Patent Publication Number: US-2023160388-A9

Title: Water Heating System and Valving for These

Description:
FIELD OF THE INVENTION 
     The present invention relates to freshwater stations or district water heating systems, and in particular in improvements to the primary circuit and the secondary circuit of such systems. More particularly the present invention can be used with solar water heating systems, electric boosted solar systems, gas boosted solar systems, cogeneration systems and hybrid systems. 
     BACKGROUND OF THE INVENTION 
     Solar thermal water heating systems with solar panels are subject to temperature and duty cycle events which threaten the integrity of the collector or its pipes. In the case of freezing temperatures and ice formation, or over-temperature situations where continuing to heat the working fluid at the collector when there is solar energy absorbed but which can no longer be dissipated within the system, resulting in the super heating of the working fluid, both situations can cause pressurising of the system. In either of these circumstances, one solution is to drain the solar collector of working fluid and store it in a reservoir for pumping back to the collector or collectors when needed. These are known as drain-back systems. 
     In commercial applications duty standby pumps are often used for pump skids. When one pump is in operation the other pump is switched off. In order to prevent flow from being “short circuited” from one pump to the other, one way valves are installed at the exit of each of the individual pumps. “Short circuiting” can occur because the type of pump used is usually a non-positive displacement type, therefore permitting fluid to flow through the pump body even when the impeller is not in operation. Such systems are not able to use a drain back feature in solar applications, because the installation of one way valves in the circuit makes backward flow not possible. 
     Water heating systems that utilise a heat exchanger to separate the working fluid such as solar or cogeneration systems traditionally control the outlet temperature on the potable water side via a form of thermostatic mixing valve. The thermostatic mixing valve blends hot and cold water to produce the desired temperature. The valve can be either electronically controlled or via a thermostatic element. When such a valve is used there is an inherent increase in pressure drop across the valve caused by the pump in the circuit when the valve closes to restrict the flow of hot water. This increase in pressure drop effectively means the pump is continuing to draw maximum power even in times where there is little or no load on the system. 
     A second disadvantage of a valve based system is that, due to the large pressure drop across the valve, large pumps and their associated high cost and power requirements are a necessity. 
     Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application. 
     SUMMARY OF THE INVENTION 
     The present invention provides a pump system for use with a solar collector system which is used to heat a heat transfer fluid, the solar collector system including a storage tank for the heat transfer fluid used in the solar collector system, the pump system having a first and second pump arranged in parallel which can pump the heat transfer fluid from the storage tank to a solar collector, so that should one pump fail the other pump can function, wherein the outlet of the first pump and the outlet of the second pump are connected to a valve arrangement, whereby when the first pump operates, the outlet of the second pump is substantially closed by the flow from the first pump and when the second pump operates, the outlet of the first pump is substantially closed by the flow from the second pump. 
     The valve arrangement can have three ports and a valve member which effectively closes a first pump&#39;s outlet port when a second pump is operating and the first pump is not, and closes the second pump&#39;s outlet port when a first pump is operating and the second pump is not operating. 
     The valve arrangement can have a flap which closes the first pump&#39;s outlet port and moves to a second location when activated by the first pump to close the second pump&#39;s outlet port. 
     The outlet ports can be located on respective pipes which connect to the pumps. 
     The pump system can be provided as part of a skid. 
     The present invention also provides a solar water heating system having a pump system described above wherein the heat transfer fluid is not potable water. 
     The present invention also provides a solar water heating system having a pump system described above wherein the heat transfer fluid is potable water. 
     The present invention further provides a valve for a pump system having two pumps and which will allow drain back of a pumped fluid, the valve including a body having first and second ports for respectively connecting to respective pump outlets or conduits from the outlets, and a third port, whereby when a pump is pumping the third port is an outlet from the body, and when the pumps are not pumping, the third port is an inlet to the body. 
     Between the first and second ports is located a valve member which can move so as to close off one of the first or second ports depending upon which pump is operating. 
     The valve member can be a flap. 
     The flap can be connected by a hinge means to the body which allows movement of the flap between the first and the second ports. 
