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Title:
ENERGY EXCHANGE ASSEMBLY WITH MICROPOROUS MEMBRANE
Document Type and Number:
WIPO Patent Application WO/2014/138859
Kind Code:
A1
Abstract:
An energy exchange assembly may include one or more membrane panels. The one or more membrane panels may include a microporous membrane that has a pore size between 0.02 and 0.3 micrometers (µm) and a porosity between 45% and 80%. Optionally, the energy exchange assembly may further include a plurality of spacers that define air channels. The air channels may be configured to receive air streams therethrough. Each of the one or more membrane panels may be disposed between two spacers. The one or more membrane panels may be configured to allow a transfer of sensible energy and latent energy across the one or more membrane panels between the air channels.

Inventors:
ERB BLAKE NORMAN (CA)
HANSON STEPHEN (CA)
AFSHIN MOHAMMAD (CA)
Application Number:
PCT/CA2014/000169
Publication Date:
September 18, 2014
Filing Date:
March 04, 2014
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
VENMAR CES INC (CA)
International Classes:
F28F21/00; F24F12/00; F28F3/08
Foreign References:
EP0661502A21995-07-05
AU2011286700A12012-12-06
Other References:
See also references of EP 2972048A4
Attorney, Agent or Firm:
SMART & BIGGAR (Vancouver, British Columbia V6E 3P3, CA)
Download PDF:
Claims:
WHAT IS CLAIMED IS:

1. An energy exchange assembly, comprising: one or more membrane panels, wherein the one or more membrane panels include a microporous membrane that has a pore size between 0.02 and 0.3 micrometers (μιη) and a porosity between 45% and 80%.

2. The energy exchange assembly of claim 1, further comprising a plurality of spacers that define air channels configured to receive air streams therethrough, the one or more membrane panels each disposed between two spacers, the one or more membrane panels configured to allow a transfer of sensible energy and latent energy across the one or more membrane panels between the air channels.

3. The energy exchange assembly of claim 2, wherein the plurality of spacers includes a first group of spacers and a second group of spacers, the first group of spacers is orthogonally oriented with respect to the second group of spacers.

4. The energy exchange assembly of claim 1 , wherein the microporous membrane is devoid of at least one of a hydrophilic or hydrophobic coating.

5. The energy exchange assembly of claim 1 , wherein the pore size of the microporous membrane is between 0.04 and 0.2 μπ .

6. The energy exchange assembly of claim 1, wherein the porosity of the microporous membrane is between 50% and 75%.

7. The energy exchange assembly of claim 1 , wherein the microporous membrane of the one or more membrane panels has a thickness between 15 and 30 μηι.

8. The energy exchange assembly of claim 1, wherein the microporous membrane has a vapor diffusion resistance below 40 seconds/meter (sec/m) and an air permeability below 0.06 ft /min/ft .

9. The energy exchange assembly of claim 1, wherein the one or more membrane panels further include a backing layer bonded to the microporous membrane for support, the one or more membrane panels having a stiffness of at least 20 MPa mm.

10. The energy exchange assembly of claim 8, wherein the backing layer includes a non-woven mesh with a larger pore size and porosity than the microporous membrane, wherein the backing layer does not significantly affect the transmission of vapor or air through the one or more membrane panels.

11. The energy exchange assembly of claim 1, wherein the microporous membrane is formed of at least one of expanded polytetrafluoroethylene (ePTFE), polypropylene (PP), nylon, polyvinylidene fluoride (PVDF), or polyethersulfone (PES).

12. An energy exchange system, comprising: a supply air flow path configured to channel supply air to an enclosed structure; a regeneration air flow path configured to channel regeneration air from the enclosed structure to an outside environment; and an energy exchange assembly disposed within the supply air flow path and the regeneration air flow path, wherein the energy exchange assembly comprises: a plurality of spacers; and a plurality of membrane panels, each membrane panel including a microporous membrane that has a pore size between 0.02 and 0.3 micrometers (μιτι) and a porosity between 45% and 80%, wherein each of the spacers is positioned between two of the membrane panels to define air channels through the spacer between the two membrane panels, the air channels configured to receive air streams therethrough, the membrane panels configured to allow a transfer of sensible energy and latent energy across the membrane panels between the air channels.

13. The energy exchange system of claim 12, wherein the microporous membrane is devoid of at least one of a hydrophilic or hydrophobic coating.

14. The energy exchange system of claim 12, wherein the pore size of the microporous membrane is between 0.04 and 0.2 μηι.

15. The energy exchange system of claim 12, wherein the porosity of the microporous membrane is between 50% and 75%.

16. The energy exchange system of claim 12, wherein the microporous membrane has a vapor diffusion resistance below 40 seconds/meter (sec/m) and an air permeability below 0.06 ft /min/ft .

17. The energy exchange system of claim 12, wherein the plurality of spacers includes a first group of spacers and a second group of spacers, the first group of spacers is orthogonally oriented with respect to the second group of spacers.

18. The energy exchange system of claim 12, wherein the membrane panels further include a backing layer bonded to the microporous membrane for support, the membrane panels having a stiffness of at least 20 MPa»mm.

19. The energy exchange system of claim 18, wherein the backing layer includes a non-woven mesh with a larger pore size and porosity than the microporous membrane, wherein the backing layer does not significantly affect the transmission of vapor or air through the membrane panels.

