oSIST prEN 15315:2005

Heating systems in buildings - Energy performance of buildings - Overall energy use, primary energy and CO2 emissions

The purpose of this standard is to:
   collate results from other standards that specify calculation of energy consumption within a building;
   account for energy generated in the building, some of which may be exported for use elsewhere;
   present a summary on tabular form of the overall energy use of the building;
   specify calculation of primary energy consumption and carbon dioxide emission for the building as a whole;
   establish general principles for the calculation of primary energy factors and carbon dioxide emission factors.
This standard will provide:
a definition of system boundaries (e.g. building, installations, energy supply) and calculation periods;
general definition of the overall energy use (i.e. determine which services are taken into account within the system boundaries);
definition of energy terms (energy use, primary energy, etc.);
definition of the data interfaces with other standards in order to report the overall energy use of buildings;
general procedures for taking into consideration decentralised energy production based on renewable energy and CHP (combined heat and power production), e.g. to show how on-site energy generation offsets energy demand;
identification of the energy streams across system boundaries;
principles for assessing primary energy consumption and CO2 emission of buildings (i.e. principles for determining primary energy factors and carbon dioxide emission factors);
general principles for taking into account the interactions between the different energy uses (e.g. calculation of recovered losses and gains).
The objective of specifying the details of the energy performance calculation for a building is to:
- underline the particularity of a project (e.g. efforts made on bioclimatic design);
- show the strong and the weak points in the overall energy performance of the building and to highlight potential gains:
- distinguish between thermal uses and specific electrical uses;
- indicate the outputs required f

Heizsysteme in Gebäuden - Energieeffizienz von Gebäuden - Gesamtenergieverbrauch, Primärenergie und CO2-Emissionen

Der Zweck dieser Norm besteht in Folgendem:
Zusammenstellen und Ordnen der Ergebnisse weiterer Normen, in denen die Berechnung des Energieverbrauchs in einem Gebäude festgelegt wird;
Bestimmung der in einem Gebäude erzeugten Energie, die teilweise für den Verbrauch an anderer Stelle nach außen abgegeben werden kann;
Liefern einer tabellarischen Zusammenfassung des Gesamtenergieverbrauchs des Gebäudes;
Festlegung der Berechnung des Primärenergieverbrauchs und der Kohlendioxid Emissionen für das gesamte Gebäude;
Festlegung allgemeiner Grundsätze für die Berechnung der Primärenergiefaktoren und der Faktoren für die Kohlendioxid Emission;
Die vorliegende Norm bietet Folgendes:
-   eine Definition der Anlagengrenzen (z. B. Gebäude, Installationen, Energieversorgung) und der Berechnungszeiträume;
-   eine allgemeine Definition des Gesamtenergieverbrauchs (d. h. die Bestimmung der Leistungen, die innerhalb der Anlagengrenzen berücksichtigt werden);
-   eine Definition der energiebezogenen Begriffe (Energieverbrauch, Primärenergie usw.);
-   eine Definition der Datenschnittstellen mit weiteren Normen, um Angaben zum Gesamtenergieverbrauch von Gebäuden machen zu können;
-   allgemeine Verfahren zur Berücksichtigung einer auf erneuerbaren Energien und KWK (Kraft Wärme Kopplung) beruhenden dezentralen Energieerzeugung, z. B. um darzustellen, wie die Energieerzeugung vor Ort den Energiebedarf verändert;
-   Identifizierung von über die Anlagengrenzen hinaus verlaufenden Energieströmen;
-   Grundsätze für die Bewertung des Primärenergieverbrauchs und der CO2 Emissionen von Gebäuden, (d. h. Grundsätze für die Bestimmung von Primärenergiefaktoren und Faktoren für die Kohlendioxid Emissionen);
-   allgemeine Grundsätze für die Berücksichtigung der Wechselwirkungen zwischen den verschiedenen Energieverwendungszwecken (z. B. Berechnung der rückgewonnenen Verluste und Gewinne).

