Note: Descriptions are shown in the official language in which they were submitted.
CA 02824726 2013-08-22
DEDICATED OUTDOOR AIR SYSTEM WITH PRE-HEATING AND METHOD
FOR SAME
BACKGROUND OF THE INVENTION
[0001] Embodiments
generally relate to a system and method for pre-heating a
dedicated outdoor air system (DOAS), and more particularly, to a high
efficiency DOAS,
gas heat exchanger or heater, and the like.
[0002]
Enclosed structures, such as occupied buildings, factories and animal
barns, and the like generally include an HVAC system for conditioning
ventilated and/or
recirculated air in the structure. The HVAC system includes a supply air flow
path and a
return and/or exhaust air flow path. The supply air flow path receives air,
for example
outside or ambient air, re-circulated air, or outside or ambient air mixed
with re-circulated
air, and channels and distributes the air into the enclosed structure. The air
is conditioned
by the HVAC system to provide a desired temperature and humidity of supply air
discharged into the enclosed structure. The exhaust air flow path discharges
air back to
the environment outside the structure, or ambient air conditions outside the
structure.
Without energy recovery, conditioning the supply air typically requires a
significant
amount of auxiliary energy. This is especially true in environments having
extreme
outside air conditions that are much different than the required supply air
temperature and
humidity. Accordingly, energy exchange or recovery systems are typically used
to
recover energy from the exhaust air flow path. Energy recovered from air in
the exhaust
flow path is utilized to reduce the energy required to condition the supply
air.
[0003]
Conventional energy exchange systems may utilize energy recovery
devices (for example, energy wheels and permeable plate exchangers) or heat
exchange
devices (for example, heat wheels, plate exchangers, heat-pipe exchangers and
run-around
heat exchangers) positioned in both the supply air flow path and the exhaust
air flow path.
A Dedicated Outdoor Air System (DOAS) conditions ambient/outside air to
desired
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supply air conditions through a combination of heating, cooling,
dehumidification, and/or
humidification. In extremely cold conditions, however, frost may form on one
or more
energy recovery devices within a DOAS. For example, in extremely cold
conditions, frost
may form on an enthalpy wheel that first encounters outside air within the
DOAS.
Additionally, when a gas heater is added to a typical DOAS, the gas heater may
only be
80% efficient. As such, there is a desire and need to increase the efficiency
of such a
system.
SUMMARY OF THE INVENTION
[0004]
Certain embodiments of the present disclosure provide an energy
exchange system that may include an energy recovery device configured to be
disposed
within supply and exhaust air flow paths, a heater configured to be disposed
within the
supply air flow path, wherein the heater is configured to generate flue gas,
at least one
pre-heater configured to be upstream from the energy recovery device within
one or both
of the supply and exhaust air flow paths, and a heat transfer device
operatively connected
to the heater and the at least one pre-heater. The heat transfer device is
configured to
receive energy from the flue gas from the heater and transfer heat from the
flue gas to
liquid within the heat transfer device. The liquid is configured to be
channeled to the pre-
heater(s) so that heat is transferred from the liquid to supply air within the
supply air flow
path before the supply air encounters the energy recovery device.
[0005] The system
may also include pipes, tubes, conduits, or plenum
connected between the heat transfer device and the heater. The flue gas is
configured to
pass from the heater to the heat transfer device via the one or more of pipes,
tubes,
conduits, or plenum.
[0006]
The energy exchange system may be a Dedicated Outdoor Air System
(DOAS). The energy recovery device may be one or more of an enthalpy wheel, a
sensible wheel, a desiccant wheel, a plate heat exchanger, a plate energy
exchanger, a heat
pipe, or a run-around loop.
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[0007]
The system may also include a heat exchanger that includes the heater
and at least one radiator coil configured to contain a heat transfer liquid.
The radiator
coil(s) may be configured to be disposed within or around a portion of the
supply air flow
path. The heat exchanger may be a liquid-to-gas heat exchanger. The heat
exchanger
may include one or more of a parallel flow heat exchanger, a counter flow heat
exchanger,
or a cross flow heat exchanger.
[0008]
The pre-heater(s) may include a liquid-circulating coil in fluid
communication with the heat transfer device. The liquid-circulating coil may
be
configured to be disposed within or around a portion of the supply air flow
path.
[0009] The system
may also include a liquid-circulating coil configured to be
disposed within or around a flue gas passage. The liquid-circulating coil is
configured to
receive vented flue gas from the heater. The liquid-circulating coil is
configured to be in
fluid communication with the pre-heater.
[0010]
The heater may be configured to be downstream from the energy
recovery device within the supply air flow path. The heater may be configured
to be
upstream from the energy recovery device within the supply air flow path.
[0011]
The system may also include at least one additional heat exchanger
operatively connected to the heat transfer device.
