Thermoelectric Air Conditioning System with Integrated Solid Desiccant-Based Dehumidification for Separate Sensible and Latent Cooling

Abstract

A novel cooling system is disclosed. It includes one or more thermoelectric (TE) modules, each TE module having at least one semiconductor element located between two ceramic plates. The ceramic plates also include one or more electrodes. The cooling system further includes one or more heat exchangers, where the heat exchangers are in contact with at least one ceramic plate. In addition, the system includes one or more solid desiccant-based dehumidification compartments. Further, the cooling system is configured to direct air over both the TE modules and the desiccant dehumidifier.

Claims

1. A cooling system, comprising: a. one or more thermoelectric (TE) modules, each TE module comprising at least one semiconductor element located between two ceramic plates; wherein the ceramic plates further comprise one or more electrodes; b. one or more heat exchangers; wherein the heat exchangers are in contact with at least one ceramic plate; and c. one or more desiccant wheels, wherein the wheels are capable of rotating; wherein the cooling system is configured to direct air over both the TE modules and the desiccant wheels.

2. The cooling system of claim 1 wherein the ceramic plates comprise a material selected from the group consisting of hexagonal boron nitride, aluminum oxide and combinations thereof.

3. The cooling system of claim 1 wherein the semiconductor element comprises a material selected from the group consisting of Bi.sub.0.5Sb.sub.1.5Te, Bi.sub.2Te.sub.2.7Se.sub.0.3 and combinations thereof.

4. The cooling system of claim 1 wherein the at least one semiconductor element is bonded to at least one electrode.

5. The cooling system of claim 1 wherein the desiccant wheels comprise a material selected from the group consisting of micro-porous metal foam, micro-porous ceramic foam, and combinations thereof.

6. The cooling system of claim 1 wherein the desiccant wheels are coated in one or more solid desiccants selected from the group consisting of mesoporous silica particles, silica aerogels, zeolite, carbon-based materials, hygroscopic salts, and combinations thereof.

7. A cooling system, comprising: a. one or more thermoelectric (TE) modules, each TE module comprising at least one semiconductor element located between two ceramic plates; wherein the ceramic plates further comprise one or more electrodes; b. one or more heat exchangers; wherein the heat exchangers are in contact with at least one ceramic plate; and c. one or more solid desiccant-coated heat exchangers (DCHX), wherein each DCHX comprises one or more substrates selected from the group consisting of micro-porous metal foam, micro-porous ceramic foam, metal plate fins with millimeter spacing, and combinations thereof; wherein the cooling system is configured to direct air over both the TE modules and the desiccant-coated substrates.

8. The cooling system of claim 7 wherein the ceramic plates comprise a material selected from the group consisting of hexagonal boron nitride, aluminum oxide and combinations thereof.

9. The cooling system of claim 7 wherein the semiconductor element comprises a material selected from the group consisting of Bi.sub.0.5Sb.sub.1.5Te, Bi.sub.2Te.sub.2.7Se.sub.0.3 and combinations thereof.

10. The cooling system of claim 7 wherein the at least one semiconductor element is bonded to at least one electrode.

11. The cooling system of claim 7 wherein the one or more substrates comprise metal foam.

12. The cooling system of claim 7 wherein the desiccant for the DCHX is selected from the group consisting of mesoporous silica particles, silica aerogels, zeolite, carbon-based materials, hygroscopic salts, and combinations thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The objects and advantages of the disclosed invention will be further appreciated in light of the following detailed descriptions and drawings in which:

[0011] FIG. 1 is a schematic of an embodiment of the TE A/C system of the present invention. Three stages are shown for separate sensible and latent cooling (SSLC), and waste heat recovery. Waste heat from the exhaust air is captured to preheat water for hot water storage.

[0012] FIG. 2 is a schematic of another embodiment of the TE A/C system of the present invention. This embodiment has stationary desiccant-coated heat exchangers (DCHX). Valves (not shown) are used to redirect air flow and switch dehumidification and regeneration processes between the two identical DCHXs.

[0013] FIG. 3 is a cross-sectional schematic of an embodiment of the thermoelectric (TE) module of the present invention.

[0014] FIG. 4 is a cross-sectional schematic of an embodiment of the system of the present invention in a circular pipe geometry. The figure shows that concentric inlet (inner pipe) and outlet (outer pipe) circular air ducts are interfaced with round-plate TE coolers in the middle.

[0015] FIG. 5 is a cross-sectional schematic of an embodiment of the system of the present invention in a circular pipe geometry with multiple desiccant wheels. The figure shows the circular pipe system with three desiccant wheels overlapping over the inlet area at front for separate latent cooling. The inlet air passes through the wheels one after another for subsequent dehumidification of inlet air.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The details of one or more embodiments of the disclosed subject matter are set forth in this document. Modifications to embodiments described in this document, and other embodiments, will be evident to those of ordinary skill in the art after a study of the information provided herein.

