U.S. patent application number 14/648322 was filed with the patent office on 2015-11-26 for summer bypass for heat recovery unit.
The applicant listed for this patent is GREENWOOD AIR MANAGEMENT LIMITED. Invention is credited to Mark BELLE, Daniel BYNE, Gordon FLACK, Darius RAHIMI.
Application Number | 20150338122 14/648322 |
Document ID | / |
Family ID | 49713406 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150338122 |
Kind Code |
A1 |
BYNE; Daniel ; et
al. |
November 26, 2015 |
SUMMER BYPASS FOR HEAT RECOVERY UNIT
Abstract
There is provided a heat recovery ventilation unit comprising a
first air flow path and a second air flow path and a heat exchanger
in which the first air flow path is in heat exchange contact with
the second air flow path; the unit further comprising an air flow
path selector in the first air flow path which is arranged to
select between the first air flow path and a third air flow path
which bypasses the heat exchanger; wherein the air flow path
selector is located between an inlet filter of the first air flow
path and the heat exchanger. Providing the bypass selector between
the filter and the heat exchanger, air is always filtered, even in
the bypass mode, thus reducing particulate matter drawn into the
building during bypass operation.
Inventors: |
BYNE; Daniel; (Rustington,
Sussex, GB) ; FLACK; Gordon; (Rustington, Sussex,
GB) ; RAHIMI; Darius; (Rustington, Sussex, GB)
; BELLE; Mark; (Rustington, Sussex, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GREENWOOD AIR MANAGEMENT LIMITED |
Rustington, Sussex |
|
GB |
|
|
Family ID: |
49713406 |
Appl. No.: |
14/648322 |
Filed: |
November 29, 2013 |
PCT Filed: |
November 29, 2013 |
PCT NO: |
PCT/GB2013/053168 |
371 Date: |
May 29, 2015 |
Current U.S.
Class: |
165/54 |
Current CPC
Class: |
F24F 13/16 20130101;
Y02B 30/56 20130101; F24F 13/12 20130101; F24F 2012/007 20130101;
F24F 12/006 20130101; Y02B 30/563 20130101 |
International
Class: |
F24F 12/00 20060101
F24F012/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2012 |
GB |
1221652.9 |
Claims
1. A heat recovery ventilation unit comprising a first air flow
path and a second air flow path and a heat exchanger in which the
first air flow path is in heat exchange contact with the second air
flow path; the unit further comprising an air flow path selector in
the first air flow path which is arranged to select between the
first air flow path and a third air flow path which bypasses the
heat exchanger; wherein the air flow path selector is located
between an inlet filter of the first air flow path and the heat
exchanger.
2. A heat recovery unit as claimed in claim 1, wherein the heat
recovery unit comprises structures formed from plastic which form
the third air flow path.
3. A heat recovery unit as claimed in claim 1, wherein the air flow
path selector comprises a barrier which is movable between a first
configuration in which air is directed to the heat exchanger and a
second configuration in which air is directed to bypass the heat
exchanger.
4. A heat recovery unit as claimed in claim 3, wherein the barrier
is operable to slide between the first configuration and the second
configuration.
5. A heat recovery unit as claimed in claim 4, wherein the barrier
is a foldable barrier and wherein one of the first and second
configurations is the folded state of the foldable barrier and the
other of the first and second configurations is the unfolded state
of the foldable barrier.
6. A heat recovery unit as claimed in claim 5, wherein the first
configuration is the folded configuration and the second
configuration is the unfolded configuration.
7. A heat recovery unit as claimed in claim 5, wherein the foldable
barrier comprises a first section, a second section and a third
section, the first section being foldably connected to the second
section and the second section being foldably connected to the
third section, and wherein in the folded configuration the fold
between the first section and the second section is substantially a
right angle and the fold between the second section and the third
section is substantially 180 degrees so that the second and third
sections are substantially parallel.
8. A heat recovery unit as claimed in claim 7, wherein the barrier
is driven between the first and second configurations by an
electric motor.
