Note: Descriptions are shown in the official language in which they were submitted.
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INDUCTION SUPPLY AIR TERMINAL UNIT WITH INCREASED AIR INDUCTION RATIO,
METHOD OF PROVIDING INCREASED AIR INDUCTION RATIO
The present invention relates to an induction supply air terminal device
where primary air flow is used to induce a secondary air flow with increased
air
induction ratio.
An induction supply air terminal device essentially comprises of a primary
supply air chamber, mixing chamber and at least one heat exchanger. From the
primary supply air chamber the primary air is supplied out via one or several
nozzles
into a mixing chamber. The secondary air is conducted into the mixing chamber
through a heat exchanger, where this secondary air can be heated or cooled.
The
primary supply air induces secondary air and they both mix in the mixing
chamber.
This mixed air is then conducted into the air-conditioned room space.
The present invention provides such an induction supply air terminal device,
wherein the air induction ratio between the primary air and the secondary air
is
increased without compromising on equipment capacity, or resulting in enhanced
energy costs, or outside (primary air flow) requirements.
Room space air handling solutions often comprise supply of air via a cooling
or heating or chilled beam. In such a chilled beam, the supply air is supplied
to the
room, while a certain room air volume is sucked in through induction effect
into a
mixing chamber through a heating or cooling coil and is thereby heated or
cooled
therein, and then mixed with the supply air and circulated back into the room.
Chilled beams are components of air treatment systems used for cooling,
heating, or ventilation purposes. Cooling beams or heating beams or chilled
beams
as they are generally referred to, provide several advantages for spaces of
designated volumes in that the cooling or heating capacity can be satisfied by
different modes such as supply of cold or hot water piped to the chilled beam
rather
than by requiring air handling units to handle the entire cooling or heating
load.
Chilled beams can be either passive or active, depending on the nature of the
convection process that is adopted. Passive chilled beams adopt a natural
convection
process where the air treatment device is provided in a box that is recessed
or hung
from a ceiling. In active chilled beams, ventilation air is introduced into
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pressurized chamber, also referred to as plenum or supply air chamber, and
then
through small air nozzles in order to enhance the natural convection of air.
An important consideration in any chilled beam system is that the moisture
content of the room air must necessarily be below dew point conditions. This
is
important to avoid the condensation in the chilled beam or water pipes
surfaces.
Dew point conditions are typically determined based on the coldest temperature
on
the surface of the chilled beam. Internal latent load is removed through
ventilation
only if the primary air is sufficiently dry and also present in high volume.
Traditional
dehumidification technology required a stipulated minimum required ventilation
1.0 rate in
order to keep the moisture level of indoor air at a desired level since
moisture
removal was limited in these technologies. Improvements in dehumidification
technologies in air handling units have meant that greater dehumidification of
air is
possible, thereby lowering the minimum required ventilation rate even further
or as
may be mandated by code or design.
An active chilled beam's cooling capacity is based on the amount of room air
(secondary air) circulating through the heat exchanger. This secondary air
volume is
dependent on the induction ratio of nozzle and the primary air volume. Now
when
primary air volume can be reduced, the induction ratio has to improve in order
to
keep the secondary air volume and thus the cooling capacity the same.
The following table exemplifies some of the challenges/issues in increasing
air induction ratios:
Primary air Primary air Required
AHU capacity of Required volume as per
volume as per secondary air Required
Internal moisture moisture primary air EN 15251
ASHRAE 62.1 volume in induction ratio
load removal volume standard standard chilled beam
(primary : total)
(kg/s) (g/kg) (I/s) (I/s) (I/s) (Vs)
SS 1 45.8 15.0 8.0 60 1:2.3
55 2 22.9 15.0 8.0 60 1:3.6
55 3 15.3 15.0 8.0 60 1:4.9
55 4 11.5 15.0 8.0 = 60 1:6.2
55 5 9.2 15.0 8.0 60 1:7.5
To have the highest possible induction with lowest possible primary air flow
rate is beneficial in terms of HVAC-system energy use. The induction ratio
should be
the highest possible with the lowest possible primary air flow and shortest
possible
induction length.
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In current products, induction ratio is controlled by changing the nozzle
size.
Smaller nozzles have respectively higher induction ratios due to higher
perimeter
length compared to same total area of nozzles with bigger diameter. When
nozzle
becomes bigger, the air jet diameter in discharge slot becomes bigger and
therefore
the minimum distance between nozzles also increases. This limits the number of
nozzles per linear length of beam. Respectively, with small nozzle the maximum
primary air volume is limited based on the chamber pressure. Another concept
to
increase induction ratio is to shape the nozzle such that with same face area
the
perimeter length of nozzle is longer. This can be achieved by shaping the
nozzle as
flower instead of a circle. Third method is to have a venturi in the mixing
chamber.
