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|United States Patent Application
Woods, Mark Conley
;   et al.
May 8, 2003
Environmental control kit for sealed cabinets
A heat exchanger kit useful for installation in an existing electrical
equipment cabinet, said cabinet having an enclosure adapted to contain
heat-generating electrical equipment, at least one access opening, and a
door providing a closure for said access opening; the kit including a
replacement door for the cabinet and mounted thereon, a louvered shroud,
creating an enclosure within said shroud defined by the replacement door
and the shroud, an air-to-air heat exchanger mounted on the exterior of
the replacement door, and supported thereby, for removing heat from the
interior of the cabinet while maintaining the substantially closed
environment within the cabinet. The heat exchanger has a first air flow
path for air drawn from the exterior of said cabinet and a second air
flow path from the interior of said cabinet, where the first and second
air flow paths are perpendicular to one another and are substantially
isolated from each other; and further including at least one fan for
circulating air through at least one of a first and a second air flow
Woods, Mark Conley; (Pflugerville, TX)
; Allen, William George; (Austin, TX)
Attn: Darla P. Fonseca
Office of Intellectual Property Counsel
3M Innovative Properties Company
P.O. Box 33427
3M Innovative Properties Company
December 18, 2002|
|Current U.S. Class:
|Class at Publication:
What is claimed is:
1. A heat exchanger kit useful for installation in an existing electrical
equipment cabinet, said cabinet having an electronic equipment
compartment adapted to contain heat-generating electrical equipment, at
least one access opening, and a door providing a closure for said access
opening, said kit comprising a replacement door having interior and
exterior surfaces for said cabinet having mounted thereon: a shroud
creating an enclosure within said shroud defined by said replacement door
and said shroud, an air-to-air heat exchanger mounted on the exterior
surface of the replacement door, and being supported thereby, for
removing heat from the interior of said cabinet while maintaining said
substantially closed environment within said cabinet, said heat exchanger
having a first air flow path for air drawn from the exterior of said
cabinet and a having a second air flow path from the interior of said
cabinet, said first and second air flow paths being perpendicular to one
another and being substantially isolated from each other; and at least
one fan for circulating air through each of said first and said second
air flow path.
2. The heat exchanger kit of claim 1, wherein said fan comprises a pair of
fans to be located adjacent to one another, and further comprises a
baffle located between said pair of fans for dividing the flow path into
two parallel air flow paths substantially isolated from one another.
3. The heat exchanger kit of claim 1, further comprising upper and lower
air flow plenums to be mounted to an exterior surface of said replacement
door, said heat exchanger being supported between said air flow plenums.
4. The heat exchanger kit of claim 2, wherein said pair of fans circulate
air through the first air flow path.
5. The heat exchanger kit of claim 2, wherein said pair of fans circulate
air through the second air flow path.
6. The heat exchanger kit of claim 1, wherein said fan is mounted on said
exterior of said replacement door to perform air intake.
7. The heat exchanger kit of claim 1, wherein said fan is mounted on said
interior surface of said replacement door to perform air outflow.
8. The heat exchanger kit of claim 2, wherein said pair of fans are
mounted on said exterior of said replacement door to perform air intake.
9. The heat exchanger kit of claim 2, wherein said pair of fans are
mounted on said interior surface of said replacement door to perform air
10. The heat exchanger kit of claim 1, wherein said heat exchanger
enclosure extends outward from the replacement door to the louvered
shroud, such that said enclosure does not protrude into said electronic
11. A heat pump kit useful for installation in an existing electrical
equipment cabinet, said cabinet having an electronic equipment
compartment adapted to contain heat-generating electrical equipment, at
least one access opening, and a door providing a closure for said access
opening, said kit comprising a replacement door for said cabinet having
mounted thereon: a shroud creating an enclosure within said shroud
defined by said replacement door and said shroud, a compressor driven
heat pump mounted on the exterior of the replacement door, and being
supported thereby, for removing heat from the interior of said cabinet
while maintaining said substantially closed environment within said
cabinet, said heat pump having evaporator and condenser sections, each
section having at least one fan for circulating air through a flow path.