9. A heat recovery unit as claimed in claim 1, wherein the barrier
comprises a plurality of sections, each slidable with respect to
the others such that the sections are movable between an overlapped
configuration and a non-overlapped configuration.
10. A heat recovery unit as claimed in claim 1, wherein the heat
recovery unit is configurable such that either the first flow path
or the second flow path is for incoming air.
Description
[0001] The invention relates to heat exchangers or heat recovery
units used in ventilation systems. In particular, the invention
relates to a summer bypass arrangement for such heat recovery
units.
[0002] Heat exchangers are used in many technologies for
transferring heat between two fluid flows. The present invention
relates more specifically to gas heat exchangers where heat is
exchanged between two different gas flows.
[0003] Ventilation systems can either be balanced or unbalanced. In
an unbalanced system, air is extracted from a building (typically
certain areas of the building such as kitchens and bathrooms) and
is expelled to the outside in order to get rid of unwanted moisture
and/or odours. The system relies on the extracted air being
replaced naturally by air flowing into the building through natural
openings, such as through window vents, or under doors. This system
works well in older "leakier" buildings where there are plenty of
natural openings through which air can enter or leave the
building.
[0004] However in more modern buildings improved seals tend to be
employed around windows and doors in order to improve the thermal
efficiency of the building and reduce the amount of warm air
escaping from within the building. In such cases, a balanced
ventilation system may be more appropriate. A balanced ventilation
system does not just extract air from the building and exhaust it
to the outside, but also draws replacement air into the building,
thus maintaining the air pressure within the building. Such systems
therefore have one flow path for air coming into the building and
another flow path for air being expelled from the building. The air
being drawn in from outside is typically colder than the air being
expelled and therefore, for improved thermal efficiency, a heat
exchanger can be employed to transfer some of the heat from the
outgoing air flow into the incoming air flow.
[0005] In normal operation, air within the building is heated to a
desired temperature via normal heating systems and the heat
recovery unit (comprising the heat exchanger and various controls)
then aims to minimise heat losses in the exhausted air by using it
to heat up the incoming cold air, thus reducing load on (and energy
usage of) the heating system. It will be appreciated that the
system can also be used in warm conditions where the inside air is
cooled to a temperature below the outside temperature and the heat
exchanger operates by using the cold outgoing air to cool down the
warm incoming air, again improving thermal efficiency and reducing
load on the cooling system.
[0006] However, not all buildings have air conditioning or other
air cooling facilities. During warm conditions, this can lead to
the heat exchanger working the wrong way. For example, when the
outside temperature is above the inside temperature, the heat
exchanger will initially act to cool the incoming air by heat
exchanging with the outgoing air. However, as the heat exchanger is
not 100% efficient, the inside temperature gradually rises to
equalise with the outside temperature. If there is then any heating
within the house (e.g. sunlight streaming through a window and
causing a local heating effect), the air temperature within the
house will rise above that of the outside air. The incoming outside
air is then further heated by the outgoing inside air (as per
normal operation in cold weather), causing further heating within
the house. In such warm conditions, the heat exchanger works
against the desires of the building's occupants. For this reason,
heat recovery units are typically fitted with a summer bypass
mechanism whereby when certain conditions are met one of the
airstreams is switched to bypass the heat exchanger so as to
prevent any further heat exchange. Either the incoming or outgoing
airstream can be bypassed in this manner. With no heat exchange
taking place, the warmer air within the house is simply replaced
with cooler air from outside and the temperatures should
equalise.
[0007] According to the invention there is provided a heat recovery
ventilation unit comprising a first air flow path and a second air
flow path and a heat exchanger in which the first air flow path is
in heat exchange contact with the second air flow path; the unit
further comprising an air flow path selector in the first air flow
path which is arranged to select between the first air flow path
and a third air flow path which bypasses the heat exchanger;
wherein the air flow path selector is located between an inlet
filter of the first air flow path and the heat exchanger.
