# BS EN 15026-2007

BRITISH STANDARD BS EN 15026:2007 Hygrothermal performance of building components and building elements — Assessment of moisture transfer by numerical simulation The European Standard EN 15026:2007 has the status of a British Standard ICS 91.120.10; 91.080.01 BS EN 15026:2007 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 August 2007 © BSI 2007 ISBN 978 0 580 54741 6 National foreword This British Standard is the UK implementation of EN 15026:2007. The UK participation in its preparation was entrusted to Technical Committee B/540, Energy performance of materials components and buildings. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Amendments issued since publication Amd. No. Date CommentsEUROPEANSTANDARD NORMEEUROPÉENNE EUROPÄISCHENORM EN15026 April2007 ICS91.080.01 EnglishVersion Hygrothermalperformanceofbuildingcomponentsandbuilding elementsAssessmentofmoisturetransferbynumerical simulation Performancehygrothermiquedescomposantsetparoisde bâtimentsEvaluationdutransfertd humiditépar simulationnumérique WärmeundfeuchtetechnischesVerhaltenvonBauteilen undBauelementenBewertungderFeuchteübertragung durchnumerischeSimulation ThisEuropeanStandardwasapprovedbyCENon28February2007. CENmembersareboundtocomplywiththeCEN/CENELECInternalRegulationswhichstipulatetheconditionsforgivingthisEurope an Standardthestatusofanationalstandardwithoutanyalteration.Uptodatelistsandbibliographicalreferencesconcernings uchnational standardsmaybeobtainedonapplicationtotheCENManagementCentreortoanyCENmember. ThisEuropeanStandardexistsinthreeofficialversions(English,French,German).Aversioninanyotherlanguagemadebytra nslation undertheresponsibilityofaCENmemberintoitsownlanguageandnotifiedtotheCENManagementCentrehasthesamestatusas the officialversions. CENmembersarethenationalstandardsbodiesofAustria,Belgium,Bulgaria,Cyprus,CzechRepublic,Denmark,Estonia,Finland, France,Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Poland,P ortugal, Romania,Slovakia,Slovenia,Spain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTANDARDIZATION COMITÉEUROPÉENDENORMALISATION EUROPÄISCHESKOMITEEFÜRNORMUNG ManagementCentre:ruedeStassart,36B1050Brussels ©2007CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.EN15026:2007:EEN 15026:2007 (E) 2 Contents Page Foreword3 Introduction .4 1 Scope5 2 Normative references6 3 Terms, definitions, symbols and units 6 3.1 Terms and definitions .6 3.2 Symbols and units.6 4 Hygrothermal equations and material properties 8 4.1 Assumptions8 4.2 Transport of heat and moisture9 4.3 Material properties.11 5 Boundary conditions.13 5.1 Internal conditions.13 5.2 External conditions14 6 Documentation of input data and results15 6.1 General15 6.2 Problem description15 6.3 Hygrothermal model and numerical solution .16 6.4 Calculation report16 Annex A (normative) Benchmark example – Moisture uptake in a semi-infinite region .18 A.1 General18 A.2 Problem description18 A.3 Results19 Annex B (informative) Design of Moisture Reference Years 22 Annex C (informative) Internal boundary conditions 23 Bibliography 24 EN 15026:2007 (E) 3 Foreword This document (EN 15026:2007) has been prepared by Technical Committee CEN/TC 89 “Thermal performance of buildings and building components”, the secretariat of which is held by SIS. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by October 2007, and conflicting national standards shall be withdrawn at the latest by October 2007. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard : Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EN 15026:2007 (E) 4 Introduction This standard defines the practical application of hygrothermal simulation software used to predict one- dimensional transient heat and moisture transfer in multi-layer building envelope components subjected to non steady climate conditions on either side. In contrast to the steady-state assessment of interstitial condensation by the Glaser method (as described in EN ISO 13788), transient hygrothermal simulation provides more detailed and accurate information on the risk of moisture problems within building components and on the design of remedial treatment. While the Glaser method considers only steady-state conduction of heat and vapour diffusion, the transient models covered in this standard take account of heat and moisture storage, latent heat effects, and liquid and convective transport under realistic boundary and initial conditions. The application of such models has become widely used in building practice in recent years, resulting