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Dual HVAC and Light Duct System: An innovative approach increasing
the daylight utilization in buildings
Conference Paper · January 2013
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Lighting Research and
Technology
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Dual ducting: An innovation to increase the use of daylight in buildings
MS Mayhoub
Lighting Research and Technology published online 16 September 2014
DOI: 10.1177/1477153514548472
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Lighting Res. Technol. 2014; 0: 1–18
Dual ducting: An innovation to increase
the use of daylight in buildings
MS Mayhoub PhD
Architecture department, Faculty of Engineering, Al-Azhar University, Cairo,
Egypt
Received 30 March 2014; Revised 9 July 2014; Accepted 30 July 2014
Daylight guidance systems deliver daylight into remote parts of buildings.
However, they still lack market penetration. The primary difficulty lies within the
installation process. Daylight guidance systems use light ducts to distribute
daylight, which occupy significant amounts of space. The integration of light
ducts and heating, ventilation and air conditioning ducts is a promising solution.
This study compares the differences and similarities of the two ducting systems,
suggests an integrated system and evaluates the potential of and challenges
faced by the proposed dual ducting system. A schematic application is completed
and demonstrates that the dual ducting system has the economic potential
to reduce costs, avoid conflicts between building systems and simplify the
installation of daylight guidance systems.
1. Introduction
Research into ways to reduce the consumption of electricity within buildings inevitably
leads to the greater use of natural resources.
The current interest in daylighting systems
(DLSs) within buildings is motivated primarily by the desire to conserve energy in order to
reduce energy bills. Targets have been
expanded of late in order to protect the
environment and also to satisfy the human
desire for an association with nature.
Comprehensive studies have been carried
out to develop innovative DLSs with the
ability to meet the current needs for daylight.
Two main approaches have been developed to
allow daylight to effectively penetrate deeper
within new buildings and to control and
distribute direct sunlight. The methods use
Address for correspondence: MS Mayhoub, Architecture
Department, Faculty of Engineering, Al-Azhar University,
Nasr City Campus, 11371, Cairo, Egypt.
E-mail: msmayhoub@hotmail.com
either enhanced conventional techniques or
transfer daylight via guidance systems.1
The first approach incorporates devices
such as louvres or light shelves to improve the
conventional technique’s performance.2–5
The second approach aims to deliver daylight
into windowless and remote spaces within
buildings via light wells, light pipes or fibre
optics.6–9 The systems which depend upon
this approach are typically called daylight
guidance systems (DGS). Although many
DGS have been developed over the last few
decades, none of them has strongly penetrated the market. The tubular daylight guidance system (TDGS) is believed to be the
most commercially available. It has proven to
be of universal acceptance and has a broad
spectrum of applicability, although it still has
certain installation limitations.1
There are three major obstacles to market
penetration: first, the system is not costeffective; second, it is not easily integrated
into building design and third, the poor
quality of daylighting provided. In addressing
ß The Chartered Institution of Building Services Engineers 2014
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these issues, this study proposes an innovative
method to increase the use of DGS in
buildings.
diameter and can thus be routed in buildings in
similar way to electric cables.7,18,19
3. DGS challenges
2. Daylight guidance systems
DGS generally consist of three components: a
light collector which harvests daylight, a light
guide transport which coveys daylight to
where it is required and a diffuser which
spreads daylight uniformly across the space.10
The light collector technology determines
under which sky conditions the DGS are
most efficient and significantly influences the
initial costs of the system. The light guide type
considerably affects the ease with which the
DGS can be integrated into the building. The
light diffusers mainly depend on the illumination function. Reviewing the effects which the
DGS components have upon the building
reveals that the widespread use of the DGS is
determined by the light guide, and more
specifically, its ease of installation.11,12
DGS can be classified into two groups based
on light guide size, which determines the
potential transportation distance, the capability to integrate into the building, the possibility
of fitting into new or existing buildings, the
suitability for varying types of building and the
applicability within diverse constructions. The
first group of DGS incorporates the use of light
ducts (pipes), whilst the second uses fibre optics
(or occasionally liquid guides).
Light ducts are normally used with DGS
that collect diffused daylight. These are not
designed to concentrate direct sunlight. Light
ducts have relatively large circular or rectangular cross-sections, typically in the range
0.20–0.50 m diameter or around 0.25 0.60 m;
depending on the distance the daylight has
to be transported and the amount of light
required.13–15 Larger ducts up to 1.75 m diameter are used in some applications.16,17
Conversely, fibre optics are usually used with
DGS which highly concentrate direct sunlight.
