WO2024025919A1

WO2024025919A1 - Internal recirculation with low pulse fire control

Info

Publication number: WO2024025919A1
Application number: PCT/US2023/028642
Authority: WO
Inventors: Jonathan Vincent; Bruce Hill; Chad VANDERROEST
Original assignee: Bradford White Corporation
Priority date: 2022-07-28
Filing date: 2023-07-26
Publication date: 2024-02-01

Abstract

A method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow is disclosed. A water supply is introduced into a heat exchanger configured to transfer heat to the water supply from a burner when the water supply is contained in the heat exchanger. A pulse fire duration is determined for the burner and a pre-defined condition of the water supply is sensed. When the pre-defined condition is sensed, the burner is activated to fire for the pulse fire duration, and the burner is deactivated after the pulse fire duration is elapsed. The pre-defined condition of the water supply is monitored, such that when the pre-defined condition is sensed again, the burner is activated to fire for another pulse fire duration, and the burner is deactivated after the another pulse fire duration is elapsed.

Description

INTERNAL RECIRCULATION WITH LOW PULSE FIRE CONTROL

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application Ser. No. 63/393,086, titled "INTERNAL RECIRCULATION WITH LOW PULSE FIRE CONTROL," filed July 28, 2022, the entirety of which is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The disclosed subject matter relates generally to tankless water heaters, and more particularly, to a method for delivering low flow and heated water from tankless water heaters and/or for avoiding freezing of a water supply in tankless water heaters.

BACKGROUND OF THE INVENTION

There remains a need for improvements in tankless water heaters in terms of at least one of heat exchange performance and cost. For example, there remains a need for improvements when delivering low flow and heated water from tankless water heaters, for avoiding freezing of water in tankless water heaters, and/or other improvements.

SUMMARY OF THE INVENTION

The subject matter disclosed herein is directed to tankless water heaters, and more particularly, to a method for delivering low flow and heated water from tankless water heaters and/or for avoiding freezing of a water supply in tankless water heaters.

In one example, a method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow is disclosed. The method comprises introducing a water supply into a heat exchanger configured to transfer heat to the water supply from a burner when the water supply is contained in the heat exchanger. The method further comprises determining a pulse fire duration for the burner based on at least one of (i) a target temperature change (°F) of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water supply contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof. The method also comprises sensing a pre-defined condition of the water supply, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water supply. When the pre-defined condition is sensed, the method comprises activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger, and deactivating the burner to terminate the transfer of heat to the water supply contained in the heat exchanger after the pulse fire duration is elapsed. The method further comprises monitoring for the pre-defined condition of the water supply, such that when the pre-defined condition is sensed again, the method comprises activating the burner to fire for another pulse fire duration to again transfer heat to the water supply contained in the heat exchanger, and deactivating the burner to again terminate the transfer of heat to the water supply contained in the heat exchanger after another pulse fire duration is elapsed.

In another example, a tankless water heating appliance configured to heat water in conditions of low water flow or no water flow is disclosed. The tankless water heating appliance comprises a heat exchanger configured to transfer heat to the water from a heat source when the water is contained in the heat exchanger. The tankless water heating appliance comprises at least one sensor configured to sense a pre-defined condition of the water, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water. The tankless water heating appliance comprises a controller configured to: calculate a pulse fire duration for the heat source based on at least one of (i) a target temperature change (°F) of the water upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof. The controller is also configured to receive, from the at least one sensor, a signal indicating when the pre-defined condition is sensed. When the pre-defined condition is sensed, the controller is configured to activate the burner to fire for the pulse fire duration to transfer heat to the water contained in the heat exchanger, and deactivate the burner to terminate the transfer of heat to the water contained in the heat exchanger after the pulse fire duration is elapsed. The controller is also configured to monitor for the pre-defined condition of the water, such that when the pre-defined condition is sensed again, the controller is configured to activate the burner to fire for another pulse fire duration to again transfer heat to the water contained in the heat exchanger, and deactivate the burner to again terminate the transfer of heat to the water contained in the heat exchanger after the another pulse fire duration is elapsed. In still another example, a tankless water heating appliance configured to heat water in conditions of low water flow or no water flow is disclosed. The tankless water heating appliance comprises a heat exchanger configured to transfer heat to the water from a heat source when the water is contained in the heat exchanger. The tankless water heating appliance comprises at least one sensor configured to sense a pre-defined condition of the water, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water. The tankless water heating appliance comprises a controller configured to: calculate a pulse fire duration for the heat source based on at least one of (i) a target temperature change (°F) of the water upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof. The controller is also configured to receive, from the at least one sensor, a signal indicating when the pre-defined condition is sensed. When the pre-defined condition is sensed, the controller is configured to activate the burner to fire for the pulse fire duration to transfer heat to the water contained in the heat exchanger, and deactivate the burner to terminate the transfer of heat to the water contained in the heat exchanger after the pulse fire duration is elapsed. The controller is also configured to monitor for the pre-defined condition of the water, such that when the pre-defined condition. Further, the heat exchanger comprises a coiled conduit shaving a plurality of rotations extending between an inlet of the heat exchanger and an outlet of the heat exchanger, the number of plurality of rotations being selected to increase the volume of the water to be heated in the coiled conduit of the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description is best understood when read in connection with the accompanying drawings, with like elements having the same reference numerals. When a plurality of similar elements are present, a single reference numeral may be assigned to the plurality of similar elements with a small letter designation referring to specific elements. When referring to the elements collectively or to a non-specific one or more of the elements, the small letter designation may be dropped. This emphasizes that according to common practice, the various features of the drawings are not drawn to scale unless otherwise indicated. On the contrary, the dimensions of the various features may be expanded or reduced for clarity. Included in the drawings are the following figures: FIG. 1 depicts an exemplary method for delivering low flow and heated water from an exemplary tankless water heater.

