Abstract:
A control system for controlling delivery of either heated or cooled water over a common water line to a plurality of heat exchangers. The control system includes a hydronic system controller which polls the heating or cooling demands of zone controllers controlling the respective delivery of water to the individual heat exchangers. The hydronic system controller is operative to implement a changeover between delivery of heated water to delivery cooled water or vice versa. The implemented changeover preferably includes checking the temperature of the water being returned to the source or sources for heating or cooling the water as well as defining a changeover time period which must occur in the event that the temperature of the water in the return line is not within a predefined range.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to systems for adding or removing heat from a confined space in order to control the temperature in that space. In particular, this invention relates to hydronic systems which employ water as the heat exchange medium for adding or removing heat from a confined space. 
   Hydronic systems may employ different approaches as to how to deliver water to spaces that are to be heated or cooled. For instance, hydronic systems may use a first conduit to deliver heated water and a second conduit to deliver cooled water to one or more heat exchangers servicing the spaces to be heated or cooled. These systems will also use separate return conduits to circulate the water back to the heating and cooling sources which heat or cool the water before it is again delivered to the one or more heat exchangers. The above described hydronic systems are often referred to as “four pipe” hydronic systems because there are two delivery conduits or pipes which deliver the water to the one or more heat exchangers and two return conduits or pipes which circulate water back to the heating and cooling sources. 
   Another type of hydronic system uses a single conduit to deliver either heated or cooled water from the heating or cooling sources to the one or more heat exchangers in the spaces to be heated or cooled. This type of hydronic system will also use a single return conduit to circulate the water from the one or more heat exchangers back to the heating and cooling sources. This latter type of hydronic system is typically referred to as a “two-pipe” system because the one or more heat exchangers have one common supply conduit or pipe and one common return conduit or pipe. 
   The above-described two-pipe hydronic system provides a flow of water to the various heat exchangers at an appreciably lower cost in terms of piping versus the “four-pipe” hydronic system. However the two pipe system cannot easily change from circulating heated water to circulating cooled water to the heat exchangers. In this regard, the cooling source which could be a chiller does not perform well when it is receiving substantially warm water in the return line as a result of the two pipe system having previously been in a heating mode. The same is true for a boiler that is receiving substantially cooler water than it normally is deigned to operate with. 
   The inability to changeover or switch the two-pipe hydronic system between heating and cooling or vice versa has previously led to switching the system to either heating or cooling, depending on the season of the year. For instance, changeovers would be implemented on particular calendar dates indicating normal change of seasonal weather conditions. On the other hand, a changeover might be implemented depending on a separately sensed outdoor air temperature indicating whether the two-pipe hydronic system should be in either heating or cooling for the day. The above described changeover controls do not allow a hydronic system to respond to heating or cooling demands that may change throughout the day. The above described systems moreover do not respond to different demands for cooling or heating throughout a building on a given day. 
   OBJECTS OF THE INVENTION 
   It is an object of this invention to provide a two-pipe hydronic system with the capability to automatically change from one operating mode to another operating mode at any time regardless of outdoor air temperature or calendar date. 
   It is another object of this invention to provide a two-pipe hydronic system that will be responsive to different demands for cooling or heating throughout a building on a given day. 