     The valve member closes off the first or second ports to a substantial extent, that is watertight sealing is not required by the valve. 
     The flap can be manufactured from a metal, a polymeric material or a composite material. 
     Valve seats surrounding the first and second ports can be manufactured from a metal, a polymeric or a composite material. 
     Surrounding the first port or the second port or the third port is one of the following: a male thread, a female thread. 
     Surrounding a respective port is a female thread. 
     The flap can be held rotatable in the body, or pivotally held in the body, by means of opposed pins which seal to the body and pass into the body. 
     The present invention also provides a water heating system having a primary circuit to supply a heated heat transfer fluid to a heat exchanger, which supplies heat to a secondary circuit having potable water therein, wherein the primary circuit includes at least one pump to circulate the heat transfer fluid through the heat exchanger, and a control system to control the operation and output flow rate of at least one pump, characterized in that the control system measures the temperature, or an indication of the temperature of the potable water after it has left the heat exchanger, so as to control the output flow rate of the at least one pump. 
     The primary circuit can heat the heat transfer fluid by one of or a combination of more than one of the following: solar; gas, electric, cogeneration means; gas boosted solar; electric boosted solar. 
     The secondary circuit can have or be one or more of the following: is a freshwater station system; is a district water heating system; a pump; a filter; a cold water supply; an over temperature shut down mechanism. 
     The water heating system can be such that the heat exchanger is provided in a delivery skid whereby there are two heat exchangers present on the skid, with respective isolation valves and having parallel connections to an incoming conduit and an outgoing conduit, whereby one of said heat exchangers is present in a redundancy capacity. 
     The system can have multiple skids connected to each other to provide the heat exchanger of the system. 
     The present invention also provides a heat exchanger apparatus comprising a frame to support at least two heat exchangers, between an inlet conduit and an outlet conduit, wherein the at least two heat exchangers having connection to the inlet and outlet conduit in parallel, the connection being via isolation valves and forming a liquid supply inlet and heated liquid outlet, and each heat exchanger having fluid connection, via isolation valves, to a primary circuit to receive a heat transfer fluid to transfer heat to the liquid, characterized in that at least one of the heat exchangers is present in a redundant capacity. 
     The inlet conduit and the outlet conduit have flanged ends to allow connection to an adjacent like heat exchanger apparatus, and or a conduit closure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of a preferred embodiment will follow, by way of example only, with reference to the accompanying figures of the drawings, in which: 
         FIG.  1    illustrates a schematic view of a solar water heating system with primary and secondary circuits, the primary circuit deriving heat exclusively mainly from solar but is also provided with an electric booster; 
         FIG.  2    illustrate a schematic view of a water heating system similar to that of  FIG.  1   , except that the system includes a direct gas booster in the form of a gas boost on the secondary circuit; 
         FIG.  3    illustrate a schematic view of a water heating system similar to that of  FIG.  1   , except that the system includes an indirect booster in the form of a gas boost on the primary circuit; 
         FIG.  4    illustrate a schematic view of a water heating system similar to that of  FIG.  1   , except that the system is a hybrid system and includes dual indirect boosters in the form of a gas boost and an electric boost on the primary circuit; 
         FIG.  5    illustrate a schematic view of a water heating system, except that the system includes co-generation unit and chiller in the primary circuit; 
         FIG.  6    illustrates a perspective view of a flap valve body; 
         FIG.  7    illustrates a cross section through the valve of  FIG.  6   ; 
         FIG.  8    illustrates a front view of the valve of  FIG.  6   ; 
         FIG.  9    illustrates an end view of the valve of  FIG.  6   ; 
         FIG.  10    illustrates an alternative valve arrangement in the form of a ball valve showing operating condition with one pump on; 
         FIG.  11    illustrates the valve arrangement of  FIG.  10   , where both pumps are off in a first operating condition; 
         FIG.  12    illustrates the valve arrangement of  FIG.  10   , where both pumps are off in a second operating condition 
         FIG.  13    illustrates another ball valve arrangement showing condition with one pump on; 
         FIG.  14    illustrates the valve arrangement of  FIG.  13    where both pumps are off; 
         FIG.  15    is a front view of a delivery skid; 
         FIG.  16    is a side view of the delivery skid of  FIG.  15   ; 
         FIG.  17    illustrates dual delivery skids assembled in parallel for use in the systems of  FIGS.  1  to  5   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT OR EMBODIMENTS 
     Illustrated in  FIG.  1    is a schematic of a solar water heating system  10  which comprises a primary circuit made up of a solar collector  11  (only one illustrated for ease of illustration—whereas a gang or bank of such collectors is normally used), a solar pump skid  12 , heat transfer fluid tank  13  which serves as a drain back tank, and a delivery skid  14  (which includes a heat exchanger  14 . 1 -only one illustrated for ease of illustration—whereas a gang or bank 2 or more of such skids  14  can be used as described below in respect to  FIGS.  15  to  17   ), and a potable hot water delivery circuit or secondary circuit  15 , which are all plumbed and connected together as described below. 
