Patent Publication Number: US-6668136-B2

Title: Integral heating and cooling unit

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an integral heating and cooling unit and, more particularly to a unit integrating electric heating elements and a cooling heat exchanger. 
     BACKGROUND OF THE INVENTION 
     Many applications in manufacturing and other fields require controlling the temperature of a fluid. For example, in the field of plastics, the temperature for the dies used for injection molds must be carefully controlled. A heat transfer or working fluid is used to bring the dies to an elevated temperature. Sometimes, the temperature must be rapidly reduced to properly facilitate the injection molding process. In this instance, the working fluid must be quickly cooled. To heat and cool the working fluid for the dies, a separate heater and cooling heat exchanger may be used to control the temperature of the working fluid. 
     The common approach in the prior art to create a system that both heats and cools a working fluid typically involves plumbing or connecting a heater to a cooler. FIG. 1 illustrates a system  10  that is capable of heating and cooling a working fluid. A heater unit  40  is plumbed or piped to a cooling unit  50  to achieve both heating and cooling of a working fluid  12  according to the prior art. The working fluid  12 , such as a heat transfer fluid or oil, enters the system  10  via a pipe  20 . The pipe  20  connects to the heating unit  40 , which includes a heating element  42 . The connection of the pipe  20  to the heating unit  40  involves a joint or weld  30  to assemble. The working fluid  12  passes through the heating unit  40  where heat from the heating element  42  elevates the temperature of the fluid  12 . 
     The working fluid  12  then leaves the heating unit  40  via a plumbing pipe  22 . The plumbing pipe  22  brings the heated working fluid  12  to a cooling unit  50 . One type of cooling unit  50  is a heat exchanger that uses a cooling fluid  52  to drop the temperature of the working fluid  12 . The plumbing of the heating unit  40  to the cooling unit  50  with the pipe  22  involves additional joints or welds  31 ,  32  to assemble. The cooling fluid  52 , such as water, enters the cooling unit  50  via a pipe  54 . The connection of the pipe  54  to the cooling unit  50  also involves a joint or weld  33  to assemble. 
     In the cooling unit  50 , heat from the working fluid  12  may transfer to the cooling fluid  52  depending on the heat transfer characteristics of the cooling unit  50  and the mass flow rates of the two fluids  12 ,  52 . The working fluid  12  then leaves the cooling unit  50  via pipe  24 , and the cooling fluid  52  leaves the heat exchanger through a pipe  56 . The connections of the pipes  24 ,  56  to the heat exchanger  50  also involves joints or welds  34 ,  35  to assemble. 
     The difficult assembly of all of the components and the space required for those components presents one problem in the prior art system  10  that both heats and cools. Plumbing the heater unit  40  to the cooling unit  50  affects the number of components and amount of piping required in assembling the system  10 . The increased number of components also multiplies the number of joints or welds  30 - 35  required, which in turn results in a greater potential for leaks to occur. Additional insulation of the system may be necessary with the increased amount of piping. Similarly, the increased number of components also adds to the cost for the system  10 . 
     The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     To that end, the present invention includes an integral heating and cooling unit for controlling the temperature of a working fluid. The heating and cooling unit has an outer housing, at least one electric heating element, and a cooling heat exchanger. The outer housing defines a plenum and has a working fluid inlet, a working fluid outlet, a cooling fluid inlet, and a cooling fluid outlet. The working fluid inlet and outlet are in fluid communication with the plenum. The electric heating element is attached to the outer housing and extends into the plenum to heat the working fluid. The cooling heat exchanger is attached to the outer housing and extends through the plenum to cool the working fluid. The cooling heat exchanger is capable of receiving a cooling fluid from the cooling fluid inlet and sending the cooling fluid to the cooling fluid outlet. 
     The outer housing may further include a first flange, a second flange, and a tubular shell. In this embodiment, the tubular shell slides over the flanges and is welded to the outer perimeter of the flanges. The cooling heat exchanger may have a variety of designs. In one design, the cooling heat exchanger includes a tube and a plurality of longitudinal fins. The tube is attached to the first and second flanges. In a second design, the cooling heat exchanger includes a tube that is at least partially corrugated. The tube (with corrugations) is attached to the first and second flanges. In yet a third design, the cooling heat exchanger includes a spiral tube having two ends. The ends of the spiral tube are attached to the first and second flanges. In a fourth design, the inlet and outlet of the cooling heat exchanger are attached to the same flange. The cooling heat exchanger is coiled and extends within the outer housing. 
