Method and system for dehumidification and atmospheric moisture extraction with minimal energy consumption

Abstract

A method, system, and device for managing humidity in an HVAC system includes a nanostructured desiccant porous material configured to adsorb moisture from an inlet stream at a first atmospheric pressure and release moisture from the material when exposed to a second atmospheric pressure, the second atmospheric pressure being lower than the first atmospheric pressure, the nanostructured desiccant porous material being located within a specific location to allow the passage of moist air across the material and allow the adsorption of moisture onto the material. When coupled with a vacuum pump, the moisture can be collected and released from the material and the system, regenerating the material for future use and removing moisture from the stream at a significantly lower cost than existing processes.

Description

[Background technology]

[0001] (Federally funded research and development) This disclosure was made with government support under contract DE-AC0576RL01830 awarded by the U.S. Department of Energy. The government has certain rights in this invention.

[0002] (Priority Claim) This application claims the benefit of the earlier filing date of U.S. Patent Application No. 16 / 993,699, filed August 14, 2020, which is incorporated herein by reference in its entirety.

[0003] (Background to the disclosure) Humidity control of building air today is mostly achieved passively through condensation on the evaporator coils in HVAC systems. Moisture condensation generates significant amounts of latent heat, which increases the cooling load on the HVAC system and therefore increases overall energy use by 30% or more, depending on the local environment. Commercially available dehumidifiers are currently excessively large and expensive for use in the residential market and are rarely used in commercial buildings except where moisture control challenges dictate. None of these systems offer options for managing CO2 or other gases, such as volatile organic compounds (VOCs), which are becoming increasingly problematic as building envelopes become more dense. This disclosure provides examples and systems that offer a direction forward in overcoming these problems and offer advantages not found in the prior art.

[0004] Additional advantages and novel features of the present disclosure are described below and will be readily apparent from the description and implementations set forth herein. Therefore, the following description of the present disclosure is intended to be illustrative of the present disclosure and should not be construed as limiting in any way. Summary of the Invention [Means for solving the problem]

[0005] (summary) The following description provides examples of methods, systems, and devices for managing humidity in HVAC systems, particularly in ways that are significantly better and more cost-effective than those currently available. In one application, a humidity management system for an HVAC system is described, including a nanostructured desiccant porous material configured to adsorb moisture from an inlet stream at a first atmospheric pressure and release moisture from the material when exposed to a second atmospheric pressure, the second atmospheric pressure being lower than the first atmospheric pressure. Preferably, the nanoporous material is located within a structured material such as a desiccant bed, but other configurations, including 3D arrays, including configurations in rods, coatings on fins, or other structures, are also contemplated in certain applications. Multiple numbers of these structures can be interconnected, with or without connections to other features such as heat pipes in seals. A vacuum pump is preferably connected to the system and adapted to reduce the atmospheric pressure and provide sufficient suction to the nanostructured porous material to remove moisture from the nanostructured porous material, thus regenerating the adsorbent material.

[0006] In some embodiments, the nanostructured porous material may be MOF, zeolite, mesoporous silica, covalent organic framework material, porous organic polymer, and porous carbon. In one set of embodiments, the material is MOF, more specifically, MOF303, 801, or 841, with MOF303 or 801 showing the best performance in some situations.

[0007] In some cases, heat is used to enhance the performance of materials in the device. Heat can be transferred to these materials through operatively connected heat pipes or other means that bring heated materials from warmer parts of the system to the bed or structure to which the desiccant material is connected or merged. In one arrangement, the heat pipes are operatively connected to a set of fins with desiccant material attached to them. Moisture in the air passing across the fins then contacts and is adsorbed by the material. Providing pairs or sets of desiccant material-containing beds or other structures within the air passageways allows contact between the moisture-containing beds and the desiccant material as the air continuously dries while moving across the structures. This can enable continuous drying and increased efficiency. Additionally, when properly positioned and structured, the passages to these structures can be opened and closed to allow several passages, allowing one set to operate dehumidifying while a vacuum is applied to another section, removing moisture from the system and regenerating the adsorbent.

[0008] A method for drying moisture from ambient air is described. In the method, a moisture-containing air stream is passed over a nanostructured porous material configured to adsorb moisture from the inlet stream at a first atmospheric pressure and release moisture from the material when exposed to a second atmospheric pressure, the second atmospheric pressure being lower than the first atmospheric pressure. This causes moisture to collect on the nanostructured porous material, and reducing the ambient atmospheric pressure releases the moisture from the nanostructured porous material, regenerating the nanostructured porous material for additional moisture capture. The reduction in ambient pressure may be provided by a vacuum pump. The nanostructured porous material may be encapsulated in at least two operatively separated beds, whereby one bed is positioned to capture moisture from the air stream and the other is positioned to release the captured moisture. If desired, a heat transfer material can be provided in operative fluid communication between the first and second beds so that heat generated from one process can be passed to support the other process. In some cases, the heat transfer material may be contained within a conduit or heat pipe, resulting in more cost-effective heating and cooling by reducing the energy demands on the HVAC system.