     The solar collection panel or collector  11  has an entry port  11 . 1  in its base and an exit port  11 . 2  at its top so that heated transfer fluid can exit the collector and via conduit  100  transfers to or makes it way to the drain back tank  13 . The collector  11  includes a temperature sensor  11 . 3  which has its signals delivered to the controller  12 . 5  on the solar pump skid  12 . 
     Delivering heat transfer fluid from the tank  13  to the collector  11  is the function of the pump skid  12 , which has a first pump  12 . 1  and a second pump  12 . 2 , which are of the non-displacement type such as an impeller type pump. The type of pump selected must be of the sort that will allow fluid to flow from the conduit  200  to the conduit  500  and back to the tank  13 , if the pumps  12 . 1  and  12 . 2  are not operating. This type of pump is needed to ensure that the system  10  allows for the drain back of the heat transfer fluid from the collector  11  via conduit  200  back through pump  12 . 1  and or  12 . 2  and then back to the tank  13 . 
     The conduit  500  draws heat transfer fluid from the tank  13  from a lower location thereon as the cooler heat transfer fluid is available from such a lower location. Whereas, the heated transfer fluid exiting the collector  11  via outlet  11 . 2  enters the tank  13  at an intermediate height thereon, with the heated heat transfer fluid being drawn off via conduit  300  from the top of the tank  13  for conveying to the inlet of the delivery skid  14 . Whereas the conduit  400  returns the cooled heat transfer fluid which exits the heat exchanger  14 . 1  and conveys it back to the base of the tank  13 , where it can be re-delivered to the collector  11  via conduit  500 , pump skid  12  and conduit  200 . 
     The pump skid  12  has the parallel plumbed pumps  12 . 1  and  12 . 2  powered from the control unit  12 . 5 . The outlets of the pumps  12 . 1  and  12 . 2  connect to the inlet ports on either side of a flap of a flap valve  12 . 3 , with the outlet of the valve  12 . 3  connecting to the inlet of conduit  200 . The construction of the valve  12 . 3  will be described in more detail below with respect to  FIGS.  6  to  10   . 
     The pumps  12 . 1  and  12 . 2  are assembled with appropriate conduits each so as to be in parallel, so that should one pump fail, the other pump can be operated. With suitable isolation valves, not illustrated, this will allow the replacement of the non-operating pump while the other pump is operating. 
     In addition, the valve  12 . 3  is structured such that when the first pump  12 . 1  is operating, while the outlet of the first pump  12 . 1  and the outlet of said second pump  12 . 2  are connected to the valve  12 . 3 , then when the first pump  12 . 1  operates the outlet of the second pump  12 . 2  is substantially closed due to the flow from the first pump  12 . 1  acting against the flap of the flap valve  12 . 3 . Then and when the second pump  12 . 2  operates- and pump  12 . 1  is not, the outlet of the first pump  12 . 1  is substantially closed by the flow from the second pump  12 . 2  acting against the flap of the flap valve  12 . 3 . 
     The valve  12 . 3  is arranged so that valve member or flap  12 . 37  of valve  12 . 3  effectively closes a first pump  12 . 1  outlet port when the second pump  12 . 2  is operating and the first pump  12 . 1  is not, and closes the second pump  12 . 2  outlet port when the first pump  12 . 1  is operating and the second pump  12 . 2  is not operating. 