in a significant improvement in the accuracy and reproducibility of hygrothermal simulation. The following examples of transient, one-dimensional heat and moisture phenomena in building components can be simulated by the models covered by this standard: drying of initial construction moisture; moisture accumulation by interstitial condensation due to diffusion in winter; moisture penetration due to driving rain exposure; summer condensation due to migration of moisture from outside to inside; exterior surface condensation due to cooling by longwave radiation exchange; moisture-related heat losses by transmission and moisture evaporation. The factors relevant to hygrothermal building component simulation are summarised below. The standard starts with the description of the physical model on which hygrothermal simulation tools are based. Then the necessary input parameters and their procurement are dealt with. A benchmark case with an analytical solution is given for the assessment of numerical simulation tools. The evaluation, interpretation and documentation of the output form the last part. Inputs • Assembly, orientation and inclination of building components • Hygrothermal material parameters and functions • Boundary conditions, surface transfer for internal and external climate • Initial condition, calculation period, numerical control parameters Outputs • Temperature and heat flux distributions and temporal variations • Water content, relative humidity and moisture flux distributions and temporal variations Post processing • Energy use, economy • heat transport by moisture-dependent thermal conduction; • latent heat transfer by vapour diffusion; • moisture storage by vapour sorption and capillary forces; • moisture transport by vapour diffusion; • moisture transport by liquid transport (surface diffusion and capillary flow). The equations described in this standard account for the following climatic variables: • internal and external temperature; • internal and external humidity; • solar and longwave radiation; • precipitation (normal and driving rain); • wind speed and direction. The hygrothermal equations described in this standard shall not be applied in cases where: • convection takes place through holes and cracks; • two-dimensional effects play an important part (e.g. rising damp, conditions around thermal bridges, effect of gravitational forces); • hydraulic, osmotic, electrophoretic forces are present; • daily mean temperatures in the component exceed 50 °C. EN 15026:2007 (E) 6 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 12664, Thermal performance of building materials and products — Determination of thermal resistance by means of guarded hot plate and heat flow meter methods — Dry and moist products of medium and low thermal resistance EN 12667, Thermal performance of building materials and products — Determination of thermal resistance by means of guarded hot plate and heat flow meter methods — Products of high and medium thermal resistance EN 12939, Thermal performance of building materials and products — Determination of thermal resistance by means of guarded hot plate and heat flow meter methods — Thick products of high and medium thermal resistance EN ISO 7345, Thermal insulation – Physical quantities and definitions (ISO 7345:1987) prEN ISO 9346:2005, Hygrothermal performance of buildings and building materials - Mass transfer - Physical quantities and definitions (ISO/DIS 9346:2005) prEN ISO 10456, Building materials and products - Hygrothermal properties -Tabulated design values and procedures for determining declared and design thermal values (ISO/DIS 10456:2005) EN ISO 12571, Hygrothermal performance of building materials and products – Determination of hygroscopic sorption properties (ISO 12571:2000) EN ISO 12572, Hygrothermal performance of building materials and products – Determination of water vapour transmission properties (ISO 12572:2001) prEN ISO 15927-3, Hygrothermal performance of buildings - Calculation and presentation of climatic data - Part 3: Calculation of a driving rain index for vertical surfaces from hourly wind and rain data (ISO/DIS 15927- 3:2006) 3 Terms, definitions, symbols and units 3.1 Terms and definitions For the purposes of this document, the terms and definitions given in prEN ISO 9346:2005 and EN ISO 7345 apply. Other terms used are defined in the relevant clauses of this standard. 