Thermal energy storage heaters for swimming pools / spas and methods of operating same

Abstract

A thermal energy storage heater for rapidly heating pool / spa water includes an insulated housing defining first and second chambers, a heat transfer fluid for storing thermal energy, a valve that is positioned and adjustable to control a rate of discharge of heat transfer fluid from the first chamber to the second chamber, a heating element positioned in the first chamber to increase the temperature of heat transfer fluid stored therein, and a heat exchanger positioned in the second chamber and configured to receive pool / spa water. The heater is operable in at least a first mode where heat transfer fluid is retained in the first chamber and heated by the heating element, and a second mode where the heat transfer fluid is provided to the second chamber and thermal energy is extracted therefrom by pool / spa water flowing through the heat exchanger. A method of rapidly heating pool / spa water is also provided.

Description

THERMAL ENERGY STORAGE HEATERS FOR SWIMMING POOLS / SPAS AND METHODS OF OPERATING SAMESPECIFICATION BACKGROUNDRELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Application Serial No. 63 / 534.523 filed on August 24, 2023. the entire disclosure of which is expressly incorporated herein by reference.FIELD OF THE INVENTION

[0002] The present disclosure relates to the field of swimming pool / spa heaters. More particularly, the present disclosure relates to thermal energy storage heaters for swimming pools and spas, and methods of operating same.RELATED ART

[0003] Jurisdictions around the world and domestically, including California and other states, are engaging in de-carbonization efforts to reduce or eliminate carbon dioxide and other greenhouse gas emissions from buildings and household equipment. These efforts include the introduction of bills, and enactment of laws, that limit the future sale and usage of natural gas and / or liquid propane gas for swimming pool / spa heaters. In view of these efforts, the pool / spa industry7is turning to electrical heat sources for their pool / spa heating needs, including heat pumps and resistive element heaters.

[0004] However, current electrical heating sources for residential pools and spas do not generate as much thermal energy7as gas heaters due, at least in part, to limitations on the amount of electrical power available to residential homes. For example, heat pumps can generate up to ~ 140k Btu / hr while resistive elements can generate up to ~38k Btu / hr, which is significantly less than the most common natural gas and liquid propane gas heaters that are rated at 400k Btu / hr and 250k Btu / hr. As such, heat pumps generally cannot heat water to as high of a temperature as gas heaters. As a result, the maximum spa temperature achievable by a heat pump may not always meet the expectations of a spa owner.

[0005] Additionally, residential spas are located in nearly all geographies and used during all seasons. However, both ambient temperature and humidity can limit the heat capacity7ofheat pumps, but generally do not affect the heat capacity of gas heaters. For example, cold or low humidity conditions can reduce the capacity of a heat pump. As another example, during operation, heat pump pool / spa heaters can form frost on the evaporator coil in environments of low ambient temperature and high humidity, which can reduce the heating capacity of the heat pump. Accordingly, the foregoing effect of ambient temperature and humidity on heat pump heating capacity is a particular issue for residential spas that are located in colder climates and / or used in colder seasons.

[0006] Accordingly, the heaters, systems, and methods disclosed herein address the foregoing and other needs.SUMMARY

[0007] The present disclosure relates to thermal energy storage heaters for rapidly heating pool / spa water, and methods of operating same.

[0008] In accordance wi th aspects of the present disclosure a thermal energy storage heater for rapidly heating pool / spa water is provided. The thermal energy storage heater includes an insulated housing, a heat transfer fluid configured to store thermal energy, a valve, a heating element, and a heat exchanger. The insulated housing defines a first chamber and a second chamber. The valve is positioned between the first chamber and the second chamber, and is adjustable to control a rate of discharge of heat transfer fluid from the first chamber to the second chamber. The heating element is positioned in the first chamber and configured to increase the temperature of heat transfer fluid that is stored in the first chamber. The heat exchanger is positioned in the second chamber and configured to receive pool / spa water. The thermal energy- storage heater is operable in at least a first mode of operation and a second mode of operation. When operated in the first mode of operation, the valve is closed, the heat transfer fluid is stored in the first chamber, the heating element increases the temperature of the heat transfer fluid over a period of time, and the heat transfer fluid stores thermal energy-. When operated in the second mode of operation, the valve is at least partially open, the heat transfer fluid is discharged into the second chamber, pool / spa water flows through the heat exchanger, and thermal energy- is extracted from the heat transfer fluid discharged into the second chamber by the pool / spa water flowing through the heat exchanger.

[0009] In some aspects, the heating element can be an electrical heating element. In other aspects, the heat transfer fluid can be Therminol 62, Therminol 66, Therminol 68, or Therminol 72.

[0010] In still other aspects, the valve can be adjustable based on a temperature of the pool / spa water downstream of the heat exchanger to control the rate of discharge of heat transfer fluid from the first chamber into the second chamber.

[0011] In some aspects, the thermal energy- storage heater can include a mixing valve in fluidic communication with an outlet of the heat exchanger and a bypass line that permits pool / spa water to flow to the mixing valve without first flowing through the heat exchanger.In such aspects, the mixing valve can be controllable based on a temperature of the pool / spa water downstream of the heat exchanger to adjust the amount of water from the bypass line that is mixed with the water provided by the outlet of the heat exchanger to the mixing valve.

[0012] In other aspects, the thermal energy storage heater can include a return line that can be configured to return heat transfer fluid from the second chamber to the first chamber. In such aspects, the thermal energy storage heater can also include a pump provided in the return line. The pump can be configured to pump heat transfer fluid from the second chamber to the first chamber. Additionally, the pump can be controllable based on a temperature of the heat transfer fluid in the second chamber.

[0013] In still other aspects, the thermal energy' storage heater can include an inlet valve that can be configured to control the flow of pool / spa water to the heat exchanger.

[0014] In accordance with other aspects of the present disclosure a method of rapidly heating pool / spa water is provided. The method involves increasing the temperature of a heat transfer fluid, which is configured to store thermal energy and is stored in a first chamber of an insulated housing having a heating element positioned in the first chamber. The method further involves receiving a call for rapid heating, and causing pool / spa water to flow through a heat exchanger positioned in a second chamber of the insulated housing. The method also involves causing the heat transfer fluid in the first chamber to be discharged into a second chamber of the insulated housing, and extracting thermal energy from the heat transfer fluid discharged into the second chamber by the pool / spa water flowing through the heat exchanger.

[0015] In some aspects, the method can include confirming that pool / spa water is flowing through the heat exchanger prior to causing the heat transfer fluid in the first chamber to be discharged into the second chamber.

