FIELD OF INVENTION The present invention relates generally to regenerator heat exchange devices, and, more particularly, to a hybrid rotary heat regenerator with a matrix containing both latent heat exchange material and sensible heat exchange material in adjustable proportions.

BACKGROUND OF THE INVENTION Regenerative heat exchange devices are well known for their ability to transfer heat, water vapor, or both between the treated airstream and die regenerating airstream so as to conserve energy, while at the same time improving the quality of indoor air. One type of regenerative heat exchange device is the rotary air-to-air heat exchanger typically in the form of a rotary heat exchange wheel including a matrix of heat exchange material. For example, see Canadian Patent No. 1,200,237 (Hoagland) and U.S. Patent Nos. 4,432, 409 (Steele) and 4,875,520 (Steele, et al.,), all assigned to the present assignee (and hereinafter referred to as the '237, '409 and '520 Patents, respectively) and incorporated herein by reference. These heat exchange matrices are usually porous so as permit passage of the incoming and outgoing air streams through the wheel. Use of these devices in ventilating, heating and/or air conditioning systems can reduce heating and cooling costs, particularly in systems where heat and moisture from stale air being exhausted to outdoors is recovered and transferred to the incoming fresh air. For simultaneous flow regenerative devices of the rotary wheel type, the wheel is slowly rotated through both the treated and regenerating airstreams so that the treated airstream is directed through one sector of the slowly revolving wheel, while the regenerating airstream is simultaneously directed through another sector of the wheel. Heat and moisture are simultaneously absorbed from the warmer airstream at the one sector and removed from the wheel by the cooler, dryer airstream at the other sector. Means can be provided for heating the regenerating air stream in order to raise the

temperature of the airstream relative to the wheel and to lower the relative humidity so that the outgoing regenerative airstream will more effectively absorb both heat and water from the heat exchange device. For stationary periodic flow regenerators, the indoor and outdoor airstreams are alternately directed through the entire exchange device, with one airstream directed through the matrix first in one direction and then the other airstream is directed through the matrix in the opposite direction. It is well known to make regenerators with a sensible heat exchange material (capable of absorbing sensible heat) coated with a desiccant material (capable of absorbing moisture and thus latent heat). Such regenerators are used in heating and/or air conditioning systems where the transfer of both sensible and latent heat is desired, as, for example, in the case of air conditioning systems used in summer climates characterized by hot and humid outdoor air. In such climates, it is often desirable to either bring fresh air in from the outdoors or recirculate the indoor air with the ultimate purpose of reducing the indoor temperature and humidity. Thus, in the former case the regenerators are used to transfer sensible and latent heat from incoming air to the outgoing air, while in the latter case latent heat is transferred from the recirculated indoor airstream to the outdoor regenerating airstream. To achieve maximum latent heat transfer in such conditions, as is well known in the prior art, a suitable sensible heat exchange material such as plastic (i.e. , high molecular weight, synthetic polymers), aluminum, or Kraft or other fibrous paper is completely and uniformly coated with a desiccant material in accordance with processes known to those skilled in the art. We have determined, however, that under some circumstances maximum latent heat transfer may not be desirable. For example, under winter conditions it is often desired to remove substantial amounts of moisture from the building through ventilation with a sensible wheel but when the outdoor air becomes very cold and dry the moisture removal provided by a sensible matrix wheel may become excessive. In this case it becomes desirable to have some desiccant coating present to increase moisture retention but a fully desiccant coated wheel may retain excessive amounts of moisture. Thus some "tailoring" of the latent transfer characteristics may be desired. As another example, animal breeding inside a building may require a continual flow of fresh air from the outdoors to help minimize the spread of

