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IEA
I NTERNATIONAL E NERGY A GENCY
E NERGY C ONSERVATION
IN
B UILDINGS
AND
C OMMUNITY S YSTEMS
Annex Definition
Annex35
HybVent
Hybrid Ventilation in New and Retrofitted Office Buildings
Aalborg University, May 2017
IEA-BCS Annex 35: HybVent
ANNEX 35
HYBRID VENTILATION IN NEW AND RETROFITTED
OFFICE BUILDINGS
1.
DESCRIPTION OF TECHNICAL SECTOR AND DEFINITIONS
1.1.
Description of Technical Sector
Immediately after the energy crisis in 1973 attention was focused on thermal insulation,
airtightness of buildings and heat recovery to decrease energy consumption of heating and
cooling of buildings. Buildings were designed to be isolated from the outdoor environment
with an indoor environment controlled by artificial lighting, mechanical ventilation and
heating and cooling systems.
Today, in the design of new buildings and retrofit of old buildings, the attention has turned
towards a more integrated design with focus not only on thermal insulation, airtightness
and heat recovery but also on optimal use of sustainable technologies as passive solar
gains, daylighting and natural ventilation. Buildings are designed to interact with the
outdoor environment and they are utilizing the outdoor environment to create an acceptable
indoor environment whenever it is beneficial.
The extent to which sustainable technologies can be utilized depends on outdoor climate,
building use, building location and design. Under optimum conditions sustainable
technologies will be able to satisfy the demands for heat, light and fresh air. In some cases
supplementary mechanical systems will be needed and in other cases it will not be possible
to use sustainable technologies at all.
In thermally well insulated office buildings, which are more and more frequent in IEA
countries, ventilation (and cooling) account for more than 50% of the energy requirement,
and a well-controlled and energy-efficient ventilation system is a prerequisite of low energy
consumption. Natural ventilation and passive cooling are sustainable, energy-efficient and
clean technologies as long as they can be controlled. These technologies are well accepted
by occupants and should therefore be encouraged wherever possible.
Unfortunately, the design of energy-efficient ventilation systems in office buildings has
often become a question of using either natural ventilation and passive cooling or
mechanical ventilation and cooling. This prevents a widespread use of sustainable
technologies because a certain performance cannot be guaranteed under all conditions. In
fact in the majority of cases a combination of systems would be beneficial depending on
outdoor climate, building design, building use and the main purpose of the ventilation
system.
The number of office buildings to be retrofitted in most IEA countries is now much larger
than the potential for new buildings. In many cases there is a large potential for use of
sustainable technologies either as a supplement to the existing mechanical systems or as a
replacement for conventional systems.
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IEA-BCS Annex 35: HybVent
Therefore, there is certainly a need for development of innovative hybrid ventilation
systems.
Suitable design tools as we know them for mechanical systems are not available for hybrid
ventilation systems. Valid design tools would give architects and engineers the necessary
confidence in system performance, which in many cases, is the decisive factor for choice of
system design.
The scope of this annex is therefore to obtain better knowledge of the use of hybrid
ventilation technologies and to focus on development of control strategies for hybrid
ventilation, on development of methods to predict hybrid ventilation performance in office
buildings and on implementation and demonstration of hybrid ventilation in real buildings.
Thorough control of hybrid ventilation in new as well as in retrofitted buildings requires a
completely integrated approach to building design, its technical systems (lighting, heating),
occupant behaviour, topography of surroundings, climatic and meteorological conditions,
etc. The integrated approach is the basic strategy applied in this annex.
Therefore, in development of methods to predict hybrid ventilation performance preference
is given to combined models, describing as far as possible all involved phenomena to give
realistic results, even if simplifying assumptions are required.
The fact that input data are not known with perfect accuracy is also taken into account. It
has no meaning to develop a sophisticated method if the uncertainty of input data results in
output data which are not more reliable than output from a simpler method.
1.2.