   SUMMARY OF THE INVENTION 
   The above and other objects are achieved by providing a two-pipe hydronic system with control logic, which continually polls the spaces or zones in which heating or cooling may be demanded so as to determine whether there is a predominance of either heating or cooling being demanded. The polling also checks to see whether a determined predominance of demand for either heating or cooling meets certain minimum demand requirements. In the event that minimum demand requirements are met, then a system demand is set reflecting the polling results. For instance, the system demand would be set for heated water if the predominance of polled spaces reflected that more spaces requested heating than requested cooling and that the number of spaces requesting heating exceeded some minimum number of spaces required to implement a changeover from cooling to heating. The system demand does not, however, allow for an immediate changeover to heating in the event that a changeover to heating is being requested by the polling results. In particular, the system will first check to see whether the current mode of operation has run for a minimum time period before stopping the then active heating or cooling equipment. When the minimum time period has expired and the particular active equipment has been stopped, the control will preferably inquire as to whether a particular water temperature in the return line is within a range of temperatures. The system may also inquire as to whether a particular period of time has elapsed since the previously activated equipment was turned off. It is only after the return water temperature is within range or the period of time since turning off the previously activated equipment has elapsed, if the latter is required, that the control logic will proceed to actually authorize the start up of the particular heating or cooling equipment pursuant to the request of the polling results. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a schematic view of a two-pipe hydronic system having both a chiller and a boiler for delivering cooled or heated water to heat exchangers and a system controller and a series of zone controllers associated therewith; 
       FIG. 2  is a flow chart of the method used by the system controller within  FIG. 1  so as to control the activation or deactivation of the chiller or the boiler of  FIG. 1 ; and 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , a two-pipe hydronic system is seen to include a chiller  10  and a boiler  12 . Hot water from the boiler  12  may flow through a two-position changeover valve  14  to fan coil heat exchanger  18 ,  20  and  22 . Alternatively, the chiller  10  may provide chilled water to the fan coil heat exchangers  18 ,  20  and  22  via the two position valve  14 . It is to be understood that each fan coil heat exchanger may use the delivered water to condition air in a space that is to be heated or cooled. This is often referred to as a “zone of heating or cooling”. Water from either the chiller  10  or the boiler  12  flows through the fan coil heat exchanger  18  in the event that a zone controller  24  authorizes such a flow by positioning of a control valve  26 . The zone controller  24  may also divert any water flow around the fan coil heat exchanger  18  by a further positioning of the control valve  26 . It is to be appreciated that the fan coil heat exchanger  20  operates in a similar fashion in response to the positioning of a control valve  28  under the control of a zone controller  30 . It is furthermore to be appreciated that the last fan coil heat exchanger  22  in the hydronic system will also be controlled by the positioning of a control valve  32  under the control of a zone controller  34 . Water flow to each heat exchanger within each corresponding fan coil can either fully bypass the heat exchanger, fully flow through the heat exchanger, or partially flow through the heat exchanger and bypass. The control valve position is determined by the zone controller and is a function of the zone&#39;s heating or cooling requirement and the operating mode of the water loop. Each zone controller  24 ,  30  and  34  is also connected to a corresponding temperature sensor such as  38 ,  40  and  42 , which senses the temperature in the respective zone serviced by the fan coil heat exchanger and provides such temperature information to the respective zone controller. Each zone controller will furthermore have a stored setpoint value for the particular zone. This may be a temperature that is arbitrarily defined by an individual either through a programmable thermostat or other device suitable for entering setpoint information. Each zone controller will either have a demand for heat or a demand for cooling or essentially a demand for neither heating or cooling depending on the sensed temperature in the zone versus the zone&#39;s stored setpoint. 
   Each individual zone demand is provided to a system controller  44  via a bus  46 . The system controller  44  controls pumps  48  and  50  so as to thereby pump return water from the heat exchangers  18 ,  20  and  22  into a respective boiler  12  or chiller  10 . It is to be appreciated that only one of the two pumps  48  or  50  will be activated at any time by the system controller  44  so as to thereby protect the boiler or chiller from unnecessary exposure to return water not having the proper temperature range for the operation of the respective equipment. In order to assure that the proper temperature range is present in the return line, a temperature sensor  52  senses the return water temperature and provides the same to the system controller  44 . 