The fibre optics are just a few centimetres in
High daylight concentrating DGS, which in
the majority of cases use fibre optics, are more
applicable due to their ease of installation than
non-concentrating systems that use light
ducts. Nevertheless, both have some major
challenges which prevent their widespread use.
There are three main problems associated
with the high daylight concentrating systems.
The first is that their costs are exceptionally
high compared with all other DGS. For
instance, assuming an exchange rate of 140
Japanese yen to E1, a small Himawari
system package (includes a 12-Lens collector,
two 5-m optical fibre cables, two luminaires
and mount) has a price of E5750 in 2014 and
a Parans system package (includes a SP3
collector, six 5-m optical fibre cables and two
medium luminaires) has a price of E5000.
This economic issue may be overcome by
progress in technology and mass production
launching, although this is debatable as
the Himawari system dates back to the early
1970s and is still comparable in price to
the recently commercially launched Parans
system.20
The second problem is that less expensive
daylight concentrating devices, plastic fibre
optics and some types of light guides are
highly likely to change the characteristics
of daylight.21 Expensive materials or more
development of existing materials may help to
mitigate this problem, but this should not be
at the expense of economic viability. For
example, the quartz-glass optical fibres which
are used in the Himawari system cost
E135/m,1,2 which is approximately 10 times
the cost of acrylic fibre optics. Similarly, the
cost of acrylic mirrors is more than 10 times
that of glass mirrors.22
The third problem is that the daylight
concentrating systems only work efficiently
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under clear sky conditions.12,23 Nothing can
resolve this issue, as it is related to regional
climate conditions and the laws of physics.
Therefore, the use of these systems is recommended only in regions where a clear sky is
dominant.
Alternatively, non-concentrating systems
are relatively economical, are more likely to
maintain daylight colour characteristics and
are capable of delivering both direct and
diffused daylight. The main drawback is the
large size of the light guide, which limits its
applicability, especially within multi-storey
buildings. TDGSs are applicable over a wide
range of building uses and geographical
locations, although they still have serious
limitations. They are mostly installed at the
highest level of buildings, due to difficulty in
the guide penetration of usable working
spaces, although it is technically capable of
delivering daylight further. In some applications, when appropriate to install a sun pipe
within a central vertical space, daylight has
been delivered over a distance of up to 36 m.17
For any DLS to become widespread in its
use, it is essential that it is available at a
competitive price, can deliver daylight with
minimal changes in its characteristics, can
provide a uniform illuminance distribution
and is easily applied. According to these
criteria, in the short term, making progress to
overcome the challenges associated with light
ducts appears more promising than finding a
way to concentrate the diffused daylight to be
channelled by optical fibres.
4. A dual ducting system
4.1 Why a dual ducting system is proposed
Applicability and efficiency, in terms of
both light quality and quantity, are the key
words for any DLS success. Many DGS are
successful in terms of efficiency, but they still
not widely applicable. Suitability and integration are, in turn, the key words for the
applicability of DGS. The non-concentrating
3
systems are suitable for use under all sky
conditions and geographical locations.
Integration, therefore, remains an obstacle
for the use of DGS to become widespread.
However, this can be largely overcome
through the development of improvements
to ease the installation. Here, a dual ducting
system is proposed to improve and ease the
installation and integration of the light guide
into buildings.
The majority of commercial buildings, and
a high proportion of other building types,
have heating, ventilation and air conditioning
(HVAC) systems which use duct networks
already integrated with the other building
systems. The HVAC ducts are capable of
reaching most spaces and are of comparable
size to light ducts. Thus, they are a prime
target for the development of dual ducts; a
single duct to transport and distribute both
air and light (Figure 1).
4.2 Some considerations
The main criteria to be considered in order
to successfully develop a dual ducting system
are summarised as follows:
Ease of installation: This is the main
objective of this proposal. However, route
modifications of the HVAC duct network
may be required for a uniform illuminance
distribution, which in time would increase
the air distribution efficiency. In addition,
duct bends would require minimisation in
order to avoid excessive light attenuation.
Furthermore, additional duct extensions are
likely to be required in order to connect the
network with the roof- or façade-mounted
daylight collectors.
