CROSS-REFERENCE TO RELATED APPLICATION
This application is related to and claims priority from provisional application U.S. Ser. No. 61/378,661 filed Aug. 31, 2010 in the names of Lawrence C. Hoagland and Donald Steele and entitled Three Path Energy Ventilation System
This application disclosure relates generally to energy efficient air transfer systems, and more particularly to air transfer systems that include multiple rotary air to air, thermal energy exchange units, and multiple pathways for directing air through the thermal energy exchange units.
Energy recovery air transfer systems include air handlers, ventilation systems (ERVs), and HVAC systems, as well as some type of heat exchanger for conserving energy. Rotary air to air heat exchangers usually include a porous wheel and conserve energy by being mounted so as to rotate between two separate counter-flowing airstreams (usually one flowing into a building and one flowing out of the building) so as to transfer thermal energy and, depending on the construction of the wheel, moisture between the airstreams. For example, in hot humid climates hot and humid air that is brought into a building first passes through one half of the energy recovery wheel as it rotates through the intake/supply air. As the wheel continues to rotate through the counter-flowing air streams, heat and/or moisture is transferred from the wheel to the outgoing cooler drier return/exhaust air. As a result, the temperature and humidity of the intake air is reduced before, for example, being transferred through an air conditioning unit. This reduces the load on the air conditioning unit, conserving energy.
In designing large HVAC systems, particularly for large buildings, components become large, expensive and difficult to manage. Large rotary air-to-air heat exchange wheels are usually mounted in cassettes so that they can be more easily installed and serviced when necessary. With rotary air to air heat exchange wheels designed for large airflows (say above 25,000 CFM) the physical size of the cassette becomes too large to ship in one piece. Some assembly must be done on site.
With increasingly large, single wheel, rotary heat exchangers, the bending forces on the spokes caused by counter-flowing airstreams increase as a function of the square of the rotary heat exchanger wheel radius. The design must provide for these increased forces, so a structurally stronger and hence heavier wheel and frame design is necessary as the size of the wheel is increased.
BACKGROUND LISTING OF PRIOR ART
See EP 2093507; EP 2116785; KR 10094085; U.S. Pub. App. No. 20110146941; U.S. Pat. Nos. 4,113,004; 4,462,459; 4,513,809; 4,754,806; 4,982,575; 5,353,606; 5,542,968; 5,997,277; 6,199,368; 6,355,091; 6,823,135; 7,484,381; 7,886,986; WO 2008069559 and WO 2009136413.
With all other design factors being equal, the amount of energy that can be transferred with a rotary air-to-air heat exchange wheel is a function of the open surface area within the porous wheel over which the airstream flows. Accordingly, in accordance with the teachings disclosed herein a large wheel is replaced with four, or more, rotary air-to-air heat exchange wheels of similar combined surface area and utilized in at least a three-path counter-flowing airstream configuration so that many benefits can be realized over utilizing a large single rotary air-to-air heat exchange wheel.
In accordance with aspect of the teachings provided herein, a system is provided for transferring thermal energy between incoming supply air and outgoing exhaust air. The system comprises: at least four rotary heat exchange units positioned in an array so that incoming supply air and outgoing exhaust air passes through each of the wheels as counter flowing air streams; and partitions defining at least three pathways for directing the counter flowing air streams through the rotary heat exchange units.
In accordance with aspect of the teachings provided herein, a method of transferring thermal energy between incoming supply air and outgoing exhaust air, the method comprising:
positioning at least four rotary heat exchange units in an array in an air transfer system so that incoming supply air and outgoing exhaust air passes through each of the wheels as counter flowing air streams; and
defining at least three pathways for directing the counter flowing air streams through the rotary heat exchange units.
As used herein the term “heat exchange” applies to devices that transfer sensible and/or latent heat.
These, as well as other components, steps, features, objects, benefits, and advantages, will now become clear from a review of the following detailed description of illustrative embodiments, the accompanying drawings, and the claims.
BRIEF DESCRIPTION OF DRAWINGS
The drawings disclose illustrative embodiments. They do not set forth all embodiments. Other embodiments may be used in addition or instead. Details which may be apparent or unnecessary may be omitted to save space or for more effective illustration. Conversely, some embodiments may be practiced without all of the details which are disclosed. When the same numeral appears in different drawings, it refers to the same or like components or steps:
In the drawings:
FIG. 1 is a front view of a prior art large rotary air-to-air heat exchange wheel assembly of the type used in an energy recovery ventilation system;
FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;
FIG. 3 is a front view of one embodiment of an energy recovery ventilation system designed in accordance with teachings herein and including four smaller rotary air-to-air heat exchange wheels providing the equivalent air flow and heat exchange of the single wheel assembly shown in FIG. 1;
FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 3 showing one arrangement of three pathways for the two counter flowing airstreams for the embodiment shown in FIG. 3;
FIG. 5 is a perspective view of the FIG. 3 embodiment showing the arrangement of an array of the rotary air-to-air heat exchange wheels, and the paths for the counter flowing airstreams;
FIGS. 6-8 shown various views of a cassette assembly for the four wheel array shown in FIGS. 3-5; and
FIG. 9 is a more detailed view of the pathways of the counter flowing airstreams of an air handler system.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Illustrative embodiments are now discussed. Other embodiments may be used in addition or instead. Details which may be apparent or unnecessary may be omitted to save space or for a more effective presentation. Conversely, some embodiments may be practiced without all of the details which are disclosed.
