SIST EN 15255:2007
Thermal performance of buildings - Sensible room cooling load calculation - General criteria and validation procedures
Thermal performance of buildings - Sensible room cooling load calculation - General criteria and validation procedures
This European Standard sets out the level of input and output data, and prescribes the boundary conditions required for a calculation method of the sensible cooling load of a single room under constant or/and floating temperature taking into account the limit of the peak cooling load of the system. It includes a classification scheme of the calculation method and the criteria to be met by a calculation method in order to comply with this European Standard.
The purpose of this European Standard is to validate calculation methods used to:
- evaluate the maximum cooling load for equipment selection and cooling system design;
- evaluate the temperature profile when the cooling capacity of the system is reduced;
- provide data for evaluation of the optimum possibilities for load reduction;
- allow analysis of partial loads as required for system design, operation and control.
The validation procedure is used to check the room sensible heat balance model, taking into account:
- the external surface heat balance;
- the conduction through the building envelope;
- the effect of the thermal mass of the structures;
- the internal surface heat balance;
- the air heat balance;
- the heat balance solution method.
All other aspects are given either by fixed boundary conditions or by input data and are not in the focus of the model validation. It is assumed, that for all these other matters e.g. embedded heating and cooling systems, prescriptive models have to be used according to existing European Standards.
Informative Annex A gives a simplified method for cooling load calculation.
Wärmetechnishes Verhalten von Gebäuden - Berechnung der wahrnehmbaren Raumkühllast - Allgemeine Kriterien und Validierungsverfahren
Diese Europäische Norm legt die erforderlichen Ein und Ausgangsdaten sowie die Randbedingungen fest, die für ein Verfahren zur Berechnung der wahrnehmbaren Kühllast eines einzelnen Raumes bei konstanter und/oder gleitender Temperatur und unter Berücksichtigung der Spitzenkühllast der Anlage erforderlich sind. Sie enthält ein Schema zur Einstufung des Berechnungsverfahrens und der Kriterien, die das Berechnungsverfahren erfüllen muss, um dieser Europäischen Norm zu entsprechen.
Der Zweck dieser Europäischen Norm besteht in der Validierung von Berechnungsverfahren, die für Folgendes eingesetzt werden:
Bewertung der maximalen Kühllast für die Auswahl der Ausrüstung und die Bemessung der Kühlanlage;
Bewertung des Temperaturprofils bei verringerter Kühlkapazität der Anlage;
Bereitstellung von Daten für die Bewertung der geeignetsten Möglichkeiten zur Verringerung der Last;
Ermöglichen der Analyse der Teillasten, die für die Bemessung, den Betrieb und die Regelung der Anlage erforderlich ist.
Das Validierungsverfahren wird angewendet, um das Modell der Wärmebilanz des Raumes bezogen auf die sensible Wärme zu überprüfen, wobei Folgendes berücksichtigt wird:
Wärmebilanz für die Außenoberfläche;
Wärmeleitung durch die Gebäudehülle;
Einfluss der thermischen Speicherkapazität des Bauwerkes;
Wärmebilanz für die Innenoberfläche;
Wärmebilanz für die Luft;
Lösungsverfahren für die Wärmebilanz.
Alle weiteren Aspekte sind in Form von feststehenden Randbedingungen oder Eingangsdaten angegeben und stehen nicht im Mittelpunkt der Modellvalidierung. Es wird vorausgesetzt, dass für alle diese weiteren Aspekte, z. B. eingebettete Heiz- und Kühlsysteme, vorgeschriebene Modelle in Übereinstimmung mit bestehenden Europäischen Normen anzuwenden sind.
Der informative Anhang A enthält ein vereinfachtes Verfahren für die Berechnung der Kühllast.
Performance thermique des bâtiments - Calcul de la charge de refroidissement en chaleur sensible d'un local - Criteres généraux et procédures de validation
La présente Norme européenne fixe le niveau des données d'entrée et de sortie, et prescrit les conditions limites nécessaires à la méthode de calcul de la charge de refroidissement sensible d'un local individuel à température constante et/ou flottante, en tenant compte de la limite de la charge de refroidissement maximale du système. Elle comporte un schéma de classification de la méthode de calcul ainsi que les critères que la méthode de calcul doit remplir pour être conforme à la présente Norme européenne.