FIG. 2 depicts an exemplary heat exchanger.

FIG. 3 depicts a schematic of an exemplary control methodology.

FIG. 4 depicts an exemplary method for avoiding freezing of a water supply in an exemplary tankless water heater.

FIG. 5 depicts an exemplary method for heating water in a tankless water heating appliance, according to aspects of the invention.

FIG. 6 depicts an exemplary method for heating water in a tankless water heating appliance and avoids freezing of the water supply contained in the heat exchanger, according to aspects of the invention.

FIG. 7 depicts an exemplary method for heating water in a tankless water heating appliance and avoids overheating of the water supply contained in the heat exchanger, according to aspects of the invention.

FIG. 8 depicts an exemplary method for heating water in a tankless water heating appliance in response to a minimum user demand for the water supply, according to aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Water heaters use a source of energy, such as electricity or fuel such as oil or natural gas, which is consumed by a burner, to heat the water. Further, tankless water heaters include multiple components, e.g., a heat exchanger (Hx), a flow rate sensor, and/or temperature sensors. Flow sensors provide signals corresponding to certain flow rates of water. At low flow rates, as sensed by flow sensors, one or more components of the water heater, e.g. a blower, gas valve, and a spark ignitor may work in concert to generate products of combustion for heating the water. Further, freezing of water supply (e.g. water in the heating circuit) may conventionally be avoided via use of electrical heating elements.

Aspects of the disclosed subject matter relate to a method for delivering low flow and heated water from tankless water heaters and/or for avoiding freezing of a water supply in tankless water heaters. The disclosed methods may provide improvements in operation of tankless water heaters. Such improvements may be created, for example, due to the low flow hot water delivery by using a noisy or sporadic flowrate signal and a high-volume heat exchanger to initiate pulse firing while maintaining temperature stability and safety, making it possible to deliver less than 0.5 gallons per minute (GPM). Such improvement may be created, for example, due to providing anti-freeze benefits, by allowing the use of fewer electric heating elements, or without electric heating elements entirely, or using a high mass heat exchanger with and/or without an internal pump for reheating water within the heat exchanger and plumbing in very low ambient temperatures.

The subject matter disclosed herein is described primarily with respect to tankless water heaters. However, the subject matter of this disclosure is applicable to any type or variety of heat exchanger, including any heat exchanger designed to exchange heat between a flow of gas and a fluid (gas or liquid). In particular, this disclosure is not limited to devices for heating water (i.e. H2O). As used herein, the terms "water heater," "water heating appliance," and "water heating" are intended to encompass any system, device, or method adapted to generate and maintain a source of heated fluid.

The term "rapid change" as used herein and throughout the specification is to be construed as a change (e.g. change in temperature) in the water supply that occurs as the water supply is presently flowing in the system, i.e., a change in temperature of water as detected by one or more temperature sensors. The term "rapid change" may therefore be distinguishable from the standard turning ON/OFF from increasing or decreasing of the water supply temperature to room temperature. It may also relate to a change that exceeds a predetermined or threshold rate of change. Further, the term "water supply" as used herein and throughout the specification is not intended to be limited to a particular source of water (e.g. inlet, outlet, etc.), but instead is intended to encompass water having a range of temperatures and flowing (or configured to flow) along a water pathway within or from or to a water heater.

Referring now to FIGS. 1-3, a method 100 for delivering low flow and heated water from tankless water heaters is provided in FIG. 1. The method 100 includes one or more steps including introducing a water supply into a heat exchanger; sensing a temperature of the water supply; detecting a low flow condition of the water supply; and activating a burner to fire for a predetermined duration. Additional details of method 100 are set forth below.

In a first step 110, a water supply is introduced into a heat exchanger. In an example, a heat exchanger 1000 (FIG. 2) comprises a coil-type heat exchanger. FIG. 2 depicts an exploded view of heat exchanger 1000, showing a frontal cover 150, a divider plate insulation 152, a coil 154, a divided plate 156, a coil casing 158, a casing top 160, and back casing 162. Heat exchanger 1000 is a larger volume coil type, which is configured to store a larger volume of water compared to standard heat exchangers used in conventional tankless water heaters. In an exemplary embodiment, heat exchanger 1000 includes a coiled conduit configured to contain the water to be heated. The coiled conduit may comprise a plurality of rotations extending between an inlet for the water to be heated and an outlet for heated water. The number of the plurality of rotations is selected to increase the volume of the water to be heated in the coiled conduit between the inlet and the outlet. In one embodiment, the heat exchanger is a single coil including at least 10 rotations, preferably at least 15 rotations, and more preferably at least 17 rotations, but more or fewer rotations are contemplated as well. In a non-limiting example, the volume of the water to be heated may be in a range between 0.4 to 0.9 gallons of water. In a preferred embodiment, the range is between 0.5 to 0.75 gallons. Additionally or optionally, the length of coiled conduit when uncoiled may be in a range between 30 to 50 feet. In a preferred embodiment, the length is 40 feet. Further, the coiled conduit may have a cross- sectional area of at least 0.8 square inches and/or an uncoiled length of at least 40 feet, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

The larger volume coil type heat exchanger 1000 will yield slower water temperature change (e.g. increase) over time. One skilled in the art would understand this relationship, as expressed by the following equation: Mass* Delta T * Heat Capacity = BTU. An increase in mass (because of the larger volume heat exchanger 1000) decreases change in temperature (Delta T) for a given energy input.

In operation, this means a water heating system having heat exchanger 1000 can tolerate a burner that is "ON" for a longer period of time, with low or no flow of water. On the other hand, standard water heaters typically may not fire a pulse for a shorter duration, in consideration of one or more safety hazards, i.e., water and heat exchanger material will overheat. Accordingly, use of a larger volume coil type heat exchanger 1000 would desirably support firing the burner with little to no flow of water.

