AU2012261603A1 - A Hot Water System Scavenging Method and Arrangement - Google Patents

Abstract

A method of operating a water heating system having a heat source remote from a storage tank and connected there to by a pipe circuit to deliver heated water from the heat source to the tank and withdraw water from the tank for heating by the heat source, the system including a pump arranged to pump water around the pipe circuit between the heat source and the tank, wherein the pump is a reversible pump having a forward mode and a reverse mode, the method including the steps of: determining when the temperature of water from the tank is below a predetermined a first temperature; operating the pump in the reverse mode to displace water in the delivery pipe between the inlet of the tank and the outlet of the heat source with water from the upper portion of the tank, operating the pump in the forward mode to deliver heated water from the heat source to the tank. S r-------------------------------1 1.001 1.050 L | | ---------------- 1.016 ..........-. -.... 1.028 1.020 1-014 1.032 1-2 - 1.005

Description

1 A Hot Water System Scavenging Method and Arrangement Field of the invention [001] This invention relates to water heating systems and addresses the problem of cooling of water in the pipes of the system. Background of the invention [002] In water heating systems which have a source of heat remote from a storage tank, the heat source is connected to the tank via a pipe system. The pipe system can carry potable water from the tank, or it can carry heat transfer fluid to a heat exchanger proximate to or incorporated in the tank. Where the heat source is remote from the water tank, the heat transfer fluid or water can be circulated by a pump. A dead leg in this context refers to a volume of water or heat transfer fluid in a hot water pipe circuit which can lose heat, such as in a length of pipe between a heat source and a hot water storage tank and intended to carry heated water or heat transfer fluid. Particularly where the water in the dead leg is only drawn off or circulated intermittently, the temperature of the water in the dead leg will fall towards ambient temperature over time. When the pump is restarted, the cooled water will be delivered to the tank before heated water begins to be delivered. Delivery can be initiated by usage of heated water from the system or by heat loss from the storage tank. Water from the heat source is usually injected into the stored hot water which is at a desired temperature. If the injected water is cooler than the desired temperature, the resulting mixed water will be below the desired temperature. This is a particular problem in many hot water systems, such as solar, heat pumps and others including those which use top down heating. [003] 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 [004] An embodiment of the invention includes a method of replacing at least some of the cooled water in a dead leg which is part of a circuit adapted to deliver heated water in a forward direction from a heating source to a heated water store with heated water, the method including the steps of delivering heated water in a reverse direction from a heated water store into the dead leg in response to the occurrence of one or more trigger conditions. [005] The trigger condition can be a period of elapsed time. [006] The trigger condition can be a temperature condition.

2 [007] The invention also provides a system for implementing the method. [008] An embodiment of the invention proposes the use of a reversible pump to initially circulate water in a dead leg between a heat source and a heated water source to displace at least some of the cooled water in the dead leg with heated water from the heated water store. This recirculates the cooled water through the heat source before delivery to the heated water store. Such a recirculation method is referred to herein as "scavenging". [009] The present invention provides a water heating system having a storage tank and a heat source remote from the storage tank and connected thereto by a pipe circuit including a delivery pipe section to deliver heated water from the heat source to the tank and a withdrawal pipe section to withdraw water from the tank for heating by the heat source, the system including a pump arranged to pump water around the pipe circuit between the heat source and the tank, wherein the pump is a reversible pump having a forward mode and a reverse mode, the system being adapted to operate the pump in the reverse mode to displace at least some water in the delivery pipe between the inlet of the tank and the outlet of the heat source with water taken from the tank proximate to the inlet to the tank. [010] The displacement can occur before reversing flow and delivering water from the heat source to the inlet of the tank. [011] The system being adapted to operate the pump in response to a predetermined condition. [012] The reverse mode can be implemented before the forward mode delivering heated water from the heat source to the tank. [013] The system can include control means adapted to control the operation of the pump. [014] The control means can be adapted (programmed) to displace an amount of water equivalent to the volume of the dead leg in the reverse mode. [015] The controller can be adapted to operate the pump in the reverse mode until a specified thermal condition is achieved. [016] The invention also provides a method of operating a water heating system having a heat source remote from a storage tank and connected there to by a pipe circuit to deliver heated water from the heat source to the tank and withdraw water from the tank for heating by the heat source, the system including a pump arranged to pump water around the pipe circuit between the heat source and the tank, wherein the pump is a reversible pump having a forward mode and a reverse mode, the method including the steps of: determining when a predetermined condition occurs, operating the pump in the reverse mode to displace 3 water in the delivery pipe between the inlet of the tank and the outlet of the heat source with water from the tank. [017] The pump can be turned off when the water in the tank is above a predetermined temperature and when the predetermined condition has not occurred. [018] The pipe circuit can have a delivery section connecting the output of the heat source to a circulating input of the water store, and a withdrawal section connecting a circulating output of the water store to the input of the heat source. [019] The reverse mode can be stopped when at least a substantial part of the liquid in the delivery section of the pipe circuit has been replaced with heated water from the water store, displacing cooled water by recirculating it through the heat source for re-heating and until the heat source reaches operating temperature. [020] The method can include the step of operating the pump in the forward mode to deliver heated water from the heat source to the tank. . [021] The predetermined condition can be when the water in the tank requires heating. [022] The predetermined condition can be when water in the dead leg requires heating. [023] The predetermined condition can include a period of elapsed time. [024] The predetermined condition can include a temperature threshold. [025] The predetermined condition can include a operating temperature threshold of the heat source. Brief description of the drawings [026] The embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [027] Figure 1 is a schematic illustration of a top down water heater system adapted for use according to an embodiment of the invention; [028] Figure 2 is a flow diagram illustrating a mode of operating the scavenging system using a temperature sensor; [029] Figure 3 is a flow diagram illustrating an alternative mode of operating the scavenging system using a timer only. [030] Figure 4 is a flow diagram illustrating a mode of operating the scavenging system according to an embodiment of the invention.