[0009] The purpose of the foregoing Abstract is to enable the U.S. Patent and Trademark Office and the general public, particularly scientists, engineers, and persons of ordinary skill in the art who are not familiar with patent or legal terminology or language, to quickly determine the nature and substance of the present technical disclosure from a cursory inspection. The Abstract is not intended to define the present disclosure, as measured by the claims, or to be in any way limiting as to the scope of the present disclosure.

[0010] Various advantages and novel features of the present disclosure are set forth herein and will become more readily apparent to those skilled in the art from the following detailed description. In the foregoing and following description, the inventors have shown and described only preferred embodiments of the present disclosure as illustrations of the best modes contemplated for carrying out the disclosure. As will be recognized, the present disclosure is capable of modifications in various respects without departing from the present disclosure. Accordingly, the drawings and description of the preferred embodiments set forth hereinafter are to be regarded as illustrative in nature and not as restrictive. The present invention provides, for example, the following items. (Item 1) 1. A humidity control system for an HVAC system, comprising: 1. A humidity management system comprising: a nanostructured desiccant porous material configured to adsorb moisture from an inlet flow at a first atmospheric pressure and release moisture from the material when exposed to a second atmospheric pressure, the second atmospheric pressure being lower than the first atmospheric pressure. (Item 2) Item 10. The humidity management system of item 1, wherein the nanostructured desiccant porous material is located within at least one desiccant bed. (Item 3) 3. The humidity management system of claim 1 or claim 2, further comprising a vacuum pump adapted to provide sufficient suction to the nanostructured desiccant porous material to reduce the air pressure and remove moisture from the nanostructured desiccant porous material. (Item 4) 4. The humidity management system according to any one of items 1-3, wherein the nanostructured desiccant porous material is selected from the group consisting of MOFs, zeolites, mesoporous silica, covalent organic framework materials, porous organic polymers, and porous carbons. (Item 5) 5. The humidity management system of claim 4, wherein the nanostructured desiccant porous material is a MOF material. (Item 6) 6. The humidity management system of claim 5, wherein the nanostructured desiccant porous material comprises a MOF selected from the group consisting of MOF303, 801, or 841. (Item 7) 7. The humidity management system of claim 6, wherein the nanostructured desiccant porous material comprises MOF303 or 801. (Item 8) 8. The humidity management system of any of items 1-7, further comprising a heat delivery system for delivering heat to the nanostructured desiccant porous material. (Item 9) Item 9. The humidity management system of item 8, wherein the heat delivery system includes a heat pipe operatively configured to deliver heat to the nanostructured desiccant porous material. (Item 10) 10. The humidity management system of any of items 1-9, wherein the nanostructured desiccant porous material is embodied in a coating on fins. (Item 11) 11. The humidity management system of any of items 1-10, further comprising a first set of desiccant-containing beds and a second set of desiccant-containing beds, each of the first and second desiccant-containing beds containing a nanoporous desiccant material configured to remove moisture from an airflow passing across the bed. (Item 12) Item 12. The humidity management system of item 11, wherein the first desiccant bed and the second desiccant bed contain the same nanoporous desiccant material. (Item 13) Item 13. The humidity management system of any of items 1-12, wherein the nanostructured desiccant porous material is configured in a three-dimensional shape. (Item 14) Item 14. The humidity management system of item 13, wherein the three-dimensional shape is a rod. (Item 15) Item 15. The humidity management system of item 13 or item 14, wherein the three-dimensional shape is positioned within an air passage. (Item 16) 1. A method for removing moisture from an air stream without additional heating, said method comprising: 1. A method comprising passing a moisture-containing air stream across a nanostructured porous material configured to adsorb moisture from the inlet stream at a first atmospheric pressure and release moisture from the nanostructured porous material when exposed to a second atmospheric pressure, the second atmospheric pressure being lower than the first atmospheric pressure, to collect moisture on the nanostructured porous material, and then reducing the ambient atmospheric pressure to release moisture from the nanostructured porous material and regenerate the nanostructured porous material for additional moisture capture. (Item 17) 17. The method of claim 16, wherein the reduction in ambient pressure is provided by a vacuum. (Item 18) Item 18. The method of claim 16 or 17, wherein the nanostructured porous material is encapsulated in at least two operatively separated beds, whereby one bed is positioned to capture moisture from an airflow and the other is positioned to release the captured moisture. (Item 19) Item 19. The method of item 18, wherein the at least two operatively separated beds comprise a first bed and a second bed, and the method further comprises providing a heat transfer material in operative fluid communication between the first bed and the second bed such that heat generated from one process is passed to support the other process. (Item 20) 20. The method of claim 19, wherein the heat transfer material is contained within a conduit. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows a detailed schematic diagram of one example of an embodiment of the invention described in this description.

