Patent ID: 12222133

DETAILED DESCRIPTION

The present disclosure relates to climate control systems such as heating, ventilation, and air conditioning (HVAC). In the commercial sector, HVAC systems are a major energy consumer, and many solutions have been proposed to increase the energy efficiency of these systems. Humidity control alone can consume roughly a quarter to one third of the energy requirements on an HVAC system, depending on climate (see, e.g., Airedale: “Vodacom case study,” www.airedale.com/web/About-Airedale/The-News-HVACNodacom.htm).

This disclosure relates to an efficient method of dehumidification and/or atmospheric water harvesting using a combination of desiccant materials and efficient integrated design. A fan with blades that includes a desiccant (e.g., a hierarchically porous, super-moisture absorbing material) on a surface of the blades is driven via a motor. The driving fan is used to circulate air, as in any HVAC system, while also optimizing convection at the surface of the moisture absorbing material, rather than directing air over a desiccant or cooling-coils. A desiccant material may use phase-changing polymers such as poly(N-isopropylacrylamide) combined with highly adsorbent materials such as Cl-doped polypyrrole is used which reduces the temperature required to regenerate the desiccant from >100 C to roughly 40 C, further increasing efficiency by allowing the material to be re-generated using low quality (waste) heat from other processes. Generally, low quality waste heat is heated air that is at a temperature <50 C, although may encompass higher temperatures, e.g., <60 C, <70 C, etc.

Existing dehumidifiers come in at least two forms, either in the form of mechanical or desiccant dehumidification. Mechanical dehumidification applies a vapor cycle similar to what is used in air-conditioners. Intake or recirculated air is over-cooled below its dew point by directing it over cooling-coils to condense the water vapor and reduce humidity. Afterward, the air is heated to its desired temperature before being circulated. This process is energy inefficient due to the over-cooling and heating cycles required to generate the dehumidified air. A desiccant dehumidifier uses a rotating wheel containing a regenerable desiccant to absorb moisture and reduce the humidity of incoming air. Hot air is passed through one part of the wheel as it rotates to regenerate the desiccant. Typical desiccant materials include nano-porous silica and zeolites which absorb moisture through capillary condensation. These materials need to be heated to temperatures exceeding 100 C in order to be regenerated. This heat is either generated through electrical heating or through waste heat sources.

In contrast to existing desiccant dehumidifiers, embodiments described herein may use a set of fans being run in parallel. The fans may have blades comprising an electro-spun mat of a super moisture-sorbent material which readily absorbs atmospheric moisture down to 30% RH and has much lower cycling temperatures (˜38 C, thus requiring lower quality heat) and also produces liquid water rather than vapor. Each fan's mass can be monitored in time, and once a steady state is reached the fan is heated using waste heat from building utilities (e.g., via a system of valves), which may be readily implemented in facilities with large quantities of information and computer technology (ICT) equipment, such as data centers or telecommunications installations. Other sources of waste heat may be used, such as heat from electrical or hydraulic motors in a manufacturing facility.

The dehumification (or water harvesting) system shown inFIG.1directs waste heat101to the water-filled fans100to regenerate the desiccant material. Humid air104is drawn to the regenerated fans102. By eliminating a separate heat/mass exchanger, inefficiencies in redirecting air flow are eliminated. The volume taken up by fan blades in a separated system is also effectively eliminated. These two factors allow for a larger diameter fan to be used. Larger diameter fans have higher efficiencies and rotate at slower speeds for the same air flow rate while requiring the same or reduced motor size.

This disclosure describes an efficient method of dehumidification and/or atmospheric water harvesting using a combination of novel desiccant materials and efficient integrated design. A set of fans with blades comprising highly moisture-absorbing material is driven via a motor. The driving fan is be used to circulate air (either drawing in humid intake air over dry fan blades or waste heat over moisture-saturated blades using a set of control valves). As opposed to typical HVAC desiccant wheel systems, the fan is the desiccant rather than using a fan to re-direct air over a desiccant wheel. Use of desiccant fan blades reduces inefficiencies inherent in a desiccant wheel arrangement.

The embodiments described herein employ a material that can be regenerated with lower quality heat (e.g., lower temperature) and can uptake more moisture per unit mass than a typical desiccant. The highly-moisture sorbent material uses phase-changing polymers, such as poly(N-isopropylacrylamide), which undergo a phase change becoming hydrophobic above 40° C. as a means to regenerate the desiccant (from >100° C. for typical desiccants). An adsorbent material, such as Cl-dope polypyrrole, is typically added to the phase-changing polymer to increase its vapor absorption capacity and kinetics. These materials can be electrospun into fibrous mats with hierarchical structures and/or combined with cross-linking materials to generate monoliths of varying porosity and pore size distribution.