Systemes de chauffage dans les bâtiments - Performance énergétique des bâtiments - Energie globale, énergie primaire et émissions de CO2

Ogrevalni sistemi v stavbah - Energijske lastnosti stavb - Splošna raba energije. osnovna energija in emisije CO2

General Information

• Status: Not Published
• ICS: 91.140.10 - Central heating systems
• Technical Committee: OGS - Heating for buildings
• Current Stage: 98 - Abandoned project (Adopted Project)
• Start Date: 18-May-2017
• Due Date: 23-May-2017
• Completion Date: 18-May-2017
• Mandate: M/343 - Mandate to CEN, CENELEC and ETSI for the elaboration and adoption of standards for a methodology calculating the integrated energy performance of buildings and estimating the environmental impact, in accordance with the terms set forth in Directive 2002/91/EC
• Ref Project: prEN 15315 - Heating systems in buildings - Energy performance of buildings - Overall energy use, primary energy and CO2 emissions

Relations

• Merged Into: SIST EN 15603:2008 - Energy performance of buildings - Overall energy use and definition of energy ratings
• Effective Date: 07-Mar-2023
• Child: SIST EN 15603:2008 - Energy performance of buildings - Overall energy use and definition of energy ratings
• Effective Date: 22-Dec-2008

Overview

The European standard oSIST prEN 15315:2005, titled Heating systems in buildings - Energy performance of buildings - Overall energy use, primary energy and CO2 emissions, has been developed by CEN Technical Committee CEN/TC 228. This standard provides a comprehensive framework to evaluate the overall energy performance of buildings by integrating energy consumption data from various building services and systems. It focuses on calculating the total energy use, primary energy consumption, and carbon dioxide (CO2) emissions associated with heating, cooling, ventilation, domestic hot water, and lighting within buildings.

This document helps consolidate energy calculation results from related standards while accounting for energy generated onsite, including renewable energy and combined heat and power (CHP) systems. By establishing clear definitions, system boundaries, and calculation methods, oSIST prEN 15315:2005 supports more consistent and transparent energy performance assessments in buildings across Europe.

Key Topics

• System Boundaries and Calculation Periods
  Defines the extent of the building system under study (including installations and energy supply chains) and the timeframe over which energy calculations are performed. This ensures uniformity in assessment scope.

• Overall Energy Use Definition
  Identifies which building services (heating, cooling, ventilation, hot water, lighting) are considered in calculating energy performance and how on-site renewable energy production offsets overall energy demand.

• Energy Terminology
  Provides precise definitions for terms such as net energy, delivered energy, primary energy, primary energy factors, and CO2 emission factors to harmonize the language used in building energy assessments.

• Primary Energy and CO2 Emission Calculations
  Specifies methodologies to calculate the primary energy consumption (energy from natural resources before any transformation) and CO2 emissions for the entire building based on delivered energy and relevant factors.

• Inclusion of Decentralized Energy Production
  Recognizes renewable energy sources and onsite CHP systems, allowing for credits where generated energy reduces fossil fuel consumption or is exported for external use.

• Energy Stream Identification Across Boundaries
  Tracks energy inputs and outputs to and from the building system, enabling comprehensive accounting of energy flows including losses and recovered gains.

• Interaction Between Energy Uses
  Incorporates feedback effects between different energy services (e.g., recovered losses) to reflect real operational efficiencies accurately.

Applications

• Building Energy Performance Assessment
  Enables architects, engineers, and energy consultants to measure and report the overall energy consumption and environmental impact of heating systems and other building services.

• Energy Efficiency Improvement Planning
  Assists in identifying strengths and weaknesses in building energy use, revealing opportunities for enhancing bioclimatic design, system efficiencies, and renewable integration.

• Policy and Regulation Compliance
  Supports authorities and policymakers in setting performance benchmarks and regulatory requirements focused on reducing primary energy usage and lowering CO2 emissions from the built environment.

• Design of Heating and Renewable Systems
  Guides designers in assessing the impact of different heating systems, including biomass, solar thermal, heat pumps, and CHP, on the total energy performance of buildings.

• Energy Reporting and Certification
  Provides standardized calculation procedures to produce reliable energy performance certificates and reports that are consistent across European markets.

