Abstract:
A heat management system for a building having at least one cooling device is provided. The heat management system includes a refrigeration system in heat exchange contact with a cooling system for providing cooling energy to the cooling system and to the cooling device. The cooling system includes at least two independent flow paths in heat exchange contact with the cooling device for cooling the cooling device. In addition, the heat management system includes a defrost system in heat exchange contact with the cooling device through the independent flow paths wherein the defrost system can be operated to independently defrost each flow path of the cooling system. The system is efficient to operate in conjunction with a geothermal system and provides effective building atmosphere de-humidification.

Description:
FIELD OF THE INVENTION 
     A heat management system for a building having at least one cooling device is provided. The heat management system includes a refrigeration system in heat exchange contact with a cooling system for providing cooling energy to the cooling system and to the cooling device. The cooling system includes at least two independent flow paths in heat exchange contact with the cooling device for cooling the cooling device. In addition, the heat management system includes a defrost system in heat exchange contact with the cooling device through the independent flow paths wherein the defrost system can be operated to independently defrost each flow path of the cooling system. The system is efficient to operate in conjunction with a geothermal system and provides effective building atmosphere de-humidification. 
     BACKGROUND OF THE INVENTION 
     Heating, cooling, and de-humidification systems within large buildings, such as grocery stores, are implemented to provide the multiple purposes of heating the building in winter, cooling the building in summer, cooling food products during both winter and summer and de-humidifying the building in the summer. 
     Normally, in the example of a grocery store, these systems are implemented independently of one another. For example, a primary food cooling system would be established to operate a grocery store&#39;s banks of freezers and coolers with its own system of refrigeration compressors, condensors and evaporators independently of a store&#39;s air conditioning system (having its own compressors, condensers and evaporators) which may also be independent of the store&#39;s heating system. In the summer, dehumidification systems may also be implemented to prevent the build-up of frost on food packages in open coolers or freezers. 
     With respect to a grocery store&#39;s cooling system for freezers and coolers, the evaporators or cooling coils of a food cooling system must be defrosted on a regular basis to ensure that the cooling system remains efficient. Specifically, refrigeration systems require frequent defrosting of the cooling coils of a freezer or cooler to remove frost which condenses on the cooling coils from the air passing over the cooling coils. In particular, open coolers or freezers are in contact with the air within a store and, accordingly, over time will circulate the humid air within the store through the cooler. On humid days, the condensation resulting from cooling can be substantial, resulting in significant frost build-up on both the cooling coils and the food products within the cooler/freezer. As frost builds up on the cooling coils, its effectiveness for cooling is reduced and, if left un-defrosted, will reduce the cooling efficiency of the cooler/freezer. Accordingly, regular defrosting of the coils is required to remove the frost from the coils. The defrosting cycle also contributes to the dehumidification of the store by the overall removal of water vapour from the atmosphere. 
     In a typical store, a defrost cycle is run every 6 hours wherein either the compressor is turned off and a defrost heater is activated to melt any condensed ice off the evaporator coils or the flow of refrigerant through the coils is reversed so that hot refrigerant is allowed to melt the frost build-up from the inside of the coil to the outside of the coil. In the case of an external heater, because heating is taking place externally and the heat transfer coefficient through air is low, the defrost cycle may take 30 minutes to complete such that the temperature within freezer or cooler may rise substantially thus increasing the risk of food spoilage as well as resulting in overall inefficient power consumption. During the defrost cycle, any melted water is allowed to drain away. 
     As indicated above, during this defrost process the temperature within the freezer/cooler may rise substantially to temperatures which affect the growth of micro-organisms on the food products resulting in an increased risk of food spoilage and the associated risk of food poisoning to the consumer. Furthermore, the repeated freeze—partial melt and re-freeze cycles in a freezer will have a significant impact on the shelf-life of the food products within the freezer often leading to a premature deterioration of the food and, hence, substantial wastage of the food. This leads to increased costs to both the store owner and consumer. In coolers, as opposed to freezers, this effect and the risk of food spoilage is more significant as the temperatures are higher. 
