1. Experimental Investigation of
Heat and Moisture Transfer in Multidimensional
Building Envelope Details
Ali Vaseghi- MASc Candidate
Dr. Fitsum Tariku-Supervisor
Acknowledgements
Natural Sciences and Engineering Research Council of Canada (NSERC) and the School of Construction and the Environment at the British Columbia Institute of Technology (BCIT)
Building Science Graduate Program
INTRODUCTION
OBJECTIVE
c) Air Conditioning System
Simulates various boundary conditions
Exterior boundary condition:
Seasonal dynamic condition
Interior boundary condition: material
lab air condition (45-55% RH, 21°C)
Buildings consume a significant amount of energy for space heating and cooling. According to NRCan (2011), about two-third of residential and half of commercial and institutional buildings’ energy use are for space conditioning. Transmission heat loss through building envelope components constitute the major portion of the space thermal load (heating and cooling loads). Heat flow and moisture transfer phenomena in multidimensional details are different than in regions such as mid-point of wall (1D). In complex 3D details of building envelope, highly conductive structural materials and poor thermal insulations create structural thermal bridging. Ignoring or representing the thermal bridging and moisture transfer effects in a simplistic manner by designers or energy simulation tools leads to errors in whole building energy performance results and interior surface temperature predictions, which in turn has an impact on thermal comfort, condensation, mould formation and HVAC design. The errors will be magnified with high thermal mass and complex building envelope details.
As the need for more energy efficient buildings increases so does the need for more accurate modeling tools. Unfortunately, very little experimental research has been conducted on effect of coupled heat and moisture transfer in complex building envelop details. In this project, the transient multi-dimensional thermal and moisture transfer phenomena in a number of common three-dimensional (3D) building envelope details will be investigated through laboratory experiments. The experimental data will be used for calculating the equivalent thermal mass and heat resistance, and estimating an accurate transient heat transfer value and method for each test specimens. In a separate project, the benchmarked values will be used to develop a procedure for incorporating thermal bridge effects in Hygrothermal models.
d) Instrumentation
Test specimens: Moisture pin, RH and
temperature sensors and heat flux
transducer
Inside the experimental chamber:
temperature and RH sensors to
monitor the test condition
METHODOLOGY
Test specimens of common building envelope details that are known to have significant thermal bridges such as wall/floor slab, wall/balcony, wall/roof, exterior walls corners and parapet and roof intersections will be fabricated. The specimens will be instrumented with heat flux transducers, temperature, relative humidity and moisture content measurement sensors and will be mounted on an environmental chamber. The thermal and moisture transfer through the specimens under different indoor and outdoor boundary conditions will be measured. The experimental data will be analyzed to quantify the heat loss and the risk of moisture condensation on the building envelope details.
EXPECTED FINDINGS
A series of measurements will be
carried out in the environmental
chamber
Heat flow and moisture transfer of
critical Regions will be extracted from
recorded Data through DAQ
Transient heat transfer coefficients of
specimens over the dynamic behavior of heat and moisture
transmittance will be drawn
Results fed to hygrothermal model (HAMFit) to validate the data as well as the model
Mould growing on interior wall corner
Intersection of walls to slab
Whole building 3D isothermal map (antherm)
Infrared photography of test specimen
Current Calculation of Linear Transmittance & Effective U-value
Linear transmittance is the additional heat flow caused by linear building envelope components such as corners, slab edges, parapets and transitions between assemblies. The linear transmittance and overall effective U-value for any building envelope section are calculated as below:
Experimental setup
a) Test Specimens
corner wall
wall/floor slab,
wall/balcony slab
wall/roof ,
Hour
b) Experimental Chamber
Where:
U= Total effective assembly thermal transmittance (W/m2K)
U0= Clear field thermal transmittance (W/m2K)
Atotal= The total opaque wall area (m2)
L= Length of linear thermal bridge (m)
Ψ= Linear transmittance-thermal bridge (W/mK)
χ = Point transmittance-thermal bridge (W/K)
U= Assembly thermal transmittance with thermal bridge (W/m2K)
Q= Assembly heat flow with thermal bridge (W/K)
Q0= Clear field heat flow (W/K)
BCIT material lab
Test specimens placed inside the
the chamber
Exterior: galvanized sheet metal
Interior: 3” XPS
Air sealed
Hour
Linear transmittance of a floor slab
Clear Field wall