     In another embodiment, the present invention includes an integral heating and cooling unit for controlling the temperature of a working fluid. However, in this embodiment, the heating and cooling unit has an inverse arrangement of the heating and cooling function. The heating and cooling unit has an outer housing, a heat exchanger, and at least one electric heating element. The outer housing defines a plenum and has a working fluid inlet, a working fluid outlet, a cooling fluid inlet, and a cooling fluid outlet. The cooling fluid inlet and the cooling fluid outlet are in fluid communication with the plenum. The heat exchanger is attached to the outer housing and extends through the plenum. The heat exchanger is capable of receiving the working fluid from the working fluid inlet and sending the working fluid to the working fluid outlet. The electric heating element extends within the heat exchanger and is capable of heating the working fluid. 
     Another embodiment of the present invention includes a system for heating and cooling a working fluid. The system includes a controller, a working fluid flow control means, and a heating and cooling unit. The working fluid flow control means is electrically connected to the controller to control the flow of the working fluid. The heating and cooling unit has an outer housing, at least one electric heating element, and a cooling heat exchanger. The outer housing defines a plenum to carry the working fluid. The electric heating element is mounted to the outer housing and electrically connected to the controller. The electric heating element extends into the plenum and is capable of heating the working fluid. The cooling heat exchanger is mounted to the outer housing and extends through the plenum. The cooling heat exchanger is capable of cooling the working fluid. 
     The system may further include a cooling fluid flow control means that is electrically connected to the controller to control the flow of a cooling fluid. The outer housing of the heating and cooling unit has a working fluid inlet, a working fluid outlet, a cooling fluid inlet, and a cooling fluid outlet. The cooling heat exchanger is capable of receiving the cooling fluid from the cooling fluid inlet and sending the cooling fluid to the cooling fluid outlet. The outer housing may further include a first flange, a second flange, and a tubular shell. The tubular shell is attached to the first and second flanges. The heat exchanger for the system may also have several designs including a tube with fins, a tube that is at least partially corrugated, and a tube that is at least partially spiral or coiled. 
     In another embodiment of the present invention, the system may have a heating and cooling unit with an inverse arrangement of the heating and cooling functions. For instance, the system has a controller, a working fluid flow control means, and a heating and cooling unit. However, the heating and cooling unit has an outer housing, a heat exchanger, and at least one electric heating element. The outer housing defines a plenum for carrying a cooling fluid. The heat exchanger carries the working fluid and extends through the plenum to cool the working fluid. The electric heating element is mounted within the heat exchanger and capable of heating the working fluid. 
     In yet another embodiment, the present invention includes a method for assembling a heating and cooling unit that is capable of controlling the temperature of a working fluid. The method includes the steps of: providing a first and second flange where the flanges have a plurality of holes; providing a heat exchanger tube; welding the heat exchanger tube to the first and second flanges; providing a plurality of heating elements; welding the plurality of heating elements to the first flange; providing a tubular shell; sliding the tubular shell over the outer perimeter of the first and second flanges; and welding the tubular shell to the first and second flanges. The heat exchanger tube may have several designs including a tube with fins, a tube that is at least partially corrugated, and a tube that is at least partially spiral. 
     The above summary of the present invention is not intended to represent each embodiment, or every aspect of the present invention. This is the purpose of the figures and detailed description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the followed detailed description and upon reference to the drawings. 