20. The energy exchange system of claim 12, wherein the microporous membrane is formed of at least one of expanded polytetrafluoroethylene (ePTFE), polypropylene (PP), nylon, polyvinylidene fluoride (PVDF), or polyethersulfone (PES).

Description:
ENERGY EXCHANGE ASSEMBLY WITH

MICROPOROUS MEMBRANE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application relates to and claims priority benefit from United States Patent Application No. 14/192,019, entitled "Energy Exchange Assembly With Microporous Membrane," filed February 27, 2014, which, in turn, relates to and claim priority benefits from United States Provisional Patent Application No. 61/784,638, entitled "Air-To-Air Energy Recovery Core With Microporous Membrane," filed March 14, 2013, which is hereby expressly incorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

[0002] Embodiments of the present disclosure generally relate to an energy exchange assembly, such as an energy recovery core, that incorporates a microporous membrane.

[0003] Energy exchange assemblies are used to transfer energy, such as sensible and/or latent energy, between fluid streams. For example, air-to-air energy recovery cores are used in heating, ventilation, and air conditioning (HVAC) applications to transfer heat (sensible energy) and moisture (latent energy) between two airstreams. A typical energy recovery core is configured to precondition outdoor air to a desired condition through the use of air that is exhausted out of the building. For example, outside or supply air is channeled through the energy recovery core in proximity to exhaust air. Energy between the supply and exhaust air streams is transferred therebetween. In the winter, for example, cool and dry outside air is warmed and humidified through energy transfer with the warm and moist exhaust air. As such, the sensible and latent energy of the outside air is increased, while the sensible and latent energy of the exhaust air is decreased. The energy recovery core typically reduces post-conditioning of the supply air before it enters the building, thereby reducing overall energy use of the system.

[0004] Air-to-air recovery cores may include a membrane through which heat and moisture are transferred between air streams. The membrane may be separated from adjacent membranes using a spacer. In an energy recovery core, the amount of heat transferred is generally determined by a temperature difference and convective heat transfer coefficient of the two air streams, as well as the material properties of the membrane. The amount of moisture transferred in the core is generally governed by a humidity difference and convective mass transfer coefficients of the two air streams, but also depends on the material properties of the membrane.

[0005] One known type of membrane used in an energy recovery core is a non- porous hygroscopic membrane. This membrane has a hygroscopic coating which is bonded to a resin or paper-like substrate material. The hygroscopic coating is used to drive moisture transfer through the membrane, while the substrate is used for an added layer of support. The hygroscopic coating may be configured to allow very little air transfer through the membrane at standard operating differential pressures. However, the ability for the membrane to transfer moisture typically depends on the relative humidity of the air. In a very humid environment, hygroscopic membranes have a low vapor diffusion resistance. In low humidity environments, however, hygroscopic membranes have a high vapor diffusion resistance. As such, an energy recovery core including such membranes generally exhibits a large change in latent effectiveness between heating and cooling conditions.

[0006] Another known type of membrane used in an energy recovery core is a composite polymer membrane. The composite polymer membrane has a thin vapor- promoting polymer film coated on a porous polymer substrate. The polymer film is used to drive moisture transfer through the membrane and prohibit airflow through the membrane at standard operating differential pressures. The porous polymer substrate may be used to reinforce the membrane while allowing the transfer of vapor therethrough. In adding and bonding multiple polymer layers together, however, the resistance to moisture transfer (i.e., the vapor diffusion resistance) through the membrane increases. Depending on the polymer film used in the composite membrane, the vapor diffusion resistance may be highly dependent on the relative humidity of the air streams. SUMMARY OF THE DISCLOSURE

[0007] Certain embodiments of the present disclosure provide an energy exchange assembly that may include one or more membrane panels. The one or more membrane panels may include a microporous membrane that has a pore size between 0.02 and 0.3 micrometers (μιη) and a porosity between 45% and 80%.

[0008] Optionally, the energy exchange assembly may further include a plurality of spacers that define air channels. The air channels may be configured to receive air streams therethrough. Each of the one or more membrane panels may be disposed between two spacers. The one or more membrane panels may be configured to allow a transfer of sensible energy and latent energy across the one or more membrane panels between the air channels. Optionally, the pore size of the microporous membrane may be between 0.04 and 0.2 μηι. The porosity of the microporous membrane may be between 50% and 75%. The microporous membrane may have a vapor diffusion resistance below 40 seconds/meter

3 2

(sec/m) and an air permeability below 0.06 ft /min/ft .

[0009] Certain embodiments of the present disclosure provide an energy exchange system that may include a supply air flow path configured to channel supply air to an enclosed structure, a regeneration air flow path configured to channel regeneration air from the enclosed structure to an outside environment, and an energy exchange assembly disposed within the supply air flow path and the regeneration air flow path. The energy exchange assembly may include a plurality of spacers and a plurality of membrane panels. Each membrane panel may include a microporous membrane that has a pore size between 0.02 and 0.3 micrometers (μιη) and a porosity between 45% and 80%. Each of the spacers may be positioned between two of the membrane panels to define air channels through the spacer between the two membrane panels. The air channels may be configured to receive air streams therethrough. The membrane panels may be configured to allow a transfer of sensible energy and latent energy across the membrane panels between the air channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 illustrates a perspective top view of an energy exchange assembly, according to an embodiment of the present disclosure.

