Abstract:
Systems and methods for airflow management around palletized cases of goods in a warehouse storage facility are provided, in which airflow around each individual layer of cases is facilitated while airflow “spillage” around the sides, top or bottom of pallet assemblies is minimized or eliminated. One exemplary device for such airflow management includes palletized product spacers disposed between respective layers of vertically stacked cases, in which the product spacers facilitate a substantially unidirectional longitudinal airflow. Another exemplary airflow management device is a series of automatically adjustable air dams disposed at the tops of respective pallet assemblies which prevent air spillage and establish intermediate air manifold spaces. Yet another device is a lateral pallet spacer prevents direct abutment of the side surfaces of neighboring pallet assemblies and thereby ensures that the air manifold spaces are in fluid communication with the spacers of multiple pallet assemblies.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/844,078, filed Mar. 15, 2013 and entitled SPACER FOR A WAREHOUSE RACK-AISLE HEAT TRANSFER SYSTEM, and this application claims the benefit under Title 35, U.S.C. Section 119(e) of U.S. Provisional Patent Application Ser. No. 61/891,117, filed Oct. 15, 2013 and entitled HEAT TRANSFER SYSTEM FOR WAREHOUSED GOODS, the entire disclosures of which are hereby expressly incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a warehouse that is capable of altering and/or holding steady the temperature of a quantity of product housed in cases forming pallet assemblies and storing such product, e.g., bulk foods. More particularly, the present disclosure relates to spacing, stacking and heat transfer structures used in such a warehouse. 
     2. Description of the Related Art 
     Freezer warehouses are known in which large pallets of items including meats, fruit, vegetables, prepared foods, and the like are frozen in blast rooms of a warehouse and then are moved to a storage part of the warehouse to be maintained at a frozen temperature until their removal. 
     U.S. patent application Ser. No. 12/877,392 entitled “Rack-Aisle Freezing System for Palletized Product”, filed on Sep. 8, 2010, the entire disclosure of which is hereby explicitly incorporated by reference herein, relates to an improved system for freezing food products. Shown in  FIG. 1  is a large warehouse  2  that can be used to freeze and maintain perishable foods or like products. Large pallets of items, including meats, fruits, vegetables, prepared foods, and the like, are sent to warehouse  2  to be frozen employing a system whereby the palletized foods are frozen on storage racks. 
       FIG. 2  shows a top view of the interior of warehouse  2 , in which rows of palletized product are shown such that pallet assemblies  52   a  abut chamber  6 . As shown in  FIG. 3 , rows of racking  14  (see also  FIG. 8 ) are positioned between aisles  10  and chambers  6 . Each chamber  6  is enclosed by a pair of end walls  15  and top panel  17 . Spacers  20  ( FIGS. 5-7 ) separate respective rows of cases  22  to create a palletized product stack in the form of pallet assembly  52   a  which can be disposed and sealed against the exterior of racking  14  ( FIG. 3 ) via forklifts  18  (see, e.g.,  FIGS. 3 and 4 ). 
     Air handlers  8 , e.g., chillers ( FIG. 2 ) provided in the interior of warehouse  2  produce conditioned, e.g., cold air and maintain the temperature of ambient air within the warehouse space at a desired temperature, e.g., +55° F. to −30° F. While warehouse  2  could be utilized to either freeze or thaw a quantity of product housed in cases contained on pallet assemblies  52   a , the remaining description will use the example of a warehouse freezer, it being understood that similar arrangements and principles will be applied to a warehouse utilized to thaw product, with the air handler comprising a heater as opposed to a chiller. 
     Adjacent pairs of racking structures  14  ( FIGS. 2-4 ) define a plurality of adjacent airflow chambers  6  ( FIGS. 2 and 4 ) having air intake openings on opposite sides thereof and a plurality of air outlets having air moving devices, such as exhaust fans  12 , on top panels  17 , which cause freezing air to be drawn into chambers  6  through the air intake openings in racking  14  and to then exhaust into the warehouse space. The plurality of airflow chambers  6  are each defined by a pair of end walls  15  and top wall  17  having one or more air outlets and exhaust fans  12  associated therewith ( FIG. 3 ). Pallet assemblies  52   a  ( FIG. 5 ) are pressed against the intake openings in racking  14  such that a seal is formed between the pallets and the intake openings via side periphery seals, a bottom periphery seal, and a top periphery seal. The seals together define each respective intake opening. Freezing air is drawn through air pathways  16  ( FIGS. 2, 4, and 5 ) within the palletized product in a direction towards chamber  6  to thereby quickly freeze the product. As shown in  FIG. 5 , spacers  20  may be placed between rows of cases  22  of product in an attempt to provide air pathways  24  through which airflow can enter chamber  6 . 
     U.S. patent application Ser. No. 13/074,098 entitled “Swing Seal for a Rack-Aisle Freezing and Chilling System”, filed on Mar. 29, 2011, the entire disclosure of which is hereby explicitly incorporated by reference herein, discloses a top periphery seal useable to seal an intake opening as described above and which automatically adjusts to the height of pallet assembly  52   a  as illustrated in  FIG. 6 . As illustrated in  FIG. 6 , pallet assembly  52   a  (comprised of a plurality of cases  22  stacked on spacers  20  and pallet  4 ) can be positioned along pallet guide  56  and pressed against intake opening  54  such that a seal is formed between pallet assembly  52   a  and intake opening  54  via side periphery seals, a bottom periphery seal and an automatically adjustable top periphery seal surrounding intake opening  54 . With such a construction, chilling or freezing air is drawn through air pathways  16  formed through pallet assembly  52   a , as illustrated in  FIGS. 2, 4 and 5 . 
       FIG. 5  illustrates predicate spacer  20  which is formed in an undulating “egg carton” configuration. As illustrated in  FIG. 7 , individual cases  22  can crush under the weight of the product contained therein and the product contained in cases stacked directly above to cause overlap of cases  22  with a spacer  20  and prohibit airflow between product cases  22  positioned on opposite sides of the obstructed spacer  20 . Undulating spacers  20  are particularly susceptible to obstruction due to drooping or sagging cases  22  due to the inconsistent support structure caused by the “hill and valley” configuration of such spacers.  FIG. 7  illustrates case crushing and drooping at various sides and levels of pallet assembly  52   a ; however, this phenomenon is, in practice, more prevalently seen with respect to the spacers  20  separating lower rows of cases  22 , as the bottom of pallet assembly  52   a  contains the heaviest cumulative load of cases  22  stacked thereon. 
     In the above described installation, utilizing “egg carton” spacers  20 , heat transfer from chilled ambient air in warehouse  2  to the products contained in cases  22  is effected through forced convection which is facilitated by the irregular shape of egg carton spacers  20  to allow airflow in all directions through pallet assembly  52   a . Alternative spacers such as wood slat spacers may also be utilized to separate cases  22  on pallet  4 ; however, spacers employed in warehouse installations utilized to keep the quantity of product at a desired temperature through forced convection are designed to allow for airflow in all directions. Because air can flow in all directions through predicate spacers  20  described above, thorough cooling or thawing of a product may not be achieved, as air entering between adjacent rows of product cases may exit pallet assembly  52   a  before encountering all of the cases of the row in question. Further, crushing and/or drooping of cases  22  may restrict airflow, as described above. 
     Another mechanism of heat transfer, i.e., conduction, can also be utilized to transfer heat to or from product. Predicate spacers  20  described above are made either of wood or plastic, which is not sufficiently thermally conductive to effect heat transfer via conduction. Therefore, in installations utilizing such spacers, heat transfer is effected solely by the use of forced convection. 
     SUMMARY 
     The present disclosure provides devices and methods for airflow management around palletized cases of goods in a warehouse storage facility, in which airflow around each individual layer of cases is facilitated while airflow “spillage” around the sides, top or bottom of pallet assemblies is minimized or eliminated. One exemplary device for such airflow management includes palletized product spacers disposed between respective layers of vertically stacked cases, in which the product spacers facilitate a substantially unidirectional longitudinal airflow. Another exemplary airflow management device is a series of automatically adjustable air dams disposed at the tops of respective pallet assemblies which prevent air spillage and establish intermediate air manifold spaces. Yet another device is a lateral pallet spacer prevents direct abutment of the side surfaces of neighboring pallet assemblies and thereby ensures that the air manifold spaces are in fluid communication with the spacers of multiple pallet assemblies. 
     Combination of some or all the present devices and methods for airflow management may facilitate the use of a racking system in which multiple pallet assemblies are arranged side by side within a single deep rack bay and between a loading aisle and an air exhaust pallet, thereby facilitating greater economy of warehouse space without compromising the capacity for a thermal management unit (e.g., blast freezer) to effect a uniform and timely temperature change of each case contained in the racking system. 