[0008] Existing heat recovery units have typically installed the
summer bypass diverter (selector) outside the air filter so that
when the diverter is in the summer bypass mode, the diverted
airflow does not pass through the filter. If it is the outgoing
airstream that is diverted, and thus unfiltered, the lack of
filtration may be of less concern. However many heat recovery units
are now designed to be reversible in some fashion so that the two
flow paths within the unit can be allocated to incoming/outgoing
airstreams at the point of installation, thus allowing greater
flexibility to the installer. With such devices, if only a single
summer bypass is provided on one of the airflow paths, that path
may be allocated to the incoming airstream when the unit is
installed. However the incoming airstream is then not filtered and
particulate matter such as dust or pollen enters the building
rather than being filtered out.
[0009] By providing the summer bypass diversion (i.e. the place in
the flow path where the air is redirected so that it does not pass
through the heat exchanger) after the filter, the quality of air
within the building is maintained in all conditions and regardless
of which flow path is allocated to be incoming air upon
installation.
[0010] The heat recovery units are typically designed for
installation in a relatively small space such as a kitchen
cupboard. They are therefore designed to be as small and compact as
possible. The air filters are typically positioned quite close to
the heat exchanger and therefore once air has passed through the
filter it is within a much more constrained space where there is
little room for creating alternative flow paths which could be used
to create a bypass flow path.
[0011] Due to a combination of the cost and simplicity of
manufacturing and the insulation properties, heat recovery units
have typically been made from foam materials such as expanded
polystyrene (EPS). However the molding process for such materials
has two important consequences. Firstly it limits the minimum
thickness of the components to about 10 mm, i.e. no piece can be
less than about 10 mm thick. Secondly it is difficult or impossible
to mold complex shapes. This provides certain limitations on the
interior of the unit. With these limitations, the potential airflow
paths within the unit are restricted. Particularly in smaller units
with less interior volume inside the unit, complex airflow paths
cannot be created.
[0012] Preferably the interior components of the heat recovery unit
are formed from plastic rather than foam. Plastic can be molded
into more intricate shapes and is much thinner than the foam.
Plastic can be injection molded to 1.6 mm. Therefore by using
plastic, more space is created inside the unit without making the
unit any larger. Also, as more intricate shapes can be molded, a
more complex path becomes viable, e.g. with tighter curves. This
allows an alternative flow path to be routed through the unit
without increasing the size of the unit or reducing the size of the
heat exchanger. It also allows a flow path to be formed on the
filtered side of the filter. Preferably therefore the heat recovery
unit comprises structures formed from plastic which form the third
air flow path. Preferably the plastic structures are less than 5 mm
thick, more preferably less than 3 mm thick and most preferably
less than 2 mm thick.
[0013] Some foam panel may still be used in key areas for thermal
efficiency, e.g. on the insides of some external panels or inside
the unit to isolate airflows of different temperatures as the
thermal insulation characteristics of plastic are not as good as
foam. However the use of foam is avoided in areas which form the
third air flow path which bypasses the heat exchanger.
[0014] It should be noted that the filter cannot simply be moved
closer to the inlet port without reducing efficiency. If the filter
were placed adjacent to the inlet port then only a small area of
the filter equal to the area of the inlet port would actually be
used. By contrast, positioning the filter away from the inlet port
allows the air from the inlet port to expand and disperse inside
the unit, thus making better use of the filter. This arrangement
provides less air resistance and reduces the pressure drop across
the filter. It is therefore preferred that the filter be spaced
from the air inlet port so as to allow the incoming airflow to
disperse before passing through the filter.