[001 1] Figure 2 illustrates a perspective exploded top view of two adjacent layers of the energy exchange assembly shown in Figure 1, according to an embodiment of the present disclosure.

[0012] Figure 3 illustrates an end view of two adjacent layers of the energy exchange assembly shown in Figure 1 , according to an embodiment of the present disclosure.

[0013] Figure 4 illustrates a magnified microporous membrane of the energy exchange assembly shown in Figure 1, according to an embodiment of the present disclosure.

[0014] Figure 5 illustrates a graph plotting vapor diffusion resistance versus mean relative humidity for comparison between three membranes.

[0015] Figure 6 illustrates a simplified schematic view of an energy exchange system operatively connected to an enclosed structure, according to an embodiment of the present disclosure.

[0016] Before the embodiments are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of "including" and "comprising" and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. DETAILED DESCRIPTION OF THE DISCLOSURE

[0017] 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 the 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.

[0018] Figure 1 illustrates a perspective top view of an energy exchange assembly 10, according to an embodiment of the present disclosure. The energy exchange assembly 10 may be an energy recovery core, a plate heat exchanger, or the like configured to transfer energy between fluid streams, such as first and second air streams 12 and 14. As such, the energy exchange assembly 10 may be an air-to-air energy recovery core assembly.

[0019] The energy exchange assembly 10 may include a plurality of microporous membranes 16 separated by spacers 18. The membranes 16 may be formed of a microporous material that is configured to allow sensible and latent energy to pass therebetween. The membranes 16 may be designed with a pore size and a porosity that achieves a desired balance of air permeability and vapor permeability. For example, the characteristics of the microporous membranes 16 may be designed to enhance the transfer of vapor across the membranes 16 while also reducing the air transfer across the membranes 16. By stacking the membranes 16 and the spacers 18, channels 19 are formed that allow the first and second air streams 12 and 14 to pass through the energy exchange assembly 10.

[0020] The energy exchange assembly 10 may be oriented so that the first air stream 12 may be outside air that is to be conditioned, while the second air stream 14 may be exhaust, return, or scavenger air that is used to condition the outside air before the outside air is supplied to downstream HVAC equipment and/or an enclosed space as supply air. Heat and moisture may be transferred between the first and second air streams 12 and 14 through the membranes 16 within the energy exchange assembly 10.

[0021] The microporous membranes 16 and spacers 18 may be secured between outer upstanding brackets 20, a base 22, and a top wall 24. As shown, the brackets 20 may generally be at the corners of the energy exchange assembly 10. The base 22, the top wall 24, and the brackets 20 provide a main housing defining an internal chamber into which the membranes 16 and the spacers 18 are secured.

[0022] The energy exchange assembly 10 may include a plurality of layers or levels 26 which are vertically stacked along an elevation axis z. Each layer 26 may include a spacer 18 positioned between two microporous membranes 16. One membrane 16 may be below the spacer 18, while the other membrane 16 in the layer 26 is disposed above the spacer 18. In an embodiment, the spacers 18 and membranes 16 are stacked in an alternating pattern such that only one membrane 16 separates adjacent spacers 18. Thus, adjacent layers 26A, 26B may share one membrane 16. The spacers 18 in adjacent layers 26A, 26B may be oriented orthogonally to each other such that the air channels 19 through the spacers 18 channel the air in different directions. For example, the air channels 19 in the layers 26A may be oriented parallel to an axis y, while the air channels 19 in the layers 26B may be oriented parallel to an axis x, which is perpendicular (or oriented at an acute angle) to the axis y. Thus, the levels 26A may be oriented to receive the second air stream 14 at an inlet side 30 and direct the second air stream 14 to an outlet side 31, while the levels 26B may be oriented to receive the first air stream 12 at an inlet side 32, which is perpendicular to the inlet side 30, and direct the first air stream 12 to an outlet side 33, which is perpendicular to the outlet side 31. Therefore, the air stream 14, passing through the levels 26A, travels in a cross-flow direction with the air stream 12 passing through the levels 26B. In this manner, sensible and/or latent energy may be exchanged between the levels 26A and 26B.

[0023] For example, as shown in Figure 1, the first air stream 12 may enter the inlet side 32 as cool, dry air. As the first air stream 12 passes through the energy exchange assembly 10, the temperature and humidity of the first stream 12 are both increased through energy transfer with the second air stream 14 that enters the energy exchange assembly 10 through the inlet side 30 as warm, moist air. Accordingly, the first air stream 12 passes out of the outlet side 33 as warmer, moister air (as compared to the first air stream 12 before passing into the inlet side 32), while the second air stream 14 passes out of the outlet side 31 as cooler, drier air (as compared to the second air stream 14 before passing into the inlet side 30). In general, the temperature and humidity of the first and second air streams 12 and 14 passing through the levels 26A and 26B tends to at least partially equilibrate with one another. For example, warm, moist air within the levels 26A is cooled and dried by heat exchange with the cooler, drier air in the levels 26B. Cool, dry air within the levels 26B is warmed and moistened by the warmer, cooler air within the levels 26A. As a result, the second air stream 14 that passes through the levels 26A may be cooler and drier after passing through the energy exchange assembly 10. Conversely, the first air stream 12 that passes through the levels 26B may be warmer and moister after passing through the energy exchange assembly 10.