[0012]
The system may also include at least one return air duct configured to
fluidly connect the supply air flow path with the exhaust air flow path.
[0013]
The heat transfer device may be remote from the heater and the pre-
heater. Optionally, the heat transfer device and the heater may be disposed
within a
common housing.
[0014]
The system may include at least one bypass duct configured to be
disposed within the supply air flow path. The at least one bypass duct may be
configured
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to bypass at least a portion of the supply air around one or both of the pre-
heater or the
energy recovery device.
[0015] Certain embodiments of the present disclosure provide a
method of
operating a Dedicated Outdoor Air System having a supply air flow path that
allows
supply air to be supplied to an enclosed structure and an exhaust air flow
path that allows
exhaust air from the enclosed structure to be exhausted to the atmosphere. The
method
may include capturing flue gas generated by a heater, channeling the flue gas
to a heat
transfer device, transferring heat from the flue gas to liquid within the heat
transfer device,
circulating the liquid to a pre-heater, and transferring heat within the
liquid to supply air
within the supply air flow path.
[0016] The method may also include venting the flue gas from the
heat
transfer device after heat from the flue gas has been transferred to the
liquid within the
heat transfer device. The method may also include recirculating the liquid
back to the
heat transfer device after the heat within the liquid has been transferred to
the supply air.
The method may also include passing the heated supply air to an energy
recovery device
after the heat within the liquid has been transferred to the supply air. The
method may
also include preventing frost from forming on the energy recovery device
through the
channeling operation. The method may also include bypassing at least a portion
of the
supply air around one or both of the pre-heater or an energy recovery device.
[0017] Certain embodiments of the present disclosure provide a Dedicated
Outdoor Air System (DOAS) that may include a heater configured to be disposed
within a
supply air flow path, a pre-heater configured to be upstream from the heater
within the
supply air flow path, and a heat transfer device operatively connected to the
heater and the
pre-heater. The heat transfer device is configured to receive flue gas from
the heater and
transfer heat from the flue gas to liquid within the heat transfer device. The
liquid is
configured to be channeled to the pre-heater so that heat is transferred from
the liquid to
supply air within the supply air flow path.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 illustrates a schematic view of an energy
exchange system,
according to an embodiment.
[0019] Figure 2 illustrates a schematic view of the energy
recovery device,
according to an embodiment.
[0020] Figure 3a illustrates a schematic view of a heat
exchanger, according to
an embodiment.
[0021] Figure 3b illustrates an isometric top view of an
exemplary furnace,
according to an embodiment.
[0022] Figure 4 illustrates an isometric view of a radiator coil of a heat
exchanger, according to an embodiment.
[0023] Figure 5 illustrates an isometric view of a radiator coil
of a heat
exchanger, according to an embodiment.
[0024] Figure 6 illustrates an isometric view of a radiator coil
of a heat
exchanger, according to an embodiment.
[0025] Figure 7 illustrates an isometric view of a radiator coil
of a heat
exchanger, according to an embodiment.
[0026] Figure 8 illustrates a schematic view of an energy
recovery system,
according to an embodiment.
[0027] Figure 9 illustrates a schematic view of an energy recovery system,
according to an embodiment.
[0028] Figure 10 illustrates a schematic view of an energy
recovery system,
according to an embodiment.
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[0029]
Figure 11 illustrates a process of operating a direct outdoor air system,
according to an embodiment.
DETAILED DESCRIPTION OF THE DRAWINGS
[0030]
The foregoing summary, as well as the following detailed description
of certain embodiments will be better understood when read in conjunction with
the
appended drawings. As used herein, an element or step recited in the singular
and
proceeded with the word "a" or "an" should be understood as not excluding
plural of said
elements or steps, unless such exclusion is explicitly stated. Furthermore,
references to
"one embodiment" are not intended to be interpreted as excluding the existence
of
additional embodiments that also incorporate the recited features. Moreover,
unless
explicitly stated to the contrary, embodiments "comprising" or "having" an
element or a
plurality of elements having a particular property may include additional such
elements
not having that property.
[0031]
Figure 1 illustrates a schematic view of an energy exchange system 100
according to an embodiment. The system 100 is shown as a Dedicated Outdoor Air
System (DOAS). The system 100 is configured to partly or fully condition air
supplied to
an enclosed structure 102, such as a building or an enclosed room. The system
100
includes an air inlet 104 fluidly connected to a supply air flow path 106. The
supply air
flow path 106 may channel supply air 108 (such as outside air, air from a
building
adjacent to the enclosed structure 102, or return air from a room within the
enclosed
structure 102) to the enclosed structure 102. Supply air 108 in the supply air
flow path
106 may be moved through the supply air flow path 106 by a fan or fan array
110. The
illustrated embodiment shows the fan 110 located downstream of an energy
recovery
device 112 and a gas-fired heater or heat exchanger 114. The heat exchanger
114 may be
or include the gas-fired heater. Optionally, the fan 110 may be positioned
upstream of the
energy recovery device 112 and/or the heat exchanger 114. Also, alternatively,
air 108
within the supply air flow path 106 may be moved by multiple fans or a fan
array or
before and/or after the heat exchanger 114.