     The foregoing and other aspects of the present invention will be best understood with reference to a detailed description of specific embodiments of the invention, which follows, when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates a prior art system capable of heating and cooling a working fluid; 
     FIG. 2 illustrates a schematic cross-sectional view of a system having an integral heating and cooling unit according to the present invention; 
     FIG. 3 illustrates a side view of a preferred embodiment of an integral heating and cooling unit according to the present invention; 
     FIGS. 4A-4D illustrate perspective views of embodiments of heat exchangers that may be used for the integral heating and cooling unit; 
     FIG. 5 illustrates a perspective view of an embodiment of a tubular heating element that may be used for the integral heating and cooling unit; 
     FIG. 6 illustrates an end perspective view of the integral heating and cooling unit of FIG. 3; 
     FIG. 7 illustrates a schematic cross-sectional view of another embodiment of a integral heating and cooling unit according to the present invention; and 
     FIG. 8 illustrates a perspective view of a preferred embodiment of a system having an integral heating and cooling unit, a pump, a controller and fluid connections according to the present invention. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modification, equivalents and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrative embodiments will now be described with reference to the accompanying Figures. FIG. 2 illustrates a schematic cross-sectional view of a system  100  for heating and cooling a working fluid  112 . The system  100  operates as part of an overall process where the working fluid  112  must be both heated and cooled. As stated previously, one such process involves the heating and cooling of a heat transfer fluid for controlling the temperature of injection molding dies for plastics. The working fluid  112 , such as a heat transfer fluid or oil, flows through the system  100 , where it may be heated and cooled independently or in tandem. Once modified, the working fluid  112  travels out of the system  112  to a further portion of the process (not shown), such as heating the dies of an injection molding process. 
     In one embodiment, the system  100  includes an integral heating and cooling unit  200 , a controller  150 , flow control means  120 ,  140 , and sensors  160 ,  162 ,  164 . The integral heating and cooling unit  200  is used to heat and cool the working fluid  112 . The integral heating and cooling unit  200  combines the functions of a circulation heater and a heat exchanger. Accordingly, the integral heating and cooling unit  200  has an outer housing  210 , a heat exchanger  220 , and heating elements  250 . In one embodiment, the outer housing  210  defines a plenum  212  and includes a shell  214 , an inlet flange  230  and an outlet flange  240 . The heat exchanger  220  extends through the plenum  212 . The heating elements  250  are attached to the outer housing  210  and extend into the plenum  212 . 
     During operation of the system  100 , the working fluid  112  enters the system  100  from a source (not shown) via external piping. A working fluid flow control means  120  may be used to control the movement of the working fluid  112  through the system  100 . The working fluid flow control means  120  may include a pump, a valve, a motor or other means. The working fluid  112  then enters the integral heating and cooling unit  200  through a first inlet  232  in the inlet flange  230 . Once inside the integral heating and cooling unit  200 , the working fluid  112  circulates in the plenum  212  and contacts the heating elements  250 . In this way, the plenum  212  acts as a circulation heater where heat transfers from the heating elements  250  to the working fluid  112  depending on the fluid flow and the power to the heating elements  250 . 
     In the plenum  212 , the working fluid  112  also contacts the heat exchanger  220 . The working fluid  112  thus comes into heat transfer relation with both the heat exchanger  220  and the heating elements  250 . Depending on the flow of a cooling fluid  132  in the heat exchanger pipe  220 , the working fluid  112  expels heat through the heat exchanger  220  to the cooling fluid  132 . The modified working fluid  112  then leaves via a first outlet  242  in the outlet flange  240  and may then pass to further portions of the process (not shown). 
     In another aspect of the operation of the system  100 , the cooling fluid  132 , such as a heat transfer fluid or water, enters the system  100  via external piping. The cooling fluid  132  may come from a chiller or condenser (not shown). A cooling fluid flow control means  140  for controlling the movement of the cooling fluid  132  through the system  100  may also be provided. For example, the cooling fluid  132  may have existing head pressure and a solenoid valve may open to allow the cooling fluid  132  to enter the system  100 . Alternatively, a pump may be used to move the cooling fluid  132  through the system  100 . 
     The cooling fluid  132  enters the integral heating and cooling unit  200  through a second inlet  234  in the inlet flange  230 . The cooling fluid  132  passes through the heat exchanger  220  and comes into heat transfer relation with the working fluid  112  in the plenum  212 . The cooling fluid  132  then leaves via a second outlet  244  in the outlet side  240 . The modified cooling fluid  132  may then pass to a chiller of condenser (not shown) to expel heat to an external heat sink. 