   Referring now to  FIGS. 2A ,  2 B, and  2 C, a process utilized by a programmable microprocessor within the system controller  44  is illustrated. The process begins with an initialization step  100 , which sets the initial values of the following variables: “changeover timer”, “heat run timer”, “cool run timer”, “system demand” and “system mode”. The microprocessor within the system controller  44  will proceed to a step  102  and poll each of the zone controllers for their respective zone demands for heating or cooling. It is to be appreciated that this is preferably done by addressing each zone controller  24 ,  30  and  34  via the bus  46  and requesting the specific zone demand of the zone controller. The zone demand will of course be a function of the difference between setpoint and sensed temperature in the respective zone. The zone demands are stored in a memory associated with the microprocessor within the system controller  44  in a step  104 . The microprocessor proceeds to a step  106  and computes the percentage of the polled zone controllers that have heating demands. This is preferably done by first adding up the number of zone controllers having a heating demand and dividing this number by the total number of zone controllers present within the hydronic system. The results are stored as “percent heating requirement”. The microprocessor within the system controller proceeds to a step  108  and computes the percentage of zone controllers having cooling demands in a similar fashion. In other words, the microprocessor first adds up the number of zone controllers having cooling demands and divides this number by the total number of zone controllers in the hydronic system and stores the result as “percent cooling requirement”. 
   The microprocessor proceeds to a step  110  and inquires whether the percent heating requirement computed in step  106  is greater than the percent cooling requirement computed in step  108 . The microprocessor within the system controller  44  will proceed to step  112  in the event that the percent heating requirement exceeds the percent cooling requirement. Referring to step  112 , the processor will inquire as to whether the percent heating requirement computed in step  106  is greater than a “minimum heat demand”. The minimum heat demand is preferably a stored percentage value in the memory associated with the microprocessor. This percentage value should be slightly less than the percentage of zone controllers that must be demanding heat in the system of  FIG. 1  in order for the system to change over to providing heated water. When this percentage is exceeded, the microprocessor within the system controller will proceed in a step  114  to set “system demand” equal to heat. 
   Referring again to step  110 , in the event that the percent heating requirement does not exceed the percent cooling requirement, the processor proceeds to a step  116  and inquires as to whether percent cooling requirement is greater than percent heating requirement. In the event that the answer is yes, the processor will proceed to a step  118  and inquire as to whether the percent cooling requirement is greater than a minimum cooling demand for the hydronic system of  FIG. 1 . This minimum cooling demand will be slightly less than the percentage of zone controllers that must be demanding cooling in order to have the processor proceed in a step  120  to set system demand equal to cool. 
   Referring again to step  116 , in the event that the percent cooling requirement is not greater than the percent heating requirement, then the processor will proceed to a step  122  and determine if both the percent cooling and the percent heating equal zero. If both are equal and zero, the processor will proceed to set the “system demand” equal to none in a step  124 . In the event that both demands are not equal to zero in step  122 , then the processor will proceed directly to a step  128 . 
   Referring to step  128 , it is to be appreciated that the processor will have proceeded from either step  114 , step  120  or step  124  to this step with a particular setting of system demand. The processor will also have proceeded to this step from step  122  without changing the present system demand established previously. For instance, if the “system demand” is “none” as a result of its initial setting in step  100 , then it will continue to be so after exiting step  122  along the “no” path. If on the other hand, the “system demand” were previously set in a prior execution of the logic, then that would be the system demand setting after exiting step  122  along the “no path”. 
   It is noted that the processor inquires as to whether the system demand equals none in step  128 . Assuming the system demand is heat as a result of step  114 , the processor will proceed along the no path out of step  128  to a step  130  and inquire as to whether the value of system demand equals the value of “system mode”. Since the processor will be operating immediately after initialization, the system mode value will be none prompting the processor to proceed along the no path to a step  132 . 
   Referring to step  132 , the processor will inquire whether the value of system mode is equal to none. Since system mode will be equal to none initially, the processor will proceed along the yes path to a step  134  and read the water temperature from sensor  52  in the return line of the hydronic system. The processor proceeds in a step  136  to inquire as to whether the water temperature read in step  134  is greater than ten degrees Centigrade and less than thirty-two degrees Centigrade. Since the hydronic system is not recovering from any previous heating or cooling mode of operation, the water temperature in the return line should be within this range of temperatures. This will prompt the processor to proceed along the yes path to a step  138  wherein inquiry is made as to whether system demand is equal to cool. Since the system demand was set equal to heat in step  114 , the processor will proceed out of step  138  along the no path to a step  140  and set the two way valve  14  to heating. The processor will activate pump  48  and deactivate pump  50  in a step  142  before proceeding to step  144  wherein the boiler  12  is activated. 
