US20140083648A1

Movatterモバイル変換

Info

Publication number: US20140083648A1
Application number: US13/625,912
Authority: US
Inventors: Maury Brad Wawryk
Original assignee: Venmar CES Inc
Current assignee: Nortek Air Solutions Canada Inc
Priority date: 2012-09-25
Filing date: 2012-09-25
Publication date: 2014-03-27
Also published as: CA2824726A1

Abstract

A Dedicated Outdoor Air System (DOAS) includes a heater configured to be disposed within a supply air flow path, at least one pre-heater configured to be upstream from the heat exchanger within one or both of the supply and exhaust air flow paths, 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.

Description

BACKGROUND OF THE INVENTION

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.

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) 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. 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

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.

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.

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.

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.

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.

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.

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.

The system may also include at least one additional heat exchanger operatively connected to the heat transfer device.

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.

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.

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 to bypass at least a portion of the supply air around one or both of the pre-heater or the energy recovery device.

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.

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.

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.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 2 illustrates a schematic view of the energy recovery device, according to an embodiment.

FIG. 3aillustrates a schematic view of a heat exchanger, according to an embodiment.

FIG. 3billustrates an isometric top view of an exemplary furnace, according to an embodiment.

FIG. 4 illustrates an isometric view of a radiator coil of a heat exchanger, according to an embodiment.

FIG. 5 illustrates an isometric view of a radiator coil of a heat exchanger, according to an embodiment.

FIG. 6 illustrates an isometric view of a radiator coil of a heat exchanger, according to an embodiment.

FIG. 7 illustrates an isometric view of a radiator coil of a heat exchanger, according to an embodiment.

FIG. 8 illustrates a schematic view of an energy recovery system, according to an embodiment.

FIG. 9 illustrates a schematic view of an energy recovery system, according to an embodiment.

FIG. 10 illustrates a schematic view of an energy recovery system, according to an embodiment.

FIG. 11 illustrates a process of operating a direct outdoor air system, according to an embodiment.

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.

FIG. 1 illustrates a schematic view of anenergy exchange system100 according to an embodiment. Thesystem100 is shown as a Dedicated Outdoor Air System (DOAS). Thesystem100 is configured to partly or fully condition air supplied to anenclosed structure102, such as a building or an enclosed room. Thesystem100 includes anair inlet104 fluidly connected to a supplyair flow path106. The supplyair flow path106 may channel supply air108 (such as outside air, air from a building adjacent to theenclosed structure102, or return air from a room within the enclosed structure102) to theenclosed structure102.Supply air108 in the supplyair flow path106 may be moved through the supplyair flow path106 by a fan orfan array110. The illustrated embodiment shows thefan110 located downstream of anenergy recovery device112 and a gas-fired heater orheat exchanger114. Theheat exchanger114 may be or include the gas-fired heater. Optionally, thefan110 may be positioned upstream of theenergy recovery device112 and/or theheat exchanger114. Also, alternatively,air108 within the supplyair flow path106 may be moved by multiple fans or a fan array or before and/or after theheat exchanger114.

Airflow passes from theinlet104 through the supplyair flow path106 where thesupply air108 first encounters apre-heater116. Abypass duct117 may be disposed in the supplyair flow path106. Thebypass duct117 may be connected to the supplyair flow path106 through aninlet damper119 upstream from the pre-heater116, and anoutlet damper121 downstream from thepre-heater116. When the

dampers

119 and121 are fully opened,supply air108 may be diverted or bypassed around thepre-heater116. The

dampers

117 and121 may be modulated to allow a portion of thesupply air108 to bypass around thepre-heater116.

Additionally, adamper123 may be disposed in the supplyair flow path106 upstream from thepre-heater116. When fully closed, thedamper123 preventssupply air108 from passing into thepre-heater116. Thedamper123 may be modulated in order to allow a portion of thesupply air108 to a portion of thesupply air108 to pass through the pre-heater116, while a remaining portion of thesupply air108 is bypassed through thebypass duct117.