[0012] [Figure 2] FIG. 2 shows a comparison of the amount of power used to regenerate the present desiccant bed system compared to the load on the HVAC compressor removed as a function of the humidity level of the building's return air.

[0013] [Figure 3] FIG. 3 shows examples of various exemplary candidate moisture sorbent materials based on their working capacity over various ranges of relative humidity (9 RH).

[0014] [Figure 4] Figure 4 shows the water sorption performance of three exemplary MOFs (303, 841, and 801) at 25°C.

[0015] [Figure 5] Figure 5 shows the volumetric energy consumption for an isothermal AWE system for two fan efficiencies.

[0016] [Figure 6] FIG. 6 shows the volumetric water uptake of certain selected nanoporous materials.

[0017] [Figure 7] FIG. 7 shows the results for enhanced water sorption capacity via SO3H functionalization in UIO-66.

[0018] [Figure 8] FIG. 8 shows another embodiment of the invention in which the desiccant is coated onto fins made from graphene or other lightweight but thermally conductive support.

[0019] [Figure 9] FIG. 9 shows an implementation of a second schematic embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The following description includes one example of the present disclosure. It will be apparent from this description that the present disclosure is not limited to these exemplified embodiments, but also includes various modifications and embodiments thereof. Therefore, the description should be considered illustrative rather than limiting. While the present disclosure is susceptible to various modifications and alternative constructions, it is to be understood that there is no intention to limit the disclosure to the specific forms disclosed, but rather, the present disclosure is intended to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the present disclosure.

[0021] In one set of illustrations, a novel desiccant system for humidity management through a building's HVAC system is described. A new nanostructured porous material with an ultra-high moisture capacity is integrated into a desiccant bed and thermally coupled to a heat pipe. Building air is then passed across these beds to remove moisture. However, instead of using heat for desiccant regeneration as commercial dehumidifiers do, these advanced adsorbents support easy removal of adsorbed moisture at room temperature using a simple vacuum pump. The system thus eliminates the additional latent cooling load from condensation on the HVAC system's evaporator coil. The energy savings obtained more than compensate for the energy required to operate the vacuum pump, and the equipment footprint and capital cost are half that of today's commercial desiccant dehumidification systems. The system design can also support the inclusion of additional adsorbent materials within the desiccant bed, allowing for control of CO2 levels or removing VOCs from building air.

[0022] The operating principle is very simple: warm building air is passed over a desiccant bed, which removes moisture. The treated air is then passed through an air handler to an evaporator and cooled as in a standard HVAC system. However, the moisture content of the incoming air is reduced sufficiently so that its dew point is below the temperature of the evaporator coil, thus preventing condensation. Once the desiccant reaches its moisture uptake capacity, the building airflow is switched to contact a second desiccant bed, which has completed its regeneration cycle. The use of new ultra-high moisture capacity desiccant materials (MOFs and other desiccants) in our system allows for a sufficiently compact unit that it can fit within the confines of standard air handler ducts used in most commercial and residential HVAC installations. This integrated design eliminates the need for extensive modifications to the building's air handler layout and the space required for a large, dedicated dehumidification system, making it ideal for both new installations and retrofits.

[0023] Our much simpler approach uses a commercial off-the-shelf (COTS) vacuum pump to provide suction to the desiccant beds during their regeneration cycle. The desiccant bed temperature is controlled through the use of heat pipes to provide thermal coupling between the desiccant beds. This provides a passive, yet highly efficient, heat transfer mechanism that "offsets" the heat of water vapor adsorption generated in the active desiccant beds during dehumidification and the endothermic heat of desorption consumed in the desiccant bed undergoing regeneration. Thus, the desiccant beds are regenerated isothermally at building air temperature, without increasing the sensible heat load on the evaporator from desiccant regeneration. Water vapor released from the vacuum pump is simply vented to the ambient.