Related Standards

oSIST prEN 15315:2005 complements and interfaces with several other related standards and documents, including:

• prEN wi 7 to prEN wi 11 – Methods for calculation of system energy requirements and efficiencies for heating systems, domestic hot water, and storage.
• prEN wi 13 – Energy requirements for lighting in buildings.
• prEN wi 14 and wi 17 – Calculation methods for energy use in space heating and cooling, including simplified and validation procedures.
• prEN wi 20 – Calculation methods for energy impact of ventilation systems.
• EN ISO 7345 – Definitions related to thermal insulation and physical quantities.

It also aligns with CEN/TC 89, TC 156, TC 169, and TC 247 committees working on related aspects of building energy performance and sustainability.

---

By adopting oSIST prEN 15315:2005, stakeholders involved in building design, operation, and regulation can ensure a holistic approach to energy assessment that incorporates modern heating technologies, renewable integration, and comprehensive environmental impact calculations. This enables more efficient and environmentally responsible buildings, supporting the EU’s goals for energy sustainability and carbon reduction.

Standards Content (Sample)

SLOVENSKI oSIST prEN 15315:2005

PREDSTANDARD
september 2005
Heating systems in buildings - Energy performance of buildings - Overall energy
use, primary energy and CO2 emissions
ICS 91.140.10 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD
DRAFT
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2005
ICS
English version
Heating systems in buildings - Energy performance of buildings -
Overall energy use, primary energy and CO2 emissions
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee CEN/TC 228.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations which
stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other language
made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same
status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
: This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
Warning
shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 15315:2005: E
worldwide for CEN national Members.

Contents Page
Foreword.3
Introduction .4
1 Scope .5
2 Normative references .6
3 Definitions and symbols .7
4 Principle of the method.10
5 Calculation of the primary energy and CO emissions.18
Annex A (informative) Primary energy factors and CO emission factors .23
Annex B (informative) Overview of the different parameters influencing the integrated energy
performance of buildings.24

Foreword
This document (prEN 15315:2005) has been prepared by Technical Committee CEN/TC 228 “Heating
systems in buildings”, the secretariat of which is held by DS.
This document is currently submitted to the CEN Enquiry.
The subjects covered by CEN/TC 228 are the following:
- design of heating systems (water based, electrical etc.);
- installation of heating systems;
- commissioning of heating systems;
- instructions for operation, maintenance and use of heating systems;
- methods for calculation of the design heat loss and heat loads;
- methods for calculation of the energy performance of heating systems.
Heating systems also include the effect of attached systems such as hot water production systems.
All these standards are systems standards, i.e. they are based on requirements addressed to the system as a
whole and not dealing with requirements to the products within the system.
Where possible, reference is made to other European or International Standards, a.o. product standards.
However, use of products complying with relevant product standards is no guarantee of compliance with the
system requirements.
The requirements are mainly expressed as functional requirements, i.e. requirements dealing with the function
of the system and not specifying shape, material, dimensions or the like.
The guidelines describe ways to meet the requirements, but other ways to fulfil the functional requirements
might be used if fulfilment can be proved.
Heating systems differ among the member countries due to climate, traditions and national regulations. In
some cases requirements are given as classes so national or individual needs may be accommodated.
In cases where the standards contradict with national regulations, the latter should be followed.