After thesupply air108 passes through theenergy recovery device112 in the supplyair flow path106, thesupply air108, which at this point has been conditioned, encounters theheat exchanger114. Theheat exchanger114 then further or fully heats theair108 in the supplyair flow path106 to generate a change in air temperature toward a desired supply state that is desired for supply air discharged into theenclosed structure102. For example, during a winter mode operation, theheat exchanger114 may further condition the pre-conditioned air by adding heat to thesupply air108 in the supplyair flow path106.

The exhaust or returnair118 from theenclosed structure102 is channeled out of theenclosed structure102, such as by way ofexhaust fan122 or fan array within theexhaust flow path120. As shown, theexhaust fan122 is located upstream of theenergy recovery device112 within the exhaustair flow path120. However, theexhaust fan122 may be downstream of theenergy recovery device112 within the exhaustair flow path120.

Theexhaust air118 passes through a regeneration side or portion of theenergy recovery device112. Theenergy recovery device112 is regenerated by theexhaust air118 before conditioning thesupply air108 within the supplyair flow path106. After passing through theenergy recovery device112, theexhaust air118 is vented to atmosphere through anair outlet124.

In an alternative embodiment, additional bypass ducts and dampers may be disposed within the supplyair flow path106 and/or the exhaustair flow path120 in order to bypass airflow around theenergy recovery device112.

FIG. 2 illustrates a schematic view of theenergy recovery device112, according to an embodiment. A portion of theenergy recovery device112 is disposed within the supplyair flow path106, while another portion of theenergy recovery device112 is disposed within the exhaustair flow path120. Theenergy recovery device112 is configured to transfer heat and/or moisture between the supplyair flow path106 and the exhaustair flow path120. Theenergy recovery device112 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 inFIG. 2, theenergy device112 may be an enthalpy wheel.

An enthalpy wheel is a rotary air-to-air heat exchanger. As shown, supply air within the supplyair flow path106 passes in a direction counter-flow to the exhaust air within exhaustair flow path120. 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 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 is the medium for sensible energy transfer. As the wheel rotates between the supply and exhaust

air flow paths

106 and120, 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

106 and120, respectively. As the enthalpy wheel rotates, heat is picked up from the air within the exhaustair flow path120 and transferred to the supply air within the supplyair flow path106. As such, waste heat energy from the air within the exhaustair flow path120 is transferred to the matrix material and them from the matrix material to thesupply air108 within the supplyair flow path106, thereby raising the temperature of thesupply air108 by an amount proportional to the temperature differential between the air streams.

Optionally, theenergy recovery device112 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, theenergy recovery device112 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, theenergy recovery device112 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, theenergy recovery device112 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, toFIG. 1, assupply air108 enters the supplyair flow path106 through theinlet104, theunconditioned supply air108 encounters the pre-heater116 before theenergy recovery device112, 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 thesupply air108 will be raised as it moves through the pre-heater116 and encounters theenergy recovery device112. As such, in winter conditions, theenergy recovery device112 warms and/or humidifies the supply air.

A similar process occurs as theexhaust air118 encounters theenergy recovery device112 in the exhaustair flow path120. The sensible and/or latent energy transferred to theenergy recovery device112 in the exhaustair flow path120 is then used to pre-condition the air within the supplyair flow path106. Overall, theenergy recovery device112 pre-conditions thesupply air108 in the supplyair flow path106 before it encounters theheat exchanger114, and alters theexhaust air118 in the exhaustair flow path120. In this manner, theheat exchanger114 does not use as much energy as it normally would if the energy recovery device112 (and/or the pre-heater116) was not in place. Therefore, theheat exchanger114 operates more efficiently.