disease, at different humidity levels than humans would find desirable. Thus, during hot and humid summer days it might be desirable to reduce the humidity within such a building to a level below the outside humidity level, but above that which humans find comfortable. Such problems are not necessarily solved by substituting a sensible heat regenerator wheel having a matrix made entirely of heat exchange materials without a desiccant coating for a wheel having a matrix made entirely of heat exchange materials provided with a uniform coating of desiccant material. The only moisture recovered by the sensible heat regenerator without a desiccant coating material is that which condenses on the matrix when the dew point of the airstream is above the temperature of the surface of the matrix. As a result, under such circumstances some condensation occurs on the matrix. The condensed moisture is reevaporated back into the warmer and drier exhausted airstream passing through the matrix. This type of condensation and reevaporation may not be substantial enough to offset the overall ventilation provided by the system, leaving the building with undesirably hot and humid indoor air (summer conditions) or undesirably dry air (winter conditions). In addition to varying according to climate, the latent heat exchange efficiency desired in a regenerator also may vary according to the use of the building it services. The humidity level desired in an office building, for example, tends to differ from that desired in a building where especially sensitive materials or industrial processes are maintained. Furthermore, in some situations, the latent heat exchange efficiency desired may not be fully determinable until the regenerator is tested at the building itself. For such varieties of environments, neither regenerators made entirely of heat exchange materials uniformly coated with desiccant material, nor regenerators made entirely of sensible heat exchange materials (not coated with desiccant material) provide the desired latent heat exchange efficiencies. The need for regenerators with latent heat exchange efficiencies between those provided by the present sensible heat regenerators which are not provided with desiccant material and regenerators made with materials uniformly coated with a desiccant material could, at least in theory, be met by developing new coating methods. Such methods could involve the use of different desiccants and different desiccant concentrations. However, in view of the amount of research and testing

needed to develop these methods, this approach may not be cost effective. Furthermore, this approach would not provide a means for varying the latent heat transfer efficiency of the regenerator at the building site itself, after manufacture of the regenerator.

OBJECTS OF THE INVENTION It is a general object of the present invention to reduce or substantially overcome the problems of the prior art. Another object of the invention is to provide, without developing new coating methods, a rotary heat regenerator with a latent heat transfer efficiency between the latent heat transfer efficiencies of regenerators made entirely with heat exchange materials uniformly coated with desiccant and those of sensible heat regenerators made entirely with heat exchange materials without desiccant materials. And another object of the invention is to provide a rotary heat regenerator wheel which has a latent heat transfer efficiency which can be easily adjusted on site, after manufacture, to fit the particular application of the wheel.

SUMMARY OF THE INVENTION The above and other objects of the invention are achieved, at least in part, by providing a rotary heat regenerator with a regenerator matrix having layers of heat exchange material, a selected portion of which is desiccant-coated and a selected portion of which is not coated in a predetermined proportion as a function of the desired latent heat transfer efficiency. More specifically, in one embodiment of the invention, the matrix is in the form of a wheel comprising at least two strips of heat exchange materials wound together in a spiral around a hub. At least one of the strips is coated with a desiccant material, while at least one other strip is not so coated and is primarily used to transfer sensible heat. In accordance with another embodiment of the invention, the matrix of the regenerator wheel includes a plurality of removable segments or elements. At least one of the segments is made of a heat exchange material coated with a desiccant material, while at least one other segment is not coated and is primarily used to transfer sensible heat.

Thus, through the incorporation of both desiccant-coated and uncoated heat exchange material into a matrix in adjustable proportions, the present rotary heat regenerator is able to, without development of new coating methods, transfer latent heat with an efficiency between that of purely sensible heat regenerators and that of regenerators made of heat exchange materials uniformly coated with a desiccant. In accordance with one aspect of the present invention, through division of the matrix into removable elements together containing a combination of desiccant-coated and uncoated heat exchange material, the present rotary heat regenerator is further able to transfer latent heat with an efficiency which can be adjusted after manufacture, on site during installation or after operating experience dictates a desired change. Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein only two preferred embodiments are shown and described, simply by way of illustration of the best mode of the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the present invention, reference should be had to the following drawings, wherein: Fig. 1 is a graph of the relationship between heat transfer efficiency and the surface available for heat transfer; Fig. 2 is a perspective view of one rotary heat exchange wheel comprising a matrix made in accordance with the present invention and showing the lower side thereof; Fig. 3 is a cross-sectional view taken of a portion of the matrix along line A- A shown in Fig.2, and comprising both strips of desiccant coated material and strips of sensible heat exchange material which are not so coated;

