DEDICATED OUTDOOR AIR SYSTEM WITH PRE-HEATING AND METHOD FOR SAME

BACKGROUND OF THE DISCLOSURE

Embodiments of the present disclosure generally relate to a dedicated outdoor air system (DOAS) having one or more pre-heaters.

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.

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) is an energy exchange system that conditions ambient/outside air to desired 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. Frost on the enthalpy wheel typically reduces the efficiency and effectiveness of the enthalpy wheel.

Additionally, in extremely cold conditions, a heater of a DOAS may draw increased power over a relatively long period of time in order to adequately heat air that is ultimately supplied to an enclosed structure. As such, the energy requirements and costs of operation of the heater may increase.

SUMMARY OF THE DISCLOSURE

Certain embodiments of the present disclosure provide an energy exchange system that may include an energy recovery device, at least one first pre-heater, and at least one boiler. The energy recovery device is configured to be disposed within supply and exhaust air flow paths. The first pre-heater(s) is configured to be positioned within one or both of the supply and exhaust air flow paths, and may include one or more coils configured to circulate a first liquid, such as water, that is configured to transfer heat to air within the supply and/or exhaust air flow paths. The boiler(s) is operatively connected to the first pre-heater(s) and is configured to heat the first liquid.

The first pre-heater(s) may be configured to be upstream of the energy recovery device within the supply air flow path.

The system may also include a heater or heat exchanger configured to be downstream of the energy recovery device within the supply air flow path. The first pre-heater(s) may be configured to be positioned within the supply air flow path between the energy recovery device and the heater.

The boiler(s) may include a main tank configured to retain the first liquid. The boiler(s) may also include a heating element configured to heat the first liquid.

The first pre-heaters may include multiple first pre-heaters configured to be positioned within the supply air flow path. The multiple first pre-heaters may be operatively connected to a single boiler. Alternatively, each of the first pre-heaters may be connected to separate and distinct boilers.

The energy exchange system may also include at least one second pre-heater configured to pre-heat air within one or both of the 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, and a heat transfer device operatively connected to the heater and the at least one second 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 a second liquid, such as water, within the heat transfer device. The second liquid is configured to be channeled to the second pre-heater(s) so that heat is transferred from the second liquid to supply air within the supply air flow path before the supply air encounters the energy recovery device.

The heater may be downstream from the energy recovery device within the supply air flow path. Alternatively, the heater may be upstream from the energy recovery device within the supply air flow path. The first pre-heater(s) may be positioned with the supply air flow path between the energy recovery device and the heater.

The energy exchange system may also include at least one bypass duct configured to be disposed within the supply air flow path. The bypass duct(s) is configured to bypass at least a portion of the supply air around one or both of the at least one first pre-heater or the energy recovery device.

Certain embodiments of the present disclosure provide a method of operating an energy exchange 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 heating a first liquid within an internal chamber of a boiler, pumping the first liquid from the boiler to at least one first pre-heater disposed within one or both of the supply air flow path and the exhaust air flow path, pre-heating air within the one or both of the supply air flow path and the exhaust air flow path with the first liquid within the at least one first pre-heater, and pumping the first liquid from the at least one first pre-heater back to the boiler.

The method may also include capturing flue gas generated by a heater, channeling the flue gas to a heat transfer device, transferring heat from the flue gas to a second liquid within the heat transfer device, circulating the second liquid to at least one second pre-heater disposed within one or both of the supply air flow path and the exhaust air flow path, and transferring heat within the second liquid to the air within one or both the supply air flow path and the exhaust air flow path.

Certain embodiments of the present disclosure provide a DOAS that may include a heater configured to be disposed within a supply air flow path, a first pre-heater configured to be upstream from the heater within the supply air flow path, wherein the first pre-heater is configured to pre-heat the supply air through heat transfer with a first liquid that circulates through the first pre-heater, and a boiler operatively connected to the first pre-heater, wherein the boiler is configured to heat the first liquid. The DOAS may also include a second 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 second pre-heater. The heat transfer device is configured to receive flue gas from the heater and transfer heat from the flue gas to a second liquid within the heat transfer device. The second liquid is configured to be channeled to the second pre-heater so that heat is transferred from the second liquid to supply air within the supply air flow path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of an energy exchange system, according to an embodiment of the present disclosure.

FIG. 2 illustrates a simplified internal view of a boiler, according to an embodiment of the present disclosure.

FIG. 3 illustrates an isometric view of a coil of a pre-heater, according to an embodiment of the present disclosure.

FIG. 4 illustrates an isometric view of a coil of a pre-heater, according to an embodiment of the present disclosure.

FIG. 5 illustrates an isometric view of a coil of a pre-heater, according to an embodiment of the present disclosure.

FIG. 6 illustrates an isometric view of a coil of a pre-heater, according to an embodiment of the present disclosure.

FIG. 7 illustrates a schematic view of the energy recovery device, according to an embodiment of the present disclosure.

FIG. 8 illustrates a schematic view of an energy exchange system, according to an embodiment of the present disclosure.

FIG. 9 illustrates a schematic view of an energy exchange system, according to an embodiment of the present disclosure.

FIG. 10 illustrates a schematic view of an energy exchange system, according to an embodiment of the present disclosure.

FIG. 11
a illustrates a schematic view of a heat exchanger, according to an embodiment of the present disclosure.

FIG. 11
b illustrates a schematic view of a heat exchanger, according to an embodiment of the present disclosure.

FIG. 12 illustrates an isometric top view of an exemplary furnace, according to an embodiment of the present disclosure.

FIG. 13 illustrates a schematic view of an energy recovery system, according to an embodiment of the present disclosure.

FIG. 14 illustrates a schematic view of an energy recovery system, according to an embodiment of the present disclosure.

FIG. 15 illustrates a schematic view of an energy recovery system, according to an embodiment of the present disclosure.