[0015] The airflow path selector may be any suitable mechanism for
opening and closing the two airflow paths. The mechanism could use
two independent shutters, linked to the same or different controls,
but preferably a single shutter is used which opens one path while
closing the other path and vice versa. Louvers are an example of
one kind of shutter. As the louvers are rotated through 90 degrees,
they open and close the gaps between them, thus opening and closing
one airflow path. One of the end louvers could be positioned in a
wall perpendicular to that airflow path so that when the end louver
is parallel to the wall (allowing air flow through the first
airflow path) it closes off an opening in the wall leading to an
alternative (bypass) airflow path. When the louvers are rotated to
close the first airflow path, this alternative airflow path would
then be opened. However it is preferred not to use louvers as they
add resistance to air passing through (between) them.
[0016] It is preferred to use a barrier which is moved out of the
way so as to open one path and close the other. Preferably the air
flow path selector comprises a barrier which is movable between a
first configuration in which air is directed to the heat exchanger
and a second configuration in which air is directed to bypass the
heat exchanger.
[0017] A single rotating barrier can be used, rotatable about one
edge to move between its first and second configurations so that it
selects between closing different airflow paths. Such an
arrangement avoids the air resistance problem of using multiple
louvers, but it is not particularly space efficient as the barrier
must be large enough to block the larger of the two airflow paths
and also must be given room to rotate between its two
positions.
[0018] Preferably the barrier is operable to slide between the
first configuration and the second configuration.
[0019] A slidable barrier can avoid the need for swinging room
which would be required by a rotatable barrier. If the two airflow
paths are located adjacent to one another and are of the same
cross-sectional size/shape then a slidable barrier can provide an
efficient solution. If the two airflow paths are adjacent, but not
in the same direction a bendable barrier (e.g. a sectioned barrier)
may be used to slide along bent tracks so that the barrier moves
from being in front of (blocking) one path to being in front of
(blocking) the other path.
[0020] However the airflow paths may not be of the same dimension,
the summer bypass path not having resistance caused by the heat
exchanger and therefore not needing to be of such great diameter.
As space is a concern with heat recovery units, as described above,
an efficient barrier solution is required in situations where there
is such a discrepancy in opening size of the two alternative flow
paths.
[0021] Preferably therefore the barrier is a foldable barrier and
one of the first and second configurations is the folded state of
the foldable barrier and the other of the first and second
configurations is the unfolded state of the foldable barrier. In
particularly preferred embodiments the first configuration
(blocking the bypass path while allowing airflow to the heat
exchanger) is the folded configuration and the second configuration
(blocking airflow to the heat exchanger while allowing airflow
through the bypass path) is the unfolded configuration. As
discussed above, the bypass channel will tend to be of smaller
dimensions than the heat exchanger channel and so can be blocked
off with a smaller barrier, i.e. a folded configuration of the
barrier may be used to block the heat exchanger channel. This
provides highly efficient usage of space as the unit does not need
to be configured to accommodate unused parts of the barrier which
are not required to cover the relevant opening of the bypass
channel.
[0022] In some preferred embodiments the foldable barrier comprises
a first section, a second section and a third section, the first
section being foldably connected to the second section and the
second section being foldably connected to the third section, and
wherein in the folded configuration the fold between the first
section and the second section is substantially a right angle and
the fold between the second section and the third section is
substantially 180 degrees so that the second and third sections are
substantially parallel.
[0023] With this configuration all three sections together form the
barrier for the heat exchanger path (the first airflow path) with
the barrier in a flat (unfolded) state. In the folded state, the
second and third sections are folded perpendicular to the first
section, with the third section folded back on the second section
such that they are in an overlapping relationship. The second and
third sections together block the bypass path (the third airflow
path).
[0024] It is particularly preferred that the first, second and
third sections are all rectangular and of substantially equal size
and shape. With this configuration, the area of the barrier in its
folded state is equal to approximately one third of its area when
unfolded. Therefore the heat exchanger flow path (first air flow
path) can have a cross-sectional area around three times that of
the bypass flow path (third air flow path).