     In order to address the problems of inefficient defrost cycles, the use of water based cooling solutions have been proposed to provide a more efficient defrost cycle. In these systems, a gas-based refrigeration system is used to cool a water solution which is circulated through cooling cools in the freezer or cooler. The use of a water based solution for cooling has the effect of enabling rapid defrost cycles to be run, primarily as a result of the thermal mass of the water based solution. That is, in comparison with flowing a refrigerant gas through the cooling coils, the heat transfer coefficient for circulating a warm water-based liquid through the coiling coils is substantially greater than the heat transfer coefficient for circulating a warm refrigerant gas through the coiling coils. 
     Water based systems have permitted defrost cycles to be completed within a few minutes such that the temperature of the freezer or cooler does not rise to the same extent as with a refrigerant gas-based system. Furthermore, a water based cooling system allows a defrost cycle to be run every hour which minimizes the total amount of frost which may build up on a cooling coil over this time. This is compared to a gas based system which can only be defrosted every 4 hours or so due to the time required for a defrost cycle. 
     While a water based cooling system has advantages with respect to defrost cycles, the energy efficiency ratio (EER, measured in BTU(of cooling)/watts(energy utilized), and a measure of the cooling efficiency) remains similar to that of a conventional gas-based refrigeration system. In particular, refrigerant gas based cooling systems utilizing refrigerant gas to air heat transfer may have an EER in the order of 6 BTU/watt for a 0° F. (cooler temperature) to 140° F. (condenser temperature) thermal bridge while a water based cooling system utilizing water to air transfer under similar conditions would have a slightly lower EER. 
     As such, a number of problems exist with respect to prior art systems with respect to the ability of these systems to effectively provide efficient cooling of freezers and coolers, in combination with effective defrost systems, de-humidification systems and building heating and cooling systems. 
     For example, situations often exist where these independent systems work against one another or very inefficiently with respect to one another. This may involve, for example, air conditioners attempting to cool air including waste heat from a cooling system or defrosting system or waste heat from a cooling system not being utilized to heat the building in the winter. 
     Accordingly, there has been a need for a system which integrates all the heating and cooling systems of a building into an efficient system which effectively manages the transfer of heat between freezers, coolers, air conditioning, heating, dehumidification and defrost systems and in particular there has been a need for a system which does not allow the air temperature within a freezer/cooler to rise substantially during the defrost cycle and which allows for highly effective dehumidification of the building atmosphere. The development of such a system will also reduce the capital and maintenance costs associated with each of these systems. 
     Specifically, there has been a need for a geothermal based system integrated to the heating and cooling system of a building to provide improved overall system energy efficiency as well as a specific need for a dual flow path, water based cooling system which provides efficient defrosting cycles and which also provide effective dehumidification to a building atmosphere. 
     A review of the prior art has revealed that such a system has heretobefore not been realized. For example, U.S. Pat. No. 5,000,257 discloses a heat exchanger having a radiator and a condenser in proximal relationship with one another; U.S. Pat. 4,002,201 discloses a multiple fluid stacked heat exchanger; U.S. Pat. No. 4,176,525 discloses a combined environmental and refrigeration system for use in grocery stores and the like; U.S. Pat. No. 5,586,444 discloses a control system for multiple cooling case in a grocery store; U.S. Pat. No. 4,288,993 discloses a refrigeration system having primary and secondary refrigeration systems in heat exchanging contact with each other; U.S. Pat. No. 5,570,585 discloses a cooling system that operates to cool and store a product load having two compressor systems that are configured to operate independently or together as a single stage compressor; and, U.S. Pat. No. 4,191,024 discloses a defrosting method for use in a refrigeration system that alternately uses one of two coolers while the other is defrosting. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, there is provided a heat management system for a building having at least one cooling device, the heat management system comprising: 
     a refrigeration system in heat exchange contact with a cooling system for providing cooling energy to the cooling system, the cooling system including at least two independent flow paths in heat exchange contact with the cooling device for cooling the cooling device; and, 
     a defrost system in heat exchange contact with the cooling device through each respective independent flow path wherein the defrost system includes means to independently defrost each independent flow path. 
     In further and more specific embodiments of the invention, the independent flow paths include a plurality of cooling coils defining first and second sides of the cooling system wherein the first and second sides are positioned so as to partially overlap with the other side which preferably define a non-linear boundary. Still further, it is preferred that the cooling system includes an air flow system for circulating air over the cooling system for effecting heat transfer between the air and the cooling system and air flowing over the cooling system follows a tortuous path. 
