U.S. patent application number 16/454647 was filed with the patent office on 2020-12-31 for air handling unit with indirect air-side economizer and decoupled variable speed scavenger and condenser fan control.
The applicant listed for this patent is Munters Corporation. Invention is credited to Michael D. Herwald, Bradley J. Perdew.
Application Number | 20200413571 16/454647 |
Document ID | / |
Family ID | 1000005272744 |
Filed Date | 2020-12-31 |
United States Patent
Application |
20200413571 |
Kind Code |
A1 |
Perdew; Bradley J. ; et
al. |
December 31, 2020 |
AIR HANDLING UNIT WITH INDIRECT AIR-SIDE ECONOMIZER AND DECOUPLED
VARIABLE SPEED SCAVENGER AND CONDENSER FAN CONTROL
Abstract
A cooling system includes a housing containing indirect heat
exchange and active refrigeration sub-systems to provide cooled
process air to a space. The indirect heat exchange sub-system
includes a horizontal plate-type heat exchanger having scavenger
passages that are longer in one direction than process air passages
are in a transverse direction. One group of compressors and
associated condensers is located within the housing near a right
end wall and another group is located near a left end wall. Process
air fans are provided for directing process air from the space,
through the heat exchanger, and back into the space. Scavenger fans
direct scavenger air through the heat exchanger. At least two
condenser fans are provided, one at the top of the housing near the
right end wall and the other at the top of the housing near the
left end wall.
Inventors: |
Perdew; Bradley J.;
(Raphine, VA) ; Herwald; Michael D.; (Clifton
Forge, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Munters Corporation |
Selma |
TX |
US |
|
|
Family ID: |
1000005272744 |
Appl. No.: |
16/454647 |
Filed: |
June 27, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 2013/205 20130101;
H05K 7/20745 20130101; F24F 13/30 20130101 |
International
Class: |
H05K 7/20 20060101
H05K007/20; F24F 13/30 20060101 F24F013/30 |
Claims
1. A cooling system, including an indirect heat exchange sub-system
and an active refrigeration sub-system, for cooling process air and
providing the process air to a space, the system comprising: a
housing having front and back side walls facing one another in a
first direction, left and right end walls facing one another in a
second direction transverse to the first direction, and a bottom
and a top facing one another in a third direction transverse to the
first and second directions, the housing further including a
process air supply opening connecting with the space, a process air
return opening connecting with the space, a heat exchanger
scavenger air inlet opening, a heat exchanger scavenger air exhaust
opening, condenser air inlet openings, and condenser air exhaust
openings; a horizontal plate-type heat exchanger of the indirect
heat exchange sub-system provided in the housing, the horizontal
plate-type heat exchanger including stacked horizontal plates
separated by scavenger passages, the scavenger passages extending
in the first direction, the stacked horizontal plates defining
horizontal process air passages extending in the second direction,
the scavenger passages being longer in the first direction than the
process air passages are in the second direction; two groups of
compressors and associated condensers of the active refrigeration
sub-system, each of the two groups including at least one
compressor and at least one associated condenser, one of the two
groups being located within the housing near the right end wall and
the other of the groups being located within the housing near the
left end wall; at least one process air fan for directing the
process air from the process air return opening, through the
horizontal process air passages of the horizontal plate-type heat
exchanger, and then through the process air supply opening and into
the space; at least one heat exchanger scavenger fan for directing
scavenger air from ambient, through the scavenger passages of the
horizontal plate-type heat exchanger, and then back to ambient; and
two groups of condenser fans for directing condenser air from
ambient, through the condensers, and then back to ambient, each of
the two groups including at least one condenser fan, one of the two
groups of condenser fans being located at the top of the housing
near the right end wall and the other of the two groups of
condenser fans being located at the top of the housing near the
left end wall.
2. The cooling system according to claim 1, wherein the active
refrigeration sub-system further includes an evaporator, disposed
between the horizontal plate-type heat exchanger and the process
air supply opening.