4 [031] Figure 5 is a flow diagram illustrating a mode of operating the scavenging system utilising a timer. [032] The numbering convention used in the drawings is that the digits in front of the full stop indicate the drawing number, and the digits after the full stop are the element reference numbers. Where possible, the same element reference number is used in different drawings to indicate corresponding elements. [033] It is understood that the drawings are intended to be illustrative rather than exact reproductions, and are not necessarily drawn to scale. The orientation of the drawings is chosen to illustrate the features of the objects shown, and does not necessarily represent the orientation of the objects in use. Detailed description of the embodiment or embodiments [034] The invention can be used with both direct and indirect water heating systems. An indirect water heating system uses an intermediate heat transfer fluid to transfer heat from a heat source to potable water in a storage tank via a heat exchanger at or in the tank. A direct water heating system heats the potable water at the heat source and delivers the heated water to the tank. An embodiment of the invention will be described with reference to a direct water heating system. [035] An embodiment of the invention provides a water heating system in which the heat source is connected to a heated water storage tank via a circulating pipe arrangement. In heating mode, the heated water can be delivered to the upper part of the tank, while water from the lower part of the tank is drawn off for delivery to the heat source. In practice, the water in the heated water delivery pipe will lose heat when the water is not actually being circulated between the heat source and the storage tank. Thus, when circulation of water recommences, some cool water will be delivered to the tank before the heated water arrives. Accordingly, the embodiments of the invention provide a system and method in which the water in the circulating pipe system is pumped in the reverse direction, either periodically, or on a temperature basis, so that the cooled water in the heated water delivery pipe is pumped to the inlet side of the heat source and displaced by heated water from the storage tank. This mode of operation can be used to ensure that water in the heated water delivery pipe is maintained at an elevated temperature. [036] The process of displacing the water in the dead leg will be referred to herein as scavenging. [037] Figure 1 illustrates a top-down water heating system 1.001 with a split system heat pump. The water heating system includes a heated water storage tank 1.002 having a 5 heated water inlet 1.004, proximate the top of the tank, and a circulating outlet 1.006 proximate the lower portion of the tank. Water can be drawn off for use via outlet 1.003, and replenished by mains water inlet 1.005. [038] A heat exchanger 1.012 delivers heat to the water heating side of the exchanger from a system 1.014 which produces the heat. System 1.014 can be, for example, an air conditioning system. The circulating pipe circuit includes pipe 1.020 delivering heated water to the inlet 1.004, and cooler water withdrawal pipe 1.022 which delivers water from the outlet 1.006 to the inlet of the heat exchanger 1.012. Where the system has been idle for some time, the heated water in the pipe 1.020 will loose heat to atmosphere and cool. Once the water in pipe 1.020 cools below the temperature in the tank, running the pump will cause an initial stream of cool water to be delivered to the tank at 1.004. [039] The invention proposes to overcome this by running the pump 1.010 backwards or in reverse for a sufficient period of time to return the water in pipe 1.020 to the heat source 1.012 for reheating. This operation can be carried out immediately before a heating cycle commences, or periodically, or based on the temperature of the heat exchanger 1.012 or based on the temperature of the water in the pipe 1.020. [040] The water heating system is a direct heating system, that is, the potable water from the tank is heated directly in the remote heat exchanger 1.012. In normal operation, a pump 1.010 draws water from tank 1.002 via outlet 1.006 and circulates the water from the tank 1.002 via circulating pipe section 1.022 through the heat exchanger 1.012 to heat the water, which is returned to the tank 1.002 via circulating pipe section 1.020 and inlet 1.004. [041] The tank can be fitted with one temperature sensor, or with multiple temperature sensors 1.008 located to monitor the temperature of the tank at several heights. Additional temperature sensors, such as 1.028, 1.030, can be located to monitor the temperature at various locations around the system. A further temperature sensor 1.050 can monitor ambient temperature. [042] The temperature sensors can supply temperature information to a programmable controller or microprocessor 1.016. The controller can also control the operation of the pump 1.010 in response to one or more of the inputs from the temperature sensors. [043] The pump 1.010 is a motor driven water pump. The pump can be capable of circulating water in either direction through the heat exchanger. The pump can be a DC pump. [044] The tank can include a second heat source, such as electrical element 1.032.