Definitions
Hybrid ventilation systems can be described as systems providing a comfortable internal
environment using different features of both natural ventilation and mechanical systems at
different times of the day or season of the year. It is a ventilation system where mechanical
and natural forces are combined in a two mode system. The basic philosophy is to maintain
a satisfactory indoor environment by alternating between and combining these two modes
to avoid the cost, the energy penalty and the consequential environmental effects of yearround air conditioning. The operating mode varies according to the season and within
individual days, thus the current mode reflects the external environment and takes
maximum advantage of ambient conditions at any point in time. The main difference
between conventional ventilation systems and hybrid systems is the fact that the latter are
intelligent systems with control systems that automatically can switch between natural and
mechanical mode in order to minimize the energy consumption.
Hybrid ventilation should dependent on building design, internal loads, natural driving
forces, outdoor conditions and season fulfil the immediate demands to the indoor
environment in the most energy-efficient manner. The control strategies for hybrid
ventilation systems in office buildings should maximize the use of ambient energy with an
effective balance between the use of advanced automatic control of passive devices and the
opportunity for users of the building to exercise direct control of their environment. The
control strategies should also establish the desired air flow rates and air flow patterns at the
lowest energy consumption possible. The figure below shows the definition of hybrid
ventilation applied in Annex 35.
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IEA-BCS Annex 35: HybVent
Definition of Hybrid Ventilation
Hybrid Ventilation is a two-mode system which is controlled to minimize the
energy consumption while maintaining acceptable indoor air quality and
thermal comfort. The two modes refer to natural and mechanical driving forces
Purpose of Ventilation
All hybrid systems have to provide air for indoor air quality purposes, but in
addition some also provide air for thermal conditioning and thermal comfort
during working hours
Purpose of Control System
The purpose of the control system is to establish the desired air flow rate and
air flow pattern at the lowest energy consumption possible
Figure 1. Annex 35 definitions of hybrid ventilation and purpose of ventilation and control system.
2.
OBJECTIVES
The objectives of Annex 35 are
 to develop control strategies for hybrid ventilation systems in new and retrofitted
office and educational buildings
 to develop methods to predict hybrid ventilation performance in hybrid ventilated
buildings
 to promote energy and cost-effective hybrid ventilation systems in office and
educational buildings
 to select suitable measurement techniques for diagnostic purposes to be used in
buildings ventilated by hybrid ventilation systems
3.
MEANS
3.1.
Subtasks
The following three subtasks will be carried out in order to reach the objectives:
Subtask A: Development of control strategies for hybrid ventilation
Subtask B: Theoretical and experimental studies of performance of hybrid
ventilation. Development of analysis methods for hybrid ventilation
Subtask C: Pilot studies of hybrid ventilation
3.1.1.
Subtask A: Development of Control Strategies
Integration of a natural and a mechanical ventilation system in a common hybrid
ventilation system requires development of new control strategies. The objective of this
subtask is to develop strategies that can control hybrid ventilation systems at any time and
for a certain combination of internal loads, outdoor conditions and comfort requirements
can ensure that the immediate demands to the indoor environment are fulfilled in the most
energy efficient manner.
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IEA-BCS Annex 35: HybVent
The participants shall achieve this objective, by means of a typical case in their own
country and climate, by theoretical studies, laboratory experiments and pilot studies of the
performance of different control strategies in a hybrid ventilated office or educational
building. The main focus shall be on development of strategies for switching between
ventilation modes and for combining central automatic and individual manual control.
The cost-effectiveness of different ventilation and control strategies shall be investigated
by comparing capital cost and operational costs against a typical refurbishment or new
building. Assessment philosophies and analysis methods of hybrid ventilation concepts
shall be developed in the framework of Energy Performance Standardisation Regulations.
3.1.2.
Subtask B: Development of Analysis Methods
The objective of this subtask is to achieve a better understanding and a better control of the
hybrid ventilation process, which is a prerequisite for a successful application of hybrid
ventilation and, based on this knowledge, to develop analysis methods for hybrid
ventilation design.
The participants shall achieve the objective by investigating the different elements of the
air flow process in hybrid ventilation from air flow around buildings, air flow through
openings, air flow in rooms to air flow between rooms in a building. The development of
analysis methods shall focus partly on combining existing analysis methods and partly on
developing new analysis methods for air flow control and thermal conditioning in hybrid
ventilated buildings. The work shall focus on two major developments.
The first development is a model that should be able to predict statistical occurrences of
energy and air flow rates in hybrid ventilated buildings. The model shall be developed by
combining available physical models of the phenomena involved with stochastic models.