12. An outdoor telecommunications cabinet having the heat exchanger kit of
claim 1 mounted on an access opening thereto.
13. An outdoor telecommunications cabinet having a plurality of access
openings, at least one of said access openings having the heat exchanger
kit of claim 1 mounted thereon.
14. An outdoor telecommunications cabinet having a plurality of access
openings, each access opening having the heat exchanger kit of claim 1
15. An outdoor telecommunications cabinet having the heat pump kit of
claim 11 mounted on an access opening thereto.
FIELD OF THE INVENTION
 The present invention relates to a kit for use in an electrical
equipment cabinet to provide an environmental control system to exchange
air to remove heat or provide active cooling for the cabinet interior.
More specifically, the invention relates to a ready-to-mount kit which
can be installed into an already in-use cabinet, employing a modular,
cross-flow heat exchanger or air conditioner that is mounted on the
exterior of the cabinet door.
BACKGROUND OF THE INVENTION
 Outdoor electrical equipment cabinets are often used to protect
sensitive electronic equipment such as telecommunications equipment from
tampering, vandalism and adverse environmental conditions. The electronic
components housed in the cabinets produce heat when operating. Therefore,
a heat exchanger or other cooling system is required to remove the heat
from the cabinets. As the electronic components become smaller and
operate at higher power densities, cabinets need to dissipate heat more
 One example of a conventional outdoor electrical equipment cabinet
is disclosed in U.S. Pat. No. 4,535,386 (Frey, Jr. et al.). This cabinet
employs a heat exchanger to dissipate internally generated heat. The heat
exchanger exchanges heat between the air in the cabinet and the ambient
air outside the cabinet, without allowing the interior and ambient air to
mix. In this way, a substantially closed or sealed environment can be
maintained within the cabinet, while still allowing for adequate heat
dissipation. The heat exchanger is located in the main portion of the
cabinet, in proximity to the electronics requiring cooling. However, the
presence of the heat exchanger in the cabinet can interfere with the
cables used to interconnect the various electronic components, making the
routing of these cables somewhat more difficult. Also, since the heat
exchanger occupies a significant amount of space, the cabinet must
usually be made larger to accommodate it.
 U.S. Pat. No. 5,467,250 (Howard et al.) discloses an electrical
equipment cabinet that employs a door-mounted heat exchanger so that the
heat exchanger does not occupy internal space required for the electrical
equipment while maintaining a closed or sealed environment within the
cabinet. An arrangement of ducts and vents is used to force interior and
exterior air through channels in the heat exchanger using powered fans
mounted within the main portion of the cabinet. The mounting of the heat
exchanger on or within the door of the cabinet makes more efficient use
of the space available within the cabinet.
 However, the heat exchanger employed in Howard et al. is a parallel
flow heat exchanger in which the channels conducting interior air are
parallel to the channels conducting exterior air. The housing in which
the heat exchanger is located contains two sets of interdigitated vents
for conducting internal and external air through the heat exchanger. In
order to ensure that the flow of exterior air remains isolated from the
flow of interior air, each set of interdigitated vents must be in precise
registration with either the channels conducting interior air or the
channels conducting exterior air. One problem with this arrangement is
that the manufacturing and assembly is difficult because of the precise
 Other problems and service issues associated with the above types
of air-to-air fan-forced heat exchanger systems installed on cabinets
remotely located from the cabinet owner's office include fan failures,
core clogging, etc. If the heat exchanger system has only one air moving
device (e.g., fan or blower) on each flow circuit, then failure of a
single fan effectively kills the heat exchange function (near 100%
performance reduction). If multiple fans are employed on each flow
circuit, failure of one fan can create a open air outlet which allows the
some of the airflow delivered by the active fan to backflow through the
dead fan rather than flowing through the core, resulting in useless
re-circulatory airflow which lowers the overall performance of the heat
exchanger system below that which would be achieved if the second fan
were not present.
 Heat exchanger core clogging/fouling is caused by dust and grime
present in the outdoor air. Clogging can reduce the performance of the
heat exchanger system over time by clogging the air passages through the
heat exchanger core, reducing airflow. The core's performance is also
reduced when dust or grime coats the core's heat transfer surface,
increasing overall thermal resistance.