[0024] Figure 2 illustrates a perspective exploded top view of two adjacent layers 26 of the energy exchange assembly 10 shown in Figure 1, according to an embodiment of the present disclosure. The layers 26 include alternating spacers 18 and microporous membranes 16, which are stacked on top of each other in a layer stack 202. The microporous membranes 16 may form a part of membrane panels 206, which are alternatively stacked with the spacers 18. The membrane panels 206 may each include a sheet of the microporous membrane 16 and an outer frame 208 to which the membrane 16 is attached, disposed, or integrated. The outer frame 208 may be a plastic or other polymer frame that retains the microporous membrane 16 in a stretched or at least tight configuration within an inner space (not shown) defined by the frame 208. The frame 208 may engage the spacers 18 when assembling the layer stack 202. In an alternative embodiment, the membrane panels 206 do not include an outer frame 208.

[0025] The microporous membranes 16 may include thin, porous sheets composed of expanded polytetrafluoroethylene (ePTFE), polypropylene (PP), nylon, polyvinylidene fluoride (PVDF), polyethersulfone (PES), combinations thereof, or the like. The membranes 16 may be hydrophobic or hydrophilic (for example, if composed of nylon). The membranes 16 optionally may be manufactured by a dry stretch process, a wet stretch process, or another process. In at least one embodiment, the membrane panels 206 may include a backing layer (not shown in Figure 2) that is bonded to the microporous membrane 16 to provide structural support to the membrane 16. The backing layer may be a spunbond non-woven or a non-woven mesh. The backing layer may be made from materials including polypropylene (PP), polyethylene (PE), polyester, nylon, fiberglass, and/or the like. The backing layer of the membrane panel 206 provides support to the microporous membrane 16, making the membrane 16 stiffer and more durable. In at least one embodiment, each backing layer is bonded to a single sheet or layer of the microporous membrane 16 to form each membrane panel 206.

[0026] The spacers 18 may be formed of plastic, metal, or the like. As shown in Figure 2, the spacers 18 include walls 210 that are aligned parallel to each other, and connecting cross-bars 212 that structurally support the walls 210. The air channels 19 are formed between adjacent walls 210 and extend along the length of the walls 210. For example, the walls 210 may engage the membrane panels 206 above and below the spacer 18. The height of the walls 210 may define the height of the channels 19. The cross-bars 212 may have a small height relative to the walls 210 to prohibit the cross-bars 212 from impeding the flow of air through the channels 19. In alternative embodiments, the spacers 18 may have various other sizes and shapes. For example, the spacers may be corrugated with curved, undulating walls or saw tooth angled walls instead of upstanding walls.

[0027] During assembly of the layer stack 202, a lower spacer 18A is mounted on top of a lower membrane panel 206A. A middle membrane panel 206B is subsequently mounted on top of the spacer 18 A. An upper spacer 18B is then mounted on the middle membrane panel 206B, and an upper membrane panel 206C is mounted on the upper spacer 18B. As used herein, relative or spatial terms such as "top," "bottom," "upper," "lower," and "middle" are only used to distinguish the referenced elements and do not necessarily require particular positions or orientations in the energy exchange assembly 10 (shown in Figure 10) or in the surrounding environment of the energy exchange assembly 10. The stacking pattern may continue to produce an energy exchange assembly 10 of a desired height. In an embodiment, the upper spacer 18B is rotated 90° relative to the lower spacer 18 A. Consequently, the channels 19 through the spacer 18 A are orthogonal to the channels 19 through the spacer 18B, so that air flows through the channels 19 of the adjacent layers 26A, 26B in a cross-flow direction. Alternatively, the membranes 16 and the spacers 18 may be arranged to support various other air flow orientations, such as counter-flow, concurrent flow, and the like.

[0028] Figure 3 illustrates an end view of two adjacent layers 26 of the layer stack 202 (shown in Figure 2) according to an embodiment of the present disclosure. The two layers 26 include three membrane panels 206 and two spacers 18 that separate the panels 206. The spacers 18 may each include upstanding parallel walls 210 that define air channels 19 therebetween. For example, the spacers 18 may be oriented orthogonally to each other such that the walls 210 of the upper spacer 18B are oriented perpendicularly to the walls 210 of the lower spacer 18 A. Air flow is configured to flow in the directions 220 and 222 through the air channels 19 between the membrane panels 206. Direction 220 is shown to extend into the page, and direction 222 is shown to extend towards the right. Optionally, the directions 220, 222 may be reversed. The first air stream 12 (shown in Figure 1) may be configured to flow in the direction 222, and the second air stream 14 (Figure 1) may be configured to flow in the direction 220. Sensible and latent energy may be transferred to or from the air streams in the direction of arrows 224 through the membrane panels 206. The membrane panels 206 include a microporous membrane (shown in Figure 2) that is designed to maximize the amount of vapor that transfers across the membrane panels 206 while minimizing the transfer of air across the panels 206.