[0025] In an alternative arrangement, the barrier comprises a
plurality of sections, each slidable with respect to the others
such that the sections are movable between an overlapped
configuration and a non-overlapped configuration. In the overlapped
configuration, the barrier covers a smaller cross-sectional area
and is therefore preferably used to block the bypass flow path
(third air flow path). In the non-overlapped configuration the
barrier has a much larger cross-sectional area and is therefore
preferably used to block the heat exchanger flow path (first air
flow path). This arrangement is particularly beneficial if the two
air flow paths are adjacent and initially directed in the same
direction.
[0026] Preferably only a leading section of the barrier is driven.
As the sections are moved from the overlapped configuration to the
non-overlapped configuration, each of the sections (except the
last) is arranged to pull an adjacent section. Thus, starting from
the overlapped configuration, each section in turn slides over its
adjacent section into a non-overlapped state and then pulls the
next section behind it. Once the sections have all reached a
non-overlapped configuration, the barrier is pulled further so that
the final section is moved out of the way of the third air flow
passage (bypass passage), thus opening it to air flow. Preferably
the barrier comprises three sections each of approximately the same
size and the third air flow passage has an opening approximately
one third of the size of the opening of the first air flow
passage.
[0027] It will be appreciated that in the non-overlapped
configuration there may still be some small overlap between the
adjacent barrier sections. The term "non-overlapped configuration"
is used to refer to the overall state, being one in which the
adjacent sections are substantially (or predominantly)
non-overlapping.
[0028] In preferred embodiments the barrier is driven between the
first and second configurations by an electric motor. Previously
available heat recovery units have operated the summer bypass
diverter using a wax actuator. The wax actuator changes between an
actuated state and a non-actuated state through change of phase of
the wax (solid to liquid and vice versa). The temperature required
to melt the wax is greater than the air temperatures in question
and therefore to maintain the actuator (and the barrier) in the
configuration in which the wax is melted requires continual
application of energy through a heating element. This is therefore
an inefficient and non-eco-friendly solution. It is therefore
preferred not to use a wax actuator. The use of a motor is more
costly and requires more components, but means that power is only
consumed as the barrier is moved from one position to the other
position. No power is consumed by leaving the barrier in a given
position.
[0029] In some preferred embodiments, the third path passes over
the top of the heat exchanger. In other preferred embodiments the
third path passes underneath the heat exchanger. The latter
arrangement is more suitable in a larger heat recovery unit where
there is more room underneath the heat exchanger. In smaller heat
recovery units, the heat exchanger is located close to the bottom
of the unit, but there is some room for a bypass airflow path in
the upper section of the unit around the air inlet and outlet
conduits.
[0030] Preferably the heat recovery unit is configurable such that
either the first flow path or the second flow path is for incoming
air. The other path is then for outgoing air. It does not matter
which of the paths (incoming or outgoing) contains the bypass path
as both air flow paths are filtered before entering the heat
exchanger and the bypass simply avoids thermal contact in the heat
exchanger.
[0031] Activation of the summer bypass can be done manually, e.g.
via a manual switch or an electronic switch. However it is
preferably activated and deactivated based on data received from
the sensors (e.g. data on inside and outside air temperatures) and
internal logic (preferably programmed into the control unit).
[0032] Although it will be appreciated that the above system has
been described in terms of domestic ventilation systems (and this
is the preferred application), it will be appreciated that the
technology also applies to other heat exchange ventilation
systems.
[0033] Preferred embodiments of the invention will now be
described, by way of example only, and with reference to the
accompanying drawings in which:
[0034] FIG. 1 shows a partially cut away view of a first embodiment
of the invention;
[0035] FIG. 2 shows a sectional view of the first embodiment with
the bypass path closed;
[0036] FIG. 3 shows a sectional view of the first embodiment with
the bypass path open;
[0037] FIG. 4 shows a cut-away view of the first embodiment with
the bypass path open;
[0038] FIGS. 5 to 7 show a barrier mechanism of the first
embodiment;
[0039] FIG. 8 shows a first view of a second embodiment with a
bypass path open;
[0040] FIG. 9 shows a second view of the second embodiment with the
bypass path open;
[0041] FIG. 10 shows a barrier of the second embodiment with the
bypass path open; and
[0042] FIG. 11 shows the barrier of the second embodiment with the
bypass path closed.