 If an intake filter is used to mitigate the previous problem, the
filter will eventually get clogged with dust and dirt such that intake
airflow will be reduced, lowering the overall performance of the heat
exchanger system. Therefore, filters typically require frequent
 Because the cabinets are located remotely, frequent maintenance
visits are both inconvenient and expensive. If the filter panel is
external to the cabinet, it is subject to tampering by vandals or
unauthorized personnel. If access requires entering the cabinet where the
sensitive/expensive/hazardous electronics are located, the task must be
performed by highly trained personnel, which adds to the maintenance
 Further, the remote cabinets may be located in residential areas,
where noise emission is restricted. As the volume of outside air moved by
the heat exchanger system increases, the noise level inevitably rises.
Therefore it is advantageous to maximize the heat dissipation realized by
a given amount of ambient airflow.
 System replacement/upgrading capability is crucial. The equipment
cabinet's cooling requirements may change over time as the electronics
are upgraded and/or replaced. This requires that any cooling solution
also be upgradeable. It may be necessary to retrofit the cooling solution
onto existing cabinets in the field.
 Outdoor equipment cabinets represent a substantial investment for
telecommunications companies; and thousands of such cabinets without any
environmental control system already are present in both residential and
commercial settings. As subscribers upgrade services it is not feasible
to simply replace all the traditional non-environmentally controlled
cabinets with new cabinets. The cost is prohibitive, labor time
extensive, and service would be interrupted during the replacement time
period. For this reason, there is a need for a retrofit solution that can
be added to traditional cabinets in place to enable them to provide the
necessary environmental control for the new upgraded electronic
equipment. The combination of a large filter and a high efficiency heat
exchanger that is mounted inside a shroud significantly reduces the
amount of maintenance, i.e., clogged filter changes required, as well as
allowing filter replacement to be done by lesser technical personnel as
they need not be qualified to access the electronic equipment. These and
other needs are met by the present invention, as hereinafter described.
SUMMARY OF THE INVENTION
 The present invention provides an environmental control kit for use
in electrical equipment cabinets containing heat-generating electrical
 In another aspect, the invention provides an electrical equipment
cabinet comprising an add-on environmental control system kit that has
been installed in the cabinet.
 More specifically, the environmental control kit includes an
air-to-air cross-flow heat exchanger that can be mounted on and supported
by the door of an electrical equipment cabinet, and which operates to
remove heat from the interior of the cabinet while maintaining the
substantially closed environment therein. The kit includes a replacement
door for the cabinet having the appropriate orifices drilled therein. For
practical purposes, the heat exchanger kit is assembled on the
replacement door prior to delivery to the field. The heat exchanger
defines a first air flow path for air drawn from the exterior of the
cabinet and a second air flow path for air drawn from the interior of the
cabinet. The first and second air flow paths are approximately
perpendicular to, and substantially isolated from, one another. A fan
element for each flow path is also mounted in an enclosed space created
between the door and the louvered shroud for circulating air through one
of the first and second air flow paths.
 In accordance with another aspect of the invention, the kit is
mounted on the exterior of the replacement door and has a shroud or
housing fit over the heat exchanger, thus creating an enclosed region
that extends outward from the former exterior of the door so that the
electronic equipment enclosure is separate from and does not need to be
accessed to access the heat exchanger enclosure.
 In accordance with one aspect of the invention, the fan element for
each flow path includes a pair of fans. In one embodiment, the fans may
be located adjacent to one another. In a highly preferred embodiment, a
baffle is located between the pair of fans for dividing the original flow
path into two parallel air flow paths that are substantially isolated
from one another.
 In accordance with another aspect of the invention, the cabinet
also includes upper and lower air flow plenums, which are mounted to an
interior surface of the door. The cross-flow heat exchanger element is
supported between the air flow plenums in a removably engagable manner.
 In accordance with yet another aspect of the invention, the
replacement door includes first and second external air vents conducting
external air through one of the air flow paths.
 As used herein, these terms have the following meanings.