6 [045] Figure 2 is a flow diagram illustrating a mode of operating the scavenging system using temperature sensing according to an embodiment of the invention. [046] In operation of the top-down water heating system, the controller monitors the temperature sensor 1.008 which corresponds to a portion of the tank. The controller will run the pump 1.010 to bring the temperature of the selected tank temperature sensor to the required operating temperature. In order to prevent hunting, the operating temperature will be within a range TMIN to TMAX. The controller will then shut off the pump until the temperature falls below TMIN [047] The flow diagram of Figure 2 illustrates this mode of operating the system without the scavenging feature of the present invention. The controller first identifies the selected tank sensor at step 2.102. At step 2.104, the controller checks that the heat source can deliver useful heat energy to the water. To deliver useful heat energy, the temperature of the heat should be above the temperature of the water in the tank. This step is illustrated as a comparison between the temperature TTKf from the selected tank sensor with the temperature TIN from a temperature sensor 1.028 at the heat exchanger 1.012. Sensor 1.028 can be located proximate the heat exchanger outlet. If TIN is less than TTKI the controller 1.020 ensures that the pump is turned off (step 2.006) to prevent warmer water from the tank being circulated through the cooler heat exchanger. Periodically thereafter, for example via delay step 2.108, the controller can monitor these temperatures to determine when the heat exchanger is hotter than the water in the tank. [048] The controller can alternatively or additionally monitor the temperature at the upper portion of the tank to ensure the heat exchanger is hotter. [049] At step 2.110, the controller analyses the selected tank sensor output to determine if the water has reached the upper operating temperature TMAX [050] If the water has reached TMAX, the controller turns the pump off at step 2.114 and then continues to monitoring the temperature of the tank at step 2.116. [051] A further step of ensuring that the heat source can deliver useful heat to the water can optionally be performed at 2.118. [052] If the water has not reached the maximum temperature TMAX the controller checks whether the pump is operating and turns the pump on (step 2.122) or continues pump operation (step 2.112) until TMAX is reached. [053] Figure 3 is a flow diagram illustrating the operation of the scavenging system controlled by a timer.