Economic viability: The proposed duct
network is estimated to be more economical
than the costs of the HVAC and DGS duct
networks due to the reduction in the overall
length of the duct. Although the highly
reflective materials have recently became
available at lower cost, it would not be
economic to change the entire duct network,
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Facade collector
HVAC
Ducts
and/or roof
collector
Dual
Ducting
System
Figure 1 Façade light collectors (bottom left: Core SunCentral system collector) and/or roof collectors (top left: TDGS
collector) are proposed to be connected to the HVAC ducts (right) after modification to produce a dual ducting system
and thus this would only be required where
there is a need to channel daylight.
Output devices: The existing HVAC output
devices can be developed to be hybrid outputs
and to diffuse both air and daylight; otherwise, separate illuminance output devices may
be connected to the duct network.
Operation requirements: Great attention
has to be paid to avoid the precipitation of
air particulates and condensation on the duct
and diffuser surfaces. Solid or liquid particulates such as dust, smoke and air vapour (if
condensed) significantly reduce the duct’s
reflectance. Fire or smoke spread hazards
throughout the ducts also have to be avoided.
Thermal and acoustic insulation are also
essential. Air pressure in the ducts has to be
maintained in spite of the change of the duct
sizes.
4.3 Systems incorporated in a dual
ducting system
The dual ducting system is achieved by the
integration of both the HVAC and DLSs. A
review was carried out to determine which
types of both systems have the potential to be
incorporated.
4.3.1 DGS review
Many DGS, using light ducts to
deliver and/or distribute daylight, have been
developed. However, only the commercially
available systems will be reviewed, since
they are more likely to be efficiently
integrated.
The TDGSs are linear structures which
channel daylight by means of optical interactions into the core of buildings. They are
effective under both clear and overcast skies.
They consist of a clear dome which collects
sunlight and skylight, with the use of a rigid
or flexible tube made up of/or lined with a
highly reflective material in order to redirect
the light, together with a light output device
made up of an opal, a prismatic material or
an array of Fresnel lenses. The light collector
may be located on the roof of the building,
enabling light from the zenith of the sky to be
gathered. Alternatively, light may be gathered
from a façade-mounted collector. Zenithal
openings allow intensive use of daylight;
however, these may cause glare or overheating. For a horizontal opening, the quantity of
the delivered solar flux depends on façade
orientation and season.13,24 The light pipe
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performance is affected by solar altitude,
aspect ratio of the pipe, light pipe bends and
cross-sectional shape.6,25 The reflective internal lining material can be silver-coated plastic
film, polished and silvered aluminium or
polymeric aluminium.26
The Heliobus DLS is a custom-produced
system using a heliostat that tracks, collects
and concentrates sunlight. A tracking mirror
or Fresnel lens is usually located on the roof
and uses light sensors, pulse motors and
computers to track the sun. A second mirror
or lens directs a concentrated beam of
sunlight into a vertical prismatic light guide
which transfers light by total internal reflection into the building core (Figure 2(a)).27
Reflective diffusing extractor foil distributes
daylight over the entire surface of the guide
which allows each floor along the guide path
to receive similar quantities of light.13,16,27 A
similar concept is used to build a DGS with
a 36-m-long light pipe which has a doubleskin construction; an outer light-diffusing
tube, which consists of tensioned translucent
Lycra fibre, that reflects the sunlight horizontally into each floor, with a core consisting of prismatic glass panels with optical
film. The glass pipe tapers from a diameter
of 1.75 m at the top to 0.50 m at the bottom
(Figure 2(b)).17
5
The SunCentral DLS is suitable for multistorey buildings. It consists of a light collector
of reflective louvres which pan and rotate
redirecting sunlight as a stationary beam
throughout the day. The collector tracks the
sun autonomously and projects a stationary
collimated beam of sunlight along any side of
the building or through an atrium or light
well. The light is intercepted by optics
integrated within an overhang which is positioned on every floor of the building.
Sunlight is concentrated and directed into
the façade integrated optical spandrel and is
then channelled into luminaires which transport sunlight up to 15 m into the building
core. The luminaire has a dual function of
transporting and transmitting sunlight. Its
cross-section is approximately 0.1 m 0.28 m
and is composed of aluminium tube lined with
prismatic film and a semi-translucent emitter
side (Figure 2(c)).14
The Sunportal DLS is suitable for largeand small-scale architectural applications.
It actively captures sunlight by a heliostat
with an ultra-sunlight concentrator. The
light travels through a series of compact
optical relay lenses (0.20 m diameter) over a
distance of up to 200 m or through mini
optical relay lenses (0.10 mm diameter) over
a distance of up to 30 m (Figure 2(d)).