In a second step 120, a low flow condition of the water supply is detected. One skilled in the art would understand from the description herein that the detected "low flow condition" may comprise a transient flow condition, which is distinguishable from a "low flow condition" detected during steady state conditions using the flow sensor (i.e. where fluid properties within the system experience nominal or no changes over time). In an example, a flow sensor 1102 detects and provides signals for water flow rate along a water pathway 1112 through the water heater. Optionally, a number of pulses per second is detected or measured.

Conventional flow rate sensors generate a noisy or unreliable signal corresponding to a flow rate of 0.2-0.4 gallons per minute (GPM). One skilled in the art would understand from the description herein that the noise or unreliable signal is a known characteristic of turbine flow meters, which follow the run of GPM as shown by the following equation: Flow Rate(GPM)= K*frequency(Hz). A controller having a pulse signal counter with a time component is configured to detect a pulse from the turbine. Under no flow conditions, no pulses are sensed because the turbine does not move.

Under normal operating conditions, the turbine spins. Each time a magnet mounted on the turbine passes a sensor (e.g. a Hall-effect sensor) adjacent the turbine, a controller having the pulse signal counter receives a pulse, and adds a pulse count to the pulse signal counter. If the pulse signal counter is cleared (zeroed) every second, a number of pulses in each second (Hz) is received and interpreted by the controller. For example, 20 pulses detected in 1 second would be directly proportional to a flowrate (GPM), as indicated by the equation above.

Under low flow conditions, e.g. <0.5 GPM, sporadic movement in the turbine can be detected. The sporadic movement may generate a few pulses in one second, then no pulses in the sequential second, or a few pulses in one second followed by the turbine stopping for a few sequential seconds, then moving again. This sporadic movement of the turbine creates a predetermined low flow rate disturbance comprising the "noisy" or "unreliable" signal.

In a third step 130, a temperature of the water supply is detected. In an example, one or more temperature sensors 1108 detect the temperature of the water supply as water flows through the water pathway 1112 within the water heater 1100 (FIG. 3). In an exemplary embodiment, sensing the temperature of the water supply comprises sensing an inlet temperature measured at an inlet 1106 and an outlet temperature measured at an outlet 1110.

In a fourth step 140, a burner is activated to fire for a predetermined duration. In an example, the burner is activated to fire for a short duration. The burner may be activated to fire when at least one of a predetermined critical temperature of the water supply has been detected (e.g. in step 130) and when a predetermined low flow rate disturbance has been detected (e.g. in step 120). In an exemplary embodiment, the predetermined critical temperature of the water supply is a range from 30°F to 46°F, or more particularly at <38°F. The predetermined or short duration may be between 0 to 30 seconds, with use of heat exchanger 1000.

Optionally, an internal or recirculation pump 1104 may be activated to increase the water supply available for heating. In an exemplary embodiment, the recirculation pump activation step may occur sequentially after step 120 and/or before step 130. In another exemplary embodiment, when a decrease in the number of pulses per second is detected (e.g. in step 120), the flow rate decreases (e.g. as detected by the flow rate sensor 1102 in step 120), the inlet temperature decreases (e.g. as detected by the temperature sensor 1108 in step 130), or a combination thereof, the recirculation pump 1104 is activated to increase the water supply for heating. Still further, the burner may be activated to heat the water supply for a predetermined number of pulses and for the predetermined duration (e.g. 0 to 30 seconds). At the end of the pulse fire cycle, the water heater 1100 enters standby mode, in which it awaits a draw from a user, or for the temperature sensor 1108 to reach the predetermined critical temperature (e.g. <38°F) again and/or the predetermined Sow flow rate disturbance has been detected, for another reheating pulse fire cycle.

Additionally or optionally, method 100 includes a step 150 comprising detecting a flow draw for a predetermined draw duration. In an exemplary embodiment, the predetermined draw duration comprises a short draw or burst of water from the water supply (e.g. between 1 to 3 seconds). In another exemplary embodiment, the detected flow draw is configured to activate the recirculation pump 1104 to increase the water supply for heating (e.g. after step 120 and/or before step 130), activate the burner to fire for the predetermined duration (e.g. in step 140), or a combination thereof.

FIG. 1 depicts an example method comprising steps that are performed sequentially in the order recited. However, it should be understood from the description herein that one or more steps may be omitted and/or performed out of the described sequence of the process while still achieving the desired result.

As discussed above, method 100 is configured for delivering low flow and heated water from a tankless water heating appliance. An exemplary tankless water heating appliance for use with one or more steps of method 100 is configured to deliver low flow and heated water. The tankless water heating appliance comprises a conduit configured to contain water to be heated and a heat exchanger, such as heat exchanger 1000, configured to transfer heat to the water when the water is contained in the conduit.

In an exemplary embodiment, the heat exchanger 1000 comprises a coiltype heat exchanger. As shown in FIG. 2, heat exchanger 1000 may include a frontal cover 150, a divider plate insulation 152, a coil 154, a divided plate 156, a coil casing 158, a casing top 160, and back casing 162. Heat exchanger 1000 is a larger volume coil type, which is configured to store a larger volume of water compared to standard heat exchangers used in conventional tankless water heaters. In an example, heat exchanger 1000 includes a coiled conduit configured to contain the water to be heated. The coiled conduit may comprise a plurality of rotations extending between an inlet for the water to be heated and an outlet for heated water. The number of the plurality of rotations is selected to increase the volume of the water to be heated in the coiled conduit between the inlet and the outlet. In a non-limiting example, the volume of the water to be heated may be in a range between 0.4 to 0.9 gallons of water. In a preferred embodiment, the range is between 0.5 to 0.75 gallons. Additionally or optionally, the length of coiled conduit when uncoiled may be in a range between 30 to 50 feet. In a preferred embodiment, the length is 40 feet. Further, the coiled conduit may have a cross-sectional area of at least 0.8 square inches and/or an uncoiled length of at least 40 feet, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

The tankless water heating appliance also includes a burner configured to generate heat for transfer to the water via the heat exchanger when the water is contained in the conduit. The tankless water heating appliance comprises a temperature sensor configured to detect a temperature of the water when the water is contained in the conduit. In an example, the temperature sensor detects the temperature of the water at the inlet which receives water to be heated and the outlet for delivering heated water.