     The valve  12 . 3  as illustrated in  FIGS.  6  to  10    comprises a valve body  12 . 31  of brass or brass alloy (or any appropriate material), and in which is formed two ports  12 . 331  and  12 . 321  each respectively surrounded by a sealing rim  12 . 371  which when heat transfer fluid flows into the body act as inlets to the valve  12 . 3 . The two ports  12 . 331  and  12 . 321  feed to the third port  12 . 341  which acts as an outlet when heat transfer fluid flows out of the valve body and as an inlet when heat transfer fluid flows into the valve body in a drain back condition. 
     It can be seen that the longitudinal axes  5  (normal to the plane of the ports  12 . 331  and  12 . 321 ) are at 60 degrees to each other. This ensures that the pivoting or rotating flap  12 . 37  only rotates through 60 degrees from closing one port to closing the other port. The angle between the longitudinal axes  5 , being at 60 degrees, is not essential for the action and or function of the flap  12 . 37 . This measurement was selected so that the angled valve seats  12 . 371  can be readily machined through the ports  12 . 331  and  12 . 321 . The ports  12 . 331  and  12 . 321  could have been located 180 degrees apart and the valve will function effectively 
     The flap  12 . 37  is made of stainless steel, and it will be noted that none of the flap  12 . 37  or the seats or sealing rims  12 . 371  include any polymeric linings, mouldings or seats, and this makes the valve  12 . 3  robust and relatively cheap to manufacturer which will give a good service life with little to no maintenance and very little risk of failure. While such mouldings are not necessary as a leak tight seal is not required, this is not to say they couldn&#39;t be added if desired or required. 
     The flap  12 . 37  is of a circular configuration with a pivot tube  12 . 372  at its base, which pivot tube  12 . 372  will sit in the part cylindrical sub housing  12 . 35  at the base of the valve body  12 . 31 . The opposite ends of the pivot tube  12 . 372  on the flap  12 . 37  pivotally or rotatably hold the flap  12 . 37  in the body  12 . 31  by interaction with opposed inwardly extending pivot pins on the ends of machine screws  12 . 36 . The heads of the respective machine screws  12 . 36  have a sealing washer (not illustrated) between the head and the sub housing  12 . 35  so that no leakage occurs in use. 
     The ports  12 . 321 ,  12 . 331  and  12 . 341  are each surrounded by female threaded hexagonal formation  12 . 32 ,  12 . 33  and  12 . 34 , so that they can respectively connect to the outlets of the pumps  12 . 1  and  12 . 2  and the inlet to conduit  200 . While a female threaded connection is illustrated, it will be readily understood that any appropriate connection mechanism can be utilised, including, amongst others, push fit connections, slip joints, O-ring connections, male threaded connections, grooved coupling and grooved fittings such as those available under the Victualic brand, and any appropriate fitting mechanism. 
     The opposed side surfaces of the stainless steel flap  12 . 37  makes contact with the brass or brass alloy seats  12 . 371  to close the respective port of the other pump when a pump is running, however a perfect seal is not required, and as such no sealing components or polymeric seats are used. While specific materials such as stainless steel for flap  12 . 37  and brass or brass alloy for the valve body  12 . 31  and seats  12 . 371  are mentioned it will be understood that any appropriate material for such components can be used including other metals, polymeric materials or composite materials. 
     The valve  12 . 3  while one of the pumps  12 . 1  or  12 . 2  is operating closes a return path for fluid which would otherwise go through the non-operating pump. However the valve  12 . 3  also allows, when both pumps are not operating, the ability for heat transfer fluid to drain back from the inlet  11 . 1  of the collector  11  back through the valve  12 . 3  and through the pump  12 . 1  or  12 . 6  depending on which side the flap  12 . 37  was resting against. So when one of the pumps is working its associated port in valve body  12 . 31  is an inlet, and the other pumps port is an outlet which is closed off by the flap, and the third port which connects to the conduit  200 , is an outlet from the valve when a pump is operating, but is an inlet to the valve when the pumps are off. 