Theheat exchanger114 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, theheat exchanger114 may be a liquid-to-air heat exchanger. In general, the liquid and air are separated so that they do not mix. Theheat exchanger114 may include radiator coils that are positioned within or around the supplyair flow path106. Liquid, such as water or glycol, is circulated through the coils. Assupply air108 passes by the coils, heat from the liquid is transferred to thesupply air108, thereby further warming thesupply air108 before it passes into theenclosed structure102. 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-heater116 in order to pre-condition thesupply air108 before it encounters theenergy recovery device112. Alternatively, theheat exchanger114 may not include radiator coils, but may simply be a gas heater disposed within the supplyair flow path106, and configured to convert gas to heat and heat thesupply air108.

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 than2/3) 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.

FIG. 3aillustrates a schematic view of theheat exchanger114, according to an embodiment. As noted above, theheat exchanger114 is disposed within the supplyair flow path106. Theheat exchanger114 includes ahousing126 that contains a gas-firedheater128, such as a furnace, andradiator coils130 that contain a liquid, such as water or glycol. Theheater128 may generate heat through combustion. Theheater128 heats the radiator coils130 so that the liquid therein is heated. The radiator coils130 are positioned within and/or around the portion of the supplyair flow path106 that passes through theheat exchanger114. Assupply air108 passes through theheat exchanger114, the temperature of thesupply air108 increases as it passes through the radiator coils130. That is, the heat of the liquid within the radiator coils130 is transferred to thesupply air108. Consequently, the temperature of thesupply air108 is increased as it passes out of theheat exchanger114.

The flue gas from theheater128 is vented through avent132 on or within thehousing126. Theheat exchanger114 may include a fan (not shown) that channels the flue gas into thevent132. Optionally, the fan may be disposed downstream of thevent132 within aconduit134. Theconduit134 may be one or more pipes, tubes, plenum, or the like. For example, theconduit134 may be a series of pipes that connect thevent132 to another heat transfer device. The flue gas from thevent132 then passes into theconduit134 that sealingly engages thevent132 so that the flue gas may be channeled to another heat transfer device, as described below.

Alternatively, theheat exchanger114 may not include the radiator coils130. Instead, theheat exchanger114 may simply include the gas firedheater128 disposed within the supplyair flow path106.

FIG. 3billustrates an isometric top view of anexemplary furnace129, according to an embodiment. Thefurnace129 is one example of a heater128 (shown inFIG. 3a). Thefurnace129 includes ahousing127 having a plurality ofheating elements131 that span betweenlateral walls133 of thehousing129. Theheating elements131 may include channeled rods having openings through which flames pass, thereby generating heat. Thefurnace129 may be connected to a source of gas (not shown) that fuels thefurnace129. As gas enters theheating elements131 and is ignited through an igniting element or pilot light within acontrol section135, flames are generated. Additionally, flue gas is also generated from the heating elements. The temperature of the flame generated by theheating elements131 may be approximately 2700° F., which generates a flue gas temperature of approximately 400° F. Various other furnaces may be used as theheater128.FIG. 3bmerely shows one example of a furnace.

Theheating elements131 may include tubes that contain gas that is ignited to produce heat. The gas may make several passes through thetubes131 before passing to thevent132, shown inFIG. 3a. As air within the supplyair flow path106 passes over thetubes131, the air is heated.

FIG. 4 illustrates an isometric view of aradiator coil130aof theheat exchanger114, according to an embodiment. As shown inFIG. 4, theradiator coil130amay be atubular member140 having acircumferential channel142 surrounding anair passage144, which may be a portion of the supplyair flow path106. Liquid, such as water or glycol, is circulated through thecircumferential channel142. In this manner, liquid L may flow parallel to thesupply air108 as it passes through theair passage144. 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 inFIG. 4).

FIG. 5 illustrates an isometric view of aradiator coil130bof theheat exchanger114, according to an embodiment. In this embodiment, a plurality oftubes146 havingfluid channels148 surround anair passage150, which may be a portion of the supplyair flow path106. Liquid L, such as water or glycol, is circulated through thefluid channels148. In this manner, liquid may flow parallel to thesupply air108 as it passes through theair passage150. Optionally, the liquid may flow in a direction counter to the direction of the air flow.