Single nozzle Flower Cluster
4 mm 5.9 mm 4x 2mm
Face area (mm2) 12.6 12.6 12.6
Perimeter (mm) 12.6 22.3 25.2
As can be seen, several methods have been proposed in the art to enhance or
increase air induction ratios. Some of the solutions include modifying the
nozzles or
holes intended for pass-through of supply air.
These solutions provided for in the art, include variations in the designs of
the nozzles or holes through which the primary air passes, exits and where the
air
flow after these holes makes the condition for the re-circulating room air to
reach a
mixing zone where both air flows are brought together prior to flow out into
the
room. The flow out from the pressure chamber is controlled by a number of
holes or
nozzles which are configured to different forms.
This type of device typically has several nozzles to induce the secondary air
flow. These nozzles can be either holes, slots, punched collars, conical
shaped???), or
any other shape. In case of multiple nozzles, they may be arranged in such a
manner
that they form one or several elongate row. Smaller nozzles have higher
induction
ratio, but also smaller primary air flow rate at any given static chamber
pressure. The
size of the nozzle is selected in order to supply the required primary air
flow at a
given primary air chamber pressure.
An induction supply air terminal device is used with various primary air flow
rates, therefore the same device may comprise of bigger and/or smaller nozzles
or
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nozzles with adjustable face area for setting the desired supply air flow.
Common for
the solutions is the ratio between the primary and secondary air quantities is
controlled so that the desired primary air flow and cooling/heating capacity
is met.
Examples of known solutions are described in WO 98/09115, where the induction
supply air terminal device includes a primary air chamber where several
nozzles or
discharge opening exists.
EP 1 188992 A2 with characterized discharge holes (nozzles here)comprises
of two groups (7, 8) that are laterally directed in different directions.
These consist of
two elongated slots (13, 16) equidistantly placed and having adjustable area
for
setting the desired supply air-flow.
Likewise, WO 2011/040853 A1 with characterized discharge holes of different
sizes are comprised in different groups. At any given point of time each group
can
have only one active discharge hole, wherein these active discharge hole in
each
group are of similar characteristic and equidistantly placed from the active
hole in
the adjoining group. It is used to regulate the primary air-flow rate.
WO 96/28697 and EP 0 813 672 B1 describes a nozzle with scallop-shaped
outlet edge. This has an effect on reducing noise output from the nozzle and
improves mixing of primary and secondary air flow thereby increasing the rate
at
which the primary air flow can induce the secondary air flow. In this example
the
preferred nozzle shape has a perimeter to cross-sectional area ratio that is
equal to
or greater than 1.3 times the perimeter to cross-sectional area ratio for a
circle of
the same area.
While smaller nozzles have bigger induction ratio, the smaller face area
means that they are not able to supply as much primary air as bigger nozzles
and
therefore also the amount of induced secondary air flow is smaller. Reducing
the
distance between the nozzles (d) to a value smaller than the diameter of the
air jet
(h), results in reduced induction length (I) and thereby reduced secondary air
flow.
Another method to induce a higher level of secondary air flow is to use a
venturi inside a mixing chamber. The venturi increases the secondary air flow
when
its neck size is equal to that of the diameter of the of the air jet. It is
also seen that
when the air jet central line velocity is higher, the effect of the venturi is
better.
Therefore, with the small air flow rate, the optimum location of the venturi
is closer
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to the nozzle than that with the higher air flow rate. Based on varying needs,
this
induction supply air terminal device can be used with different air flow rates
and
therefore with adjustable venturi location.
As an example EP 0 813 672 B1 describes an induction supply air terminal
device with a mixing chamber comprising of a fixed venturi having generally a
circular cross-section of varying diameter along its length.
OBJECTIVES OF THE INVENTION
Optimal venturi location and diameter is dependent on the primary air
volume and nozzle size. Different combinations give different jet sizes in the
venturi
neck. If the neck diameter is too small or too big compared to the jet
diameter or is
located in the non-optimum distance from the nozzle, as it may be a case with
fixed
venturi, it is not effectively increasing induction or may even reduce it.
The present invention firstly increases the induction near the nozzle due to
having many smaller nozzles (cluster)with higher perimeter area compared to
face
area supplying the air from the pressurized plenum to a mixing chamber.
Secondly,
the adjustable venturi allows to locate the venture neck optimally and
therefore
further increase the induction near the discharge opening. This combination
gives
the highest induction ratio and therefore allows the design of an active
chilled beam,
where lower primary air volume gives the required cooling capacity per linear
meter.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The state-of-art operation of device and innovation is described in the
enclosed drawings, wherein
Figure 1 describes the operation principle of an induction supply air terminal
device.