[0024] The use of new ultra-high moisture capacity desiccant materials (MOFs and other desiccants) in our system allows for a sufficiently compact unit that it can fit within the confines of standard air handler ducts used in most commercial and residential HVAC installations. This integrated design eliminates the need for extensive modification of a building's air handler layout and space for a large, dedicated dehumidification system, making it ideal for both new installations and retrofits.

[0025] Figures 1-9 illustrate various features and sample embodiments. In one example shown attached, a configuration is shown in which the use of a new ultra-high moisture capacity desiccant material allows for a sufficiently compact unit that it can fit within the confines of standard air handler ducts used in most commercial and residential HVAC installations. This integrated design eliminates the need for extensive modification of a building's air handler layout and space for a large, dedicated dehumidification system, making it ideal for both new installations and retrofits.

[0026] 1 shows a schematic diagram of one embodiment of the present invention, in which a desiccant bed 20 containing a desired material 22, preferably a metal-organic framework material such as MOF (more preferably MOF 303, 842, or 841, although various other materials can also be utilized depending on the needs and requirements of the user), is operatively positioned to allow moist, typically warm, air from a source such as the warm air return in a conventional HVAC unit to pass across the desiccant bed 20, with the material 22 in the desiccant bed 20 absorbing moisture from the moist air onto the material, allowing drier air to pass through the desiccant bed 20. The newly dried air can then be passed for cooling through the standard parts of a typical HVAC system, which can include an evaporator operatively connected to receive refrigerant from an expansion valve, whereby refrigerant flows through the evaporator to a compressor, which pumps the refrigerant through a fan-cooled condenser coil and back to the expansion valve, which controls the passage of refrigerant back into the evaporator. The now dry and cooled air can then be passed to a desired location. The desiccant bed 20 is also operatively connected to a vacuum pump 24, which provides suction to the material 22 within the desiccant bed 20 to remove moisture from the desiccant bed and evacuate the moisture elsewhere.

[0027] The operating principle is very simple: warm building air is passed over a desiccant bed, which removes moisture. The now-dried air is then passed through an air handler to an evaporator and cooled, as in a standard HVAC system. Desiccant regeneration occurs as suction draws moisture from the desiccant bed material and discharges it to a separate location. In continuously operating systems, trays of desiccant can be used, whereby once the desiccant from the first bed reaches its moisture-uptake capacity, the building airflow is switched to contact a second desiccant bed, which has completed its regeneration cycle. This process can be performed alternately or sequentially across several beds, with each bed being regenerated by vacuum suction while another captures moisture from a moist, typically warm, air source.

[0028] Various types of materials can be utilized as desiccant materials 22. Previous research into the development of various adsorbents for advanced refrigeration systems has established a unique database of moisture adsorption properties of various nanoporous materials, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic polymers (POPs), zeolites, mesoporous silica, and porous carbon. Our recent work has demonstrated the remarkable thermodynamic properties of certain hydrophilic nanoporous materials with large moisture sorption capacity and hydrothermal stability, establishing substantial and transformative improvements in the size, weight, and cost of commercial adsorption refrigeration devices (McGrail et al., 2014).

[0029] In this direction, we reviewed the data collected on these hydrophilic materials and developed materials that primarily emphasize the adsorption kinetics and precise tuning of their moisture adsorption properties. The tunability of the materials is advantageous for this application because the desorption kinetics must be facile under simple vacuum without any heating. To this end, we followed two main approaches for tailoring the desiccant materials: (i) providing suitably shaped / sized hydrophilic / hydrophobic functional groups on the organic linkers, and (ii) modifying / tuning the hydrophilicity of pre-reserved metal-containing cluster nodes with different functional groups. The result was an adsorbent material that exhibited mild hydrophobic properties at low RH, accompanied by a sharp sigmoidal rise in moisture adsorption (Type V isotherm) at RH >20%.

[0030] An example of the ability to tailor adsorbent properties through pore tailoring or pore engineering design concepts involving SO3H functionalization on MOF UIO-66 nodes exhibiting desired isotherm types and moisture sorption behavior is illustrated in Figure 7. Varying the concentration of SO3H groups on the nodes clearly affects their moisture sorption properties. Similarly, adding different hydrophilic terminal functional groups (HCCO) to the clusters significantly improves the water sorption behavior. - , CH3COO - , HO / OH, and PhCOO -) provides precise control of the water uptake step over a range of RH, due to the variation in hydrophobic / hydrophilic pore properties associated with differences in pore / cluster / functionality shapes and sizes.