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[0032]
Airflow passes from the inlet 104 through the supply air flow path 106
where the supply air 108 first encounters a pre-heater 116. A bypass duct 117
may be
disposed in the supply air flow path 106. The bypass duct 117 may be connected
to the
supply air flow path 106 through an inlet damper 119 upstream from the pre-
heater 116,
and an outlet damper 121 downstream from the pre-heater 116. When the dampers
119
and 121 are fully opened, supply air 108 may be diverted or bypassed around
the pre-
heater 116. The dampers 117 and 121 may be modulated to allow a portion of the
supply
air 108 to bypass around the pre-heater 116.
[0033]
Additionally, a damper 123 may be disposed in the supply air flow path
106 upstream from the pre-heater 116. When fully closed, the damper 123
prevents
supply air 108 from passing into the pre-heater 116. The damper 123 may be
modulated
in order to allow a portion of the supply air 108 to a portion of the supply
air 108 to pass
through the pre-heater 116, while a remaining portion of the supply air 108 is
bypassed
through the bypass duct 117.
[0034] The pre-
heater 116 heats the air 108 is it passes therethrough. The pre-
heater 116 heats the incoming supply air 108 before it encounters a process
side or portion
of the energy recovery device 112. An additional pre-heater may be disposed
within the
supply air flow path 106 downstream from the pre-heater 116 and upstream from
the
energy recovery device 112. The additional pre-heater is configured to add
more heat to
the supply air 108 during extremely cold conditions. The pre-heater 116 may,
alternatively, be disposed within the exhaust air flow path 120 upstream from
the energy
recovery device 120. Additionally, alternatively, a pre-heater may be disposed
within the
exhaust air flow path 120 upstream from the energy recovery device as well as
the pre-
heater 116 within the supply air flow path 106. As explained in more detail
below with
respect to Figure 2, the energy recovery device 112 uses exhaust air 118 from
an exhaust
flow path 120 to condition the supply air 108 within the supply air flow path
106. For
example, during a winter mode operation, the energy recovery device 112 may
condition
the supply air 108 within the supply air flow path 106 by adding heat and/or
moisture. In
a summer mode operation, the energy recovery device 112 may pre-condition the
air 108
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by removing heat and moisture from the air. An additional energy recovery
device (not
shown) may be positioned within the supply air flow path 106 downstream from
the heat
exchanger 114, and upstream from the enclosed structure 102. Additionally,
while the
energy recovery device 112 is shown upstream from the heat exchanger 114
within the
supply air flow path 106, the energy recovery device 112 may, alternatively,
be positioned
downstream of the heat exchanger 114 and upstream of the enclosed structure
102 within
the supply air flow path 106.
[0035]
After the supply air 108 passes through the energy recovery device 112
in the supply air flow path 106, the supply air 108, which at this point has
been
conditioned, encounters the heat exchanger 114. The heat exchanger 114 then
further or
fully heats the air 108 in the supply air flow path 106 to generate a change
in air
temperature toward a desired supply state that is desired for supply air
discharged into the
enclosed structure 102. For example, during a winter mode operation, the heat
exchanger
114 may further condition the pre-conditioned air by adding heat to the supply
air 108 in
the supply air flow path 106.
[0036]
The exhaust or return air 118 from the enclosed structure 102 is
channeled out of the enclosed structure 102, such as by way of exhaust fan 122
or fan
array within the exhaust flow path 120. As shown, the exhaust fan 122 is
located
upstream of the energy recovery device 112 within the exhaust air flow path
120.
However, the exhaust fan 122 may be downstream of the energy recovery device
112
within the exhaust air flow path 120.
[0037]
The exhaust air 118 passes through a regeneration side or portion of
the energy recovery device 112. The energy recovery device 112 is regenerated
by the
exhaust air 118 before conditioning the supply air 108 within the supply air
flow path 106.
After passing through the energy recovery device 112, the exhaust air 118 is
vented to
atmosphere through an air outlet 124.
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CA 02824726 2013-08-22
[0038]
In an alternative embodiment, additional bypass ducts and dampers
may be disposed within the supply air flow path 106 and/or the exhaust air
flow path 120
in order to bypass airflow around the energy recovery device 112.