     A controller  150  is electrically connected to the flow control means  120  and  140 , heating elements  150 , and a plurality of sensors  160 ,  162 , and  164 . Those of ordinary skill in the art will recognize that the controller may include relays, contactors and other circuitry to operate the system  100  and may be based on a microprocessor. The controller  150  actuates the flow control means  120 ,  140  to individually control the flow of the working fluid  112  and cooling fluid  132  within the system  100 . To control the flow of the working fluid  112  in the system  100 , the controller  150  actuates the flow control means  120  for moving the working fluid  112  through the system  100 . The working fluid  112  enters the integral heating and cooling unit  200  through the inlet  232  and passes into the plenum  212  between the heat exchanger  220  and the outer chamber  210 . 
     To generate heat within the plenum  212 , the heating elements  250  connect to a power supply from the controller  150 . The controller  150  supplies power to the heating elements  250  and regulates the heating of the working fluid  112  in the plenum  212 . In one embodiment, a temperature sensor  160  inserts into the inlet flange  230  to measure the temperature of the working fluid  112  in the plenum  212 . In the plenum  212 , the heat transfer relation of the working fluid  112  with the heating elements  250  defines a heating function for the integral heating and cooling unit  200 . 
     The modified working fluid  112  exits through the outlet  242 . The controller  150  may also connect to a sensor  162  located on the outlet of the heating and cooling unit  200 , which monitors the flow rate, pressure and/or temperature of the working fluid  112  as it leaves the system  100  and travels further in the process. 
     To control the flow of cooling fluid  132 , the controller  150  actuates the cooling fluid flow control means  140  for moving the cooling fluid  132  through the heat exchanger  220  in the integral heating and cooling unit  200 . The cooling fluid  132  enters the integral heating and cooling unit  200  through the inlet  234  and passes through the heat exchanger  220 . With cooling fluid  132  passing through the heat exchanger, the heat transfer relation of the cooling fluid  132  with the working fluid  112  in the plenum  212  defines a cooling function of the integral heating and cooling unit  200 . The modified cooling fluid  132  exits through the outlet  244 . The controller  150  may connect to a sensor  164  located on the outlet of the heating and cooling unit  200 , which monitors the flow rate, pressure and/or temperature of the cooling fluid  112  and maintains certain mass flow rates. 
     The integral heating and cooling unit  200  juxtaposes the operation of the heating function with that of the cooling function. The heating and cooling functions may operate independently or in tandem. First, the heating function may be operated alone. For example, one or more of the heating elements  250  may be supplied power to heat the working fluid  112  in the plenum  212 . The controller  150  monitors the temperature of the fluid  112  with the sensor  160 . The controller  150  further controls the flow of the working fluid by monitoring the fluid  112  with sensor  162  and actuating the flow control means  120 . The controller  150  may not pass the cooling fluid  132  through the heat exchanger  220 . In this instance, the integral heating and cooling unit  200  acts as a circulation heater to elevate the temperature of the working fluid  112 . 
     Alternatively, the cooling function may operate alone. The heating elements  250  may be turned off by the controller  150  and the cooling fluid  132  passed through the heat exchanger  220 . The cooling fluid  132  extracts heat from the working fluid  112  in the plenum  212 . In this instance, the integral heating and cooling unit  200  acts strictly as a heat exchanger between the two fluids  112 ,  132 . 
     Still further, the integral heating and cooling unit  200  juxtaposes the operation of the heating function with the cooling function by operating the heating and cooling functions in tandem. More specifically, the cooling function works in conjunction with the heating function to control the temperature of the working fluid  112 . For example, the heating elements  250  may continuously heat the working fluid  112  flowing in the plenum  212 . The cooling fluid  132  may simultaneously pass through the heat exchanger  220  to extract heat from the working fluid  112 . 
     The controller  150  monitors the temperatures and mass flow rates of the fluids and actuates the flow control means  120 ,  140  for moving the fluids  112 ,  132 . By monitoring and controlling the fluids in tandem, the controller  150  ensures that the temperature and mass flow rate of the working fluid  112  meet the requirements of the process as it leaves the system  100 . In this instance, the integral heating and cooling unit  200  acts as a circulation heater with a concomitant heat exchanger to control or modulate the temperature of the working fluid  112 . 