[0029] Figure 4 illustrates a magnified microporous membrane 16 of the energy exchange assembly 10 shown in Figure 1 , according to an embodiment. In order to balance the air permeability with vapor permeability (for example, vapor diffusion resistance), the microporous membrane 16 may have a specific range of characteristics. For example, the microporous membrane 16 may include various pores 402 that extend through the thin membranes 16. The pores 402 may have a pore size or diameter 404 that is less than 0.5 micrometers (μπι). In an embodiment, the pore size 404 of the pores 402 is between 0.01 and 0.4 μηι. As used herein, the term "between" that introduces a range of values means "between and including" such that the range includes the listed end values. More specifically, the pore size 404 may be between 0.02 and 0.3 μηι. More specifically, the pore size 404 may be between 0.04 and 0.2 μηι, or more specifically between 0.06 and 0.1 μηι. The pore size 404 and/or range of sizes is selected to reduce the vapor diffusion resistance of the membrane 16 to allow vapor transfer while also sufficiently reducing air permeability through the membrane 16. In an embodiment, the shape of the pores 402 is not limited. For example, the pores 402 may be elliptical, as shown in Figure 4, or may be rectangular, circular, or the like.

[0030] The microporous membrane 16 may have a porosity between 40% and 80%. The porosity is the fraction or percentage of voids or empty spaces within a material. In an embodiment, the porosity of the microporous membrane 16 may be between 45% and 80%. More specifically, the porosity may be between 50% and 75%, or more specifically between 55% and 70%.

[0031] In an embodiment, the microporous membrane 16 may have a membrane vapor diffusion resistance below 50 second/meters (sec/m) (measured using the DMPC method with the inlet air streams set to 5% relative humidity (RH) and 95% RH) and an air permeability below 0.08 ft 3 /min/ft 2 (0.041 cm 3 /sec/cm 2 ) at 0.5 inches of water (inH 2 0) (based on ASTM D737) (approximately 125 Pa). More specifically, the membrane vapor diffusion resistance may be below 40 sec/m and the air permeability below 0.06 ft 3 /min/ft 2

3 2

(0.03 cm /sec/cm ) at 0.5 inH 2 0. For example, the membrane vapor diffusion resistance may be below 35 sec/m and the air permeability below 0.0574 ft 3 /min/ft 2 (0.029 cm /sec/cm ) at 0.5 inH 2 0.

[0032] Referring now back to Figure 2, the thickness of the microporous membrane 16 also affects the rigidity and moisture vapor transfer rate (MVTR), which is directly related to the vapor diffusion resistance. For example, the rigidity of the membrane 16 increases by selecting a thicker material with the same pore size and porosity. However increasing the thickness of the membrane 16 reduces the MVTR. Therefore, the thickness may be selected to achieve a balance between rigidity and MVTR. The thickness of the membrane 16 may be reduced while preserving rigidity by laminating the membrane 16 onto the backing layer (not shown). For example, the thickness of the membrane 16 may be less than 50 μηι, such as between 10 and 40 μιη. More specifically, the thickness of the membrane 16 may be between 15 and 40 μηι. When the membrane 16 is bonded to the backing layer, the thickness of the membrane panel 206 may be between 100 and 400 μηι, such as between 200 and 300 μπι. The backing layer may have higher pore sizes and porosities relative to the microporous membrane 16, so the backing layer does not significantly affect (for example, has only a negligible impact on) vapor transmission and/or air transmission through the membrane panel 206. In at least one embodiment, the backing layer and the membrane 16 have a combined stiffness (defined as the product of the modulus of elasticity and the material thickness) above 15 MPa*mm. More specifically, the stiffness may be above 25 MPa » mm.

[0033] As an example, a microporous membrane for use in an air-to-air energy recovery core may be made out of polypropylene, with a pore size of 0.06 μπι, a porosity of 55%, and a thickness of 25 μιτι, and may be bonded it to a polyethylene mesh backing. The resulting membrane may have a vapor diffusion resistance of 28 sec/m, airflow permeability of 0.0146 ft 3 /min/ft 2 (0.0074 cm 3 /sec/cm 2 ) at 0.5 inches of water (inH 2 0) (approximately 125 Pa), and a stiffness of 55 MPa » mm. When the resulting membrane is used in the membrane panels of an energy exchange core having a size of 21 in. x 21 in. x 18.625 in. (53.3 cm x 53.3 cm x 47.3 cm) and a channel thickness of 3.5 mm, the resulting performance of the energy exchange core is a total effectiveness of 55% and an Outdoor Air Correction Factor of 1.07 at a differential pressure of 5 inH 2 0 (based on ASHRAE Standard 84) (approximately 1.244 kPa).

[0034] As another example, a microporous membrane for use in an air-to-air energy recovery core may be formed of polypropylene, having a pore size of 0.1 μιη, a porosity of 67%, and a thickness of 20 μιη, and is bonded it to a 3.0 oz. (approximately 85 g) polypropylene spunbond non-woven backing. The resulting membrane has a vapor diffusion resistance of 17 sec/m, airflow permeability of 0.0382 ft 3 /min/ft 2 (0.019

3 2

cm /sec/cm ) at 0.5 inH 2 0, and a stiffness of 27 MPa » mm. When the resulting membrane is used in the same energy exchange assembly of size 21 in. x 21 in. x 18.625 in. (53.3 cm x 53.3 cm x 47.3 cm) with a channel thickness of 3.5 mm, the resulting performance is a total effectiveness of 60% and an Outdoor Air Correction Factor of 1.07 at a differential pressure of 2 inH20 (based on ASHRAE Standard 84) (approximately 250 Pa).