This procedure includes a sensitivity study and error analysis as well as comparisons with
experiments and simulations with other models.
The second development is an analysis model that combines existing thermal simulation
models with existing air flow models. In this way the thermal dynamics of the building can
be taken into account in predicting the performance of hybrid ventilation, which is very
important both with regard to the driving forces and the air flow requirements.
3.1.3.
Subtask C: Pilot Studies of Hybrid Ventilation
The objective of this subtask is through pilot studies to implement hybrid ventilation
systems and demonstrate their performance.
The participants shall achieve this objective by analysis of hybrid ventilation components
and systems. The participants shall monitor pilot studies to collect data on performance
(IAQ, thermal comfort and energy consumption) and to evaluate corresponding control
strategies and analysis methods. The pilot studies shall include both retrofitted and new
build designs and shall highlight similarities and differences in climatic issues (including
seasonal differences), institutional and cultural issues (developers and occupants), and
technology transfer issues. The pilot studies shall concentrate on success stories of hybrid
ventilation but also critically highlight problematic cases. New diagnostic measurement
techniques may be developed and reported.
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IEA-BCS Annex 35: HybVent
3.2.
Participating Countries
An overview of participating countries and their subtask affiliation is shown in Table 1.
Table 1. Overview of participation in Annex 35.
Country
Australia
Belgium
Canada
Denmark
Finland
France
Germany
Greece
Italy
Japan
Norway
Sweden
The Netherlands
United Kingdom
U.S.A.
3.3.
Subtask A
Subtask B
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Subtask C
X
(X)
X
X
X
X
X
X
X
X
Programme of Work
An overview of programme of work is shown in Table 2.
Table 2. Overview of programme of work.
Task
Research Method
State-of-the-art
Review
Subtask A
 Definition of requirements and
evaluation criteria for control
strategies
 Development of strategies for
switching between and combining
ventilation modes
 Development of strategies for
combination of automatic and
manual individual control
 Control system design
 Demonstration and
evaluation of control
strategies
 Survey of available analysis
methods
 Achieve better understanding of the
physics of hybrid ventilation (air
flow control)
 Integration of air flow and thermal
simulation models
 Development of probabilistic
analysis method
 Application and
evaluation of analysis
methods
 Survey of existing systems
and solutions to specific
problems
 Market survey of
components
 Survey of building codes
 Analysis of hybrid ventilation
components and systems
 Analysis of barriers for hybrid
ventilation application
 Cost-benefit analysis of hybrid
ventilation
 Demonstration of hybrid
ventilation performance
 Technology transfer
Development of
Analysis Methods
Subtask C
Pilot Studies
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Implementation and
Demonstration
 Survey of existing strategies
 Local versus central control
Development of
Control Strategies
Subtask B
Theoretical and
Experimental Studies
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IEA-BCS Annex 35: HybVent
3.3.1.
Subtask A
The participating countries in subtask A shall based on existing buildings perform a stateof-the-art review of existing control strategies and algorithms applicable for hybrid
ventilation, including a critical view on the integration with BEMS and on individual
contra whole building control. They shall also based on existing buildings provide a market
survey of commercially available control systems, automatic control devices, algorithms,
etc. The results shall be summarized and included in the state-of-the-art report.
In the development of new control strategies the focus will be on different issues in the
participating countries and will cover a range of hybrid ventilation system and building
designs.
Australia will investigate the impact of occupant individual control of heating, cooling and
lighting on energy consumption in an office building. Denmark will focus on development
and evaluation of control strategies and automatic control systems for open plan offices
that allow control of local indoor climate. France will focus on theoretical definition,
experimental evaluation and implementation of fuzzy control strategies and automatic
tuning techniques of controllers in office and educational buildings. Norway will develop
and evaluate control strategies for a hybrid ventilation system with heat recovery and focus
on controlling air flows in a three storey office building, on individual floors and in
individual rooms, respectively. The United Kingdom's input will based on the state-of-theart review of control devices, systems and strategies; parametric analysis will be carried out
using computer ventilation modelling to estimate their performance.