     The integral heating and cooling unit  200  of the present invention may have many different configurations based on the specific applications to which it is intended. For example, it is understood that the number and design of electric heating elements may vary to achieve specific temperature levels or to allow for specific mass flow rates of the working fluid  112  within the plenum  212 . Likewise, the heat exchanger  220  may consist of many tubes or a spiraling tube in addition to other embodiments in order to increase the surface area and the heat transfer capability of the heat exchanger  220 . The heat exchanger  220  may involve cross-flow or counter-flow, besides the parallel-flow described herein. Moreover, the heat exchanger  220  may be integrally formed outside of the outer housing  210  in an inverse configuration, or the physical location of the heat exchanger  220  to the heating elements  250  may also vary. 
     Referring specifically to the integral heating and cooling unit of the present invention, FIG. 3 illustrates a preferred embodiment of an integral heating and cooling unit  300  with a shell  314  partially cutaway. The integral heating and cooling unit  300  defines a combination heater, heat exchanger and circulation heater all in a seamless vessel or outer housing  310  defining a plenum  312  therein. 
     The shell  314  in the present embodiment is a hollow cylindrical tube. Two flanges  330 ,  340  weld to the open ends of the shell  314  to complete the assembly. A heat exchanger pipe  320  having an axial bore (not visible) therethrough situates longitudinally within the shell  314 . The pipe  320  may include a plain exterior surface or may further include a plurality of heat exchange fins  322 . 
     The heat exchange pipe  320  connects to the first or inlet flange  330  at one end and connects to the second or outlet flange  340  at the other end of the pipe  320 . The inlet and outlet flanges  330 ,  340  may be of any number of shapes, including round, oval, square or rectangular depending on the shape of the shell  314  and the required application. 
     Referring to FIGS. 3 and 6, the inlet flange  330  includes a working fluid inlet  332  towards the perimeter of the flange  330 . Likewise, the outlet flange  340  includes a working fluid outlet  342  towards the perimeter of the flange  340  and away from the heat exchange pipe  320 . The working fluid inlet  332  and the working fluid outlet  342  communicate directly with the plenum  312  within the shell  314 . The outlet flange  340  may further include a drain outlet communicating with the plenum  312 , which is used to clear the plenum  312  of working fluid when not in use. 
     The inlet flange  330  further includes a cooling fluid inlet  334 , which aligns with the axial bore of the heat exchange pipe  320 . The outlet flange  340  also includes a cooling fluid outlet  344  (not visible), which also aligns with the axial bore of the heat exchange pipe  320 . The cooling fluid inlet  334  and the cooling fluid outlet  344  communicate directly with the heat exchange pipe  320 . 
     The plenum  312  (within outer housing  310 ) further contains a plurality of heating elements  350  situated therein. In one embodiment, the heating elements  350  connect to one of the flanges (here, the inlet flange  330 ) by a plurality of holes  336   a-f  therein and situate around the pipe  320  within the plenum  312 . In particular, each of the heating elements  350  includes a first termination  354   a-f  and a second termination  356   a-f  attached to one of the holes  336   a-f . The terminations  354   a-f ,  356   a-f  project outside the heating and cooling unit  300  for connection to a power source (not shown). Also in the inlet flange  330 , a plurality of holes  338  may be provided for the addition of temperature sensors and fluid probes (not shown). 
     To provide representative dimensions and values related to the preferred embodiment, the integral heating and cooling unit  300  may have a length of approximately 30 inches and a diameter of approximately 8 inches. The heating elements  350  may provide an example heating capacity of 24 kW each, while the cooling capacity of the heat exchanger  220  may be approximately 42 kW. The mass flow rate for fluids passing through the integral heating and cooling unit  300  may approach 20 gallons per minute or more. 
     The present invention offers a number of advantages over conventional techniques of plumbing or piping a cooling unit to a heating unit. More than simply interconnecting a heater with a heat exchanger, the integral heating and cooling unit  300  contains an electric heater and heat exchanger all inside a single unit. As such, the integral heating and cooling unit  300  provides more efficient heating and cooling capacities by juxtaposing the heating and cooling functions. The close proximity of the heating and cooling functions minimizes heating and cooling loses when the functions operate separately or in tandem. Furthermore, the heat exchanger  320  locates adjacent to the maximum amount of working fluid, thus providing maximum cooling. 