[0035] Figure 5 illustrates a graph 500 plotting vapor diffusion resistance versus mean relative humidity for comparison between three membranes. The graph 500 compares a microporous membrane 502, as described herein, to other known membranes, including a non-porous hygroscopic membrane 504 and a composite polymer membrane 506. As shown in Figure 5, the microporous membrane 502 may have less vapor diffusion resistance than both the non-porous hygroscopic membrane 504 and the composite polymer membrane 506. In addition, the microporous membrane 502 may have a low (or even negligible) dependency on humidity, as shown by the relative lack of a slope 508 in the trend line for the microporous membrane 502. The vapor diffusion resistance of the other two membranes 504, 506 may be at least moderately dependent on humidity.

[0036] As seen in Figure 5, the disadvantage of the non-porous hygroscopic membrane 504 is that the ability for the membrane to transfer moisture is highly dependent on the relative humidity of the air. In a very humid environment, hygroscopic membranes have a low vapor diffusion resistance, while in a low humidity environment, the membranes have a high vapor diffusion resistance. This characteristic is shown by the drastic slope 510 in Figure 5 as the humidity increases.

[0037] One of the primary disadvantages of the composite polymer membrane 506 is that by adding and bonding multiple polymer layers together, the resistance to moisture transfer through the membrane increases. Thus, as shown in Figure 5, the vapor diffusion resistance is significantly higher than that of the microporous membrane 502. Depending on the polymer film used in the composite membrane 506, the vapor diffusion resistance may also be at least moderately dependent on the relative humidity of the air, as seen in Figure 5 by the negative slope 512 of the trend line for the composite membrane 506.

[0038] In addition, although not shown in Figure 5, manufacturing the microporous membrane as a single layer membrane with a supporting backing layer may be cheaper to produce than typical multi-layer membranes. The typical multi-layer membranes either incorporate a hydrophobic or hydrophilic coating or an additional second membrane layer in order to achieve low water vapor diffusion resistance and low air permeability. In an exemplary embodiment, the microporous membrane does not include any additional coating or layer, excluding the support backing which does not affect vapor diffusion or air permeability.

[0039] Figure 6 illustrates a simplified schematic view of an energy exchange system 300 operatively connected to an enclosed structure 302, according to an embodiment of the present disclosure. The energy exchange system 300 may include a housing 304, such as a self-contained module or unit that may be mobile (for example, the housing 304 may be moved among a plurality of enclosed structures), operatively connected to the enclosed structure 302, such as through a connection line 306, such as a duct, tube, pipe, conduit, plenum, or the like. The housing 304 may be configured to be removably connected to the enclosed structure 302. Alternatively, the housing 304 may be permanently secured to the enclosed structure 302. As an example, the housing 304 may be mounted to a roof, outer wall, or the like, of the enclosed structure 302. The enclosed structure 302 may be a room of a building, a commodities storage structure, or the like.

[0040] The housing 304 includes a supply air inlet 308 that connects to a supply air flow path 310. The supply air flow path 310 may be formed by ducts, conduits, plenum, channels, tubes, or the like, which may be formed by metal and/or plastic walls. The supply air flow path 310 is configured to deliver supply air 312 to the enclosed structure 302 through a supply air outlet 314 that connects to the connection line 306. The supply air 312 may be received in the supply air flow path 310 from the atmosphere (for example, an outside environment). Alternatively, the supply air 312 may be received from the enclosed structure 302 as return supply air.

[0041] The housing 304 also includes a regeneration air inlet 316 that connects to a regeneration air flow path 318. The regeneration air flow path 318 may be formed by ducts, conduits, plenum, tubes, or the like, which may be formed by metal and/or plastic walls. The regeneration air flow path 318 is configured to channel regeneration air 320 received from the enclosed structure 302 to the atmosphere (for example, an outside environment) through an exhaust air outlet 322. Alternatively, the regeneration air 320 may be received from the atmosphere and channeled back to the atmosphere through the exhaust air outlet 322.

[0042] As shown in Figure 6, the supply air inlet 308 and the regeneration air inlet 316 may be longitudinally aligned. For example, the supply air inlet 308 and the regeneration air inlet 316 may be at opposite ends of a linear column or row of ductwork. A separating wall 324 may separate the supply air flow path 310 from the regeneration air flow path 318 within the column or row. Similarly, the supply air outlet 314 and the exhaust air outlet 322 may be longitudinally aligned. For example, the supply air outlet 314 and the exhaust air outlet 322 may be at opposite ends of a linear column or row of ductwork. A separating wall 326 may separate the supply air flow path 310 from the regeneration air flow path 318 within the column or row.

[0043] The supply air inlet 308 may be positioned above the exhaust air outlet 322, and the supply air flow path 310 may be separated from the regeneration air flow path 318 by a partition 328. Similarly, the regeneration air inlet 316 may be positioned above the supply air outlet 314, and the supply air flow path 310 may be separated from the regeneration air flow path 318 by a partition 330. Thus, the supply air flow path 310 and the regeneration air flow path 318 may cross one another proximate to a center of the housing 304. While the supply air inlet 308 may be at the top and left of the housing 304, the supply air outlet 314 may be at the bottom and right of the housing 304. Further, while the regeneration air inlet 316 may be at the top and right of the housing 304, the exhaust air outlet 322 may be at the bottom and left of the housing 304.