L'objet de la présente Norme européenne est de valider les méthodes de calcul utilisées pour :
évaluer la charge de refroidissement maximale qui déterminera le choix de l'équipement et la conception du système de refroidissement ;
évaluer le profil de température lorsque la capacité de refroidissement du système est réduite ;
fournir des données pour l'évaluation des possibilités optimales de réduction de la charge :
analyser les charges partielles pour la conception, l'exploitation et la régulation du système.
La procédure de validation sert à vérifier le modèle de balance thermique sensible du local, en tenant compte :
de la balance thermique superficielle extérieure ;
de la conduction /conductivité ? de l'enveloppe du bâtiment ;
de l'effet des masses thermiques des structures ;
de la balance thermique superficielle intérieure ;
de la balance thermique de l'air ;
de la méthode de solution de la balance thermique.
Tous les autres aspects sont indiqués soit par dles conditions limites fixes/fixées ?, soit par les données d'entrées et ne constituent pas le point central de la validation du modèle. On suppose que pour toutes ces autres questions, par exemple, pour les systèmes de chauffage et de refroidissement intégrés, des modèles normatifs doivent être utilisés d'après les Normes européennes existantes.
L'Annexe A informative indique une méthode simplifiée de calcul de la charge de refroidissement.
Toplotne značilnosti stavb - Izračun senzibilne hladilne obremenitve prostora - Splošna merila in validacija postopka
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Wärmetechnishes Verhalten von Gebäuden - Berechnung der wahrnehmbaren Raumkühllast - Allgemeine Kriterien und ValidierungsverfahrenPerformance thermique des bâtiments - Calcul de la charge de refroidissement en chaleur sensible d'un local - Criteres généraux et procédures de validationThermal performance of buildings - Sensible room cooling load calculation - General criteria and validation procedures91.120.10Toplotna izolacija stavbThermal insulationICS:Ta slovenski standard je istoveten z:EN 15255:2007SIST EN 15255:2007en,de01-december-2007SIST EN 15255:2007SLOVENSKI
STANDARD
SIST EN 15255:2007
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 15255August 2007ICS 91.140.99; 91.120.10 English VersionEnergy performance of buildings - Sensible room cooling loadcalculation - General criteria and validation proceduresPerformance thermique des bâtiments - Calcul de la chargede refroidissement en chaleur sensible d'un local - Critèresgénéraux et procédures de validationWärmetechnisches Verhalten von Gebäuden - Berechnungder wahrnehmbaren Raumkühllast - Allgemeine Kriterienund ValidierungsverfahrenThis European Standard was approved by CEN on 6 July 2007.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of 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.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2007 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15255:2007: ESIST EN 15255:2007
EN 15255:2007 (E) 2 Contents Page Foreword.3 Introduction.4 1 Scope.5 2 Normative references.5 3 Terms, definitions, symbols and units.6 3.1 Terms and definitions.6 3.2 Symbols and units.8 3.3 Subscripts.9 4 Basic assumptions.10 5 Data requirement.10 5.1 General.10 5.2 Climatic data.11 5.3 Descriptions of the envelope elements.11 5.3.1 General.11 5.3.2 Boundary conditions.11 5.3.3 Heat transfer coefficients.12 5.3.4 Geometrical and thermophysical parameters of the room envelope.13 5.4 Cooling system device.14 5.4.1 General.14 5.4.2 Convective device.14 5.4.3 Cooled surface device.14 5.5 Classification of the cooling load calculation method.15 6 Report of the calculation.15 6.1 General.15 6.2 Input data.15 6.3 Output data.16 7 Validation procedures.16 7.1 General.16 7.2 Reference room.17 7.3 Climatic data.21 7.4 Test cases.23 7.5 Parameters to be calculated.28 7.6 Test results.29 Annex A (informative)
Example of calculation method based on a simplified model.30 A.1 Introduction.30 A.2 Calculation of internal air and operative temperatures for a given value of applied cooling power.30 A.2.1 Presentation.30 A.2.2 Determination of the air and operative temperatures.32 A.2.3 Terms in Equations (A.1), (A.2), (A.3), (A.4) and (A.5).34 A.3 Calculation of internal temperatures and required cooling power.38 A.3.1 General description.38 A.3.2 Calculation procedure for control on air temperature.42 A.3.3 Calculation procedure for control on operative temperature.43 Bibliography.45
SIST EN 15255:2007