The water heating appliance also includes a controller. The controller is configured to receive, from the temperature sensor, a signal indicating the temperature of the water. For example, the signal may indicate a predetermined critical temperature change or difference of the water. In an exemplary embodiment, the detected temperature difference of a first temperature of the water supply and a second temperature of the water supply may be in a range between 15°F to 20°F. When the predetermined critical temperature change of the water has been detected by the temperature sensor, the controller activates the burner to fire for a predetermined duration. In an exemplary embodiment, the predetermined duration is between 0 and 30 seconds. Additionally or optionally, the burner may heat the water contained in the conduit for a predetermined number of pulses and for the predetermined duration.

Additionally or optionally, the water heating appliance includes a flow detector configured to detect a low flow condition of the water when the water is contained in the conduit. The controller is configured to receive, from the flow detector, a signal indicating the presence or absence of the low flow condition. In operation, when at least one of the predetermined critical temperature change of the water has been detected and the predetermined low flow condition has been detected, the burner is activated to fire for the predetermined duration. Additionally or optionally, when the predetermined critical temperature change of the water has not been detected, and the predetermined low flow condition has been detected, the burner is activated to fire for the predetermined duration. Still further, when the controller receives, from the temperature sensor, the signal indicating the temperature of the water, the controller may determine whether the predetermined critical temperature change of the water has been detected. In so doing, the controller may also detect a low flow condition of the water when the water is contained in the conduit, and the controller may activate the burner to fire for the predetermined duration.

Turning now to FIGS. 3-4, a method 200 for avoiding freezing of a water supply in a tankless water heater is provided. In standard tankless water heaters, freezing is avoided via use of electrical heating elements in the water pathway. However, with use of a larger heat exchanger (e.g. heat exchanger 1000 as discussed above), the ability to pulse fire with no or low flow water is supported, thereby eliminating the need for some or all of the electrical heating elements in a water pathway (e.g. water pathway 1112 in FIG. 3) to avoid freezing of a water supply. The method 200 comprises detecting a change in temperature (e.g. approaching 32°F) of the water supply; activating a burner to pulse fire to heat the water supply; and delaying firing of the burner until the predetermined temperature of the water supply is detected again. Additional details of method 200 are similar to method 100, but method 200 differs in some respects relative to method 100, which are explained further below.

In a first step 210, a change in temperature of the water supply is detected. In an example, one or more temperature sensors 1108 detect the temperature of the water supply. In an exemplary embodiment, sensing a change in temperature of the water supply comprises detecting a change in temperature of water as the water flows along the water pathway 1112 and as detected by one or more temperature sensors 1102.

In a second step 220, a burner is activated to pulse fire to heat the water supply. In an example, the burner is activated to fire for a predetermined duration (e.g. a short duration). The burner may be activated to fire when a change in temperature of the water supply has been detected (e.g. in step 210). In an exemplary embodiment, the rapid change in temperature may comprise a detected temperature between a range from 30°F to 46°F, or more particularly at <38°F.

In an optional third step 230, a rapid change in temperature is sensed or detected prior to the end of the predetermined duration of the pulse.

In a fourth step 240, firing of the burner is delayed. In an example, firing of the burner is delayed as the water heater 1100 enters standby mode, in which it awaits a draw from a user, or for the temperature sensor 1108 to detect the rapid change in temperature of the water supply and/or a predetermined low flow rate disturbance has been detected (as discussed above with respect to method 100) again for another reheating pulse fire cycle.

FIG. 4 depicts an example of a method comprising steps that are performed sequentially in the order recited. However, it should be understood from the description herein that one or more steps may be omitted and/or performed out of the described sequence of the process while still achieving the desired result.

As discussed above, method 200 is configured for delivering low flow and heated water from a tankless water heating appliance. An exemplary tankless water heating appliance for use with method 200 is configured to avoid freezing of a water supply. The tankless water heating appliance comprises a conduit configured to contain water to be heated and a heat exchanger, such as heat exchanger 1000, configured to transfer heat to the water when the water is contained in the conduit.

The tankless water heating appliance also includes a heat source configured to generate heat for transfer to the water via the heat exchanger when the water is contained in the conduit. In an exemplary embodiment, the heat source comprises a burner. In an alternative embodiment, the heat source comprises at least one electric heating element.

The tankless water heating appliance also comprises a temperature sensor configured to detect a temperature of the water. A controller is configured to receive, from the temperature sensor, a signal indicating the temperature of the water. For example, the signal may indicate a change in the temperature of the water exceeds the predetermined threshold temperature change. In an exemplary embodiment, the predetermined threshold temperature change comprises a detected rapid change in temperature of the water supply, the detected rapid change comprising a range of temperatures between 30°F to 46°F, or more particularly at <38°F. When the change in the temperature of the water exceeds the predetermined threshold temperature change, the controller delays firing of the burner until another change in the temperature of the water exceeding the predetermined threshold temperature change is detected.

Referring now to FIG. 5, according to aspects of the invention, a method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow, such as method 500, is disclosed. As used herein and throughout the specification, the term "low flow" and/or "low water flow" is intended to mean a minimum flowrate able to generate a reliable flow sensor signal. This can be, for example, a flow rate of up to 0.5 gallons per minute (GPM) in some circumstances. Likewise, the term "heat exchanger" may include a plate heat exchanger, coiled heat exchanger and other heat exchangers that would be known to one skilled in the art.