Fig. 4 is a cross-sectional view taken of a portion of the matrix along line A- A shown in Fig. 2, and comprising an alternative arrangement to that shown in Fig. 3; and Fig. 5 is a front view of an alternative rotary heat exchange wheel, positioned within a rotary heat exchange system, the wheel comprising a matrix made in accordance with the present invention; Fig. 6 is a perspective view of a part of the wheel of Fig. 5 with segments removed; and Fig. 7 is a perspective view of one of the segments used in the Fig. 5 embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS The invention is based in part upon the realization that a desirable latent heat transfer efficiency (between those provided by regenerator devices comprising a matrix solely made of a sensible heat exchange material and regenerator devices comprising a matrix solely made of a heat exchange material uniformly coated with a desiccant) can be achieved, without developing new coating methods, by utilizing both types of materials in the same regenerator in a proportion directly related to the desired latent heat transfer efficiency. The desiccant, latent heat exchange materials provide surface area for moisture transfer. As stated above, even though moisture that can be recovered by sensible heat exchange material (without a desiccant coating material) is that which condenses on the material when the dew point of the airstream is above the temperature of the surface of the material, for purposes herein such a material is referred herein as a "sensible heat exchange material" and is used primarily to transfer sensible heat. A "latent heat exchange material" material, however, includes a desiccant that is used for transferring at least latent heat (associated with moisture) and may be capable of also transferring sensible heat, as for example, where the desiccant material is coated on a sensible heat transfer material. Thus, the latter term includes enthalpy exchangers. Moisture transfer efficiency, like sensible heat transfer efficiency, varies as a function of the available transfer surface area. The relationship, as shown graphically in Fig. 1, is not linear, but exponential. At low efficiencies, i.e., near zero percent, doubling the surface

transfer area will essentially double the efficiency; while at higher efficiencies, i.e., near 100%, doubling the surface transfer area will result in efficiency increases of less than 50%. At around 80% to 85% efficiency, a common operating point for regenerators made of plastic heat exchange materials, doubling the surface transfer area will result in an efficiency increase of around 8% to 10%, e.g., from approximately 70% to 80% or from approximately 80% to 88%. Accordingly, we have found that a regenerator matrix made of 50% plastic sensible heat exchange material and 50% latent desiccant-coated heat plastic exchange material will have approximately the some sensible heat transfer efficiency of the regenerator matrix made of 100% sensible heat exchange material, but only approximately 70%-80% of the moisture transfer efficiency of the regenerator matrix made of 100% latent, desiccant-coated heat exchange material (depending on the position along the curve of Fig. 1). A regenerator with these efficiencies will provide suitable sensible heat recovery, and often a much more suitable moisture recovery, compared to regenerators having matrices made of entirely latent, desiccant-coated material or of entirely sensible heat exchange material. Furthermore, regenerators can be tailored to provide various other sensible heat and moisture transfer efficiency combinations for other climatic conditions and different building uses by altering the amounts of latent and sensible heat exchange materials in the regenerator matrix. In each of the preferred embodiments of the hybrid rotary heat regenerator of the present invention, the layers of heat exchange material forming the regenerator matrix are made from strips of plastic (e.g., high molecular weight, synthetic polymers), aluminum, Kraft or other fibrous paper, or steel. Plastic of a type capable of being heat sealed, such as polystyrene, is preferably used. The strips are preferably continuously spirally wound about a central hub, forming a disk-shaped matrix of curved layers, in a manner described in the '237, '409 and '520 Patents. Those skilled in the art will recognize that other matrix construction techniques may be employed, and matrices of other configurations, such as those containing flat layers, or a honeycomb structure, may be produced. As described in greater detail hereinafter in connection with Figs. 3 and 4 and in the '237, '409, and '520 Patents, suitable spacing means are provided in matrix so as to form gas passageways in an axial direction through the wheel.

In one preferred embodiment, where the plastic matrix is adapted to be used as an integral whole, adjacent layers are joined together with an adhesive or the matrix is partially cut, for example with a heated tool, along a plurality of radial lines, fusing adjacent plastic layers, as shown in Fig. 2 and described and shown in the '409 Patent, leaving grooves shown at 18 in Fig. 2. The grooves 18 are used for seating radial support spokes (not shown), without which the matrix would tend to be excessively floppy. In addition, to impart further rigidity to the wheel, one or more reinforcing rods of plastic or metal can be used. In another preferred embodiment described in greater detail hereinafter in connection with Figs. 5-7, the plastic matrix comprises a plurality of separate wedge-shaped matrix elements (described in greater detail in connection with Figs. 5-7), formed, for example, by cutting completely through the spiral wound strips with a heated tool from one face to the opposite face so that the resulting wedge-shaped elements each have arc- shaped strips fused at their ends along the cut line. The hybrid rotary heat regenerator of the present invention is adaptable for either residential or commercial use. A preferred matrix 10 for a hybrid rotary heat regenerator of the present invention especially adapted for residential use is illustrated in Fig. 2. A suitable housing for the matrix 10 and a suitable drive train for causing the matrix 10 to rotate in such housing are described in U.S. Patent No. 5,002,016 (Hoagland, et al.) assigned to the present assignee (hereinafter the '016 Patent) and incorporated herein by reference. In the matrix 10 of Fig. 2, the heat exchange material 16 consists of two strips made of a sensible plastic heat exchange material, one coated with a desiccant, the other uncoated, spirally wound together around the hub 12. More plastic strips, coated or uncoated, can be wound together about the hub 12, depending upon the latent heat transfer efficiency desired. Grooves 18, cut into the heat exchange material 16 for the seating of support spokes (not shown), extend radially from the hub 12 to the matrix periphery. A strip of pile or brush-like material 20 on the periphery functions as a seal between the periphery of the wheel and the surrounding housing (not shown) within which the wheel sits when in use. Two examples of arrangements for the plastic strips are illustrated in Figs. 3 and 4, wherein the matrix is formed with two strips made of a plastic sensible heat