Figure 2 shows the operation principle of nozzle in case of different nozzle
distances and assuming that primary air flow rate (4) and nozzle (5) size and
shape is
the same in all nozzles.
Figure 3 presents a principle of nozzle (bigger and smaller nozzle) operation
as well as array of clustered nozzles, their induction ratios, required
primary air flow
rates and amount of induced air (numbers are only indicative to describe the
principle).
Figure 4 describes the principles of innovation i.e. multiple nozzle cluster.
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Figure 5 presents examples of arrays of multiple nozzle clusters.
Figure 6 describes the operation principle of induction supply air terminal
device with a venturi.
Figure 7 describes an adjustable venturi neck based on the primary air
volume (qv), induced secondary air volume and nozzle surface area (A) to
achieve
optimum velocity (v) in the venturi neck.
Figure 8 describes an adjustable venturi arrangement wherein different
optimally shaped and sized elements are utilised either alone or in groups to
create a
venture neck.
Figure 9(a) describes a device provided with solely a cluster nozzle
arrangement.
Figure 9(b) describes a preferred embodiment of the invention wherein the
combination of a cluster nozzle arrangement with a fixed venturi is provided.
Figure 9(c) describes a preferred embodiment of the invention wherein the
combination of a adjustable venturi with a single nozzle is provided.
Figure 9(d) describes a preferred embodiment of the invention wherein the
combination of a cluster nozzle arrangement with a adjustable venturi is
provided.
SUMMARY OF THE INVENTION
The present invention relates to an induction supply air terminal device
where primary air flow is used to induce a secondary air flow wherein the
nozzles are
provided in the form of a cluster arrangement, comprising one or more clusters
of
three or more nozzles each. The clusters can be arranged according to pre-
determined patterns depending on the pattern of air induction that is desired.
The present invention also provides an induction supply air terminal device
equipped with an adjustable venturi, where both the distance and the neck size
can
be adjusted based on the primary air volume and the nozzle surface area.
In another embodiment, the present invention also provides an induction air
terminal supply device where the primary airflow is used to induce a secondary
air
flow wherein the nozzles are provided in the form of a cluster arrangement
comprising one or more clusters of three or more nozzles each, and therein a
venture device is provided to enhance the flow of secondary air. The venturi
can be
either a fixed venturi or an adjustable venturi.
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DETAILED DESCRIPTION OF THE INVETNION
In the present invention, the nozzle arrangement comprises a cluster of small
nozzles instead of being placed equidistant in an elongate row. The clusters
can be
formed of different patterns as is depicted in Figure 5. In this case air jets
from a
cluster of multiple nozzles create multiple air jet zone of length (11). These
multiple
air jets converge into a single air jet at a distance 11, forming into a
single air jet zone
of length (12). The distance (d1) between an array of nozzles in a cluster is
smaller
than the distance (d2) between two clusters of nozzles.
The resultant induction ratio of an air jet created by an array of multiple
nozzles in a cluster is bigger compared to the induction ratio of an air jet
of single
nozzle with the same face area as of the clustered nozzles together.
A cluster can have an array of nozzles starting from 3 in number to more,
based on the required surface area to be catered to.
The secondary air flow induced by primary air flow from a single nozzle of
surface area equivalent to that of an array of multiple nozzles in a cluster
is smaller
than the secondary air flow induced by the same amount of primary air flow
from a
cluster of multiple nozzles.
Accordingly, the present invention provides an induction supply air terminal
device that comprises of primary supply air chamber (1), at least one mixing
chamber (2) which opens into the air-conditioned room space, at least one or
no
heat exchanger(3) The device is provided with an array of multiple nozzles in
a
cluster (5) that supplies primary air flow (4) into at least one mixing
chamber (2) to
induce a secondary air flow (6) heated or cooled as it flows through a heat
exchanger
(3) and conducted into the mixing chamber (2), wherein both this primary
supply air
(4) and secondary air (6) mix, whereby this mixed air (7) is then conducted
into the
air-conditioned room space (8) with an increased induction ratio.
In one embodiment, the array of multiple nozzles in a cluster can have three
or more number of nozzles.
In another embodiment, the nozzles in a cluster can be circular, rectangular,
elliptical or scalloped in shape.
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In yet another embodiment of the invention, the nozzles in a cluster can be
holes or punched collars in a sheet metal plate or conical nozzle that is
fixed over the
opening in the sheet metal.
In another embodiment of the invention, the nozzles in a cluster can be
either made of metal (steel or aluminium), plastic or rubber.