[0016] In some other aspects, the heating element can be an electrical heating element, while in other aspects the heat transfer fluid can be Therminol 62, Therminol 66, Therminol 68, or Therminol 72.

[0017] In still other aspects, the step of causing the heat transfer fluid in the first chamber to be discharged into the second chamber can include adjusting a valve positioned betweenthe first chamber and the second chamber to control a rate of discharge of the heat transfer fluid. In such aspects, the valve can be adjusted based on a temperature of the pool / spa water dow nstream of the heat exchanger to control the rate of discharge of heat transfer fluid from the first chamber into the second chamber.

[0018] In other aspects, the method can involve the step of adjusting a mixing valve in fluidic communication with an outlet of the heat exchanger and a bypass line that permits pool / spa water to flow to the mixing valve without first flowing through the heat exchanger based on a temperature of the pool / spa water downstream of the heat exchanger to adjust the amount of w ater from the bypass line that is mixed with the water provided by the outlet of the heat exchanger to the mixing valve.

[0019] In some aspects, the method can include the step of returning, w ith a pump, heat transfer fluid from the second chamber to the first chamber through a return line. In such aspects, the pump can be controlled based on a temperature of the heat transfer fluid in the second chamber.

[0020] In other aspects, the step of causing the pool / spa water to flow through the heat exchanger can include adjusting an inlet valve to control the flow of pool / spa water to the heat exchanger.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The foregoing features of the invention will be apparent from the following Detailed Description, taken in connection with the accompanying drawings, in which:

[0022] FIG. 1 is a diagram illustrating a system for controlling a pool / spa heat pump and associated thermal energy7storage heater, in accordance with the present invention;

[0023] FIG. 2 is a schematic diagram of a thermal energy storage heater of the present invention;

[0024] FIG. 3 is a flowchart illustrating exemplary processing steps carried out by the system of FIG. 1;

[0025] FIG. 4 is a flowchart illustrating exemplary7processing steps carried out by a heat transfer fluid valve metering subroutine of FIG. 3;

[0026] FIG. 5 is a flowchart illustrating exemplary processing steps carried out by a return pump control subroutine of FIG. 3;

[0027] FIG. 6 is a flowchart illustrating exemplary processing steps carried out by a mixing valve control subroutine of FIG. 3;

[0028] FIG. 7 is a schematic diagram of another embodiment of a thermal energy storage heater of the present disclosure;

[0029] FIG. 8 is a diagram illustrating the system of FIG. 1 with the pool / spa heat pump in fluidic communication with the thermal energy storage heater: and

[0030] FIG. 9 is an exemplary7graph illustrating heat transfer to pool water and change in pool water temperature versus time for the system of FIG. 8.DETAILED DESCRIPTION

[0031] The present disclosure relates to thermal energy storage heaters for swimming pools and spas, and systems and methods for controlling same, as described in detail below in connection with FIGS. 1-9.

[0032] FIG. 1 is a diagram illustrating a system for controlling a pool / spa heat pump and associated thermal energy storage heater in accordance with the present disclosure, indicated generally at 10. The system 10 includes a controller 12 for controlling operation of a pool / spa heat pump 16 and thermal energy storage heater 18, 118, and thermal energy storage heater control logic 14 executed by the controller 12 and selectively operating the thermal energy storage heater 18, 118. Specifically , as will be discussed in greater detail in connection with FIGS. 3-6. the control logic 14 controls operation of the thermal energy storage heater 18, 118 (and associated valves and pumps) in order to rapidly, effectively, and safely transfer stored thermal energy into pool / spa water.

[0033] The controller 12 could form part of the heat pump 16 (e.g., it could be implemented as a controller board having an associated processor and memory and positioned within the heat pump 16), or it could be part of a separate control device in communication with the heat pump 16 and thermal energy storage heater 18, 118, e.g., a pool / spa control system 19 that is in communication with the heat pump 16 and thermal energy storage heater 18, 118 (e.g., via a communications network 22). It should also be understood that the controller 12 could form part of the thermal energy storage heater 18 (e.g., it could be implemented as a controller board having an associated processor and memory and positioned within the thermal energy storage heater 18). The netw ork 22 could be a wired communications network (e.g., an RS-485 serial communications network, an Ethernet network, etc.), a wireless communications network (e.g., a WiFi network, a Bluetooth network, a cellular data network, a ZigBee netw ork, a mesh wireless network, etc.), the Internet, or some other ty pe of network. Further, the control logic 14 could be stored on and executed by a cloud-based pool / spa control system 20, which is in communication with, and remotely controls operation of. the heat pump 16 and the thermal energy^ storage heater 18, 118 via the netw ork 22. Optionally, one or more user devices (e.g., a cellular phone, a tablet computer, a laptop computer, etc.) could be in communication with one or more of the heat pump 16, the thermal energy storage heater 18, 118, the pool / spacontrol system 19, and the cloud-based pool / spa control system 20. The control logic 14 could be embodied as non-transitory, computer-readable instructions (e.g., firmware) stored on a computer-readable medium (e.g., a memory) of the controller 12 and executed by a processor (e.g., microprocessor, microcontroller, etc.) of the controller 12. The control logic 14 could be programmed in any suitable high- or low-level programming language, such as C, C++, C#, Python, assembly language, or any other suitable programming language.

[0034] FIG. 2 is a schematic diagram of a thermal energy storage heater 18 of the present disclosure. The thermal energy’ storage heater 18 can include an insulated housing 26, a heating element 28, a heat exchanger 30, a heat transfer fluid valve 32, an inlet valve 34, a mixing valve 36, a return pump 38, and a power source 40. The insulated housing 26 defines a thermal energy' storage chamber 42 and a thermal energy’ extraction chamber 44, which are separate chambers connected by a fluid line 46, e.g.. pipe, having the heat transfer fluid valve 32 positioned therein. The thermal energy storage chamber 42 is an insulated chamber that has a volumetric capacity (e.g., 55 gallons) and contains a heat transfer fluid 48, which can be a commercially available heat transfer fluid such as, Therminol 62, Therminol 66, Therminol 68, Therminol 72, etc. It should be understood that the volumetric capacity' of the thermal energy storage chamber 42 can be varied depending on the desired heating output. For example, the thermal energy storage chamber 42 can be sized to contain a sufficient volume of heat transfer fluid 48 capable of delivering 400k Btu in a short period of time. The thermal energy storage chamber 42 also contains the heating element 28, w hich is positioned in the thermal energy’ storage chamber 42 in contact with the heat transfer fluid 48 and receives electrical energy from the power source 40. The heating element 28 can be a resistive heating element, such as, a cartridge heater, a tubular heater, a band heater, a strip heater, an etched foil heater, a ceramic heater, etc., and can include one or more heating elements. In particular, the heating element 28 can be configured to operate on 230 VAC and 50 Amps service, which is a common maximum standard residential electrical circuit, such as a 38k Btu / hr (11 kW) resistive heating element. For example, the heating element 28 can be a CSPAXI11 heating element by Hayward Industries, Inc.