[0031] While these examples were deemed viable for one example, in other sequences, materials with Type V isotherm shoulders in the 20-65% RH range and work capacities greater than 50 wt% were selected. Two zirconium-based MOFs, MOF-841 and MOF-801, and the aluminum-based MOF-303, were specifically chosen for their high chemical stability and required water sorption capacity, as well as regenerative properties demonstrated by cycle testing to ensure no degradation of adsorption properties. Furthermore, we anticipate that these materials can be synthesized in commercial quantities using PNNL's atomization-condensation reactor technology (MOTKURI, 2016) or other synthesis methods.

[0032] MOF-801 and MOF-303 have been shown to perform best under current operating conditions. Because the required amount of adsorbent is expected to be in the kilogram-scale range, we have successfully synthesized MOF-801 in bulk, which has already been prepared and tested at approximately 100 gram scale. To prepare these MOFs, 50 mmol of each of fumaric acid and ZrOCl2·8HO were dissolved in a 500 mL screw-cap jar in a mixture of DMF and formic acid (200 mL and 70 mL), respectively, and then heated overnight at 130 °C to yield MOF-801 as a white precipitate. Similarly, MOF-303 was synthesized using 43.1 mmol of 3,5-pyrazoledicarboxylic acid monohydrate dissolved in deionized HO (approximately 750 mL) to which base (NaOH or LiOH solution, approximately 65 mmol) was added dropwise under vigorous stirring. The resulting mixture was heated in a preheated oven at 120 °C for 60–90 min. After cooling to RT, 43.1 mmol of AlCl3·6H2O was slowly added to the solution with constant vigorous stirring. Any precipitate that formed in the solution was dissolved under prolonged sonication. The clear solution was transferred to an autoclave and heated in the oven at 100 °C for 15–24 h to obtain the MOF powder. The obtained MOF powder material was activated by solvent and thermal activation before being exposed to moisture sorption. The activated material was characterized using powder X-ray diffraction (PXRD) for crystallinity, thermogravimetric analysis to understand the material's stability, and N2 adsorption isotherms for porosity measurements. Fully characterized samples were tested for their moisture sorption measurements at room temperature and then extended to the multiple temperatures required for this study.

[0033] Once the materials were characterized, they were scaled up for bulk production using PNNL's atomization condensation reactor technology (MOTKURI, 2016). This technology provides a low-cost and scalable method for producing adsorbent materials (e.g., MOFs) in bulk quantities. While these specific materials were demonstrated in one application, various other materials have also been identified for use in such systems. A non-exclusive and non-limiting list includes, but is not limited to, zeolites such as AlPO4-34, AlPO4-LTA, AlPO4-CHA, 13X, and SAPO-34; mesoporous silicas such as MCM-41 and SBA-15; Zr- and Al-based MOFs; MIL-group MOFs; MOFs containing Co2Cl2 (BTDD); covalent organic frameworks; porous organic polymers; and porous carbons.

[0034] Figure 6 shows the water uptake kinetics for several MOFs. These results demonstrate design flexibility in that particle sizes can be reduced from these nominal values ​​to increase moisture flux rates if achieving continuous diffusive transport over these distances proves difficult. Overall, our systems analysis indicates that water uptake in the adsorbent should reach 11 wt % in the targeted 90-second half-cycle. As shown in Figure 6, there is solid evidence that this uptake rate is achievable. Adsorbent development teams will need to narrow down desiccants that can achieve this uptake rate through a combination of physical properties, including specific surface area, particle size, and intracrystalline water diffusion.

[0035] The system design team ensured that water vapor transport to the desiccant surface was sufficient to support the rate of moisture uptake by the desiccant, while minimizing backpressure on the ventilation fan and saving energy. Achieving this balance is expected to be most difficult during the adsorption portion of the cycle. Because vacuum is applied nearly uniformly across the desiccant bed during desorption, the rate of moisture removal should also be relatively uniform. Because the desorption rate can be well controlled by varying the suction pressure, maintaining an approximate balance between the rate of moisture adsorption in one chamber and the rate of desorption in the other should be easily achievable with appropriate sensors monitoring temperature and discharge RH and feedback through the control system.