[0039]
Figure 2 illustrates a schematic view of the energy recovery device 112,
according to an embodiment. A portion of the energy recovery device 112 is
disposed
within the supply air flow path 106, while another portion of the energy
recovery device
112 is disposed within the exhaust air flow path 120. The energy recovery
device 112 is
configured to transfer heat and/or moisture between the supply air flow path
106 and the
exhaust air flow path 120. The energy recovery device 112 may be one or more
of
various types of energy recovery devices, such as, for example, an enthalpy
wheel, a
sensible wheel, a desiccant wheel, a plate heat exchanger, a plate energy
(heat and
moisture) exchanger, a heat pipe, a run-around loop, or the like. As shown in
Figure 2,
the energy device 112 may be an enthalpy wheel.
[0040]
An enthalpy wheel is a rotary air-to-air heat exchanger. As shown,
supply air within the supply air flow path 106 passes in a direction counter-
flow to the
exhaust air within exhaust air flow path 120. For example, the supply air may
flow
through a lower portion, such as the lower half, of the wheel, while the
exhaust air flows
through an upper portion, such as the upper half, of the wheel. Alternatively,
supply air
may flow through a different portion of the wheel, such as a lower 1/3, 1/4,
1/5, or the
like, of the wheel, while exhaust air flows the remaining portion of the
wheel. The wheel
may be formed of a heat-conducting material with an optional desiccant
coating.
[0041]
In general, the wheel may be filled with an air permeable material
resulting in a large surface area. The surface area is the medium for sensible
energy
transfer. As the wheel rotates between the supply and exhaust air flow paths
106 and 120,
respectively, the wheel picks up heat energy and releases it into the colder
air stream.
Enthalpy exchange may be accomplished through the use of desiccants on an
outer surface
of the wheel. Desiccants transfer moisture through the process of adsorption,
which is
driven by the difference in the partial pressure of vapor within the opposing
air streams.
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CA 02824726 2013-08-22
[0042]
Additionally, the rotational speed of the wheel also changes the amount
of heat and moisture transferred. For example, an enthalpy wheel transfers
both sensible
and latent energy. The slower the rate of rotation, the less moisture is
transferred.
[0043]
The enthalpy wheel may include a circular honeycomb matrix of heat-
absorbing material that is rotated within the supply and exhaust air flow
paths 106 and
120, respectively. As the enthalpy wheel rotates, heat is picked up from the
air within the
exhaust air flow path 120 and transferred to the supply air within the supply
air flow path
106. As such, waste heat energy from the air within the exhaust air flow path
120 is
transferred to the matrix material and them from the matrix material to the
supply air 108
within the supply air flow path 106, thereby raising the temperature of the
supply air 108
by an amount proportional to the temperature differential between the air
streams.
[0044]
Optionally, the energy recovery device 112 may be a sensible wheel, a
plate exchanger, a heat pipe, a run-around apparatus, a refrigeration loop
having a
condenser and evaporator, a chilled water coil, or the like.
[0045]
Alternatively, the energy recovery device 112 may be a flat plate
exchanger. A flat plate exchanger is generally a fixed plate that has no
moving parts. The
exchanger may include alternating layers of plates that are separated and
sealed. Because
the plates are generally solid and non-permeable, only sensible energy may be
transferred.
Optionally, the plates may be made from a selectively permeable material that
allows for
both sensible and latent energy transfer.
[0046]
Alternatively, the energy recovery device 112 may be a run-around
loop or coil. A run-around loop or coil includes two or more multi-row finned
tube coils
connected to each other by a pumped pipework circuit. The pipework is charged
with a
heat exchange fluid, typically water or glycol, which picks up heat from the
exhaust air
coil and transfers the heat to the supply air coil before returning again.
Thus, heat from an
exhaust air stream is transferred through the pipework coil to the circulating
fluid, and
then from the fluid through the pipework coil to the supply air stream.
CA 02824726 2013-08-22
[0047]
Also, alternatively, the energy recovery device 112 may be a heat pipe.
A heat pipe includes a sealed pipe or tube made of a material with a high
thermal
conductivity such as copper or aluminum at both hot and cold ends. A vacuum
pump is
used to remove all air from the empty heat pipe, and then the pipe is filled
with a fraction
of a percent by volume of coolant or refrigerant, such as water, ethanol,
glycol etc. Heat
pipes contain no mechanical moving parts. Heat pipes employ evaporative
cooling to
transfer thermal energy from one point to another by the evaporation and
condensation of
a working fluid or coolant.
[0048]
Referring again, to Figure 1, as supply air 108 enters the supply air
flow path 106 through the inlet 104, the unconditioned supply air 108
encounters the pre-
heater 116 before the energy recovery device 112, which may be an enthalpy
wheel, flat
plate exchanger, heat pipe, run-around, or the like, as discussed above.
During winter
months, when the air is cold and dry, the temperature and/or humidity of the
supply air
108 will be raised as it moves through the pre-heater 116 and encounters the
energy
recovery device 112. As such, in winter conditions, the energy recovery device
112
warms and/or humidifies the supply air.