EN 15255:2007 (E) 3 Foreword This document (EN 15255:2007) 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 February 2008, and conflicting national standards shall be withdrawn at the latest by February 2008. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association (Mandate M/343), and supports essential requirements of EU Directive 2002/91/EC on the energy performance of buildings (EPBD). It forms part of a series of standards aimed at European harmonisation of the methodology for the calculation of the energy performance of buildings. An overview of the whole set of standards is given in prCEN/TR 15615. Attention is drawn to the need for observance of EU Directives transposed into national legal requirements. Existing national regulations (with or without reference to national standards) may restrict for the time being the implementation of this European Standard. This European Standard is one of a series of standards on general criteria and validation procedures for transient calculation methods for the design and the evaluation of the thermal and energy performance of buildings and building components. No existing European Standard is superseded. The target audience of this European Standard are software developers of building simulation tools and policy makers in the building regulation sector. The standard specifies the boundary conditions and the simplifications needed to reach calculation results for the building part which are comparable. It needs to be emphasized that there exist more sophisticated energy simulation methods and procedures including interactions with the heating, cooling, ventilating and lighting systems which may be used for the design and optimization process of a building but are not in line with existing European Standards. This European Standard provides the means (in part) to assess the contribution that building products and services make to energy conservation and to the overall energy performance of buildings. 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. SIST EN 15255:2007
EN 15255:2007 (E) 4 Introduction The proper design and sizing of air conditioning systems requires the calculation of the cooling load in the space to be conditioned (room cooling load). The variables affecting the room cooling load calculation are numerous, often difficult to define precisely and always intricately inter-related. Many cooling load components vary widely in magnitude during a 24-hour period. Since these cyclic changes are often out of phase with each other, they need to be analyzed to establish the maximum room cooling load for a building or zone. The maximum cooling capacity for a zoned building is the largest hourly total of the simultaneous zone loads throughout a design day; but it needs to handle the peak cooling load for each zone at its peak hour. This means that a calculation method needs to be able to determine the cooling load of each zone throughout the calculation period. A large number of calculation methods are available in Europe. These methods generally are based on different solution techniques that include simplifications of the real phenomena. According to those simplifications they are able to consider specific or general situations. One specific situation is represented by the calculation of the maximum peak load of a single zone for convective source with the control of the air temperature. This European Standard includes the criteria and the level of input and output data required for a simplified calculation method of the cooling load of a single room. A simplified load calculation method is given in the informative Annex A. Any calculation method satisfies the standard if it complies with the assumptions, data requirements and the validation procedures described in Clause 7. The series of European Standards, giving general criteria and validation procedures for the building part of energy simulation models for the different calculation subjects, are listed below. European Standard Subject EN ISO 13791 EN ISO 13792 Temperature calculations (air and operative) EN 15255 Load calculations (sensible cooling) EN 15265 Energy need calculations (heating and cooling)
SIST EN 15255:2007