FIG. 16 illustrates a process of operating a direct outdoor air system, according to an embodiment of the present disclosure.

FIG. 17 illustrates a process of operating a direct outdoor air system, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

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.

As explained below, embodiments of the present disclosure provide an energy exchange system that may include one or more pre-heaters configured to pre-heat supply air before an energy recovery device and/or a heat exchanger, such as a heater. Accordingly, embodiments of the present disclosure provide an energy exchange system that operates more efficiently than known systems.

FIG. 1 illustrates a schematic view of an energy exchange system 10, according to an embodiment of the present disclosure. The system 10 is shown as a Dedicated Outdoor Air System (DOAS). The system 10 is configured to partly or fully condition air supplied to an enclosed structure 12, such as a building or an enclosed room. The system 10 includes an air inlet 14 fluidly connected to a supply air flow path 16. The supply air flow path 16 may channel supply air 18 (such as outside air, air from a building adjacent to the enclosed structure 12, or return air from a room within the enclosed structure 12) to the enclosed structure 12. Supply air 18 in the supply air flow path 16 may be moved through the supply air flow path 16 by a fan or fan array 20. The fan 20 may be located downstream of an energy recovery device 22 and a pre-heater 24. Optionally, the fan 20 may be positioned upstream of the energy recovery device 22 and/or the pre-heater 24. Also, alternatively, supply air 18 within the supply air flow path 16 may be moved by multiple fans or a fan array or before and/or after the pre-heater 24.

Airflow passes from the inlet 14 through the supply air flow path 16 where the supply air 18 first encounters the pre-heater 24. A bypass duct 26 may be disposed in the supply air flow path 16. The bypass duct 26 may be connected to the supply air flow path 16 through an inlet damper 28 upstream from the pre-heater 24, and an outlet damper 30 downstream from the pre-heater 24. When the dampers 28 and 30 are fully opened, supply air 18 may be diverted or bypassed around the pre-heater 26. The dampers 28 and 30 may be modulated to allow a portion of the supply air 18 to bypass around the pre-heater 26. Alternatively, the system 10 may not include the bypass duct 26.

Additionally, a damper 32 may be disposed in the supply air flow path 16 upstream from the pre-heater 24. When fully closed, the damper 32 prevents supply air 18 from passing into the pre-heater 24. The damper 32 may be modulated in order to allow a portion of the supply air 18 to pass through the pre-heater 24, while a remaining portion of the supply air 18 is bypassed through the bypass duct 26. Alternatively, the system 10 may not include the damper 32

The pre-heater 24 heats the supply air 18 is it passes therethrough. The pre-heater 24 heats the incoming supply air 18 before it encounters the energy recovery device 22. An additional pre-heater may be disposed within the supply air flow path 16 downstream from the pre-heater 24 and upstream or downstream from the energy recovery device 22. The additional pre-heater is configured to add more heat to the supply air 18 during extremely cold conditions. The pre-heater 24 may, alternatively, be disposed within an exhaust air flow path 40 upstream from the energy recovery device 22. Additionally, alternatively, a pre-heater may also be disposed within the exhaust air flow path 40 upstream from the energy recovery device 22. As explained in more detail below with respect to FIG. 7, the energy recovery device 22 uses exhaust air 42 from the exhaust flow path 40 to condition the supply air 18 within the supply air flow path 16. For example, during a winter mode operation, the energy recovery device 22 may condition the supply air 18 within the supply air flow path 16 by adding heat and/or moisture. In a summer mode operation, the energy recovery device 22 may pre-condition the supply air 18 by removing heat and moisture from the air. While the energy recovery device 22 is shown downstream from the pre-heater 24 within the supply air flow path 16, the energy recovery device 22 may, alternatively, be positioned upstream of the pre-heater 24 within the supply air flow path 16.

After the supply air 18 passes through the energy recovery device 22 in the supply air flow path 16, the supply air 18, which at this point has been conditioned, may encounter a heat exchanger 44, such as a heater. The heat exchanger 44 then further heats the supply air 18 in the supply air flow path 16 to generate a change in air temperature toward a desired supply state that is desired for supply air discharged into the enclosed structure 12. For example, during a winter mode operation, the heat exchanger 44 may further condition the pre-conditioned air by adding heat to the supply air 18 in the supply air flow path 16.

The exhaust or return air 42 from the enclosed structure 12 is channeled out of the enclosed structure 12, such as by way of exhaust fan 46 or fan array within the exhaust flow path 40. As shown, the exhaust fan 46 is located upstream of the energy recovery device 22 within the exhaust air flow path 40. However, the exhaust fan 46 may be downstream of the energy recovery device 22 within the exhaust air flow path 40. The exhaust air 42 passes through a regeneration side or portion of the energy recovery device 22. The energy recovery device 22 is regenerated by the exhaust air 42 before conditioning the supply air 18 within the supply air flow path 16. After passing through the energy recovery device 22, the exhaust air 42 is vented to atmosphere through an air outlet 48.

In an alternative embodiment, additional bypass ducts and dampers may be disposed within the supply air flow path 16 and/or the exhaust air flow path 40 in order to bypass airflow around the energy recovery device 22.

The pre-heater 24 is operatively connected to a boiler 50. The boiler 50 provides heated liquid, such as water, to the pre-heater 24 in order to pre-heat the supply air 18 within the supply air flow path 16. The pre-heater 24 may include one or more coils 51 that surround a portion of the supply air flow path 16. The coils 51 are configured to channel heated liquid, such as water, from an inlet 52 to an outlet 54. The inlet 52 connects to a liquid outlet 56 of the boiler 50 through a liquid delivery line 57, such as a conduit, tube, duct, or the like. Similarly, the outlet 54 connects to a liquid inlet 58 of the boiler 50 through a liquid reception line 59, such as a conduit, tube, duct, or the like. One or more pumps 60 may be disposed within the liquid delivery and/or reception lines 57, 59 in order to move the liquid between the boiler 50 and the coils 51 of the pre-heater 24.