[0043] FIG. 1a shows a first embodiment of the invention. The first
embodiment is a smaller sized heat recovery unit designed to fit
inside a kitchen cupboard. The unit is approximately 560 mm by 550
mm by 300 mm.
[0044] The heat recovery unit 100 has two inlet ports and two
outlet ports as follows: a first inlet 110, a first output 120, a
second inlet 130 and a second outlet 140. Underneath first inlet
110 is a first filter 160. Underneath second inlet 130 is a second
filter 170. In the middle of the unit is a heat exchanger 150.
[0045] In normal operation, as shown in FIG. 1a, a first air flow
path passes through first inlet 110, then through the heat
exchanger 150, then through first centrifugal fan 180 (not shown in
FIG. 1a) and then through first outlet 120.
[0046] A second air flow path passes through second inlet 130, then
through the heat exchanger 150, then through second centrifugal fan
190 (not shown in FIG. 1a) and then through second outlet 140.
[0047] These flow paths are illustrated in FIG. 2. Arrow 200 shows
the first air flow path and arrow 210 shows the second air flow
path. These two flow paths are for normal operation when the two
air flow paths are in heat exchange relationship, i.e. both pass
through the heat exchanger where they are in heat exchange contact,
but no air or moisture is exchanged. The warmer airstream transfers
its heat to the colder airstream. First airstream 200 passes
through first filter 160 before it reaches the heat exchanger.
Second airstream 210 passes through second filter 170 before it
reaches the heat exchanger.
[0048] FIGS. 1b corresponds to FIG. 1a, but show the unit is summer
bypass mode. FIG. 3 corresponds to FIG. 2, but shows the airflows
when the unit is in summer bypass mode.
[0049] The only difference between FIGS. 1a and 1b is that in FIG.
1a an air flow barrier (air flow diverter) 300 is in a folded
configuration which blocks the bypass air flow path while allowing
air to flow along the first air flow path through the heat
exchanger. In FIG. 1b the air flow barrier 300 is in an unfolded
(flat) configuration which blocks air flow in the first air flow
path from passing through the heat exchanger and instead redirects
it through the bypass flow path. The operation of the barrier 300
will be described further below.
[0050] The bypass flow path is shown in FIG. 3 and is indicated by
arrow 220. The flow path of the second air flow path (through the
second inlet port 130, heat exchanger 150 and second outlet port
140) is indicated by arrow 210, as in FIG. 2. This second air flow
path is unaltered in the summer bypass mode.
[0051] With the barrier 300 in the summer bypass configuration, air
entering the first inlet is redirected around the alternative,
bypass flow path 220. This path passes over the top of the heat
exchanger 150, behind the second air inlet 130, between the second
air inlet 130 and the first air outlet 120, and down to the bottom
of the unit to the point at which air from the first inlet 110
would exit the heat exchanger 150 if the unit were in normal
operation mode. This is the location of the centrifugal fan 180
which drives the air along the flow path (either the first air flow
path in normal operation or the bypass path in bypass operation).
The fan 180 then drives the air up and out of the first outlet 120.
An alternative view of this bypass flow path is shown in FIG. 4
which is a partially cut away view of the heat recovery unit
100.
[0052] It can be seen from FIGS. 3 and 4 that the bypass flow path
220 still passes through the first filter 160. This path 220 is
possible largely due to manufacturing the structures of the heat
recovery unit from plastics rather than from foam. As can be seen
from the partial cross-sections in FIGS. 1a and 1b, the structures
are thin (about 1.6 mm). If these were made from foam they would be
about 10 mm or greater in thickness. The path 220 would not be
possible with the thicker material without making the whole unit
larger. In particular, as described above, the path 220 passes over
the top of the heat exchanger and around the first outlet 120 and
second inlet 130. If made from foam, this area in the top of the
unit 100 would be far too constricted to act as a bypass path.