     In the  FIGS.  1  to  4    there is illustrated check valves  12 . 4  located between the outlet of the pumps  12 . 1  and  12 . 2  and the valve  12 . 3 . However, this is for representation purposes only, because from the previous description it will be understood that the operation of one pump such as  12 . 1  ensures that the pumped flow, will not head towards the other pump, such as  12 . 2 , because the pressure from pump  12 . 1  pushes the flap  12 . 37  against the seat  12 . 371  on the inlet/outlet which leads to or form the pump  12 . 2 . With the opposite occurring when the pump  12 . 2  is operated and the pump  12 . 1  is not. 
     It will be noted that the controller  12 . 5  in addition to receiving a signal from temperature sensor  11 . 3  also receives temperature signals from sensors  13 . 1  at the bottom of the tank  13  and sensor  13 . 2  at the top of the tank  13 . Depending upon the temperatures available at the top sensor  13 . 2  the controller  12 . 5  can activate the electric element  13 . 3  to boost the temperature of the heat transfer fluid in the tank  13 . 
     The heat transfer fluid in the system described above can be any appropriate heat transfer fluid which includes non-potable water or such like based liquids. However it will be understood that the heat transfer fluid could also be potable water. 
     As illustrated in  FIG.  1    the delivery skid  14  as mentioned above includes a heat exchanger  14 . 1 , which receives heated transfer fluid from the tank  13  in the primary circuit for the purpose of heating potable water in the heat exchanger  14 . 1  for the secondary circuit  15 . The delivery skid  14  also includes two pumps  14 . 2  and  14 . 3  (the second pump being available in case of failure of the first pump- or to share the load in an intermittent use modality) and two respective check valves  14 . 4 , which in this instance, unlike valves  12 . 4 , serve a check valve purpose. Heat transfer fluid transfers from tank  13  via conduit  300  and exits the heat exchanger  14 . 1  and the delivery skid  14  back to the tank  13  via the conduit  14 . 
     On the secondary circuit side in the delivery skid  14 , the conduit  600  carries heated potable water from the delivery skid  14  to the end users in this case represented by showering people icons  15 . 3 . The secondary circuit  15  includes a return conduit  700 , a pump  15 . 2  and non-return valve  15 . 1  and conduit  800 . At the end of conduit  800  the conduit  800  enters a junction, a branch of which has incoming cold water supply via a one way valve  15 . 4 , and the other branch being conduit  900  to take back cold water and return heated water to the heat exchanger  14 . 1  to be re-heated. Preferably in the delivery skid  14  there is also located an inline filter  14 . 5 . 
     An important feature of the delivery skid  14  is that the control system which operates the heat exchange fluid passing through the heat exchanger  14 . 1  measures the temperature at the outlet of the heat exchanger of the potable water circuit  15  by temperature sensor and sender  14 . 6 , which is adjacent to an over temperature cut out  14 . 7 . In response to the temperature measured at sensor  14 . 6  the flow rate out of the pump  14 . 2  or  14 . 3  is increased so as to increase the temperature of the water at  14 . 6  or the flow rate is decreased to decrease the temperature at the sensor  14 . 6 . If the temperature cut out  14 . 7  is activated the pumps  14 . 2  and Or  14 . 3  can be switched off. Prior art systems would otherwise use cold water mixing to obtain the desired output potable water temperature. 
     Thus on the secondary side and the interface between the primary and secondary sides, the water heating system  10  has a primary circuit to supply a heated heat transfer fluid to the heat exchanger  14 . 1 , which supplies heat to a secondary circuit  15  having potable water therein, wherein the primary circuit includes at least one pump  14 . 2  or  14 . 3  to circulate the heat transfer fluid to and through the heat exchanger  14 . 1 , and a control system to control the operation and output flow rate of at least one pump  14 . 2  or  14 . 3 , whereby the control system measures the temperature, or an indication of the temperature of said potable water after it has left the heat exchanger  14 . 1  at location of sensor  14 . 6 , so as to control the output flow rate of the at least one pump  14 . 2  or  14 . 3 . 