EN 15255:2007 (E) 5 1 Scope This European Standard sets out the level of input and output data, and prescribes the boundary conditions required for a calculation method of the sensible cooling load of a single room under constant and/or floating temperature taking into account the limit of the peak cooling load of the system. It includes a classification scheme of the calculation method and the criteria to be met by a calculation method in order to comply with this European Standard. The purpose of this European Standard is to validate calculation methods used to: evaluate the maximum cooling load for equipment selection and cooling system design; evaluate the temperature profile when the cooling capacity of the system is reduced; provide data for evaluation of the optimum possibilities for load reduction; allow analysis of partial loads as required for system design, operation and control. The validation procedure is used to check the room sensible heat balance model, taking into account: the external surface heat balance; the conduction through the building envelope; the effect of the thermal mass of the structures; the internal surface heat balance; the air heat balance; the heat balance solution method. All other aspects are given either by fixed boundary conditions or by input data and are not in the focus of the model validation. It is assumed that for all these other matters e.g. embedded heating and cooling systems, prescriptive models have to be used according to existing European Standards. Informative Annex A gives a simplified method for cooling load calculation. 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 410, Glass in building — Determination of luminous and solar characteristics of glazing EN 13363-2, Solar protection devices combined with glazing — Calculation of total solar energy transmittance and light transmittance — Part 2: Detailed calculation method EN 15377-1, Heating systems in buildings — Design of embedded water based surface heating and cooling systems — Part 1: Determination of the design heating and cooling capacity prEN ISO 6946, Building components and building elements — Thermal resistance and thermal transmittance — Calculation method (ISO/DIS 6946:2005) SIST EN 15255:2007
EN 15255:2007 (E) 6 EN ISO 7345:1995, Thermal insulation — Physical quantities and definitions (ISO 7345:1987) EN ISO 9251:1995, Thermal insulation — Heat transfer conditions and properties of materials — Vocabulary (ISO 9251:1987) EN ISO 9288:1996, Thermal insulation — Heat transfer by radiation — Physical quantities and definitions (ISO 9288:1989) prEN ISO 9346:2007, Hygrothermal performance of buildings and building materials — Physical quantities for mass transfer — Vocabulary (ISO/DIS 9346:2005) EN ISO 10077-1, Thermal performance of windows, doors and shutters — Calculation of thermal transmittance — Part 1: General (ISO 10077-1:2006) prEN ISO 13370, Thermal performance of buildings — Heat transfer via the ground — Calculation methods (ISO/DIS 13370:2005) prEN ISO 13786, Thermal performance of building components — Dynamic thermal characteristics — Calculation methods (ISO/ 13786:1999) EN ISO 13792:2005, Thermal performance of buildings — Calculation of internal temperatures of a room in summer without mechanical cooling — Simplified methods (ISO 13792:2005) 3 Terms, definitions, symbols and units 3.1 Terms and definitions For the purposes of this document, the terms and definitions given in EN ISO 7345:1995, EN ISO 9288:1996, EN ISO 9251:1995, prEN ISO 9346:2007 and the following apply. 3.1.1 internal environment closed space delimited from the external environment or adjacent spaces by a building fabric component 3.1.2 envelope element element of a building fabric delimited by two parallel surfaces, one of them is exposed to the room under consideration 3.1.3 room air air of the internal environment 3.1.4 internal air temperature temperature of the room air 3.1.5 internal surface temperature temperature of the internal surface of each element of the envelope 3.1.6 mean radiant temperature uniform surface temperature of an enclosure in which an occupant would exchange the same amount of radiant heat as in the actual non-uniform enclosure SIST EN 15255:2007
EN 15255:2007 (E) 7 3.1.7 operative temperature uniform temperature of an enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual non-uniform environment NOTE As approximation, the operative temperature is calculated as mean value of the air temperature and the mean radiant temperature. 3.1.8 thermal source component which exchanges heat with the internal environment 3.1.8.1 convective thermal source thermal source that exchanges heat only with the air 3.1.8.2 surface source thermal source that exchanges heat with the surrounding surfaces by long-wave radiation and with the air by convection 3.1.9 internal design temperature internal temperature assumed as reference for the system control.