Introduction
This standard specifies a general framework for the assessment of overall energy use of a building and
calculation of overall energy performance in terms of primary energy and CO emissions. Separate standards
specify calculation of the energy consumption of services within a building (i.e. heating, cooling, ventilation,
domestic hot water, lighting). In the present standard, these energy consumptions are considered for calcula-
tion of the overall energy use.
Allowance is made for energy that may be generated within, or on the surface of, the building, and which is
used to offset fuel and power drawn from other sources. Electrical energy generated in excess of the
instantaneous demand is considered, provided it is exported to the public supply for use elsewhere.
A comprehensive approach is needed for appropriate evaluation of all options to improve the energy
performance of buildings. The assessment is not limited to the building alone, but takes into account the wider
environmental impact of the energy supply chain. From an assessment of overall energy use, building owners
and policy-makers can gain an understanding of the relative merits of alternative options.
The user shall refer to other European Standards or to national documents for input data and detailed
calculation procedures not provided by this standard. Local values for factors needed to calculate the primary
energy consumption and CO emissions should be defined in a national annex.
1 Scope
The purpose of this standard is to:
 collate results from other standards that specify calculation of energy consumption within a building;
 account for energy generated in the building, some of which may be exported for use elsewhere;
 present a summary on tabular form of the overall energy use of the building;
 specify calculation of primary energy consumption and carbon dioxide emission for the building as a
whole;
 establish general principles for the calculation of primary energy factors and carbon dioxide emission
factors.
This standard will provide:
 a definition of system boundaries (e.g. building, installations, energy supply) and calculation periods;
 general definition of the overall energy use (i.e. determine which services are taken into account within
the system boundaries);
 definition of energy terms (energy use, primary energy, etc.);
 definition of the data interfaces with other standards in order to report the overall energy use of buildings;
 general procedures for taking into consideration decentralised energy production based on renewable
energy and CHP (combined heat and power production), e.g. to show how on-site energy generation
offsets energy demand;
 identification of the energy streams across system boundaries;
 principles for assessing primary energy consumption and CO emission of buildings (i.e. principles for
determining primary energy factors and carbon dioxide emission factors);
 general principles for taking into account the interactions between the different energy uses (e.g.
calculation of recovered losses and gains).
The objective of specifying the details of the energy performance calculation for a building is to:
 underline the particularity of a project (e.g. efforts made on bioclimatic design);
 show the strong and the weak points in the overall energy performance of the building and to highlight
potential gains:
 distinguish between thermal uses and specific electrical uses;
 indicate the outputs required from related standards, in which calculation of energy consumption of
services within a building are specified.
This work will be coordinated with CEN/TC TC 89, TC 156, TC 169, and TC 247.
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 ISO 7345, Thermal insulation - Physical quantities and definitions
prEN wi 7, Heating systems in buildings - Method for calculation of system energy requirements and system
efficiencies – Part 1: General
prEN wi 8, Heating systems in buildings - Method for calculation of system energy requirements and system
efficiencies – Part 2.1: Space heating emission systems
prEN wi 9 part 2.2.1, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 2.2.1: Space heating generation systems, Combustion systems
prEN wi 9 part 2.2.2, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 2.2.2: Space heating generation systems, Heat pump systems
prEN wi 9 part 2.2.3, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 2.2.3: Space heating generation systems, Thermal solar systems
prEN wi 9 part 2.2.4, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 2.2.4: Space heating generation systems, The performance and quality of CHP
electricity and heat (incl. on-site and micro-CHP)
prEN wi 9 part 2.2.5, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 2.2.5: Space heating generation systems, The performance and quality of district
heating and large volume systems
prEN wi 9 part 2.2.6, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 2.2.6: Space heating generation systems, The performance of other renewables
heat and electricity
prEN wi 9 part 2.2.7, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 2.2.7: Space heating generation systems, Biomass combustion systems
prEN wi 10, Heating systems in buildings - Method for calculation of system energy requirements and system
efficiencies – Part 2.3: Space heating distribution systems
prEN wi 11 part 3.1, Heating systems in buildings - Method for calculation of system energy requirements and
system efficiencies – Part 3.1: Domestic hot water systems, characterisation of needs (tapping requirements)
prEN wi 13, Energy performance of buildings – Energy requirements for lighting
prEN wi 14, Energy performance of buildings – Calculation of energy use for space heating and cooling –
Simplified method
prEN wi 17, Thermal performance of buildings – Calculation of energy use for space heating and cooling –