3.2 Symbols and units Symbol Quantity Unit c mspecific heat capacity of dry material J/(kg⋅K) c wspecific heat capacity of liquid water J/(kg⋅K) D wmoisture diffusivity m 2 /s E soltotal flux density of incident solar radiation W/m 2EN 15026:2007 (E) 7 g density of moisture flow rate kg/(m²⋅s) g pdensity of moisture flow rate of available water from precipitation kg/(m²⋅s) g vdensity of water vapour flow rate kg/(m²⋅s) g wdensity of liquid water flow rate kg/(m²⋅s) g w,maxdensity of water flow rate which can be absorbed at the surface of a material kg/(m²⋅s) h surface heat transfer coefficient W/(m 2 ⋅K) h cconvective heat transfer coefficient W/(m 2 ⋅K) h especific latent enthalpy of evaporation or condensation J/kg h rradiative heat transfer coefficient W/(m 2 ⋅K) K liquid conductivity s/m p aambient atmospheric pressure Pa p sucsuction pressure Pa p vpartial water vapour pressure Pa p v,apartial water vapour pressure in the air Pa p v,spartial water vapour pressure at a surface Pa p v,satsaturated water vapour pressure Pa p wwater pressure inside pores Pa q density of heat flow rate W/m 2q latdensity of latent heat flow rate W/m 2q sensdensity of sensible heat flow rate W/m 2R wliquid moisture flow resistance of interface m/s R H2Ogas constant of water vapour J/(kg⋅K) s d,sequivalent vapour diffusion thickness of a surface layer m T thermodynamic temperature K T aair temperature of the surrounding environment K T eqequivalent temperature of the surrounding environment K EN 15026:2007 (E) 8 T rmean radiant temperature of the surrounding environment K T surfsurface temperature K t time s v wind speed m/s w moisture content kg/m 3x distance m α solsolar absorptance - δ 0vapour permeability of still air kg/(m⋅s⋅Pa) δ pvapour permeability of material kg/(m⋅s⋅Pa) ε longwave emissivity of the external surface - λ thermal conductivity W/(m⋅K) ϕ relative humidity - µ diffusion resistance factor - ρ adensity of air kg/m³ ρ mdensity of solid matrix kg/m³ ρ wdensity of liquid water kg/m³ σ sStefan-Boltzmann constant W/(m 2 ⋅K 4 ) 4 Hygrothermal equations and material properties 4.1 Assumptions The hygrothermal equations specified in the following clauses contain the following assumptions: • constant geometry, no swelling and shrinkage; • no chemical reactions are occurring; • latent heat of sorption is equal to latent heat of condensation/evaporation; • no change in material properties by damage or ageing; • local equilibrium between liquid and vapour without hysteresis; • moisture storage function is not dependent on temperature; • temperature and barometric pressure gradients do not affect vapour diffusion. The development of the equations is based on the conservation of energy and moisture. The mathematical expression of the conservation laws are the balance equations. The conserved quantity changes in time, only if it is transported between neighbouring control volumes. EN 15026:2007 (E) 9 Heat conservation shall be expressed by () () x q q t T w c c ∂ + ∂ − = ∂ ∂ ⋅ ⋅ + ⋅ lat sens w m m ρ (1) The increase of the moisture content of a control volume shall be determined by the net inflow of moisture. The moisture flow rate equals the sum of the vapour flow rate and the flow rate of liquid water. x g t w ∂ ∂ − = ∂ ∂(2) l v g g g + =(3) The relative humidity shall be defined by the following equation: () T p p sat v, v = ϕ (4) The pressure acting on the water inside a building material due to the capillary forces is different from the pressure of the surrounding air. The difference is called suction. p suc= p a- p w(5) The suction of the pore water is related to the relative humidity of the surrounding air by the Kelvin equation: p suc= -ρ w R H2OT lnϕ (6) The relation between the state variables ϕ, p v , p suc , T and the moisture content of a building material is defined by the moisture storage function. The moisture storage function of a building material shall be expressed either as the moisture content as a function of suction (suction curve), w(p suc ), or as the moisture content as a function of the relative humidity (sorption curve), w(ϕ). 4.2 Transport of heat and moisture 4.2.1 Heat transport 4.2.1.1 Heat transport inside materials Heat transport shall be composed of sensible and latent components. Sensible heat transport shall be calculated with Fourier’s law with a thermal conductivity which depends on moisture content. x T w q ∂ ∂ ⋅ − = ) ( sens λ (7) Latent heat transport shall be calculated by the following equation: v e lat g h q = (8) 4.2.1.2 Heat transport across boundaries The heat flow from the surrounding environment into the construction consists