[0035] The heating element 28 generates heat, for example, 38k Btu / hr, that is transferred to the heat transfer fluid 48 over time and stored by the heat transfer fluid 48 contained in the thermal energy' storage chamber 42. That is, the heating element 28 gradually heats the heat transfer fluid 48 to a high temperature (e.g., 500° F) over a period of time, e.g., twenty -four hours. The heating element 28 can be shut off once the maximum temperature of the heat transfer fluid 48 is reached, and can be intermittently turned back on to replace any heat lost so as to maintain the heat transfer fluid 48 at the maximum temperature. The heat transfer fluid 48 can store the equivalent of, for example, 300k-400k Btu of energy (or other amounts depending on the heat transfer fluid being utilized), which, as described in detail herein, can be rapidly transferred to pool / spa water flowing through the heat exchanger 30 when there is a call for rapid heating. Accordingly, the heat transfer fluid 48 can be maintained at a set or maximum temperature, or thermal capacity', at all times so that it can be discharged into the thermal energy’ extraction chamber 44, e.g.. by way of the fluid line 46 and heat transfer fluid valve 46, as soon as a call for rapid heating is received.

[0036] The heat exchanger 30 is positioned within the thermal energy extraction chamber 44, and includes an inlet 50 and an outlet 52. The heat exchanger 30 can be any heat exchanger commonly used in the art that is configured to be exposed to the heat transfer fluid, e.g., a tube-and-fin heat exchanger, a microchannel heat exchanger, etc. The inlet 50 is configured to receive pool / spa water from the inlet valve 34, which is positioned between an inlet pipe 54 and the heat exchanger 30, and controls the flow of water to the heat exchanger 30. When the inlet valve 34 is closed, water is prevented from flowing to the heat exchanger 30 and instead flows through a bypass line 56 (e.g., pipe, tube, etc.) that transfers the water to the mixing valve 36 without passing through the thermal energy extraction chamber 44. When the inlet valve 34 is open, water is allowed to flow into the thermal energy extraction chamber 44, into and through the heat exchanger 30 positioned within the thermal energy extraction chamber 44, and out from the thermal energy extraction chamber 44 to the mixing valve 36. Water flowing through the heat exchanger 30 can extract thermal energy' from heat transfer fluid 48 that is transferred / discharged from the thermal energy' storage chamber 42 to the thermal energy extraction chamber 44 when the heat transfer fluid valve 32 is open, which causes the water flowing through the heat exchanger 30 to rapidly increase in temperature.

[0037] The inlet pipe 54 can be in fluidic communication with the heat pump 16, or another heater of the pool / spa system, such that it receives pre-conditioned, e.g., pre-heated, water therefrom. Alternatively, the inlet pipe 54 can be in fluidic communication with a separate branch of the pool / spa plumbing system that bypasses the heat pump 1 , such that the water provided to thermal energy storage heater 18 is not pre-conditioned, e.g.. pre-heated. Thus,the thermal energy storage heater 18 can be used to supplement the heat pump 16 (or other heater) or as an independent heating source.

[0038] The insulated housing 26 additionally includes a recirculation port 58 that is positioned in the thermal energy extraction chamber 44 and in fluidic communication with a return line 60 (e.g., pipe, tube, etc.) The return pump 38 is positioned within the return line 60 and configured to pump cool heat transfer fluid 48 out from the thermal energy extraction chamber 44 and return the cool heat transfer fluid 48 to the thermal energy storage chamber 42 where it can be reheated by the heating element 28.

[0039] The thermal energy storage heater 18 functions in at least two main modes of operation: a rest mode and a rapid heat mode. During the rest mode, the heat transfer fluid 48 is retained in the thermal energy storage chamber 42 and the heating element 28 is operated to gradually heat the heat transfer fluid 48 to a high temperature (e.g.. 500° F) over a period of time, e.g., twenty-four hours. The heat transfer fluid 48 maintains the high temperature and thus stores the thermal energy, e.g., the equivalent of 300k-400k Btu of energy. The storage of thermal energy by the heat transfer fluid 48 is assisted by the insulated housing 26, which includes sufficient insulation to efficiently retain the heat within the thermal energy storage chamber 42. However, some thermal energy loss can occur over time. Accordingly, the heating element 28 can be intermittently turned back on to replace any heat lost so as to maintain the heat transfer fluid 48 at the maximum temperature.

[0040] The thermal energy storage heater 18 operates in the rapid heat mode once a call for rapid heat is made, which can be based on a user selection and / or a consideration of different factors. For example, a user can select a mode of operation, e.g., spa mode, and, in response, the system 10, e.g., the controller 12, can call for rapid heat from the thermal energy storage heater 18. Additionally and / or alternatively, the controller 12 can receive a user’s selection of a mode of operation, e.g., spa mode, and consider other factors, e.g., current water temperature, target water temperature, time to heat to target water temperature, etc., before issuing a call for rapid heat. That is, the controller 12 can determine whether it is necessary to request rapid heating from the thermal energy storage heater 18 based on various considerations.

[0041] Upon receiving a call for rapid heat, the inlet valve 34 is opened and the mixing valve 36 is adjusted to allow water exiting the heat exchanger 30 to pass there through andto the pool / spa. In this regard, the mixing valve 36 can be adjusted to allow a mix of water from the heat exchanger 30 and the bypass line 56 to pass there through, or to allow only water from the heat exchanger 30 to pass there through. The control logic 14 can then confirm that water is flowing through the heat exchanger 30 before opening the heat transfer fluid valve 32. For example, this can be based on a flow meter, pressure meter, or other sensor placed in the outlet 52 of the heat exchanger 30. This flow confirmation is made to ensure that water is flowing through the heat exchanger 30 prior to opening the heat transfer fluid valve 32 and dispensing high-temperature heat transfer fluid 48 into the thermal energy extraction chamber 44 to prevent any pool / spa water from boiling, which could occur if the pool / spa water is provided to the heat exchanger 30 after the heat exchanger 30 has been exposed to the high-temperature heat transfer fluid 48 for a period of time.