Generally, method 500 comprises the step of: introducing a water supply into a heat exchanger; determining a pulse fire duration for the burner; sensing a predefined condition of the water supply; and monitoring for the pre-defined condition of the water supply. Additional features of method 500 is discussed below, with reference to a tankless water heating appliance in accordance with aspects of the invention.

In step 510, a water supply is introduced into a heat exchanger. In an exemplary embodiment, the water supply is introduced into the heat exchanger 1000 that is configured to transfer heat to the water supply from a burner when the water supply is contained in the heat exchanger.

In a non-limiting example, the step of introducing the water supply comprise introducing the water supply into a plurality of rotations of a coiled conduit of the heat exchanger. The plurality of rotations of the coiled conduit may include at least 17 rotations. Further, the plurality of rotations of the coiled conduit of the heat exchanger may have an uncoiled length of at least 40 feet. Still further, the plurality of rotations of the coiled conduit of the heat exchanger may include a cross-sectional area of the coiled conduit of at least 0.8 square inches. The coiled conduit of the heat exchange may have a volume capacity of 0.3 to 2.0 gallons, or more specifically, the volume capacity of 0.4 to 0.7 gallons.

In step 520, a pulse fire duration for the burner is determined or calculated. In an exemplary embodiment, the pulse fire duration for the burner is based on at least one of (i) a target temperature change (°F) of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water supply contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour), or a combination thereof. Additionally or optionally, the pulse fire duration is calculated according to the following equation:

In a non-limiting example, the target temperature change of the water supply upstream of, downstream of, or within the heat exchanger includes a range between 1°F to 49°F and is detected based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger. In another non-limiting example, the target temperature change of the water supply upstream of, downstream of, or within the heat exchanger includes a range between 5°F to 40°F and is detected based on at least one of the inlet temperature at the inlet of the heat exchanger and the outlet temperature at the outlet of the heat exchanger.

In step 530, a pre-defined condition of the water supply is sensed. In an exemplary embodiment, the pre-defined condition is selected from the group consisting of (i) a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water supply. As used herein and throughout the specification, the term "temporal flow condition" may be intended to mean a flow condition of the water supply that is sensed or detected by a flow meter/sensor or switch. Still further, the flow condition of the water supply that is sensed or detected by the flow meter/sensor or switch may be utilized as an indicative or confirmatory assessment of the flow condition of the water supply.

When the pre-defined condition is sensed, the burner is activated to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger, and the burner is deactivated to terminate the transfer of heat to the water supply contained in the heat exchanger after the pulse fire duration is elapsed. In an exemplary embodiment, the burner is activated for 5 seconds to 35 seconds, or more particularly for 10 seconds to 30 seconds.

In a non-limiting example, the step of sensing the pre-defined condition of the water supply includes sensing the temperature indicative of a water temperature of the water supply. Further, sensing the temperature indicative of the water temperature of the water supply may comprise sensing at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger. In another non-limiting example, the burner may have a minimum heating capacity from 11,000 BTU/hr to 26,000 BTU/hr. In particular, the burner includes the minimum heating capacity from 16,000 BTU/hr to 20,000 BTU/hr. More particularly the burner includes the minimum heating capacity from 13,000 BTU/hr to 20,000 BTU/hr.

In yet another non-limiting example, the step of sensing the pre-defined condition of the water supply includes sensing the minimum temporal flow condition of the water supply based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger. Additionally or optionally, the step of sensing the pre-defined condition of the water supply includes sensing the minimum temporal flow condition of the water supply using a flow detector configured to sense flow of the water supply.

In step 540, the pre-defined condition of the water supply is monitored. In an exemplary embodiment, the pre-defined condition of the water supply is monitored, such that when the pre-defined condition is sensed again, the burner is activated to fire for another pulse fire duration to again transfer heat to the water supply contained in the heat exchanger, and the burner is deactivated to again terminate the transfer of heat to the water supply contained in the heat exchanger after the another pulse fire duration is elapsed. As used herein and throughout the specification, the "another pulse fire duration" may be different from the pulse fire duration, and/or may be shorter than the pulse fire duration.

Additionally or optionally, heating of the water supply in the tankless water heating appliance in accordance with method 500 is performed without the need for a heat source other than the burner.

FIG. 5 depicts an example of a method comprising steps that are performed sequentially in the order recited. However, it should be understood from the description herein that one or more steps may be omitted and/or performed out of the described sequence of the process while still achieving the desired result.

Referring now to FIG. 6, according to aspects of the invention, a method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow and the method of heating water in the tankless water heating appliance avoids freezing of the water supply contained in the heat exchanger, such as method 600, is disclosed. Generally, method 600 is similar to and may contain one or more steps of method 500 discussed above. In particular, method 600 comprises the steps of: sensing the pre-defined condition of the water supply includes sensing a temperature indicative of a minimum water temperature of the water supply upstream of, downstream of, or within the heat exchanger; and activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger. Additional features of method 600 is discussed below, with reference to a tankless water heating appliance in accordance with aspects of the invention.

In step 610, the pre-defined condition of the water supply is sensed by sensing a temperature indicative of a minimum water temperature of the water supply upstream of, downstream of, or within the heat exchanger. In an exemplary embodiment, at least one of an inlet temperature at the inlet of the heat exchanger and an outlet temperature at the outlet of the heat exchanger, is sensed.

In step 620, the burner is activated to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger. In an exemplary embodiment, activation of the burner includes pulsed activation of the burner to fire such that heat is transferred to the water supply contained in the heat exchanger, thereby avoiding the freezing of the water supply in the heat exchanger of the tankless water heating appliance. In an exemplary embodiment, the burner is pulsed activated to fire for the pulse fire duration.