Belgium, Denmark, The Netherlands will work on a classification of hybrid ventilation
systems and assessment philosophies and analysis methods of hybrid ventilation concepts
will be developed in the framework of Energy Performance Standardisation Regulations.
The results shall be documented in technical reports and be public available on the
homepage of Annex 35. All countries shall summarize their findings and contribute written
material to the final report as agreed.
3.3.2.
Subtask B
The participating countries in subtask B shall perform a state-of-the-art review of the
available analysis methods for prediction of hybrid ventilation performance. These
methods include analytical/empirical methods, zonal and multizone methods, probabilistic
methods and computational fluid dynamics. The results shall be summarized and included
in the state-of-the-art report.
The participating countries will focus on achieving a better understanding of the air flow
process and on development of new analysis methods related to hybrid ventilation.
Hybrid ventilation air flow process
Individual elements of the air flow process in hybrid ventilation will be investigated as well
as the air flow process of whole systems.
Greece will work on translation of meteorological data from weather stations into urban
data. Belgium will study wind pressures around buildings and the impact on predicted
performances, while Denmark will based on theoretical studies investigate the impact of air
flow and local climate around buildings on the optimum location of air inlets and outlets.
Denmark and Italy will by systematic tests of hybrid ventilation components as air inlets
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IEA-BCS Annex 35: HybVent
and outlets obtain the necessary performance data for component characterization. Italy and
Germany will investigate, optimize and model solar chimney performance and Italy will
develop a model for ventilated roofs and facades. Australia and Canada will investigate air
flow patterns, energy transport and air flow control in a hybrid ventilated building with
solar chimneys and under floor plenum for passive cooling. Greece and Sweden will
develop models for buoyancy driven flow in stairwells. Sweden will study and develop
models for inter-zonal buoyancy driven and forced air flows through both vertical and
horizontal openings. Sweden will develop tracer gas methods that are capable of evaluating
such flows.
Finland, Germany, Japan and Sweden will, based on simulation studies with different
simulation techniques, analyse and develop hybrid ventilation concepts for office and
educational buildings. Finland will focus on development of concepts for office buildings
in Finish climates, while Germany and Sweden will focus on educational buildings, and
Japan on improvement of hybrid ventilation concepts based on the task-ambient ventilation
principle.
Multizone methods
Both Australia , Finland and U.S.A. will develop analysis methods that combine an
existing thermal simulation model with an existing multizone air flow model. In Australia
it will be a further development of the program CHEMIX where as in the U.S.A. it will be
an integration of the multizone air flow model COMIS into the thermal building simulation
model Energy Plus.
Zonal methods
Canada, France and Italy will develop and improve zonal models for the prediction of
thermal comfort, indoor air quality and thermal stratification in hybrid ventilated buildings.
The main emphasis will be placed on the special boundary conditions and ventilation
systems that prevail in hybrid ventilated buildings as well as implementation of the
prediction of different control strategies.
Probabilistic methods
Denmark will develop a probabilistic analysis method for hybrid ventilation that can
predict the probability of critical incidents as unsatisfactory air flow, poor indoor air quality
or large energy consumption for a specific design. Italy will develop a probabilistic
approach to inlet and outlet performance based on computer calculations and experimental
evaluation of the results. Australia will apply a probabilistic approach to study output
uncertainties, due to uncertainties in input parameters, of the solutions obtained from
simple analytical methods.
Simple analytical methods
Australia and Denmark will develop new and simple analytical methods for the design of
hybrid ventilation in single and multizone buildings. Germany and United Kingdom will
investigate and demonstrate the applicability of developed analysis methods by parametric
analysis and comparisons with measurements in existing buildings. Greece will incorporate
developed models in the Building Performance TOOLBOX. Norway will develop and
implement simple analytical models in the simulation program SCIAQ while Sweden
expand the NatVent program to include hybrid ventilation predictions.
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IEA-BCS Annex 35: HybVent
The results shall be documented in technical reports and be available on the homepage of
Annex 35. All countries shall summarize their findings and contribute written material to
the final report as agreed.
3.3.3.
Subtask C
The participating countries in subtask C shall perform a state-of-the-art review of hybrid
ventilation systems with examples of existing systems and solutions to specific problems.