     The disclosure, in one form thereof, provides a spacer for use between adjacent pairs of stacked cases, the spacer comprising: a plurality of substantially planar, elongate upper support surfaces extending in a first x-y plane of a Cartesian coordinate system; a plurality of substantially planar, elongate lower support surfaces extending in a second x-y plane of a Cartesian coordinate system, the second x-y plane spaced from the first x-y plane by a distance in the z-direction; the lower support surfaces respectively interposed between adjacent pairs of the upper support surfaces; a plurality of sidewalls each connecting one of the upper support surfaces to an adjacent one of the lower support surfaces, such that the upper and lower support surfaces cooperate with the sidewalls to form an undulating profile of lands and valleys, adjacent pairs of the sidewalls each defining an airflow channel having a cross-sectional area defined by a distance between the adjacent pairs of sidewalls along the y-direction and a distance between the upper and lower support surfaces in the z-direction, and each the airflow channel having a longitudinal extent along the x-direction; and a plurality of stiffeners interconnecting the adjacent pairs of the sidewalls with an adjacent one of the upper support surfaces, the stiffeners disposed in a y-z plane. 
     The disclosure, in another form thereof, provides an installation for cooling to a desired temperature, heating to the desired temperature or maintaining at the desired temperature in a quantity of product, the installation comprising: a plurality of pallet assemblies; a warehouse space having a plurality of racks defining a plurality of bays positioned adjacent to an aisle, each of the plurality of bays sized to receive the plurality of pallet assemblies along a bay depth, the pallet assemblies each loaded with a quantity of product to be set at the desired temperature; at least one air handler operably connected to the warehouse space to condition an ambient air in the warehouse space, the at least one air handler having an output sufficient to achieve and maintain a temperature of the ambient air in the warehouse space at the desired temperature; at least one air flow chamber in fluid communication with a plurality of air intake openings formed through each of the plurality of racks to facilitate airflow into each of the plurality of bays; at least one fan in fluid communication with the at least one air flow chamber, the fan operable to create a circulation of the ambient air flowing through the plurality of air intake openings, through the plurality of pallet assemblies along the bay depth, and finally into the at least one air flow chamber where the ambient air is exhausted back to the warehouse space; at least one of the plurality of pallet assemblies comprising: a pallet having a case support surface defining a case support surface area; a plurality of cases containing the quantity of product, the plurality of cases arranged within a profile defined by the case support surface area; a lateral pallet spacer protruding outwardly from the case support surface area and oriented to abut an adjacent one of the plurality of pallet assemblies when the plurality of pallet assemblies are arranged along the bay depth, whereby the lateral pallet spacer establishes and maintains a lateral separation space between each pair of adjacent pallet assemblies in a respective one of the bays within the plurality of racks; and at least one product spacer, each the product spacer comprising: a substantially planar upper support surface extending in an x-y plane of a Cartesian coordinate system, the upper support surface defining a spacer outer perimeter of a size and shape about congruent to the case support surface area of the pallet; a substantially planar lower support surface spaced from the upper support surface along the z-direction; and a plurality of supports extending between the upper support surface and the lower support surface along a trajectory having a directional component along a z-axis of the Cartesian coordinate system, whereby each of the plurality of supports space the upper support surface from the lower support surface, the upper support surface, the lower support surface and the supports cooperating to define at least one longitudinal airflow channel extending along the x-direction, the at least one airflow channel spanning a pair of opposing sides of the at least one product spacer; each of the plurality of cases stacked on the pallet of one of the plurality of pallet assemblies in a plurality of case layers, each of the plurality of case layers separated from another of the plurality of case layers by one of a plurality of the product spacers; and one of the plurality of pallet assemblies arranged along the bay depth being in an upstream location in direct fluid communication with one of the plurality of air intake openings, such that the circulation created by the at least one fan causes airflow through the channel in the at least one product spacer of the pallet assembly in the upstream location, then into the lateral separation space between the plurality of pallet assemblies arranged along the bay depth, and then through the channel in the at least one product spacer of the next downstream pallet assembly. 
     The disclosure, in a further form thereof, provides a method of maintaining a quantity of a product at a desired temperature, comprising: preparing a plurality of pallet assemblies by stacking a plurality of cases and a plurality of spacers on respective pallets so that respective rows of the plurality of cases are separated from each one another along a z-axis of a Cartesian coordinate system by the spacers, the spacers comprising: a substantially planar upper support surface extending in an x-y plane of a Cartesian coordinate system, the upper support surface defining a spacer outer perimeter of a size and shape about congruent to a case support surface area of the pallet; a substantially planar lower support surface spaced from the upper support surface along the z-direction; a plurality of supports extending between the upper support surface and the lower support surface along a trajectory having a directional component along a z-axis of the Cartesian coordinate system, whereby each of the plurality of supports space the upper support surface from the lower support surface, the upper support surface, the lower support surface and the supports cooperating to define at least one longitudinal airflow channel extending along the x-direction, the at least one airflow channel spanning a pair of opposing sides of the spacer; and installing a lateral pallet spacer on each pallet assembly, after the step of stacking a plurality of cases and a plurality of spacers on the pallet, such that the lateral pallet spacer protrudes outwardly from a case support area of the pallet along the x-direction; loading the plurality of pallet assemblies into a bay of a rack so that multiple ones of the plurality of pallet assemblies are arranged side by side along the x-direction, and such that each lateral pallet spacer is oriented to abut an adjacent one of the plurality of pallet assemblies; and directing a thermally conditioned airflow into the bay, through an upstream one of the plurality of pallet assemblies via the airflow channel of the spacer, into a manifold space created by the lateral pallet spacer such that a positive air pressure is created in the manifold space, and into a next adjacent downstream one of the plurality of pallet assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned and other features and objects of this disclosure, and the manner of attaining them, will become more apparent and the disclosure itself will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a warehouse incorporating a heat transfer system in accordance with the present disclosure; 
         FIG. 2  is a diagrammatic top view of a heat transfer warehouse incorporating the system of the present disclosure; 
         FIG. 3  is a perspective view of the interior of the warehouse illustrated in  FIG. 1 ; 
         FIG. 4  is a perspective, end view of two rows of racking separated by an airflow chamber; 
         FIG. 5  is a perspective view showing a desired airflow through a pallet assembly; 
         FIG. 6  is a perspective view illustrating loading of pallet assemblies into the racking illustrated, e.g., in  FIGS. 3 and 4 ; 
         FIG. 7  is a perspective view of a pallet assembly incorporating a predicate spacer; 
         FIG. 8  is a perspective view of a portion of a racking structure accommodating  24  pallet assemblies on each side thereof; 
         FIG. 9  is an end view of a pallet assembly in accordance with the present disclosure; 
         FIG. 10  is a perspective view of a spacer in accordance with the present disclosure; 
         FIG. 11  is a perspective view of an alternative embodiment spacer in accordance with the present disclosure; 
         FIG. 12  is a perspective view illustrating a stack of a plurality of the spacers illustrated in  FIG. 10 , with an automated suction lifting device being utilized to remove and transport one of the spacers; 
         FIG. 13  is a perspective view of an alternative embodiment spacer in accordance with the present disclosure; 
         FIG. 14  is a sectional view of the spacer of  FIG. 13  taken along line  14 - 14 ; 
         FIG. 15  is a partial, end view of the spacer illustrated in  FIG. 10 ; 
         FIG. 16  is a partial, end view of an alternative embodiment spacer in accordance with the present disclosure; 
         FIG. 17  is an end view of yet another alternative embodiment spacer in accordance with the present disclosure; 
         FIG. 18  is a partial, end view of a further alternative embodiment spacer in accordance with the present disclosure; 
         FIG. 19  is a partial perspective view of an additional alternative embodiment spacer in accordance with the present disclosure; 
         FIG. 20  is a partial perspective view of yet another alternative embodiment spacer in accordance with the present disclosure; 
         FIG. 20 a    is a partial perspective view of still another alternative embodiment spacer similar to the spacer of  FIG. 21 , in which another alternative end stiffener design is used; 
         FIG. 20 b    is a partial perspective view of a portion of the spacer shown in  FIG. 20 , illustrating an optional secondary stiffener; 
         FIG. 21  is a front elevation view of the spacer shown in  FIG. 20 , it being understood that a rear elevation view thereof is identical; 
         FIG. 21 a    is a front elevation view of the spacer shown in  FIG. 20 a   , it being understood that a rear elevation view thereof is identical; 
         FIG. 21 b    is a front elevation, partial view of an alternative spacer similar to the spacer of  FIG. 21 , in which yet another alternative end stiffener design is used; 
         FIG. 22  is a left side elevation view of the spacer shown in  FIG. 20 , it being understood that the right side elevation view thereof is identical; 
         FIG. 22 a    is a left side elevation view of the spacer shown in  FIG. 20 a   , it being understood that the right side elevation view thereof is identical; 
         FIG. 23  is a top plan view of the spacer shown in  FIG. 20 ; 
         FIG. 23 a    is a top plan view of the spacer shown in  FIG. 20   a;    
         FIG. 24  is a bottom plan view of the spacer shown in  FIG. 20 ; and 
         FIG. 24 a    is a bottom plan view of the spacer shown in  FIG. 20 a   ; and 
         FIG. 25  is a perspective view of a warehouse racking structure in accordance with the present disclosure, in which multiple pallet assemblies are disposed in a single deep racking bay define upstream and downstream pallet assemblies relative to the directional airflow utilized by an air handling system; 
         FIG. 26  is an elevation view of a portion of the racking structure shown in  FIG. 25 , illustrating detail thereof; and 
         FIG. 27  is a perspective view of a lateral pallet spacer in accordance with the present disclosure. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplifications set out herein illustrate embodiments of the disclosure, in several forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the disclosure to the precise forms disclosed. 