In operation, the boiler 50 heats liquid within a tank of the boiler 50. The heated liquid is then delivered to the coils 51 of the pre-heater 24 by way of the liquid delivery line 57. The boiler may heat the liquid, such as water, to a temperature of approximately 180° F. As such, the heated liquid may not boil, but instead remain in a liquid state as it is pumped into the coils 51. The heated liquid within the coils 51 exchanges energy with the supply air 18 as the supply air passes through the pre-heater 24. The heat from the liquid is transferred to the supply air 18, thereby increasing the temperature of the supply air 18, but reducing the temperature of the liquid within the coils 51. The reduced-temperature liquid passes out of the outlet 54 into the liquid reception line 59, which, in turn, channels the reduced-temperature liquid back to the boiler 50. The boiler 50 then re-heats the reduced-temperature liquid, and the process repeats. Accordingly, the pre-heater 24 heats the supply air 18 before the supply air 18 encounters the energy recovery device 22. The boiler 50 provides heated liquid, such as heated water, to the coils 51 of the pre-heater 24 so that the pre-heater 24 can pre-heat the supply air 18 before it encounters the energy recovery device 22 and the heat exchanger 44.

As shown, the pre-heater 24 is positioned upstream from the energy recovery device 22 within the supply air flow path 16. Alternatively, the pre-heater 24 may be downstream from the energy recovery device 22 within the supply air flow path 16. Additionally, the pre-heater 24 may be downstream from the heat exchanger 44 within the supply air flow path 16. As such, the pre-heater 24 may be a heating device that is a post-heater. Also, alternatively, additional pre-heaters may be disposed within the supply air flow path 16. For example, an additional pre-heater may be disposed between the pre-heater 24 and the energy recovery device 22 within the supply air flow path 16. Also, additional pre-heaters may be disposed with the supply air flow path 16 between the energy recovery device 22 and the heat exchanger 44, and/or downstream from the heat exchanger 44. Each of the pre-heaters within the system 10 may be operatively connected to respective boilers. Alternatively, multiple pre-heaters may be operatively connected to a single boiler.

Additionally, alternatively, the boiler 50 may be operatively connected to the heat exchanger 44, such as through conduits, pipes, or the like, so that flue gas from the boiler 50 is provided to the heat exchanger 44. The higher temperature flue gas from the boiler 50 may be used to heat fluid, whether air or water, within the heat exchanger 44. Thus, the boiler 50 may directly heat air within the supply air flow path 16, as well as provide heated flue gas to the heat exchanger 44, which also heats air within the supply air flow path. Moreover, the heat exchanger 44 and/or the boiler 50 may also be operatively connected to a pre-heater disposed within the exhaust air flow path 40 upstream from the energy recovery device 22. Accordingly, the heat exchanger 44 and vented flue gas from the boiler 50 may also be used to condition air within the exhaust air flow path 40.

FIG. 2 illustrates a simplified internal view of the boiler 50, according to an embodiment of the present disclosure. The boiler 50 includes a main tank 70 defining an internal chamber 72 that retains a liquid 73, such as water. A heating element 74 may be positioned proximate the base of the main tank 70 and is configured to heat the liquid 73 within the internal chamber 72. The heating element 74 may be an electric or gas heater, for example. While shown proximate the base of the main tank 74, the heating element 74 may be positioned at or within any portion of the main tank 70. For example, the heating element 74 may include electric heating coils positioned within walls that define the main tank 70.

The internal chamber 72 is in fluid communication with the liquid outlet 56 and the liquid inlet 58. Accordingly, heated liquid may be pumped through the liquid outlet 56, into the liquid delivery line 57, and into the pre-heater 24 (shown in FIG. 1). Similarly, reduced-temperature liquid may be pumped through the liquid reception line 59, into the liquid inlet 58, and into the internal chamber 72.

An exhaust port 76 may be formed through a portion of the main tank 70. The exhaust port 76 is configured to allow steam within the internal chamber 72 to pass out of the internal chamber 72. Alternatively, the main tank 70 may not include the exhaust port 76. Additionally, the boiler 50 may also include a chimney 78 configured to exhaust any combustion gases, such as flue gases, generated by the heating element 74. Alternatively, the chimney 78 may be connected to a flue gas delivery line, which may be used to increase the temperature of the supply air, such as through an additional pre-heater, for example, as explained below.

The boiler 50 may be one or more of various types of boilers. For example, the boiler 50 may be a fire tube boiler, water tube boiler, packaged boiler, fluidized bed combustion boiler, atmospheric fluidized bed combustion boiler, pressurized fluidized bed combustion boiler, atmospheric circulating fluidized bed combustion boiler, stoker fired boiler, pulverized fuel boiler, waste heat boiler, thermic fluid heater, hydronic boiler, and/or the like. As noted, FIG. 2 merely illustrates a simplified configuration for a boiler. Any type of boiler that is configured to heat liquid may be used. As noted, the boiler 50 may be operated to heat the liquid below a boiling point in order to provide heated liquid to the coils 51 (shown in FIG. 1) of the pre-heater 24.

FIG. 3 illustrates an isometric view of a coil 51a of the pre-heater 24, according to an embodiment of the present disclosure. As shown in FIG. 3, the coil 51a may be a tubular member 80 having a circumferential channel 82 surrounding an air passage 84, which may be a portion of the supply air flow path 16 (shown in FIG. 1). Liquid, such as water or glycol, is circulated through the circumferential channel 82. In this manner, liquid L may flow parallel to the supply air 18 as it passes through the air passage 84. Optionally, the liquid may flow in a direction counter to the direction of the air flow (in this example, the lines L would flow in the opposite direction than shown in FIG. 3).