Additionally or optionally, a rate of temperature change of the outlet temperature is sensed, prior to the end of the pulse fire duration. When the sensed rate of temperature change of the outlet temperature exceeds a predetermined rate of temperature change prior to the end of the pulse fire duration, the burner is deactivated to terminate the transfer of heat to the water supply contained in the heat exchanger. This step may be used to prevent overheating the water supply in the heat exchanger.

Additionally or optionally, method 600 is configured to avoid freezing of the water supply without activating a pump for the purpose of avoiding the freezing of the water supply.

FIG. 6 depicts an example of a method comprising steps that are performed sequentially in the order recited. However, it should be understood from the description herein that one or more steps may be omitted and/or performed out of the described sequence of the process while still achieving the desired result.

Referring now to FIG. 7, according to aspects of the invention, a method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow and the method of heating water in the tankless water heating appliance avoids overheating of the water supply contained in the heat exchanger, such as method 700, is disclosed. Generally, method 700 is similar to and may contain one or more steps of method 500 and/or 600 discussed above. In particular, method 700 comprises the steps of: sensing a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger; and activating step comprises pulsed activation of the burner to fire to transfer heat to the water supply contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance. Additional features of method 700 is discussed below, with reference to a tankless water heating appliance in accordance with aspects of the invention.

In step 710, a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger is sensed. In an exemplary embodiment, the minimum rate of temperature change of an inlet temperature at the inlet of the heat exchanger or an outlet temperature at the outlet of the heat exchanger, is sensed. Further, the minimum rate of temperature change of the inlet temperature or the outlet temperature is performed for a duration that is shorter than another duration when the pre-defined condition of the minimum temporal flow condition is not satisfied, e.g. such as during steady state conditions. Still further, the minimum rate of temperature change comprises a temperature difference of 15°F to 20°F over the duration.

In step 720, the burner undergoes pulsed activation of the burner to fire to transfer heat to the water supply contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance.

Additionally or optionally, a minimum temporal flow condition of the water supply is sensed.

Additionally or optionally, method 700 is configured to avoid overheating of the water supply without activating a recirculation pump for the purpose of avoiding the overheating of the water supply. For example, method 700 can be configured to be performed without activating a recirculation pump for the purpose of avoiding the overheating of the water supply.

FIG. 7 depicts an example of a method comprising steps that are performed sequentially in the order recited. However, it should be understood from the description herein that one or more steps may be omitted and/or performed out of the described sequence of the process while still achieving the desired result.

Referring now to FIG. 8, according to aspects of the invention, a method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow and includes heating the water supply in response to a minimum user demand for the water supply established by detecting a flow draw for a predetermined draw duration, such as method 800, is disclosed. Generally, method 800 is similar to and may contain one or more steps of methods 500, 600, and/or 700 discussed above. In particular, method 800 comprises the steps of: sensing a minimum temporal flow condition of the water supply; and activating step comprises pulsed activation of the burner to fire to transfer heat to the water supply contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance. Additional features of method 800 is discussed below, with reference to a tankless water heating appliance in accordance with aspects of the invention.

In step 810, a minimum temporal flow condition of the water supply is detected. In an exemplary embodiment, the sensed minimum temporal flow condition of the water supply is indicative of a minimum user demand for the water supply established. In a non-limiting example, the minimum user demand is determined by detecting a flow draw for a predetermined draw duration. In a non-limiting example, predetermined draw duration may be in a range of up to 5 seconds. The minimum user demand may be configured to send a signal to a controller of the tankless water heating appliance to initiate heating of the water in the heat exchanger. In another non-limiting example, the minimum temporal flow condition of the water supply is sensed based on a number of pulses per second detected by a flow meter. In another exemplary embodiment, a minimum rate of temperature change of the inlet temperature is sensed. In still another exemplary embodiment, a decrease in an inlet temperature or an outlet temperature is detected.

In step 820, the burner is activated to fire to transfer heat to the water supply contained in the heat exchanger when the flow of the water supply exceeds the minimum temporal flow condition. In an exemplary embodiment, the burner is further deactivated to terminate the transfer of heat to the water supply contained in the heat exchanger, thereby triggering monitoring for the pre-defined condition of the water supply.

In step 830, a recirculation pump is activated to deliver the water supply for heating. In an exemplary embodiment, when the flow draw for the predetermined duration is detected, one or more of the recirculation pump, the burner, or a combination thereof is activated. In yet another exemplary embodiment, one or more of a recirculation pump and the burner is activated, when a signal indicative of flow decreases , the inlet temperature decreases, the minimum rate of temperature change of the inlet temperature is detected, or a combination thereof.

FIG. 8 depicts an example of a method comprising steps that are performed sequentially in the order recited. However, it should be understood from the description herein that one or more steps may be omitted and/or performed out of the described sequence of the process while still achieving the desired result.

According to aspects of the invention, an exemplary tankless water heating appliance for use with one or more steps of methods 500, 600, 700, and/or 800 is configured to heat water in conditions of low water flow or no water flow. In an exemplary embodiment, the tankless water heating appliance comprises a heat exchanger configured to transfer heat to the water from a heat source when the water is contained in the heat exchanger. In a non-limiting example, the heat exchanger comprises a coil-type heat exchanger, such as heat exchanger 1000 (FIG. 2). Heat exchanger 1000 is a larger volume coil type, which is configured to store a larger volume of water compared to standard heat exchangers used in conventional tankless water heaters. In an example, heat exchanger 1000 includes a coiled conduit configured to contain the water to be heated. The coiled conduit may comprise a plurality of rotations extending between an inlet for the water to be heated and an outlet for heated water. The number of the plurality of rotations, such as at least 17 rotations, is selected to increase the volume of the water to be heated in the coiled conduit between the inlet and the outlet. In a non-limiting example, the volume of the water to be heated may be in a range between 0.3 to 2.0 gallons of water. In a preferred embodiment, the range is between 0.4 to 0.7 gallons of water. Additionally or optionally, the length of coiled conduit when uncoiled may be in a range between 30 to 50 feet. In a preferred embodiment, the length is 40 feet. Further, the coiled conduit may have a cross-sectional area of at least 0.8 square inches and/or an uncoiled length of at least 40 feet, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