     Another advantage of the integral heating and cooling unit  300  is the conservation of space. The integral heating and cooling unit  300  defines a single unit that holds a heat exchanger inside a circulation heater. The design of the integral heating and cooling unit  300  eliminates the need for plumbing a heater to a cooler. Having both the heater and the heat exchanger incorporated together in the integral heating and cooling unit  300  eliminates the piping to join them. The elimination of additional piping greatly reduces the potential for leaks to occur. The design reduces the number of parts and is lighter than requiring two separate assemblies. The entire heating and cooling unit  300  defines one seamless unit and is designed to be a disposable item should replacement be required. 
     Due to the simplified construction, the cost for assembly is comparable to a replacement immersion heater. For a brief example of the assembly, the flanges  330 ,  340  are predrilled with access holes for future connections of tubing and heating elements. The flanges  330 ,  340  weld to each end of the heat exchanger pipe  220 . The heating elements  350  are attached to holes  336   a-f  of the flange  330  and welded into place. Alternatively, the heating elements  350  may be screw plug type heaters and threaded into holes in the flange  330 . The shell  314  slides over the assembly, and the flanges  330 ,  340  weld thereto. In one embodiment, the shell  314  is a seamless tube to reduce the chances of leaks. 
     The welding of the flanges  330 ,  340  to the shell  314  seals the plenum  312 . The inlet tubing (not shown) welds to the inlets  332 ,  34  on the inlet flange  330 , and the outlet tubing (not shown) welds to the outlets  342 ,  344  on the outlet flange  340 . All the welds to the inlets  332 ,  334  and outlets  342 ,  344  are located on the flat surfaces of the flanges  330 ,  340 , which simplifies the mating of the parts. The inlets  332 ,  334  and outlets  342 ,  344  in flat surfaces of the flanges  330 ,  340  also minimizes the number of joints and total parts for the present invention. 
     Referring specifically to the heat exchanger  320  of the present embodiment, FIG. 4A illustrates an embodiment of a heat exchanger  320   a  with attached flanges  330 ,  340 . In an effort to reduce difficulties in assembly, the cooling function uses only one part, i.e., the heat exchanger pipe  320   a . Each end of the pipe  320   a  welds to a flange  330 ,  340 . The heat exchanger pipe  320   a  defines a tube having a plurality of longitudinal fins  322  running along the exterior surface of the pipe  320   a . The longitudinal fins  322  increase the surface area of the heat exchanger pipe  320   a  and improve its heat transfer capability. 
     As seen in FIG. 4A, the rigid heat exchanger pipe  320   a  with longitudinal fins  322  could present a problem with thermal expansion and contraction depending on the specific application. Under certain conditions, the expansion and contraction of the heat exchanger pipe  320   a  could compromise the integrity of the integral heating and cooling unit  300 . Specifically, leaks could develop in the welds between the pipe  320   a  and the flanges  330 ,  340  or between the flanges  330 ,  340  and the shell  314 . Accordingly, referring to FIG. 4B, another embodiment of a heat exchanger pipe  320   b  uses corrugated, flexible tubes. The corrugations  328  along the pipe  320   b  allow for thermal expansion and contraction of the pipe  320   b  due to changes in temperature. The corrugations  328  also give additional surface area to the pipe  320   b  for heat transfer. 
     Referring to FIG. 4C, yet another embodiment of a heat exchanger pipe  320   c  defines a spiraling tube having a thin metal wall. Each end of the pipe  320   c  welds to flanges  330 ,  340 . The spiraling tube  320   c  greatly increases the surface area of the pipe  320   c  and improves its heat transfer capability. To provide representative values, the tube  320   c  may span a length of approximately 30 inches and spiral in 40-50 revolutions. The tube  320   c  creates a helix with an outside diameter between 2-3 inches. The surface area for the pipe  320   c  could be approximately 3-4 square feet, which greatly increases the heat transfer capability. 
     Referring to FIG. 4D, another embodiment of a heat exchanger pipe  320   d  is defined by a coiled or wrapped tube having a thin metal wall. Unlike the embodiment in FIG. 4C, in this embodiment each end of the pipe  320   d  is welded or otherwise attached to only one flange  330  or  340 . The coiled or wrapped tubing greatly increases the surface area of the pipe  320   d  and improves its heat transfer capability. Moreover, the coiled design permits some decrease of thermal expansion within the plenum. 