FIG. 6 illustrates an isometric view of aradiator coil130cof theheat exchanger114, according to an embodiment. In this embodiment, theradiator coil130cmay include a series of fluid-filledplates152 disposed within anair passage154 that forms part of the supplyair flow path106. In this manner, thesupply air108 may flow across and parallel or counter to the liquid within theplates152.

FIG. 7 illustrates an isometric view of aradiator coil130dof theheat exchanger114, according to an embodiment. In this embodiment, thecoil130dincludes a plurality of liquid-carryingtubes156 that cross one another. Thetubes156 are disposed within anair passage158 that forms part of the supplyair flow path106. In this manner, thesupply air108 may flow across and parallel or counter to the liquid L within thetubes156.

Any of the radiator coils shown and described with respect toFIGS. 4-7 may be used with respect to a heat transfer device in addition to, or in lieu of, theheat exchanger114. For example, if theheat exchanger114 does not include radiator coils, but instead simply includes a gas heater, the radiator coils may be used with respect to a heat transfer device, such as described below.

Additionally, referring toFIGS. 3a-7, as noted, theheating elements131 of thefurnace129 may include tubes that contain gas that is ignited to produce heat. Smaller tubes may be disposed within each of thetubes131, similar to the configurations shown inFIGS. 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-heater116, shown inFIG. 1. In this manner, the heat transfer liquid may be directly heated within the furnace and transferred to the pre-heater116 to heat thesupply air106. As such, the temperature of the heat transfer liquid may be increased as it is directly heated within thefurnace129 and directly transferred to the pre-heater.

Referring toFIGS. 3a-7, theheat exchanger114 may be configured for parallel-flow, counter-flow, cross-flow, or a combination thereof. Theradiator coil130 shown inFIG. 3amay be any of the radiator coils130a,130b,130c,or130d.In parallel flow, thesupply air108 and the liquid within theradiator coil130 enter theheat exchanger114 at the same end, and travel parallel to one another to the other side. In counter-flow, thesupply air108 enters at a front end of theheat exchanger114, while the liquid enters theradiator coil130 at the back end. In cross-flow, thesupply air108 and the liquid within the radiator coil are generally perpendicular to one another within theheat exchanger114.

Referring toFIGS. 1 and 3a, as noted above, flue gas from theheat exchanger114 is vented to theconduit134. Theconduit134 channels the flue gas to aheat transfer device160, 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 theheat transfer device160. As the flue gas passes through theheat transfer device160, the heat from the flue gas is transferred to the liquid within the radiator coils of theheat transfer device160. The decreased-temperature flue gas (as heat from the flue gas has been transferred to the liquid) is then vented to the atmosphere through avent162. However, the liquid within the radiator coil of theheat transfer device160, having an increased temperature through heat transfer with the flue gas, is channeled to the pre-heater116 through aconduit164. The heated liquid is then passed from theconduit164 into aninlet165 of acoil166 of the pre-heater116. The pre-heater116 may also include radiator coils similar to that described above with respect toFIGS. 3a-7. The liquid passed into thecoil166, the temperature of which has risen due to the heat transfer with the flue gas, then transfers the increased heat to supplyair108 that passes through thepre-heater116. Accordingly, thesupply air108 is pre-heated (that is, the temperature of thesupply air108 is increased) before it encounters theenergy recovery device112.

As the liquid within thecoil166 circulates therethrough, the temperature of the liquid decreases, as its heat is transferred to thesupply air108. The cooled liquid within theradiator coil166 passes out of theradiator coil166 through anoutlet167 and into aconduit168 that connects back to theheat transfer device160. The liquid is then heated again by heat transfer with the flue gas, and the process repeats.

Apump170 may be disposed within either of the

conduits

164,168, or both. The pump(s)170 aids in circulating the liquid between theheat transfer device160 to thepre-heater116. However, in at least one embodiment, thesystem100 does not include the pump.

