Patent Application
20140245772
The invention relates generally to an air temperature and humidity control device, and more particularly, to an air temperature and humidity control device integrating more than one heat pump.
Conventional air conditioning systems generally do not perform humidity control functions in an energy efficient manner. When humidity control is desired, air conditioners based on direct expansion (DX) may be operated to condense moisture in the air through supercooling. The drier, supercooled air is then reheated for comfort before entering into a facility to be air conditioned. Significant energy is consumed during the supercooling and reheating of the air, which renders the process inefficient. Moreover, water condensation on the metallic DX coils may cause corrosion problems, which increases the maintenance cost of the air conditioning systems.
In light of the need for more efficient humidity control, air conditioning systems with solid desiccant wheels integrated in temperature control units have been developed. The solid desiccant wheel is loaded with a solid desiccant and is positioned just upstream of the temperature control unit so that cooled air transversely passes over a section of the rotating desiccant wheel, during which the moisture in the air is absorbed by the desiccant. The remaining section of the desiccant wheel is reheated so that the absorbed moisture can be desorbed to regenerate the desiccant. While capable of achieving low humidity outputs, systems based on desiccant wheels are space-consuming and inefficient, as energy is required to regenerate the desiccant. Moreover, because the desiccant wheel is relatively cumbersome and not easy to install or uninstall, the capacity and operation of the systems based on desiccant wheels are generally not intended to accommodate a wide range of operations.
In addition to desiccant wheels, humidity control may be achieved using a system having a heat pump coupled to a liquid desiccant loop. The liquid desiccant, such as lithium chloride for example, is cooled and heated by the heat pump. The desiccant loop includes two contact towers loaded with packing materials or two membrane-type contactors for example. Several sprinklers are provided at the top end of the tower to distribute the liquid desiccant (cooled or heated by the heat pump) onto the packing materials, while air is blown from the bottom end of the contact tower as the liquid desiccant trickles down the packing material. As a result of the direct contact between the desiccant and air, water may be absorbed from the air into the desiccant or desorbed from the desiccant into the air. Simultaneously, the air may be heated or cooled by the liquid desiccant. Because of its integration with a heat pump, the liquid desiccant system discussed above requires less energy for desorbing water from the liquid desiccant, i.e. the regeneration of the liquid desiccant.
However, as the operation of the system requires direct contact between numerous streams of liquid desiccant and air, entrainment of liquid desiccant droplets into the air stream is inherent to spraying direct contact technologies. Such liquid desiccant entrainment (or liquid desiccant carryover) can cause corrosion of ductwork and human health issues. Moreover, similar to the desiccant wheels, the contact towers of the above-discussed system are relatively cumbersome in construction and not easy to modulate to accommodate a wide range of operations.
To address prevalent issues associated with direct contact systems, other systems without direct contact include a contactor having at least one contact module with a porous sidewall that is permeable to water vapor and impermeable to the liquid desiccant employed. The contactor may include at least one contact module with a porous sidewall having exterior and interior sides, wherein the interior side of the sidewall defines an internal space in which the liquid desiccant flows. The blower generates an air flow along the exterior side of the sidewall in order to provide desirable temperature and humidity.
The contactors in these non-direct contact systems commonly include a hydrophobic porous material with limited heat transfer potential, but better mass transfer potential when compared to conventional refrigerant evaporator and condensing technologies. In addition, the performance, size and cost of such materials for the hydrophobic porous contactors needed in these systems places a practical limit on the amount of sensible heat removal that can be achieved economically from the incoming air. Building codes may require that a large fraction of outdoor (ambient) be processed and delivered to the conditioned space within a given temperature and humidity range. The contactor-based temperature and humidity control devices may not be able to process the large fraction of outdoor or process air to desirable conditions in a cost-effective and energy efficient manner.
According to one embodiment of the invention, an air temperature and humidity control device is provided including a first heat pump having a compressor, an expansion valve, a condenser, and an evaporator. The first heat pump has a refrigerant circulating there through. A humidity controller includes a first contactor fluidly coupled to the evaporator and condenser of the first heat pump. The first contactor includes at least one contact module having a porous sidewall that defines an internal space through which a hygroscopic material flows. A first air flow is in communication with the porous sidewall of the first contactor such that heat and/or water vapor transfers between the first air flow and the hygroscopic material. The device also has a second heat pump including a first coil. The first coil is arranged generally downstream from the first contactor relative to the first air flow.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Referring now to the FIGS. an air temperature and humidity control device 10 is schematically illustrated. The air temperature and humidity control device 10 generally includes a first heat pump 20 and a humidity controller 30. As illustrated, the closed loop first heat pump 20 includes a compressor 22, a condenser 24, an expansion valve 26, and an evaporator 28. In operation, a refrigerant R is circulated through the various components of the heat pump 20 in a known manner so that the refrigerant R is in a compressed state (releasing heat) in the condenser 24 and is in an expanded state (heat absorbing) in the evaporator 28. The refrigerant R may be an environmentally friendly refrigerant, such as R-410 for example; however other suitable refrigerants are within the scope of the invention.
The humidity controller 30 includes a first contactor 32 having hygroscopic material L flowing there through, such as liquid desiccant including an aqueous lithium chloride solution for example. Other suitable hygroscopic materials are within the scope of the invention. The first heat pump 20 and humidity controller 30 may be thermally coupled together so as to allow the hygroscopic material L to be heated in the condenser 24 and cooled in the evaporator 28. In one embodiment, the first contactor 32 is fluidly coupled to the evaporator 28 and the condenser 24 through a first conduit 34 and a second conduit 36, respectively. As illustrated in the FIGS., the hygroscopic material L may be driven by a pump 38 to flow sequentially through the evaporator 28, the first contactor 32, and the condenser 24.