[0044] Alternatively, the supply air flow path 310 and the regeneration air flow path 318 may be inverted and/or otherwise re-positioned. For example, the exhaust air outlet 322 may be positioned above the supply air inlet 308. Additionally, alternatively, the supply air flow path 310 and the regeneration air flow path 318 may be separated from one another by more than the separating walls 324 and 326 and the partitions 328 and 330 within the housing 304. For example, spaces, which may contain insulation, may also be positioned between segments of the supply air flow path 310 and the regeneration air flow path 318. Also, alternatively, the supply air flow path 310 and the regeneration air flow path 318 may simply be straight, linear segments that do not cross one another. Further, instead of being stacked, the housing 304 may be shifted 90 degrees about a longitudinal axis aligned with the partitions 328 and 330, such that that supply air flow path 310 and the regeneration air flow path 318 are side-by-side, instead of one on top of another.

[0045] An air filter 332 may be disposed within the supply air flow path 310 proximate to the supply air inlet 308. The air filter 332 may be a standard HVAC filter configured to filter contaminants from the supply air 312. Alternatively, the energy exchange system 300 may not include the air filter 332.

[0046] An energy transfer device 334 may be positioned within the supply air flow path 310 downstream from the supply air inlet 308. The energy transfer device 334 may span between the supply air flow path 310 and the regeneration air flow path 318. For example, a supply portion or side 335 of the energy transfer device 334 may be within the supply air flow path 310, while a regenerating portion or side 337 of the energy transfer device 334 may be within the regeneration air flow path 318. In an alternative embodiment, the energy transfer device 334 or an additional energy transfer device may be disposed within the supply air flow path 310 downstream of the energy exchange assembly 336 and within the regeneration air flow path 318 upstream of the energy exchange assembly 336 in order to provide energy transfer between the supply air 312 and the regeneration air 320. The energy transfer device 334 may be a desiccant wheel, a heat pipe, or a heat plate, for example. However, the energy transfer device 334 may be various other systems and assemblies, such as including liquid-to-air membrane energy exchangers (LAMEEs), as described below.

[0047] An energy exchange assembly 336, which may be formed as described above with respect to Figures 5-16, is disposed within the supply air flow path 310 downstream from the energy transfer device 334. The energy exchange assembly 336 may be positioned at the junction of the separating walls 324, 326 and the partitions 328, 330. The energy exchange assembly 336 may be positioned within both the supply air flow path 310 and the regeneration air flow path 318. As such, the energy exchange assembly 336 is configured to transfer energy between the supply air 3 2 and the regeneration air 320.

[0048] One or more fans 338 may be positioned within the supply air flow path 310 downstream from the energy exchange assembly 336. The fan(s) 338 is configured to move the supply air 312 from the supply air inlet 308 and out through the supply air outlet 314 (and ultimately into the enclosed structure 302). Alternatively, the fan(s) 338 may be located at various other areas of the supply air flow path 310, such as proximate to the supply air inlet 308. Also, alternatively, the energy exchange system 300 may not include the fan(s).

[0049] The energy exchange system 300 may also include a bypass duct 340 having an inlet end 342 upstream from the energy transfer device 334 within the supply air flow path 310. The inlet end 342 connects to an outlet end 344 that is downstream from the energy transfer device 334 within the supply air flow path 310. An inlet damper 346 may be positioned at the inlet end 342, while an outlet damper 348 may be positioned at the outlet end 344. The dampers 346 and 348 may be actuated between open and closed positions to provide a bypass line for the supply air 312 to bypass around the energy transfer device 334. Further, a damper 350 may be disposed within the supply air flow path 310 downstream from the inlet end 342 and upstream from the energy transfer device 334. The damper 350 may be closed in order to allow the supply air 312 to flow into the bypass duct 340 around the energy transfer device 334. The dampers 346, 348, and 350 may be modulated between fully-open and fully-closed positions to allow a portion of the supply air 312 to pass through the energy transfer device 334 and a remaining portion of the supply air 312 to bypass the energy transfer device 334. As such, the bypass dampers 346, 348, and 350 may be operated to control the temperature and humidity of the supply air 312 as it is delivered to the enclosed structure 302. Examples of bypass ducts and dampers are further described in United States Patent Application No. 13/426,793, entitled "System and Method For Conditioning Air In An Enclosed Structure," which was filed March 22, 2012, and is hereby incorporated by reference in its entirety. Alternatively, the energy exchange system 300 may not include the bypass duct 340 and dampers 346, 348, and 350.

[0050] As shown in Figure 6, the supply air 312 enters the supply air flow path 310 through the supply air inlet 308. The supply air 312 is then channeled through the energy transfer device 334, which pre-conditions the supply air 312. After passing through the energy transfer device 334, the supply air 312 is pre-conditioned and passes through the energy exchange assembly 336, which conditions the pre-conditioned supply air 312. The fan(s) 338 may then move the supply air 312, which has been conditioned by the energy exchange assembly 336, through the energy exchange assembly 336 and into the enclosed structure 302 through the supply air outlet 314.

[0051] With respect to the regeneration air flow path 318, an air filter 352 may be disposed within the regeneration air flow path 318 proximate to the regeneration air inlet 316. The air filter 352 may be a standard HVAC filter configured to filter contaminants from the regeneration air 320. Alternatively, the energy exchange system 300 may not include the air filter 352.