Further, the tankless water heating appliance comprises at least one sensor configured to sense a pre-defined condition of the water, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water. In another exemplary embodiment, the target temperature change is in a range between 1°F to 49°F, and the target temperature change is based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger. More particularly, the target temperature change is in a range between 5°F to 40°F. In another embodiment, the at least one sensor is configured to sense the minimum temporal flow condition of the water supply based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger. Further, the at least one sensor is configured to sense the minimum temporal flow condition of the water supply using a flow detector configured to sense flow of the water supply. Still further, the tankless water heating appliance comprises a controller. In an exemplary embodiment, the controller is configured to calculate a pulse fire duration for the heat source based on at least one of (i) a target temperature change (°F) of the water upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof. In an exemplary embodiment, the controller is configured to calculate the pulse fire duration according to the following equation:

In an exemplary embodiment, the pulse fire duration is between 5 seconds to 35 seconds, and more particularly between 10 seconds to 30 seconds.

In addition, the controller is configured to receive, from the at least one sensor, a signal indicating when the pre-defined condition is sensed. When the predefined condition is sensed, the controller is configured to activate the burner to fire for the pulse fire duration to transfer heat to the water contained in the heat exchanger, and the controller is configured to deactivate the burner to terminate the transfer of heat to the water contained in the heat exchanger after the pulse fire duration is elapsed. Additionally, the controller is configured to monitor for the pre-defined condition of the water, such that when the pre-defined condition is sensed again, the controller activates the burner to fire for another pulse fire duration to again transfer heat to the water contained in the heat exchanger, and deactivates the burner to again terminate the transfer of heat to the water contained in the heat exchanger after the another pulse fire duration is elapsed.

In a non-limiting example, the controller is configured to receive, from the temperature sensor, a signal indicating the temperature of the water. In particular, the at least one sensor including a temperature sensor is configured to sense the temperature indicative of a water temperature of the water supply. Namely, the at least one sensor is configured to detect at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

The tankless water heating appliance also includes a heat source, such as a burner, configured to generate heat for transfer to the water via the heat exchanger when the water is contained in the heat exchanger. In an exemplary embodiment, the burner has a minimum heating capacity from 11,000 BTU/hr to 26,000 BTU/hr, or more particularly, a minimum heating capacity from 16,000 BTU/hr to 20,000 BTU/hr. In another exemplary embodiment, the tankless water heating appliance is configured to heat water without the need for the heat source being other than a burner.

According to an aspect of the invention, the tankless water heating appliance is configured to avoid freezing of the water contained in the heat exchanger. In an exemplary embodiment, the tankless water heating appliance is configured to avoid freezing of the water without activating a pump for the purpose of avoiding the freezing of the water. To achieve this objective, the at least one sensor is configured to sense a temperature indicative of a minimum water temperature of the water supply upstream of, downstream of, or within the heat exchanger , and the heat source is configured to transfer heat to the water contained in the heat exchanger, thereby avoiding the freezing of the water in the heat exchanger of the tankless water heating appliance. In an exemplary embodiment, the heat source is configured to transfer heat to the water contained in the heat exchanger for the pulse fire duration. In one nonlimiting example, the heat source comprises a burner. In another non-limiting example, the heat source comprises at least one heating element. Further, the at least one sensor is configured to detect at least one of an inlet temperature at the inlet of the heat exchanger and an outlet temperature at the outlet of the heat exchanger. Still further, the at least one sensor is configured to detect a rate of temperature change of the outlet temperature, prior to the end of the pulse fire duration. In this way, when the rate of temperature change of the outlet temperature exceeds a predetermined rate of temperature change prior to the end of the pulse fire duration, the controller is configured to deactivate the heat source to terminate the transfer of heat to the water contained in the heat exchanger.

According to another aspect of the invention, the tankless water heating appliance is configured to avoid overheating of the water contained in the heat exchanger. In this exemplary embodiment, the tankless water heating appliance avoids overheating of the water without activating a recirculation pump for the purpose of avoiding the overheating of the water. To achieve this, the at least one sensor is configured to sense a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger, and the heat source is configured to transfer heat to the water contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance. Namely, the at least one sensor is configured to sense the minimum rate of temperature change of an inlet temperature at the inlet of the heat exchanger or an outlet temperature at the outlet of the heat exchanger. In so doing, the at least one sensor is configured to sense the minimum rate of temperature change of the inlet temperature or the outlet temperature, for a duration that is shorter than another duration when water is not heated in conditions of low water flow or no water flow. In a non-limiting example, the at least one sensor is configured to sense the minimum rate of temperature change in a range between 15°F to 20°F over the duration. Additionally or optionally, the at least one sensor is configured to sense a minimum temporal flow condition of the water.

According to another aspect of the invention, the tankless water heating appliance is configured to heat water in response to a minimum user demand for the water. In an exemplary embodiment, the minimum user demand is established by detecting a flow draw for a predetermined draw duration. Further, the at least one sensor is configured to sense a minimum temporal flow condition of the water, and the heat source is configured to transfer heat to the water contained in the heat exchanger when the flow of the water exceeds the minimum temporal flow condition. In a nonlimiting example, the at least one sensor is configured to sense the minimum temporal flow condition of the water, based on a number of pulses per second detected by a flow meter. Additionally or optionally, the at least one sensor is configured to sense a minimum rate of temperature change of the inlet temperature. The at least one sensor may also be configured to detect a decrease in an inlet temperature or an outlet temperature. Still further, the heat source is deactivated to terminate the transfer of heat to the water contained in the heat exchanger, thereby triggering the controller to monitor for the pre-defined condition of the water.