[0042] Upon confirmation that water is flowing through the heat exchanger 30, the heat transfer fluid valve 32 is opened an initial amount to allow the high-temperature heat transfer fluid 48 stored in the thermal energy storage chamber 42 to flow into the thermal energy extraction chamber 44 via the fluid line 46 and heat transfer fluid valve 32. For example, the heat transfer fluid valve 32 can be initially opened either completely or partially. The high-temperature heat transfer fluid 48 in the thermal energy extraction chamber 44 rapidly transfers the heat stored thereby to the pool / spa water flowing through the heat exchanger 30 causing the pool / spa water to quickly increase in temperature.

[0043] Once the fluid valve 32 is opened an initial amount, it can thereafter be adjusted, e.g., metered, based on the temperature of water exiting the heat exchanger 30 and / or the temperature of water being provided to the pool / spa, e.g., at a point dow nstream of the heat exchanger 30 and / or the mixing valve 36, to prevent the pool / spa w ater from reaching an upper temperature limit, which can be user defined or based on agency safety limits. For example, the upper temperature limit can be 140° F or slightly less than 140° F to provide a comfortable buffer. Thus, the fluid valve 32 can be controlled to maintain a safe temperature of outlet w ater being returned to the pool / spa. Additionally, the mixing valve 36 can be controlled to adjust the amount of pool / spa water from the bypass line 56 that is mixed with the pool / spa water exiting the heat exchanger 30 in order to increase or decrease the temperature of the w ater being returned back to the pool / spa. In particular, since the pool / spa water flowing through the bypass line 56 will have a lower temperature than the pool / spa water exiting the heat exchanger 30, the mixing valve 36 can be adjusted to (a) reduce theamount of water from the bypass line 56 that is mixed with the water exiting the heat exchanger 30 to increase the temperature of the water being returned to the pool / spa, or (b) increase the amount of water from the bypass line 56 that is mixed with the water exiting the heat exchanger 30 to decrease the temperature of the water being returned to the pool / spa. Accordingly, the mixing valve 36 can be controlled / adjusted to maintain the outlet water temperature within an acceptable range.

[0044] The heat transfer fluid 48 is retained within the thermal energy extraction chamber 44, and the insulated housing 26 is sufficiently insulated to efficiently retain the heat within the thermal energy extraction chamber 44. Accordingly, a majority of the heat stored by the heat transfer fluid 48 is transferred to the pool / spa water flowing through the heat exchanger 30. Thus, the heat transfer fluid 48 within the thermal energy' extraction chamber 44 will continue to cool as pool / spa water is circulated through the heat exchanger 30 and energy is transferred thereto via the heat exchanger 30. After a period of time, the heat transfer fluid 48 can cool below a useful level at which point the return pump 38 can be activated to pump cooled heat transfer fluid 48 from the thermal energy extraction chamber 44 to the thermal energy storage chamber 42 by w ay of the return line 60, such that the cooled fluid 48 can be reheated in the thermal energy’ storage chamber 42.

[0045] FIGS. 3-6 are flowcharts illustrating exemplary' steps carried out by the system 10 of FIG. 1. Specifically, FIGS. 3-6 illustrate exemplary steps carried out by the control logic 14 to control the thermal energy storage heater 18 in accordance with the present disclosure. Beginning in step 62 of FIG. 3, the controller 12 receives a call for rapid heating. This can be, for example, based on a user selecting a mode of operation, e.g., spa mode, and / or based on a consideration of other factors, e.g., current water temperature, target water temperature, time to heat to target water temperature, etc. In step 64. the inlet valve 34 and the mixing valve 36 are opened / adjusted to allow water to flow through the heat exchanger 30 and meter the amount of w ater flowing through the bypass line 56. For example, the mixing valve 36 can be initially adjusted in step 64 so that all of the water provided to the thermal energy storage heater 18 flows through the heat exchanger 30 and no water flow s through the bypass line 56.

[0046] In step 66, a determination is made as to whether w ater is flowing through the heat exchanger 30. This can be made, for example, based on the reading of a flow sensor,pressure sensor, or other sensor in the heat exchanger 30 or at the outlet 52 thereof. The determination made in step 66 ensures that pool / spa water is flowing through the heat exchanger 30 before the heat transfer fluid 48 is dispensed into the thermal energy extraction chamber 44 to prevent any pool / spa water from boiling, which could occur if the pool / spa water is provided to the heat exchanger 30 after the heat exchanger 30 has been exposed to high-temperature heat transfer fluid 48 for a period of time. If a negative determination is made in step 66, e.g., water is not flowing through the heat exchanger 30, then the process proceeds to step 67 and a shutdown procedure is performed, as this could be indicative of an error, e.g.. a faulty inlet valve 34 and / or mixing valve 36. The shutdown procedure can include, for example, closing the heat transfer fluid valve 32, closing the inlet valve 34, adjusting the mixing valve 36 to permit pool / spa water provided by the bypass line 56 to flow through the mixing valve 36, and completely returning all heat transfer fluid 48 from the thermal energy' extraction chamber 44 to the thermal energy storage chamber 42. If a positive determination is made in step 66, then in step 68 the heat transfer fluid valve 32 is opened. Next, the process proceeds to and performs a heat transfer fluid valve 32 metering sub-routine in step 70, a return pump 38 control sub-routine in step 72, and a mixing valve 36 control sub-routine in step 74, which can be performed in parallel, as shown, or in series.

[0047] The heat transfer fluid valve 32 metering sub-routine 70 is shown in greater detail in FIG. 4. The heat transfer fluid valve 32 metering sub-routine 70 ensures that the outlet water temperature, e.g., the temperature of the water being returned to the pool / spa, is less than an upper temperature limit, which can be user defined or based on agency safety limits. For example, the upper temperature limit can 140° F or slightly less than 140° F to provide a comfortable buffer. It should be understood that the steps shown in FIG. 4 are merely exemplary', and additional and / or alternative steps can be performed to effectively meter the heat transfer fluid valve 32 and ensure that the temperature of water being returned to the pool / spa does not exceed an upper limit.