3. The cooling system according to claim 1, wherein the at least
one compressor and the at least one associated condenser of each
group of the two groups of compressors and associated condensers of
the active refrigeration sub-assembly are disposed one above the
other.
4. The cooling system according to claim 1, wherein the condenser
fans are vertically aligned with at least a part of the process air
supply opening and the process air return opening,
respectively.
5. The cooling system according to claim 1, wherein a ratio of the
length of the scavenger passages in the first direction to the
length of the process air passages in the second direction defines
a heat exchanger aspect ratio, the heat exchanger aspect ratio
being greater than 1.0.
6. The cooling system according to claim 5, wherein the heat
exchanger aspect ratio is 1.5.
7. The cooling system according to claim 1, wherein each group of
the two groups of compressors and associated condensers of the
active refrigeration sub-system includes at least two
compressors.
8. The cooling system according to claim 1, wherein each group of
the two groups of condenser fans includes at least two condenser
fans.
9. A cooling system, including an indirect heat exchange sub-system
and an active refrigeration sub-system, for cooling process air and
providing the process air to a space, the system comprising: a
housing having front and back side walls facing one another in a
first direction, two end side walls facing one another in a second
direction transverse to the first direction, and a bottom and a top
facing one another in a third direction transverse to the first and
second directions, the housing further including a process air
supply opening connecting with the space, a process air return
opening connecting with the space, a heat exchanger scavenger air
inlet opening, a heat exchanger scavenger air exhaust opening,
condenser air inlet openings, and condenser air exhaust openings; a
horizontal plate-type heat exchanger of the indirect heat exchange
sub-system provided in the housing; two groups of compressors and
associated condensers of the active refrigeration sub-system, each
of the two groups including at least one compressor and at least
one associated condenser, one of the two groups being located
within the housing near one of the end side walls and the other of
the two groups being located within the housing near the other of
the end side walls; and two groups of condenser fans for directing
condenser air from ambient, through the condensers, and then back
to ambient, each of the two groups including at least one condenser
fan, one of the two groups of condenser fans being located at the
top of the housing near the one side end wall and vertically
aligned with at least a part of the process air supply opening, and
the other of the two groups of condenser fans being located at the
top of the housing near the other end side wall and vertically
aligned with at least a part of the process air return opening.
10. The cooling system according to claim 9, wherein the active
refrigeration sub-system further includes an evaporator, disposed
between the horizontal plate-type heat exchanger and the process
air supply opening.
11. The cooling system according to claim 9, wherein the at least
one compressor and the at least one condenser of each group of the
two groups of compressors and associated condensers of the active
refrigeration sub-system are disposed one above the other.
12. The cooling system according to claim 9, wherein a ratio of the
length of the horizontal plate-type heat exchanger in the first
direction to the width of the heat exchanger in the second
direction defines a heat exchanger aspect ratio, the heat exchanger
aspect ratio being greater than 1.0.
13. The cooling system according to claim 12, wherein the heat
exchanger aspect ratio is 1.5.
14. The cooling system according to claim 9, wherein each group of
the two groups of compressors and associated condensers of the
active refrigeration sub-system includes at least two
compressors.
15. The cooling system according to claim 9, wherein each group of
the two groups of condenser fans includes at least two condenser
fans.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] This disclosure is directed to systems and methods for
removing heat from recirculated air from an enclosed space,
particularly from a data center, in an efficient and effective
manner. Data centers include data servers and other equipment,
which draw significant amounts of power and generate significant
amounts of heat. Data center heat rejection, particularly in an
economical manner, has become an increasing challenge.