     In still further embodiments, a cold storage system is operatively connected to the cooling system, the defrost system is in heat exchange contact with the refrigeration system to receive heat from the refrigeration system for defrosting and/or a heat storage system is operatively connected to the defrost system. 
     In a further embodiment the defrost system further includes a building heating system operatively connected to the defrost system for transferring heat to the building which may be a combination of a radiant floor heating system or a water/air heat pump system. 
     In another preferred embodiment,the system is further adapted to transfer waste heat from the refrigeration system and/or building to a geothermal system. 
     In accordance with a more specific embodiment of the invention, a heat management system is provided, the heat management system comprising: 
     at least one cooling device; 
     a refrigeration system in heat exchange contact with a cooling system for providing cooling energy to the cooling system, the cooling system including: 
     at least two independent flow paths in heat exchange contact with the cooling device for cooling the cooling device; 
     a plurality of cooling coils defining first and second sides of the cooling system wherein the first and second sides are positioned so as to partially overlap with the other side and define a non-linear boundary; 
     an air flow system for circulating air over the cooling coils for effecting heat transfer between the air and the cooling system; and, 
     a cold storage system operatively connected to the independent flow paths; 
     a defrost system in heat exchange contact with the cooling device through each respective independent flow path, the defrost system also in heat exchange contact with the refrigeration system to receive heat from the refrigeration system for defrosting wherein the defrost system also includes means to independently defrost each independent flow path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of the heating, cooling and dehumidification system in accordance with the invention; 
     FIG. 2 is a schematic drawing of a specific embodiment of the heating, cooling and dehumidification system in accordance with the invention; 
     FIG. 2A is a schematic drawing a second embodiment of the heating, cooling and dehumidification system in accordance with the invention; 
     FIG. 2B is a schematic drawing a further embodiment of the heating, cooling and dehumidification system in accordance with the invention; 
     FIG. 3 is a schematic cutaway drawing of a typical grocery freezer cooler; 
     FIG. 3A is a schematic cutaway of a rack of coiling coils  128  in accordance with the invention; and, 
     FIG. 3B is a schematic representation of a cooling rack showing air flow through a cooling rack. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the invention and with reference to FIG. 1, a heating and cooling system  10  for a building, such as a grocery store is shown. The heating and cooling system includes a number of systems which enable the efficient transfer of heat to allow: 
     1) the operation of coolers and freezers in the building; 
     2) the defrosting of the above coolers and freezers; 
     3) the efficient de-humidification of the building atmosphere; 
     4) the heating of the building; and, 
     5) the cooling of the building. 
     More specifically, the system  10  includes a refrigeration system  12 , a water based cooling system  14 , a defrost system  16 , heat storage system  19  and an optional geothermal system  18  and optional building heating/cooling system  20 . In order that heat transfer is enabled between each of these modules, appropriate system connectors including piping and valves, heat exchangers and heat storage systems are also provided. That is, the refrigeration system  12  is connected to the water cooling system  14  through a first heat exchanger  12   a , the geothermal system  18  is connected to refrigeration system  12  through second heat exchanger  18   a , the defrost system  16  is connected to the heat storage system  19  through a third heat exchanger  16   a . Furthermore, heat exchanger  18   a  may be connected to a fourth heat exchanger  19   a.    
     The system  10  operates to allow for the efficient transfer of heat to and from the ground for the purposes of heating or cooling a building. The system also operates to provide specific cooling capabilities to freezers and/or coolers and to efficiently de-humidify the building atmosphere. 
     More specifically, the refrigeration system  12  operates to transfer heat from the water based cooling system  14  to the ground through geothermal system  18 , to the heat storage system  19  and building heating system  20  and/or to the defrost system  16 , The defrost system  16  operates to transfer heat to the freezers/coolers  1  for defrosting and to de-humidify the building atmosphere. The heating system  20  and heating/cooling system  20   a  operate to transfer heat to the building atmosphere and/or cool the building atmosphere. 
     FIG. 2 shows details of an embodiment of a system which enables the operation of coolers and freezers in the building, the defrosting of the coolers and freezers, the efficient de-humidification of the building atmosphere and the optional heating and/or cooling of the building atmosphere. 