FIG. 4 illustrates an isometric view of a coil 51b of the pre-heater 24, according to an embodiment of the present disclosure. In this embodiment, a plurality of tubes 86 having fluid channels 88 surround an air passage 90, which may be a portion of the supply air flow path 16 (shown in FIG. 1). Liquid L, such as water or glycol, is circulated through the fluid channels 88. In this manner, liquid may flow parallel to the supply air 18 as it passes through the air passage 90. Optionally, the liquid may flow in a direction counter to the direction of the air flow.

FIG. 5 illustrates an isometric view of a coil 51c of the pre-heater 24, according to an embodiment of the present disclosure. In this embodiment, the coil 51c may include a series of fluid-filled plates 92 disposed within an air passage 94 that forms part of the supply air flow path 16 (shown in FIG. 1). In this manner, the supply air 18 may flow across and parallel or counter to the liquid within the plates 92.

FIG. 6 illustrates an isometric view of a coil 51d of the pre-heater 24, according to an embodiment of the present disclosure. In this embodiment, the coil 51d includes a plurality of liquid-carrying tubes 96 that cross one another. The tubes 96 are disposed within an air passage 98 that forms part of the supply air flow path 16 (shown in FIG. 1). In this manner, the supply air 18 may flow across and parallel or counter to the liquid L within the tubes 96.

Any of the coils shown and described with respect to FIGS. 3-6 may be used with respect to the pre-heater 24, heat exchanger, heater, or other such heat transfer device.

Referring to FIGS. 1-6, the pre-heater 24 may be configured for parallel-flow, counter-flow, cross-flow, or a combination thereof. The coils 51 shown in FIG. 1 may include any of the coils 51a, 51b, 51c, and/or 51d. In parallel flow, the supply air 18 and the liquid within the coils 51 enter the pre-heater 24 at the same end, and travel parallel to one another to the other side. In counter-flow, the supply air 18 enters at a front end of the pre-heater 24, while the liquid enters the coils 51 at the back end. In cross-flow, the supply air 18 and the liquid within the coil are generally perpendicular to one another within the pre-heater 24. Therefore, while FIG. 1 shows the liquid delivery line 57 at a downstream end of the pre-heater 24, and the liquid reception line 59 at an upstream end of the pre-heater 24, it is understood that these positions may be reversed.

The pre-heater 24 and the boiler 50 may be retrofit to any DOAS, thereby improving the efficiency of the DOAS.

FIG. 7 illustrates a schematic view of the energy recovery device 22, according to an embodiment of the present disclosure. A portion of the energy recovery device 22 is disposed within the supply air flow path 16, while another portion of the energy recovery device 22 is disposed within the exhaust air flow path 40. The energy recovery device 22 is configured to transfer heat and/or moisture between the supply air flow path 16 and the exhaust air flow path 40. The energy recovery device 22 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 FIG. 7, the energy device 22 may be an enthalpy wheel.

An enthalpy wheel is a rotary air-to-air heat exchanger. As shown, supply air within the supply air flow path 16 passes in a direction counter to the exhaust air within exhaust air flow path 40. 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 ⅓, ¼, ⅕, or the like, of the wheel, while exhaust air flows through the remaining portion of the wheel. The wheel may be formed of a heat-conducting material with an optional desiccant coating.

In general, the wheel may be filled with an air permeable material resulting in a large surface area. The surface area may be the medium for sensible energy transfer. As the wheel rotates between the supply and exhaust air flow paths 16 and 40, 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.

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.

The enthalpy wheel may include a circular honeycomb matrix of heat-absorbing material that is rotated within the supply and exhaust air flow paths 16 and 40, respectively. As the enthalpy wheel rotates, heat is picked up from the air within the exhaust air flow path 40 and transferred to the supply air within the supply air flow path 16. As such, waste heat energy from the air within the exhaust air flow path 40 is transferred to the matrix material and then from the matrix material to the supply air 18 within the supply air flow path 16, thereby raising the temperature of the supply air 18 by an amount proportional to the temperature differential between the air streams.

Optionally, the energy recovery device 22 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.

Alternatively, the energy recovery device 22 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.

Alternatively, the energy recovery device 22 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.

Also, alternatively, the energy recovery device 22 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.

Referring again, to FIG. 1, as supply air 18 enters the supply air flow path 16 through the inlet 14, the unconditioned supply air 18 encounters the pre-heater 24 before the energy recovery device 22, 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 18 will be raised as it moves through the pre-heater 24 and encounters the energy recovery device 22. As such, in winter conditions, the energy recovery device 22 warms and/or humidifies the supply air.

A similar process occurs as the exhaust air 42 encounters the energy recovery device 22 in the exhaust air flow path 40. The sensible and/or latent energy transferred to the energy recovery device 22 in the exhaust air flow path 40 is then used to pre-condition the air within the supply air flow path 16. Overall, the energy recovery device 22 pre-conditions the supply air 18 in the supply air flow path 16 before it encounters the heat exchanger 44, and alters the exhaust air 42 in the exhaust air flow path 40. In this manner, the heat exchanger 44 does not use as much energy as it normally would if the energy recovery device 112 (and/or the pre-heater 24) was not in place. Therefore, the heat exchanger 44 operates more efficiently.

The heat exchanger 44 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 44 may be a liquid-to-air heat exchanger. In general, the liquid and air are separated so that they do not mix. The heat exchanger 44 may include radiator coils that are positioned within or around the supply air flow path 16. Liquid, such as water or glycol, may be circulated through the coils. As supply air 18 passes by the coils, heat from the liquid is transferred to the supply air 18, thereby further warming the supply air 18 before it passes into the enclosed structure 12. 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 may be channeled to a heating device, such as another pre-heater, in order to pre-condition the supply air 18 before it encounters the energy recovery device 22, as described in U.S. patent application Ser. No. 13/625,912, entitled “Dedicated Outdoor Air System With Pre-Heating And Method For Same,” which was filed Sep. 25, 2012, and is hereby incorporated by reference in its entirety. Alternatively, the heat exchanger 44 may not include radiator coils, but may simply be a gas heater disposed within the supply air flow path 16, and configured to convert gas to heat and heat the supply air 18.