A first blower 40 is configured to generate an air flow A over the adjacent first contactor 32. The air flow A may include air from any of a number of sources including, but not limited to, process air, exhaust air, outdoor air, or a combination thereof for example. The first blower 40 may be an electric fan positioned adjacent to the first contactor 32, or an air outlet or exhaust of a heating ventilation and air conditioning (HVAC) system for example. As the air flow A from the first blower 40 passes over the first contactor 32, heat and/or water transfers between the air flow A and the hygroscopic material L in the first contactor 32 such that after passing over the first contactor 32, the air flow A has a desirable air temperature and/or humidity. In one embodiment, the first contactor 32 serves as an absorber, transferring moisture and/or heat from the air flow A to the hygroscopic material L.
The humidity controller 30 additionally includes a second contactor 42 through which the hygroscopic material L flows. The second contactor 42 may also be thermally coupled to the condenser 24 and the evaporator 28 through a third conduit 44 and a fourth conduit 46, respectively. As illustrated in
A second blower 48 may be provided to generate an air flow B over the second contactor 42. Similar to the air flow A over the first contactor 32, air flow B may include air from any of a number of sources including, but not limited to, process air, exhaust air, outdoor air, or a combination thereof for example. In one embodiment, the second blower 48 may include an electric fan positioned adjacent to the second contactor 42, or alternatively, the electric fan may be substituted by an air outlet of an HVAC system. As the air flow B passes over the second contactor 42, heat and/or water transfers between the air flow B and hygroscopic material L in the second contactor 42 to allow the device to provide a desirable air temperature and/or humidity. In one embodiment, the second contactor 42 serves as a desorber, removing moisture to regenerate the hygroscopic material L.
To facilitate the thermal coupling between the heat pump 20 and humidity controller 30, the evaporator 28 and the condenser 24 may be configured as refrigerant-hygroscopic material heat exchangers. As a non-limiting example, the refrigerant-hygroscopic material heat exchangers may be of a shell-and-tube design, in which a bundle of tubes is disposed within an outer shell. In operation, one fluid flows through the tubes and another fluid flows along the tubes (through the shell) to allow heat transfer between the two fluids. Alternatively, the refrigerant-hygroscopic material heat exchangers may also be of a brazed or welded plate design for compactness and increased heat exchange effectiveness. The refrigerant-hygroscopic material heat exchangers described herein are exemplary and other suitable heat exchangers known to one of ordinary skill in the art are also within the scope of this invention. The humidity controller 30 may include a hygroscopic material-hygroscopic material heat exchanger (not shown) configured to recuperate heat between the flow of hygroscopic material L from the first contactor 32 and the flow of hygroscopic material L from the second contactor 42. In addition, the humidity controller may include one or more bypass flows so that at least a portion of the hygroscopic material L can bypass certain components of the humidity controller 30 to facilitate efficiency and control.
In one non-limiting embodiment, illustrated in
In order to facilitate humidification and dehumidification, the porous sidewall 52 of the contact module 50 may be permeable to water vapor, and impermeable to the hygroscopic material L so as to form a closed loop. Thus in one embodiment, the porous sidewall 52 is made of a hydrophobic porous material, such as a plastic (polymeric) porous material for example.
Referring again to
As illustrated in
The first contactor 32 is arranged generally downstream of the evaporator 28 so that the hygroscopic material L may be cooled in the evaporator 28, such as to a temperature below the ambient temperature for example, before passing through the first contactor 32. The hygroscopic material L cools the at least one contact module 50 of the first contactor 32 as it flows there through. As a result, the cooled contact modules 50 are configured to absorb heat, for example from air flow A adjacent the exterior side 56 of the contact modules 50. The hygroscopic nature may cause the hygroscopic material L to absorb water vapor from the air flow A. Thus, in one embodiment, the at least one contact module 50 of the first contactor 32 decreases both the temperature and the humidity of the air flow A along its exterior side 56.
As illustrated in
The second contactor 42 is positioned downstream from the condenser 24 such that as the hygroscopic material L passes through the condenser 24, the hygroscopic material L is heated, such as to a temperature above the ambient temperature for example. As the heated hygroscopic material L flows through the at least one contact module 50 of the second contactor 42, the water vapor differential across the porous sidewall 52 causes the hygroscopic material L to release water vapor into the air flow B. The resultant hygroscopic material L is more concentrated than the hygroscopic material L entering the second contactor 42. At the same time, the at least one contact module 50 of the second contactor 42, heated by the hygroscopic material L flowing there through, releases heat to the air flow B along the exterior side 56 of the contact modules 50. Thus, the contact modules 50 of the second contactor 42 may function to increase both the temperature and humidity of the air flow B along its exterior side.
The second coil 66 of the second heat pump 60 may be generally aligned with and arranged downstream from the second contactor 42. As illustrated in
Referring now to
Referring now to
With reference now to
The air temperature and humidity control device illustrated in
The air temperature and humidity control device 10 may be further simplified, as illustrated in
The disclosed air temperature and humidity control device 10 may be arranged in any of a variety of configurations, allowing for tradeoffs between system complexity, cost, physical size, efficiency, and controllability.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
This application claims the benefit of U.S. provisional patent application Ser. No. 61/772,240 filed Mar. 4, 2013, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61772240 | Mar 2013 | US |