     Referring specifically to the heating elements  350  of the present embodiment, FIG. 5 illustrates a perspective view of an embodiment of a heating element  350 . The heating element  350  defines a tubular electric element  352  in which a current passing through generates heat. The tubular element  352  has a first termination  354  and a second termination  356 . From the first termination  354 , the tubular element  352  extends in a longitudinal portion  358 . A bend or fold-back  359  returns the tubular element  352  in another parallel, longitudinal portion  358 . A further plurality of bends  359  and parallel, longitudinal portions  358  wind the tube  352  to the second termination  356 . The winding tubular element  352  forms an elongated, compact heating coil, which is ideal for placement in the plenum  312  of the heating and cooling unit  300  of FIG.  3 . 
     The winding bends  359  and parallel, longitudinal portions  358  of the heating element  350  increases the surface area to provide heating. The winding heating element  350  further reduces the number of heaters required for the heating and cooling unit  300 . Thus, the number of terminations and buss bars is reduced on the heating and cooling unit  300  and the wiring scheme is simplified. 
     Referring to FIG. 6, an end view of the heating and cooling unit  300  of FIG. 3 reveals a preferred arrangement for the access holes and the tubular heating elements. The inlet flange  330  is predrilled with access holes  332 ,  334  for future fluid connections. The working fluid inlet  332  lies towards the perimeter of the flange  330  and communicates with the plenum  312  in which the heating elements  350  situate. The cooling fluid inlet  334  lies towards the center of the flange  330  and communicates with the heat exchanger pipe  320  passing through the plenum  312 . 
     The outlet flange  340 , positioned at the other end of the pipe  320 , also has predrilled access holes for future fluid connections. The outlet flange  340  includes the working fluid outlet  342  lying towards the perimeter of the flange  340  and includes the cooling fluid outlet (not visible) situated towards the center of the flange  340 . 
     The integral heating and cooling unit  300  assumes a particular horizontal arrangement. Most notably in the present view, the working fluid outlet  342  always positions towards the top of the horizontal arrangement. In this position the working fluid outlet  342  provides the integral heating and cooling unit  300  with an automatic vent or purge feature. When the plenum  312  is first filled with working fluid, the position of the working fluid outlet  342  towards the top of the outlet flange eliminates the necessity to bleed the plenum  312  of air. The design eliminates the need to include additional ports for bleeding air from the plenum  312 . 
     The end view of the heating and cooling unit  300  in FIG. 6 further reveals a preferred arrangement for the heating elements  350 . The inlet flange  330  includes a plurality of holes  336   a-f  for attachment of the heating elements  350 . Also, a plurality of holes  338  provides for the insertion of temperature probes or sensors (not shown) into the plenum  312 . The heating elements  350  weld into the plurality of holes  336   a-f  in a special pattern. Primarily, the pattern allows access for the fluid connections  332 ,  334  in the inlet flange  330  and also provides room for the probes in the access holes  338 . 
     The present embodiment includes six heating elements  350  welded to the access holes  336   a-f  in the inlet flange  330 . Each heating element  350   a-f  has two terminations  354   a-f ,  356   a-f  that install in the access holes  336   a-f . The heating elements  350  mount to the flange  330  in a manner to maximize their coverage in the plenum  312 : however; the heating elements  350  are not symmetrically spaced around a 360-degree circle. The spacing is limited to less than 360° to allow room for the fluid connections  332 ,  334 , the sensor holes  338  and the heat exchange pipe  320 . Also, each heating element  350 , as it is spaced around the flange  330 , is further provided with a slight degree of tilt with respect to the perimeter of the flange  330 . This preferred arrangement of the heating elements  350   a-f  enhances the fluid velocity within the plenum  312  and improves the heat transfer from the heating elements  350   a-f  to the working fluid in the plenum  312 . It is also understood that the heater elements may be screw plug type elements. In such a case, the base of the screw plug is threaded into holes of the flange  330 . 