FIG. 8 illustrates a schematic view of an energy exchange system 800, according to an embodiment of the present disclosure. The energy exchange system 800 is similar to the system 10, except that a pre-heater 802, which is operatively connected to a boiler 804, is downstream from an energy recovery device 806 and upstream from a heat exchanger 808 within a supply air flow path 810. The pre-heater 802 and the boiler 804 may be configured to operate as described above.

Alternatively, the pre-heater 802 may be downstream from the heat exchanger 808 within the supply air flow path 810. Also, an additional pre-heater may be positioned within the supply air flow path 810 upstream from the energy recovery device 806. The additional pre-heater 802 may be operatively connected to the boiler 804, or to a separate and distinct boiler.

FIG. 9 illustrates a schematic view of an energy exchange system 900, according to an embodiment of the present disclosure. The energy exchange system 900 is similar to the system 10, except that the system 900 includes a pre-heater 902 upstream from an energy recovery device 904 within a supply air flow path 906, as well as a pre-heater 908 downstream from the energy recovery device 904, but upstream from a heat exchanger 910, within the supply air flow path 906. The pre-heaters 902 and 908 may both be operatively connected to a common boiler 912. Separate and distinct liquid delivery lines 914 and 916 connect the boiler 912 to each of the pre-heaters 910 and 902, respectively. Optionally, a single liquid delivery line may extend from the boiler 912 and branch off to the separate and distinct pre-heaters 910 and 902. Similarly, liquid reception lines 918 and 920 may connect the pre-heaters 902 and the 908, respectively, to the boiler 912. The liquid reception lines 918 and 920 may merge together, as shown in FIG. 8, into a single line 922 that channels reduced-temperature liquid from each pre-heater 902 and 908 into the boiler 912. Alternatively, separate and distinct liquid reception lines may connect directly to the boiler 912.

FIG. 10 illustrates a schematic view of an energy exchange system 1000 according to an embodiment of the present disclosure. The system 1000 is configured to partly or fully condition air supplied to an enclosed structure 1002, such as a building or an enclosed room. The system 1000 includes an air inlet 1004 fluidly connected to a supply air flow path 1006. The supply air flow path 1006 may channel supply air 1008 (such as outside air, air from a building adjacent to the enclosed structure 1002, or return air from a room within the enclosed structure 1002) to the enclosed structure 1002. Supply air 1008 in the supply air flow path 1006 may be moved through the supply air flow path 1006 by a fan or fan array 1010. The illustrated embodiment shows the fan 1010 located downstream of an energy recovery device 1012 and a gas-fired heater or heat exchanger 1014. The heat exchanger 1014 may be or include the gas-fired heater. Optionally, the fan 1010 may be positioned upstream of the energy recovery device 1012 and/or the heat exchanger 1014. Also, alternatively, air 1008 within the supply air flow path 1006 may be moved by multiple fans or a fan array or before and/or after the heat exchanger 1014.

Airflow passes from the inlet 1004 through the supply air flow path 1006 where the supply air 1008 first encounters a pre-heater 1009 operatively connected to a boiler 1011, as described above. The pre-heater 1009 may be upstream from a pre-heater 1016 with the supply air flow path 1006. Optionally, the pre-heater 1016 may be upstream from the pre-heater 1009 within the supply air flow path 1006.

A bypass duct 1017 may be disposed in the supply air flow path 1006 downstream or upstream from the pre-heater 1009. The bypass duct 1017 may be positioned in the supply air flow path 1006 between the pre-heaters 1009 and 1016. The bypass duct 1017 may be connected to the supply air flow path 1006 through an inlet damper 1019 upstream from the pre-heater 1016 (but downstream from the pre-heater 1009), and an outlet damper 1021 downstream from the pre-heater 1016. Alternatively, the inlet damper 1019 may be upstream from the pre-heater 1009 within the supply air flow path 1006. When the dampers 1019 and 1021 are fully opened, supply air 1008 may be diverted or bypassed around the pre-heater 1016 (and/or the pre-heater 1009). The dampers 1019 and 1021 may be modulated to allow a portion of the supply air 1008 to bypass around the pre-heater 1016 (and/or the pre-heater 1009).

Additionally, a damper 1023 may be disposed in the supply air flow path 1006 upstream from the pre-heater 1016 and/or the pre-heater 1009. When fully closed, the damper 1023 prevents supply air 1008 from passing into the pre-heater 1016 and/or the pre-heater 1009. The damper 1023 may be modulated in order to allow a portion of the supply air 1008 to pass through the pre-heater 1016 and/or the pre-heater 1009, while a remaining portion of the supply air 1008 is bypassed through the bypass duct 1017.

The pre-heater 1009 heats the air 1008 as it passes therethrough, as explained above with respect to FIGS. 1 and 2, for example. Additionally, the pre-heater 1016 heats the air 1008 is it passes therethrough. The pre-heater 1016 heats the incoming supply air 1008 before it encounters a process side or portion of the energy recovery device 1012. An additional pre-heater may be disposed within the supply air flow path 1006 downstream from the pre-heater 1016 and upstream from the energy recovery device 1012. The additional pre-heater is configured to add more heat to the supply air 1008 during extremely cold conditions. The pre-heater 1016 may, alternatively, be disposed within an exhaust air flow path 1020 upstream from the energy recovery device 1012. Additionally, alternatively, a pre-heater may be disposed within the exhaust air flow path 120 upstream from the energy recovery device 1012 as well as the pre-heater 1016 within the supply air flow path 1006. As explained above, the energy recovery device 1012 uses exhaust air 1018 from the exhaust flow path 1020 to condition the supply air 1008 within the supply air flow path 1006. An additional energy recovery device (not shown) may be positioned within the supply air flow path 1006 downstream from the heat exchanger 1014, and upstream from the enclosed structure 1002. Additionally, while the energy recovery device 1012 is shown upstream from the heat exchanger 1014 within the supply air flow path 1006, the energy recovery device 1012 may, alternatively, be positioned downstream of the heat exchanger 1014 and upstream of the enclosed structure 1002 within the supply air flow path 1006. Additionally, the positions of the pre-heaters 1009 and 1016 may be reversed, such that the pre-heater 1009 is downstream from the pre-heater 1016 within the supply air flow path 1006.