[0049]
A similar process occurs as the exhaust air 118 encounters the energy
recovery device 112 in the exhaust air flow path 120. The sensible and/or
latent energy
transferred to the energy recovery device 112 in the exhaust air flow path 120
is then used
to pre-condition the air within the supply air flow path 106. Overall, the
energy recovery
device 112 pre-conditions the supply air 108 in the supply air flow path 106
before it
encounters the heat exchanger 114, and alters the exhaust air 118 in the
exhaust air flow
path 120. In this manner, the heat exchanger 114 does not use as much energy
as it
normally would if the energy recovery device 112 (and/or the pre-heater 116)
was not in
place. Therefore, the heat exchanger 114 operates more efficiently.
[0050]
The heat exchanger 114 may be or include a gas heater that coverts gas
to heat, for example. Alternatively, the heater exchanger may be configured to
transfer
heat from liquid to air, for example. That is, the heat exchanger 114 may be a
liquid-to-air
heat exchanger. In general, the liquid and air are separated so that they do
not mix. The
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heat exchanger 114 may include radiator coils that are positioned within or
around the
supply air flow path 106. Liquid, such as water or glycol, is circulated
through the coils.
As supply air 108 passes by the coils, heat from the liquid is transferred to
the supply air
108, thereby further warming the supply air 108 before it passes into the
enclosed
structure 102. The radiator coils may be heated through combustion, for
example, such as
through a gas-fired heater. Heated gas from the heater is vented as flue gas.
As explained
below, the vented flue gas is channeled to the pre-heater 116 in order to pre-
condition the
supply air 108 before it encounters the energy recovery device 112.
Alternatively, the
heat exchanger 114 may not include radiator coils, but may simply be a gas
heater
disposed within the supply air flow path 106, and configured to convert gas to
heat and
heat the supply air 108.
[0051]
In general, flue gas is a gaseous combustion product from a furnace or
heating device. The flue gas may be formed primarily of nitrogen (for example,
more
than 2/3) derived from the combustion of air, carbon dioxide, and water vapor,
as well as
excess oxygen, which is also derived from the combustion of air.
[0052]
Figure 3a illustrates a schematic view of the heat exchanger 114,
according to an embodiment. As noted above, the heat exchanger 114 is disposed
within
the supply air flow path 106. The heat exchanger 114 includes a housing 126
that
contains a gas-fired heater 128, such as a furnace, and radiator coils 130
that contain a
liquid, such as water or glycol. The heater 128 may generate heat through
combustion.
The heater 128 heats the radiator coils 130 so that the liquid therein is
heated. The
radiator coils 130 are positioned within and/or around the portion of the
supply air flow
path 106 that passes through the heat exchanger 114. As supply air 108 passes
through
the heat exchanger 114, the temperature of the supply air 108 increases as it
passes
through the radiator coils 130. That is, the heat of the liquid within the
radiator coils 130
is transferred to the supply air 108. Consequently, the temperature of the
supply air 108 is
increased as it passes out of the heat exchanger 114.
[0053]
The flue gas from the heater 128 is vented through a vent 132 on or
within the housing 126. The heat exchanger 114 may include a fan (not shown)
that
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channels the flue gas into the vent 132. Optionally, the fan may be disposed
downstream
of the vent 132 within a conduit 134. The conduit 134 may be one or more
pipes, tubes,
plenum, or the like. For example, the conduit 134 may be a series of pipes
that connect
the vent 132 to another heat transfer device. The flue gas from the vent 132
then passes
into the conduit 134 that sealingly engages the vent 132 so that the flue gas
may be
channeled to another heat transfer device, as described below.
[0054]
Alternatively, the heat exchanger 114 may not include the radiator coils
130. Instead, the heat exchanger 114 may simply include the gas fired heater
128
disposed within the supply air flow path 106.
[0055] Figure 3b
illustrates an isometric top view of an exemplary furnace
129, according to an embodiment. The furnace 129 is one example of a heater
128
(shown in Figure 3a). The furnace 129 includes a housing 127 having a
plurality of
heating elements 131 that span between lateral walls 133 of the housing 129.
The heating
elements 131 may include channeled rods having openings through which flames
pass,
thereby generating heat. The furnace 129 may be connected to a source of gas
(not
shown) that fuels the furnace 129. As gas enters the heating elements 131 and
is ignited
through an igniting element or pilot light within a control section 135,
flames are
generated. Additionally, flue gas is also generated from the heating elements.
The
temperature of the flame generated by the heating elements 131 may be
approximately
2700oF, which generates a flue gas temperature of approximately 400oF. Various
other
furnaces may be used as the heater 128. Figure 3b merely shows one example of
a
furnace.