General criteria and validation procedures
prEN wi 20, Ventilation for buildings – Calculation methods for energy requirements due to ventilation systems
in buildings
3 Definitions and symbols
3.1 Definitions
For the purposes of this document, the definitions given in EN ISO 7345 and the following terms and
definitions apply:
3.1.1
building net energy (useful energy)
energy supplied by ideal energy systems (no system losses are taken into account) to provide the required
services for heating, cooling, ventilation, domestic hot water and lighting. Recovered losses and gains are
taken into account
3.1.2
building system
technical equipments for heating, cooling, ventilation, domestic hot water and lighting
3.1.3
CO emission factor
quantity of CO emitted to the atmosphere per unit of energy source (kg CO / kWh energy source)
2 2
3.1.4
CO annual emission factor (system-average for an entire year)
emission factor calculated by estimating the total CO emissions during a year and dividing that figure by the
total energy delivered over the year
3.1.5
CO marginal emission factor (average for an entire year)
emission factor applied to multi-plant generation systems and depending on the plant merit order (priority
order in which the plants are put into operation as demand changes), the size of the system and the demand
pattern
3.1.6
calculation period
time period (time step) considered for calculation of the energy losses and gains (e.g. month, day, boosted
subperiod), ref. prEN wi 7
3.1.7
co-generation (building bound)
combined generation of power (electricity) and heat, where heat delivery is restricted to the buildings. The
total amount of heat to be delivered by the building bound co-generation unit can be determined unequivocal.
Other cases of co-generation will be considered as district heating
3.1.8
cooling
process of heat extraction for thermal comfort
3.1.9
delivered energy
energy supplied to the building through the system boundary to satisfy the energy requirements for heating,
cooling, ventilation, domestic hot water and lighting
3.1.10
energy carrier
substance or phenomenon that can be used either to produce mechanical work or heat or to operate chemical
or physical processes
3.1.11
energy demand
energy to be delivered by an ideal energy system (no system losses are taken into account) to provide the
required service to the end user (e.g. to maintain the internal set-point temperature of a heated space)
3.1.12
energy requirements
energy supplied to the technical system (system losses are taken into account) to provide the required service.
Energy requirements can be specified for each subsystem (e.g. distribution, storage) and express the energy
supplied to the subsystem
3.1.13
energy supplied
energy made available. Energy can be supplied at different levels (e.g. termed “net energy” or “useful energy”
when made available to the consumer after final conversion to provide the required service)
3.1.14
net energy
energy supplied by the energy systems to provide the required services, e.g. maintaining the building at the
specified internal temperature, ventilating a space, lighting a space. Recovered losses and gains are taken
into account
3.1.15
overall energy use of the building
energy delivered to the energy systems for heating, cooling, ventilation, domestic hot water and lighting. The
overall energy takes into account the delivered energy and the energy produced inside the building and
delivered back to the market
3.1.16
primary energy
energy that has not been subject to any conversion or transformation process (e.g. oil in the oil fields). Primary
energy may be either resource energy or renewable energy or a combination of both
3.1.17
primary energy factor
primary energy divided by delivered energy, where primary energy is the energy required to supply one unit of
delivered energy of the same type, taking into account the primary energy required for extraction, processing,
storage, transport, generation, transformation, transmission, distribution, and any other operations necessary
for delivery of energy to the building in which the delivered energy will be used. Delivery operations may call
for energy of various types (e.g., electricity, oil), and each of those should be given as primary energy using
the appropriate primary energy factor
3.1.18
primary resource energy factor
resource energy divided by delivered energy, where resource energy is the energy required to supply one unit
of delivered energy, taking into account the resource energy required for extraction, processing, storage,
transport, generation, transformation, transmission, distribution, and any other operations necessary for
delivery of energy to the building in which the delivered energy will be used. Any renewable energy
component of the delivered energy is ignored. Delivery operations may call for energy of various types (e.g.
electricity, oil), and each of those should be given as resource energy using the appropriate primary resource
energy factor.
3.1.19
recoverable losses
part of the losses from the heating, cooling, ventilation, domestic hot water and lighting systems, which may
be recovered to lower the energy requirements
3.1.20
recovered loss
part of the recoverable losses which are recovered to lower the energy requirements
3.1.21
renewable energy
energy taken from a source which is not depleted by extraction (e.g. solar, wind)
3.1.22
resource energy
energy taken from a source which is depleted by extraction (e.g. fossil fuels)
3.1.23
system
technical equipment providing a required service (e.g. heating system providing the required service for
heating)
3.1.24
utilisation factor
fraction of recoverable losses or gains that can be recovered.
3.1.25
ventilation heat loss
heat loss resulting from heating of the average amount of air per time unit that enters a building or part of a
building in one way or another