[0036] Tuning the desiccant material by (i) providing suitably shaped / sized hydrophilic / hydrophobic functional groups on the organic linkers and (ii) modifying / tuning the hydrophilicity of the pre-reserved metal-containing cluster nodes with different functional groups allows for the desired ease of removal under defined conditions. The adsorbent exhibits mildly hydrophobic characteristics at low RH, with a sharp sigmoidal rise in moisture sorption (Type V isotherm) at RH >20%. An example of the ability to tailor adsorbent properties through pore engineering and tailoring the adsorbent with desired isotherm type and SO3H functionalization is shown (see Figure 7). Varying the concentration of SO3H groups on the nodes clearly affects its moisture adsorption properties. Similarly, providing clusters with different hydrophilic terminal functional groups (HCCO) results in a significant improvement in moisture adsorption properties. - , CH3COO - , HO / OH, and PhCOO - ) provides precise control of the moisture uptake step over a range of RH, due to variations in hydrophobic / hydrophilic pore properties associated with differences in pore / cluster / functionality shape and size. Adsorbent materials that demonstrate promising properties include those with an optimal Type V isotherm shoulder within the 20-65% RH range and two or three candidates with a working capacity greater than 50 wt%. Preferably, desiccant materials with high chemical stability are utilized to preserve the long-term performance of the present system.

[0037] Conventional desiccant-based dehumidifiers (desiccant wheels, desiccant beds) regenerate the desiccant by heating, which severely limits their applications because 1) a heat source temperature of typically >80°C is required for desiccant regeneration, 2) the heat of adsorption released during dehumidification increases the temperature of the desiccant, thereby reducing its dehumidification capacity, and 3) hot desiccant increases the temperature of the discharge air, increasing the cooling load on the evaporator and reducing energy savings.

[0038] This much simpler approach allows the desiccant beds to be regenerated using a commercial off-the-shelf (COTS) vacuum pump. The desiccant bed temperature can be controlled through the use of heat pipes to provide thermal coupling between the desiccant beds. This provides a passive, yet highly efficient, heat transfer mechanism that "offsets" the heat of water vapor adsorption generated in the active desiccant bed during dehumidification and the endothermic heat of desorption consumed in the desiccant bed undergoing regeneration. Thus, the desiccant beds are regenerated isothermally at building air temperature, without increasing the sensible heat load on the evaporator from desiccant regeneration. Water vapor released from the vacuum pump is simply vented to the ambient.

[0039] In one preferred embodiment, the desiccant bed is thermally coupled with a "heat pipe." This provides a passive, yet highly efficient, heat transfer mechanism that "offsets" the heat of water vapor adsorption generated in the active desiccant bed and the endothermic heat of desorption consumed in the desiccant bed undergoing regeneration. This isothermal moisture extraction cycle (IWEC) allows the dry air stream to cool the condenser unit with little temperature change above ambient. A vacuum pump is used to provide suction against the desiccant bed during its regeneration cycle and to provide moderate compression to raise the vapor pressure sufficiently to condense into liquid water. Because the compression work is performed only on the water vapor, this minimizes energy consumption. Finally, the condensate is pumped to atmospheric pressure for release into a storage vessel (which consumes a small amount of additional energy).

[0040] This innovative AWE system concept eliminates the heat transfer process in traditional temperature swing designs that results in significant energy losses. It is also possible to very accurately assess the overall energy consumption for the system from the power required for 1) the fan to move air across the desiccant bed and condenser, 2) the vacuum pump, and 3) the liquid moisture pump. The airflow (CFM) required to bring enough air into the system to produce the required amount of moisture is simply given by:

number

[0041] For fan power, we use data provided in Clarke and Ward (2006) on fan efficiency in a typical ventilation system, as shown in Figure 2. As would be expected, fan efficiency decreases as back pressure increases. This provides an important constraint on the design of the desiccant bed. Excessive pressure drop, and therefore high power consumption, would result from attempting to pass airflow through a bed of finely packed desiccant particles. To avoid this, our system design concept passes airflow through channels between the fins, similar to a radiator design, thus providing minimal back pressure for the fan. For analytical purposes here, we used two fan efficiency values, namely, 10 and 3 CFM / W, to complete the energy consumption calculations for our AWE system.

[0042] With the simple assumptions outlined above, energy consumption for our design falls along a single curve determined by the ambient airflow mixing ratio. Fan power consumes approximately 80% of the total energy budget. The results provide confidence that our AWE system can achieve the 42 W·hr / L target if the system design provides low backpressure for the fan. It is likely that an adsorbent optimized for 43°C, 60% RH conditions will perform poorly in the more challenging 27°C, 10% RH humidity conditions, resulting in much higher power consumption, and vice versa.

[0043] Figure 8 shows an example of a modified heat pipe radiator design desiccant bed system shaped similarly to a radiator, with a set of thermally conductive fins made from a very lightweight material, such as graphene, coated with a desiccant. As air flows through the channels between the fins, the heat pipes remove heat from each adsorbent bed for transfer to the other chamber with the same set of beds undergoing regeneration. Heat transfer simulations of this design using the computational fluid dynamics (CFD) code ANSYS-Fluent confirmed a maximum temperature rise in the adsorbent bed of only 5°C for the 43°C, 60% RH case with the lowest airflow rate (1,000 CFM). This confirms our design premise that it is possible to thermally couple the adsorption-desorption chambers and operate the AWE system nearly isothermally.

