METHOD AND SYSTEM FOR DEHUMIDIFICATION AND ATMOSPHERIC WATER EXTRACTION WITH MINIMAL ENERGY CONSUMPTION

Abstract

Methods, systems and devices for managing humidity within an HVAC system including a nanostructured desiccant porous material configured to adsorb water from an inlet stream at a first air pressure and to release water from that material when subjected to a second air pressure when the second air pressure is lower than the first air pressure is located within a particular location so as to allow for the passage of wet air over the materials and allow adsorption of the water on to the material. When coupled with a vacuum pump water can be collected and released from the materials and the system, regenerating the material for future use and removing water from a stream at a significantly lower cost than existing processes.

Claims

1. A humidity management system for an HVAC system comprising: a nanostructured desiccant porous material configured to adsorb water from an inlet stream at a first air pressure and to release water from that material when subjected to a second air pressure wherein said second air pressure is lower than the first air pressure.

2. The humidity management system of claim 1 wherein the nanoporous material is located within at least one desiccant bed.

3. The humidity management systems of claim 1 further comprising a vacuum pump adapted to provide suction to the nanostructured porous material sufficient to lower the air pressure and remove water from the nanostructured porous material.

4. The humidity management system of claim 1 wherein the nanostructured porous material is selected from the group consisting of: MOFs, Zeolites, Mesoporous silica, Covalent organic framework materials; Porous organic polymers; and Porous carbon.

5. The humidity management system of claim 4 wherein the nanostructured porous material is a MOF material.

6. The humidity management systems of claim 5 wherein the nanostructured porous material comprises: a MOF selected from the group consisting of MOF 303, 801 or 841.

7. The humidity management system of claim 6 wherein the nanostructured porous material comprises MOF 303 or 801.

8. The humidity management system of claim 3 further comprising a heat delivery system for delivering heat to the nanostructured porous material.

9. The humidity management system of claim 3 wherein the heat delivery system includes a heat pipe operatively configured to deliver heat to the nanoporous material.

10. The humidity management system of claim 1 wherein the nanoporous desiccant material is embodied within a coating upon a fin.

11. The desiccant system of claim 8 further comprising a first set of desiccant containing beds and a second set of desiccant beds, each of said first and second desiccant beds containing a nano-porous desiccant material configured to remove water from an air stream passing over said beds.

12. The desiccant system of claim 9 wherein said first desiccant beds and said second desiccant beds contain the same nano-porous desiccant material.

13. The desiccant system of claim 1 wherein the nanostructured porous material is configured within a three dimensional shape.

14. The desiccant system of claim 11 wherein the three dimensional shape is a rod.

15. The desiccant system of claim 11 wherein the three dimensional shape is positioned within an air passage pathway.

16. A method for removing water from an air stream without additional heating, the method comprising the step of: passing an air stream containing water over a nanostructured porous material configured to adsorb water from an inlet stream at a first air pressure and to release water from that material when subjected to a second air pressure wherein said second air pressure is lower than the first air pressure to collect water onto the nanostructured porous material then reducing the ambient air pressure to release water from the nanostructured porous material and regenerate the nanostructured porous material for additional water capture.

17. The method of claim 16 wherein the reduction in ambient pressure is provided by a vacuum.

18. The method of claim 17 wherein the nanostructured porous material is encapsulated in at least two operationally separated beds whereby one bed is positioned to capture water from an air current and the other is positioned to release captured water.

19. The method of claim 18 further comprising the step of providing a heat transfer material in operative fluid connection between the first bed and the second bed so that the heat given off from one process is passed on to assist in the other process.

20. The method of claim 18 wherein the heat transfer material is contained within a conduit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 shows a detailed schematic of one example of embodiment of the invention described in the present description.

[0012] FIG. 2 shows a comparison of the amounts of power used to regenerate the desiccant bed system of the present application compared to the load on the HVAC compressor eliminated as a function of humidity level in the building return air.

[0013] FIG. 3 shows examples of various exemplary candidate water adsorbent materials based on working capacities for various ranges of relative humidity (9RH)

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

[0015] FIG. 5 shows the Volumetric Energy Consumption for the Isothermal AWE System for Two Fan Efficiencies.

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

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

[0018] FIG. 8 shows another embodiment of the present invention wherein desiccant is coated on fins made of graphene or other lightweight but thermally conductive support.

[0019] FIG. 9 shows an example of a second schematic example of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0020] The following description includes one example of the present disclosure. It will be clear from this description that the disclosure is not limited to these illustrated embodiments but that the disclosure also includes a variety of modifications and embodiments thereto. Therefore, the present description should be seen as illustrative and not limiting. While the disclosure is susceptible of various modifications and alternative constructions, it should be understood, that there is no intention to limit the disclosure to the specific form disclosed, but, on the contrary, the disclosure is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the disclosure.