2. Description of the Related Art
[0002] Computer servers historically were cooled by refrigeration
air-conditioning and the supply air was delivered into the data
centers by all available means, including through raised flooring,
to individually cool each computer server. More recently, data
center cooling technology introduced construction of specific air
pathways with segregated, enclosed cold air supply aisles ("cold
aisles") and separate hot air return aisles ("hot aisles") within
data centers in an attempt to keep from commingling cold air with
hot air in an open space. Such construction aids in providing
necessary cooling capacity more economically and reduces the
potential for server hot spots. The industry also determined that
warmer server inlet conditions for Class I and II data centers was
acceptable. That, combined with advances in hot and cold aisle
containment systems and designs, permits data center cooling units
to deliver warmer air to cool the servers than previously thought
possible. In 2008, an expanded envelope for air conditions entering
the servers in data centers was approved, bringing the maximum
recommended server inlet temperature up to 80.6.degree. F. The
above change in recommended inlet air temperature for the data
servers caused engineers to seek new energy efficient solutions to
manage the thermal loads in the data centers.
[0003] In a typical indirect air-side economizer (IASE)
installation, outside (scavenger) air (0/A) enters the IASE through
an inlet and flows through one side of an air-to-air heat
exchanger. Warm return air (R/A) from the environment which the
IASE supports such as, for example, a data center, and specifically
the return air from a hot aisle, enters the IASE from another inlet
and flows separately through an opposite side of the air-to-air
heat exchanger. The scavenger air flow and the return air flow are
completely separated from one another by one of a number of
different methodologies. These methodologies may include sealed
heat exchanger plates and/or sealed heat exchanger tubing, or
separating partitions in the case of heat pipe type heat
exchangers. As the return air flows through a plate-type air-to-air
heat exchanger, it transfers its heat to the cooler scavenger air
through the plate surface that completely separates and segregates
the two airstreams. The outside scavenger air may be used at its
ambient temperature, or may be otherwise evaporatively cooled,
either prior to entering the air-to-air heat exchanger or by direct
spray of water onto the surfaces of the heat exchanger. Use of
evaporative pre-cooling may enhance the heat rejection potential,
particularly in instances where the outside air has a Wet-Bulb
Depression (WBD), which is a difference between the dry-bulb and
wet bulb temperature, of 10.degree. F. or more. A water-side
economizer coil, piped to an external cooling tower, may be
installed, for example, upstream of the direct evaporative cooler,
providing additional cooling for the scavenger air and associated
heat rejection. As another option, the IASE can be supplemented by
a separate refrigeration system, such as a direct expansion (DX)
refrigeration system. The evaporator of the DX system can be placed
in the process air stream to either further cool the process air or
be the sole source for cooling when ambient conditions render the
IASE ineffective.
SUMMARY OF THE INVENTION
[0004] According to one aspect, the present invention is directed
to a cooling system, including an indirect heat exchange sub-system
and an active refrigeration sub-system, for cooling process air and
providing the process air to a space. The cooling system includes a
housing, a horizontal plate-type heat exchanger of the indirect
heat exchange sub-system, two groups of compressors and associated
condensers of the active refrigeration sub-system, at least one
process air fan, at least one heat exchanger scavenger fan, and two
groups of condenser fans. The housing has front and back side walls
facing one another in a first direction, left and right end walls
facing one another in a second direction transverse to the first
direction, and a bottom and a top facing one another in a third
direction transverse to the first and second directions. The
housing further includes a process air supply opening connecting
with the space, a process air return opening connecting with the
space, a heat exchanger scavenger air inlet opening, a heat
exchanger scavenger air exhaust opening, condenser air inlet
openings, and condenser air exhaust openings. The horizontal
plate-type heat exchanger is provided in the housing and includes
stacked horizontal plates separated by scavenger passages, the
scavenger passages extending in the first direction, the horizontal
plates defining horizontal process air passages extending in the
second direction, and the scavenger passages being longer in the
first direction than the process air passages are in the second
direction. Each of the two groups of compressors and associated
condensers includes at least one compressor and at least one
associated condenser, one of the groups being located within the
housing near the right end wall and the other of the groups being
located within the housing near the left end wall. The at least one
process air fan directs the process air from the process air return
opening, through the process air passages of the heat exchanger,
and then through the process air supply opening and into the space.