Figure 2 (a) A Heliobus system light guide, (b) a 36-m-long light pipe, (c) a SunCentral system light guide and
(d) a Sunportal system light guide
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A transparent tube diffuser is used to
illuminate the space.15
4.3.2 HVAC systems review
network for air supply, return and fresh
air feed.
4.3.2.2 HVAC duct types and requirements
4.3.2.1 HVAC system types and components
HVAC systems include cooling systems,
heating systems and all-air systems, but they
are frequently referred to as air conditioning
(AC) systems. Many varieties of AC systems
are used within buildings; however, only airduct systems, rather than ductless, are relevant to this study. This study will focus on the
components and principles of a central AC
system, as they are widely used and utilise a
large-duct network across the whole building.
The central AC circulates cool air through a
system of supply and return ducts. Supply
ducts and registers (i.e. openings in the walls,
floors or ceilings, covered by grills) carry
cooled air from the air conditioner to the
internal spaces of the building. This cooled air
becomes warmer, as it circulates through the
space; then it flows back to the central air
conditioner through return ducts and registers. The system components and location
within the building depends upon whether air,
water or both are used for the cooling
process. At most, the system consists of a
water chiller/boiler, a cooling tower, an airhandling unit and an air-duct distribution
HVAC ducts and pipes must be thermally
and acoustically insulated in order to achieve
the desired levels of comfort and to reduce
energy consumption in addition to contributing to fire safety. Thermal insulation materials such as glass wool, stone wool or mineral
wool have an additional advantage of significantly reducing the operational and airflow
noise. HVAC ducts are available in different
types, such as metal ducts, glass wool ductboards, plastic ducts and flexible ducts as
summarised in Table 1.
Metal ducts are constructed from metal
sheets (galvanised, stainless steel, copper or
aluminium). They are cut and shaped to the
required geometry for the air distribution
system. They require outer or inner thermal
insulation, the most common material for
which is glass wool incorporated onto an
aluminium foil. Glass wool duct-boards are
constructed with high-density glass wool.
Ducts are shaped from the boards by cutting
and folding in order to obtain the required
geometry. The internal face of the duct has an
aluminium coating, a glass mat or a fabric
layer. The plastic ducts are constructed
Table 1 HVAC duct type classification
Type
Material
Shaping
Thermal insulation
Metal duct
Galvanised, stainless steel,
copper or aluminium sheets
High-density glass wool board
faced with an aluminium
coating, a glass mat or a
fabric layer on the internal
side
Plastic or foam boards faced
with an aluminium coating
on both internal and external
sides
Consists of two aluminium and
polyester concentric tubes
Cutting and shaping
Cutting and folding
Glass wool blanket faced with
an aluminium foil
Provide thermal insulation
Cutting and folding
Provide thermal insulation
Glass wool duct
Plastic duct
Flexible duct
HVAC: heating, ventilation and air conditioning
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with plastic or foam boards, shaped by
cutting and folded to produce the required
cross-sectional geometry. The boards are
usually faced with an aluminium coating on
both the internal and external sides. The
flexible ducts usually consist of two aluminium and polyester concentric tubes. A glass
wool layer is inserted between the two tubes
as thermal insulation. They are mainly used
to connect main air ducts and terminal
units.28
4.3.2.3 Air filters
Air filters are typically located somewhere
along the return ducts. They are available in a
wide variety of media and budgets.
Performance is determined by the size and
density of the material used as well as the
particle size and the volume (see Table 2).
Flat or panel air filters, with a minimum
efficiency reporting value (MERV) of 1 to 4,
have reasonable efficiency on large particles.
They remove less than 20% of the fine
airborne dust particles (medium particles of
1–10 mm) and up to 80% of the large particles
(410 mm).
Pleated or extended surface filters have a
larger surface area with a MERV of 5 to 12.
They are reasonably efficient at removing
small to large particles. They remove up to
7
75% of medium particles and more than 95%
of the large particles.
Bag filters, with a MERV of 13 to 16,
have a micro-fine fibre glass or synthetic
media. They remove more than 95% of the
medium particles and 98% of the large
particles.
The high-efficiency particulate air (HEPA)
filters, with a MERV between 17 and 19, have
a minimum particle removal efficiency of
99.97% of the small (0.3 mm) particles. They
are not normally installed within residential
HVAC systems.
Electrostatic precipitators use an electrostatic attraction process to trap small particles
and have an initial dust-spot efficiency of up
to 98%.29–31
4.3.2.4 Air outlet
HVAC outlets have a wide variety of
locations, shapes and materials, as they are
the section of the system which is most visible.