7 [054] Steps 3.102 to 3.118 correspond to steps 2.102 to 2.118. When the controller determines that the temperature in the tank is below TMIN, and that the heat source is capable of delivering useful heat energy, the controller initially runs the pump in the reverse mode until the temperature at the heat source outlet (sensor 1.028) is of the same order as the temperature as the tank sensor TTKn. At step 3.124 a timer step is included so as to safeguard against a situation where the tank may have water which is warm but not hot enough for use, but which is much higher than the water coming in. In this situation the pump may run in reverse for too long, which can reduce the temperature layer stratification in the tank. When the water in the dead leg has thus been scavenged, the controller runs the pump in the forward mode. [055] In an alternative embodiment, the controller can be adapted to run the pump in reverse for a period sufficient to displace the dead leg water with water from the top of the tank, instead of measuring the temperature from the sensor 1.028. [056] In a further mode of operation, such as shown in Figure 4, the pump can be run in reverse according to a time schedule. For example, the pump can be run in reverse after a predetermined time period, based, for example, on the time taken for the volume of water in the pipe to be displaced by the pump and or the heat source to reach operating temperature. In Figure 4, the system first determines whether or not heating is required at step 4.142. If heating is required, a timer is started at step 4.144, and the pump is run in reverse at 4.146. The system checks whether a predetermined pre-condition is met, eg, whether the reverse pumping has been running for a time period sufficient to return the dead leg water to the heater for re-heating. This also results in water from the storage tank replacing the water in the dead leg. If the pre-condition is not met, a time check is carried out at 4.150 to determine if a predetermined time period has expired. When the pre-condition is met, or when the time check from 4.150 is satisfied, the pump is then switched to the forward mode at 4.152. The forward mode time is checked at step 4.154 to determine if the water in the tank has been raised to the required temperature. This can be determined, for example by determining the time required to circulate the water in the tank through the external heat exchanger. When the condition of step 4.154 is met, the system stops the pump and returns to monitoring when the next cycle of heating is due. [057] Figure 5 illustrates a system which responds to a thermal pre-condition. [058] It is important to note that while the embodiments show top down heating systems in the figures, it will be understood that the invention is applicable to all water heating systems which, by virtue of their setup and pipe circuit arrangements, include a dead leg in them.

8 [059] It will be noted in the system and method, in respect of the embodiments described above, that water is not diverted from the heating circuit, but instead, the flow is reversed within the heating circuit. [060] 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. [061] 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. [062] 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.

Claims (11)

1. A water heating system having a heat source remote from a storage tank and connected thereto by a pipe circuit to deliver heated water from the heat source to the tank and withdraw water from the tank for heating by the heat source, the system including a pump arranged to pump water around the pipe circuit between the heat source and the tank, wherein the pump is a reversible pump having a forward mode and a reverse mode, the system being adapted to operate the pump in the reverse mode to displace water in the delivery pipe between the inlet of the tank and the outlet of the heat source with water from the tank, before delivering water from the heat source to the tank.

2. A water heating system as claimed in claim 1, including control means adapted to control the operation of the pump.

3. A water heating system as claimed in claim 2, wherein the control means is adapted to displace at least part of the water of the dead leg in the reverse mode.

4. A water heating system as claimed in claim 2, wherein the controller is adapted to operate the pump in the reverse mode until a specified thermal condition is achieved.

5. A water heating system as claimed in claim 2, wherein the controller is adapted to operate the pump in the reverse mode until a specified time period is achieved.

6. A water heating system as claimed in claim 4 wherein the thermal condition is that the temperature of the output of the heat source is approximately equivalent to a predetermined temperature.

7. A method of operating a water heating system having a heat source remote from a storage tank and connected thereto by a pipe circuit to deliver heated water from the heat source to the tank and withdraw water from the tank for heating by the heat source, the system including a pump arranged to pump water around the pipe circuit between the heat source and the tank, wherein the pump is a reversible pump having a forward mode and a reverse mode, the method including the steps of: determining when the temperature of water in the delivery section of the pipe circuit or heat source outlet is below a predetermined first temperature; operating the pump in the reverse mode to displace water in the delivery pipe between the inlet of the tank and the outlet of the heat source with water from the tank, then operating the pump in the forward mode to deliver heated water from the heat source to the tank.

8. A method as claimed in claim 7 wherein the reverse mode is stopped when at least a substantial part of the liquid in the delivery section of the pipe circuit has been replaced with 10 heated water from the water store, displacing cooled water by recirculating it through the heat source for re-heating.

9. A method as claimed in claim 8 wherein reverse mode is operated until the heat source reaches operating temperature.

10. A water heating system having a heat source remote from a storage tank being substantially as herein described with reference to the accompanying figures of the drawings.

11. A method of operating a water heating system having a heat source remote from a storage tank being substantially as herein described with reference to the accompanying figures of the drawings