[0048] In step 76, a determination is made as to whether the outlet yvater temperature, e.g., the temperature of the water being returned to the pool / spa, has exceed an upper temperature limit, e.g.. 140° F. If a positive determination is made, then step 78 occurs. In step 78, a determination is made as to whether the heat transfer fluid valve 32 is completely closed. If a negative determination is made in step 78, e.g., the heat transfer fluid valve 32 is not completely closed, then the process proceeds to step 80. In step 80, the heat transfer fluidvalve 32 is closed by a predetermined amount, e.g., an angular value, to reduce the amount of heat transfer fluid 48 being transferred from the thermal energy storage chamber 42 to the thermal energy extraction chamber 44 and thus reduce the amount of heat being transferred to the pool / spa water flowing through the heat exchanger 30. The process then proceeds back to step 76 in which it is again determined if the outlet water temperature is greater than an upper temperature limit. Turning back to step 78, if a positive determination is made, e.g., the heat transfer fluid valve 32 is completely closed, then step 82 occurs in which the mixing valve 36 is adjusted to allow pool / spa water in the bypass line 56 to mix with the pool / spa water exiting the heat exchanger 30 in order to reduce the temperature of the water being returned back to the pool / spa and bring it within an acceptable range. Accordingly, step 82 essentially functions as a back-up safety measure in case the heat transfer fluid valve 32 is completely closed and the outlet water temperature is still greater than the upper temperature limit. Next, the process returns back to step 76 in which it is again determined if the outlet water temperature is greater than an upper temperature limit. If a negative determination is made in step 76, then the heat transfer fluid valve 32 metering sub-routine 70 is exited and step 84 (FIG. 3) is performed, which is discussed in greater detail below.

[0049] The return pump 38 control sub-routine 72. which occurs after the opening of the heat transfer fluid valve in step 68, is shown in greater detail in FIG. 5. The return pump 38 control sub-routine 72 controls operation of the return pump 38 to return heat transfer fluid 48 from the thermal energy extraction chamber 44 to the thermal energy' storage chamber 42 once the fluid 48 has cooled below a useful temperature level so that the fluid 48 can be reheated in the thermal energy storage chamber 42. It should be understood that the steps shown in FIG. 5 are merely exemplary, and additional and / or alternative steps can be performed to effectively control the return pump 38.

[0050] In step 86, a determination is made as to whether the temperature of the heat transfer fluid 48 in the thermal energy extraction chamber 44 is less than a minimum temperature. If a positive determination is made in step 86, then in step 88 it is determined if the return pump 38 is already activated. If a negative determination is made in step 88, e.g., the return pump 38 is not already activated, then the process 72 proceeds to step 90 in which the return pump 38 is activated. After the return pump 38 is activated in step 90, then the return pump 38 control sub-routine 72 is exited and step 84 (FIG. 3) is performed, which is discussed in greater detail below. Additionally, if a positive determination is made in step88, e.g., the return pump 38 is already activated, then the return pump 38 control sub-routine 72 is exited and step 84 (FIG. 3) is performed. Turning back to step 86, if a negative determination is made, e.g., the temperature of the heat transfer fluid 48 within the thermal energy extraction chamber 44 is greater than the minimum temperature, then the process proceeds to step 92. In step 92, it is determined if the return pump 38 is presently activated. If a positive determination is made in step 92, e.g., the return pump 38 is presently activated, then the process 72 proceeds to step 94 in which the return pump 38 is deactivated, as there is no longer a need to recirculate the heat transfer fluid 48. After the return pump 38 is deactivated in step 94, then the return pump 38 control sub-routine 72 is exited and step 84 (FIG. 3) is performed. Additionally, if a negative determination is made in step 92, e.g.. the return pump 38 is not presently activated, then the return pump 38 control sub-routine 72 is exited and step 84 (FIG. 3) is performed.

[0051] The mixing valve 36 control sub-routine 74, which occurs after the opening of the heat transfer fluid valve in step 68, is shown in greater detail in FIG. 6. The mixing valve 36 control sub-routine 74 controls operation of the mixing valve 36 to adjust the outlet water temperature and maintain the outlet water temperature within a desired range. It should be understood that the steps shown in FIG. 6 are merely exemplary, and additional and / or alternative steps can be performed to effectively control the mixing valve 36 and ensure that the temperature of w ater being returned to the pool / spa is maintained within a desired range.

[0052] In step 96, a determination is made as to whether the outlet water temperature, e.g., the temperature of the water being returned to the pool / spa, has exceed an upper temperature limit, e.g., 104° F, which can be a user defined desired temperature. If a positive determination is made, then step 98 occurs. In step 98, the mixing valve 36 is adjusted to increase the amount of pool / spa water from the bypass line 56 that is mixed with the pool / spa water exiting the heat exchanger 30 in order to decrease the temperature of the water being returned back to the pool / spa since the pool / spa water flowing through the bypass line 56 will have a low er temperature than the pool / spa water exiting the heat exchanger 30. This adjustment is made to lower the outlet water temperature to within an acceptable range. After the mixing valve 36 is adjusted in step 98, then the mixing valve 36 control sub-routine 74 is exited and step 84 (FIG. 3) is performed. If a negative determination is made in step 96, e.g., the outlet water temperature is not greater than an upper temperature limit, then in step 100 a determination is made as to whether the outlet water temperature is less than alower temperature limit. If a positive determination is made, then step 102 occurs. In step 102, the mixing valve 36 is adjusted to reduce the amount of pool / spa water from the bypass line 56 that is mixed with the pool / spa water exiting the heat exchanger 30 in order to increase the temperature of the water being returned back to the pool / spa. This adjustment is made to increase the outlet water temperature to within an acceptable range. After the mixing valve 36 is adjusted in step 102, then the mixing valve 36 control sub-routine 74 is exited and step 84 (FIG. 3) is performed. If a negative determination is made in step 100, e.g., the outlet water temperature is not less than a lower temperature limit, then the mixing valve 36 control sub-routine 74 is exited and step 84 (FIG. 3) is performed.

[0053] In step 84, a determination is made as to whether rapid heating is still required. This determination can be based on one or more of a number of factors including, but not limited to, the currently selected mode of operation (e.g., has spa mode been turned off), the currently selected heating mode (e.g.. has a rapid heat button been deactivated), the current pool / spa water temperature, the capacity of the heat pump 16 (e g., can the heat pump 16 maintain the current water temperature at the desired temperature), etc. If a positive determination is made in step 84, then the process returns to and performs the heat transfer fluid valve 32 metering sub-routine in step 70. the return pump 38 control sub-routine in step 72, and the mixing valve 36 control sub-routine in step 74. Accordingly, sub-routines 70, 72, and 74 can be continuously performed so long as rapid heating is still required. If a negative determination is made in step 84, then the process proceeds to step 67 and the shutdown procedure is performed, as rapid heating is no longer needed. The shutdown procedure can include, for example, closing the heat transfer fluid valve 32, closing the inlet valve 34, adjusting the mixing valve 36 to permit pool / spa water provided by the bypass line 56 to flow through the mixing valve 36, and completely returning all heat transfer fluid 48 from the thermal energy extraction chamber 44 to the thermal energy storage chamber 42 for reheating.