3.2 Symbols and units
For the purposes of this document, the following symbols and units (Table 1) and indices (Table 2) apply:
Table 1 : Symbols and units
Symbol Name of quantity Unit
E
emission kg
f
conversion factor -
Q quantity of heat, energy kWh

Table 2 : Indices
aux auxiliary h heating energy p primary
rb recoverable
c cooling i, j indices rp primary resource
CO2 CO2 in input to system sc cooling system
sg generation system
d distribution l lighting sh heating system
elect electrical n  net sv ventilation system
sw domestic hot water system
g generation out output from system w domestic hot water

4 Principle of the method
4.1 Overall energy use - integrated energy performance of buildings
The integrated energy performance of buildings depends on:
 the building envelope and required services expressed by the building net energy (building energy
requirements, building losses, building gains);
 the building systems (heating system, cooling system, etc) expressed by the energy streams across the
system boundary. Renewables and energy production inside the building are taken into account;
 the interaction between the building envelope and the building systems;
 the choice of the energy carrier (fossil fuels, renewables).
The performance of the energy chain situated outside the building and related to the energy sources is taken
into account in calculation of the primary energy and the CO emissions.
Figure 1 illustrates the elements influencing the integrated energy performance of buildings.

Figure 1 — Elements influencing the integrated energy performance of buildings (example).

The following assumptions apply for calculation of the integrated energy performance of buildings:
a) System boundary
The building envelope constitutes the system boundary.
Inside the system boundary, only the defined uses (heating, cooling, ventilation, domestic hot water and
lighting) are taken into account. Other uses like electrical consumption for household devices (TV sets,
refrigerators, etc.) are not taken into account.
Energy can be imported or exported through the system boundary. All the energy streams across the system
boundary are identified. Some of these energy streams can be quantified by meters (e.g. gas, electricity,
district heating and water) in case the system devices (boiler, chiller, cooling tower, etc.) are located outside
the building envelope. If the system devices form part of the building system, they are considered to be inside
the system boundary.
For active solar energy systems, the generation devices (solar panels: thermal and photovoltaic) are
considered as located just outside the system boundary. The auxiliary energy needed to supply the energy
from the source (solar panel) to the building is considered inside the system boundary, but the incident solar
radiation on the panels is not taken into account, because it does not cross the system boundary (see figure
2). Passive solar radiation (the incident solar radiation entering through the openings of the building) is taken
into account because it crosses the system boundary.

Figure 2 — System boundary: Examples of energy streams across system boundary
Assessment of energy performance shall not be limited to the buildings where the energy consumption takes
place. A holistic approach calls for a framework that defines end-user savings as savings carried out along the
entire energy chain (e.g. district heating and cooling). The performance of the energy chain situated outside
the system boundary is taken into account in calculation of primary energy and CO emissions.
b) Calculation period
The objective of the calculation is to determine the annual overall energy use, primary energy and CO
emission. This may be done in one of the following two different ways:
 using annual data for the system operation period and performing the calculations using annual average
values;
 dividing the year into a number of calculation periods (e.g. months, weeks) and performing the
calculations for each period using period-dependent values and sum up the results for all the periods over
the year.
c) Interactions between the building envelope and the building system - Calculation of recovered
losses and gains
The interactions between the different energy uses (heating, cooling, ventilation, etc.) are taken into account
by calculation of recovered losses which could have a positive (e.g. heat) or negative (e.g. cooling) impact on
the energy performance of the building.
Two approaches are admitted for calculation of the building net energy (see figure 3):
 a holistic approach considering all recoverable losses and gains (in the building part and in the system
part). Calculation of the recovered losses for heating and cooling is defined in prEN wi 14.
As the recoverable system losses depend on the building net energy, and the building net energy
depends on the recovered system losses, an iteration is required:
 calculate the building net energy, taking into account only the recovered losses and gains of lighting
and passive solar radiation and internal losses and gains (ignore the recoverable system losses);
 perform the system calculation and determine the recoverable system losses;
 calculate again the building net energy, taking into account all recoverable losses and gains (in the
building part and in the system part);
 perform the system calculation again.
 a simplified approach taking into account recoverable losses and gains excluding the recoverable losses
of the heating, cooling, ventilation and domestic hot water systems. The recovered system heat losses
are deducted from the loss of each considered part. This will avoid iterations:
 calculate the building net energy, taking into account only the recovered losses and gains of lighting
and passive solar radiation and intern
...