     DETAILED DESCRIPTION 
     As described in detail below, the present disclosure provides a system and method for directing airflow past the upper and lower surfaces of cases  22  contained in respective pallet assemblies  52  (see, e.g.,  FIG. 9 ). For example, in industrial blast freezer operations, it is desirable to ensure consistent airflow past the top and bottom surfaces of cases  22  among all the layers thereof within pallet assembly  52 , which ensures consistent transfer of heat away from the products contained therein during a blast freezing operation. This consistent heat transfer, in turn, ensures that product contained within cases  22  all freezes at approximately the same time, such that a sampling of temperature readings from among many cases  22  within a warehouse  2  ( FIGS. 1-3 ) will be representative of the temperature of all cases of product placed in warehouse  2 , provided cases  22  contain similar product and were initially placed within warehouse  2  at the same time. Thus, where temperature may be sampled at easily accessible outer cases  22  from among an array of pallet assemblies  52 , food safety and quality of the non-sampled cases can be ensured by proper airflow and thermal management. 
     As described in detail below, spacers  30 ,  130  are provided to facilitate airflow across the entire downstream extent of pallet assemblies  52 , thereby ensuring heat transfer airflows to all of cases  22  among the various layers stacked upon pallets  4 . In addition, air dams  158  ( FIG. 26 ) and lateral pallet spacers  160  may be provided to create intermediate zones of high pressure between successively downstream pallet assemblies  52 , also facilitating downstream airflow past individual layers of cases  22  and even heat transfer resulting from such airflow. 
     1. Planar Palletized Product Spacer. 
     Referring to  FIG. 10 , spacer  30  includes a substantially planar first surface  32  extending in an x-y plane of a Cartesian coordinate system. For the purposes of this document, “substantially planar” is meant to denote nominally planar. Similarly, spacer  30  includes substantially planar second surface  34  opposite first surface  32  and extending generally parallel to first surface  32 . Substantially planar first surface  32  and substantially planar second surface  34  both present a consistent support structure for abutting cases  22 , as depicted in  FIG. 9 . Because of the consistent support surface provided by substantially planar first surface  32  and substantially planar second surface  34 , the drooping and blockage of airflow associated with egg carton spacer  20  (see, e.g.  FIGS. 5 and 7 ) is avoided. 
     Substantially planar first surface  32  and substantially planar second surface  34  are both formed from plates of material having a thermal conductivity of at least 3 W/m·K, at least 5 W/m·K, or at least 10 W/m·K so that spacer  30  is operable to effect heat transfer with product contained in cases  22  via conduction. Referring to  FIG. 10 , supports  36  extend between first surface  32  and second surface  34  to define a plurality of airflow channels  38  spanning airflow inlet side  40  and airflow outlet side  42  of spacer  30 . Airflow channels  38  may be oriented along either the length or the width of the spacer, depending upon the warehouse installation being utilized. Supports  36  span the entire length of first surface  32  and second surface  34  and block airflow from exiting an airflow channel  38  along a trajectory defined by the y-axis of the Cartesian coordinate system depicted in  FIG. 10 . When used with reference to a plane or axis of a Cartesian coordinate system, “along” is meant to denote a trajectory coextensive with such plane or axis or parallel to such plane or axis. A plurality of spacers  30  can be utilized to create pallet assembly  52 , as illustrated in  FIG. 9 . In this configuration, pallet assembly  52  is usable in a temperature controlled warehouse to either freeze or thaw a quantity of product housed in cases  22  contained on pallet assemblies  52 . With spacers  30 , heat transfer to or from the product contained within cases  22  can be effected by both conduction and forced conduction, as further described below. Pallet assemblies  52  in accordance with the present disclosure can be associated with warehouse assembly  2  in the same way as prior art pallet assemblies  52   a  described above. 
     Pallet assemblies  52  form a part of warehouse installation  2  depicted, e.g., in  FIG. 2 . The general structure and components of warehouse  2  are described above in the background section of this document. A portion of this description will be repeated here to facilitate an understanding of the present invention. As illustrated in  FIG. 2 , warehouse  2  includes rack rows  26  separated by chambers  6  and aisles  10 . As illustrated in  FIGS. 3 and 4 , racks  14  are sized for receiving a plurality of pallet assemblies  52 . As depicted, e.g., in  FIG. 9 , pallet assemblies  52  include pallet  4 , on which a plurality of cases  22  are stacked, with spacers  30  interposed between layers of cases  22 . Racking  14  can be sized to receive a different number of pallet assemblies, as necessary. Different assemblies of racking  14  are illustrated, e.g., in  FIGS. 3, 4 and 8 . 
     With pallet assemblies  52  arranged in rows and columns on racks  14 , warehouse installation  2  can be utilized to maintain the quantity of product contained in cases  22  at a desired temperature. As illustrated in  FIGS. 3 and 4 , aisles  10  are sufficiently wide to allow forklifts  18  to access pallet assemblies  52 . Typical aisle width is between 5 feet to 14 feet depending on the type of lift equipment. Pallet assemblies  52  each include a pallet  4  at the bottom thereof. As used in this document, “pallet” is used to denote a standard warehouse pallet of box section open at least two ends (some pallets are called 4-way pallets due to fork openings on all 4-sides) to allow the entry of the forks of a forklift so that a palletized load, i.e., pallet assembly  52 , can be raised and moved about easily. 
     As described above, racks  14  define air intake openings fluidly connected to a chamber  6 , which, in the exemplary embodiment illustrated is enclosed by a pair of end walls  15  and top panel  17 . Pallet assemblies  52  are disposed and sealed against the air intake openings formed in racks  14 . Referring to  FIG. 2 , air handlers  8  are operably connected to warehouse space  2  so that air handlers  8  can condition the ambient air in warehouse space to a desired temperature. In the event that warehouse space  2  is utilized to freeze product contained in cases  22 , air handlers  8  may produce air on the order of −5° F. to −30° F. In the event that warehouse space  2  is utilized to thaw product contained in cases  22 , air handlers  8  may produce air on the order of 30° F. to 60° F. Fans  12  circulate ambient air conditioned by air handlers  8  such that air conditioned by air handlers  8  flows through pallet assemblies  52  and thereafter through the air intake openings formed in racks  14 . 
     As mentioned above, each pallet assembly  52  includes a plurality of cases  22  stacked atop a pallet  4 , with spacers  30  separating each layer of cases  22 . Referring to  FIG. 10 , each spacer  30  includes substantially planar first surface  32  and substantially planar second surface  34 , with a plurality of supports  36  extending between first surface  32  and second surface  34  along a trajectory defined by the z-axis of the Cartesian coordinate system illustrated in  FIG. 10 . Stated another way, first surface  32  is separated from second surface  34  along the z-axis by supports  36 . First surface  32  and second surface  34  extend in the x-y plane of the Cartesian coordinate system illustrated in  FIG. 10 . 
     Each of first surface  32  and second surface  34  are sized and shaped to be about congruent to the outer perimeter of pallet  4 . In one exemplary embodiment, pallet  4  comprises a standard 40 inch by 48 inch rectangular outer perimeter. With such a pallet, first surface  32  and second surface  34  will both be substantially rectangular in shape and about 40 inches by about 48 inches. Stated another way, first surface  32  and second surface  34  are both nominally rectangular and nominally measure about 40 inches by 48 inches. In certain alternative embodiments, spacers  30  will be slightly oversized with respect to pallet  4 , e.g., by having an overhang of up to an inch relative to the perimeter of pallet  4 . These embodiments are also considered to be sized and shaped “about congruent” to the outer perimeter of pallet  4 . Alternative pallet sizes, such as a standard European pallet may be utilized. Spacers  30  will be about congruent to whatever pallet they are designed for use with. 
     In certain embodiments, spacers  30  will be oversized along the z-axis of the Cartesian coordinate system depicted in  FIG. 10 . For example, spacer  30  may include a dimension of about 41 inches along the z-axis as compared to a corresponding dimension of pallet  4  of 40 inches. Because cases  22  are sized to be positioned into configurations corresponding to the standard 40 inch by 48 inch pallet, a spacer sized at 41 inches along the x-axis can provide for an overlap of one inch with respect to a row of cases at either airflow inlet side  40  or airflow outlet side  42 . A spacer  30  measuring 41 inches along the x-axis may also be utilized to provide an overlap of one-half inch at both airflow inlet side  40  and airflow outlet side  42 . In an alternative embodiment, spacer  30  measures 42 inches along the x-axis to provide for additional overlap. In this embodiment, the consistent surfaces provided by substantially planar first surface  32  and substantially planar second surface  34  together with the overlap along the x-axis cooperate to prevent drooping or sagging of cases  42  which would block airflow through channels  38 , which is further described hereinbelow. Generally speaking, it is contemplated that spacer  30  may have any dimension along the x-axis between 40 and 42 inches. 