     Illustrated in  FIG.  2    is a water heating system  210 , which is similar to the system  10  of  FIG.  1    and like parts and components have been like numbered. The system  210  differs from the system  10 , in that system  210  does not include an indirect electric booster element  13 . 3  as part of the tank  13 , but instead a direct booster in the form of a gas water heater  15 . 5  is located between the outlet of the heat exchanger  14 . 1  and the end users  15 . 3 , on the end of conduit  600 , and connects to the end users  15 . 3  by intermediate conduit  650 . The gas water heater  15 . 5  takes it signal to begin or cease operating from the solar pump skid  12 &#39;s main controller  12 . 5 , with potable water being pumped through the secondary circuit  15  and water heater  15 . 5  by the pump  15 . 2 . 
     Illustrated in  FIG.  3    is a water heating system  310 , which is similar to the system  10  of  FIG.  1    and like parts and components have been like numbered. The system  310  differs from the system  10 , in that system  310  does not include an indirect electric booster element  13 . 3  as part of the tank  13 , but instead a indirect booster in the form of a gas heat transfer fluid heater  13 . 5  which is located on the end of conduit  550  which takes heat transfer fluid from tank  13  at an intermediate height location on tank  13 , and the heat transfer fluid exits heater  13 . 5  and re-enters the tank  13  at a high location via conduit  560  which has a pump  13 . 6  controlled by the pump skid  2 &#39;s main controller  12 . 5 . The gas heat transfer fluid heater  13 . 5  takes it signal to begin or cease operating from the solar pump skid  12 &#39;s main controller  12 . 5 . 
     Illustrated in  FIG.  4    is a water heating system  410  which is similar to that of system  310  of  FIG.  3    and like parts and components have been like numbered. The system  410  differs from the system  310  in that a tank wired and controlled electric heating element  13 . 35  is present. The system  410  is thus considered a hybrid system as it utilises one or a combination of more than one of the electric element  31 . 35 , solar collector  11  and or gas heater  13 . 5  to provide the heated transfer fluid in the tank  13 . This hybrid system  410  can use energy from any one or more of the solar, gas or electric inputs depending upon time of operation etc., so as to operate the system  410  as cost effectively as is possible with the mixture of three energy sources and the respective tariffs and or costs associated with each. 
     Illustrated in  FIG.  5    is a water heating system  510 , which is similar to previous systems in that a heat transfer fluid tank  13  is provided and which interacts with a delivery skid  14  with its heat exchanger  14 . 1  like in other systems. Like parts and components have been like numbered. The system  510  differs from previous systems in is that the primary circuit is comprised of a co-generation unit  111  which utilises a fuel via intake  111 . 2  such as natural or coal seam gas, which is burnt in a burner/engine  111 . 5  with air induced from intake  111 . 3 . The rotary motion from engine  111 . 5  is used to rotate a generator  111 . 9 , with electricity fed to the building or grid via conductor  111 . 10 . The combustion products from the engine  111 . 5  are fed, via a catalytic converter  111 . 4  to a heat recovery heat exchanger  111 . 6  which heats heat transfer fluid to 80 to 95 degrees C. and which exits the unit by conduit  100  to be delivered to the tank  13 . The cooled exhaust gasses exit the system via exhaust  111 . 8 . When the tank has sufficient heated transfer fluid at the desired temperature, as electricity may need to continue to be generated, the excess heated transfer fluid is diverted back along conduit  160  where it is optionally combined with cooled heat transfer fluid from conduit  150 , and is fed back to the co-generation unit, or if too hot still, is re-directed via valve  111 . 11  to conduit  170  then to a chiller unit  111 . 12 , and then back to the co-generation unit  111  via conduit  180  pump  111 . 7  and conduit  190 . 