They may be installed within walls, floors or
ceilings and covered by bars, grills, blades
or louvres. They may be linear, rectangular
or round in shape. They are usually made up
of steel, aluminium or plastic; however, they
may be even made up of wood or copper.
The air ‘outlet’ is used in this study
Table 2 Air filter types
Type
MERV
Efficiency
Flat or panel air filters
1–4
Pleated or extended
surface filters
5–8
520%
Up to
Up to
Up to
9–12
Bag filters
13–16
HEPA filters
17–19
Electrostatic filters
1–16
of medium particles
80% of large particles
35% of medium particles
90% of large particles
Up to 75% of medium particles
More than 95% of large
particles
495% of medium particles
498% of large particles
More than 99.97% of small
particles
Up to 98% of particles
Applications
Minimum filtration residential
building
Better residential
Commercial buildings
Industrial workplaces
Superior residential
Better commercial
Hospital laboratories
Superior commercial
Hospital surgery room
Electronics and pharmaceutical
manufacturing
MERV: minimum efficiency reporting value; HEPA: high-efficiency particulate air
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to refer to the HVAC register, grill or
diffuser.
5. Dual ducting system application
A theoretical study is applied to an office
building in the design stage to investigate the
dual ducting system’s application potential.
An office building has been selected, as they
are major employment locations and constitute a large sector of the total building stock.
For almost all office buildings, working hours
coincide with daylight hours, and HVAC
systems are installed. Both DLSs and
HVAC manufacturers have targeted offices
as a major market.32 For the studied building,
the designed HVAC system is assessed, the
applicable DGS is studied and the integration
of the two systems is investigated. The study
shows how the two systems appear if installed
together within the building and examines the
benefits of the installation of the proposed
dual ducting system.
5.1 Defining the space
The selected space is an open office area in
a multi-storey building. Open areas are a
favourable solution in office buildings and
represent an easy start for a new application.
The building height is approximately 15 m,
and the investigated space is about 265 m2.
The southern and eastern sides of the space
are fully glazed and the remaining sides are
solid walls. The maximum depth of the space
is 11.80 m from the southern façade and
18.40 m from the eastern façade (Figure 3).
The height of the space is 3.40 m, and a false
ceiling was installed leaving 2.70 m clear
height. The open office areas are centrally
air conditioned.
5.2 Potential to gain daylight
Due to the installation of a glazed façade,
excessive daylight will be provided in the
perimeter zone adjacent to the southern and
eastern facades, whilst poor daylighting
is expected in the remote area. Façademounted daylight collectors can be used to
channel daylight into the back of the space.
The façade collectors should be preferably
mounted on the southern façade; however,
they could also be mounted on the eastern
façade if required. The façade collectors could
also be used to provide daylight for all stories.
A roof-mounted collector could also be used
to provide daylight for the upper floor. In
addition, the vertical shaft which is used to
route the HVAC ducts could be used to install
vertical light guides connected to the roofmounted collectors to reach the lower floors
(see Figure 3).
5.3 Designed HVAC system
The designed HVAC system includes a
central AC system for the open office areas in
all stories. The external units of the AC are
located on the roof and connected to four
supply and return vertical ducts, each of size
1.15 m 0.50 m. The vertical supply air ducts
(SAD) carry the cooled air into the horizontal
duct network that extends across the ceiling
cavity. The return air ducts (RAD) collect the
warm air from the ceiling cavity. The size of
the horizontal SAD starts from 1.15 m 0.50 m and decreases after every branch until
reaches 0.45 m 0.20 m at the ends. The air
outlets are positioned in a grid of 2.70 m
spacing with a checkerboard pattern of
supply and return outlets (Figure 4).
5.4 Addition of the DGS
A façade-mounted system, such as the
SunCentral system, can be used. The collectors can be integrated into the curtain wall.
Light guides with a cross-section of
0.1 m 0.28 m up to 0.25 m 0.60 m can be
routed in the ceiling cavity in coordination
with the AC ducts. As shown in Figure 5,
the light guides may be routed in between
the AC ducts, but they will cross some small
branches in addition to the main duct at the
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Northern solid façade
9
Eastern glazed façade
Slab opening for a
vertical shaft to
rout the HVAC
ducts
11.80 m
18.40 m
The office
open space
N
Southern glazed façade
Figure 3 Typical floor plan of the studied area
Four vertical ducts
1.15m × 0.50m
each
The main
horizontal
branch
1.15m × 0.50m
The smallest
horizontal
branch
0.45m × 0.20m
Figure 4 The AC duct network on the typical floor plan
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Four vertical ducts
AC ducts
Light Guides
Air return
outlet
Light collector
Air supply
outlet
Figure 5 Light guides routed in between the AC ducts
back of the space. The small branches height
is 0.20 m, while the main duct is 0.50 m, and
thus the light guide may only be routed
beneath the small branches without conflict.