[0056]
The heating elements 131 may include tubes that contain gas that is
ignited to produce heat. The gas may make several passes through the tubes 131
before
passing to the vent 132, shown in Figure 3a. As air within the supply air flow
path 106
passes over the tubes 131, the air is heated.
[0057]
Figure 4 illustrates an isometric view of a radiator coil 130a of the heat
exchanger 114, according to an embodiment. As shown in Figure 4, the radiator
coil 130a
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may be a tubular member 140 having a circumferential channel 142 surrounding
an air
passage 144, which may be a portion of the supply air flow path 106. Liquid,
such as
water or glycol, is circulated through the circumferential channel 142. In
this manner,
liquid L may flow parallel to the supply air 108 as it passes through the air
passage 144.
Optionally, the liquid may flow in a direction counter to the direction of the
air flow (in
this examples, the lines L would flow in the opposite direction than shown in
Figure 4).
[0058]
Figure 5 illustrates an isometric view of a radiator coil 130b of the heat
exchanger 114, according to an embodiment. In this embodiment, a plurality of
tubes 146
having fluid channels 148 surround an air passage 150, which may be a portion
of the
supply air flow path 106. Liquid L, such as water or glycol, is circulated
through the fluid
channels 148. In this manner, liquid may flow parallel to the supply air 108
as it passes
through the air passage 150. Optionally, the liquid may flow in a direction
counter to the
direction of the air flow.
[0059]
Figure 6 illustrates an isometric view of a radiator coil 130c of the heat
exchanger 114, according to an embodiment. In this embodiment, the radiator
coil 130c
may include a series of fluid-filled plates 152 disposed within an air passage
154 that
forms part of the supply air flow path 106. In this manner, the supply air 108
may flow
across and parallel or counter to the liquid within the plates 152.
[0060]
Figure 7 illustrates an isometric view of a radiator coil 130d of the heat
exchanger 114, according to an embodiment. In this embodiment, the coil 130d
includes a
plurality of liquid-carrying tubes 156 that cross one another. The tubes 156
are disposed
within an air passage 158 that forms part of the supply air flow path 106. In
this manner,
the supply air 108 may flow across and parallel or counter to the liquid L
within the tubes
156.
[0061] Any of the
radiator coils shown and described with respect to Figures
4-7 may be used with respect to a heat transfer device in addition to, or in
lieu of, the heat
exchanger 114. For example, if the heat exchanger 114 does not include
radiator coils,
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but instead simply includes a gas heater, the radiator coils may be used with
respect to a
heat transfer device, such as described below.
[0062]
Additionally, referring to Figures 3a-7, as noted, the heating elements
131 of the furnace 129 may include tubes that contain gas that is ignited to
produce heat.
Smaller tubes may be disposed within each of the tubes 131, similar to the
configurations
shown in Figures 4 and 5. For example, a main gas tube may surround a
concentric liquid
tube that contains heat transfer liquid. The liquid tube may be in fluid
communication
with the pre-heater 116, shown in Figure 1. In this manner, the heat transfer
liquid may be
directly heated within the furnace and transferred to the pre-heater 116 to
heat the supply
air 106. As such, the temperature of the heat transfer liquid may be increased
as it is
directly heated within the furnace 129 and directly transferred to the pre-
heater.
[0063]
Referring to Figures 3a-7, the heat exchanger 114 may be configured
for parallel-flow, counter-flow, cross-flow, or a combination thereof. The
radiator coil
130 shown in Figure 3a may be any of the radiator coils 130a, 130b, 130c, or
130d. In
parallel flow, the supply air 108 and the liquid within the radiator coil 130
enter the heat
exchanger 114 at the same end, and travel parallel to one another to the other
side. In
counter-flow, the supply air 108 enters at a front end of the heat exchanger
114, while the
liquid enters the radiator coil 130 at the back end. In cross-flow, the supply
air 108 and
the liquid within the radiator coil are generally perpendicular to one another
within the
heat exchanger 114.
[0064]
Referring to Figures 1 and 3a, as noted above, flue gas from the heat
exchanger 114 is vented to the conduit 134. The conduit 134 channels the flue
gas to a
heat transfer device 160, such as a heating coil, that may include an internal
coil structure,
similar to those described above. The heated flue gas passes through an
internal chamber
(not shown) of the heat transfer device 160. As the flue gas passes through
the heat
transfer device 160, the heat from the flue gas is transferred to the liquid
within the
radiator coils of the heat transfer device 160. The decreased-temperature flue
gas (as heat
from the flue gas has been transferred to the liquid) is then vented to the
atmosphere
through a vent 162. However, the liquid within the radiator coil of the heat
transfer device
CA 02824726 2013-08-22
160, having an increased temperature through heat transfer with the flue gas,
is channeled
to the pre-heater 116 through a conduit 164. The heated liquid is then passed
from the
conduit 164 into an inlet 165 of a coil 166 of the pre-heater 116. The pre-
heater 116 may
also include radiator coils similar to that described above with respect to
Figures 3a-7.