[0052] The energy exchange assembly 336 may be disposed within the regeneration air flow path 318 downstream from the air filter 352. The energy exchange assembly 336 may be positioned within both the supply air flow path 310 and the regeneration air flow path 318. As such, the energy exchange assembly 336 is configured to transfer sensible energy and latent energy between the regeneration air 320 and the supply air 312.

[0053] A heater 354 may be disposed within the regeneration air flow path 318 downstream from the energy exchange assembly 336. The heater 354 may be a natural gas, propane, or electric heater that is configured to heat the regeneration air 320 before it encounters the energy transfer device 334. Optionally, the energy exchange system 300 may not include the heater 354.

[0054] The energy transfer device 334 is positioned within the regeneration air flow path 318 downstream from the heater 354. As noted, the energy transfer device 334 may span between the regeneration air flow path 318 and the supply air flow path 310.

[0055] As shown in Figure 6, the supply side 335 of the energy transfer device 334 is disposed within the supply air flow path 310 proximate to the supply air inlet 308, while the regeneration side 337 of the energy transfer device 334 is disposed within the regeneration air flow path 310 proximate to the exhaust air outlet 322. Accordingly, the supply air 312 encounters the supply side 335 as the supply air 312 enters the supply air flow path 310 from the outside, while the regeneration air 320 encounters the regeneration side 337 just before the regeneration air 320 is exhausted out of the regeneration air flow path 318 through the exhaust air outlet 322.

[0056] One or more fans 356 may be positioned within the regeneration air flow path 318 downstream from the energy transfer device 334. The fan(s) 356 is configured to move the regeneration air 320 from the regeneration air inlet 316 and out through the exhaust air outlet 322 (and ultimately into the atmosphere). Alternatively, the fan(s) 356 may be located at various other areas of the regeneration air flow path 318, such as proximate to the regeneration air inlet 316. Also, alternatively, the energy exchange system 300 may not include the fan(s).

[0057] The energy exchange system 300 may also include a bypass duct 358 having an inlet end 360 upstream from the energy transfer device 334 within the regeneration air flow path 318. The inlet end 360 connects to an outlet end 362 that is downstream from the energy transfer device 334 within the regeneration air flow path 318. An inlet damper 364 may be positioned at the inlet end 360, while an outlet damper 366 may be positioned at the outlet end 362. The dampers 364 and 366 may be actuated between open and closed positions to provide a bypass line for the regeneration air 320 to flow around the energy transfer device 334. Further, a damper 368 may be disposed within the regeneration air flow path 318 downstream from the heater 354 and upstream from the energy transfer device 334. The damper 368 may be closed in order to allow the regeneration air to bypass into the bypass duct 358 around the energy transfer device 334. The dampers 364, 366, and 368 may be modulated between fully-open and fully-closed positions to allow a portion of the regeneration air 320 to pass through the energy transfer device 334 and a remaining portion of the regeneration air 320 to bypass the energy transfer device 334. Alternatively, the energy exchange system 300 may not include the bypass duct 358 and dampers 364 and 166.

[0058] As shown in Figure 6, the regeneration air 320 enters the regeneration air flow path 318 through the regeneration air inlet 316. The regeneration air 320 is then channeled through the energy exchange assembly 336. After passing through the energy exchange assembly 336, the regeneration air 320 passes through the heater 354, where it is heated, before encountering the energy transfer device 334. The fan(s) 356 may then move the regeneration air 320 through the energy transfer device 334 and into the atmosphere through the exhaust air outlet 322.

[0059] As described above, the energy exchange assembly 336, which may be foraied according to any of the methods described above, may be used with respect to the energy exchange system 300. Optionally, the energy exchange assembly 336 may be used with various other systems that are configured to condition outside air and supply the conditioned air as supply air to an enclosed structure, for example. The energy exchange assembly 336 may be positioned within a supply air flow path, such as the path 310, and a regeneration or exhaust air flow path, such as the path 318, of a housing, such as the housing 304. The energy exchange system 300 may include only the energy exchange assembly 336 within the paths 310 and 318 of the housing 304, or may alternatively include any of the additional components shown and described with respect to Figure 6.

[0060] Embodiments of the present disclosure provide an energy exchange assembly, such as an energy recovery core, that utilizes a microporous membrane in membrane panels to increase the latent effectiveness of the assembly. The membrane panels may not require a hydrophilic layer or multiple composite layers, other than a structural backing layer which may be added for support. The microporous membrane may not be significantly dependent on the relative humidity of the air, which allows the energy exchange assembly to have a similar effectiveness in a hot, humid climate and a cool, dry climate. The microporous membrane may include many pores, which allow water vapor through the membrane. The pore size of the pores may be designed to increase the water vapor transfer rate and reduce the vapor diffusion resistance. Some air may also pass through the pores across the membrane, but the amount of airflow may be maintained at an acceptable level by optimizing the properties of the membrane. For example, the properties of the microporous membrane, such as pore size and porosity, may be designed to achieve a balance between optimizing vapor transfer while maintaining acceptable air leakage.

[0061] 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, 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. § 1 12(f), unless and until such claim limitations expressly use the phrase "means for" followed by a statement of function void of further structure.

[0062] 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.