   The processor proceeds to set “system mode” equal to heat in a step  146 . The processor will proceed from step  146  to a step  147  and send the system mode setting of “heat’ to the zone controllers  24 ,  30 , and  34 . Each zone controller will use the communicated setting to determine how to position its control valve. In this regard, if the local demand is for heating, then the control valve will be positioned by the zone controller so as to deliver hot water from the boiler to the fan coil heat exchanger. If the local demand is however for cooling, then the hot water from the boiler will bypass the fan coil heat exchanger. It is to be appreciated that the above assumes that the local zone controller is not able to independently determine whether the water being delivered is hot or cold. In the event that the zone controllers possess the capability of independently determining the temperature of the water being delivered, then they will implement the positioning of their respective control valves without the need to receive the system mode setting from the system controller  44 . 
   The processor will proceed from step  147  to a step  148  wherein a predefined time delay will be implemented before returning to step  102 . It is to be appreciated that the amount of time delay will be an arbitrary timed amount for a given hydronic system so as to delay the system controller before it again polls the zone controllers in step  102 . 
   Referring again to steps  102 - 124 , the processor within the system controller will poll the zone controllers and thereafter compute the percentages of zone controllers having heat demands and the percentage of zone controllers having cooling demands before again determining whether or not the percentage heating requirement is greater than the percentage cooling requirement in a step  110 . Assuming that the zone controllers continue to have essentially the same demands, then the percent heating requirement will continue to exceed the percent cooling requirement so as to thereby prompt the processor to proceed from step  110  to step  112  and again inquire as to whether the minimum heat demand has been exceeded before again setting the system demand equal to heat in step  114 . The processor will proceed to step  128  and again inquire as to whether the system demand is equal to none. Since the system demand will be equal to heat, the processor will proceed to step  130  and inquire as to whether system demand equals system mode. Since system mode will now be equal to heat, the processor will proceed along the yes path to a step  150  and inquire as to whether system mode equals heat. Since system mode will be equal to heat, the processor will proceed to a step  152  and increment a “heat run timer”. The heat run timer will be incremented for the first time since the heat run timer was initially set equal to zero. It is to be appreciated that the amount by which the heat timer will be incremented will preferably be the same as the amount of delay set forth in step  146  between successive executions of the control logic. The processor will proceed from step  152  to step  148  wherein the delay will be again implemented before returning to step  102 . 
   It is to be appreciated that the processor within the system controller will continue to execute the control logic in the manner that has been previously discussed until there has been a change in the demands of the zone controllers so as to cause a change in the percentage heating requirement and percentage cooling requirements as computed in steps  106  and  108 . Assuming that the results produce a higher cooling requirement than heating requirement, then the processor will proceed out of step  110  to step  116  and hence to step  118  since the percentage cooling requirement will now exceed the percentage heating requirement. This will prompt the processor to inquire as to whether the percentage cooling requirement is greater than the minimum cooling demand required in step  118 . Assuming that the minimum cooling demand percentage has been met, the processor will proceed to set system demand equal to cool in step  120 . It is hence to be appreciated that the polling logic of steps  102  through  124  will have recognized a change in the zone controller demands sufficient to prompt the change of system demand from heat to cool. 
   The processor proceeds from step  120  to a step  128  and inquires as to whether system demand equals none. Since system demand will now be equal to cool, the processor will proceed along the no path to step  130  and inquire as to whether system demand still equals the value of system mode. Since system demand will have changed from heat to cool, the processor will proceed along the no path to step  132  and inquire as to whether system mode equals none. Since system mode will still be equal to heat, the processor will proceed along the no path to a step  154  and inquire as to whether system mode equals heat. Since system mode will still be equal to heat, the processor will proceed to a step  156  and inquire as to whether heat run timer is greater than minimum heat run. It will be remembered that the heat run timer will have been successively incremented in step  152  each time the processor within the system controller executes the control logic of  FIG. 2 . Assuming that the hydronic system has been in a heating mode of operation for a considerable period of time, the heat run timer will normally exceed any minimum amount of time established for a heat run of the hydronic system of  FIG. 1 . It is to be appreciated that this particular time value for minimum heat run will be stored in memory for use by the processor within the system controller. Assuming that the heat run timer has exceeded this minimum heat run value, the processor will proceed to a step  158  and stop the operation of the boiler  12 . It is to be appreciated that this may be a signal from the system controller to the burner control within the boiler  12 . 