     In accordance with this embodiment, a basic refrigeration system  100  is provided including a compressor  102 , condenser  104 , expansion valve  106 , and evaporator  108 . The refrigeration system operates to circulate a refrigerant around the system to enable the transfer of heat into and out of the system. As is known, the compressor  102  compresses a refrigerant gas whereby the compressed refrigerant passes through a condenser  104  wherein heat from the compressed refrigerant is given off. Thereafter, the compressed refrigerant passes through an expansion valve  106  wherein the compressed refrigerant is allowed to expand to a gas which absorbs heat when passed through an evaporator coil system  108  and returned to the compressor  102 . At both the condenser side  104  and evaporator side  108 , heat exchangers  110  and  112  respectively may be configured to the refrigeration system  100  to allow heat to efficiently move into or out of the system  100 . 
     A cooling system  120  is connected to the evaporator side  108  of the refrigeration system  100  through heat exchanger  112  to allow cooling of a water based cooling solution such as a water/alcohol mixture. Heat from the cooling system  120  is given up to the evaporator  108  thereby cooling the water solution within the cooling system  120 . The cold water solution may be stored in an optional but preferred holding tank  122  from which it is delivered to a cooler  124  through separate flow paths  126   a  and  126   b  (sides I and II) to a cooling coil system  128  within the cooler  124 . The cold storage tank is preferably provided in order to provide thermal mass in the event of sudden loads being placed on the system such as loading a freezer or cooler. 
     The separate and distinct flow paths  126   a  and  126   b  allow each side of the cooling coil system  128  to be independently defrosted which in addition to providing efficient defrosting also enhances the building atmospheric dehumidification, explained in greater detail below. The cold fluid circulating through the cooler  124  receives heat from the contents of the cooler  124 , such as food, thereby cooling the cooler contents. Fluid is returned to the heat exchanger  112  through pump  130 . 
     A defrost system  150  is also connected to the cooler  124  to allow the cooling coils  128  to be defrosted. The defrost system is a closed coil system containing a defrost fluid of the same composition as the cooling solution described above. The defrost system overlaps with the cooling system  120  in the region of the cooler  124 . Specifically, the cooling coils  128  include a shared flow path between valves A and B and C and D which allows the defrost fluid to be circulated through the cooling coils  128 . Preferably, the defrost loop  150  is closed in order to prevent contamination of the cooling fluid. The defrost system  150  includes a pump  152  for circulating the fluid within the loop. The defrost fluid is heated by heat exchanger  154 , preferably a counter-current coil-in-coil heat exchanger. 
     Heating of the defrost fluid is preferably obtained from a heat storage system  160  deriving heat from the heat rejected by the cooler  124  through the cooling system and the compressor  100  of the refrigeration system. The heat storage system  160  includes a pump  162  for circulating fluid through the heat storage system  160 . The heat storage system is connected to heat exchanger  154  and heat exchanger  164  thereby forming a closed loop. As an option, the heat storage system  160  includes a heat storage tank  166  for holding a volume of heating fluid (normally water) which may be used for a building heating system  170  or to provide heating if sudden loads are placed on the system. 
     The heating system  170  includes a pump  172  for pumping fluid to a specific heating system  174 . The specific heating system  174  may be an infloor radiant heating system or water/air heating system. A valve E may be controlled to effect flow of fluid to the secondary heating system  174 . The heating system  160  preferably receives heat from the coolers  124  and compressor  102  through the condenser  104  of the refrigeration system  100 . In one embodiment, the connection of the heating system loop  160  could be direct to the heat exchanger  110 . 
     In a preferred embodiment, a geothermal system  180  is provided between heat exchangers  110  and  164  which is further connected to supply well  182  and return well  184  and/or ground loop  186 . The circulation of fluid through the geothermal system is accomplished by pumps  188  and  190 . The specific flow of fluid is directed by valves F and G which may be used to selectively direct fluid through heat exchanger  110  only or through both heat exchangers  110  and  164 . Valves F and G may also be utilized in order to enable the circulation of fluid through the ground loop  186  or from supply well  182  and return well  184  through pump  190 . 
     In a still further embodiment, heating/cooling system  200  may be configured directly to the ground loop  180  system  180  which may also incorporate a heat/cold storage tank  202 . The heating/cooling system  200  may operate according to the principles of a standard ground source heat pump. 