In a preferred mode of the invention, the air jets from a cluster of multiple
nozzles create multiple air jet zone of length (11) that converge into a
single air jet at
a distance l, forming into a single air jet zone of length (12).
In a further embodiment, the distance (c11) between an array of nozzles in a
cluster is smaller than the distance (d2) between any two clusters of nozzles.
In the embodiment where air induction ratio is enhanced by use of an
adjustable venturi, whether used in combination with a single nozzle or
multiple
nozzles in clusters or otherwise, the resultant induction ratio of an air jet
created by
a nozzle or an array of multiple nozzles in a cluster in combination with a
venturi is
larger than when compared to the induction ratio of an air jet resulting from
nozzles
alone.
Turning now to figure 6, the location (x) of the venturi (9) is based on the
central line velocity (v) in the venturi neck and the diameter (h) of the air
jet.
Therefore, with the smaller exit velocity (ve) in the nozzle, the venturi neck
shall be
nearer to the nozzle than it is with higher exit velocity (ve) in the nozzle.
This exit
velocity (ve) depends on primary air flow rate (4) and the face area of the
nozzle(s).
The central line velocity (v) is dependent on the exit velocity (ve) in the
nozzle and
the secondary air flow (6). At the same time the neck diameter (y) of venturi
needs
to be set equal to the diameter (h) of the air jet at the same location (x).
Referring now to Figure 8, the venturi (9) consists of two different optimally
sized and shaped elements that can be used singly or together to create the
venturi
neck (9). The core part of the venturi (9a) creates the basic venturi neck (9)
for bigger
mixed airflows (7). The reduction part (9b) of the venturi (9) is optimally
shaped so
that when two of them are installed parallel they both reduces the size of the
venturi
neck (y4<y3) and shifts the distance of neck(x4<x3) nearer the nozzle (5).
Reduction
parts (9b) can be installed in opposite directions to create the medium size
neck
(y4<y5<y3) and/or to change the course of mixed air flow jet (7). The core
part (9a)
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and reduction part (9b) of the venturi are both removable and re-installable.
Both
the core part (9a) and reduction part (9b) of the venturi can be made from
solid
material, be hollow, inflatable or formed from a sheet metal plate.
In the embodiment comprising use of a venturi device whether in
combination with a solo nozzle or nozzle clusters, the induction supply air
terminal
devicethat comprises of primary supply air chamber (1), at least one mixing
chamber (2) which opens into the air-conditioned room space, at least one or
no
heat exchanger (3), single or an array of multiple nozzles in a cluster (5)
that
supplies primary air flow (4) into at least one mixing chamber (2) to induce a
secondary air flow (6) heated or cooled as it flows through a heat exchanger
(3) and
conducted into the mixing chamber (2), wherein both this primary supply air
(4) and
secondary air (6) mix, whereby this mixed air (7) is then conducted into the
air-
conditioned room space (8), wherein an adjustable venturi (9) is provided to
increase the secondary air flow rate (6).
In one embodiment, the location (x) of the venturi (9) is based on the
optimum central line velocity (v) in the venturi neck, which depends on the
primary
air flow rate(4),the face area of the nozzle(s) and the secondary air flow
(6).
In another embodiment, the neck diameter (y) of venturi is set equal to the
diameter (h) of the air jet at the same location (x).
In another embodiment, the location (x) of the venturi (9) and/or the neck
diameter (y) of the venturi (9) is adjusted manually or automatically using an
actuator. In another embodiment, the venturi (9) shape and type can vary -
solid,
inflatable or bent metal/plastic sheet fixed at one end and with an adjustable
another end.
It is observed through experiments carried out that there is a definite
enhancement in the air induction ratios using the various arrangements
embodied in
the invention, viz.
(a) a cluster nozzle arrangement with a fixed venture;
(b) an adjustable venture with a single nozzle
(c) an adjustable venture with a cluster of nozzles
(d) chilled beams provided with each of the above combinations.
This data is summarised in the Table below:
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Single nozzle Flower Cluster
Single + venturi
4 mm 5.9 mm 4x 2 mm 4 mm
Face area (mm2) 12.6 12.6 12.6 12.6
Perimeter (mm) 12.6 22.3 25.2 12.6
Pressure 70 Pa 63 Pa 58 Pa 62 Pa
Distance Jet's total air
volume (Vs)
0 mm 0.1 0.1 0.1 0.1
20 mm 0.42 0.44 0.52 0.31
40 mm 0.68 0.66 0.74 0.56
60 mm 0.91 0.87 0.95 0.92
80 mm 1.1 1.06 1.13 1.17
10
20
10