   The processor will proceed from step  158  to a step  160  and set the changeover timer. The change over timer will be set equal to a predetermined changeover time period, “T” that the hydronic system of  FIG. 1  must experience before it can be switched from heating to cooling or vice versa. This changeover time period will have been stored in memory associated with the processor. The processor will proceed in a step  162  to set system mode equal to none and both heat run timer and cool run timer equal to zero. The processor will then proceed to step  148  and again implement the prescribed amount of delay before the next execution of the control logic. 
   At such time as the next execution occurs, the processor will again poll the zone controllers in a step  102  and compute the percentage heat requirement and cooling requirement in steps  106  and  108 . Assuming that the percentage cooling requirement continues to now exceed percentage heating requirement, the processor will again execute steps  110 , and  116  through  120  and again set the system demand equal to cool. This will prompt the processor to proceed through step  128  to step  130  since system demand will be equal to cool. Since system demand will not equal system mode at this time, the processor will proceed along the no path to step  132  to inquire whether system mode equals none. Since system mode will have been previously set equal to none in step  162 , during the previous execution of the control logic, the processor will proceed along the yes path to step  134  and read the water temperature from the water temperature sensor  52  in the return line of the hydronic system. The processor will proceed to inquire as to whether the water temperature read from sensor  52  is between the range of temperatures set forth in step  136 . Since the boiler will have just recently been turned off, the water temperature in the return line should be above thirty two degrees Centigrade so as to prompt the processor to proceed along the no path out of step  136  to a step  164  and inquire as to whether the changeover timer set in step  160  is equal to zero. The changeover timer will have just been set equal to a predetermined changeover time in the previous execution of the control logic. This will prompt the processor to proceed along the no path to a step  166  and decrement the changeover time previously loaded into the change over timer. It is to be appreciated that the amount of time thereby decremented will be essentially the delay time defined by step  148  between successive executions of the control logic. The processor proceeds from step  166  to step  148  wherein the delay is again implemented before the next successive execution of the control logic. 
   It is to be appreciated that successive executions of the control logic will occur as long as the zone controllers continue to indicate a higher percentage cooling requirement than heating requirement and that this higher percentage cooling requirement remains greater than the minimum cooling demand. At some point during the successive executions of the control logic, the processor may note in step  136  that the water temperature in the return line is within the range of the temperatures set forth in step  136 . On the other hand, the processor may note that the changeover timer has been decremented to zero in step  164  before the water temperature in the return line is within range. In either case, the processor will proceed from step  136  or step  164  to step  138  and inquire as to whether the system demand equals cool. Since the system demand will have been continually set equal to cool each time step  120  is encountered, the processor will proceed to step  168  and set the two way valve  14  to a cooling position. The processor will thereafter proceed to step  170  and activate the pump  50  and deactivate the pump  48 . The processor will then proceed to a step  172  and start the chiller  10 . The processor will thereafter set the system mode equal to cool in a step  174 . The processor will proceed to send the system mode setting of “cooling’ to the zone controllers  24 ,  30 , and  34 . Each zone controller will use the communicated setting to determine how to position its control valve. In this regard, if the local demand is for cooling, then the control valve will be positioned by the zone controller so as to deliver cooled water from the chiller to the fan coil heat exchanger. If the local demand is however for heating, then the cooled water from the chiller will bypass the fan coil heat exchanger. It is to be appreciated that the above assumes that the local zone controller is not able to independently determine whether the water being delivered is hot or cold. In the event that the zone controllers possess the capability of independently determining the temperature of the water being delivered, then they will implement the positioning of their respective control valves without the need to receive the system mode setting from the system controller  44 . 