After the supply air 1008 passes through the energy recovery device 1012 in the supply air flow path 1006, the supply air 1008, which at this point has been conditioned, encounters the heat exchanger 1014. The heat exchanger 1014 then further or fully heats the air 1008 in the supply air flow path 1006 to generate a change in air temperature toward a desired supply state that is desired for supply air discharged into the enclosed structure 1002. For example, during a winter mode operation, the heat exchanger 1014 may further condition the pre-conditioned air by adding heat to the supply air 1008 in the supply air flow path 1006.

The exhaust or return air 1018 from the enclosed structure 1002 is channeled out of the enclosed structure 1002, such as by way of exhaust fan 1022 or fan array within the exhaust flow path 1020. As shown, the exhaust fan 1022 is located upstream of the energy recovery device 1012 within the exhaust air flow path 1020. However, the exhaust fan 1022 may be downstream of the energy recovery device 1012 within the exhaust air flow path 1020.

The exhaust air 1018 passes through a regeneration side or portion of the energy recovery device 1012. The energy recovery device 1012 is regenerated by the exhaust air 1018 before conditioning the supply air 1008 within the supply air flow path 1006. After passing through the energy recovery device 1012, the exhaust air 1018 is vented to atmosphere through an air outlet 1024.

In an alternative embodiment, additional bypass ducts and dampers may be disposed within the supply air flow path 1006 and/or the exhaust air flow path 1020 in order to bypass airflow around the energy recovery device 1012.

The supply air 1008 encounters the pre-heater 1016 before the energy recovery device 1012, which may be an enthalpy wheel, flat plate exchanger, heat pipe, run-around, or the like, as discussed above. The pre-heaters 1009 and 1016 pre-heat the supply air 1008, and the energy recovery device 1012 pre-conditions the supply air 1008 in the supply air flow path 1006 before the supply air 1008 encounters the heat exchanger 1014. In this manner, the heat exchanger 1014 does not use as much energy as it normally would if the pre-heaters 1009, 1016, and the energy recovery device 1012 were not in place. Therefore, the heat exchanger 1014 operates more efficiently.

The heat exchanger 1014 may be or include a gas heater that coverts gas to heat, for example. Heated gas from the heater is vented as flue gas. As explained below, the vented flue gas is channeled to the pre-heater 1016 in order to pre-condition the supply air 1008 before it encounters the energy recovery device 1012.

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 ⅔) 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.

FIG. 11
a illustrates a schematic view of the heat exchanger 1014, according to an embodiment. As noted above, the heat exchanger 1014 is disposed within the supply air flow path 1006. The heat exchanger 1014 may be a heater that includes a housing 1026 that contains a gas-fired heater 1028, such as a furnace. Optionally, a boiler as described above may be used in place of the gas-fired heater 1028. The heater 1028 may generate heat through combustion. The heater 1028 heats the supply air 1008 as it passes through the heat exchanger 1014 within the supply air flow path 1006. As supply air 1008 passes through the heat exchanger 1014, the temperature of the supply air 1008 increases as it is heated by the heater 1028. Consequently, the temperature of the supply air 1008 is increased as it passes out of the heat exchanger 1014.

The flue gas from the heater 1028 is vented through a vent 1032 on or within the housing 1026. The heat exchanger 1014 may include a fan (not shown) that channels the flue gas into the vent 1032. Optionally, the fan may be disposed downstream of the vent 1032 within a conduit 1034. The conduit 1034 may be one or more pipes, tubes, plenum, or the like. For example, the conduit 1034 may be a series of pipes that connect the vent 1032 to another heat transfer device. The flue gas from the vent 1032 then passes into the conduit 1034 that sealingly engages the vent 1032 so that the flue gas may be channeled to another heat transfer device, as described below.

Alternatively, the heat exchanger 1014 may include radiator coils that contain circulating liquid, such as water, that is heated by the heater 1028. The heated liquid exchanges heat energy with the supply air 1008 as it passes through the radiator coils 1030. The radiator coil may be configured as shown and described in FIGS. 3-6.

FIG. 11
b illustrates a schematic view of a heat exchanger, according to an embodiment of the present disclosure. The heat exchanger 1114 may be disposed within a supply air flow path 1106. The heat exchanger 1114 includes a housing 1126 that contains a boiler 1128 and radiator coils 1130 that contain a liquid, such as water, that is heated by the boiler 1128. The boiler 1128 may generate heat through combustion. The boiler 1128 heats liquid that circulates through the radiator coils 1130. The radiator coils 1130 are positioned within and/or around the portion of the supply air flow path 1106 that passes through the heat exchanger 1114. As supply air 1108 passes through the heat exchanger 1114, the temperature of the supply air 1108 increases as it passes through the radiator coils 1130. That is, the heat of the liquid within the radiator coils 1130 is transferred to the supply air 1108. Consequently, the temperature of the supply air 1108 is increased as it passes out of the heat exchanger 1114.

The flue gas from the boiler 1128 is vented through a vent 1132 on or within the housing 1126. The heat exchanger 1114 may include a fan (not shown) that channels the flue gas into the vent 1132. Optionally, the fan may be disposed downstream of the vent 1132 within a conduit 1134. The conduit 1134 may be one or more pipes, tubes, plenum, or the like. For example, the conduit 1134 may be a series of pipes that connect the vent 1132 to another heat transfer device. The flue gas from the vent 1132 then passes into the conduit 1134 that sealingly engages the vent 1132 so that the flue gas may be channeled to another heat transfer device, as described below.