[0054] FIG. 7 is a schematic diagram of another embodiment of a thermal energy storage heater 118 of the present disclosure. The thermal energy storage heater 118 of FIG. 7 is similar in principle to the thermal energy storage heater 18 of FIG. 2 in that it uses a heat transfer fluid 148 to store thermal energy and rapidly transfer the stored thermal energy to pool / spa water flowing through a heat exchanger 130; however, the thermal energy storage heater 118 of FIG. 7 utilizes a heat transfer fluid 148 that operates in the vapor phase, asopposed to liquid phase, and uses a gravity feed system to return the heat transfer fluid 148 back to a thermal energy storage chamber 142 once it has cooled and returned to a liquid phase. Accordingly, similar elements are generally denoted by the same reference numeral, but incremented by 100.

[0055] The thermal energy storage heater 118 can include an insulated housing 126, a heating element 128, a heat exchanger 130, a heat transfer fluid valve 132, an inlet valve 134, a mixing valve 136, a return valve 138. and a power source 140. The insulated housing 126 defines a thermal energy storage chamber 142 and a thermal energy extraction chamber 144, which are separate chambers connected by a first fluid line 146a, e.g., a pipe, having the heat transfer fluid valve 132 positioned therein, and a second fluid line 146b, e.g., a pipe, having the return valve 138 positioned therein. The thermal energy storage chamber 142 is an insulated chamber that has a volumetric capacity (e.g., 55 gallons) and contains the heat transfer fluid 148. which can be a commercially available heat transfer fluid, such as. for example, Therminol VP-1, Therminol VP-3, Therminol LT, etc. It should be understood that the volumetric capacity of the thermal energy storage chamber 142 can be varied depending on the desired heating output. For example, the thermal energy storage chamber 142 can be sized to contain a sufficient volume of heat transfer fluid 148 capable of delivering 400k Btu in a short period of time. The thermal energy storage chamber 142 also contains the heating element 128, which is positioned in the thermal energy storage chamber 142 in contact with the heat transfer fluid 148 and receives electrical energy from the power source 140. The heating element 128 can be a resistive heating element, such as. a cartridge heater, a tubular heater, a band heater, a strip heater, an etched foil heater, a ceramic heater, etc., and can include one or more heating elements. In particular, the heating element 128 can be configured to operate on 230 VAC and 50 Amps sendee, which is a common maximum standard residential electrical circuit, such as a 38k Btu / hr (11 kW) resistive heating element. For example, the heating element 129 can be a CSPAXI11 heating element by Hayward Industries, Inc.

[0056] The heating element 128 generates heat, for example, 38k Btu / hr, that is transferred to the heat transfer fluid 148 over time, which causes the heat transfer fluid 148 to boil and is stored by the heat transfer fluid 148 contained in the thermal energy storage chamber 142. That is, the heating element 128 gradually heats the heat transfer fluid 148 to a high temperature (e.g., 500° F) over a period of time, e.g., twenty-four hours, and boils the heattransfer fluid 148 so that it changes phase to vapor. The heating element 128 can be shut off once the maximum temperature of the heat transfer fluid 148 is reached, and can be intermittently turned back on to replace any heat lost so as to maintain the heat transfer fluid 148 at the maximum temperature. The heat transfer fluid 148 can store the equivalent of, for example. 300k-400k Btu of energy (or other amounts depending on the heat transfer fluid being utilized), which can be rapidly transferred to pool / spa water flowing through the heat exchanger 130 when there is a call for rapid heating. Accordingly, the heat transfer fluid 148 can be maintained at a set or maximum temperature, or thermal capacity, at all times so that it can be discharged into the thermal energy’ extraction chamber 144. e.g., by way of the first fluid line 146a and heat transfer fluid valve 146, as soon as a call for rapid heating is received.

[0057] The heat exchanger 130 is positioned within the thermal energy extraction chamber 144, and includes an inlet 150 and an outlet 152. The heat exchanger 130 can be any heat exchanger commonly used in the art that is configured to be exposed to the heat transfer fluid, e.g., a tube-and-fin heat exchanger, a microchannel heat exchanger, etc. The inlet 150 is configured to receive pool / spa water from the inlet valve 134, which is positioned between an inlet pipe 154 and the heat exchanger 130. and controls the flow of water to the heat exchanger 130. When the inlet valve 134 is closed, water is prevented from flowing to the heat exchanger f 30 and instead flows through a bypass line 156 that transfers the water to the mixing valve 136 without passing through the thermal energy extraction chamber 144. When the inlet valve 134 is open, water is allowed to flow into the thermal energy’ extraction chamber 144, into and through the heat exchanger 130 positioned within the thermal energy extraction chamber 144, and out from the thermal energy' extraction chamber 144 to the mixing valve 136. Water flowing through the heat exchanger 130 can extract thermal energy’ from heat transfer fluid 48 that is transferred / discharged from the thermal energy storage chamber 142 to the thermal energy’ extraction chamber 144 when the heat transfer fluid valve 132 is open, which causes the water flowing through the heat exchanger 130 to rapidly increase in temperature.

[0058] The inlet pipe 154 can be in fluidic communication with the heat pump 16, or another heater of the pool / spa system, such that it receives pre-conditioned, e.g., pre-heated, water therefrom. Alternatively, the inlet pipe 154 can be in fluidic communication with a separate branch of the pool / spa plumbing system that bypasses the heat pump 16, such thatthe water provided to thermal energy- storage heater 118 is not pre-conditioned, e.g., preheated. Thus, the thermal energy storage heater 118 can be used to supplement the heat pump 16 (or other heater) or as an independent heating source.

[0059] The thermal energy storage heater 118 functions in at least two main modes of operation: a rest mode and a rapid heat mode. During the rest mode, the heat transfer fluid 148 is retained in the thermal energy- storage chamber 142 and the heating element 128 is operated to gradually heat the heat transfer fluid 148 to a high temperature (e.g., 500° F) over a period of time, e.g.. twenty -four hours. This heating causes the heat transfer fluid 148 to boil and change phase from liquid to vapor. The vapor phase heat transfer fluid 148 is retained in the thermal energy storage chamber 142, and maintains the high temperature and thus stores the thermal energy-, e.g., the equivalent of 300k-400k Btu of energy-. The storage of thermal energy by the heat transfer fluid 148 is assisted by the insulated housing 126, which includes sufficient insulation to efficiently retain the heat within the thermal energy storage chamber 142. However, some thermal energy^ loss can occur over time. Accordingly, the heating element 128 can be intermittently turned back on to replace any heat lost so as to maintain the heat transfer fluid 148 at the maximum temperature. Additionally, an interior upper wall 158 of the thermal energy storage chamber 142 can be angled to force the vapor phase heat transfer fluid 148 toward the heat transfer fluid valve 132.