In order to go under the main duct, the false
ceiling has to be lowered by 0.20 m to allow
more space (see Figure 6). Alternatively, the
light guide may stop before the main duct,
leaving some 3 m at the back of the space
without daylight. In order to keep equal
spaces between the light guides and to get
proper connections between them and the
light collectors, other conflicts occur between
the light guides and air outlets. This means
either the air outlet spacing or the light guide
spacing will be irregular to avoid the
overlaying.
A roof-mounted system, such as the TDGS
or Heliobus, can be used. The collector,
whether dome or heliostat, could be installed
on the roof and connected to vertical sunpipe(s) routed in the AC vertical shaft. In this
case, the vertical sunpipes will not side emit
daylight as is the case in most Heliobus
installations. Alternatively, they could be
connected to horizontal light guides to distribute the daylight where required in all stories.
The horizontal guides will suffer the same
conflicts as the façade-mounted system.
5.5 How the two systems can be integrated
The light guides and AC ducts can be
integrated in one network as illustrated in
Figure 7. The horizontal air ducts need to be
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1.15m × 0.50m
Air Duct
0.45m × 0.20m
Air Duct
0.25m × 0.60m
Light Duct
11
Façade mounted
Light collector
False Ceiling
Conflict might
occur with the
usage of larger
ducts
Enough ceiling
cavity for both
duct networks
Glazed Facade
0.25m × 0.60m
Light Duct
False Ceiling line
1.15m × 0.50m
Air Duct-
Conflict might
occur with the
usage of larger
ducts
Figure 6 Section and isometric of the space illustrate the relationship between the light guides and the duct networks
slightly re-routed in order to join the façademounted collectors. The spacing distance needs
to be modified to suit the new layout of the light
and air outlets and to allow proper locations for
the light collectors on the façade. The ducts
need to be extended to reach the façade where
the collectors are installed (Figures 7 and 8).
Wherever the ducts are extended, an air stopper
could be used after the last air outlet. This could
be made up of clear glass or acrylic to allow the
passage of light only and to avoid any possible
drop in the air pressure due to the duct’s added
volume. The layout of the electric luminaires
needs to be modified in order to allocate the
daylight luminaires, whether linear (through
the bottom surface of the duct) or distinct
luminaires (traditional-like circular or rectangular luminaire).
As illustrated in Figure 9, additional roofmounted collector(s) may be installed on the
top of the vertical air ducts, where transparent light openings can be added to allow
the entry of the collected daylight. The
daylight may be channelled throughout the
vertical ducts and emitted via wall-mounted
luminaires to light the lift lobbies. Moreover,
a proportion of the daylight which is channelled by the vertical ducts can be transported
into the horizontal ducts and distributed in
the working space. Additional luminaires may
be added in the main horizontal air ducts
for this purpose (see Figure 7).
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Wall-mounted luminaire connected
to the vertical light duct
Four vertical ducts
AC ducts
Daylight luminaire
may be added in
the main duct
Ceiling tiles contain:
Concealed light
outputs & air supply
and return outputs
Air stopper
Dual ducts
Façade mounted
light collector
Figure 7 The false ceiling plan consists of gypsum board and gypsum tiles include the air and light outlets. The dual
ducting system is coordinated with the ceiling levels and furniture
AC: air conditioning
5.6 Benefits of using dual ducting systems
5.6.1 Saving in terms of duct reduction
The proposed system aims to ease the installation of the DGS and reduce the capital cost
(i.e. initial cost of the ducts and installation
cost). A single duct network, as illustrated in
Figure 9, can be installed instead of two, as
illustrated in Figure 5. The proposed network
has a longer overall length of ducts than that of
the air network, however, it is shorter than
the total of the two separate networks. Wherever
air only is transported, the specified air ducts are
used, but when both air and light are transported, the dual ducts are used.
The saving in the capital cost will be
estimated in terms of the reduction in length
of the ducts regardless of the cost of manual
labour and materials at this stage of the study.