FIG. 12 illustrates an isometric top view of an exemplary furnace 1029, according to an embodiment of the present disclosure. The furnace 1029 is one example of a heater 1028 (shown in FIG. 11). The furnace 1029 includes a housing 1027 having a plurality of heating elements 1031 that span between lateral walls 1033 of the housing 1027. The heating elements 1031 may include channeled rods having openings through which flames pass, thereby generating heat. The furnace 1029 may be connected to a source of gas (not shown) that fuels the furnace 1029. As gas enters the heating elements 1031 and is ignited through an igniting element or pilot light within a control section 1035, flames are generated. Additionally, flue gas is also generated from the heating elements. The temperature of the flame generated by the heating elements 1031 may be approximately 2700° F., which generates a flue gas temperature of approximately 400° F. Various other furnaces may be used as the heater 1028. FIG. 12 merely shows one example of a furnace.

The heating elements 1031 may include tubes that contain gas that is ignited to produce heat. The gas may make several passes through the tubes before passing to the vent 1032, shown in FIG. 11. As air within the supply air flow path 1006 passes over the tubes 1031, the air is heated.

Smaller tubes may be disposed within each of the tubes. 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 1016 and/or the pre-heater 1009, shown in FIG. 10. In this manner, the heat transfer liquid may be directly heated within the furnace and transferred to the pre-heater 1016 and/or the pre-heater 1009 to heat the supply air 1006. As such, the temperature of the heat transfer liquid may be increased as it is directly heated within the furnace 1029 and directly transferred to the pre-heater.

Referring to FIGS. 10 and 11, flue gas from the heat exchanger 1014 is vented to the conduit 1034. The conduit 1034 channels the flue gas to a heat transfer device 1060, such as a heating coil, that may include an internal coil structure, similar to those described above. Alternatively, the flue gas may be transferred to a heating element within the boiler 1011 instead of, or in addition to, the heat transfer device 1060. The heated flue gas passes through an internal chamber (not shown) of the heat transfer device 1060 and/or the boiler 1011. As the flue gas passes through the heat transfer device 1060 and/or the boiler 1011, the heat from the flue gas is transferred to the liquid within the radiator coils of the heat transfer device 1060 and/or the internal chamber of the boiler 1011. 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 1062, for example (or through a chimney of the boiler 1011, as described with respect to FIG. 2). However, the liquid within the radiator coil of the heat transfer device 1060, having an increased temperature through heat transfer with the flue gas, is channeled to the pre-heater 1016 through a conduit 1064. The heated liquid is then passed from the conduit 1064 into an inlet 1065 of a coil 1066 of the pre-heater 1016. The pre-heater 1016 may also include radiator coils similar to those described above with respect to FIGS. 3-6. The liquid passed into the coil 1066, the temperature of which has risen due to the heat transfer with the flue gas, then transfers the increased heat to supply air 1008 that passes through the pre-heater 1016. Accordingly, the supply air 1008 is pre-heated (that is, the temperature of the supply air 1008 is increased) before it encounters the energy recovery device 1012.

As the liquid within the coil 1066 circulates therethrough, the temperature of the liquid decreases, as its heat is transferred to the supply air 1008. The cooled liquid within the radiator coil 1066 passes out of the radiator coil 1066 through an outlet 1067 and into a conduit 1068 that connects back to the heat transfer device 1060. The liquid is then heated again by heat transfer with the flue gas, and the process repeats.

A pump 1070 may be disposed within either of the conduits 1064, 1068, or both. The pump(s) 1070 aids in circulating the liquid between the heat transfer device 1060 to the pre-heater 1016. However, in at least one embodiment, the system 1000 does not include the pump.

While the pre-heaters 1009, 1016, and the heat transfer device 1060 are described as including liquid-conveying coils, the pre-heaters 1009, 1016 and the heat transfer device 1060 may be, or include, various other liquid-carrying and/or heating structures and components. For example, the pre-heater 1016 may include fluid-conveying plates. Similarly, the heat transfer device 1060 may be a heating plate(s). Additionally, each of the pre-heaters 1009, 1016 and the heat transfer device 160 may also include separate and distinct heating devices, similar to the heater 1028 shown in FIG. 11. However, the liquid that is circulated between the heat transfer device 1060 and the pre-heater 1016 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 1060 and the pre-heater 1016 may be also heated through an electric heater.

Additionally, while the heat transfer device 1060 is shown as being separate, distinct, and remote from the heat exchanger 1014 and the pre-heater 1016, the heat transfer device 1060 may be contained within a housing of the heat exchanger 1014 or the pre-heater 1016. For example, the heat transfer device 1060 may be mounted directly to the vent of the heat exchanger 1014 inside or outside of the housing of the heat exchanger 1014. As such, the heat exchanger 1014 and the heat transfer device 1060 may be disposed within a common housing.

The supply air 1008 (for example, air supplied from outdoor and/or ambient air) is pre-heated by the pre-heaters 1009 and 1016. The pre-heaters 1009 and 1016 increase the temperature of the supply air 1008 so that it will not form frost on the energy recovery device 1012. The pre-heater 1016 may increase the temperature of the supply air 1008 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 1000 is increased. Additionally, the pre-heaters 1009 and 1016 provide a more efficient system, in that they pre-heat the supply air 1008, thereby reducing the overall energy consumption of the downstream heat exchanger 1014 to further heat the supply air 1008.

Moreover, the pre-heaters 1009 and 1016 and the heat transfer device 1060 may be retrofit to any DOAS, thereby improving the efficiency of the DOAS.