NOTE The internal design temperature may be the internal air temperature or the operative temperature. SIST EN 15255:2007
EN 15255:2007 (E) 8 3.2 Symbols and units The principal symbols used are listed in the following table. Other symbols are defined where they are used within the standard. Symbol Quantity Unit A area m2 As
sunlit area m2 cp specific heat capacity of air at constant pressure J/(kg⋅K) cd coefficient of discharge - d layer thickness m f correction factor - fdf solar distribution factor - fic internal convective factor - flf solar loss factor - fs sunlit factor - fsa solar to air factor - h surface heat transfer coefficient W/(m2⋅K) I intensity of solar radiation W/m2 l length m m& mass flow rate kg/s P power W q density of heat flow rate W/m2 R thermal resistance m2⋅K/W T thermodynamic temperature K t time s U thermal transmittance under steady state conditions W/(m2⋅K) V volume m3 v velocity m/s SIST EN 15255:2007
EN 15255:2007 (E) 9 α solar absorptance - ε total hemispherical emissivity
- Φ heat flow rate
W Λ thermal conductance W/(m2·K) λ thermal conductivity W/(m·K) ρ solar reflectance - ρ density kg/m3 θ Celsius temperature °C τe solar direct transmittance -
3.3 Subscripts a air lr long wave radiation av average mr mean radiant b building n normal to surface c convection op operative cd conduction out out of section D direct solar radiation r radiation d diffuse solar radiation ref reference e external sa solar to air ec external cavity se external surface ef external floor set set point value eq equivalent si internal surface g ground sk sky i internal sr short wave radiation ic internal cavity T total if internal floor t time il inlet section v ventilation SIST EN 15255:2007
EN 15255:2007 (E) 10
va ventilation through air cavity 4 Basic assumptions For the purposes of this standard the following basic assumptions are considered as minimum requirements: the room is considered to be a closed space delimited by enclosure elements; the air temperature is uniform throughout the room; the thermophysical properties of all materials composing the enclosure elements are constant; the convective heat transfer coefficients are fixed; the heat conduction through each enclosure element is one-dimensional and the surface of each enclosure element is isothermal; air spaces within envelope components are treated as air layers bounded by two isothermal surfaces; the mean radiant temperature is calculated as the area-weighted average of the internal surface temperatures of each component; the operative temperature is calculated as the arithmetic mean of the internal air temperature and the mean radiant temperature; the distribution of the solar radiation on the internal surfaces of the components of the room is time independent; the distribution of the radiative heat flow due to internal gains is uniform; the long-wave radiative and the convective heat transfers at the internal surface of each component are treated separately; thermal bridges are treated by steady state calculations. 5 Data requirement 5.1 General For evaluating the hourly values of the room cooling load and the internal temperatures the following information is required: the design climatic data for the location; the descriptions of the envelope elements (area, exposure, boundary conditions); for each envelope element the calculation of the thermophysical parameters (steady state and transient conditions) and the solar factors of the opaque and the transparent components; the design internal temperature; the schedule of the ventilation and infiltration rate; SIST EN 15255:2007
EN 15255:2007 (E) 11 the scheduled values of the convective and radiative heat flow due to lighting and occupants; the scheduled values of the convective and radiative heat flow due to internal equipment and appliances; the characteristics of the cooling system and maximum room cooling power. 5.2 Climatic data For a location with given latitude and longitude the following hourly climatic data are required: external air temperature; the intensity of solar radiation (direct normal and diffuse horizontal); the external radiant temperature (sky and surrounding); the ground albedo. NOTE Design climatic data, derived from EN ISO 15927-4, can be included in a national annex. 5.3 Descriptions of the envelope elements 5.3.1 General The following types of room enclosure elements are considered: external components:
opaque walls, windows including external and/or internal shading devices, roof and floor; internal components: adjacent to similar rooms (adiabatic elements);
adjacent to rooms with pre-defined conditions; components with a fixed known surface temperature (cooling surface). The thermophysical properties shall be calculated according to the standards for specific elements, such as windows and glazing according to EN ISO 10077-1, EN 410 and EN 13363-2, walls and roofs according to prEN ISO 6946 and prEN ISO 13786 and ground floors according to prEN ISO 13370. For each of these situations the boundary conditions are defined in 5.3.2. 5.3.2 Boundary conditions 5.3.2.1 External components Boundary conditions are the hourly values of the climatic data defined in 5.2 and solar shading by the horizon, overhangs and fins. For an element in contact with the ground the design external temperature shall be defined in accordance with prEN ISO 13370. 5.3.2.2 Internal components 5.3.2.2.1 Adjacent to similar rooms (adiabatic components) The air temperature, the mean radiant temperature and the solar radiation absorbed by the surface are the same at the external and the internal surfaces of the component. SIST EN 15255:2007