     Supports  36  extend along the x-axis of the Cartesian coordinate system depicted in  FIG. 10 . Supports  36  cooperate with the opposing plates forming substantially planar first surface  32  and substantially planar second surface  34  to form airflow channels  38  spanning opposing sides of spacer  30 . Specifically, airflow channels  38  span air inlet side  40  and air outlet side  42 . Channels  38  allow a flow of conditioned air created by air handlers  8  and circulated by fans  12  to enter airflow inlet side  40  of channels  38 , traverse channels  38  and exit through airflow outlet side  42  of spacer  30 . In the exemplary embodiment illustrated in  FIGS. 9, 10 and 12 , supports  36  are formed of extruded aluminum box tubes. In an exemplary embodiment, the extruded aluminum box tubes forming supports  36  are formed of 14 gauge aluminum forming a tube having a square outer perimeter and a square inner perimeter defining a longitudinal channel extending the length of support  36 . 
     Each support  36  is secured to an aluminum plate defining first surface  32  and a second aluminum plate defining second surface  34 . In an exemplary embodiment, the opposing aluminum plates are formed of 14 gauge aluminum. When formed of aluminum, spacer  30  may have a thermal conductivity of at least 10 W/m·K. Supports  36  may be secured to the opposing plates using a variety of techniques including welding. Alternative materials of construction may be utilized to form spacers  30 , including various metals and polymers such as high density polyethylene or polycarbonate may be utilized. If polymeric material is utilized to form spacers  30 , then they can have a thermal conductivity of at least 3 W/m·K or at least 5 W/m·K. 
     Airflow channels  38  defined by supports  36  are longitudinal voids having a cross-section extending across the opposing plates on which first surface  32  and second surface  34  of spacer  30  are formed and between neighboring pairs of supports  36 . Airflow channels  38  provide a longitudinal airflow, i.e., a directional flow generally along the x-axis of the Cartesian coordinate system depicted in  FIG. 10 . 
     When airflow traverses airflow channels  38  from airflow inlet side  40  to airflow outlet side  42 , the flow within channels  38  may at times be turbulent, such that the airflow has vector components along the y- and z-axes of the Cartesian coordinate system depicted in  FIG. 10 ; however, the gross airflow remains along the x-axis. That is, securement of supports  36  to the opposing plates defining first surface  32  and second surface  34  substantially preclude the airflow from exiting airflow channels  38  along a trajectory defined by the y-axis. While minor discontinuities in the securement of supports  36  to the plates forming first surface  32  and second surface  34  may allow a very minor bit of airflow leakage along the y-axis, such losses will be small. Air losses from airflow channels  38  will ideally be nonexistent. In certain exemplary embodiments, accounting for manufacturing processes, airflow loss from airflow channels  38  along a trajectory defined by the y-axis could be approximately 2% or maybe even as high as 5%. In these instances, supports  36  will still be said to substantially preclude airflow from exiting airflow channels  38  along a trajectory defined by the y-axis of the Cartesian coordinate system. Similarly, the opposing plates on which first surface  32  and second surface  34  are formed preclude airflow from exiting airflow channels  38  along the z-axis. This structure therefore provides for no loss of heat transfer by the escape of airflow through the sides of spacer  30  spanning airflow inlet side  40  and airflow outlet side  42 , which enhances the efficiency of heat transfer in an installation arranged in accordance with the present disclosure. 
     Generally speaking, the top plate and bottom plate of spacers  30  from which substantially planar first surface  32  and substantially planar second surface  34  are defined, are formed of a material having a thermal conductivity of at least 3 W/m·K (watts per meter kelvin), at least 5 W/m·K, or at least 10 W/m·K. Therefore, heat transfer between spacers  30  and the product contained in cases  22  will occur via conduction as well as forced convection (with the circulating airflow of warehouse  2  contacting cases  22  between spacers  30 ). Because of the consistent surface provided by substantially planar first surface and substantially planar second surface, cases  22  will be well supported above spacers  30  and will not be able to sag to obscure airflow through airflow channels  38 . Further, this consistent surface will provide excellent conduction of heat energy between the product contained within cases  22  and spacers  30 . Generally, a metal will be used to form the top plate and bottom plate of spacers  30 . To avoid the potential of cases  22  sticking to first surface  32  and second surface  34 , the plates forming these surface may be coated with a non-stick material such as polytetrafluorethylene (PTFE), such as Teflon® sold by DuPont. In an alternative configuration a single use non-stick coating of, e.g., vegetable oil may be applied to substantially planar first surface  32  and substantially planar second surface  34 . 
     In certain embodiments of the present disclosure, substantially planar first surface  32  and substantially planar second surface  34  include perforations  44 , as illustrated in  FIG. 11 . In such an embodiment, heat transfer between spacers  30  and the product contained in cases  22  via forced convection will be increased, as airflow through air channels  38  will traverse perforations  44  and thereafter encounter cases  22 . Further, using a perforated plate to define first surface  32  and second surface  34  of spacer  30  decreases the cost of spacer  30 . In certain embodiments, perforations  44  will be limited to an individual size that is small enough to prevent droop of cases  22  into perforations  44 . In certain embodiments of the present disclosure, perforations  44  could account for removal of 90% of the material of the upper or lower plate in question that would otherwise (i.e., in the absence of the perforations) be encompassed by the outer perimeter of spacer  30 . 
     In an embodiment employing perforations  44 , suction gripping surfaces  46  defining continuous surfaces free of perforations  44  sized to receive a suction gripping device, as illustrated, e.g., in  FIG. 12  may be provided. In certain embodiments, suction gripping surfaces  46  may be sized to receive a suction cup having an outer diameter of 2 inches. To accommodate this size suction cup, the continuous surfaces free of perforations  44  may include any polygonal structure large enough to contain a 2 inch circle. Therefore, the area of such surfaces free of perforations  44  will be at least 3.2 inches and will likely be four square inches (a two inch by two inch square) or higher. 
     As described above, spacer  30  may be formed of a 14 gauge aluminum. Spacer  30  may also be formed of a 304 stainless steel material in a 14 gauge or smaller size. Mild steels may also be utilized to form spacers  30 . In the embodiment illustrated in  FIGS. 9, 10, 12 and 15 , supports  36  are spaced from each other by about 4 to 6 inches measured along the x-axis of the Cartesian coordinate system illustrated, e.g., in  FIGS. 10 and 11 . Further, supports can be approximately 0.25 to 3 inches high as measured along the z-axis of the Cartesian coordinate system illustrated, e.g. in  FIG. 10 . In embodiments in which supports  36  comprise open ended tubing, such as the box tubing illustrated in  FIGS. 10, 12, and 13-15 , supports  36  comprise further airflow channels through their length because of their open ended tubular nature. 
     In the alternative embodiment illustrated in  FIGS. 13 and 14 , spacer  30  incorporates lip  48  extending upwardly from substantially planar first surface  32  and surrounding the perimeter of first surface  32  to hold any purge or liquid that is lost, e.g., when spacers  30  are used to thaw the product contained within cases  22 . Spacers  30  of the present disclosure may define load capacities of, e.g., 1800 or 3600 pounds. Where spacer  30  has overall support surface dimensions of 40-42 inches by 48 inches as described above, this load capacity equates to as little as 128 or 135 pounds per square foot of support surface area, or as much as 257 or 270 pounds per square foot of support surface area. Moreover, it is contemplated that the support capacity of spacer  30  per square foot of support surface area may be designed to have any value within any range defined by any of the foregoing nominal values. 
       FIGS. 16-18  illustrate alternative spacers  30   a ,  30   b , and  30   c  utilizing different supports  36 A,  36 B and  36 C or some combination thereof. As illustrated in  FIG. 16 , supports  36 A extend at an angle in the y-z plane and define triangularly shaped airflow channels  38 A therebetween. The configuration illustrated in  FIG. 17  includes vertically positioned supports  36 B which extend along the z-axis to create airflow channels  38 B. Vertically extending supports  36 B may also be utilized at the ends of spacer  30 A as illustrated in  FIG. 16 . Supports  36 A and  36 B may be secured in place by, e.g., welding and may be formed of the same material, including the same gauge of material as the plates forming substantially planar first surface  32  and substantially planar second surface  34  of spacer  30 .  FIG. 18  illustrates a further alternative embodiment incorporating supports  36 C in the form of integral ends of open ended rectangular channel pieces  50 , which may each be monolithically formed as a single unitary structure. As illustrated in  FIG. 18 , open ended rectangular channels  50  which define airflow channels  38 C therethrough can be secured to one another by forming an aperture through adjacent supports  36 C and securing adjacent open ended rectangular channels  50  to one another by inserting a bolt therethrough and fastening a nut in place as illustrated in  FIG. 18 . Any of the supports  36  contemplated by the present disclosure can have a height along the z-axis of about 0.25 to 3 inches. With respect to supports such as supports  36   a  which extend at an angle in the y-z plane, the height of such support is defined as the length it travels from one end to the other along the z-axis. 