The liquid passed into the coil 166, the temperature of which has risen due to
the heat
transfer with the flue gas, then transfers the increased heat to supply air
108 that passes
through the pre-heater 116. Accordingly, the supply air 108 is pre-heated
(that is, the
temperature of the supply air 108 is increased) before it encounters the
energy recovery
device 112.
[0065] As the
liquid within the coil 166 circulates therethrough, the
temperature of the liquid decreases, as its heat is transferred to the supply
air 108. The
cooled liquid within the radiator coil 166 passes out of the radiator coil 166
through an
outlet 167 and into a conduit 168 that connects back to the heat transfer
device 160. The
liquid is then heated again by heat transfer with the flue gas, and the
process repeats.
[0066] A pump 170
may be disposed within either of the conduits 164, 168, or
both. The pump(s) 170 aids in circulating the liquid between the heat transfer
device 160
to the pre-heater 116. However, in at least one embodiment, the system 100
does not
include the pump.
[0067]
While the pre-heater 116 and the heat transfer device 160 are described
as including liquid-conveying coils, the pre-heater 116 and the heat transfer
device 160
may be, or include, various other liquid-carrying and/or heating structures
and
components. For example, the pre-heater 116 may include fluid-conveying
plates.
Similarly, the heat transfer device 160 may be a heating plate(s).
Additionally, each of the
pre-heater 116 and the heat transfer device 160 may also include separate and
distinct
heating devices, similar to the heater 128 shown in Figure 3. However, the
liquid that is
circulated between the heat transfer device 160 and the pre-heater 116 may be
primarily or
solely heated by way of heat transfer with the flue gas. Optionally, the
liquid that is
circulated between the heat transfer device 160 and the pre-heater 116 may be
also heated
through an electrical heater.
16
CA 02824726 2013-08-22
[0068]
Additionally, while the heat transfer device 160 is shown as being
separate, distinct, and remote from the heat exchanger 114 and the pre-heater
116, the heat
transfer device 160 may be contained within a housing of the heat exchanger or
the pre-
heater 116. For example, the heat transfer device 160 may be mounted directly
to the vent
of the heat exchanger 114 inside or outside of the housing of the heat
exchanger 114. As
such, the heat exchanger 114 and the heat transfer device 160 may be disposed
within a
common housing.
[0069]
Referring to Figures 1 and 3a, the supply air 108 (that is, air supplied
from outdoor and/or ambient air) is pre-heated by the pre-heater 116. The pre-
heater 116
increases the temperature of the supply air 108 so that it will not form frost
on the energy
recovery device 112. The pre-heater 116 may increase the temperature of the
supply air
108 through a circulating liquid that has been heated through a transfer of
heat from
harvested flue gas, as described above. As such, the efficiency of the system
100 is
increased.
[0070] The
following example illustrates the increased efficiency of the system
100. At point A, the supply air 108, which is outside air that enters through
the inlet 104,
flowing at a rate of 4000 cubic feet/minute (cfm), has a temperature of -20o
F. However,
the desired temperature within the enclosed space 102 at point B is 85oF,
which represents
a difference of 105oF. Therefore, the system 100 needs to raise the
temperature of the
outside air by 105 oF. It has been found that the system 100, by way of
harvesting the
energy within the flue gas from the heat exchanger 114, is able to raise the
temperature of
the outside air to a temperature that exceeds the frost point. Accordingly,
the system 100
that includes the pre-heater 116 and flue gas energy harvesting heat transfer
device 160
renders frost control unnecessary, as the supply air 108 is raised to a
temperature above
the frost point before it encounters the energy recovery device 112.
Accordingly, the
energy recover device 112 does not need to be defrosted.
[0071]
Moreover, the pre-heater 116 and the heat transfer device 160 may be
retrofitted to any DOAS, thereby improving the efficiency of the DOAS.
17
CA 02824726 2013-08-22
[0072]
Figure 8 illustrates a schematic view of an energy recovery system 180,
according to an embodiment. The system 180 is similar to the system 100,
except that the
heat exchanger 114 is upstream from the energy recovery device 112 within the
supply air
flow path 106. Therefore, the temperature of the supply air 108 is further
heated after the
pre-heater 116 before the supply air 108 encounters the energy recovery device
112.
Thus, the possibility of frost forming on the energy recovery device 112 is
further
reduced. The system 180 may also include an additional heat exchanger
downstream
from the energy recovery device 112 within the supply air flow path 106.
[0073]
Figure 9 illustrates a schematic view of an energy recovery system 190,
according to an embodiment. The energy recovery system 190 is similar to the
system
100, except that an additional heat exchanger 192 is positioned upstream the
energy
recovery device 112. The heat exchanger 192 may be a liquid-to-gas heat
exchanger.