[0044] This technology is a significant improvement over today's vapor compression refrigeration systems, providing humidity control in air-conditioned building spaces with zero energy penalty. In addition, the simple design is suitable for both new building HVAC systems and retrofit installations. Based on the expected capacity of the advanced desiccant, the dehumidifier system size for our 50RT reference case is 30 ft. 3 This is expected to be slightly over 200 feet. 3 This can be compared to a commercial building dehumidifier system for the same size airflow (17,000 cfm). Thus, the system envisioned here can be integrated into a standard HVAC air handler unit, which is not possible with current dehumidifier systems. Finally, the inventors note that the desiccant system is amenable to the addition of other adsorbent materials for selective removal of pollutants (such as CO or VOCs), which could enhance its appeal beyond energy and cost savings alone.

[0045] A second schematic design is shown in Figure 9. In Figure 9, heat of adsorption from the active bed to the regenerating bed is provided through a design utilizing heat pipes. The benefit is a passive heat transfer process, resulting in isothermal conditions during bed adsorption / regeneration. The outer surface of the heat pipe also provides a natural support for the desiccant material to be deposited. In addition to the desiccant bed design, ducting can be used to bypass the necessary airflow and vacuum isolation around each bed during regeneration. In the arrangement shown in Figure 9, the two desiccant sections are expected to be fabricated using cylindrical ducting with 1 / 4-inch diameter heat pipes installed in crossflow. Each heat pipe would be coated with a layer of adsorbent around its periphery with an optimal adsorbent layer thickness. A zigzag arrangement pattern along the direction of flow would maximize airflow exposure to the desiccant, promoting additional turbulence and mixing, resulting in higher heat and mass transfer coefficients. The bed sections would be assembled with vacuum-rated airflow isolation valves with autonomous diversion control to either the air outlet or the vacuum pump. The system will be fully instrumented with thermocouples, pressure transducers, Coriolis flow meters, and RH sensors to monitor key parameters and variables. The moisture concentration in the ambient air stream will be controlled by a mixing valve that merges the dry air stream with a variable amount of 100% RH air stream to achieve a specific humidity level. Relative humidity sensors (Omega Engineering, Inc., model RH-USB) will be installed at the desiccant bed inlet and outlet to continuously monitor RH values. This simple test system will allow us to collect all required performance information about the desiccant bed system, assess performance, perform thousands of regeneration cycles, and examine any degradation of desiccant properties.

[0046] While various preferred embodiments of the present disclosure have been shown and described, it is to be clearly understood that the present disclosure is not limited thereto and can be variously embodied for practice within the scope of the following claims.

Claims

1. 1. A humidity control system for an HVAC system, comprising: a regenerable nanostructured desiccant porous material configured to adsorb moisture from an air inlet stream at a first atmospheric pressure and release moisture when exposed to a second atmospheric pressure, the second atmospheric pressure being lower than the first atmospheric pressure, the regenerable nanostructured desiccant porous material comprising one or more materials selected from a metal organic framework material, a zeolite, a mesoporous silica, a covalent organic framework material, a porous organic polymer, or a porous carbon; a vacuum pump in communication with the regenerable nanostructured desiccant porous material, the vacuum pump adapted to provide sufficient suction to the regenerable nanostructured desiccant porous material to reduce the air pressure and remove moisture from the regenerable nanostructured desiccant porous material; at least one heat transfer pipe, the at least one heat transfer pipe thermally coupled to the regenerable nanostructured desiccant porous material and configured to alternately remove heat from and provide heat to the regenerable nanostructured desiccant porous material; a condenser positioned downstream of the regenerable nanostructured desiccant porous material and in communication with the regenerable nanostructured desiccant porous material, the condenser in communication with the vacuum pump; Humidity control system.

2. The humidity management system of claim 1 , wherein the regenerable nanostructured desiccant porous material comprises a metal organic framework material.

3. 3. The humidity management system of claim 2, wherein the metal organic framework material is selected from MOF303, MOF801, or MOF841.

4. The humidity management system of claim 1 , wherein the regenerable nanostructured desiccant porous material comprises MOF 303 or 801.

5. The humidity management system of claim 1 , wherein at least a portion of the regenerable nanostructured desiccant porous material is formed on an outer surface of at least a portion of the at least one heat transfer pipe.

6. The humidity management system of any of claims 1-5, wherein the regenerable nanostructured desiccant porous material has a three-dimensional shape.