       FIG. 19  illustrates another exemplary spacer  30   d . Spacer  30   d  includes a single airflow channel  38   d  extending between airflow inlet side  40   d  and airflow outlet side  42   d . Specifically, airflow channel  38   d  is formed between supports  36   d , which are formed at the edges of the plates defining substantially planar first surface  32   d  and substantially planar second surface  34   d  that span airflow inlet side  40   d  and airflow outlet side  42   d . Stated another way, supports  36  are aligned along the x-axis of the Cartesian coordinate system illustrated in  FIG. 19  and are secured to both of the plates forming substantially planar first surface  32   d  and substantially planar second surface  34   d  along their entire length along the x-axis at their extremities along the y-axis. Supports  36   d  are the only supports of spacer  30   d  that span the entire x-axis length of the plates forming substantially planar first surface  32   d  and substantially planar second surface  34   d . The remaining supports  36   d ′ run less than the entire x-axis length of the upper and lower plates and provide mechanical support for the opposing plates, but do not define airflow channels from airflow inlet side  40   d  to airflow outlet side  42   d . Supports  36   d ′ are shown being oriented parallel to the x-axis; however, supports  36   d ′ could be positioned in any desired orientation to provide mechanical support for the opposing plates. Supports  36   d  are sufficient to eliminate airflow from exiting the sides of spacer  30   d  spanning airflow inlet side  40   d  and airflow outlet side  42   d . Any of the various supports of the present invention may be utilized in an embodiment similar to the one presented in  FIG. 19 . Specifically, any of the supports may replace box tube support  36   d  running the entire length of the sides of spacer  30   d  and any of the supports may be truncated to provide mechanical support at desired locations and orientations throughout the body of a spacer. 
     Various exemplary spacers of the present invention and their corresponding parts are denoted with primed reference numerals and/or reference numerals including an alphabetic designator such that similar parts of the various embodiments of spacer  30  include the same numeric reference. Any of the features described with respect to any of the various embodiments of spacer  30  described above may be utilized in conjunction with any other feature of any of the alternative embodiment spacers described in the present application. 
     2. Waveform Palletized Product Spacer. 
     Turning now to  FIG. 20 , another exemplary design for a palletized product spacer is illustrated. Spacer  130  includes airflow channels  138  and  138 ′ which, like air pathways  24  of spacer  30  described in detail above, facilitate airflow along the x-direction of the illustrated Cartesian coordinate system while preventing any substantial airflow outside of channels  138 ,  138 ′ in the y-direction. Generally speaking, structures of spacer  130  are denoted by reference numerals which correspond to the reference numerals of analogous structures of spacer  30 , except with  100  added thereto. Moreover, spacers  30 ,  130  are generally interchangeable when used to vertically space apart respective rows of cases  22  in pallet assembly  52  (see, e.g.,  FIG. 9 ). 
     Spacer  130  includes a plurality of substantially planar, upper support surfaces  132  which extend in an x-y plane of the illustrated Cartesian coordinate system ( FIG. 20 ). Upper support surfaces  132  can be said to be elongate, as each surface  132  has a longitudinal extent along the x-direction that is substantially larger, such as 10-20 times larger, than the corresponding width of surface  132  along the y-direction. For purposes of the present disclosure, small interruptions in the longitudinal extent of surfaces  132 , such as by stiffener ribs  166  described in further detail below, is not considered to disrupt the overall longitudinal shape of surfaces  132 , which run from an inlet of airflow channels  138 ,  138 ′ at one side of spacer  130 , to an outlet thereof at the other side of spacer  130 . 
     Interposed between respective neighboring pairs of upper support surfaces  132  are substantially planar, elongate lower support surfaces  134  vertically spaced from upper support surfaces  132  (i.e., along the z-direction) by a total vertical distance corresponding to the overall height H ( FIG. 21 ) of spacer  130 . In an exemplary embodiment, vertical height H may be about 1.5 inches, which is large enough to provide substantial airflow through airflow channels  138 ,  138 ′, while remaining small enough to maximize the number of rows of cases  22  which can be stacked upon pallet  4  ( FIG. 26 ) for a given height of pallet assembly  52 . However, it is contemplated that height H may be as small as 0.5 inches, 1.0 inch, or 1.5 inches, or as large as 2.5 inches, 3.0 inches or 3.5 inches, or maybe any height within any range defined by any of the foregoing values. 
     Connecting respective upper support surfaces  132  to their adjacent, neighboring lower support surfaces  134  are sidewalls  136 . In one exemplary embodiment, sidewalls  136  are substantially vertical to provide columnar support for the compressive loads applied between upper and lower support surfaces  132 ,  134  when spacer  130  is used in pallet assembly  52  (as shown in  FIG. 26  and described further below). In exemplary embodiments, spacer  130  is formed from a single, unitary, monolithic material. Exemplary materials include polymers such as acrylonitrile butadiene styrene (ABS), polyester copolymer (PETG), polystyrene (PS), polycarbonate (PC), polypropylene (PP), sheet or foamed-sheet polyethylene (PE), polyvinyl chloride (PVC) and acrylic (PMMA). In order to facilitate mass-production of spacer  130  by molding techniques (e.g., vacuum forming, injection molding, foam forming, etc.), and to facilitate storage and shipping of groups of spacers  130  in a stacked and nested configuration, sidewalls  136  may be slightly angled such that any neighboring pair of sidewalls  136  diverge toward the open end of the respective airflow channel  138  or  138 ′ formed by the neighboring pair of sidewalls  136 . This divergence provides a “draft” which facilitates production of spacer  130  by injection molding (e.g., by allowing hold halves to be removed without binding to sidewalls  136 ). The draft also allows respective upper support surfaces  132  to be received within airflow channels  138 ′, and lower support surfaces  134  to be received within airflow channels  138 , so that spacers  130  can be nested with one another into large stacks that are efficiently and compactly transportable. In one exemplary embodiment, the draft angle of each sidewall  136  with respect to vertical (i.e., with respect to the z-direction) may be between 0.5 and 3 degrees, such as about 1 degree. 
     Airflow channels  138  each have a cross-sectional area bounded in the y-direction by the distance between sidewalls  136 , and in the z-direction by lower surface  162  of airflow channel  138  and the x-y plane defined by upper support surfaces  132 . As described in further detail below, thickness T of the material of spacer  130  may cooperate with the overall geometry and structure of airflow channels  138 ,  138 ′ to maximize these distances, and thereby maximize the cross-sectional area available within airflow channels  138 ,  138 ′. A large cross-sectional area provides for large airflow rate potential through channels  138 ,  138 ′ and facilitates a correspondingly large rate of thermal transfer when spacer  130  is used as a product spacer in a warehouse environment, e.g., a blast freezer. 
     The cross-sectional area of airflow channels  138 ′ is similarly bounded by sidewalls  136  along the y-direction, and by upper surface  164  ( FIG. 24 ) of channel  138 ′ and the x-y plane defined by lower support surfaces  134  in the z-direction. However, as further described below, end stiffeners  168  and intermediate stiffeners  166  ( FIG. 20 ) may slightly reduce the overall available cross-sectional area available for airflow channel  138 ′. This reduction imparts additional compressive strength to spacer  130  to increase the load-carrying capacity of spacer  130 , while also promoting air-side (i.e., upstream) turbulence without significantly reducing air flow. This turbulence may assist with the heat transfer capacity of the airflow, while the directional airflow itself maintains air movement across the entire extent of pallet assembly  52 . Similarly, lower stiffeners  170  may protrude slightly into airflow channels  138  but also provide impart compressive strength to spacer  130 . In an exemplary embodiment, stiffeners  166 ,  168  and  170  consume no more than 40% of the theoretical maximum airflow area through channels  138 ,  138 ′ respectively. In other exemplary embodiments, this area may be less than 30%, 20%, 15% or 10%, for example. 
     As best seen in  FIG. 21 , the arrangement of upper and lower support surfaces  132 ,  134  and sidewalls  136  creates an undulating, waveform-like profile of lands and valleys, in which the lands (i.e., flattened peaks) are formed by respective upper support surfaces  132 , and the valleys are formed as airflow channels  138  between each neighboring pair of upper support surfaces  132 . This arrangement allows direct convective thermal transfer from the bottom surface of the case disposed upon upper support surfaces  132 , as airflow passes through airflow channel  138  along a longitudinal path extending in the x-direction (as further described with respect to airflow management below). Similarly, convective thermal transfer can occur between the upper surface of a case upon which lower support surfaces  134  of spacer  130  rest, as air flows through airflow channels  138 ′ along the x-direction. In an exemplary embodiment, airflow channels  138 ,  138 ′ are all substantially linear, in that channels  138 ,  138 ′ define longitudinal axes that extend along a substantially straight line (i.e., nominally straight) in the x-direction. In addition, airflow channels  138 ,  138 ′ all define longitudinal extents in the x-direction that are substantially parallel (i.e., nominally parallel), which simplifies the logistics of air handling (i.e., by handlers  8  and exhaust fans  12  as described herein). 
     In addition to this high potential for heat transfer provided by spacer  130 , the planar support surface area of upper and lower support surfaces  132 ,  134  may each equal up to half of the overall coverage area of spacer  130 , where the “coverage area” is the total area in the x-y plane potentially overlaid by spacer  130 . This large support surface area provides substantial support for the adjacent surfaces of case  22  resting upon surfaces  132 ,  134 , and is enabled by orienting sidewalls  136  in vertical or near vertical orientation (e.g., a planar orientation aligned or nearly aligned with an x-z plane). Thus, if spacer  130  defines an overall width in the y-direction of 48 inches and an overall depth in the x-direction of 40 inches (i.e., the standard width and depth of a pallet), upper support surfaces  132  may cumulatively total up to half of the coverage area of 1,920 square inches (i.e., the surface area covered by spacer  130 ), or up to 960 square inches. However, in some exemplary embodiments, the cumulative support surface area of upper support surfaces  132  is slightly less than 50% in view of less-than-vertical sidewalls  136  (as discussed above), and/or interruptions in individual longitudinal upper support surfaces  132 . 