The system utilizes fan blades which act as the adsorption (and desorption) surface of the system. There may be at least two sets of blades on a central shaft driven by a single motor. As the fans rotate the blades will both be exposed to fresh air and generate air flow. In addition to using lower quality heat to desorb the moisture, the system will produce water in liquid rather than vapor form, which can be collected via gravity and re-used in other processes.

A cross sectional diagram of a system according to an example embodiment is shown inFIG.2. A first fan200(or first set of fans) will be desorbing in an enclosed or semi-enclosed volume202on a desorption side203while a second fan204is adsorbing to ambient air206on an adsorption side207. The adsorption side207may be open, semi-enclosed, or enclosed. On the adsorption side207, ambient air206flows across the fan blades from regions208to region209where it is driven over a first surface210aof a cooling partition210, which cools a second surface210bfacing the contained desorption side203and opposed to the first surface210a. The cooling partition210acts as a condenser and will be designed to have a large specific surface area and help encourage fluid flow212. The fluid flow212is directed into a water collector221, e.g., a channel or pipe.

The desorption side203utilizes circular flow that is directed from a heated wall214to the cooling partition210with a small amount of makeup air216that enters through entrance path217and exits through exit path218as humid heated air219. The makeup air216can be pre-warmed by the humid heated air219using counter-flow heat exchanger223to minimize the amount of exergy exiting the system.

Heat is emitted into the desorption side203from heater220on the heated wall214. The heater220may include a heat exchanger, heat generator (e.g., resistive heater, combustion heater), or other heater known in the art. In one embodiment, the heater220may include one or more of photovoltaic (PV) cells and solar thermal absorption layers. The PV cells can also be used to drive the fan motor224, e.g., for a portable water harvesting device that is designed for off-the grid use. In another embodiment, the heater220may include a heat exchanger driven by waste heat.

In yet another embodiment, the system may include an internal heater230integrated into the fan blades (shown on first fan200inFIG.2) instead of or in addition to the external heater220. The internal heater230could be an electrically driven heater (e.g., resistive, inductive) as indicated schematically inFIG.2. In other embodiments, the internal heater230may use cavities through which are driven a heated gas and/or liquid. All fans in the system (e.g., fans200and204) may include the same type of internal heater230, and these could be activated or deactivated depending on the operational mode of the fan, the modes being described elsewhere herein. In some embodiments, the internal heater230may switch operation to a cooler depending on an operational mode of the fan. This can be accomplished by driving different temperature fluids through internal cavities if the heater203is implemented this way, and/or using an electrically driven solid-state cooling device, e.g., a Peltier device.

The heater220(other parts of the chamber on the desorption side203) can be coated in an insulator222. If the heater220is a PV cell, transparent aerogels can be used as an insulator, which are described in commonly-owned U.S. Pat. No. 10,421,253, issued Sep. 24, 2019. The thickness of the insulator222can be determined based on an energy size and mass balance for the system, as well as insulating factor of the materials used. The energy efficiency of this system may be dependent, among other things, on the energy used for fan rotation, and on inefficiencies in the fan drive motor224, air flow (e.g., flow resistance through paths217,218), and heater220.

When a cycle is completed, the blades of fan200will be dried out and the blades of fan204will be saturated with water. At this point, the fans200,204can be switched from respective desorber to adsorber sides or vice versa, which may be considered a change from a first mode to a second mode. Where the system is small, e.g., a portable water-harvesting device, the blades and hub of each the fans200,204can be an integral piece which can be easily removed and reattached to the drive shaft without requiring tools. In such an embodiment, the heater220and insulation222of the desorber side203can be readily opened to facilitate the mode change. Since only the fans200,204need to be moved, the entire thermal mass of the hot desorption side remains.

Combining the heat/mass exchanger with the fan helps to decrease system size and weight in several ways. By eliminating a separate heat/mass exchanger, inefficiencies in redirecting air flow are eliminated. The volume taken up by fan blades in a separated system is also effectively eliminated. These two factors allow for a larger diameter fan to be used. Larger diameter fans have higher efficiencies and rotate at slower speeds for the same air flow rate while requiring the same or reduced motor size.

In another embodiment, an air treatment system can be devised such that switching of the fans is not needed. This may be useful for larger systems, such as HVAC or large water harvesting systems. An example of such a system is shown in the diagram ofFIG.3. Two fans300,301are in separate chambers302,303. The fans300,301are shown being driven by a common shaft304, but other drive arrangements are possible. The chambers302,303are similarly configured, with ambient air inlets306,307and ambient air outlets308,309. A cooling chamber310is disposed between the chambers302,303, and ducts312,313provide an air path between the chambers302,303and the cooling chamber310. Heaters320,321and insulation322,323surround part of the chambers302,303.