They shall provide a market survey of commercially available components, systems, etc.
and investigate the suitability of hybrid ventilation in different building types and urban
locations for the climatic conditions of their country. Finally, they shall provide a survey of
the building codes of their country with special focus on items that have an impact on the
applicability of hybrid ventilation. The results shall be summarized and included in the
state-of-the-art report.
The participating countries shall provide a pilot study with a hybrid ventilation system
according to the definition applied in this annex. The performance (IAQ, thermal comfort,
energy consumption, etc.) of the hybrid ventilation system with the corresponding control
strategies shall be monitored during a one year period. Measurement data shall also be
provided for evaluation of analysis methods and/or control strategies. Participants shall
provide an analysis of barriers for hybrid ventilation application as well as a cost-benefit
analysis of the alternatives to ventilation system design.
The individual research group relating to each pilot study is responsible for the collection
of data on the performance, analysis of the results and providing a technical report
describing the building, measurements and findings. This report shall be available on the
homepage of Annex 35. All countries shall summarize their findings and contribute written
material to the final report as agreed.
3.3.4.
Planned effort in Annex 35
The planned effort in Annex 35 is summarized in Table 3. It shows country contribution to
each subtask according to the planned work described in sections 3.3.1 to 3.3.3.
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IEA-BCS Annex 35: HybVent
Table 3. Planned effort in Annex 35 (staff months)
AU
B
CAN DK FIN
F
D
G
I
J
N
x
x
x
x
x
x
54
18
11
40
24
9
Contribute to state-ofthe-art and final report
x
x
x
x
x
x
x
Air flow process
5
2
35
12
20
7
S
NL UK US
Subtask A
Contribute to state-ofthe-art and final report
Development of
control strategies
x
4
x
x
Subtask B
Multizone methods
4
x
x
19
10
18
x
x
?
8
Zonal methods
36
36
36
Probabilistic methods
5
60
Simple analytical
methods
5
3
9
24
9
6
10
2
9
Subtask C
Contribute to state-ofthe-art and final report
Pilot study analysis
and measurements
3.4.
x
x
3
3
x
x
x
x
x
11
16
8
37
28
14
13
6
?
6
Annex Management
The annex shall be managed by the Operating Agent and the leaders of the subtasks A-C
(The Technical Advisory Committee). All subtasks will provide material for the two final
reports which will have two editors each.
The organization of Annex 35 is illustrated in Figure 2.
Technical
Advisory
Committee
TL
Development of
Control Strategies
OA
TL
Development of
Analysis Methods
TL
Pilot Studies
E
E
E
E
Reporting
Principles of
Hybrid Ventilation
State-of-the-art
Review
Figure 2. Organization of Annex 35 with subtasks, final reports and a Technical Advisory Committee.
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IEA-BCS Annex 35: HybVent
3.4.1.
The Operating Agent
The Operating Agent is responsible for the overall performance, time schedule, reporting,
knowledge transfer, etc. of Annex 35.
3.4.2.
Subtask Leaders
The leaders of subtasks A-C are responsible for the quality and the management of the
work within their subtask.
The subtask leader shall be a participant who provides a high level of expertise to the
subtask and undertakes in his or her country substantial research and development in the
field of the subtask. Subtask leaders shall be proposed by the Operating Agent, and
designated by the Executive Committee acting by unanimity. Changes in the leadership
may be agreed to by the Executive Committee, acting by unanimity of the participants.
The subtask leaders of subtasks A-C will:
1) Co-ordinate the work performed under the subtask
2) Assist the Operating Agent in preparing the detailed programme of work
3) Direct technical workshops and provide the Operating Agent with written
summaries of workshop results
4) Edit technical reports resulting from the Subtask and organize their publication
3.4.3.
Technical Advisory Committee
The participants shall establish a Technical Advisory Committee (the “Technical Advisory
Committee”) consisting of the leaders of subtasks A-C and the Operating Agent or their
respective designees. The Technical Advisory Committee shall assist the Operating Agent
in the co-ordination of the annex and advise the Operating Agent on the performance of the
annex.
4.
RESULTS AND END PRODUCTS
The results of Annex 35 will be summarized in two final reports and specific results of
individual subtasks will be reported in technical reports and papers.
4.1.