EN 15255:2007 (E) 12 5.3.2.2.2 Adjacent to rooms with pre-defined internal conditions At the surface opposite to the room under consideration the boundary conditions are the hourly values of the air temperature of the adjacent room. The heat flow rate by long-wave radiation is calculated from the temperature of the opposite surface component and the air temperature of the adjacent room by a long wave radiation heat transfer coefficient assumed to be constant. The heat flow rate due to short wave radiation is assumed to be zero. 5.3.2.2.3 Component with known surface temperature In this case the temperature of both surfaces of the component are known. If only the room-facing surface temperature is fixed (cooling surface), the temperature of the opposite surface depends on the location of the component. If it is an external component, the boundary conditions of 5.3.2.1 apply. If it is an internal component, the boundary conditions of 5.3.2.2.1 or 5.3.2.2.2 apply. 5.3.3 Heat transfer coefficients The following values shall be used: a) convective surface heat transfer coefficients: external surface:
hc,e = 8,0 W/(m2⋅K); internal surface of no-cooling component:
hc,i = 2,5 W/(m2⋅K); internal surface of cooling surface: vertical:
hc,i = 2,5 W/(m2⋅K); horizontal (heat flow upwards):
hc,i = 5,0 W/(m2⋅K); horizontal (heat flow downwards):
hc,i = 0,7 W/(m2⋅K); NOTE The external convective surface heat transfer coefficient for cooling load calculations is intentionally lower than for energy calculations, representing low wind speed conditions as a safe assumption. b) long-wave radiative heat transfer coefficients: internal surface:
hlr,i = 5,5 W/(m2⋅K); external surface:
hlr,e = 5,5 W/(m2⋅K); NOTE The values are typical for high emissivity
ε
= 0,9 and Tm = 300 K. c) the correction to density of heat flow rate for the longwave radiation from the external walls to the sky is given by: external vertical components:
qsk = 0 W/m2; external horizontal components:
qsk = 70 W/m2; tilted components:
qsk = 70 cos(γ) W/m2 where γ is the tilt angle from the horizontal. SIST EN 15255:2007
EN 15255:2007 (E) 13 5.3.4 Geometrical and thermophysical parameters of the room envelope 5.3.4.1 Opaque components For each component the following data are required: area (calculated from internal dimensions); thermal characteristics. The procedure for evaluating the sunlit factor due to external obstructions, fs, may be defined at national level. Otherwise, a suitable procedure is given in Annex C of EN ISO 13791:2004. 5.3.4.2 Transparent components For each transparent component the following data are required: area, including the frame; thermal characteristics; optical characteristics; sunlit fraction due to external obstructions, fs. The thermal inertia of window glazing can usually be neglected. Solar to air factor fsa The solar to air factor, fsa, takes into account that a proportion of the radiation entering through the window is immediately transformed in a heat flow rate for the internal air. This fraction depends on the presence of internal elements with very low heat capacity as carpets, furniture, etc. It is assumed to be time independent and it should be defined on a national basis; alternatively the value of fsa = 0,1 may be used. Solar loss factor flf The solar loss factor, flf, takes into account that a proportion of the solar radiation entering through the window is reflected back outside. It depends on the geometrical characteristics and solar properties of the glazing system, the exposure of the window, the solar angle and the room geometry. It is assumed to be time independent. Values of flf should be defined on a national basis; alternatively the value of flf = 0 may by used. Solar distribution factor fdf
The heat flow rate due to the solar radiation entering through the glazing system is absorbed by the internal surface of each envelope component. According to the assumptions of Clause 4, the distribution of the solar radiation is time independent. The distribution factor is defined, for each surface, as the fraction of the solar shortwave absorbed by that surface. It depends on the solar reflectivity of each internal surface. For the purposes of this standard the distribution factors should be calculated using the expressions in Table 1, as a function of the type of the system, the floor colour and the area of the envelope components. SIST EN 15255:2007
EN 15255:2007 (E) 14 Table 1 — Solar distribution factors fdf
Floor Vertical walls Ceiling Window cooled floor of dark colour 2 Af / (At + Af) Awa / (At + Af)) Ac / (At + Af) 0 all other cases Af / At Awa / At Ac / At 0
Af
is the floor area; At
is the total area except window (= Af + Awa + Ac); Awa is the vertical wall area ex
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