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Heated air gaps: a possibility to dry out dampness from building constructions
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
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 [en]
Water damage, convection, air gap, building, construction
National Category
Building Technologies
Identifiers
URN: urn:nbn:se:kth:diva-9490OAI: oai:DiVA.org:kth-9490DiVA: diva2:114183
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
List of papers
1. Air gaps in building construction avoiding dampness and mould
Open this publication in new window or tab >>Air gaps in building construction avoiding dampness and mould
2008 (English)In: Structural Survey, ISSN 0263-080X, E-ISSN 1758-6844, Vol. 26, no 3, 242-255 p.Article in journal (Refereed) Published
Abstract [en]

Purpose - Water damage is a severe problem in modern construction, causing economic loss and health implications. The patented Air Gap Method, which is a slight modification of the common infill wall construction, provides means to build houses in a more robust way, minimizing the negative effects of water damage. This full-scale study of the method aims to show how walls and floors may be built to create ventilation within the construction, with air gaps equipped with heating cables. The general hypothesis is that the patented Air Gap Method drains and evaporates dampness after water damage. The purpose of this study is to show how the method is built and how the method deals with water damage, such as a flooding, and with mould growth. Design/methodology/approach - The Air Gap Method is based on a common timber-framed construction and is completed by the provision of inlets, air gaps, slits, and outlets. The power for the convective airflow is given by an electrical heating cable. The study was carried out as a full-scale experiment using a 24m2 large apartment build by this method. This apartment was flooded with 120 litres of domestic wastewater and the drying period was compared when heating cables were switched on or not. Mould growth was also investigated. Findings - The method dries out a flooded floor in nine days when two heating cables were switched on, in 13 days with one heating cable and 21 days when the heating cables were off. The method prevents all mould growth provided that the indoor RH is lower than 65 per cent. Practical implications - The method provides means to build houses in a more robust way, minimizing the negative effects of water damage. Originality/value - The issue of ventilated construction is rarely investigated in scientific research.

Keyword
Building conservation; Buildings; Heating and ventilation services; Humidity; Water
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-9487 (URN)10.1108/02630800810887126 (DOI)2-s2.0-47949099064 (Scopus ID)
Note

QC 20100622

Available from: 2008-11-07 Created: 2008-11-07 Last updated: 2017-12-14Bibliographically approved
2. Air gap method: measurements of airflow inside air gaps of walls
Open this publication in new window or tab >>Air gap method: measurements of airflow inside air gaps of walls
2008 (English)In: Structural Survey, ISSN 0263-080X, E-ISSN 1758-6844, 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.

Keyword
Air diffusion; Buildings; Humidity; Temperature measurement; Water
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-9488 (URN)10.1108/02630800810906584 (DOI)2-s2.0-51849151932 (Scopus ID)
Note

QC 20100622

Available from: 2008-11-07 Created: 2008-11-07 Last updated: 2017-12-14Bibliographically approved

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