7. 10. The humidity management system of claim 1, wherein a regenerable nanostructured desiccant porous material is disposed within a conduit, at least a first seal configured to seal a first end of the conduit, and at least a second seal configured to seal a second end of the conduit, and wherein the regenerable nanostructured desiccant porous material is disposed between the at least first seal and the at least second seal.

8. The humidity management system of claim 1 , wherein the regenerable nanostructured desiccant porous material is coated onto a plurality of thermally conductive fins.

9. The humidity management system of claim 1 further comprising a water pump in communication with the condenser.

10. 1. A method for removing moisture from an air stream, the method comprising: passing a moisture-containing air stream across a regenerable nanostructured porous material, the regenerable nanostructured porous material configured to adsorb moisture from the inlet stream at a first atmospheric pressure and release moisture when exposed to a second atmospheric pressure, the second atmospheric pressure being lower than the first atmospheric pressure; placing the regenerable nanostructured porous material under the first atmospheric pressure; transferring heat from the regenerable nanostructured porous material while the regenerable nanostructured porous material is under the first atmospheric pressure; generating a water vapor-containing stream by placing the regenerable nanostructured porous material under the second atmospheric pressure, and increasing the vapor pressure of the water vapor-containing stream sufficiently to condense the water vapor into liquid water condensate; transferring heat to the regenerable nanostructured porous material while the regenerable nanostructured porous material is under the second pressure, wherein transferring heat comprises transferring heat through a heat pipe; A method comprising:

11. 11. The method of claim 10, wherein the regenerable nanostructured porous material comprises one or more materials selected from a metal organic framework material, a zeolite, a mesoporous silica, a covalent organic framework material, a porous organic polymer, or a porous carbon.

12. The method of claim 10 further comprising increasing the pressure of the liquid water condensate to atmospheric pressure.

13. A humidity control system, comprising: An air inlet; a first regenerable nanostructured desiccant porous material configured to adsorb moisture from an airflow at a first pressure and release moisture when exposed to a second pressure, the second pressure being lower than the first pressure, the first regenerable nanostructured desiccant porous material being positioned within a first conduit; a second regenerable nanostructured desiccant porous material configured to adsorb moisture from the airflow at a first pressure and release moisture when exposed to a second pressure, the second pressure being lower than the first pressure, the second regenerable nanostructured desiccant porous material being positioned within a second conduit; the first conduit and the second conduit are arranged to be spaced apart from each other; a second renewable nanostructured desiccant porous material; a vacuum pump in alternating communication with the first regenerable nanostructured desiccant porous material and the second regenerable nanostructured desiccant porous material; a heat transfer pipe thermally coupled to the first regenerable nanostructured desiccant porous material and the second regenerable nanostructured desiccant porous material; a condenser positioned downstream of the first regenerable nanostructured desiccant porous material and the second regenerable nanostructured desiccant porous material and in communication with the first regenerable nanostructured desiccant porous material and the second regenerable nanostructured desiccant porous material, the condenser in communication with the vacuum pump; Humidity control system.

14. The humidity management system of claim 13 further comprising a water pump in communication with the condenser.

15. 14. The humidity management system of claim 13, wherein the first regenerable nanostructured desiccant porous material and the second regenerable nanostructured desiccant porous material each comprise a metal organic framework material.

16. The humidity management system of claim 13 , wherein the first conduit and the second conduit are aligned parallel to one another.

17. 14. A method, the method comprising: operating the system of claim 13 in (A) an adsorption mode to remove moisture from an air stream; and (B) a regeneration mode to release the adsorbed moisture. the adsorption mode includes contacting the airflow at a first pressure with the first regenerable nanostructured desiccant porous material to adsorb moisture from the airflow, and transferring heat from the first regenerable nanostructured desiccant porous material to the second regenerable nanostructured desiccant porous material while the first regenerable nanostructured desiccant porous material is under the first pressure; the regeneration mode comprising: releasing moisture adsorbed by the first regenerable nanostructured desiccant porous material at a second pressure, the second pressure being lower than the first pressure; and transferring heat from the second regenerable nanostructured desiccant porous material to the first regenerable nanostructured desiccant porous material while the first regenerable nanostructured desiccant porous material is under the second pressure. method.

18. 20. The method of claim 17, comprising operating the system such that when the second regenerable nanostructured desiccant porous material operates in a regeneration mode, the first regenerable nanostructured desiccant porous material operates in an adsorption mode, and when the first regenerable nanostructured desiccant porous material operates in a regeneration mode, the second regenerable nanostructured desiccant porous material operates in an adsorption mode.

Images