The ambient air inlets306,307and ambient air outlets308,309can be selectively opened and closed via respective valves314-319to reconfigure each chamber for desorbing or adsorbing. In this configuration, chamber303is configured as a desorbing chamber, with heater321activated, valve315slightly open to provide make-up air, and valve319open to allow heated and humid air to enter the cooling chamber310. Chamber302is configure as an adsorbing chamber in this configuration, with valves314and316fully open to cause ambient air to be moved by fan300which adsorbs moisture. Fan300also cools cooling chamber wall310a, which results in cooling chamber air condensing and leaving through liquid water channel324.

By reversing the configuration of the valves314-319(e.g., valve314slightly open, valves315,317, and318open, and valve319closed), the chamber303can perform absorption and the chamber302can perform desorption. In such a case, wall310bwill be the cooling wall, heater320will be activated, and heater321will be deactivated. Note that the system may undergo a period of no activity (e.g., fans switched off, heaters deactivated, all valves closed) to allow the system to come to thermal equilibrium before changing modes.

The mode change described above can be triggered based on one or both of an adsorbing fan being saturated or a desorbing fan being desaturated. The system may include sensors to detect the saturation level of a fan. For example, the increased weight from higher sensor may be sensed using a torque sensor between the fan and a drive motor. Instead or in addition, a direct humidity sensor could be attached to a fan blade. Such sensor could transmit signals wirelessly or via a conductive rotating contact interface at the hub.

In order to achieve the structural requirements of the proposed design a mechanically robust composite of a polymer matrix containing the sorbent material can be used for the fan blades. Many methods have been explored to create composites of this type including incorporating crystalline fillers into a flexible polymer matrix (see, e.g., pubs.acs.org/doi/full/10.1021/acs.chemrev.9b00575); and covalently incorporating polymer backbones into active sorbents either postsynthetically (see, e.g., V. J. Pastore, T. R. Cook, J. Rzyev. Chem. Mater. 2018, 30, 8639-8649) or by synthesizing the MOF from a polymer ligand (see, e.g., Z. Zhang, H. T. H. Nguyen, S. A. Miller, A. M. Ploskonka, J. B. DeCoste, S. M. Cohen. J. Am. Chem. Soc. 2016, 138, 920-925, Z. Zhang, H. T. H. Nguyen, S. A. Miller, S. M. Cohen, Angew. Chem. Int. Ed. 2015, 54, 6152-6157).

One aspect in the design of the composite sorbent will be optimizing the tradeoff between large active area, low pressure drop, and mechanical robustness. This may be done with hierarchically porous systems, with porosity on multiple size scales so that surface area is high but flow impedance is low. Textiles, which have porosity on the scale of threads (100s of um to mm), individual fibers (100s of nm to 10s of um), and optionally pores in the fibers themselves (nms to 100s of nm) are one proposed solution. Polymer fibers may be easily and scalably fabricated via electrospinning. Hierarchically porous structures may also take advantage of aerogels, which have surface areas on the order of 100s of m2/g. A synthesis route for polymer aerogels has been developed (see, e.g., G. Iftime et al. Polymer Aerogel for Window Glazings, U.S. Pat. No. 10,421,253B2, Sep. 24, 2019) featuring surface areas >900 m2/g.

InFIG.4, a cross sectional view shows details of a fan400according to an example embodiment. The fan400includes two or more blades402coupled to a hub404. As shown here, the blades402and hub404may be formed integrally, e.g., cast, 3D printed, machined, etc. In other embodiments, the blades402may be formed separately from the hub404and attached in a final assembly of the fan400. There may be at least two blades402, and the blades402are generally arrayed radially about the hub404so that the fan400is balanced around a rotational axis403. The blade402is shown with a solid core, however may be perforated or otherwise allow some amount of air (or other fluid) to migrate from one major surface to another.

The fan blade402and hub404may be made from the same or different materials (in the latter case where the blade402and hub404are not formed integrally). The material may include metals such as Al, Mg, corrosion resistant steel, etc. The material may also or alternatively include polymers, composites (e.g., fiberglass, carbon fiber). The materials of the fan blade402and hub404should at least be resistant to the corrosive effects of water/humidity and have sufficient mechanical properties (e.g., strength, toughness) to withstand the predicted mechanical loading on the fan blade402(e.g., transverse forces caused by driving airflow, centrifugal forces due to rotation) and hub404(e.g., centrifugal forces due to rotation, stresses caused by imbalances in the blades402).