The at least one heat exchanger scavenger fan directs the scavenger
air from ambient, through the scavenger passages of the heat
exchanger, and then back to ambient. The two groups of condenser
fans direct condenser air from ambient, through the condensers, and
then back to ambient, each of the groups including at least one
condenser fan, one of the two groups of condenser fans being
located at the top of the housing near the right end wall, and the
other of the two groups of condenser fans being located at the top
of the housing near the left end wall.
[0005] According to another aspect, the present invention is
directed to a cooling system, including an indirect heat exchange
sub-system and an active refrigeration sub-system, for cooling
process air and providing the process air to a space, and which
includes a housing, a horizontal plate-type heat exchanger of the
indirect heat exchange sub-system provided in the housing, two
groups of compressors and associated condensers of the active
refrigeration sub-system, and two groups of condenser fans. The
housing has front and back side walls facing one another in a first
direction, two end side walls facing one another in a second
direction transverse to the first direction, and a bottom and a top
facing one another in a third direction transverse to the first and
second directions. The housing further includes a process air
supply opening connecting with the space, a process air return
opening connecting with the space, a heat exchanger scavenger air
inlet opening, a heat exchanger scavenger air exhaust opening,
condenser air inlet openings, and condenser air exhaust openings.
Each of the two groups of compressors and associated condensers
includes at least one compressor and at least one associated
condenser, one of the groups being located within the housing near
one of the end side walls and the other of the groups being located
within the housing near the other of the end side walls. The two
groups of condenser fans directing condenser air from ambient,
through the condensers, and then back to ambient, and each of the
groups includes at least one condenser fan. One of the two groups
of condenser fans is located at the top of the housing near the one
side end wall and vertically aligned with at least a part of the
process air supply opening, and the other of the two groups of
condenser fans is located at the top of the housing near the other
end side wall and vertically aligned with at least a part of the
process air return opening.
[0006] The systems and methods according to this disclosure provide
an improved and more efficient indirect air-side economizer (IASE)
that includes at least one air-to-air heat exchanger. The preferred
embodiments provide a decreased footprint for the system as
compared to prior comparable systems, which is particularly
beneficial in rooftop applications. Despite the smaller size, the
system of the present invention also provides more efficient and
economical operation.
[0007] These and other aspects and advantages will become apparent
when the description below is read in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an elevation view of an air handling unit
according to one aspect of the present invention.
[0009] FIG. 2 is a plan view of the air handling unit according to
one aspect of the present invention.
[0010] FIG. 3 is an enlarged perspective view of cross-flow heat
exchanger in the air handling unit according to one aspect of the
present invention.
[0011] FIG. 4 is a chart showing the relationship between heat
exchanger aspect ratio and the power consumed by the combination of
supply (process) fans and scavenger fans operating at the maximum
ambient dry bulb temperature of which the heat exchanger can reject
100% of data center heat exclusive of any refrigeration
cooling.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] 1. Overall System Configuration
[0013] The overall system configuration of the present invention
will now be described with reference to FIGS. 1 and 2. The
different depicted air flows will be referred to as: (1) supply air
(S/A), which is the cooled air output from the IASE to the cold
aisles of the data center; (2) return air (R/A), which is the air
returned to the IASE from the hot aisles in the data center; (3)
outside (scavenger) air (0/A), which is the air input to the IASE
from outside to the air-to-air heat exchanger in the IASE or air
passed from the outside through the condenser coils; and (4)
exhaust air (E/A), which is the air forcibly exhausted from the
IASE as the 0/A has passed through the air-to-air heat exchanger
for heat extraction or the air forcibly exhausted from the
condensers. FIGS. 1 and 2 respectively illustrate elevation and
plan views of an exemplary overall data center cooling system
according to this disclosure.
[0014] As shown in FIG. 1, a cooling system 100 for removing heat
from a data center 200 includes several components, including, for
example, an IASE and a DX refrigeration system as well as
associated controls and ductwork to control the flow of supply air
S/A to the cold aisles in the data center 200 to support cooling
and, optionally, particulate removal of room generated
contaminants. In a preferred embodiment, cooled supply air S/A from
cooling system 100 is provided through supply opening 102 to cold
aisles 202 of the data center 200 and is forced through the data
servers 204 where the cooled supply air S/A absorbs heat and exits
the data servers into hot aisles 206 as return air R/A. The return
air R/A is then passed through the hot aisles back to the cooling
system 100 including the IASE through a plenum or duct system 208.