     FIG. 7 illustrates another embodiment of an integral heating and cooling unit  400  according to the present invention. The integral heating and cooling unit  400  is shown in schematic cross-section and represents an inverse arrangement of the heating and cooling functions. An outer housing  410  in the present embodiment defines a hollow plenum  412 . In this embodiment, the outer housing  410  includes a shell  414  and flanges  430  and  440 . Two flanges  430 ,  440  weld to the open ends of the shell  414  to close the plenum  412 . A heat exchanger pipe  420  having an axial bore  424  therethrough situates longitudinally through the plenum  412 . The heat exchanger pipe  420  may include a plain exterior surface or may further include a plurality of fins  422 . Alternative, the heat exchanger pipe  420  may have corrugations, spirals, or be coiled. 
     The inlet flange  430  includes a first fluid inlet  432  towards the center of the flange  430 . Likewise, the outlet flange  440  includes a first fluid outlet  442  towards the center of the flange  440 . The first fluid inlet  432  and the first fluid outlet  442  communicate directly with the axial bore  424  of the heat exchange pipe  420 . The inlet flange  430  further includes a cooling fluid inlet  434 , which communicates with the plenum  412 . The outlet flange  440  also includes a cooling fluid outlet  444 , which also communicates with the plenum  412  of the shell  410 . 
     The axial bore  424  of the heat exchange pipe further contains a spiraling heating elements  450  situated therein. The heating element  450  connects to the inlet flange  430  so that the terminals  454 ,  456  may connect with a power supply (not shown) outside the heating and cooling unit  400 . As before, the heating and cooling functions are juxtaposed in the present embodiment. 
     To achieve the heating function, a working fluid  412  enters the heating and cooling unit  400  from a source (not shown) through a first inlet  432  in the inlet flange  430 . Once inside the integral heating and cooling unit  400 , the working fluid  412  travels through the axial bore  424  of the heat exchange pipe  420 . In the bore, the working fluid  412  comes into heat transfer relation with both the plenum  412  and the heating element  450 . The working fluid  412  then leaves via a first outlet  442  in the outlet flange  440 . The modified working fluid  412  may then pass to further portions of a process (not shown). 
     To achieve the cooling function and to further control the temperature of the working fluid, a cooling fluid  432 , such as a heat transfer fluid or water, enters the heating and cooling unit  400  through the second inlet  434  in the inlet flange  430 . The cooling fluid  432  passes through the plenum  412  and comes into heat transfer relation with the heat exchange pipe  420 . The cooling fluid  432  then leaves via a second outlet  444  in the outlet flange  440 . The modified cooling fluid  432  may then pass to a chiller of condenser (not shown) to expel heat to an external heat sink. 
     FIG. 8 illustrates a further embodiment of a system  500  having an integral heating and cooling unit  510 , a working fluid pump  520 , a controller  530  and fluid connections  540 ,  550  according to the present invention. The system  500  includes a cabinet  502 , shown partially cut away. Within the cabinet  502 , the integral heating and cooling unit  510  mounts horizontally on brackets  512 ,  514 . The fluid connections  540 ,  550  project from the rear of the cabinet  502 . 
     A first fluid pipe  542  connects to a supply of working fluid (not shown). The working fluid enters the system and may pass into an expansion and contraction tank  544  that allows for thermal expansion and contraction or collection of the fluid. The pump  520 , actuated by the controller  530 , moves the working fluid to the integral heating and cooling unit  510 . The controller  530  connects to a power supply (not shown) and supplies the heating elements (not visible) within the heating and cooling unit with power. A cooling fluid pipe  552  connects to a supply of cooling fluid (not shown). The cooling fluid enters the system  500  and is plumbed to the integral heating and cooling unit  510 . To control the flow of cooling fluid within the heating and cooling unit  510 , the controller  530  may actuate a pump or valve (not shown). 
     Inside the integral heating and cooling unit  500 , the temperature of the working fluid is modified. The fluid exits the heating and cooling unit  510  through the fluid pipe  546  and proceeds to further portions of a process (not shown). The cooling fluid exits the system  500  through the fluid pipe  554  and may proceed to a chiller or condenser (not shown). 
     While the invention has been described with reference to the preferred embodiments, obvious modifications and alterations are possible by those skilled in the related art. Therefore, it is intended that the invention include all such modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.