Also, the channel down the side of the unit towards the fan 180
would be severely constricted if the unit were made from foam
rather than plastics.
[0053] Directing the bypass flow path 220 over the top of the heat
exchanger 150 rather than over the front of the heat exchanger 150
means that the heat exchanger can extend the whole depth of the
unit (i.e. the distance from the front face to the back face) which
maximises the efficiency of the unit. In general, the larger the
heat exchanger, the better the efficiency.
[0054] FIGS. 5, 6 and 7 show the barrier 300 and illustrate its
operation between its two configurations (normal and bypass). FIG.
5 shows the barrier 300 in a folded configuration for normal
operation, with the bypass shut. FIG. 7 shows the barrier 300 in an
unfolded configuration for bypass operation, with the normal flow
path shut. FIG. 6 shows the barrier 300 in transit between the two
configurations.
[0055] Barrier 300 is formed from three rectangular sections, a
leading section 301, a middle section 302 and a trailing section
303. The leading section 301 is slidably mounted in guide rails
304, 305. Both the leading edge and the trailing edge of leading
section 301 are mounted in the guide rails 304, 305 so that leading
section 301 remains in the same orientation as it slides along the
rails 304, 305. The leading edge of middle section 302 is rotatably
mounted to the trailing edge of leading section 301. The trailing
edge of middle section 302 is rotatably mounted to the leading edge
of trailing section 303. The trailing edge of trailing section 303
is slidably mounted in the guide rails 304, 305.
[0056] The leading edge of trailing section 303 and the trailing
edge of middle section 302 are not slidably mounted to the guide
rails 304, 305 and are thus free to move in the direction
perpendicular to that of the rails 304, 305.
[0057] Leading section 301 is attached to a drive mechanism
comprising a rack 306 (to which the leading section 301 is
attached) which is driven by a pinion 307 which is in turn driven
by a motor and gearbox 308. The middle section 302 and trailing
section 303 are not connected to the drive mechanism, but are moved
merely by virtue of being connected to the leading section 301.
[0058] Operation of the barrier 300 will now be described, starting
from the position shown in FIG. 5 in which the barrier is in a
folded configuration. Middle section 302 and trailing section 303
are folded back on each other so that they overlap one another. In
this configuration they block the entrance to the summer bypass
flow path which runs from left to right in FIG. 5. Leading section
301 is parallel to the guide rails 304, 305 and is retracted as far
as possible (i.e. as close as possible to the motor and gearbox
308). Middle section 302 and trailing section 303 are perpendicular
to the guide rail 304, 305. The normal flow path through the heat
exchanger (indicated by arrow 309 in FIG. 5) is open in this
configuration.
[0059] FIG. 6 shows the barrier 300 in transit between the two
configurations. Leading section 301 has been driven along guide
rails 304, 305 by the motor and gearing 308 turning the pinion 307
which pushes the rack 306 (and leading section 301 connected
thereto) in the direction of closing the main air flow path 309. As
the leading section 301 progresses, the middle section 302 and
trailing section 303 separate and start to fold towards a flattened
state.
[0060] FIG. 7 shows the barrier 300 in its flattened (non-folded)
state with the leading section 301 driven as far forward as
possible by the motor and gearing 308, pinion 307 and rack 306. In
this position, the trailing edge of trailing section 303 has also
been pulled forward. The trailing edge of trailing section 303 has
lugs 312 which are mounted in grooves 311 in the guide rails 304,
305. Grooves 311 define the extreme positions of the trailing edge
of trailing section 303. In FIG. 7, the lugs 312 are in the extreme
forward position (furthest from the motor and gearing 308), while
in FIGS. 5 and 6 lugs 312 are in the extreme rearward position
(closest to the motor and gearing 308).