[0021] In one set of descriptions a novel desiccant system for management of humidity through a building's HVAC system is described wherein new nanostructured porous materials with ultra-high capacity for water are integrated into desiccant beds and thermally coupled to heat pipes. Building air is then passed over these beds to remove water, however instead of using heat for desiccant regeneration the way that commercial dehumidifiers do, these advanced sorbents support facile removal of adsorbed water at room temperature with a simple vacuum pump. The system thus eliminates the additional latent heat cooling load from condensation on the HVAC system evaporator coils. The energy savings obtained more than compensate for the energy required to operate the vacuum pump, and with equipment footprint and capital cost half of today's commercial desiccant dehumidification systems. The system design can also support inclusion of additional sorbent materials in the desiccant bed that permit control of CO2 levels or remove VOCs from building air.

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

[0023] Our much simpler approach provides suctions on the desiccant bed during its regeneration cycle with a commercial off-the shelf (COTS) vacuum pump. Desiccant bed temperature is controlled through the use of heat pipes to provide thermal coupling between the desiccant beds. This provides a passive but highly efficient heat transfer mechanism to cancel the heat of water vapor adsorption generated in the active desiccant bed during dehumidification with the endothermic heat of desorption consumed in the desiccant bed undergoing regeneration. Hence, the desiccant beds are regenerated isothermally at the building air temperature and do not increase the sensible heat load on the evaporator from desiccant regeneration. Discharged water vapor from the vacuum pump is just exhausted to ambient.

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

[0025] FIGS. 1-9 show various features and sample embodiments. In one example shown in the attached, a configuration is shown wherein the use of new ultra-high water capacity desiccant materials enables a sufficiently compact unit that it can fit within the confines of a standard air handler conduit used in most commercial and residential HVAC installations. This integrated design obviates need for extensive modifications to the building's air handler layout and space for a large dedicated dehumidification system making it ideal for both new installations and retrofits.

[0026] Referring now to the figures, FIG. 1, shows a schematic of a one embodiment of the invention wherein a desiccant bed 20 containing a desired material 22, preferably a metal-organic framework materials such as MOF, (and more preferably MOF 303, 842 or 841, although a variety of other materials can also be utilized depending upon the needs and necessities of the user) is operatively positioned to allow moist, typically warm from a source such as warm air return in a conventional HVAC unit to pass over the desiccant bed 20, wherein the materials 22 in the desiccant bed absorb water from the moist air onto the materials and allow drier air to pass on through the desiccant bed 20. The newly dried air can then be passed on for cooling through the standard parts of a typical HVAC system which can include an evaporator operatively connected to receive a coolant from an expansion valve whereby coolant flows through the evaporator to a compressor which pumps the coolant through a fan cooled condenser coil and back to the expansion valve which controls the passage of coolant back into the evaporator. The now dry and cooled air can then be passed to the desired location. The desiccant bed 20 is also operatively connected to ta vacuum pump 24 that provides suction to the materials 22 in the desiccant bed 20 so as to remove water from the desiccant bed and exhausts this water to another location.

[0027] The operating principle is very simple. Warm moist building air is passed over a desiccant bed that removes moisture. The now dried air is then passed through an air handler to the evaporator and cooled as in standard HVAC systems. Regeneration of the desiccant takes place as suction pulls water from the desiccant bed materials and exhausts them to a separate location. In a continuously operating system tray of desiccant can be used whereby once the desiccant from a first bed has reached its water uptake capacity, the building air flow is switched to contact a second desiccant bed that has completed its regeneration cycle, this process can be performed alternatingly or serially across a number of beds with each bed being regenerated by vacuum suction while another captures water from a moist, typically warm air source.

[0028] A variety of types of materials can be utilized as the desiccant material 22. Previous work on development of various sorbents for advanced cooling systems has established a unique database on water adsorption properties of various nano-porous materials including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic polymers (POPs), zeolites, mesoporous silica and porous carbons. Our recent work has shown remarkable thermodynamic properties of certain hydrophilic nanoporous materials with large water sorption capacities as well as hydrothermal stabilities established a sufficient and transformational improvement in size, weight, and cost of commercial adsorption chillers (MCGRAIL et al., 2014).

