by a temperature difference in the range 0.2-0.3 oC. Without heating no air flow was found.

In studies of moisture and RH in wet “slab on ground” constructions, it was noted how the slab in the room with the air gap method dried to a much higher extent than the slab in the room built in an ordinary way. It was also noted that moisture was transported from the air gap in the floor and up through the air gap in the wall. In the room with the air gap construction, the RH values beneath the floor was at a lower level (and below 75 % RH) than the RH values beneath the floor of conventional construction. Mould does not grow below 75 % RH.

In the study of a flooded intermediate floor it was noted how the thermally driven convective air flow evidently speeded up drying of the construction. Mould growth was only noted in the case where the heating cables were turned off.

Abstract [sv]

Spaltmetoden är en modifiering av det reguljära sättet av att bygga innerväggar och bjälklag. Syftet med metoden är att skapa en byggnadskonstruktion som är mindre skör med avseende på fuktskador. Detta görs med spalter där fukt kan avlägsnas genom ett termiskt drivet luftflöde som orsakas av en värmekabel. Denna avhandling innehåller ett antal experimentella studier på metoden. Spaltmetoden har studerats med avseende på 1. Samband mellan temperatur och luftflöde, 2. Uttorkning och RF nivåer i golvkonstruktioner samt 3. Översvämning av ett mellanbjälklag

1. Samband mellan temperatur och luftflöde

Temperatur och konvektivt luftflöde har studerats i en vertikal spalt och resultatet visar att luftflödet ökar med ökad effekt hos värmekabeln. Luftflödet i en vägg med en meters bredd varierade mellan 50 kubikmeter/dag (13 luftväxlingar per timme) och 140 kubikmeter/dag (36 luftväxlingar per timme). Det lägre flödet orsakades av en temperaturskillnad på 0,2-0,3 oC mellan luftspalt och rum. När värmekabeln var avstängd så registrerades inget luftflöde.

2. Uttorkning och RF nivåer i golvkonstruktioner ovan betongplatta

Detta experiment visade att fukt har transporterats från spalten i golvet genom spalten i väggen ut i rumsluften. I spaltkonstruktion var RF inuti golvkonstruktionen lägre (och understeg 75 % RF), jämfört med den konventionella konstruktionen, (mögel växer inte under 75 % RF). Det har också registrerats att betongplattan som hörde till spaltmetoden torkade ut snabbare än betongplattan som var inbyggd i ett gängse rum.

3. Översvämning av ett mellanbjälklag

I studien där ett mellanbjälklag blev översvämmat noterades att spaltmetoden förkortade torktiden från 21 dagar till 13 vid den fuktigaste mätpunkten. Mögelväxt noterades endast då värmekabeln hade varit frånslagen. 

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 53 p.
Series
Meddelande. Institutionen för byggvetenskap, ISSN 1651-5563 ; 202
Keyword
Water damage, convection, air gap, building, construction
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-9490 (URN)
Presentation
2008-11-07, B1, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Supervisors
Note
QC 20101101Available from: 2008-11-07 Created: 2008-11-07 Last updated: 2010-11-01Bibliographically approved
2. Air Gap Method: Air-Gaps in Building Construction to avoid Dampness & Mould
Open this publication in new window or tab >>Air Gap Method: Air-Gaps in Building Construction to avoid Dampness & Mould
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 55 p.
Keyword
humidity, air gaps, water damage, convection, building, construction
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-102873 (URN)978-91-7501-485-2 (ISBN)
Public defence
2012-10-12, B 1, Brinellvägen 23, KTH, Stockholm, 13:00 (Swedish)
Opponent
Supervisors
Note

QC 20120928

Available from: 2012-09-28 Created: 2012-09-27 Last updated: 2012-09-28Bibliographically approved

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