FIG. 1 illustrates a front view of a typical, large, prior art rotary air-to-air heat exchange wheel cassette assembly of the type used in ventilation systems positioned within duct work that define a dual pathway arrangement for the counter flowing airstreams. The cassette assembly shown generally within frame 20 includes a single wheel 22 mounted on an axle 24 for rotation about a rotation axis. The wheel is driven by a motor 26 and belt 28 or other device to rotate the wheel like a direct drive motor or a linear motor. The wheel 22 includes a matrix material which is porous to air flow through the matrix material. One example of a matrix material is a plastic ribbon wound around onto a hub 30 of the wheel so that a thin space is provided between adjacent layers of the ribbon material defining air passageways through the matrix. In this way the matrix material is porous to the air flow through the wheel. The plastic material will absorb thermal energy (sensible heat) from the air as the air passes through the passageways assuming that the material is cooler than the air, and as a function of the surface area defined by the ribbon material in all of the passageways. The ribbon material can be coated with a desiccant material so that moisture (and thus latent heat) in the air passing through the passageways will also be absorbed by the desiccant material.
As indicated in FIG. 2, the cassette is positioned within duct work constructed to direct two counter flowing airstreams through different portions of the wheel as the wheel rotates through the duct work. The nature of the airstreams is that one airstream will contain more heat and moisture than the other. In the case of a ventilation system used in a building in a warm humid climate, incoming supply air (SA) from the outside (OA) will contain more heat and moisture than the return air (RA) that is exhausted (EA) from the building, as shown in FIG. 2. Heat and moisture is absorbed by the wheel matrix as the air passes through the passageways exposed to outside air. As wheel rotates the heat and moisture absorbed in the bottom flow pathway of FIG. 2 is exposed to the cooler drier air provided through the upper flow pathway. The return air passing through the wheel matrix will absorb some of the heat and moisture from the wheel, before being exhausted from the building. Seals (not shown) are provided around the periphery of the wheel and between the two counter flowing airstreams so as to insure air flow is restricted in the two ducts and through the appropriate passageways of the wheel matrix.
In designing large HVAC systems, components become large, expensive and difficult to manage. With rotary air to air heat exchange wheels designed for higher airflows the physical size of the wheel cassette assembly becomes too large for easy installation and service. Usually some assembly must be done on site.
As shown in FIG. 1, for very large wheels, each wheel can include spokes 32 for helping the wheel resist the bending moment due to forces exerted by the two counter flowing airstreams. As wheel sizes increase, the bending forces on the spokes supporting the wheels caused by the forces exerted by the counter-flowing airstreams increase as the square of the wheel radius. The design must provide for these increased forces, so a structurally stronger and hence heavier wheel and frame design is necessary when using a single heat exchanger. The wheels must be constructed to resist as much as possible the bending moment of the wheel due to the forces of the counter flowing airstreams. Further, for very large wheels the matrix material may be made in pie-shaped segments 34 to reduce the size and weight of each component part of the wheel to facilitate assembly and disassembly of the wheel on site.
To understand the magnitude of the size and weight of a large wheel, the following is an example of a large wheel for an air flow of 65,000 cfm. The wheel is 182 inches in diameter and weighs 3886 pounds. In accordance with the approach described herein, the single wheel is replaced with multiple but smaller wheels designed to provide substantially the same air flow and energy transfer performance of the larger wheel. Many benefits can be achieved by using four, or more, heat exchange wheels having similar heat transfer surface area to that of one large heat exchange wheel and utilizing a three path airstream for the counter flowing airstreams through the multiple wheels.