     FIG. 2A shows an embodiment wherein the defrost system and heating systems of the building are unified into a single closed loop. In this embodiment, a refrigeration circuit  100  and cooling system  14  are provided as described previously. In this embodiment, a closed loop heating system is provided to extract heat from the refrigeration circuit  100  and from the ground source system such as a closed loop coil  186  or open loop system using supply  182  and return  184  wells. If an open loop system is used, a water/water heat exchanger  183  may be provided in order to prevent heating fluid contamination. 
     The heating system extracts heat from refrigeration circuit  110  which may be optionally stored in storage tank where it may be used to provide heat for defrosting the coolers  124  through operation of pump  162   a  and 3-way valves A, B, C and D as described previously. Furthermore, the system may include an optional heating system  170  such as in-floor radiant floor heating and/or a water/air heating system. The heating system  170  would receive heat through the operation of valves E and F. Preferably, the closed loop will use a clean heating fluid such as a water/alcohol solution. 
     A still further embodiment is shown in FIG.  2 B. In this embodiment, the building heating system utilizes separate water/air heating units  170   b  to extract heat from a ground loop  186  or open loop from supply  182  and return  184  wells. The defrost system is a separate closed loop which obtains heat from the refrigeration circuit  100  through refrigerant/water heat exchanger  110   b  and water/water heat exchanger  111 . 
     With reference to FIG. 3, a schematic cutaway drawing of a typical cooler  124  is shown. FIG. 3A is a schematic cutaway of a rack of coiling coils  128  in accordance with the invention and FIG. 3B shows the air flow through a cooling rack  128 . In a typical cooler or freezer, a rack of cooling coils is located at the back of the freezer/cooler  124  with a fan or blower  124   a  positioned beneath the cooling coils  128  to circulate air upwards and through the coiling coils  128 . Air passing over the coils is cooled, whereupon, it exits the top of the cooler/freezer and is directed toward an intake  124 c whereupon it is re-directed to the fan/blower  124   a . Thereby, through the circulation of air through the cooling coils  128  and the circulation of a cooling fluid through the coils  128 , the temperature within the freezer/cooler is reduced. In accordance with the invention, the cooling coils of the rack are separated into two distinct flow paths, designated I and II in FIG.  3 A. Generally, each side of the rack includes a series of looped piping which passes back and forth across the rack to provide a large surface area to enable effective heat transfer between the cooling fluid flowing through the piping and the air flowing over the piping  128 . By providing separate flow paths, the flow of cooling fluid through each side I and II of the rack can be independently controlled. 
     For example, and with reference to FIG. 2, during normal cooling operation, a cooling fluid is circulated through both sides I and II of the rack. In this mode valves, A, B, C and D (typically 3-way valves) are opened to allow fluid flow through the cooling circuit  120  and not through defrost loop  150 . At an appropriate time, where it is desired to defrost one side of the rack, for example side I, valves A and B would be closed to prevent cooling fluid through side I but opened to allow the flow of defrost fluid through side I under the control of pump  152 . Accordingly, by circulating a warm/hot defrost fluid through side I, side I is defrosted. Furthermore, as a result of the thermal mass of the defrost fluid, defrosting is accomplished very quickly wherein the frost on side I is melted and rapidly drips away from the cooling rack. As a result of the rapid defrosting time, and the continued flow of cooling fluid flowing through side II during defrosting of side I, the temperature within the cooler/freezer does not rise substantially. Melted water from defrosting is allowed to drain away from the system. 
     Upon completion of defrosting side I, valves A and B are returned to their original configuration and side I is cooled by cooling fluid. Similarly, in order to defrost side II, valves C and D are manipulated in a similar manner as for side I described above. 
     A particular advantage which is realized by this system is the effective and efficient dehumidification of a bulding. Dehumidification of a building is necessary, particularly in the summer months, in order to prevent excessive build-up of frost on the surfaces of the food products within a cooler/freezer as well as on the cooling coils. That is, if the relative humidity within the building is too high, the water vapour in the air will rapidly condense within the open coolers/freezers leading to a build-up of frost. Thus, it becomes necessary to control the humidity in order that customers can see the food products and to ensure that the refrigeration system operates efficiently. 