 1. The term "kit" and "ready-to-mount kit" are synonymous and refer
to a heat exchanger, blower therefore, shroud therefore, a replacement
cabinet door, and all necessary accessory and mounting equipment to mount
the exchanger kit onto an outdoor telecommunications cabinet. The use of
the term "kit" does not necessarily mean that assembly of the exchanger
itself, or mounting of the exchanger onto the replacement door by the
customer is required.
 2. The term "core plenum" means a cover for the core.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a perspective view of an outdoor electrical cabinet
incorporating a door-mounted, air-to-air heat exchanger in accordance
with the present invention.
 FIG. 2 is a perspective view showing the heat exchanger door kit
with the hinged louvered shroud open, revealing enclosed space therein,
the core plenum and the external intake blower assembly.
 FIG. 3 shows the heat exchanger core plenum removed, revealing the
respective positions of the removable heat exchanger core, the internal
intake blower assembly, and the internal vent.
 FIG. 4 is a perspective view of the door and heat exchanger system
from the cabinet's interior.
 FIG. 5 is a perspective view of all basic parts and assemblies of
the heat exchanger, viewed from the cabinet's interior (door hidden).
These parts all bolt onto the exterior door surface to form a complete
heat exchanger system.
 FIG. 6 is a perspective view of the external blower assembly.
 FIG. 7 is a perspective view of the internal blower assembly.
 FIG. 8 is a perspective view of a cross-flow heat exchanger core.
DETAILED DESCRIPTION OF THE INVENTION
 FIG. 1 illustrates an outdoor electrical equipment cabinet 100
incorporating a door-mounted air-to-air heat exchanger kit, including a
louvered shroud and a replacement door for the cabinet in accordance with
the present invention. The cabinet has an original door, which is
replaced by replacement door 101. The heat exchanger is mounted to the
exterior of the replacement door 101; the kit further includes a hinged,
louvered shroud 102 mounted over the heat exchanger. The cabinet itself
contains a number of equipment racks or channel banks in an electronic
equipment enclosure (not shown), inside the cabinet. The shroud 102 has a
large louvered panel including louvers 103 visible from the exterior of
the cabinet. The large louvered panel efficiently draws in air from the
 FIG. 2 shows a perspective view of the door with the heat exchanger
kit installed, when the shroud is open. The hinged shroud 102 forms an
enclosed space in which an inner housing 202 is located. The louvered
shroud 102 includes inflow vents and outflow vents. The inner housing,
which contains heat exchanger 202, includes the heat exchanger core 203,
and external blower assembly 204. The hinged shroud 102 has large intake
and exhaust louvers 201, and holds an intake dust filter 205, which
filters the incoming air to prevent dust from contaminating and clogging
the core 203. The hinged shroud 102 permits the filter 205 to be accessed
and replaced without the need to open the door to the electronics
enclosure. This permits personnel who are not electronic equipment
specialists to service the filters. The blower assembly 204 has circular
intakes 206 oriented at about a 65.degree. angle to the intake wall 207
of the hinged louvered shroud 102, rather than being parallel. This
reduces direct exposure of the external blowers to windblown rain and
also hinders blower motor acoustic noise from escaping the shroud. This
noise reduction can be further enhanced by providing a sound and
vibration dampening film as a liner (not shown) on the shroud 102.
 The add-on heat exchanger, including replacement door 101 and
louvered shroud 102, is mounted so that the enclosed space of the
door/heat exchanger unit extends outward from the cabinet and is separate
and apart from the cabinet interior or enclosure, where the
electrical/electronic equipment is located. This arrangement maximizes
the space within the cabinet interior reserved for electrical equipment,
and as noted, is advantageous because the heat exchanger can be serviced
without accessing the cabinet interior.
 In FIG. 3, the core plenum has been removed, revealing the
removable heat exchanger core 301, the internal blower assembly 302 and
the internal grill 303. Use of two blowers with a separating baffle
provides operational redundancy.
 FIG. 4 is a view of the door and heat exchanger from the interior
of the door. The internal blower assembly 401 and the internal grill 402
are visible from within the electronic compartment, but they do not
protrude into the compartment, thus maximizing the room inside the
cabinet for electronic equipment.