One advantage of using multiple wheels is that the combined weight of the multiple wheels can be substantially less than that of the equivalent larger wheel. One arrangement of the multiple wheel assembly is shown in FIGS. 3-5, wherein the single wheel is replaced by four wheels. The four wheels are constructed to provide an equivalent amount of exposed surface area through the passageways of the four wheels as provided by the one wheel so as to provide the same energy transfer performance. In the illustrated embodiment, wheels 40A-40D are arranged in a two-by-two array and mounted so that counter flowing air streams flow through each wheel. Each wheel is rotatably driven, for example by a separate motor 42A-42D and belt 44A-44D, or other suitable drive mechanisms. Partitions in the form of duct work divide air flow into each of the wheels into three pathways. As shown in FIGS. 3-5, the top duct 46A provides a first pathway for the return/exhaust air through the top half of the wheels 40A and 40B, the middle duct 46B provides the second pathway for the outside/supply air through the bottom half of the wheels 40A and 40B, and the top half of the wheels 40C and 40D, while the lower duct 46C provides the third pathway for the return/exhaust air through the bottom half of wheels 40C and 40D. Seals (not shown) can be provided around the periphery of each wheel and between the ducts so that air passes through only those passageways of the portions of the wheels positioned within the ducts through which they are rotating at any one moment in time. As seen in FIG. 5, blowers 48 are provided for drawing air through each of the pathways. Note that two blowers are shown for each of the pathways 46A and 46C, but that air flow can be created by one blower where the two pathways are connected together
As shown in FIGS. 6-8, each of the wheels can be mounted in a separate individual frame 50, and slidable in and out of an assembly frame 52. Frame 52 includes channels 54 for receiving each of the wheels, and an end strip 56 for securing the individual frames supporting the wheels within the assembly frame 52. As shown in FIG. 8, the assembly frame 52 can include hinges 60 so that the user can control the width or height of the entire assembly by angling the individual cassettes relative to each other. As constructed, the assembled array of energy recovery units and their component parts can be more easily installed and maintained.
The assembly can be used in other air transfer systems, such as an air handler system. An embodiment of an air handler system is shown in FIG. 9 at 70. As shown a cabinet 72, supports the wheels so that they are arranged in the array allowing counter flowing air to pass through passageways along three pathways 74A, 74B and 74C. In this arrangement the pathways 74A, 74B and 74C are defined by the cabinet 70 and partitions 76. Cabinet includes openings/louvers 78 for drawing in outside air into pathways 72A and 72C. The outside air passes through the passageways of the portions of heat exchange wheels 40 disposed in pathways 72A and 72 C before passing as supply air out of the opening(s) 80 provided at the end of the cabinet 70. The return air provided through a different opening 82 of the cabinet 70 flows through the passageways of the portions of the wheels 40 in the pathway 72B before passing as exhaust air out the opening 82. An exhaust blower 84 is provided from drawing the air through the pathway 72B. Similarly, a blower (not shown) can be sued to draw air through the pathways 72A and 72C.
The components, steps, features, objects, benefits and advantages which have been discussed are merely illustrative. None of them, nor the discussions relating to them, are intended to limit the scope of protection in any way. Numerous other embodiments are also contemplated. These include embodiments which have fewer, additional, and/or different components, steps, features, objects, benefits and advantages. These also include embodiments in which the components and/or steps are arranged and/or ordered differently. For example, the pathways are described as accommodating outside/supply air or return/exhaust air, but the arrangements can be reversed. The arrangements describe allow for ease of construction, installation, maintenance, reduced cost and weight, improved reliability and performance. Further, while the wheels are shown in a two by two array, other configurations can be used. For example, a three by two, four by two, etc. array can be used with the pathway arrangement to provide counter flowing air through each wheel. And other arrays and pathways can be configure with more than three pathways and still achieve the advantages described herein. For example, a three by three array would require 5 pathways. In addition, providing multiple heat exchange wheels in an air transfer system, one can achieve a stepped efficiency control, replacing the need for variable speed control or dampers, simply by turning off one, two, three or all heat exchange wheel motors 42. For example, with a four energy recovery unit arrangement, one can provide 100, 75, 50, 25 or 0% of designed recovery. Further, if one energy recovery exchange wheel unit fails the others can remain in operation. While this would result in reduced performance, the system would still be recovering energy, allowing scheduled maintenance instead of requiring emergency repair. By reducing the size of each wheel, individual wheel cassettes can be moved through standard doors or elevators. Further, with smaller wheel cassettes, and/or their segments, the assembly is easier to clean, eliminating the need for drain pans. The cassettes are also easier to transport to and from the building site where they are employed, with smaller wheels being able to be transported on standard size maintenance elevators, and small enough for one person to move. Finally, with each cassette being smaller, the bearing forces and bending moments (compared to a single large wheel) are much lower. The rim forces are much lower as the wheel rim velocity is a fraction of that of a comparable single cassette operating at the same RPM.
Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications which are set forth in this specification, including in the claims which follow, are approximate, not exact. They are intended to have a reasonable range which is consistent with the functions to which they relate and with what is customary in the art to which they pertain.
All articles, patents, patent applications, and other publications which have been cited in this disclosure are hereby incorporated herein by reference.
The phrase “means for” when used in a claim is intended to and should be interpreted to embrace the corresponding structures and materials which have been described and their equivalents. Similarly, the phrase “step for” when used in a claim is intended to and should be interpreted to embrace the corresponding acts which have been described and their equivalents. The absence of these phrases in a claim means that the claim is not intended to and should not be interpreted to be limited to any of the corresponding structures, materials, or acts or to their equivalents.
Nothing which has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is recited in the claims.
The scope of protection is limited solely by the claims which now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language which is used in the claims when interpreted in light of this specification and the prosecution history which follows and to encompass all structural and functional equivalents.