[0060] The thermal energy storage heater 118 operates in the rapid heat mode once a call for rapid heat is made, which can be based on a user selection and / or a consideration of different factors, as described in connection with the thermal energy- storage heater 18 shown in FIG. 2 which description is equally applicable hereto. Upon receiving a call for rapid heat, the inlet valve 134 is opened and the mixing valve 136 is adjusted to allow water exiting the heat exchanger 130 to pass there through and to the pool / spa. In this regard, the mixing valve 136 can be adjusted to allow a mix of water from the heat exchanger 130 and the by-pass line 156 to pass there through, or to allow only water from the heat exchanger 130 to pass there through. The control logic 14 can then confirm that water is flowing through the heat exchanger 130 before opening the heat transfer fluid valve 132, as described in connection with the thermal energy storage heater 18 shown in FIG. 2 which description is equally applicable hereto.

[0061] Upon confirmation that water is flowing through the heat exchanger 130, the heat transfer fluid valve 132 is opened an initial amount to allow the high-temperature heat transfer fluid 148 stored in the thermal energy' storage chamber 142 to flow into the thermal energy extraction chamber 144 via the first fluid line 146a and heat transfer fluid valve 132. For example, the heat transfer fluid valve 132 can be initially opened either completely or partially. The high-temperature heat transfer fluid 148 in the thermal energy extraction chamber 144 rapidly transfers the heat stored thereby to the pool / spa water flowing through the heat exchanger 130 causing the pool / spa water to quickly increase in temperature.

[0062] Additionally, it should be understood that the fluid valve 132 and the mixing valve 136 can be metered and / or adjusted during operation of the thermal energy7storage heater 118 in similar fashion to the fluid valve 32 and mixing valve 36 shown and described in connection w ith FIG. 2, which description is equally applicable to the thermal energy storage heater 118, fluid valve 132, and mixing valve 136. Accordingly, the fluid valve 132 and the mixing valve 136 can be controlled to prevent the pool / spa water from reaching an upper temperature limit and / or to maintain the outlet water temperature w ithin an acceptable range.

[0063] The heat transfer fluid 148 is retained within the thermal energy extraction chamber 144 and the insulated housing 126 is sufficiently insulated to efficiently retain the heat within the thermal energy' extraction chamber 144. Accordingly, a majority7of the heat stored by the heat transfer fluid 148 is transferred to the pool / spa w ater flowing through the heat exchanger 130. Thus, the heat transfer fluid 148 within the thermal energy7extraction chamber 144 will continue to cool as pool / spa w ater is circulated through the heat exchanger 130 and energy is transferred thereto via the heat exchanger 130. After a period of time, the heat transfer fluid 148 can cool below7the condensation point and will gather adjacent the return valve 138. In this regard, a bottom wall 160 of the thermal energy extraction chamber 144 can be angled downward toward the return valve 138 to cause condensed heat transfer fluid 148 to flow7toward the return valve 138 and gather adjacent thereto. In some embodiments, a small reservoir can be provided for collecting the condensed heat transfer fluid 148. Once a sufficient amount of heat transfer fluid 148 has condensed, the return valve 138 can be opened to allow the condensed heat transfer fluid 148 to return to the thermal energy storage chamber 142 via gravity feed so that the cooled fluid 148 can be reheated in the thermal energy7storage chamber 142. Alternatively, the return valve 138 canbe in an always open state so that the heat transfer fluid 148 can be continuously returned to the thermal energy storage chamber 142 once condensed.

[0064] Accordingly, while gas pool heaters utilize a flame having a temperature of -3500° F to heat residential pool / spa water, the thermal energy storage heaters 18, 118 of the present disclosure utilize a lower temperature heat transfer fluid 48, 148 to achieve the same outlet water temperature result for a period of time. Thus, the thermal energy storage heaters 18, 118 can provide a heat transfer performance similar to that of a gas heater as they are capable of delivering ~400k Btu to pool / spa water in a short period of time, but without using hydrocarbon based gas, e.g., natural gas or liquid propane, and without the ambient temperature / humidity capacity limitations of heat pumps. Additionally, the thermal energy storage heaters 18, 118 provide increased heating capacity compared to pool / spa heat pumps alone, which have a heating capacity of 140k Btu / hr, electrically resistive heating elements alone, which have a heating capacity of 38k Btu / hr, and solar heaters, which have limited heating capacities that are affected by solar availability.

[0065] Moreover, it should be understood that alternative materials could be used in place of the heat transfer fluid 48, 148 used in the thermal energy storage heaters 18, 118 described herein. For example, molten salt, rock, metal, water, etc., could be utilized.

[0066] It should also be understood that the thermal energy storage heaters 18, 118 described herein can be used in combination with, or independent of, a heat pump 16. That is, the thermal energy storage heaters 18, 1 18 could be used as the sole source of heat for a spa or could be used in conjunction with a second heat source such as the heat pump 16.

[0067] In this regard, FIG. 8 is a diagram illustrating the system 10 of FIG. 1 with the pool / spa heat pump 16 in fluidic communication with the thermal energy storage heater 18, 118, e.g., with a pipe 162, such that the pool / spa water can flow from the thermal energy storage heater 18, 118 to the heat pump 16 for additional and / or supplemental heating. For example, in this configuration, the thermal energy storage heater 18, 118 can be utilized to rapidly heat the pool / spa water at the start of a temperature request (e.g., upon receiving a call for heat that requires a large change in temperature), and the heat pump 16 can be used thereafter to maintain the water temperature, which generally requires less heat since there is a smaller temperature difference. As such, only one heat source will be active at a time, e.g., to adhere to a power budget, with the thermal energy’ storage heater 18, 118 being usedfor rapid heating and the heat pump 16 being used for maintenance heating. Additionally, whenever the heat pump 1 is off, e.g., due to hysteresis, the thermal energy storage heater 18, 118 can actively reheat the thermal fluid 48 in the thermal energy storage chamber 42. However, it should be understood that the thermal energy storage heater 18, 118 can actively reheat the thermal fluid 48 in the thermal energy storage chamber 42 while the heat pump 16 is actively heating if so desired by a user. It should also be understood that one or more alternative types of heaters can be used in place of the heat pump 16. For example, the heat pump 16 can be replaced by, or supplemented with, a gas heater, a solar heater, an electric heater, etc., such that these alternative heaters can be used in combination with the thermal energy storage heater 18, 118.