     For example, as best seen in  FIG. 20 , intermediate stiffeners  166  may interrupt respective upper support surfaces  132  along the longitudinal extent thereof (i.e., along the x-direction), slightly reducing the cumulative support surface area of upper support surfaces  132 . As further described below, intermediate stiffeners  166  may occupy up to 15% of the area of upper support surfaces  132 , and therefore up to 7.5% of the total surface area covered by spacer  130 . However, even if sidewalls  136  include a draft angle and intermediate stiffeners  166  are provided, upper support surfaces  132  of spacer  130  directly abuts and support cases  22  over at least 40% of the overall coverage area of spacer  130  ( FIG. 26 ). Lower support surfaces  134  are similarly arranged, and may be interrupted by lower stiffeners  170  ( FIGS. 21 and 24 ). Therefore, the cumulative abutting support area of lower support surfaces  134  is also at least 40%, and up to 50%, of the overall coverage area of spacer  130 . By contrast, “egg carton” type predicate spacers  20  (shown in  FIG. 7  and described above) have a comparable contact area of 25% or less. 
     The large amount of coverage area provided by upper and lower support surfaces  132 ,  134  provides support to prevent cases  22  from sagging or otherwise protruding into airflow channels  138 ,  138 ′, thereby maintaining the channels&#39; large cross-sectional airflow area. The overall width W along the y-direction of airflow channels  138 ,  138 ′ may also be controlled to prevent such sagging, as well as providing a sufficient number of “lands and valleys” (described above) to provide high mechanical strength of spacer  130 . In an exemplary embodiment, width W of airflow channels  138 ,  138 ′ is about 1 inch, which is small enough to avoid sagging of a typical cardboard case  22  into airflow channels  138 ,  138 ′ but also large enough to promote substantial airflow. Thus, if the associated width of the adjacent upper and lower surfaces  132 ,  134  are commensurate with width W (i.e., the lands and valleys of spacer  130  have equal widths along the y direction), a spacer  130  having an overall width of 48 inches may have about 25 lands and 24 valleys, while a 40-inch-wide spacer  130  may have about 21 lands and 20 valleys. In these embodiments, one additional land (formed by upper support surface  132 ) may be provided to ensure that end stiffeners  168  (further described below) are present at both terminal ends of spacer  130 . In other embodiments, it is contemplated that width W of airflow channels  138 ,  138 ′ may be as small as 0.5 inches, 1.0 inch or 1.5 inches or may be as large as 2.0 inches, 2.25 inches, or 2.5 inches, or maybe any width within any range defined by any of the foregoing values. 
     In addition to the substantial support surface area provided by the undulating lands and valleys of spacer  130 , additional shapes and structures of spacer  130  may cooperate to impart substantial compressive mechanical strength to mitigate or prevent loss of overall height H due to buckling when cases  22  are stacked upon upper support surfaces  132 . In some embodiments, a desired mechanical strength of spacer  130  may be accomplished by using rigid materials, such as aluminum, to form spacer  130 , and/or by increasing material thickness T to provide material-based compressive strength. However, production efficiency, weight and cost considerations militate against the use of heavy and/or large quantities of material in forming spacer  130 . In order to reduce overall material usage and enable the use of materials with less inherent strength, spacer  130  may include end stiffeners  168 , intermediate stiffeners  166 , lower stiffeners  170 , or any combination thereof. 
     Generally speaking, stiffeners  166 ,  168 ,  170  interconnect neighboring pairs of sidewalls  136  with the adjacent upper support surface  132  or lower support surface  134  disposed therebetween. This interconnection is accomplished by introducing one or more stiffener walls disposed in the y-z plane, as best illustrated in  FIG. 20 . For example, end stiffeners  168  form a partial closure of airflow channels  138 ′ ( FIG. 20 ) and thereby interconnect a neighboring pair of sidewalls  136  with the upper support surface  132  between the pair of sidewalls  136 . When a compressive stress is applied to upper surface  132 , the tendency of sidewalls  136  to splay apart or otherwise deform at the junction between sidewalls  136  and upper surface  132  introduces a tensile stress into the material of end stiffener  168 . Where spacer  130  is made of a material with high tensile strength, such as some polymers and especially cross-linked polymers, the shifting of this tensile stress into the material of end stiffener  168  counteracts the tendency of sidewalls  136  to splay apart, thereby creating a rigid or semi-rigid barrier against such splaying and preserving the integrity of the lands-and-valleys shape of spacer  130 . 
     Similarly, intermediate stiffeners  166  form indented portions of sidewalls  136  and upper surface  132  which protrude slightly into airflow channel  138 ′. These indented portions, in effect, create a pair of sidewall-like structures extending in the y-z plane and stiffen the adjacent sidewalls  136  in the same manner as end stiffeners  168 . In an exemplary embodiment, shown in  FIG. 2 , intermediate stiffeners  166  have a semi-circular profile defining a stiffener depth S D  of about 0.25 inches and a stiffener width S W  of about 0.25 inches (such that the semi-circular profile has a diameter of about 0.25 inches). This nominal depth and width is sufficient to impart substantial additional strength to spacer  130  while minimizing the interruption to upper support surfaces  132  and sidewalls  136 . In an exemplary embodiment, end stiffeners  168  may protrude into channels  138 ′ by an amount equal to, or less than, the protrusion formed by intermediate stiffeners  166 . 
     This exemplary protrusion geometry may leave the cross-sectional area of the respective channels  138 ′ substantially uninterrupted, e.g., by occupying less than about 20% of the overall height of channel  138 ′, where the height of channel  138 ′ is the distance along the z-direction between upper surface  164  of channel  138 ′ and the x-y plane defined by lower support surfaces  134  as shown in  FIG. 24  and noted above. Width W is similarly unobstructed by stiffeners  166  and/or stiffeners  168 , which occupy less than about 20% of channel  138 ′. Channel  138  is substantially uninterrupted by lower stiffeners  170  in a similar fashion. In addition, this minimal protrusion into sidewalls  136 , as described above, minimizes or substantially prevents lateral escape of air from channels  138  and  138 ′, instead ensuring that such airflow will be directed entirely or nearly entirely along the x-direction. 
     In addition, stiffeners  166  may be distributed at regular intervals across the longitudinal extent of upper support surfaces  132  by a spacing or amplitude A. The nominal value of amplitude A may be chosen such that intermediate stiffener  166  repeats often enough to impart the desired strength to spacer  130 , without unduly interrupting the otherwise large support surface area provided by upper support surfaces  132 . In an exemplary embodiment, amplitude A is about 3 inches, which when combined with the 0.25 inch values for depth S D  and width S W , preserves at least 85% of the available cumulative support surface area of upper support surfaces  132  available for direct abutment with a lower surface of case  22  ( FIG. 26 ). In other embodiments, amplitude A may be as little as 1 inch, 2 inches or 4 inches, or as large as 6 inches, 7 inches or 8 inches, or may be any value within any range defined by any of the foregoing values. Similarly, width S W  may be varied in proportion to amplitude A, such that width S W  is as little as ⅛ inch, ⅜ inch or ½ inch, or as large as ¾ inch, ⅞ inch or 1 inch, or any value within any range defined by any of the foregoing values. 
     Turning to  FIG. 20 b   , secondary intermediate stiffeners  167  may optionally be provided within intermediate stiffeners  166 . In the illustrated embodiment, secondary intermediate stiffeners  167  are located along an outermost upper support surface  132  of spacer  130 , so as to provide additional stiffening support along the edges of spacer  130  where higher pressures may be concentrated as a result of relatively stiff sidewalls of cases  22 . Stiffeners  167 , as shown, extend transversely to stiffeners  166  and generally along the longitudinal extent of upper surface  132 . Although stiffeners  167  are shown only along upper support surfaces  132  disposed along the lateral edge of spacer  130 , it is also contemplated that stiffeners  167  could be provided throughout stiffeners  166  as required or desired for additional strength. Of course, given that only one corner of spacer  130  is shown in  FIG. 20 b   , it is contemplated that the corresponding upper support surfaces  132  of spacer  130  along the opposite edge (not shown) may also have stiffeners  167 . In addition, although stiffeners  167  are shown and described as an optional feature of spacer  130 , stiffeners  167  may be similarly applied to spacer  130   a  shown in  FIGS. 20 a   - 24   a.    
     In addition, the barrier to lateral airflow (i.e., in the y-direction) posed by sidewalls  136  is left substantially uninterrupted by the small amount of lateral area interrupted by intermediate stiffeners  166 . In the illustrated exemplary embodiment, this interruption represents less than 2% of the total potential barrier area of each sidewall  136  (i.e., the barrier area that would exist without stiffeners  166 ), while in other exemplary embodiments the interruption may represent less than 5% of the total potential barrier area. 