[0061] The leading edge of trailing section 303 (although it could
equally be the trailing edge of middle section 302) is also
provided with lugs 314 which protrude laterally over the guide
rails 304, 305. These lugs 314 prevent the middle and trailing
sections 302, 303 from folding completely flat as the lugs 314
cannot pass the top of the guide rails 304, 305. Retaining a slight
fold in the barrier 300 in this way ensures that when the barrier
300 is moved to the folded configuration, the middle section 302
and trailing section 303 fold in the correct manner.
[0062] When the barrier 300 is fully extended in the non-folded
configuration, the trailing section 303 is pulled forward in its
grooves 311. This is so that the whole length of the barrier 300 is
available to cover the normal air passage to the heat exchanger.
When the barrier 300 is fully retracted in the folded
configuration, the trailing section 303 is pushed backward in its
grooves 311. This is so that the folded middle and trailing
sections 302, 303 are pushed back against the opening to the bypass
passage in a sealing manner, while also allowing the leading
portion 301 to be drawn fully back from the entrance to the normal
heat exchanger passage to fully open that passage.
[0063] FIGS. 8 and 9 show a second embodiment of the invention.
FIG. 8 shows a partly cutaway view of a larger heat recovery unit
400 in which the bypass passage 410 is directed underneath the heat
exchanger. The flow of air around the bypass passage 410 is
indicated by arrow 420. FIG. 9 shows a cutaway view of the second
embodiment from a different angle.
[0064] As in the first embodiment, the airflow through first inlet
110 first passes through first filter 160 before it reaches the
barrier (air flow selector) 420 which is used to select the normal
air flow passage or the bypass passage 410.
[0065] The barrier 420 in the second embodiment functions in a
different manner to that of the first embodiment. Barrier 420 is
shown in FIGS. 10 and 11. In FIG. 10 the bypass path is open, while
the normal heat exchanger flow path is closed. In FIG. 11 the
bypass path is closed, while the normal heat exchanger flow path is
open. Barrier 420 also comprises a number of sections 431-436, but
none of them are foldable. Instead, all sections 431-436 are
slidable in guide rails 440, 445.
[0066] The leading section 436 is attached to a toothed belt 450
which is driven by motor and gearing 460 to move leading section
436 back and forth in the guide rails 440, 445. Each section except
the leading section 436 has an upwardly projecting lip on its
leading edge which is caught by and pulled by a corresponding
downwardly projecting lip on the trailing edge of the section in
front of it. In this manner, as the leading section 436 is driven
forward, the lip on its trailing edge catches the lip on the
leading edge of section 435, pulling it forward. The lip on the
trailing edge of section 435 then subsequently catches the lip on
the leading edge of section 434, pulling that forward, and so on
until trailing section 431 is pulled out last. In this extended
configuration, all of the sections 431 to 436 overlap slightly and
block the main flow path to the heat exchanger which is indicated
by arrow 470 in FIG. 11. At the same time, moving trailing section
431 opens the summer bypass flow path which is indicated by arrow
480 in FIG. 10.
[0067] Each section except the trailing section 431 has a lip on
its leading edge which catches and pulls the leading edge of the
section behind it during retraction. In this manner, as leading
section 436 is driven in the direction of retraction (right to left
in FIGS. 10 and 11), it catches and pulls section 435 with it,
which in turn catches and pulls section 434 with it and so on until
trailing section 431 is pulled back to the fully retracted position
shown in FIG. 11. In this position, all of the sections 431 to 436
are stacked up over the entrance to the summer bypass air flow path
480, closing it off, while the main flow path 470 to the heat
exchanger is fully open.
[0068] As in the first embodiment, the area of the main flow path
470 is much larger than the area of the bypass path 480 (in this
case, six times as large) so as to provide less resistance for the
path which has to go through the heat exchanger.
[0069] In the second embodiment, both the normal flow path 470 and
the bypass flow path 480 head initially in the same direction,
whereas in the first embodiment the two paths are at right
angles.
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