 FIG. 5 shows all the interior parts and the subassemblies of the
heat exchanger. These parts are all typically pre-mounted onto the
replacement door's exterior surface to form a complete heat exchanger
assembly. Baffle 501 separates the flow paths of the two external blowers
502. Similarly, the interior flow baffle 503 separates the flow paths of
the two internal blowers. Having two internal blowers and two external
blowers in the kit provides operational redundancy so that if a single
blower, either external or internal, fails, the remaining blower
continues to operate, protecting the electronic equipment compartment
from a rapid increase in air temperature which could damage the sensitive
equipment and disrupt service to subscribers.
 FIG. 6 shows the external blower assembly 600. L-shaped foam blocks
601 help seal the blower paths when the assembly is mounted onto the
 FIG. 7 shows the internal blower assembly. The baffle 701 divides
the two blowers 702, the operation of which is controlled by the
controller card 703.
 FIG. 8 shows the construction of a bonded-aluminum single-pass
cross-flow heat exchanger core 800, which may be used in the present
invention. The core has finned channels 802 and 803 in arranged in
alternating perpendicular layers. Each layer includes a multiplicity of
channels. When mounted on the door, three layers form the internal
airflow path 802 and four layers form the external airflow path 803. The
extra layer for the external flow path results in less flow impedance.
This helps to offset the extra flow impedance of the external flow filter
and louvered shroud.
 The heat exchanger 202 is situated in the plenums so that the
inflow vents of the louvered shroud 102 are aligned with the inflow
openings of the horizontal channels 803 of the heat exchanger core 800.
Likewise, the outflow vents of the louvered shroud 102 are aligned with
the outflow openings of the horizontal channels 803 of the heat
exchanger. Accordingly, the horizontal channels are exposed to air
outside the sealed cabinet.
 In operation, air exterior to the cabinet 100 is drawn through the
intake vents 103 of the louvered shroud 102 so that external air flows
into the horizontal channels 803. The air exits the horizontal channels
803 and flows through output vents of the louvered shroud shell 102 to
exit the cabinet 100.
 Internal air, which contains heat generated by the electrical
equipment within the cabinet 100, is drawn into the intake openings of
the vertical channels 802 of the heat exchanger core 800. The internal
air is conducted through the vertical channels 802 and exits the heat
exchanger via the output openings of the vertical channels 802. In this
way the heat contained in the internal air is transferred to the outside
air flowing through the horizontal channels 803 of the heat exchanger
element 800 by the combination of forced convection and conductive heat
 From the foregoing description, it will be appreciated that a
continuous re-circulating flow of interior air is maintained through the
equipment located in the cabinet 100, and the vertical channels 802 of
the heat exchanger core 800. At the same time, a separate flow or circuit
of outside air is drawn in through the vents 103 of the louvered shroud
102, forced through the heat exchanger element 800 by means of the fans,
and then passes out of the cabinet 100 through the vents 103 in outer
louvered shroud 102. Since the internal and external flow circuits are
isolated from each other and do not mix, the environment within the
cabinet 100 remains sealed while heat is removed from the interior of the
cabinet by means of the heat exchanger element 800.
 To ensure that the outside circuit of air does not mix with the
internal circuit of air, the core plenum 202 may be provided with a
sealant that prevents leakage of air between the terminal ends of the
horizontal and vertical channels. The sealant, which may be a silicon
compound, for example, should be provided along the lines where the
plenums, heat exchanger element and panel 207 meet.
 The kit of the invention with its louvered shroud including a large
louvered panel and large filter combined with a high efficiency
cross-flow heat exchanger significantly reduces the number of maintenance
visits required to service the heat exchanger. This reduces costs for the
telecommunications providers who have huge numbers of such cabinets, and
allows the heat-exchanger maintenance to be provided by personnel not
qualified to access or service the complex electronic equipment inside
 If more environmental control is desired, the heat exchanger core
described herein may be replaced by a compressor driven heat pump having
an evaporator and a condenser.
 The preceding description of the present invention is merely
illustrative, and is not intended to be limiting. Therefore, the scope of
the present invention should be construed solely by reference to the
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