     Lower stiffeners  170  are the same or substantially the same as intermediate stiffeners  166 , except lower stiffeners  170  protrude upwardly into channels  138  and form an indented portion in lower support surfaces  134  and its adjacent sidewalls  136 . In the exemplary embodiment shown in  FIG. 20 , lower stiffeners  170  are disposed between neighboring pairs of intermediate stiffeners  166  along the x-direction so as to provide additional strengthening of spacer  130  where it is needed most, i.e., halfway between the two neighboring intermediate stiffeners  166 . Thus, in the exemplary embodiment of  FIG. 20 , lower stiffeners  170  define amplitude A L  equal to amplitude A, e.g., about three inches ( FIG. 24 ). 
     In an exemplary embodiment, end stiffeners  168  are provided at respective longitudinal ends of downwardly opening airflow channels  138 ′, but not at corresponding respective longitudinal ends of upwardly opening airflow channels  138 . Because palletized products (such as meat or other food products) tend to settle to the bottoms of their respective cases  22 , the lower surface of cases  22  is a primary target for maximum heat transfer capability during a blast freezing operation. Accordingly, spacer  130  is designed to facilitate maximum airflows through the upwardly-opening airflow channels  138 , which allows substantial direct air contact with the adjacent lower surface of case  22 . Such maximum airflows are provided by unencumbering airflow passage through channels  138  as much as practicable. Thus, while lower stiffeners  170  may be provided for additional mechanical strength along and between lower support surfaces  134  and the adjacent sidewalls  136 , end stiffeners  168  may be omitted to enhance airflow through channels  138 . 
     As noted above, in an exemplary embodiment, spacer  130  is formed as a single monolithic structure. This monolithic structure may include stiffeners  166 ,  168  and/or  170 , as illustrated in  FIG. 20 . When stiffeners  166 ,  168  and  170  are all included in the monolithic structure, and spacer  130  is made of a monolithic polymer material having a thickness T ( FIG. 21 ) of 0.060 inches, empirical testing has demonstrated that the compressive mechanical strength of spacer  130  is sufficient to preserve at least 95% of the overall height H of spacer  130  under a load of at least 270 pounds per square foot. This strength is sufficient to support up to seven layers of 60-pound cases of product within pallet assembly  52 , with ten such cases contained in each 40-inch-by-48-inch layer of cases  22  (as shown in  FIG. 26 ). Thus, it has been empirically determined that an exemplary embodiment of spacer  130  can be expected to maintain large and substantially fully open airflow channels  138 ,  138 ′ between adjacent layers of stacked cases  22  within pallet assembly  52 , including between the bottom two layers of cases  22 . As described in further detail below, this open airflow channel provided by spacer  130  facilitates heat transfer in a blast freezing operation, while also being producible in high volume at a low unit cost. Spacers  130  are also lightweight for their strength, e.g., less than 0.5 pounds per square foot of surface area support. 
     In addition, maintaining thickness T at 0.060 inches (which may be uniform throughout the material of spacer  130 ) and spacer height H at 1.5 inches, a channel height up to 1.44 inches is produced for airflow channels  138 ,  138 ′. Thus, the airflow channel height of spacer  130  is at least 95% of overall height H, thereby maximizing airflow passage potential for a given spacer size. 
     In an alternative embodiment, spacer  130   a  may be provided as shown in  FIGS. 20 a , 21 a , 22 a , 23 a  and 24 a   . Spacer  130   a  is identical to spacer  130 , except airflow channels  138   a ′ include polygonal (e.g., substantially rectangular) apertures formed in end stiffeners  168   a  rather than the substantially completely open channels  138 ′ shown in  FIG. 21 . All features of spacer  130  described herein are applicable to spacer  130   a , and spacers  130  and  130   a  are interchangeable in use. Channels  138   a ′ allow for longitudinal air flow in similar fashion to channels  138 ′ described in detail above. Except for the air flow area opened by the apertures admitting air to channels  138   a ′, end stiffeners  168   a  respectively form a continuous wall as illustrated. Spacer  130   a  may be manufactured with airflow channels  138   a  initially closed, i.e., end stiffeners  168   a  may respectively form walls completely blocking airflow access to the various channels  138   a ′. In order to open the rectangular aperture as illustrated, material may be selectively removed from end stiffener  168   a  after the molding of spacer  130   a  is completed, such as with an end mill or other suitable cutting tool. This allows for mass production of spacer  130   a  with a continuous end wall at end stiffener  168   a , which may have an appropriate draft angle and material thickness to facilitate efficient production by injection molding. In addition, the material of end stiffeners  168   a , which spans neighboring sidewalls  136  across the bottom of channels  138   a ′ as illustrated, provides additional stiffness and compressive strength to spacer  130   a . More particularly, the continuity of material across the bottom of channel  138   a ′ serves as a “tension strap” between neighboring sidewalls  136  to provide extra security against splaying or bowing of sidewalls  136  under a heavy compressive load on upper support surfaces  132 . 
     In another alternative embodiment, spacer  130   b  may be provided as shown in  FIG. 21 b   . Spacer  130   b  is identical to spacer  130 , except airflow channels  138   b ′ include arcuate (e.g., round) holes formed in end stiffeners  168   b  rather than the substantially completely open channels  138 ′ shown in  FIG. 21  or the rectangular channels  138   a ′. All features of spacer  130  may be equally applied to spacer  130   b , and spacers  130  and  130   b  are interchangeable in use except as otherwise provided herein. Channels  138   b ′ allow for airflow in similar fashion to channels  138 ′ described in detail above. Except for the air flow area opened by holes  138   b ′, end stiffeners  168   b  form a continuous wall as illustrated, thus providing additional compressive strength to spacer  130   b  in a similar fashion to spacer  130   a  above. 
     As noted above, spacers  130  may be sized to completely overlay a 40-inch-by-48-inch pallet. In some embodiments, channels  138 ,  138 ′ may be oriented along the 40-inch direction, and in other embodiments, channels  138 ,  138 ′ may be oriented along the 48-inch direction depending on the requirements of a particular application. In addition, spacer  130  may be slightly oversized, such as 42-inches-by-50-inches, in order to allow some “overhang” or protrusion of spacer  130  past the edges of respective layers of cases  22 , such that any overhang of the edges of cases  22  is prevented from restricting or reducing air flow through channels  138 ,  138 ′. 
     Turning again to  FIG. 20 b   , case stabilizers  140  may optionally be provided as part of the monolithic structure of spacer  130 , as illustrated. As illustrated, case stabilizers  140  are formed at the terminal ends of spacer  130 , i.e., along sidewall  136  at the edge of spacer  130  and/or at end stiffener  168 . Case stabilizers  140  protrude upwardly away from support surface(s)  132  such that cases  22  received upon spacer  130  (as shown in  FIGS. 25 and 26 ) are prevented from sliding or shifting past the edge of spacer  130 . Thus, case stabilizers  140  serve to retain cases  22  in their intended positions, fully supported by the various underlying support surfaces  132 , and to prevent part of the spacer-contacting surfaces of cases  22  from sliding out of contact with support surfaces  132  during loading, transport and other handling of pallet assemblies  52 . 
     3. Airflow Management Devices. 
     Turning now to  FIG. 25 , high-capacity racking  114  useable in warehouse  2  ( FIGS. 1-3 ) is illustrated. As described above, racking  14  can include rows and columns of pallet assemblies  52  disposed between aisles  10  and air chambers  6 , with exhaust fans  12  drawing air from respective aisles  10  through pallet assemblies  52  and into chambers  6  before exhausting the air back into the interior space of warehouse  2 . However, as shown in  FIGS. 3 and 4 , these rows and columns of pallet assemblies  52  are arranged in bays designed for only one layer of depth for pallet assemblies  52  between aisles  10  and chambers  6 . 
     By contrast, high-capacity racking  114  has bays  109  each designed to accept more than one pallet assembly  52  along the depth direction (i.e., along the x-direction of the illustrated Cartesian coordinate system). For purposes of the present disclosure, the “depth direction” corresponds to the intended direction of airflow between aisles  10  and chambers  6  (as shown in  FIG. 4 ), which is also the longitudinal direction of airflow channels  38  and/or  138  of spacers  30 ,  130 . 
     In the illustrated embodiment of  FIG. 25 , bays  109  are sufficiently deep to house five adjacent pallet assemblies  52  as illustrated. In an exemplary method of use, each pallet assembly  52  may be loaded from the back side of racking  114 , i.e., from within chamber  106 . As each pallet assembly  52  is inserted into a respective bay  109 , the pallet assembly  52  may be drawn, e.g., by gravity, into abutting engagement with a front side of racking  114 , i.e., the side facing aisle  110 . Further pallet assemblies  52  are similarly loaded within bay  109  to fill bay  109  with up to four additional pallet assemblies  52  as illustrated in  FIG. 25 . 
     Racking system  114  can be used for highly efficient space utilization within warehouse  2 , because the percentage of space occupied by aisles  110  and air chambers  106  represents a relatively smaller percentage of the total space within warehouse  2  while the space occupied by pallet assemblies  52  is a concomitantly larger percentage. On the other hand, the large “block” of pallet assemblies  52  contained within high-capacity racking  114  may be subject to the same requirements as racking  14  for consistent and efficient heat transfer for, e.g., a blast freezing operation. For example for palletized food products subject to food safety regulations and standards, predictability of freezing rates for each individual case  22  in a blast freezing operation is the same regardless of whether racking  14  or  114  is used within warehouse  2 . To this end, racking  114  includes air management systems operable to ensure consistent airflow through spacers  30  and/or  130  along the entire depth of bays  109 . In addition to spacers  30 ,  130 , these systems may also include pivotable air dams  158  and lateral pallet spacers  160 , both described in detail below. 