State-of-the-art Review
This report will describe the state-of-the-art of hybrid ventilation technologies, of control
strategies and algorithms and of analysis methods. The report will provide examples of
existing systems and show solutions to specific problems (fresh air supply, excess heat
removal, etc.) in particular office buildings located in different outdoor climates. It will,
based on the existing buildings, also include a market survey of commercially available
hybrid ventilation components.
The report will focus on the impact of differences in climate (including seasonal
differences as winter heating and summer cooling), building design, building use and
internal loads on energy performance, indoor air quality and thermal comfort.
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IEA-BCS Annex 35: HybVent
4.2.
Principles of Hybrid Ventilation
This report will describe the principles of hybrid ventilation, including solutions for
energy-efficient, comfortable and cost-effective hybrid ventilation and recommendations
on control strategies and analysis methods. The report will be written on the basis of
experience gained in annex subtasks as well as achievements from previous research (stateof-the-art review).
4.3.
Annex Beneficiaries
The “Principles of Hybrid Ventilation” report will be written for architects and engineers,
and parts of it will be available for a large public. Therefore, architects should participate in
the planning and review process of the report. This guide will provide advice for good
practice for application of hybrid ventilation in new and retrofitted buildings. The emphasis
will be on characteristic cases, which do not require specific studies.
The technical reports and analysis methods will be available for engineering offices,
helping them to provide advice to architects and to design systems, especially concerning
cases not treated in the “Principles of hybrid ventilation” report.
5.
TIME SCHEDULE
The duration of the Annex will be four years (August, 1998 - July, 2002) and the project
period is divided into three phases - a fact finding phase, a working phase and a reporting
phase. The following figure shows the time schedule for the different annex activities and
the major milestones.
Figure 3. Time Schedule and Milestones
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IEA-BCS Annex 35: HybVent
6.
FUNDING AND COMMITMENT
The work has been divided into three subtasks and each participant shall work in at least
one of the subtasks. All participants are also required to deliver information and written
materiel to the final reports as agreed in the annex. The minimum commitment in the
annex for each participant is described in paragraphs 3.2 and 3.3. Each participant shall
individually bear the costs incurred in the activities. Funding includes working costs as
well as travelling costs for participating in a minimum of two expert meetings per year in
any of the participating countries during the four-year annex period and eventual overhead
costs.
Any participating country has access to the workshops and results of all subtasks. The
participating country must designate at least one individual (an active researcher, scientist,
or engineer, here called expert) for each subtask they participate in. It is expected that the
same expert attends all expert meetings and acts as technical contact regarding the national
subtask contribution.
For the Operating Agent funding shall allow for extra 4 months per year for annex
activities, including the attendance of 2 ExCo-meetings per year. For the subtask leaders
funding shall allow for extra 2 months per year for annex activities.
7.
ANNEX 35 LEADERSHIP
7.1.
Operating Agent
The Operating Agent for the Annex shall be Per Heiselberg, Aalborg University,
Department of Building Technology and Structural Engineering, Aalborg, Denmark.
7.2.
Subtask Leaders
Leader of subtask A shall be Gerard Guarracino, E.N.T.P.E / L.A.S.H - D.G.C.B, CNRS,
Building Sciences Laboratory, Vaulx en Velin Cedex, France.
Leader of subtask B shall be Yuguo Li, CSIRO, Division of Building Construction and
Engineering, Highett Vic, Australia.
Leader of subtask C shall be Marco Citterio, ENEA, Energy Saving Department ERG
SIRE, Rome, Italy.
7.3.
Report Editors
Editors of the state-of-the-art report shall be Tor Arvid Vik, SINTEF, Architecture and
Building Technology, Trondheim, Norway and Angelo Delsante, CSIRO, Division of
Building Construction and Engineering, Highett Vic, Australia.
Editors of the report “Principles of Hybrid Ventilation” shall be …..
Possibly AIVC will contribute in the distribution of information etc………
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IEA-BCS Annex 35: HybVent
8.
ANNEX PARTICIPANTS
The participants in this annex are the following: Australia, Belgium, Canada, Denmark,
Finland, France, Germany, Greece, Italy, Japan, Norway, Sweden, The Netherlands, United
Kingdom and United States.
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