   It is hence to be appreciated that the control logic will have implemented a changeover from heating to cooling in the event that the changeover time as defined by the changeover timer elapses or in the event that the water temperature sensor is within the predefined range of water temperatures in step  136 . It is furthermore to be appreciated that the control logic can possibly implement a changeover from cooling back to heating when the percentage heating requirement exceeds the percentage cooling requirement at some point during the successive executions of control logic. At such time, the system demand will be set equal to heat in step  114  prompting the processor to proceed through steps  128 ,  130 ,  132  to step  154  to inquire whether the system mode is equal to heat. Since the system mode will still be equal to cool, the processor will proceed from step  154  along the no path to step  174  to inquire whether the system mode is equal to cool. Since system mode will still be equal to cool, the processor will proceed to a step  176  to inquire whether the cool run timer is greater than the minimum cool run time. If the cool run timer has not been sufficiently incremented so as to exceed the minimum cool run time, the processor will proceed to step  178  and increment the cool run timer before returning to step  148 . The processor will again execute the aforementioned logic steps of  114 ,  128 , 130 , 132 ,  154 ,  174  and  176  until the cool run timer exceeds the minimum cool run time. At this point, the processor will proceed to stop the chiller  10  before setting the changeover timer equal to “T” in step  160 . The processor will proceed to step  162  and set system mode equal to none and heat run timer and cool run timer equal to zero. The processor will proceed to step  148  and implement the delay before again polling the zone controllers in step  102 . Assuming that the polling continues to indicate that heating requirements exceed cooling requirements, the processor will proceed though steps  110 - 114 ,  128  to step  132 . Since the system mode is now equal to none, the processor will proceed to implement steps  134 ,  136 , and steps  164 - 166  and then  148  until such time as the water temperature read in step  134  is within range or the changeover timer has been decremented to zero. At such time, the processor will proceed to step  138  and hence to steps  140 - 146  so as to change the hydronic system to a heating mode of operation. 
   Referring again to step  116 , it is to be noted that there may a situation wherein the particular polling by the processor will indicate that there is neither a predominance of heating or cooling being required by the zone controllers. In this case, the processor will proceed to step  122  and inquire as to whether the percent cooling requirement and the percent heating requirement are both equals to zero. If this is the case, the processor proceeds to set the system demand equal to none in a step  124  prompting the processor to proceed to step  128 . Depending upon the previous system mode setting, the processor will proceed through either step  154  or step  174  in order to stop the operating equipment and set the system mode equal to none. The processor will proceed through step  148  before again implementing the aforementioned logic as long as the polling requirements remain unchanged. 
   Referring again to step  122 , in the event that the percent cooling requirement and percent heating requirement do not equal zero, the processor will proceed to step  128 . Since the system requirements and system mode will be whatever was previously determined, the processor will proceed to step  130  where it will then proceed along the yes path and increment the appropriate run timer for whatever mode it is currently in. 
   It is to be appreciated that the control logic of  FIG. 2  allows the system controller  44  to potentially initiate a changeover from either heating to cooling or vice versa in response to the polling of the zone controllers  24 , 30 , and  34 . This changeover will actually occur only when certain requirements are met. Specifically, the boiler or chiller must have been running for a minimum time. Secondly, the water temperature must be within the predefined temperature range or the changeover timer must have expired indicating that the change over time has been exceeded. It is only after such events have occurred that the system controller will authorize the repositioning of the two-way valve  14  and activation of the appropriate pumps  48  or  50  as well as the starting of the heating source or cooling source. 
   It is to be appreciated that a preferred embodiment of the invention has been disclosed. Alterations or modifications may occur to one of ordinary skill in the art. For instance, the control logic may be altered so as to not require a sensing of water temperature in the return line. In this case, the changeover time would be the governing factor as to whether a changeover would be allowed to occur. 
   It will be appreciated by those skilled in the art that further changes could be made to the above-described invention without departing from the scope of the invention. Accordingly, the foregoing description is by way of example only and the invention is to be limited only by the following claims and equivalents thereto.