[0068] FIG. 9 is an exemplary' graph 200 illustrating heat transfer to pool water and change in pool water temperature versus time for the system 10 of FIG. 8. Line 202 represents the heat transfer to pool water by the thermal energy storage heater 18, 118 during a first time period T1 and lines 204 represent the subsequent heat transfer to pool water by the heat pump 16 (or alternative heater) during a second time period T2. Line 206 represents the pool water temperature showing the change thereof due to the transfer of heat to the pool water by the thermal energy storage heater 18, 118 during the first time period T 1 and by the heat pump 16 (or alternative heater) during the second time period T2. As is evident from the graph 200 illustrated in FIG. 9, the thermal energy storage heater 18, 118 can be utilized to rapidly heat the pool / spa water during the first time period T1 , which can start upon receipt of a call for heat that requires a large change in temperature (AT), and the heat pump 16 can be used thereafter to maintain the water temperature during the second time period T2, which generally requires less heat and smaller changes in temperature (At).

[0069] Having thus described the system and method in detail, it is to be understood that the foregoing description is not intended to limit the spirit or scope thereof. It will be understood that the embodiments of the present disclosure described herein are merely exemplary' and that a person skilled in the art may make any variations and modification without departing from the spirit and scope of the disclosure. All such variations and modifications, including those discussed above, are intended to be included within the scope of the disclosure.

Claims

CLAIMSWhat is claimed is:

1. A thermal energy storage heater for rapidly heating pool / spa water, comprising: an insulated housing defining a first chamber and a second chamber; a heat transfer fluid configured to store thermal energy; a valve positioned between the first chamber and the second chamber, the valve being adjustable to control a rate of discharge of heat transfer fluid from the first chamber to the second chamber; a heating element positioned in the first chamber and configured to increase the temperature of the heat transfer fluid when the heat transfer fluid is stored in the first chamber; and a heat exchanger positioned in the second chamber and configured to receive pool / spa water, wherein the thermal energy storage heater is operable in at least (a) a first mode of operation in which the valve is closed, the heat transfer fluid is stored in the first chamber, the heating element increases the temperature of the heat transfer fluid over a period of time, and the heat transfer fluid stores thermal energy , and (2) a second mode of operation in which the valve is at least partially open, the heat transfer fluid is discharged into the second chamber, pool / spa water flows through the heat exchanger, and thermal energy is extracted from the heat transfer fluid discharged into the second chamber by the pool / spa water flowing through the heat exchanger.

2. The thermal energy storage heater of Claim 1, wherein the heating element is an electrical heating element.

3. The thermal energy storage heater of Claim 1 , wherein the heat transfer fluid is Therminol 62, Therminol 66, Therminol 68, or Therminol 72.

4. The thermal energy' storage heater of Claim 1, wherein the valve is adjustable based on a temperature of the pool / spa water downstream of the heat exchanger to control the rate of discharge of heat transfer fluid from the first chamber into the second chamber.

5. The thermal energy storage heater of Claim 1, comprising a mixing valve in fluidic communication with an outlet of the heat exchanger and a bypass line that permits pool / spa water to flow to the mixing valve without first flowing through the heat exchanger.

6. The thermal energy storage heater of Claim 5, wherein the mixing valve is controllable based on a temperature of the pool / spa water downstream of the heatexchanger to adjust the amount of water from the bypass line that is mixed with the water provided by the outlet of the heat exchanger to the mixing valve.

7. The thermal energy storage heater of Claim 1, comprising a return line configured to return heat transfer fluid from the second chamber to the first chamber.

8. The thermal energy storage heater of Claim 7, comprising a pump provided in the return line, the pump being configured to pump heat transfer fluid from the second chamber to the first chamber.

9. The thermal energy storage heater of Claim 8, wherein the pump is controllable based on a temperature of the heat transfer fluid in the second chamber.

10. The thermal energy storage heater of Claim 1, comprising an inlet valve configured to control the flow of pool / spa water to the heat exchanger.

11. A method of rapidly heating pool / spa water, comprising: increasing the temperature of a heat transfer fluid stored in a first chamber of an insulated housing with a heating element positioned in the first chamber, the heat transfer fluid being configured to store thermal energy; receiving a call for rapid heating; causing pool / spa water to flow through a heat exchanger positioned in a second chamber of the insulated housing; causing the heat transfer fluid in the first chamber to be discharged into a second chamber of the insulated housing; and extracting thermal energy from the heat transfer fluid discharged into the second chamber by the pool / spa water flowing through the heat exchanger.

12. The method of Claim 11, comprising the step of: confirming that pool / spa water is flowing through the heat exchanger prior to causing the heat transfer fluid in the first chamber to be discharged into the second chamber.

13. The method of Claim 11, wherein the heating element is an electrical heating element.

14. The method of Claim 11, wherein the heat transfer fluid is Therminol 62, Therminol 66, Therminol 68, or Therminol 72.

15. The method of Claim 11, wherein the step of causing the heat transfer fluid in the first chamber to be discharged into the second chamber includes adjusting a valvepositioned between the first chamber and the second chamber to control a rate of discharge of the heat transfer fluid.

16. The method of Claim 15, wherein the valve is adjusted based on a temperature of the pool / spa water downstream of the heat exchanger to control the rate of discharge of heat transfer fluid from the first chamber into the second chamber.

17. The method of Claim 11, comprising the step of: adjusting a mixing valve in fluidic communication with an outlet of the heat exchanger and a bypass line that permits pool / spa water to flow to the mixing valve without first flowing through the heat exchanger based on a temperature of the pool / spa water downstream of the heat exchanger to adjust the amount of water from the bypass line that is mixed with the water provided by the outlet of the heat exchanger to the mixing valve.

18. The method of Claim 11, comprising the step of: returning, with a pump, heat transfer fluid from the second chamber to the first chamber through a return line.

19. The method of Claim 18, wherein the pump is controlled based on a temperature of the heat transfer fluid in the second chamber.

20. The method of Claim 11, wherein the step of causing the pool / spa water to flow through the heat exchanger includes adjusting an inlet valve to control the flow of pool / spa water to the heat exchanger.

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