The return air R/A enters the cooling system 100 through a return
opening 104 that may include a damper 105 for controlling flow of
the return air R/A to the cooling system 100 and/or for isolating
the system during maintenance. Supply opening 102 may also include
a damper 103 for controlling flow of the supply air S/A from the
cooling system 100 and/or for isolating the system during
maintenance.
[0015] 2. Structural Details of the Cooling System 100
[0016] The main components of cooling system 100 are enclosed in a
housing 110. Housing 110 includes vertical end walls 112, 114,
vertical front and back side walls 116, 118, a horizontal ceiling
wall 120, and a horizontal floor 121, all of which define an
interior space. Within the interior space are arranged additional
structural members including a vertical fan support wall 122, a
vertical evaporator support wall 124, and compressor housings 126
and condenser housings 128 provided at opposite ends. Only the left
end compressor housing 126 is shown in FIG. 1, but a second
compressor housing 126 is positioned at a corresponding location at
the right side.
[0017] Housing 110 encloses a crossflow air-to-air heat exchanger
130 as well as the components of an auxiliary and/or backup cooling
system, such as a DX refrigeration system, including condensers
132, evaporators 134, and compressors 136 (only shown at the left
end of the housing). Several fans are provided to move the process
air, outside scavenger air for heat exchanger 130, and outside
cooling air for condensers 132. One or more variable volume plenum
fans 140 (two columns of four fans each shown in the figures),
preferably driven by direct drive motors, are mounted on fan
support wall 122 upstream of heat exchanger 130. A return air
filter bank 141 is mounted adjacent to evaporator support wall 124,
preferably upstream of evaporator 134. Plenum fans 140 pull air
from server room 200 through return opening 104 and direct the air
through heat exchanger 130 and evaporator 134, thereby cooling the
air, and then direct the cooled air back to the server room though
supply opening 102.
[0018] Heat exchanger 130 can be of several designs, but is
preferably of a crossflow horizontal plate type. In this system,
the process air is directed horizontally across plural horizontal
plates stacked vertically and separated by scavenger passages,
which define process air passages. The scavenger air is directed
horizontally through the scavenger passages in a direction
perpendicular to the process air flow direction. This enables
efficient heat transfer between the process and scavenger air flows
via the horizontal plates. The design of heat exchanger 130 is
important in maximizing cooling efficiency as well as reducing the
footprint of the system, as will be described later in more
detail.
[0019] One or more variable volume heat exchanger scavenger fans
142 (three shown in the figures) are provided on ceiling wall 120
and pull outside air through scavenger inlet 144 provided in front
side wall 116, horizontally through heat exchanger 130 and into a
chamber adjacent the heat exchanger 130 and below the heat
exchanger scavenger fans 142, and then vertically up through the
fans to outside. Heat exchanger scavenger fans 142 are preferably
axial fans with direct drive motors. Scavenger inlet 144 is
preferably provided with louvers and a bird screen, as well as a
filter or filter bank 146.
[0020] Each condenser 132 is cooled by a group of one or more axial
condenser fans 150, also disposed on the ceiling wall 120. The
condenser fans 150 are provided separate from the heat exchanger
scavenger fans 142, so that: a) the condensers are cooled by
outdoor air that has not been negatively impacted by heat absorbed
from the warm return air, and b) the fans are not required to
overcome the static pressure resulting from flow through the
condenser coils. That is, each condenser is provided with at least
one dedicated fan distinct from the scavenger fans. As a result,
when ambient conditions are such that heat exchanger 130 will
provide no benefit (e.g., at peak ambient temperatures), the heat
exchanger scavenger fans 142 are shut down and, although the DX
system is operating, the condenser fans 150 need draw air only
through the condensers 132 and not through the heat exchanger 130,
thus providing energy savings. Similarly, when the ambient
conditions are such that the heat is rejected by a combination of
passive rejection via the air-to-air heat exchangers and the DX
system, the condenser air remains equal to ambient air, not having
first absorbed heat from the air-to-air heat exchanger, allowing
the DX system to operate more efficiently. Each group of condenser
fans 150 draws outside air through opening 152, past the condenser
coils to draw heat therefrom, and then out through the fan
opening.
