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Dirk Van OrshovenMS Mechanical EngineeringIndependent energy engineerdirk.van.orshoven@skynet.be | Dick van DijkMS Applied PhysicsSenior advisor TNOdick.vandijk@tno.nl |
Following
CEN Mandate M/480 [1], a comprehensive series of European (CEN) and
international (CEN & ISO) standards is at an advanced stage of development.
The series is called the "set of EPB standards" and aims at the
international harmonization of the methodology for the assessment of the
overall and partial energy performances of buildings. The first issue of the
2015 REHVA journal [2] gave a broad overview of these standards. This article
provides further information on 1 of them, namely draft EN ISO 52003,
which is being developed in ISO/TC 163/WG 4 (joint working group of
ISO/TC 163 with ISO/TC 205) and which is due to replace EN 15217:2007
and ISO 16343:2013.
Draft
standard EN ISO 52003-1 [3], together with its accompanying draft
technical report CEN ISO/TR 52003-2 [4], gives guidance on the main
uses that can be made of the outputs (EPB indicators) of the EPB assessment
standards, in particular their use for EPB requirements and EPB ratings. This
can be called the "post processing" of the results of the EPB
assessment. The standard itself (i.e. part 1) lists and clarifies the different
steps that still need to be taken in order to make full use of the EPB
methodologies. The technical report (i.e. part 2) provides background
information supporting these tasks. Due to its overarching nature, EN ISO 52003
is closely linked to the EPB overarching standard, EN ISO 52000-1
[5].
By
describing explicitly the different policy making aspects, all parties involved
can gain a better understanding of the issues at hand, thus facilitating the
policy making process. In the case of public regulations, the parties include
not only the regulators themselves, but also all stakeholders involved in the
policy development, notably diverse organizations representing citizens,
designers, industry, craftsmen, etc.
Figure
1 shows the
relations between different EPB aspects that may be part of the
post-processing. (The numbers refer to the paragraphs in the standard.) EPB
indicators are the output provided by the EPB assessment standards. Two main
uses of these variables are the setting of requirements and the judgment of how
well/poor they perform, i.e. the rating. All this information can be included
in an EPB certificate.
For certain
EPB indicators, a specific, but important aspect is the tailoring of a
requirement or of a rating reference to each individual building (dashed
lines). This tailoring is a function of the building's category (dwelling,
office, etc.), location (determining the outdoor climate), size, etc. For many
outputs such variable (rather than constant) requirement/reference values are
essential. E.g. in order to arrive at a technical and economical strictness of
requirements that is comparable for all individual projects. To this end some
new ('post-processing') calculations may need to be defined (see below), beyond
what is already specified in the EPB standards. Sometimes this leads to the
definition of a new, derived indicator, notably by taking the ratio of the
original indicator and the tailored reference.
Figure 1. Schematic
overview of the relations between various EPB aspects.
Setting EPB
requirements involves several aspects:
·
defining
the different objectives that are pursued: e.g. a healthy and comfortable
indoor environment, energy efficiency, fabric and equipment preservation, etc.;
·
carefully
selecting an adequate mix of EPB indicators for which requirements are set:
usually a judicious combination of overall energy performances (e.g. with and
without renewable energy) and partial energy performances (e.g. on the fabric,
or the systems) is needed to fully achieve all objectives;
·
choosing
the appropriate type of quantitative requirement for each of the selected
indicators, notably whether a constant value or a variable value (see
"tailoring" below);
·
determining
the actual strictness and its evolution over time.
Each of
these aspects is discussed in detail in draft EN ISO 52003.
A numeric
indicator for an EPB feature (as produced by the EPB assessment methods) does
not yet automatically reveal the energetic quality of the building with respect
to that EPB feature. The EPB indicator needs to be compared to one or more
reference values in order to judge (rate) the good or poor performance of the
EPB feature under consideration.
A typical
reference value is for instance a representative value for new buildings or a
representative value for the average building stock.
Energy
(performance) rating is the evaluation of the energy performance against one or
more reference values, which may include ranking on a continuous or discrete
scale.
Figure
2 shows an
example of a rating (scale) based on one reference in position of energy class
D (nref=4). Upper boundaries of energy classes A to G (n=1 to 7) are
presented as the ratio to this reference.
Figure
3 shows an
example of a subsequent graphical representation for an energy label.
Figure 2.
Example of an energy performance rating (scale).
Figure 3.
Example of graphical representation of the energy performance classes for an
energy label.
For several
important EPB indicators (e.g. overall energy performances, heating and cooling
needs, mean thermal transmittance of the thermal envelope) the numeric value
that corresponds to the technical and economic optimum often varies strongly
from 1 construction project to another, depending on function, size, shape,
etc.
Similarly,
for such indicators the numeric gradation between "good" and
"bad" in a rating can also vary strongly from 1 project to another.
In order to
treat all buildings in the same manner (e.g. reflecting the same technical and
economic strictness), it is for these indicators thus of crucial importance to
use variable value requirements or references that take into account all
relevant specific features of each individual building. This is called tailoring.
The 2 practical manners for such tailoring that are found in practice are:
·
the
notional reference building approach
·
the
formula approach
Although
both approaches may appear very different at first sight, they actually result
in identical, or very similar, results if the same technical starting
assumptions are taken. They can thus both serve the purpose well.
Figure
4 illustrates
on the basis of some 200 real dwelling shapes (each individual cross) how for a
given set of technical measures (level of thermal insulation, type of boiler,
degree of airtightness, etc.) the numeric value of an overall energy
performance indicator per useful floor area can strongly vary from one project
to another. The x-axis is the ratio of the area of the envelope to the useful
floor area.
If the
reference value that is used for rating and/or to set a requirement is a fixed
value (in casu: requirement expressed as maximum value in kWh/m² floor area
disregarding building shape or size: e.g. red horizontal line), then buildings
with a relatively large envelope area[1]
(compared to the floor area) would need a large technological-economic effort
to meet the requirement, while on the other hand buildings with a relatively
small envelope area would need only a small technological- economic effort to
meet the same requirement. A more appropriate reference for the rating and/or
requirement takes into account this variation and determines project-specific,
tailored quantitative requirements.
Figure 4.
Example of the impact of a fixed (constant value) requirement versus a more
appropriate variable value (tailored).
The new
draft texts of EN ISO 52003 list explicitly the different actions
that need to be taken into account and provide background information on
various post-processing tasks (selecting EPB indicators for requirements and
ratings, tailoring and certification). In doing so, they, first of all, provide
support to the regulators. In addition, the texts inform all stakeholders, so,
that these can engage in a productive dialogue with the regulators. In this
manner, a well-considered regulation can be developed matching the
sophistication of the actual EPB assessment methods.
The authors
would like to acknowledge, for their valuable input and comments, all the
active experts in the ISO and CEN working groups to which the preparation of
these standards has been assigned, as well as all the commenters who have
provided feedback.
[4] CEN ISO/TR 52003-2, Energy
performance of buildings – Indicators, requirements, ratings and certification
– Part 2: Explanation and justification of ISO 52003-1 (in preparation; submission to Committee Approval expected in 2016).
[5] EN ISO 52000-1, Energy performance
of buildings — Overarching EPB assessment – Part 1: General framework and
procedures (in preparation; submission of FDIS to final ballot expected in
2016).
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