Two cases are assumed: in the first case, only
façade-mounted DGS will be used, and in the
second case, a roof-mounted system will be
added. In the first case, the total length of the
original horizontal air ducts is 59 m/floor. The
total length of the required horizontal daylight
guides is 38 m/floor. The proposed system
includes a 33 m/floor of specified air ducts and
38 m/floor of dual ducts. Thus, 26 m (44%) of
the specified air ducts are saved (see Figure 8).
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13
Wall-mounted luminaire connected
to the vertical light duct
Four vertical ducts
The original
duct network
The modified
duct network
These
branches of
the AC duct
network can
be saved
One duct can be
used instead of two
in all similar cases
Air supply
outlet
Equal spacing
Figure 8 Comparison between the original and the proposed duct networks illustrates the re-routing and the added
parts
AC: air conditioning
In the second case, four vertical air ducts
are used. All of them can be used to transport
daylight, but only the SAD ducts are connected to the horizontal duct network.
Consequently, both SAD and RAD can be
used to distribute light via luminaires fixed to
the vertical ducts (optimally wall mounted),
while only the SAD can be used to distribute
the light via the horizontal ducts. As a
result, up to 100% of the vertical air ducts
may be converted into dual ducts.
ducting system entirely prevents the conflict
between the HVAC ducts and light guides and
minimises the conflict with the structural
system. In this study, the horizontal light
guides extended to the back of the space without
lowering the ceiling to route two layers of the
ducts. The vertical light guides penetrated the
building slabs without need for more roof or
slab openings. They did not occupy any more
rentable space that under economic constraints
might be unacceptable.
5.6.2 Probable conflict avoided
6. Discussion
A conflict between the two networks of
ducting is likely to occur as explained previously, and this will be more complicated if the
structural system includes drop beams perpendicular to the direction of the ducts. The dual
Developing a dual ducting system has high
potential and yet gives rise to many challenges
which need to be investigated in order to
establish whether the HVAC ducts can be
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Roof mounted light collector
(e.g. Heliostat)
Roof mounted light
collector (e.g. Sunpipe
dome)
Air duct from the
external HVAC unit to
the ducts network
1. Roof mounted daylight
collector
2. Façade mounted
daylight collector
3. HVAC system outdoor
unit
4. Horizontal dual duct
5. vertical dual duct
6. Air outlet
7. Light outlet
8. Air stopper
9. Light-only duct connect
the duct network with
the daylight collector
Figure 9 The proposed dual ducting system diagram
HVAC: heating, ventilation and air conditioning
technically and economically used as light ducts.
These potentials and challenges are appraised
against the initiated criteria in Section 6.2.
6.1 Ease of installation
Combining the HVAC and illumination
systems contributes toward the achievement
of the ‘ease of installation’ target, whether in
new or existing buildings. The integration
consists of designing the duct network for
efficient air and light distribution and
determining the location of the air handling
equipment and daylight collectors. An integrated network is suggested rather than separate networks for both of the systems. However,
the integrated networks will probably require
additional ducts for connections with the light
collectors as illustrated in Figure 9.
6.2 Economic viability
The dual ducting system has the potential
to significantly reduce the overall cost of the
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duct networks due to the reduction of duct
length. The conflict between building systems
is expected to be minimised. This in turn will
reduce the required ceiling cavity. Minimal
modifications will be required to install the
DGS into existing buildings, which will inevitably reduce the installation cost and increase
their utilisation.
HVAC ducts are mostly made up of galvanised steel; however, there are stainless steel and
aluminium ducts, which are more suitable for
light delivery with some enhancement to
increase luminous reflectance. The aluminium
foil used in the internal insulation could also be
employed for this purpose. Alternatively, highreflective optical films could also be used to line
the inner surfaces of the ducts. As these
alternatives are more expensive than the galvanised steel or the non-polished aluminium, they
will apply only where dual ducts are used to
reduce the additional cost.
6.3 Output devices
The light might be emitted into the space
via linear luminaires such as those used in the
SunCentral DLS (Figure 3(c)). The semitranslucent emitter side in this case has to be
thermally and acoustically insulated and has
to be developed to allow the fixing of HVAC
outlets along it. Alternatively, distinct outlets
are required for daylighting unless translucent
materials are used to produce hybrid outlets
for both air and light. In this case, the grill
fins or diffuser louvers could be constructed
with clear plastic or glass with high-visible
transmittance. Laser cut panels could be used
for improved light distribution.33 A highly
reflective metal with a reflectance of approximately 99% can be used.34 Alternatively,
these could be coated or lined with highly
reflective optical films.35
6.4 Operational requirements
Apart from the duct’s functions, some
challenges associated with the duct installation and operation need to be considered.