[0029] In this direction, we revisited the data collected on these hydrophilic materials and developed the materials mainly emphasizing the kinetics of adsorption and precise tuning of their water adsorption properties. The tunability of the materials is advantageous in this application because desorption kinetics must be facile under simple vacuum with no heating. Because of this, we followed two major approaches for the tuning of the desiccant materials by (i) decorating organic linkers with suitably shaped/sized hydrophilic/hydrophobic functional groups and (ii) modifying/adjusting the hydrophilicity of pre-reserved metal-containing cluster nodes with different functional groups. The result was adsorbent materials that show mild hydrophobic character at low RH with a sharp sigmoidal-shaped uptick in water adsorption at RH>20% (Type V isotherm).

[0030] An example of the type of isotherm desired and ability to tune the adsorbent properties via pore-tuning or pore-engineering concepts with SO.sub.3H functionalization on the MOF UIO-66 node that shows water sorption behavior as illustrated in FIG. 7. Varying the concentration of SO3H groups on the node clearly affects its water adsorption properties. Similarly, decorating the cluster with terminal functional groups of different hydrophilicities (HCCO.sup., CH3COO.sup., H2O/OH, and PhCOO.sup.) resulted in precise control of the water uptake step over a range of RH and is attributed to variances in hydrophobic/hydrophilic pore character associated with differences in pore/cluster/functionality shape and size.

[0031] While these examples were deemed workable for one example, in other arrangements materials that have Type V isotherm shoulders in the range of 20-65% RH and with working capacity higher than 50 wt % were selected. In particular, two zirconium-based MOFs, MOF-841, MOF-801 and an aluminum-based MOF-303 were specifically chosen because of their high chemical stability and required water sorption capacities and regenerability shown by cycling tests to ensure there is no degradation of adsorption properties. Furthermore, we expect can be synthesized in commercial quantities using PNNL's atomization-condensation reactor technology (MOTKURI, 2016) or other synthesis method.

[0032] MOF-801 and MOF-303 shown to perform the best under the present operating conditions. Since the amount of sorbent required is expected to be in the range of kilogram scale, we were successful in bulk synthesis of MOF-801, prepared/tested in 100-gram scale already. To prepare these MOFs, 50 mmol of each fumaric acid and ZrOCl2.8H2O were dissolved 500 mL screw-capped jar, in a mixed solvent of DMF and formic acid (200 mL and 70 mL) and was then heated at 130 C. overnight to give a white precipitate. MOF-801. Similarly, MOF-303 was synthesized using 43.1 mmol of 3,5-pyrazoledicarboxylic acid monohydrate dissolved in deionized H.sub.2O (750 mL) to which a base (NaOH or LiOH solution, 65 mmol) was added dropwise under vigorous stirring. The resulting mixture was heated for 60-90 min in a pre-heated oven at 120 C. After cooling to RT, 43.1 mmol of AlCl.sub.3.6H.sub.2O was slowly added to the solution while constant vigorous stirring. Any precipitate formed in the solution was dissolved under extended sonication. The clear solution transferred to autoclave and heated in an oven at 100 C. for 15-24 h to get MOF powder. The obtained MOF powder materials were activated by solvent as well as thermal activation before subjecting to water adsorption. The activated materials were characterized with powder X-ray diffraction (PXRD) for crystallinity, thermogravimetric analysis to understand the stability of the materials and N2 adsorption isotherms for porosity measurements. The well characterized samples were tested their water adsorption measurements at room temperature and then extended to multiple temperatures required for this study.

[0033] Once the material characterized, the material scaled-up PNNL's atomization-condensation reactor technology (MOTKURI, 2016) for bulk production. This technology offers a low-cost and scalable route to produce sorbent materials (e.g., MOFs) in bulk quantities. While these particular materials were demonstrated in one application a variety of other materials were also identified for use in such a system. A non-exclusive and not limiting list includes but is not limited to Zeolites such as AlPO.sub.4-34, AlPO.sub.4-LTA, AlPO.sub.4-CHA, 13X, SAPO-34; Mesoporous silica, such as MCM-41, SBA-15; MOFs including Zr and Al based MOFs, MIL family MOFs, Co2Cl2(BTDD); Covalent organic frameworks; Porous organic polymers; Porous carbon.

[0034] FIG. 6 shows the water uptake kinetics for several MOFs. These results show design flexibility in that particle sizes could be reduced from these nominal values to increase the water flux if attaining continuous diffusive transport over these distances proves challenging. Overall, our systems analysis shows that water uptake in the sorbent must reach 11 wt % in the targeted 90 s half-cycle. There is solid evidence that this uptake rate is attainable as shown in FIG. 6. The sorbent development team will need to downselect to desiccants that can achieve this uptake rate through a combination of physical properties including specific surface area, particle size, and intra-crystalline water diffusion.