FIG. 13 illustrates a schematic view of an energy recovery system 1380, according to an embodiment of the present disclosure. The system 1380 is similar to the system 1000, except that a heat exchanger 1314 is upstream from an energy recovery device 1312 within a supply air flow path 1306. Additionally, a heating device 1301 operatively connected to a boiler 1303 may be downstream from the energy recovery device 1312 within the supply air flow path 1306. Because the heating device 1301 is downstream from the energy recovery device 1312 and the heat exchanger 1314, the heating device 1301 may not be considered a pre-heater. However, the heating device 1301 may be configured to operate as the pre-heaters described above. Further, the heating device 1301 may be positioned at various other portions of the supply air flow path 1036, such as between a pre-heater 1316 and the heat exchanger 1314, or between the heat exchanger 1314 and the energy recovery device 1312.

As shown in FIG. 13, the supply air 1308 is further heated after the pre-heater 1316 before the supply air 1308 encounters the energy recovery device 1312. Thus, the possibility of frost forming on the energy recovery device 1312 is further reduced. The system 1380 may also include an additional heat exchanger downstream from the energy recovery device 1312 within the supply air flow path 1306.

FIG. 14 illustrates a schematic view of an energy recovery system 1490, according to an embodiment. The energy recovery system 1490 is similar to the system 1000, except that an additional heat exchanger 1492 is positioned upstream the energy recovery device 1412, and a pre-heater 1401 operatively connected to a boiler 1403 is downstream from the energy recovery device 1412 and upstream from a heat exchanger 1414 within the supply air flow path 1406. The heat exchanger 1492 may be a liquid-to-gas heat exchanger. Flue gas from both the heat exchangers 1414 and 1492 is vented into a shared conduit 1494 that channels the combined flue gas into a coil heater 1460. The pre-heater 1401 and the boiler 1403 may be configured to operate as described above. The system 1490 may include additional pre-heaters 1401 and boilers 1403.

Alternatively, the pre-heater 1401 may be positioned at various other portions of the supply air flow path 1406. For example, the pre-heater 1401 may be positioned between a pre-heater 1416 and the heat exchanger 1492, or between the heat exchanger 1492 and the energy recovery device 1412.

Additionally, in all of the embodiments of the present disclosure, an optional return air duct may connect an exhaust air flow path 1420 with the supply air flow path 1406. For example, an air duct may be downstream of the energy recovery device 1412 in the supply air flow path 1406, and upstream of the energy recovery device 1412 in the exhaust air flow path 1420. Alternatively, or additionally, an additional return air duct may be upstream of the energy recovery device 1412 in the supply air flow path 1406 and downstream of the energy recovery device 1412 within the exhaust air flow path 1420. The return air ducts may recycle a portion of the exhaust air 1418, which may be at a much higher temperature than outdoor air, into the supply air 1408, which further increases the temperature of the supply air 1408.

FIG. 15 illustrates a schematic view of an energy recovery system 1500, according to an embodiment of the present disclosure. The system 1500 is similar to the system 1000, except that return air ducts 1502, 1504, and 1506 connect an exhaust air flow path 1520 to a supply air flow path 1506. More or less return air ducts than those shown may be used. Moreover, the return air ducts may be used with any of the systems described above.

Additionally, a pre-heater 1501 operatively connected to a boiler 1503 may be disposed within the supply air flow path 1506 between an energy recovery device 1512 and a heat exchanger 1514. The pre-heater 1501 and the boiler 1503 are configured to operate as described above. The pre-heater 1501 may be disposed at various other portions of the supply air flow path 1506. For example, the pre-heater 1501 may be disposed between a pre-heater 1516 and the energy recovery device 1512. Additional pre-heaters 1501 and boilers 1503 may also be used.

The return air duct 1506 connects to the supply air flow path 1506 upstream of the pre-heater 1516. Thus, the temperature of the supply air 1508 may be increased even before it encounters the pre-heater 1516.

FIG. 16 illustrates a process of operating a direct outdoor air system, according to an embodiment. At 1620, 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.

At 1622, the flue gas is channeled to a heating device, such as a heating coil, plate, another heat exchanger, furnace, or the like. Next, at 1624, 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 1626. At the same time, at 1628, 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 1630, 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 1632, and then the process returns to 1624.

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.

FIG. 17 illustrates a process of operating a direct outdoor air system, according to an embodiment. At 1700, liquid within a boiler is heated. The liquid may be heated below a boiling point. Next, at 1702, the heated liquid is pumped from the boiler to one or more coils of a pre-heater disposed within a supply air flow path. The pre-heater may be disposed within any portion of the supply air flow path (and/or within any portion of an exhaust air flow path). Further, the heated liquid may be pumped to multiple pre-heaters.

At 1704, heat from the heated liquid is transferred to air within the supply air flow path. As the heated liquid moves through the coil(s), the temperature of the liquid decreases, as the heat is transferred to the air. As such, reduced-temperature liquid is pumped from the coil(s) of the pre-heater back to the boiler at 1706. The process then returns to 1700.

The processes of FIGS. 16 and 17 may occur in conjunction with one another. Each process may be performed simultaneously, or one of the processes may occur before the other.

Thus, embodiments provide systems and methods of heating air within a supply air flow path. Embodiments provide a system and method of heating supply air through heated liquid circulating within one or more coils of a heating device, such as a first pre-heater. Embodiments may also capture heat energy from exhaust flue gas, and recycle the heat energy back into the supply air by way of a second pre-heater. Embodiments provide a system and method of using heated liquid and recycled flue gas energy to pre-heat an air stream to reduce the need for defrosting in cold conditions. Overall, embodiments provide a highly-efficient DOAS.

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 disclosure 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 disclosure, 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 disclosure 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. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.

This written description uses examples to disclose the various embodiments of the disclosure, including the best mode, and also to enable any person skilled in the art to practice the various embodiments of the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments of the disclosure 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.

DEDICATED OUTDOOR AIR SYSTEM WITH PRE-HEATING AND METHOD FOR SAME

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