     With reference to FIG. 3B, the dehumidification process in accordance with the invention is explained wherein the two sides of a cooling rack  124  are similarly represented as I and II having cooling tubes  128  which overlap with respect to one another. During the defrosting cycle for side I, a defrost fluid is allowed to circulate through side I of the cooling rack  124  while cooling fluid flows through side II. Air flow continues to flow upwardly through the rack  124 . As a result of the defrost fluid flowing through side I, any frost which may have built up on the exterior of the tubes  128 I will melt forming water droplets which will fall away from each tube whereupon the water will collect at the bottom of the cooler  124   b  and allowed to drain away from the system. 
     Accordingly, by effectively removing condensed water vapour from the atmosphere of the building, the defrost cycle will also dehumidify the building atmosphere. 
     More specifically, however, the defrost cycle as provided by the dual flow path system will control humidity more effectively than a system which does not employ a dual flow path. In a single flow path system, at the time a defrost cycle is initiated, the melting of frost on the exterior of a cooling tube will immediately increase the relative humidity in the proximity of the cooling tube by virtue of a proportion of the melted water becoming vapour. Accordingly, also as a result of the continued circulation of air and the time required for defrosting, during the defrost cycle, the cooler will give back to the atmosphere some of the vapour which had been previously removed. 
     In the present system, this proportion of water vapour given back to the atmosphere is reduced significantly as any newly formed water vapour will be circulated through a system of tubes which are alternately warm and cold and overlapping. Accordingly, as a result of this tortuous path, the cooling tubes will continue to have a dehumidifying effect throughout the defrost cycle as warm, humid air is in contact with dry, cold air. This can lead to dramatic increases in the overall dehumidifying process for a building. 
     Operation of the System 
     As indicated above, in addition to providing the primary functions of providing cooling energy to coolers/freezers  1 , the system also enables de-humidification of a building atmosphere as well as building heating in the winter. 
     Defrost Cycle 
     As a result of the thermal mass of a water based defrost solution, complete defrosting of one side of a cooling rack can be accomplished within 1-2 minutes of the initiation of the defrost cycle. Furthermore, during the defrost cycle, a freezer/cooler having an ambient air temperature of 0 degrees F. (−20° C.) will see an ambient temperature rise of only 5-10° F. Accordingly, in most situations, at no time will the temperature of the circulating air rise above 32° F. wherein food would potentially thaw. 
     General Operation 
     System efficiencies achieved with the subject invention in comparison to efficiencies achieved with conventional heating and cooling systems for grocery stores are substantial. For example, energy efficiency ratios (EER) for traditional refrigerant/air systems would be in the order of 4-6%, that is 4-6 BTU of cooling would be obtained for each Watt of energy used to operate the system. In a conventional system waste heat is often rejected to 120° F. air which is a more difficult thermal bridge to cross compared to rejecting heat to a water system. 
     More specifically, the above EER is compared to an EER for the subject system in the range of 18% wherein heat is rejected from a hot gas at 60° F. to a liquid at 48° F. which is a more efficient thermal bridge. 
     Winter Operation 
     In winter, cooling for the coolers/freezers  1  is required and heat for the building is required. Accordingly, waste heat from the coolers/freezers  1  and from the system compressor  102  is directed to the heat storage  19  and heating system  20 . During winter operation, geothermal energy may or may not be required for heating. In a typical grocery store installation, the total cooling requirement may be 200,000 BTU and the heating requirement 400,000 BTU. Accordingly, the 200,000 BTU waste heat from the coolers may be directed to the building. In addition, the heat generated by the compressors  102  may also be directed to the building to make up the total 400,000 BTU heating requirement. In the event that the heating requirement is greater than the capacity of waste heat from the coolers  1  and the compressors  102 , the system will obtain additional energy from the geothermal system  18 . 
     In the event that the total heating requirements of the building are less than the total amount of heat available from the compressors  102  and coolers  1 , excess heat is delivered to the geothermal system  18  for dissipation to the ground. 
     Summer Operation 
     In summer, all excess heat from the freezers  1  and compressors  102  is waste heat and is discarded either through geothermal system  18  or to the external atmosphere. In the event that building cooling is also required, ground source cooling may also be effected utilizing a ground source heat pump. 
     The terms and expressions which have been employed in this specification are used as terms of description and not of limitations, and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claims.