While the pre-heater116 and theheat transfer device160 are described as including liquid-conveying coils, the pre-heater116 and theheat transfer device160 may be, or include, various other liquid-carrying and/or heating structures and components. For example, the pre-heater116 may include fluid-conveying plates. Similarly, theheat transfer device160 may be a heating plate(s). Additionally, each of the pre-heater116 and theheat transfer device160 may also include separate and distinct heating devices, similar to theheater128 shown inFIG. 3. However, the liquid that is circulated between theheat transfer device160 and the pre-heater116 may be primarily or solely heated by way of heat transfer with the flue gas. Optionally, the liquid that is circulated between theheat transfer device160 and the pre-heater116 may be also heated through an electrical heater.

Additionally, while theheat transfer device160 is shown as being separate, distinct, and remote from theheat exchanger114 and the pre-heater116, theheat transfer device160 may be contained within a housing of the heat exchanger or thepre-heater116. For example, theheat transfer device160 may be mounted directly to the vent of theheat exchanger114 inside or outside of the housing of theheat exchanger114. As such, theheat exchanger114 and theheat transfer device160 may be disposed within a common housing.

Referring toFIGS. 1 and 3a, the supply air108 (that is, air supplied from outdoor and/or ambient air) is pre-heated by thepre-heater116. The pre-heater116 increases the temperature of thesupply air108 so that it will not form frost on theenergy recovery device112. The pre-heater116 may increase the temperature of thesupply air108 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 thesystem100 is increased.

The following example illustrates the increased efficiency of thesystem100. At point A, thesupply air108, which is outside air that enters through theinlet104, flowing at a rate of 4000 cubic feet/minute (cfin), has a temperature of −20° F. However, the desired temperature within theenclosed space102 at point B is 85° F., which represents a difference of 105° F. Therefore, thesystem100 needs to raise the temperature of the outside air by 105° F. It has been found that thesystem100, by way of harvesting the energy within the flue gas from theheat exchanger114, is able to raise the temperature of the outside air to a temperature that exceeds the frost point. Accordingly, thesystem100 that includes the pre-heater116 and flue gas energy harvestingheat transfer device160 renders frost control unnecessary, as thesupply air108 is raised to a temperature above the frost point before it encounters theenergy recovery device112. Accordingly, the energy recoverdevice112 does not need to be defrosted.

Moreover, the pre-heater116 and theheat transfer device160 may be retrofitted to any DOAS, thereby improving the efficiency of the DOAS.

FIG. 8 illustrates a schematic view of anenergy recovery system180, according to an embodiment. Thesystem180 is similar to thesystem100, except that theheat exchanger114 is upstream from theenergy recovery device112 within the supplyair flow path106. Therefore, the temperature of thesupply air108 is further heated after the pre-heater116 before thesupply air108 encounters theenergy recovery device112. Thus, the possibility of frost forming on theenergy recovery device112 is further reduced. Thesystem180 may also include an additional heat exchanger downstream from theenergy recovery device112 within the supplyair flow path106.

FIG. 9 illustrates a schematic view of anenergy recovery system190, according to an embodiment. Theenergy recovery system190 is similar to thesystem100, except that anadditional heat exchanger192 is positioned upstream theenergy recovery device112. Theheat exchanger192 may be a liquid-to-gas heat exchanger. Flue gas from both the

heat exchangers

114 and192 is vented into a sharedconduit194 that channels the combined flue gas into thecoil heater160.

Additionally, in all of the embodiments, such as shown inFIGS. 1,8, and9, an optional return air duct may connect the exhaustair flow path120 with the supplyair flow path106. For example, an air duct may be downstream of theenergy recovery device112 in the supplyair flow path106, and upstream of theenergy recovery device112 in the exhaustair flow path120. Alternatively, or additionally, an additional return air duct may be upstream of theenergy recovery device112 in the supplyair flow path106 and downstream of theenergy recovery device112 within the exhaustair flow path120. The return air ducts may recycle a portion of theexhaust air118, which may be at a much higher temperature than outdoor air, into thesupply air108, which further increases the temperature of thesupply air108.

