ADVANCED COMPUTATIONAL MODELS FOR RADON TRANSPORT AT SOIL-BUILDING INTERFACE

Botos M.L et al.

Programul Operațional Competitivitate 2014-2020, Axa prioritară POC-A1-A1.1.4-E-2015Titlul Proiectului: Sisteme inteligente privind siguranța populației prin controlul şi reducerea expunerii la radon corelate cu optimizarea eficienţei energetice

a locuinţelor din aglomerări urbane importante din România - SMART-RAD-ENNr. contract: 22/01.09.2016, cod proiect: ID P_37_229, cod MySmis: 103427

Beneficiar: Universitatea „Babeş-Bolyai” din Cluj-NapocaProiect cofinanţat din Fondul European de Dezvoltare Regională prin Programul Operaţional Competitivitate 2014-2020

The project

Nr. contract: 22/01.09.2016, cod proiect: ID P_37_229, cod MySmis: 103427Beneficiar: Universitatea „Babeş-Bolyai” din Cluj-Napoca

Proiect cofinanţat din Fondul European de Dezvoltare Regională prin Programul Operaţional Competitivitate 2014-2020

OBJECTIVE 3. Developing energy efficient solutions forcontrolling and reducing exposure to radon and other householdair pollutants in residential buildings:(1) An integrated system for advanced numerical modelling aided byexperiment(2) Mitigation: remedial actions, energy-efficient solutions-2019 – 2020: 10 houses beneficiaries with high exposure to radon(CRn > 300 Bq/m3)

OBJECTIVE 4. Technology transfer activities2020:

- Evaluation of efficiency- Exploitation of results

Introduction

Keywords : efficient numerical experiments

Simplify, simplify, simplify

find symmetries

limit the extent of your model

replace sources with analytical solutions

eliminate unnecessary details

eliminate elements having a low impact on radon transport

try to find equivalent models

reduce (if possible) your model to 2 dimensions

MethodsSoil gas – radon source

Finite elements methods (FEM)()

Generalized quadrature method (GQM)

Finite difference method(FDM)()

Finite analytical method (FAM)

Approach

Discrete crack method (DCM)

Equivalent continuum method (ECM)

Explicit (DCE) Lumped (LC)Real (DCR)volume averaging

(ECM_va) (ECM)

Discrete crack method – Real (DCR)

• Advantages: closest to the real entrance model• Disadvantages:

• A large number of integration nodes to obtain convergence

• Requires the exact position of all fissures• Needs expensive/inaccessible hardware and

software to solve• Time and resource consuming

Discrete crack method – explicit (DCE)• DCE=DCR-(Slab+Walls)

• Advantages: close to the real entrance model• Disadvantages:

• A large number of integration nodes• Requires the exact position of all fissures• Needs expensive/inaccessible hardware and

software to solve produce quality meshing• Time and resource consuming • Slow convergence process

Equivalent Continuum Method – (ECM) • ECM=DCR-(Slab+Walls+Crack)+Equivalent element• ECM=DCE-Crack+Equivalent element

Advantages: Doesn't require the exact position of fissuresCan be used to run sensitivity and parametric studies

Disadvantages: Time and resource consuming for transient modelingFlow trough gaps need to be laminar!!

ProblemHouse studied by Saâdi and Marie (2018):

• basement area 5×5 m2

• Basement volume 125 m3

• Crack width 1 mm;• Perimetral crack, total length 20 m• Air exchange in basement 1.39e-5 s-1

Slab : thickness 0.15 mpermeability: 1e-20 m2

porosity 0.2304

Wall : thickness 0.15 mpermeability 1e-17 m2

porosity 0.2304

Aggregates: thicknes 0.50 mpermeability 1e-8 m2

porosity 0.17• Effective diffusion coefficient calculated using tortuosity factor model of (Millington and Quirk 1961)• Equivalent hydraulic resistance through the fissure calculated using by analogy to Darcy law (Lamb 1932)• Inside air radon concentration is calculated by solving at end of each iteration mass-balance equation.• Steady conditions. Suction applied on the entrance interface -5 Pa.• Soil considered dry and homogeneous.

Problem

• Input parameters defining soil radon source, and soil physicalcharacteristics used :

3D-steady - Results:

• Issues: over 6 millions elements!!! Runtime: >2 days!!!!

3D Ansys FluentDCR

Tough2/EOS7Rn (Saadi, 2018)DCR

Ansys FluentDCE

Tough2/EOS7Rn (Saadi, 2018)DCE

C int [Bq m-3] 6.58 5.56 5.71 3.50

2D Model

• Build 2D model from one symmetry cross-section

To calculate the inside concentration we need to extend the 2D results to the 3D:• Radon unit mass flow is obtained by

integrating massflux (convective and diffusive) along the crack’s width and slab’s length on the 2D symmetry cross-section .

• Finding the total mass flow can be done considering the crack massflow constant along the length and on the slab varying linear

• DCR 2D Steady DCE 2D Steady ECM 2D Steady

Ansys DCR - 3D

Ansys DCR - 2D

Tough2/EOS7Rn (Saadi, 2018) DCR

Ansys DCE - 3D

Ansys DCE - 2D

Tough2/EOS7Rn (Saadi, 2018) DCE

Tough2/EOS7Rn (Saadi, 2018) ECM

AnsysECM_va2D

C int [Bq m-3] 6.58 5.81 5.56 5.71 1.34 3.50 5.22 0.21

AnsysECM 2D

10.65

Transient problem• 2D simulations were made on the same objective, the same source of radon but for the unsteady

problem. • Measured variable suctions were applied on ~9 days period of time.• Simulations for three types of soils (permeabilities in range of 10-12-10-8 and porosity between 0.5 an

0.17), using Ansys and four approaches (DCR, DCE, ECM_va, ECM)• The integration time steps constant and set to 60s. (~13500-time steps).• Inside concentration was calculated using explicit forward FDM applied on the mass-balance equation.

(Saadi,2018)

Results:

(Saadi,2018)

Results:

(Saadi,2018)Advantage: less 5000 elements!!! Runtime: <6 hours !!!!

Conclusions:

• 2D simulations can be used to make predictions on inside radon concentrations, based on the evolution of boundary conditions.

• The method is useful in case of integrated diagnose, measurements can be accompanied by parametric studies.

• Response surface method can be applied to find some important unknowns (cracks total area, air tidenes, neutral plane position).

• Once the model is set and calibrated can be used to optimize the energy consumption of remedial solutions applied to different objectives.

• Independent FEM applications can be developed and make the method more accessible:

Thank you!www.smartradon.ro

Nr. contract: 22/01.09.2016, cod proiect: ID P_37_229, cod MySmis: 103427Beneficiar: Universitatea „Babeş-Bolyai” din Cluj-Napoca

Proiect cofinanţat din Fondul European de Dezvoltare Regională prin Programul Operaţional Competitivitate 2014-2020