Flue gas from both the heat exchangers 114 and 192 is vented into a shared
conduit 194
that channels the combined flue gas into the coil heater 160.
[0074]
Additionally, in all of the embodiments, such as shown in Figures 1, 8,
and 9, an optional return air duct may connect the exhaust air flow path 120
with the
supply air flow path 106. For example, an air duct may be downstream of the
energy
recovery device 112 in the supply air flow path 106, and upstream of the
energy recovery
device 112 in the exhaust air flow path 120. Alternatively, or additionally,
an additional
return air duct may be upstream of the energy recovery device 112 in the
supply air flow
path 106 and downstream of the energy recovery device 112 within the exhaust
air flow
path 120. The return air ducts may recycle a portion of the exhaust air 118,
which may be
at a much higher temperature than outdoor air, into the supply air 108, which
further
increases the temperature of the supply air 108.
[0075] Figure 10
illustrates a schematic view of an energy recovery system
200, according to an embodiment. The system 200 is similar to the system 100,
except
that return air ducts 202, 204, and 206 connect the exhaust air flow path 118
to the supply
air flow path 106. More or less return air ducts than those shown may be used.
Moreover,
18
CA 02824726 2013-08-22
the return air ducts may be used with the systems 180 and 190 shown in Figures
8 and 9,
respectively.
[0076]
The return air duct 206 connects to the supply air flow path 106
upstream of the pre-heater 116. Thus, the temperature of the supply air 108
may be
increased even before it encounters the pre-heater 116.
[0077]
Figure 11 illustrates a process of operating a direct outdoor air system,
according to an embodiment. At 220, flue gas from a heat exchanger or heater
is vented
and captured within a conduit. The flue gas may be moved through the use of a
fan, for
example.
[0078] At 222, the
flue gas is channeled to a heating device, such as a heating
coil, plate, another heat exchanger, furnace, or the like. Next, at 224, the
heat within the
flue gas is transferred to liquid contained within the heating device. As the
flue gas passes
through the heating device and decreases in temperature (as the heat from the
flue gas is
transferred to the liquid within the heating device), the flue gas is vented
from the heating
device at 226. At the same time, at 228, the liquid, having an increased
temperature due
to heat transfer with the flue gas, is circulated to a pre-heater, which may
include a liquid-
circulating coil. Then, at 230, the heated liquid within the pre-heater is
circulated around
supply air flowing through a supply air flow path. Heat within the liquid is
transferred to
the supply air. At this time, the temperature of the liquid decreases, as a
portion of its heat
is transferred to the supply air. The liquid fully circulates through the pre-
heater and is
then recirculated back to the heating device at 232, and then the process
returns to 224.
[0079]
Additionally, flue gas and/or liquid may be bypassed to control the
amount of energy transfer. Moreover, the flow of liquid may be modulated to
control the
amount of energy transfer.
[0080] Thus,
embodiments provide a system and method of capturing heat
energy from exhaust flue gas, and recycling the heat energy back into the
supply air.
Embodiments provide a system and method of using recycled flue gas energy to
pre-heat
19
CA 02824726 2013-08-22
an air stream to reduce the need for defrosting in cold conditions. Overall,
embodiments
provide a highly-efficient DOAS.
[0081]
It is to be understood that the above description is intended to be
illustrative, and not restrictive. For example, the above-described
embodiments (and/or
aspects thereof) may be used in combination with each other. In addition, many
modifications may be made to adapt a particular situation or material to the
teachings of
the various embodiments of the invention without departing from their scope.
While the
dimensions and types of materials described herein are intended to define the
parameters
of the various embodiments of the invention, the embodiments are by no means
limiting
and are exemplary embodiments. Many other embodiments will be apparent to
those of
skill in the art upon reviewing the above description. The scope of the
various
embodiments of the invention should, therefore, be determined with reference
to the
appended claims, along with the full scope of equivalents to which such claims
are
entitled. In the appended claims, the terms "including" and "in which" are
used as the
plain-English equivalents of the respective terms "comprising" and "wherein."
Moreover,
in the following claims, the terms "first," "second," and "third," etc. are
used merely as
labels, and are not intended to impose numerical requirements on their
objects.
[0082]
This written description uses examples to disclose the various
embodiments of the invention, including the best mode, and also to enable any
person
skilled in the art to practice the various embodiments of the invention,
including making
and using any devices or systems and performing any incorporated methods. The
patentable scope of the various embodiments of the invention is defined by the
claims, and
may include other examples that occur to those skilled in the art. Such other
examples are
intended to be within the scope of the claims if the examples have structural
elements that
do not differ from the literal language of the claims, or if the examples
include equivalent
structural elements with insubstantial differences from the literal languages
of the claims.