FIG. 10 illustrates a schematic view of anenergy recovery system200, according to an embodiment. Thesystem200 is similar to thesystem100, except that

return air ducts

202,204, and206 connect the exhaustair flow path118 to the supplyair flow path106. More or less return air ducts than those shown may be used. Moreover, the return air ducts may be used with the

systems

180 and190 shown inFIGS. 8 and 9, respectively.

Thereturn air duct206 connects to the supplyair flow path106 upstream of the pre-heater116. Thus, the temperature of thesupply air108 may be increased even before it encounters thepre-heater116.

FIG. 11 illustrates a process of operating a direct outdoor air system, according to an embodiment. At220, 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.

At222, the flue gas is channeled to a heating device, such as a heating coil, plate, another heat exchanger, furnace, or the like. Next, at224, 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 at226. At the same time, at228, 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, at230, 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 at232, and then the process returns to224.

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.

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 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 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. 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 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.

Claims

What is claimed is:

1. An energy exchange system comprising:

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, wherein 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, and wherein the liquid is configured to be channeled to the at least one pre-heater 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.

2. The system ofclaim 1, further comprising one or more of pipes, tubes, conduits, or plenum connected between the heat transfer device and the heater, wherein 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.

3. The system ofclaim 1, wherein the energy exchange system is a Dedicated Outdoor Air System (DOAS).

4. The system ofclaim 1, wherein the energy recovery device is 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.

5. The system ofclaim 1, further comprising a heat exchanger, wherein the heat exchanger comprises the heater and at least one radiator coil configured to contain a heat transfer liquid, wherein the at least one radiator coil is configured to be disposed within or around a portion of the supply air flow path.

6. The system ofclaim 5, wherein the heat exchanger is a liquid-to-gas heat exchanger.

7. The system ofclaim 5, wherein the heat exchanger comprises one or more of a parallel flow heat exchanger, a counter flow heat exchanger, or a cross flow heat exchanger.

8. The system ofclaim 1, wherein the at least one pre-heater comprises a liquid-circulating coil in fluid communication with the heat transfer device, wherein the liquid-circulating coil is configured to be disposed within or around a portion of the supply air flow path.

9. The system ofclaim 1, further comprising a liquid-circulating coil configured to be disposed within or around a flue gas passage, wherein the liquid-circulating coil is configured to receive vented flue gas from the heater, and wherein the liquid-circulating coil is configured to be in fluid communication with the pre-heater.

10. The system ofclaim 1, wherein the heater is configured to be downstream from the energy recovery device within the supply air flow path.

11. The system ofclaim 1, wherein the heater is configured to be upstream from the energy recovery device within the supply air flow path.

12. The system ofclaim 1, further comprising at least one additional heat exchanger operatively connected to the heat transfer device.

13. The system ofclaim 1, further comprising at least one return air duct configured to fluidly connect the supply air flow path with the exhaust air flow path.

14. The system ofclaim 1, wherein the heat transfer device is remote from the heater and the pre-heater.

15. The system ofclaim 1, wherein energy from the flue gas prevents frost from forming on the energy recovery device.

16. The system ofclaim 1, further comprising at least one bypass duct configured to be disposed within the supply air flow path, wherein the at least one bypass duct is configured to bypass at least a portion of the supply air around one or both of the pre-heater or the energy recovery device.

17. The system ofclaim 1, wherein the heat transfer device and the heater are disposed within a common housing.

18. 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 comprising:

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.

19. The method ofclaim 18, further comprising 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.

20. The method ofclaim 18, further comprising recirculating the liquid back to the heat transfer device after the heat within the liquid has been transferred to the supply air.

21. The method ofclaim 18, further comprising passing the heated supply air to an energy recovery device after the heat within the liquid has been transferred to the supply air.

22. The method ofclaim 21, further comprising preventing frost from forming on the energy recovery device through the channeling operation.

23. The method ofclaim 18, further comprising bypassing at least a portion of the supply air around one or both of the pre-heater or an energy recovery device.

24. A Dedicated Outdoor Air System (DOAS) comprising:

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, wherein 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, and wherein 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.