[0017] The present disclosure may be understood more readily by reference to the following detailed description of the embodiments taken in connection with the accompanying drawing figures, which form a part of this disclosure. It is to be understood that this application is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting. Also, in some embodiments, as used in the specification and including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” or “approximately” one particular value and/or to “about” or “approximately” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment.

[0018] While the following terms are believed to be well understood by one of ordinary skill in the art, definitions are set forth to facilitate explanation of the disclosed subject matter. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed subject matter belongs.

[0019] As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, size, concentration or percentage is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.

[0020] The present invention involves an all solid-state, integrated system comprising a modular thermoelectric cooling subsystem, desiccant-based dehumidification subsystem for separate sensible and latent cooling (SSLC), and components for waste heat recovery from exhaust gas. The system can be used as a non-vapor compression-based air conditioning system for buildings and households. A first embodiment of the desiccant dehumidifier compartment of the present invention involves rotating desiccant wheels. A second embodiment of the desiccant dehumidifier compartment of the present invention involves stationary desiccant-coated heat exchangers. These are described in the schematics of FIGS. 1 and 2, respectively.

[0021] Referring to FIG. 1, a system 10 has exhaust air 30 entering the top and bottom of a sensible cooling repeatable segment 20. Sensible cooling repeatable segment 20 and similar segments provide sensible cooling. The sensible cooling repeatable segment 20 has a center cold-side heat exchanger 50 connected to two thermoelectric (TE) modules 55 and 57. The TE modules are connected to hot-side heat exchangers 40 and 42. Exhaust air 30 enters the hot-side heat exchangers 40 and 42, passing through to a second unit with hot-side heat exchangers 44 and 46. The exhaust air exits hot-side heat exchangers 44 and 46 and enters heating blocks 60 and 62. The exhaust air passes through to the multiple-stage desiccant wheels 70. The exhaust air next enters air-to-water heat exchangers 80 and 82. These units provide waste-heat recovery. Water 100 and 102 runs through the air-to-water heat exchangers 80 and 82 and gets heated. The pre-heated water is supplied to a hot-water storage. The exhaust air exits air-to-water heat exchangers 80 and 82 as exhaust air out 90.

[0022] With further reference to FIG. 1, air in 120 enters the system 10 through the latent cooling device 200. Dehumidified air 130 exits the latent cooling device 200 and passes into cold-side heat exchanger 52. Heat 160 from dehumidified air 130 is drawn into hot-side heat exchangers 44 and 46 through TE modules 58 and 59. Dehumidified air 130 exits cold-side heat exchanger 52 and passes into cold-side heat exchanger 50. Finally, conditioned air 180 exits the system 10.

[0023] The system 10 of FIG. 1 is a modular design with multi-stage double-side TE cooling in a segmented counter-flow configuration. It integrates double-stage solid desiccant wheels at the front for SSLC. For continuous SSLC operation, moisture is continuously discharged from the desiccant by the rotating wheel with heated exhaust air. The heated air then passes through air-to-water heat exchangers for waste-heat recovery to preheat water for hot-water storage. In one embodiment, the TE sensible cooling stage consists of multiple segments, indicated by sensible cooling repeatable segment 20 in FIG. 1, added in parallel and series depending on the performance requirements for high system scalability. Each segment is independently optimized with a heat exchanger design and applied electric current, which can be adjusted for flexible operation. Air is consecutively cooled through the cold-side heat exchangers 50 and 52 connected in series to reach the target cooling temperature.

[0024] In a second embodiment shown in FIG. 2, a dehumidifier for latent cooling 250 comprises two identical stationary solid desiccant-coated heat exchangers (DCHX) 290 and 300. The other compartments are the same as in the first configuration (see FIG. 1). In this configuration, dehumidification and regeneration are performed separately with two identical DCHXs. Rotating wheels are not needed. One DCHX 290 used for dehumidification of inlet air 120 is cooled with ambient air to remove excess heat generated during the exothermal process of dehumidification by solid desiccant. While the first DCHX 290 performs dehumidification, the other DCHX 300 is regenerated (moisture is removed from the desiccant) with the warm exhaust air 30 incoming from the sensible cooling repeatable segment 20. Additional heating of the exhaust air and the DCHX 300 itself can be performed using a heater 310 integrated with the DCHX 300 to increase the rate of regeneration. Once the DCHX 290 used for dehumidification is fully saturated, a valve (not shown) is used to redirect the inlet process air to the other DCHX 300 that has been regenerated to keep dehumidification process running. The saturated DCHX is then regenerated with exhaust air and a heater, for which another valve is used to redirect the exhaust air to that DCHX. In an alternative embodiment of this configuration, water cooling can be used instead of air cooling in the dehumidification DCHX 290 for waste-heat recovery to preheat water for hot-water storage.

[0025] This invention of TE air conditioning system can provide many advantages over the conventional air conditioning technologies. For example, the system of the present invention is completely solid-state, and non-vapor-compression-based air conditioning technology with low noise, low vibration, small form factors, high efficiency, high scalability, and demand-flexible operation.