[0035] The system design team ensured that water vapor transport to the desiccant surface is sufficient to support the rate of water uptake by the desiccant while minimizing back pressure on the ventilation fan to save energy. Achieving this balance is expected to be most challenging on the adsorption portion of the cycle. Because the vacuum is applied nearly uniformly across the desiccant beds during desorption, water removal rate should be comparatively uniform. Because the desorption rate can be well-controlled by varying the suction pressure, maintenance of an approximate balance between the rate of water adsorption in one chamber and desorption in the other chamber should be readily achievable with adequate sensors monitoring temperature and discharge RH, and feedback through a control system.

[0036] The tuning of the desiccant materials by (i) decorating organic linkers with suitably shaped/sized hydrophilic/hydrophobic functional groups and (ii) modifying/adjusting the hydrophilicity of pre-reserved metal-containing cluster nodes with different functional groups enable the desired facile removal under specified conditions. Adsorbents that show mild hydrophobic character at low RH with a sharp sigmoidal-shaped uptick in water adsorption at RH>20% (Type V isotherm). An example of the type of isotherm desired and ability to tune the adsorbent properties via pore-engineering and tuning the adsorbent with SO3H functionalization. (See FIG. 7.) Varying the concentration of SO3H groups on the node clearly affects its water adsorption properties. Similarly, decorating the cluster with terminal functional groups of different hydrophilicities (HCCO, CH3COO, H2O/OH, and PhCOO) resulted in precise control of the water uptake step over a range of RH and is attributed to variances in hydrophobic/hydrophilic pore character associated with differences in pore/cluster/functionality shape and size. Sorbent materials showing promising properties include those that have two or three candidates with optimal Type V isotherm shoulders in the range of 20-65% RH and with working capacity higher than 50 wt %. Preferably desiccant materials that have high chemical stability are utilized to preserve long term performance of the system.

[0037] Conventional desiccant-based dehumidifiers (desiccant wheels, desiccant beds) regenerate the desiccant by heating. This severely limits their application because: 1) heat source temperature typically >80 C. is required for desiccant regeneration, 2) 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, which increases cooling load on the evaporator and reduces energy savings.

[0038] This much simpler approach enables the desiccant bed to be regenerated with a commercial off-the-shelf (COTS) vacuum pump. Desiccant bed temperature can be controlled through the use of heat pipes to provide thermal coupling between the desiccant beds. This provides a passive but highly efficient heat transfer mechanism to cancel the heat of water vapor adsorption generated in the active desiccant bed during dehumidification with the endothermic heat of desorption consumed in the desiccant bed undergoing regeneration. Hence, the desiccant beds are regenerated isothermally at the building air temperature and do not increase the sensible heat load on the evaporator from desiccant regeneration. Discharged water vapor from the vacuum pump is just exhausted to ambient.

[0039] In one preferred embodiment, the desiccant beds are thermally coupled with heat pipes. This provides a passive but highly efficient heat transfer mechanism to cancel the heat of water vapor adsorption generated in the active desiccant bed with the endothermic heat of desorption consumed in the desiccant bed undergoing regeneration. This isothermal water extraction cycle (IWEC) allows the dry air stream to cool the condenser unit with a minimal temperature change above ambient temperature. A vacuum pump provides suction on the desiccant bed during its regeneration cycle and is used to provide modest compression to raise the vapor pressure sufficiently to condense to liquid water. Because the compression work is only done on the water vapor, this minimizes the energy consumption. Lastly, the condensate is pumped up to atmospheric pressure for discharge to a storage vessel (this consumes a trivial amount of additional energy).

[0040] This innovative AWE system concept eliminates the heat transfer processes in conventional temperature swing designs that produce large exergetic losses. Moreover, it is possible to quite accurately assess the overall energy consumption for this system from the power required for: 1) fan to move air across the desiccant bed and condenser, 2) vacuum pump, and 3) liquid water pump. The air flow (CFM) needed to bring enough air into the system to produce the required amount of water is just given by:

[00001]$\begin{array}{cc}\mathrm{CFM}=\frac{0.5.Math.8.Math.8.Math.6.Math.M_w.Math.{}_a}{m_a.Math.t_p.Math.{\mathrm{.Math.}}_R}& \left(1\right)\end{array}$

where M.sub.w is the mass of water the system is to produce over operating time period t.sub.p, .sub.a is the air density, and m.sub.a is the mixing ratio (kg-H.sub.2O/kg-air) determined from the standard psychrometric properties of moist air. The parameter ER is the efficiency of the overall system in removing water from the air stream and is the key parameter connecting sorbent properties with system performance. The power required for the water pump is trivial compared to these other terms and so will be neglected here. To compute the vacuum pump power, we calculate the compression power required to raise the water vapor pressure from the regenerating desiccant bed to its saturation vapor pressure assuming the condenser unit is operating with a change in temperature 10 C. above the ambient air temperature. We assume the vacuum pump is 80% efficient in the compression work performed on the water vapor. A final assumption is that suction on the desiccant bed is sufficient to remove water from the sorbent when operating just under the condenser pressure, i.e. the compression ratio is fixed and 1.2.

