EN 15255:2007

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
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

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
NOTE The internal design temperature may be the internal air temperature or the operative temperature. SIST EN 15255:2007

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

- 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

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

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

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

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

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 except window; Ac
is the ceiling area. 5.4 Cooling system device 5.4.1 General The following systems are considered:  convective device;  cool surface device;  both convective device and cool surface device. 5.4.2 Convective device A convective device means that heat is removed from the space by an air terminal device (unit) with negligible radiative effects (i.e. fan coil or air inlet). In this situation the room cooling load is represented by the heat to be removed from the space in order to maintain the prescribed internal conditions defined by the system control. 5.4.3 Cooled surface device A cooled surface device means that the heat is removed from the space by the cooled surface by convection and radiation. In this case the cooling rate is represented by the total heat to be removed by the surface of the cooled element in order to maintain the prescribed internal conditions. If the cooled surface is an embedded system its surface temperature shall be calculated according to EN 15377-1. SIST EN 15255:2007

v v v Pure convective system Limited cooling capacity + moveable shading
v v Surface + convective system
v
For each main class of method (from 1 to 4) there are two sub-classifications, according to the types of the system control that the method can model. Table 3 — Sub-classification of calculation method Control type within capability of method Sub-class
a b Air temperature v v Operative temperature
v
EXAMPLE A calculation method of class 3b is able to handle pure convective systems with infinite cooling capacity, continuous or intermittent operation, fixed cooling capacity, moveable shadings, and control of the room air or room operative temperature. It is not able to model cooled surfaces. 6 Report of the calculation 6.1 General According to this European Standard, the calculation report of cooling load shall include at least the input data specified in 6.2 and the output data as given in 6.3. 6.2 Input data a) the climatic data (hourly values of the external air temperature, solar radiation intensity, external radiant temperature); b) building characteristics: description of the building and the rooms investigated; c) for each room: 1) volume, in m3; SIST EN 15255:2007

gains related to: 1) lighting per floor area; 2) presence of people; 3) electrical appliances; f) for each element of the envelope, according to the calculation method:  area, thermal and optical characteristics used for the calculations; g) design temperature: schedule of air or operative temperature, depending on the control strategy; h) system device:  convective:
maximum cooling capacity;  cool surface device: minimum surface temperature;
area of surface;
boundary conditions. 6.3 Output data The results of the calculation are the hourly values of the room cooling load and the air, mean radiant and opera
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