[0021] Condenser housings 128 contain the condensers 132 and define
the pathway for the air drawn by condenser fans 150. Preferably,
two condenser housings are arranged near the ceiling wall and at
each end wall 112, 114, such that the condenser chamber is at an
upper end corner of housing 110. Such an arrangement minimizes the
footprint of the cooling unit 100, yet allows an extended
condensing surface area. In a preferred arrangement, as shown in
FIG. 1, the condenser housings 128 have an angled interior wall
that angles inwardly upward, such that it is narrower at its bottom
end than at its top end. As arranged, housings 128 allow condenser
fans 150 to be located above supply and return openings 102, 104.
Compressor housings 126 are disposed below condenser housings 128
such that each compressor 136 is preferably disposed adjacent to,
and in relatively close proximity to, its corresponding condenser
132. In the preferred arrangement, the bottom end of each condenser
housing 128 is joined with, shares a common wall with, or rests on
the top end of the corresponding compressor housing 126. The
locations of the compressors 136 is not limited; they can be
disposed at any location within housing 110 as long as such does
not interfere with any other component or airflow and does not
increase the footprint of the housing 110. These alternative
locations include on the horizontal floor 121 beneath heat
exchanger scavenger fans 142 or any suitable location between side
walls 112, 114.
[0022] As noted above, heat exchanger 130 is preferably of a
crossflow horizontal plate type, in which the process air is
directed horizontally across plural horizontal plates stacked
vertically and separated by scavenger passages and the scavenger
air is also directed horizontally through the scavenger passages in
a direction perpendicular to the process air flow direction.
Applicant discovered that the aspect ratio of the heat exchanger
has a significant impact on cooling efficiency and energy use, and
can minimize the footprint of the system. Generally speaking,
making the scavenger passages longer than the process air passages
provides improved efficiency and enables the system to be shortened
in the longitudinal direction of supply airflow.
[0023] Referring to FIG. 3, heat exchanger 130 is defined by a
length L in the X direction, a width W in the Y direction, and a
height H in the Z direction. The process air is directed through
the heat exchanger 130 in the longitudinal X direction and the
scavenger air is directed through the heat exchanger in the
perpendicular Y direction. Applicant has found that making the
scavenger passages longer than the process air passages improves
energy efficiency and allows to accommodate components of the DX
system within a smaller footprint. Applicant further discovered
that an aspect ratio (W/L, i.e., ratio of scavenger passage length
to process air length) of 1.5 uses the lowest total fan energy.
Various models were made and several tests were performed in order
to come to that conclusion. The results of the testing are shown in
Table 1 below.
TABLE-US-00001 TABLE 1 Plate HX Properties Heat Exchanger HX Supply
HX Scavenger Total Aspect Plate Plate HX Supply Supply Fan kW
Scavenger Scavenger Fan kW fan kW HX Ratio L W H Spacing Area
Supply Airflow APD due to Airflow APD due to due to Option (W/L)
(in) (in) (in) (in) (100 SF) Eff (SCFM) (in WG) HX (SCFM) (in WG)
HX HX A 1.0 94.5 94.5 141.5 0.472 186 46.0% 60000 1.76 20.7 34600
0.58 4.7 25.4 B 1.5 78.7 118.1 136.0 0.472 186 46.0% 60000 0.80 9.4
36000 0.90 7.6 17.0 C 2.0 66.9 133.9 141.1 0.472 186 46.0% 60000
0.58 6.8 37000 1.64 14.2 21.1
[0024] Two heat exchangers according to the present invention and a
comparative heat exchanger were constructed and tested. The
comparative heat exchanger had a square aspect ratio (W/L) of 1.0
and is identified as HX Option (or Example) A in Table 1, whereas
the heat exchangers of the present invention had aspect ratios of
1.5 and 2.0 and are identified as HX Options B and C, respectively,
in the Table. The collective surface area of the plates in each
design was substantially equal (approximately 18,600 sq. ft.).