The blade402is shown coated with a desiccant material406that is operable to adsorb airborne moisture in an ambient airflow and desorb moisture in a heated airflow. The desiccant material406may, for example, include at least one of a phase-changing polymer, silica gel or zeolite adsorbent, metal-organic framework, ionic liquid, and halogen-doped nanoparticles. In another embodiment, the desiccant material406may include quaternary salt polymers, which have excellent water adsorbing properties. For example, poly(diallyldimethyl ammonium chloride) (PDADMAC) was used in a recent dehumidification project in synergistic combination with a phase-changing polymer, where the PDADMAC absorbs moisture from the air and the phase changing polymer takes up the moisture and swells. As seen in the detail view on the right side ofFIG.4, the desiccant material406includes a hierarchical porosity as seen in portions410,411of lower porosity material being embedded within a higher porosity material408.

Note that the portion410has higher porosity than portion411, and this can be repeated with fewer or more portions of different porosity. Other material structures may also be introduced into the coating of desiccant material406, such as fibers, nanowires, vias, etc., as illustrated by nanowire mesh412These structures may be formed of a material with high thermal conductivity, such as Ag, Cu, Au, Al, SiC, graphene, etc. These thermally conductive structures can reduce thermal gradients within the fan, such as within and along the coating of desiccant material406.

In order to form the desiccant material406coating, controlled polymer aerogel synthesis and electrospinning can be used to produce hierarchically porous systems. The pore sizes can span a wide range of size scales, providing high surface area with low flow resistance. Metal-organic framework (MOF) particles can be added as inclusions, as has been demonstrated for ZIF-8 in PVP (see, e.g., R. Ostermann et al., Chem. Commun. 2011, 47, 442-444). Hydrophilicity of the porous support matrix can be enhanced through the incorporation of comonomers such as β-cyclodextrin (see, e.g., A. Alsbaiee, B. J. Smith, L. Xiao, Y. Ling, D. E. Helbling, W. R. Dichtel, Nature, 2016, 529, 190-194) or through blending with hydrophilic polymers of intrinsic microporosity (see, e.g., R. A. Kirk, M. Putintseva, A. Volkov, P. M. Budd. BMC Chem. Eng. 2019, 1, 18), as needed. Other additives such as Ag nanowires or sacrificial materials can optionally increase surface area and conductivity (see, e.g., J. Xue et al., Chem. Rev., 2019, 119, 5298-5415).

InFIG.5, a microscopic image shows an example of an electrospun structure according to an example embodiment. Electrospinning is considered a likely candidate for covering fan blades with desiccant as described above. In other embodiments, MOF sorbents may be incorporated into mesoporous polymer aerogels with controlled pore architectures, and may yield a complimentary platform for sorbent fan blade production. Blades can be produced by cutting and shaping monolithic nonwoven mats. In other embodiments, the blade shape can be fabricated from a lightweight, conductive scaffold such as a mesh or foil, and electrospinning can occur directly onto the blades.

One characteristic that may be optimized in a system as described herein is electrical efficiency. The efficiency of the electrical system can determine the fan operation characteristics along with the back pressure imposed by the adsorption/desorption subsystems. In some embodiments, the supply air can flow in channels past the surface of the polymer films. This leads to convection-diffusion type problem where Peclet number determines the transport rates. Composite material properties can be estimated using experimentally obtained pure MOF and composite material sorption characteristics. Commercially available software can provide computer simulations of 3D airflow and conjugated heat and mass transfer models using Reynolds averaged Navier-Stokes equations coupled with energy and species equation using.

InFIG.6, a flowchart shows a method according to an example embodiment. The method involves driving600an ambient airflow with fan blades of a rotating fan, the fan blades comprising a desiccant material on an outer surface. The airborne moisture is adsorbed601in the ambient airflow by the desiccant. A heated airflow is driven602with the fan blades of the rotating fan. The desiccant material desorbs603moisture to the heated airflow.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g.1to5includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

The various embodiments described above may be implemented using circuitry, firmware, and/or software modules that interact to provide particular results. One of skill in the arts can readily implement such described functionality, either at a modular level or as a whole, using knowledge generally known in the art. For example, the flowcharts and control diagrams illustrated herein may be used to create computer-readable instructions/code for execution by a processor. Such instructions may be stored on a non-transitory computer-readable medium and transferred to the processor for execution as is known in the art. The structures and procedures shown above are only a representative example of embodiments that can be used to provide the functions described hereinabove.

The foregoing description of the example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Any or all features of the disclosed embodiments can be applied individually or in any combination are not meant to be limiting, but purely illustrative. It is intended that the scope of the invention be limited not with this detailed description, but rather determined by the claims appended hereto.