Advanced

Benefits of Investigating the Thermal Component for Moisture Safety in Ventilated Attics

Claesson, Johan LU and Wallentén, Petter LU (2020) 12th Nordic Symposium on Building Physics, NSB 2020 In E3S Web of Conferences 172.
Abstract

Cold ventilated attics often have mould problems in Sweden. This is valid both for old and sometimes newly built attics. Increased insulation on the attic floor is assumed to increase the problem. To investigate this, numerical 1D models like WUFI or WUFI+ are typically used. These models give results but the physical processes are not so transparent for the user due to the complex numerical techniques involved and takes a long time to simulate. The problem is mainly related to the temperature in the attic, the ventilation rate and possible of leaks from the living space. All exposed surfaces in the attic will buffer moisture variations. But if this buffering is neglected and the leakage is treated as a constant the moisture content in... (More)

Cold ventilated attics often have mould problems in Sweden. This is valid both for old and sometimes newly built attics. Increased insulation on the attic floor is assumed to increase the problem. To investigate this, numerical 1D models like WUFI or WUFI+ are typically used. These models give results but the physical processes are not so transparent for the user due to the complex numerical techniques involved and takes a long time to simulate. The problem is mainly related to the temperature in the attic, the ventilation rate and possible of leaks from the living space. All exposed surfaces in the attic will buffer moisture variations. But if this buffering is neglected and the leakage is treated as a constant the moisture content in the attic is only dependent on the ventilation with outside air and the assumed leakage. This would make a pure thermal investigation meaningful. An analytical model for the thermal problem was developed that took into account radiation between the interior surfaces and the different boundary conditions at the outside and inside surfaces. Using this model a parameter study of exterior roofing insulation was done using a moisture transport model that only took into account convection exchange. The results were compared with WUFI Pro and WUFI+ simulations which included the moisture exchange between air and internal surfaces. The comparison showed that the pure thermal model gave, as expected, larger variations in relative humidity, but that the results were qualitatively very similar. This indicates that analytical solutions of thermal problems can be used as a base in qualitative investigations of certain combined heat and moisture problems.

(Less)
Please use this url to cite or link to this publication:
author
and
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
host publication
12th Nordic Symposium on Building Physics (NSB 2020)
series title
E3S Web of Conferences
volume
172
article number
23001
conference name
12th Nordic Symposium on Building Physics, NSB 2020
conference location
Tallinn, Estonia
conference dates
2020-09-06 - 2020-09-09
external identifiers
  • scopus:85088456730
ISSN
2555-0403
DOI
10.1051/e3sconf/202017223001
language
English
LU publication?
yes
id
d857a266-9e75-48ba-85f8-0c9e656f8972
date added to LUP
2020-08-05 07:52:56
date last changed
2020-08-12 09:09:26
@inproceedings{d857a266-9e75-48ba-85f8-0c9e656f8972,
  abstract     = {<p>Cold ventilated attics often have mould problems in Sweden. This is valid both for old and sometimes newly built attics. Increased insulation on the attic floor is assumed to increase the problem. To investigate this, numerical 1D models like WUFI or WUFI+ are typically used. These models give results but the physical processes are not so transparent for the user due to the complex numerical techniques involved and takes a long time to simulate. The problem is mainly related to the temperature in the attic, the ventilation rate and possible of leaks from the living space. All exposed surfaces in the attic will buffer moisture variations. But if this buffering is neglected and the leakage is treated as a constant the moisture content in the attic is only dependent on the ventilation with outside air and the assumed leakage. This would make a pure thermal investigation meaningful. An analytical model for the thermal problem was developed that took into account radiation between the interior surfaces and the different boundary conditions at the outside and inside surfaces. Using this model a parameter study of exterior roofing insulation was done using a moisture transport model that only took into account convection exchange. The results were compared with WUFI Pro and WUFI+ simulations which included the moisture exchange between air and internal surfaces. The comparison showed that the pure thermal model gave, as expected, larger variations in relative humidity, but that the results were qualitatively very similar. This indicates that analytical solutions of thermal problems can be used as a base in qualitative investigations of certain combined heat and moisture problems.</p>},
  author       = {Claesson, Johan and Wallentén, Petter},
  booktitle    = {12th Nordic Symposium on Building Physics (NSB 2020)},
  issn         = {2555-0403},
  language     = {eng},
  series       = {E3S Web of Conferences},
  title        = {Benefits of Investigating the Thermal Component for Moisture Safety in Ventilated Attics},
  url          = {http://dx.doi.org/10.1051/e3sconf/202017223001},
  doi          = {10.1051/e3sconf/202017223001},
  volume       = {172},
  year         = {2020},
}