     Illustrated in  FIGS.  10  to  12    is an alternative valve system  1230  which is schematically illustrated as being plumbed in with pumps  12 . 1  and  12 . 2 . In the valve system  1230 , the flap  12 . 37  of valve  12 . 3  of previous figures is replaced by a ball  1237 . The valve body  1231  has ports  12331  and  12321  to which the outlets of the pumps  12 . 1  and  12 . 2  respectively. The third port  12341  would be connected to the conduit  200  for delivery to, or receiving from, the collector  11 . The ball  1237  is preferably of stainless steel I (like flap  12 . 37 ) and the body  1231  of valve  120  is preferably of brass or a brass alloy. As illustrated in  FIG.  10   , when pump  12 . 2  is on, and pump  12 . 1  is off, the ball  1237  is pushed by the flow pressure from the pump  12 . 2  to push against the port  12331  and its seat, thereby preventing a “short circuit” forming and forcing the pumped fluid to exit the valve  1230  via port  12341 . If the pump  12 . 2  is then switched off and pump  12 . 1  remains off, as in  FIG.  11   , then when the heat transfer is under gravity or under back pressure caused by overheating in the collector  11  or freezing in the collector  11 , then the heat transfer fluid can drain back through the port  12341  and then port  12321  and back through pump  12 . 2  to the tank  13  via conduit  500 . As illustrate din  FIG.  12   , if the ball  1237  were to occupy an intermediate position then heat transfer fluid can drain back through either or both ports  12331  and  12321  back through the pumps  12 . 1  and  12 . 2  and conduit  500  to the tank  13 . 
     As illustrate din  FIGS.  13  and  14   , a valve arrangement  123 , similar to valve arrangement  1230  is schematically illustrated, in the reversed conditions to  FIGS.  10  and  11    above. The main difference between the valve  123  and  1230  is that the valve  123  has its ports  1233 . 1  and  1232 . 1  at the end of respective elbows in the valve body  123 . 1 . 
     The valves  123  and  1230  as described above are illustrated in their respective figures with their third ports  1234 . 1  and  12341  in a vertical orientation on the page. However, it will be understood that they do not need to be vertical when installed on the pump skid  12 , as gravity does not adversely affect or influence the manner of operation of the valves  123  and  1230 . 
     As the units described above are meant for commercial water heating systems such as freshwater stations and or district water systems, the tanks  13  as represented in the  FIGS.  1  to  5    are preferably of a mild steel construction and are of a capacity of the order of 1000 to 5000 litres, however any appropriate material can be used such as stainless steel, polymeric materials or composite materials such steel and enamel lined tanks. 
     Illustrated in  FIGS.  15  and  16    is a delivery skid  14 , which has a base  14 . 85  and upper structure  14 . 75  assembled thereon, which allows for the mounting of two heat exchangers  14 . 1  which are connected in parallel to the hot water supply conduit  600 . 1  at one end and to the ring main return and cold water supply entry conduit  900 . 1  at the other end. Each heat exchanger  14 . 1  connects in parallel to the conduits  600 . 1  and  900 . 1  via a respective isolation valve  14 . 95 . This allows the respective heat exchange  14 . 1  to be removed, replaced or repaired in the event of a failure, by simply closing isolation valve  14 . 95  related to the heat exchanger to be repaired or replaced, while at the same time opening the valves  14 . 95  on the adjacent heat exchanger. Having this redundancy in the delivery skid  14  ensures that there is no disruption to the supply of heated water to the end users when a heat exchanger  14 . 1  needs to go offline. 
     The conduits  600 . 1  and  900 . 1  each have respective flange  600 . 11  and  900 . 11  at their respective ends, which as will be described later allow for the connection to a like flange on an adjacent like delivery skid  14 . One flange end  600 . 11  and  900 . 1  will be blanked off by a flanged plate or cap  600 . 2  and  900 . 2 , which thereby seals that end, in the case where a single skid  14  is employed in a system. The modular nature of the delivery skid  14  allows users to connect up as many as needed for the hot water outputs required. 
     Also mounted on the base  14 . 85  and structure  14 . 75  are two pumps  14 . 2  and  14 . 3  and respective isolation valves  14 . 95 , and there are also check valves, filters sensors/senders, and temperature cut outs (item numbers  14 . 4 ,  14 . 5 ,  14 . 6 ,  14 . 7  in  FIGS.  1  to  5   ) which are not visible in  FIG.  15  or  16   . 