exchange material wound together onto the hub. In both arrangements, the means for forming spaces between adjacent strips includes regularly distributed dimples or protrusions 30 formed on one of the two strips used to form the matrix, while the other strip is flat. The dimples 30 extend in both directions from the surfaces of dimpled strip 32a so as to separate the dimpled strip 32a from the adjacent surfaces of the flat strip 32b and thus form air channels 36 for the flow of air axially through the matrix 10. In Fig. 3, the dimpled strip 32a is coated, preferably on both surfaces, with desiccant material 40 (one layer of which is shown in greatly enlarged detail) so as to provide a strip of latent heat exchange material; while the flat strip 32b is left uncoated so as to remain a strip of sensible heat exchange material. A dry desiccant, such as silica gel, is preferably used. A preferable method of uniformly coating plastic strips with dry desiccant is described in the '520 Patent. In Fig. 4, the matrix is identical to that shown in Fig. 3, except that flat strip 32b is coated with desiccant 40; while the dimpled strip 32a is made of an uncoated sensible heat exchange material. The matrix can be suitably mounted and used in a frame as shown in U.S. Patent 4,924,934, assigned to the present assignee and incorporated herein by reference. Thus, as described in Figs. 3 and 4, a matrix is formed with roughly half the surface area providing latent and sensible heat transfer, while the remaining surface area providing substantially sensible heat transfer only, with a corresponding latent heat transfer efficiency as determined by a curve similar to that shown in Fig. 1. The ratio of the two can be adjusted by adjusting the amount of surface area that is provided by latent heat transfer material relative to the surface area that is provided by the sensible heat transfer material only. For example, by using three strips coated with the desiccant and one strip of uncoated sensible heat exchange material the ratio of approximately 3 to 1 of relative surface area is achieved with a corresponding latent heat transfer efficiency as determined by the curve of the type shown in Fig. 1. With this arrangement, wheels of different ratios of coated and uncoated surface areas can be provided so that a particular wheel can be selected at the site where the rotary heat exchange regenerator is installed so as to select a desired latent heat transfer efficiency.

In an alternative arrangement, the portion of a preferred matrix 10 for a hybrid rotary heat regenerator, preferably adapted for commercial use is illustrated in Figs. 5-7, where the wheels tend to be of larger dimensions than of the residential type. In this embodiment the matrix 10 is divided into a plurality of removable wedge-shaped elements 50 of heat exchange material. A selected number of elements 50a are made of a latent heat exchange material; while the remaining elements 50b are made of a sensible heat exchange material. The proportion of elements which are desiccant-coated and nondesiccant coated can be varied according to the latent heat transfer efficiency desired. In this instance where eight elements are used, each circumscribing 45° of the wheel, nine different latent heat efficiencies can be easily provided at the site where the wheel is used, by using anywhere from zero to eight elements made of latent heat exchange material. Alternatively, one or more removable elements, each containing both latent heat exchange material and sensible heat exchange material can be used in the matrix 10 in order to provide various desired latent heat transfer efficiencies. Referring more specifically to Figs. 5 and 6, the wedge-shaped elements 50 of heat exchange material are preferably made from wheels of spirally wound plastic strips using the heated tool method described previously herein or any other suitable method. The wheel is adapted to be mounted within a rotary heat regenerator system 49, such as the type disclosed in the '016 Patent. The elements 50a containing latent heat exchange material preferably are taken from wheels formed with desiccant-coated plastic strips; the elements 50b containing sensible heat exchange material are taken from wheels preferably formed with uncoated plastic strips. Alternatively, if one or more elements containing both desiccant-coated and nondesiccant-coated heat exchange materials are used, such elements (not shown) can be taken from wheels formed with both desiccant-coated and nondesiccant-coated plastic strips, such as the wheel adapted for residential use described above. For each type of element 50a,50b, wheels wound from two or more strips, with suitable spacing means, such as dimples 30, are preferably used so as to form layers with channels for the flow of air. As in the case of the matrix described in connection with Figs. 2-4, a dry desiccant such as silica gel is preferably used for coating the strips of latent heat exchange material forming elements 50a.