[0025] In testing the designs, the supply airflow was the same in
each design (60,000 SCFM). However, because the pressure drop
increases with an increase in process air length, the supply
pressure drop was highest in Comparative Example A, was
significantly less in Invention Example B, and was lowest in
Invention Example C. This resulted in energy use by the supply fans
(plenum fans 140) being highest in Example A and lowest in Example
C.
[0026] On the other hand, the scavenger airflow differed in each
Example to keep the heat exchanger efficiency substantially equal
in each Example (e.g., 46.0%). One measure of heat exchanger
efficiency is the ratio of 1) the difference between return air and
supply air temperatures to 2) the difference in return air and
ambient (outdoor) air temperatures. Further, due to the increasing
length of the scavenger passages from Example A to Example C, the
pressure drop correspondingly increased from Example A to Example
C. As a result, the energy use by the scavenger fans was lowest in
Example A and highest in Example C. However, the total energy used
by the supply and scavenger fans in the various Examples was
highest in Example A (1.0 aspect ratio), somewhat lower in Example
C (2.0), and much lower in Example B (1.5). Accordingly, Example B
with an aspect ratio of 1.5 had the best energy efficiency.
[0027] As mentioned above, as the aspect ratio of the heat
exchanger 130 increases while keeping the effective surface area
substantially the same, the length L in the X direction
correspondingly decreases. That is, the higher the aspect ratio,
the shorter the length L. By increasing the aspect ratio, the
overall size of the housing 110 can be reduced, thus reducing the
overall footprint. In addition, the shorter heat exchanger 130
provides more room for components of the DX unit at both ends of
the housing without extending the length of the housing in the X
direction, as further explained below.
[0028] In order to provide sufficient cooling by the DX sub-system,
either alone or as a supplement to the heat exchanger 130, it is
preferred to use two or more pairs of associated compressors 136
and condensers 132. Placing both pairs at one end of the housing
110, however, would increase the size of the unit at that end.
Applicant has found that by locating one compressor/condenser pair
at each end of the housing minimizes the space required at each end
while still allowing the compressor to be positioned close to its
associated condenser. For example, by extending the housing in the
X direction beyond the supply and return openings 102, 104 just
long enough to accommodate compressors 136 and their isolating
housings will keep the housing length to its minimum required
dimension. This arrangement also allows the design to use otherwise
unused space above the supply and return openings 102, 104 so that
the condensers 138 can be located close to their associated
compressors 136 and not require any additional lengthening of the
housing. To this end, condenser housings 128, which isolate the
condenser scavenger airflow from the process air, are positioned
above the respective compressors and supply or return openings 102,
104. In a preferred embodiment, each condenser fan 150 is provided
in at least partial vertical alignment with either the supply
opening 102 or the return opening 104.
[0029] While the preferred design provides a minimal footprint,
particularly suitable for rooftop applications, efficiencies in
operation are also realized. Because the scavenger fans are
independent from the DX sub-system and can be shut down at higher
ambient conditions when the heat exchanger provides no benefit,
peak power savings are realized. Under lower ambient conditions,
the DX sub-system can be shut down and the scavenger flow can be
reduced as required for control of the process leaving air
temperature. For example, with the scavenger flow set at one-half
the process air flow at an ambient temperature of 43.degree. F.,
return air at 101.degree. F. can be lowered to 77.degree. F. supply
air.
[0030] Thus, there has been shown and described a new and useful
indirect air-side economizer system that can operate with or
without the use of water in the cooling process. Although this
invention has been exemplified for purposes of illustration and
description by reference to certain specific embodiments, it will
be apparent to those skilled in the art that various modifications,
alterations, and equivalents of the illustrated examples are
possible.
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