[0041] For fan power, we use the data provided in Clarke and Ward (2006) for fan efficiency in typical ventilation systems as shown in FIG. 2. As would be expected, the fan efficiency declines as back pressure increases. This provides an important constraint on the design of the desiccant bed. Excessive pressure drop and hence high-power consumption would result from attempting to pass the air stream through a bed of finely packed desiccant particles. To avoid that, our system design concept passes the air stream through channels between fins, similar to radiator designs, and so can provide minimal back pressure on the fan. For analysis purposes here, we used two fan efficiency values, 10 and 3 CFM/W to complete the energy consumption calculation for our AWE system.

[0042] With the simple assumptions outlined above, the energy consumption for our design falls along a single curve determined by the mixing ratio of the ambient air stream. Fan power consumes about 80% of the total energy budget. The results provide confidence that our AWE system can achieve a target of 42 W.Math.hr/L if the system design provides a low back pressure on the fan. Sorbents optimized for a 43 C., 60% RH condition are likely to perform poorly and result in much higher power consumption at the more challenging 27 C., 10% RH humidity condition and vice versa.

[0043] FIG. 8 shows an example of a modified heat pipe radiator design desiccant bed system formed similarly to a radiator with a set of thermally conductive fins made of a very lightweight material like graphene coated with desiccant. As air flow through the channels between the fins heat pipes remove heat from each adsorbing bed for transfer to the other chamber with an identical set of beds undergoing regeneration. A heat transfer simulation of this design using the computational fluid dynamics (CFD) code ANSYS-Fluent confirmed that only a 5 C. maximum temperature rise in the adsorbing bed for the 43 C., 60% RH case that has the lowest air flow rate (1000 CFM). This confirms our design premise in being able to thermally couple the adsorption-desorption chambers and operate the AWE system approximately isothermally.

[0044] This technology is a significant improvement over today's vapor-compression cooling systems and delivers humidity management in conditioned building spaces with zero energy penalty. In addition, the simple design is amenable to both new build HVAC systems and retrofit installations. Based on expected capacity of advanced desiccants, size of the dehumidifier system for our 50 RT reference case is projected at just over 30 ft.sup.3. This can be compared with a commercial building dehumidifier system for this same size air flow (17,000 cfm) of 200 ft.sup.3. Hence, the system envisioned here can be integrated in standard HVAC air handler units that is not possible with current dehumidifier systems. Last, we point out that the desiccant system is amenable to addition of other sorbent materials for selective removal of pollutants (such as CO.sub.2 or VOCs), which could enhance customer appeal beyond energy and cost savings alone.

[0045] A second schematic design is shown in FIG. 9. In FIG. 9 the heat of adsorption from the active bed to the regenerating bed is provided through a design that utilizes heat pipes. The benefit is a passive heat transfer process that yields an isothermal condition during bed adsorption/regeneration. Moreover, the exterior surfaces of the heat pipes provide a natural support for the desiccant materials to be deposited. In addition to the desiccant bed design, ducting can necessary diversion of air flow and vacuum isolation around each bed during regeneration. In the arrangement shown in FIG. 9, the two desiccant sections are expected to be fabricated using cylindrical ducting with -inch diameter heat pipes placed in the crossflow. Each heat pipe will be coated with a layer of sorbent around its periphery with the optimum sorbent layer thickness. A staggered installation pattern along the direction of flow will maximize airflow exposure to the desiccant and promote more turbulence and mixing yielding higher heat and mass transfer coefficients. Bed sections will be assembled with vacuum-rated airflow isolation valves with autonomous diversion control to either the air discharge 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. Water concentrations in the ambient air stream will be controlled by a mixing valve that merges a dry air stream with variable amounts of a 100% RH air stream to achieve a specific humidity. Relative humidity sensors (Omega Engineering, Inc., model RH-USB) are placed at the desiccant bed inlet and outlet to continuously monitor RH values. This simple test system will allow us to collect all the required performance information on the desiccant bed system to assess performance and perform thousands of regeneration cycles to look for any degradation in desiccant properties.

[0046] While various preferred embodiments of the disclosure are shown and described, it is to be distinctly understood that this disclosure is not limited thereto but may be variously embodied to practice within the scope of the following claims.