Thermal transmittance Properties of constructions Thermal transmittance

Thermal transmittance basic thermal property of building construction This simple formula can be used for constructions without thermal bridges! [W/(m2K)] internal surface resistance external surface resistance thermal resistance layer thickness thermal conductivity [m2K/W]

Thermal transmittance Requirements of ČSN 730540-2:

dew point temperature (in following lectures) Thermal transmittance Requirements of ČSN 730540-2: dependent on internal RH and on prevailing design internal temperature: table from 18 to 22 C other temperatures up to 60 % over 60 % eliminition of internal surface condensation: dew point temperature (in following lectures)

Thermal transmittance Requirements of ČSN 730540-2: dependent on internal RH and on prevailing design internal temperature: table from 18 to 22 C other temperatures up to 60 % over 60 % eliminition of condensation: recalculation:

Thermal transmittance Requirements of ČSN 730540-2: basic table values:

Thermal transmittance Requirements of ČSN 730540-2: for refurbished buildings: same values as for new buildings exceptions: historical buildings with status of monuments provable technical or legislative problems alternative for large floor constructions adjacent to ground: transmission heat loss accord. to EN ISO 13370 for Δθ = θim- θe requirement according to ČSN 730540-2

Thermal transmittance Evolution of requirements: revisions

Thermal transmittance Calculation (EN ISO 6946): Rules for inclusion of layers: thin layers can be omitted (foils, membranes) - only internal deck in ventilated constr. [m2K/W] only layers under waterproofing with exception: inverted roofs only layers above waterproofing in floors (excp.: XPS)

Thermal transmittance Calculation (EN ISO 6946): [m2K/W] Thermal conductivity [W/(m.K)]: it characterizes the ability to conduct heat it depends on number of air voids … (thermal conductivity is usually lower for materials with lower density; exception: mineral wool) … and on ratio between heat transfer in voids and in material frame itself for isotropic materials the same in all directions; otherwise different (timber, hollow bricks)

Thermal transmittance Calculation (EN ISO 6946): every material has specific dependence (various curves) water (better conductor than air, λ = 0,5 až 0,7) [m2K/W] Thermal conductivity [W/(m.K)]: depends on moisture (significant increase) and temperature (moderate increase, mainly for high temperatures, not important for BP) bult-in state (compression, moisturizing) Producers present declared values – cannot be used directly – recalculation necessary! If some data missing, increase declared value for approx. 10 %. for calculations: characteristic value (internal constructions without condensation) design value - tables in ČSN 730540-3 (normal spaces) - calculation for moist spaces (ČSN 730540-3 or EN 10456)

Thermal transmittance Calculation (EN ISO 6946): [m2K/W] Typical values:

Thermal transmittance Calculation (EN ISO 6946): Air spaces and layers: taken into account by means of equivalent thermal conductivity [m2K/W] Types of air layers: unventilated (openings less than 0,05 %) slightly ventilated (opening 0,05 to 0,15 %) ventilated (openings more than 0,15 %) included in calculation not included; only layers from interior to ventilated air space are included, ventilated air layer is modeled by means of different Rse (see following)

Thermal transmittance Calculation (EN ISO 6946): Air spaces and layers: taken into account by means of equivalent thermal conductivity [m2K/W] unventilated layers basic values from tables in EN ISO 6946 according to heat flow direction usable for border materials with usual emissivity (above 0,8) - and for thicknesses of layers under 300 mm

Thermal transmittance Calculation (EN ISO 6946): Air spaces and layers: taken into account by means of equivalent thermal conductivity [m2K/W] unventilated layers more exactly: základní hodnoty z tabulek v EN ISO 6946 podle směru toku použitelné pro hraniční materiály s běžnou emisivitou (nad 0,8) - a pro tloušťky dutin do 300 mm details in previous lectures convective-conductive heat transfer coefficient radiative heat transfer coefficient

slightly ventilated layers Thermal transmittance Calculation (EN ISO 6946): Air spaces and layers: taken into account by means of equivalent thermal conductivity [m2K/W] slightly ventilated layers traditionally: thermal resistance of slightly ventilated layer is ½ of thermal resistance of unventilated layer (and cannot be higher than 0,15 m2K/W) new approach in EN ISO 6946 (2008) : slightly ventilated layer is taken into account during calculation of U-value (details later)

Thermal transmittance Calculation (EN ISO 6946): Non-homogeneous layers: they can be approximately considered by means of eqv. thermal conductivity [m2K/W] - more exactly according to EN ISO 6946 and EN ISO 10211 (details later) A1 A2 A3

Thermal transmittance Calculation (EN ISO 6946): [W/(m2K)] default values from EN ISO 6946 0,10 0,17 0,00 0,13 0,04

Thermal transmittance Calculation (EN ISO 6946): Constructions with tapered layers: Calculation possibilities: - tapered layers are omitted (U in min. thickness) - calculation according to EN ISO 6946 (mean U-value)

Thermal transmittance Calculation (EN ISO 6946): Constructions with tapered layers: Calculation possibilities: - tapered layers are omitted (U in min. thickness) - calculation according to EN ISO 6946 (mean U-value) 4 basic shapes Roof is separated to individual areas with tapered layers characterized as one of 4 basic shapes. For every shape, formula for mean U-value is defined. Final U-value for whole roof is calculated as mean value over individual areas. + 4 formulas:

Thermal transmittance Calculation (EN ISO 6946): Constructions with slightly ventilated air layers: calculated 2x: - for unventilated layer for ventilated layer Final value: new approach, several problems area of openings total thermal resistance from surface to surface for unventilated air layer resistance from surface to surface for ventilated air layer

Thermal transmittance Calculation (EN ISO 6946): Constructions with systematic thermal bridges : regularly repeating spots in construction with increased heat flow caused by more conductive materials

Thermal transmittance Calculation (EN ISO 6946): Constructions with systematic thermal bridges: regular thermal bridges are part of the construction cannot be omitted! 200 mm of insulation without bridges: U = 0,21 W/(m2K) reality: U = 0,26 W/(m2K) Bridges: increase for 24%

Thermal transmittance Calculation (EN ISO 6946): Constructions with systematic thermal bridges: regular thermal bridges are part of the construction cannot be omitted! more calc. methods: orientational approximate exact 0,0 to 0,15 (ČSN 730540) or using eqv. th. conductivity calculation EN ISO 6946 calculation from th. field characteristic section of the construction b - SW for thermal field calculation correct values of Rsi! result: therm. coupl. coefficient L details later

Thermal transmittance Calculation (EN ISO 6946): Constructions adjacent to ground are evaluated: without ground with ground Attention: They can be very different, U-value including ground is significantly lower! for evaluation of requirements: without ground exception: alternative requirement for energy performance calculations: with ground

Thermal transmittance Calculation (EN ISO 6946): Constructions adjacent to ground are evaluated: without ground with ground Thermal transmittance including ground: EN ISO 13370 4 basic categories: floor on ground (incl. edge insulation) floor above crawl space heated basement unheated basement pro ověření požadavku: bez zeminy výjimka: alternativní požadavek pro energetické výpočty: se zeminou U-value includes also constructions under floor and ventilation

special procedures for: Thermal transmittance Calculation (EN ISO 6946): Constructions adjacent to ground special procedures for: partial basement partially heated bas. U-value includes also constructions under floor and ventilation

Thermal transmittance Calculation (EN ISO 6946): Constructions adjacent to ground Floor on ground: final thermal transmittance : w horizontal edge insulation: vertical

Thermal transmittance Calculation (EN ISO 6946): Constructions adjacent to unheated spaces are evaluated: without unheated space with unheated space similar as constructions adjacent to ground for evaluation of requirements: without unheated space for energy calculations: with unheated space

Thermal transmittance Calculation (EN ISO 6946): Constructions adjacent to unheated spaces are evaluated: without unheated space with unheated space Calculation: simplified in EN ISO 6946 detailed in EN ISO 13789 0,06 for attics with leaky roofs 0,20 for impermeable roofs no information: Ue = 2,0 + n=3

Thermal transmittance Calculation (EN ISO 6946): Corrections to thermal transmittance: for mechanical fasteners: mainly metal fasteners it can be omitted for fully plastic fasteners for air voids in thermal insulations: mainly one-layered insulations with butt joints it can be omitted for tongue-groove joints and multi-layered insulations for precipitation in case of inverted roofs: the worst situation for butt joints of XPS it can be reduced using tongue-groove joints of XPS or drainage diffusion membranes or by placement of insulation also below waterproofing

Thermal transmittance Calculation (EN ISO 6946): Corrections to thermal transmittance: for mechanical fasteners: Influence of fasteners can be omitted for: fasteners with conductivity under 1 W/(m.K) fasteners in air spaces λf … conductivity of fastener [W/(mK)], nf … number of f. in 1 m2 [1/m2], Af … cross-section area of 1 f. [m2], R1 … th. resistance of insulation [m2K/W], RT… total th. resistance from surface to surface of the construction [m2K/W]. Formula cannot be used for metal fasteners connected to metal layers – for such thermal bridges, detailed 3D calculation is necessary!

Thermal transmittance Calculation (EN ISO 6946): Corrections to thermal transmittance: for air voids in thermal insulations: R1 … th. resistance of insulation [m2K/W], RT… total th. resistance from surface to surface of construction [m2K/W]. 0,00 for insulation without gaps (more layers, tongue-groove connect.) 0,01 for gaps not causing air circulation (insulation with butt joints) 0,04 for gaps causing circulation (low-quality realisation)

factor for increased h.loss Thermal transmittance Calculation (EN ISO 6946): Corrections to thermal transmittance: for precipitation in case of inverted roofs: R1 … thermal resistance of insulation above waterproofing [m2K/W], RT… total th. resistance from surface to surface of construction [m2K/W]. factor for increased h.loss 0,0481 W.day/(m2.K.mm)) drainage factor standard 83% rate of precipi- tation

Thermal transmittance Calculation (EN ISO 10077): Windows and doors: measurement calculation EN ISO 10077: single windows coupled windows double windows Ag Af lg

Thermal transmittance Calculation (EN ISO 10077 and EN ISO 13947): Windows and doors: measurement calculation EN ISO 10077: single windows coupled windows double windows Curtain walling: calculation EN ISO 13947: characteristic section 2 methods for mean Ucw very difficult calculation