The segments can be supported in a suitable frame so that each can be easily mounted and replaced, at the site where the wheel is used. A frame, for example, is shown in Figs. 5-7, and comprises wedge-shaped openings for supporting the respective wedge-shaped elements 50. The wheel includes a matrix hub 52 comprising two circular disks 51 and 53, and provided with a mounting pin 54 so that the wheel can be rotatably mounted within a rotary exchange device. The wheel also includes a plurality of spokes 56 extending radially from and supported at one end by the hub, and supported at the other end by an outer band 58. Means, such as plastic foam strips 60, are provided on each side of each spoke for providing an air tight seal between each element 50 and each spoke 56. Means, are also provided for removably securing each of the elements 50 in the frame. The latter means preferably includes a retaining tab 61 provided on one side of the wheel at the place where the spoke connects to the outer band 58 so as to provide a retaining element for each element 50 when it is positioned in the wedge-shaped opening. A spring clip 62 is attached to the outer end of each spoke. Spring clip 62 is adapted to be compressed by the wedge-shaped element 50 when the latter is inserted in the respective opening so as to secure the wedge-shaped element in place. The spring clip includes a rectangular stop 64. Once in place each wedge is locked in place by a retainer tab 66, which is attached to one end of a spring retainer strap 68, the other end of the strap being attached to the outer surface of the outer band 58 so that the tab 66 extends through a slot 72 in the outer band into contact with the wedge. A grip 70 is preferably provided on the strap for allowing the user to pull back on the strap so that the tab will pull out of contact with the segment 50 and from the slot 72, making it possible to pull the segment 50 out of the wedge-shaped opening. As shown in Fig. 7, each of the wedge shaped elements 50 is preferably provided with a segment hub retainer attachment 74, adapted to engage hub 52 between the disks 51 and 53 so as to prevent any damage to the element 50 when inserting or removing the element. The spring clips 62 urge the wedge-shaped elements 50 toward the hub 50 so as to be sandwiched between the hub's axially opposing disks 51 and 53. Thus, to allow removal or insertion of one of the wedge-shaped elements 50, the associated grip 70 of the spring retainer strap is pulled until the retainer tab 60

is drawn back through the slot 72 of the outer band 58 away from the hub 50. When the grip 70 is released, the tab 66 snaps radially inward through the slot 72 so as to the prevent the wedge shaped element 50 from moving. The use of removable wedge-shaped elements is particularly recommended for commercial rotary heat regenerators, which are generally larger in size than residential rotary heat regenerators. When the matrix must be removed (for testing, replacement, cleaning, etc.), the less bulky elements are easier to handle than a whole, undivided matrix. However, it should be appreciated by those skilled in the art that an undivided matrix containing both desiccant-coated and nondesiccant-coated heat exchange materials can be used for commercial applications within the scope of the present invention. Conversely, it should also be appreciated by those skilled in the art that a divided matrix containing both desiccant-coated and nondesiccant- coated heat exchange materials can be used for residential applications within the scope of the present invention. Thus, a rotary heat regenerator has been described with a regenerator matrix having layers of heat exchange material, a portion of which is made of latent heat exchange material and a portion of which is made of a sensible heat exchange material. Through the incorporation of both sensible and latent heat exchange material, the present rotary heat regenerator is able to, without development of new coating methods, transfer latent heat with efficiencies between those of regenerators comprising matrices made of only sensible heat exchange material, and those regenerators made with only latent heat exchange materials. Through division of the matrix into removable elements together containing a selected combination latent heat exchange material and sensible heat exchange material, the present rotary heat regenerator is further able to transfer latent heat with efficiencies which can be adjusted after manufacture. In this disclosure, there are shown and described only two preferred embodiments of the invention, but as aforementioned, it is to be understood that the invention is capable of use in various other conditions and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.