     As illustrated in  FIG.  17   , two such delivery skids  14  are assembled side by side, where one flanged plate  600 . 2  is used to close off one end of the conduits  600 . 1 , and the flanged plated  900 . 2  to close off one end of the conduits  900 . 1 . The number of skids  14  which would be connected together to provide the assembly of delivery skids will be dependent upon the size of the system, the numbers of outlets and demand for hot water in the buildings and or complexes where the water heating systems will be installed. 
     As can be seen from  FIG.  17   , the primary flow of heat transfer fluid, the heat transfer fluid path being shown in broken line, passes into the skid  14  via the conduit  300 , as in the other systems described above, which has an inline filter  14 . 5  and this path is split so as to enter each skid  14 . This then passes to the pumps  14 . 2  and  14 . 3  as described above then to a respective the heat exchanger  14 . 1  (or both depending upon needs) then exits the skid  14  back to the tank  13  via the conduit  400 . 
     The systems described above utilise a heat exchanger  14 . 1  and pumps  14 . 2 , 14 . 3  to transfer energy in fluids to potable water at a user adjustable set point. Fluid that is heated by any means such as electric, gas, cogeneration systems, solar systems, heat pumps etc is forced through heat exchangers  14 . 1  by pump  14 . 2 ,  14 . 3 . The pumps  14 . 2 ,  14 . 3  receive an electrical control signal from a temperature sensing device  14 . 6  (and cut off  14 . 7 ). By using a proportional integral derivative controller, the pump compares this control signal to its set point and the motors speed is altered accordingly. If the temperature detected is below the set point, the pump speeds up so as to flow more fluid through the heat exchangers  14 . 1 . The effect of this higher fluid flow is a greater exchange of energy and therefore an increase in the temperature of the potable water exiting the system and being delivered to end users. Conversely if the energy required by the secondary side to maintain a set temperature falls, the flow of fluid in the primary side controlled by the pump also falls. 
     The temperature of the heat transfer fluid contained in a storage tank  13  (see  FIGS.  1  to  5   ) will rise and fall depending on its inputs and outputs, for example an electric storage water heater&#39;s temperature will rise when it is heated by an immersion element and fall due to heat loss to the surroundings. The effect of a fall in the primary side temperature will be a reduction in the amount of energy exchanged with the secondary side. This results in a fall in temperature on the secondary side. The pump reacts to this fall in temperature by increasing pump speed accordingly. 
     Flow rates on the secondary side will vary with user input. 
     The system can cope with very large fluctuations in temperature and flow either separately or simultaneously without altering the method of control. 
     The separation of fluid streams enables greater flexibility as the fluids need not be compatible with each other, for example cogeneration systems using oil additives as the heating medium coupled with potable water. 
     Due to the arrangement of components, the pressure drop across the system is very low which enables the use of highly efficiency pumps operating with very low energy input. 
     Upon failure of any sensing mechanism the systems will cease the flow of fluid thus preventing any further exchange of heat. As such the systems have a fail safe feature. 
     The systems do not require the addition of expensive valves instead utilise a more intelligent version of a pump. 
     A solar system using heat transfer fluid on one side of the heat exchanger and potable water on the other is preferred, however it will be readily understood that utilising alternative fluids, or even potable fluids, on both sides is an alternative. 
     The pumps  14 . 2  and  14 . 3  can be provided as either single headed or dual headed versions to provide duty standby. 
     Illustrated in the  FIGS.  1  to  5    are isolation valves which are represented by the symbol 
     
       
         
         
             
             
         
       
     
     and by item number  14 . 95  in  FIGS.  15  to  17   , and symbol 
     
       
         
         
             
             
         
       
     
     in  FIG.  17   . Such isolation valves generally appear at entries and exits to components, where conduits are to be connected, and they allow for the closing of such valves to assist in the removal and installation of components. 
     While the above description and embodiments are directed to potable water systems, it will be readily understood that this invention and these systems and components are able to be utilised with respect to the heating of other liquids other than potable water, such as milk processing plants and the like. 
     Where ever it is used, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear. 
     It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention. 
     While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.