[0026] In addition, the system separates sensible cooling (TE cooling) and latent cooling (desiccant wheels) and enables completely independent control of each cooling for adaptive, demand-flexible air conditioning. TE cooling is controlled by the input electric current to individual TE modules for varying degree of cooling (temperature drop) per module and COP (coefficient of performance). The performance of the desiccant dehumidifier can be controlled by adjusting the rotation speed of the wheels in the case of desiccant wheels (e.g. no latent cooling with zero rotation in a very low humidity condition) in the embodiment shown in FIG. 1. Alternatively, the performance of the desiccant dehumidifier can be controlled by adjusting the air cooling/heating for the DCHXs in the second embodiment shown in FIG. 2. The separate sensible and latent cooling also enables independent optimization of both sub-systems for maximum overall energy efficiency.

[0027] Desiccant dehumidification subsystem may require additional heating of air for efficient discharging of water vapor during the regeneration process, which could result in a reduced overall energy efficiency. In one embodiment, efficient air-to-water heat exchangers are added at the exhaust gas outlet as shown in FIG. 1, to recover waste heat from the exhaust air to preheat water for hot-water storage. The waste heat recovery will increase the overall system efficiency substantially.

[0028] The system is highly scalable in terms of the cooling capacity. Air flowrate for each TE module may be fixed, e.g. with a fixed fan speed, and multiple parallel rows of TE modules are added to meet the total air flowrate requirement. The degree of cooling (ΔT) is also scaled with multiple TE modules connected in series, as it is linearly proportional to the number of modules in series. Multiple series modules are beneficial to make the TE system operated in a high-COP mode with a low electric current input to each module, e.g. <1 A, to achieve a high overall system COP. A high system COP results in low electricity cost for the AC.

[0029] Due to the modular structure, repair and maintenance is easy and fast. Any individual faulty TE modules can be identified and replaced with a sound module. Each desiccant-coated wheel is also replaceable and/or repaired individually. The cost-effective TE module design strategy of the present invention allows the utilization of low fill factor (fractional coverage by TE elements) and low element thickness, which ensures the use of low volume of TE materials in each module for near-optimal cooling performance, reducing the material cost and the installation cost.

TE Modules

[0030] Referring to FIG. 3, in one embodiment, a TE module 370 is designed in the conventional H-geometry with p-type and n-type semiconductor elements 380 that are vertically standing towards the heat flow direction and connected via horizontal electrodes (not shown). The semiconductor elements 380 are sandwiched by two ceramic flat plates 390 made of highly thermally conducting, but electrically insulating materials such as hexagonal boron nitride and aluminum oxide (Al.sub.2O.sub.3) for good thermal interface with external heat exchangers at both sides (see FIG. 1). Useful semiconductor materials for near-room temperature application include Bi.sub.0.5Sb.sub.1.5Te for p-type, and Bi.sub.2Te.sub.2.7Se.sub.0.3. Elements of the TE module 370 are bonded to the electrodes that are pre-patterned on the ceramic plates 390. In one embodiment, the elements of the TE module are fusion-bonded to the electrodes.

System Geometry

[0031] In an embodiment of the present invention, rectangular inlet and outlet air ducts are used, and flat-plate TE modules make interfaces between the rectangular ducts as shown in FIG. 1. In another embodiment, a thermoelectric cooling system 400 includes concentric circular ducts 420 and 430 used with round-plate TE modules in the middle as shown in FIG. 4. The TE modules 440 pump heat 450 from the inner duct 430 to the outer duct 420, expelling heat with the exhaust air. This allows for sensible cooling of the inlet air. In addition, the outer duct 420 may be covered in thermal insulation 410 for better heat control. Referring to FIG. 5, several stages of rotating desiccant wheels 510 are placed in front of the circular pipe system 500 for subsequent latent cooling of the inlet air in the inner duct and discharging of moisture to the exhaust air at the outer duct.

Desiccant Dehumidification Subsystem

[0032] In one embodiment, micro-porous metal/ceramic foams are useful as the substrate for the desiccant dehumidification subsystem due to their high surface area-to-volume ratio. In another embodiment, metal plate fins with millimeter spacing are used as the substrate. Solid desiccants such as mesoporous silica particles, silica aerogels, zeolite, hygroscopic salts, and carbon-based materials can be used to coat the substrate to dehumidify the inlet air. The captured moisture is removed either by heated exhaust air that passes through the wheel in the first configuration (see FIG. 1), or by blow drying with warm exhaust air in the second configuration. For both configurations, exhaust air is heated up close to the regeneration temperature of the solid desiccant for efficient release of moisture.

[0033] It should be understood that every maximum numerical limitation given throughout this specification includes every lower numerical limitation, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this specification will include every higher numerical limitation, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this specification will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.

[0034] All documents cited are incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention.

[0035] It is to be further understood that where descriptions of various embodiments use the term “comprising,” and/or “including” those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language “consisting essentially of” or “consisting of.”

[0036] While particular embodiments of the present invention have been illustrated and described, it would be obvious to one skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.