15
Attention has to be paid to the condensation risk. Precipitation of the air particulates on the inner surfaces of the ducts and
the diffuser fins mitigates the system illumination efficiency dramatically. Regular
maintenance of the air filter or even the use
of anti-dust materials are practical solutions for this problem.36 Air filters are
already used in the HVAC systems to
improve the indoor air quality and maintain system efficiency.
The thermal and acoustic insulation of the
HVAC ducts may be effected with a dual
function duct, transferring and distributing
daylight both at once. Whilst the duct body
is insulated, the light-only aperture can be
double-glazed.
Fire protection is already considered in the
HVAC systems and needs to be considered
in the DLS. Suitability of the used techniques in HVAC systems with the DLS
needs to be investigated.
The required changes in the air-duct size and
length may have an impact on air velocity
and consequently on thermal comfort. For
instance, air pressure losses due to the
additional extensions to connect the ducts
with the building envelope might occur. This
can be avoided by recalculating the air
velocity or installing transparent air stopper
plates adjacent to the last air outlet in the
duct. The air stopper could also be used to
prevent air from reaching unwanted spaces.
7. Conclusion
Existing DGS have the potential to provide
efficient daylighting within buildings.
However, they do face some challenges that
can be summarised as reducing the initial cost
and increasing the ease of integration into
buildings. Both challenges can be overcome to
great extent by the integration of DGS and
HVAC systems, which could be achieved
through the consideration of many factors
such as the design of the duct network layout,
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Table 3 Dual ducting system factors, their expected impacts and proposed solutions
Factor
Impact
Proposed solution
Duct network layout
Duct materials
Duct network economic viability
Output devices
Ceiling layout
Air and light distribution
efficiency
Condensation risk
Illumination efficiency
Particle precipitation
Illumination efficiency
Thermal and acoustic levels
Users’ comfort
Fire risk
Air pressure
Smoke or fire spread
Thermal comfort
Requirement of re-routing
Economic viability
Need for additional ducts
Minimal bends use
Ceiling cavity height
Coordination of HVAC and illumination
systems at the design stage optimizes the
network layout and minimises the additional ducts and bends
Replacement of parts of the existing ducts
with the dual ducts eases the installation
of the DGS in existing buildings
Normal ducts to be used for air-only
distribution ducts
Highly reflective ducts to be used for dual
ducts only, such as polished metal or
optical film lined ducts
Linear or spot (circular or rectangular)
alternatives available for different ceiling
layouts
Reflective or transmissive materials can be
employed
Air-only, light-only or hybrid outputs can
be used
Ducts to be thermally insulated
Outputs to be regularly cleaned
Air filters to be used
Exposed outputs to be cleaned
Ducts to be insulated
Double-glazed light-only outputs to be
used
Optically enhanced fire dampers to be used
Air stoppers to be installed
Recalculation of air velocity
HVAC: heating, ventilation and air conditioning; DGS: daylight guidance systems
the selection of the ducting materials, the
development of the output devices and the
development and improvement of many
operating aspects. The factors that influence
the success of the dual ducting system are
summarised in Table 3. The expected impacts
on the proposed system are mentioned, and
suggested solutions are outlined.
This paper has assessed the potential for
the implementation of a dual ducting system
within an existing building. The installation of
a separate AC system and DGS required
97 m/floor of horizontal ducts and 70 m of
vertical ducts. Using this model, the utilisation of the dual ducting systems is expected to
save around 44% of the specified horizontal
air ducts. All the vertical air ducts can be
utilised to channel daylight. Additionally, use
of these ducts prevents the conflict between
the two networks. Furthermore, it is easier to
install within existing buildings by replacing
the original air ducts with the dual ducting
system without any further modifications.
More exercises with HVAC designers are
required to assess the duct’s re-routing
difficulties and effects. Field investigations
are essential to measure the illuminance and
air distribution efficiency. Laboratory studies
are crucial to examine the proposed solutions
such as the air stopper and hybrid output.
Funding
This research received no specific grant from
any funding agency in the public, commercial,
or not-for-profit sectors.
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Acknowledgement
The author thanks Prof. Konstantinos
Papamichael, California Lighting Technology
Center, for his useful and constructive
comments.
12
13
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