     Turning to  FIG. 26 , one pivoting air dam  158  is provided within bay  109  for each pallet assembly  52  received therein. Each air dam  158  is pivotally affixed to top panel  117  via pivots  172 , which may take the form of a piano-type hinge, a plurality of door-type hinges, an elastomer hinge, or any other suitable hinging structure. As each pallet assembly  52  passes from its entry point within chamber  116  towards aisle  110  ( FIG. 25 ), the upper layer of cases  22  on the pallet assembly  52  causes air dam  158  to pivot upwardly about pivot  172 . 
     Air dam  158  is a substantially rigid structure, such as hard plastic (e.g., ABS), aluminum, steel or the like. The weight of air dam  158  maintains firm contact with the upper layer of cases  22  to maintain a fluid tight seal along the upper surface of pallet assembly  52 , as shown, and this force of weight may be augmented by a spring bias or other biasing force as needed. In addition, a high pressure resulting from movement of air from air handler  8  forces air flowing past pallet assemblies  52  can also create a positive pressure differential on the upstream surface of each air dam  158 , it being understood that the highest-pressure air will be located at air handlers  8  and downstream locations will have steadily reduced air pressures. This positive pressure differential may also tend to urge air dams  158  into firm contact with their respective pallet assemblies  52 , thereby creating a substantially fluid-tight seal at the interface therebetween. Where air dams  158  are used with standard-sized pallet assemblies  52 , air dams  158  may define a width of about 40 inches or about 48 inches to correspond with the associated pallet assembly  52  disposed below air dams  158 . The overall height of air dams  158  may be any dimension suitable to a particular height variability of pallet assemblies  52 , such as about 40 inches. 
     When the next pallet assembly  52  is loaded into bay  109 , the next downstream air dam  158  similarly seals against the upper row of cases  22  and, in cooperation with the first (upstream) air dam  158 , forms a fluid tight manifold space  174  in the head space bounded by neighboring upper surfaces of adjacent pallet assemblies  52 , neighboring pairs of air dams  158 , and top panel  117 . The lateral sides of manifold space are sealed by sidewalls  115  ( FIG. 25 ). In  FIG. 25 , one of sidewalls  115  is omitted to show the internal details of racking system  114 , it being understood that such sidewalls  115  are provided on both lateral sides of manifold spaces  174  to preserve the fluid tight seal therein. Turning back to  FIG. 26 , the pivotable arrangement of air dams  158  allows pallet assemblies  52  of differing heights to be loaded into bay  109  while maintaining fluid tight manifold spaces  174 . Finally, intermediate panels  117 A provide a floor for bays  109  to seal manifold space  174  from below. Wiper seals (not shown) may also be included to seal any space that may exist between air dams  158  and the respective adjacent sidewalls  115 . 
     Intermediate panels  117 A also act as a ceiling for lower bays  109 , as illustrated, where racking  114  has multiple rows of pallet assemblies  52 . Sidewalls  115  may also provided between each column of bays  109 , facilitating creation of individualized manifold spaces  174  in columns for each pallet assembly  52  contained in racking  114 . In this way, bays  109  can be arranged in any desired number of rows and columns, similar to the arrangement of racking  14 , except with multiple pallet assemblies along the depth dimension (i.e., along the x-direction) of bays  109  as noted above. 
     Lateral pallet spacers  160  are provided as part of pallet assembly  52  when used in high-capacity racking  114 , in order to ensure that each manifold space  174  receives a consistent flow of air from air handlers  8 . As best seen in  FIG. 26 , pallet spacer  160  protrudes outwardly from the periphery of each pallet  4  along the x-direction, such that when each pallet assembly  52  is loaded into bay  109 , neighboring pairs of pallet assemblies  52  abut one another by contact between pallet spacer  160  and the next adjacent pallet  4 . Cases  22  are also arranged to be within the footprint or profile of pallet  4 , i.e., cases  22  do not overhang past the edges of pallet  4 . In this way, layers of cases  22  on neighboring pallet assemblies  52  are prevented from abutting one another, such that an intra-pallet manifold space  176  is created and maintained between neighboring pairs of pallet assemblies  52 . As illustrated in  FIG. 26 , manifold space  176  is in direct fluid communication with manifold space  174 , such that air passing through spacers  30  and/or  130  of pallet assembly  52  exits the upstream pallet assembly  52  and flows into the first manifold spaces  174 ,  176 , creating an elevated air pressure therein (as compared to the ambient air pressure within warehouse  2 ). This elevated air pressure drives the air through the next set of spacers  30 ,  130  in the adjacent downstream pallet assembly  52 , exiting into the next downstream manifold space  174  and passing into space  176 . The elevated air pressure propagates through all of the pallet assemblies  52  arranged along the depth of bay  109  in this way, finally exiting at the downstream-most outlet of spacers  30  and/or  130  of the furthest downstream pallet assembly  52 , and into chamber  106  ( FIG. 25 ) for exhaust back to warehouse  2 . In this way, cooling airflow is ensured through spacers  30  and/or  130  of each and every one of the pallet assemblies  52  contained within high-capacity racking  114 , and therefore around the upper and lower surfaces of each and every case  22  contained therein. 
     One exemplary embodiment of lateral pallet spacer  160  is shown in  FIG. 27 . Pallet spacer  160  includes main body portion  178  and insertion tongue  180 . Main body portion  178  is a generally cubic structure having a longitudinal aperture  182  formed therethrough (i.e., along the x-direction of the Cartesian coordinate system shown in  FIG. 27 ). Aperture  182  allows for airflow in the x-direction to aid in cooling the bottom-most row of cases  22  for each of pallet assemblies  52  ( FIG. 26 ). To this end, it is contemplated that pallets  4  may also include openings and/or air channels similar to spacers  30 ,  130  to allow for cooling of the bottom surfaces of the bottom most row of the cases  22 . 
     Tongue  180  may have a tongue thickness T T  and a sharpened tip  184 , which cooperate to facilitate insertion of tongue  180  into pallet assembly  52  after cases  22  and spacers  130  have already been stacked upon pallet  4 . More particularly, tongue  180  of spacer  130  may be inserted between an upper surface of pallet  4  and an adjacent lower surface of case  22 , or an adjacent lower surface of spacer  130  where spacer  130  forms the bottom-most layer of pallet assembly  52 . In an exemplary embodiment, thickness T T  is about ⅛ inch. When inserted into assembly  52 , the weight and pressure of cases  22  upon tongue  180  keeps each lateral pallet spacer  160  in place and in reliable abutment with the outer surface of pallet  4  as long as pallet assembly  52  remains loaded with cases  22 . In order to control for the frictional retention force imparted by a given weight and pressure (which in turn depends on the nature and amount of product stored in cases  22 ), tongue  180  may define a variable tongue length L T  as low as 2 inches, 4 inches or 6 inches and as large as 8 inches, 10 inches or 12 inches. Depending on the application and the amount of frictional retention force desired, length L T  may be any length within any range defined by any of the foregoing values. Because friction is the only force used to retain spacer  160  in its desired location, spacer  160  can be removed and installed among various pallet assemblies  52  with ease and repeatability, and without removing any of cases  22 . 
     It is also contemplated that several other designs may be used to effect the functionality of lateral pallet spacers  160 , including spacers integrally formed into pallets  4 , spacers bolted or otherwise affixed onto pallets  4 , or spacers attached to selected layers of cases  22 . In addition, it is contemplated that handle  186  may span the inner walls of aperture  182 , to facilitate a firm grip when inserting or removing spacer  160  from pallet assembly  52 . In  FIG. 27 , handle  186  is shown extending generally horizontally across aperture  182 , though it is also contemplated that handle  186  may extend vertically or at a chosen angle. Other gripping mechanisms may be provided instead of, or in addition to, handle  186  on lateral pallet spacer  160 . Such other gripping mechanisms may be alternative gripping portions disposed within aperture  182 , or knurling of main body  178 , for example. 
     Dimension D of main body portion  178  of spacer  160 , which is the longitudinal dimension thereof in the x-direction, may be set at any desired nominal value in order to create a sufficient size of intra-pallet manifold space  176  ( FIG. 26 ). In an exemplary embodiment, dimension D may be as little as 2 inches, 3 inches or 5 inches, or may be as large as 8 inches, 10 inches or 12 inches, or may be any dimension within any range defined by any of the foregoing values. Height H T  of main body portion  178 , which is the longitudinal dimension in the Z-direction, may be between 3 inches and 5 inches and may be set to correspond with a particular height of pallet  4 , for example. 
     Other exemplary structures, systems and methods made in accordance with the present disclosure are described in U.S. patent application Ser. No. 13/844,078, filed Mar. 15, 2013 and entitled SPACER FOR A WAREHOUSE RACK-AISLE HEAT TRANSFER SYSTEM, the entire disclosure of which is hereby expressly incorporated herein by reference. 
     While this disclosure has been described as having an exemplary design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.