In this exemplary embodiment, a recirculation pump is configured to deliver the water for heating. In a non-limiting example, the controller is configured to activate a recirculation pump, the heat source, or a combination thereof when the flow draw is detected. In another non-limiting example, the controller is configured to activate one or more of a recirculation pump and the heat source, when a number of pulses per second detected by a flow meter decreases, the inlet temperature decreases, the minimum rate of temperature change of the inlet temperature is detected, or a combination thereof.

The system and method for internal recirculation with low pulse fire control include, without limitation, the following aspects:

A method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow, the method comprising: introducing a water supply into a heat exchanger configured to transfer heat to the water supply from a burner when the water supply is contained in the heat exchanger; determining a pulse fire duration for the burner based on at least one of (i) a target temperature change (°F) of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water supply contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof; sensing a pre-defined condition of the water supply, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water supply; when the pre-defined condition is sensed, activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger, and deactivating the burner to terminate the transfer of heat to the water supply contained in the heat exchanger after the pulse fire duration is elapsed; and monitoring for the pre-defined condition of the water supply, such that when the pre-defined condition is sensed again, activating the burner to fire for another pulse fire duration to again transfer heat to the water supply contained in the heat exchanger, and deactivating the burner to again terminate the transfer of heat to the water supply contained in the heat exchanger after the another pulse fire duration is elapsed.

The method of aspect 1, wherein the step of determining the pulse fire duration for the burner includes determining the pulse fire duration according to the following equation:

Pulse fire duration (s)«(Target Temp Change (°F)xVolume (gal)xDensity of Water (lbs/gal))/(Minimum Rated Heating Capacity (BTU/hr))x3600 s.

The method of aspect 1, wherein the step of sensing the pre-defined condition of the water supply includes sensing the temperature indicative of a water temperature of the water supply, and sensing the temperature indicative of the water temperature of the water supply comprises sensing at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

The method of aspect 1, wherein the target temperature change of the water supply upstream of, downstream of, or within the heat exchanger includes a range between 1°F to 49°F and is detected based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger. The method of aspect 4, wherein the target temperature change of the water supply upstream of, downstream of, or within the heat exchanger includes a range between 5°F to 40°F and is detected based on at least one of the inlet temperature at the inlet of the heat exchanger and the outlet temperature at the outlet of the heat exchanger.

The method of aspect 1, wherein the step of sensing the pre-defined condition of the water supply includes sensing the minimum temporal flow condition of the water supply based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

The method of aspect 1, wherein the step of sensing the pre-defined condition of the water supply includes sensing the minimum temporal flow condition of the water supply using a flow detector configured to sense flow of the water supply.

The method of aspect 1, wherein step of introducing the water supply includes introducing the water supply into a plurality of rotations of a coiled conduit of the heat exchanger.

The method of aspect 8, wherein step of introducing the water supply includes introducing the water supply into at least 17 rotations of the coiled conduit.

The method of aspect 8, wherein step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into an uncoiled length of the coiled conduit of at least 40 feet.

The method of aspect 8, wherein step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into a cross-sectional area of the coiled conduit of at least 0.8 square inches.

The method of aspect 8, wherein the step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into a volume capacity of 0.3 to 2.0 gallons.

The method of aspect 12, wherein the step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into the volume capacity of 0.4 to 0.7 gallons.

The method of aspect 1, wherein the step of activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger includes activating a minimum heating capacity from 11,000 BTU/hr to 26,000 BTU/hr.

The method of aspect 14, wherein the step of activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger includes activating the minimum heating capacity from 13,000 BTU/hr to 20,000 BTU/hr.

The method of aspect 1, wherein the step of activating the burner to fire for the pulse fire duration includes activating the burner for 5 seconds to 35 seconds.

The method of aspect 16, wherein the step of activating the burner to fire for the pulse fire duration includes activating the burner for 10 seconds to 30 seconds.

The method of aspect 1, wherein the heating of the water supply in the tankless water heating appliance is performed without the need for a heat source other than the burner.

The method of aspect 1, wherein the method of heating water in the tankless water heating appliance avoids freezing of the water supply contained in the heat exchanger, wherein the step of sensing the pre-defined condition of the water supply includes sensing a temperature indicative of a minimum water temperature of the water supply upstream of, downstream of, or within the heat exchanger, and the step of activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger includes pulsed activation of the burner to fire such that heat is transferred to the water supply contained in the heat exchanger, thereby avoiding the freezing of the water supply in the heat exchanger of the tankless water heating appliance.

The method of aspect 19, wherein the method avoids freezing of the water supply without activating a pump for the purpose of avoiding the freezing of the water supply.

The method of aspect 19, wherein the sensing step comprises sensing at least one of an inlet temperature at the inlet of the heat exchanger and an outlet temperature at the outlet of the heat exchanger.

The method of aspect 19, wherein the activating step comprises pulsed activation of the burner to fire for the pulse fire duration.

The method of aspect 19, wherein the sensing step comprises sensing a rate of temperature change of the outlet temperature, prior to the end of the pulse fire duration.

The method of aspect 23, wherein when the rate of temperature change of the outlet temperature exceeds a predetermined rate of temperature change prior to the end of the pulse fire duration, the method comprises deactivating the burner to terminate the transfer of heat to the water supply contained in the heat exchanger.

The method of aspect 1, wherein the method of heating water in the tankless water heating appliance avoids overheating of the water supply contained in the heat exchanger, wherein the sensing step comprises sensing a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger, and the activating step comprises pulsed activation of the burner to fire to transfer heat to the water supply contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance.

The method of aspect 25, wherein the method avoids overheating of the water supply without activating a recirculation pump for the purpose of avoiding the overheating of the water supply.

The method of aspect 25, wherein step of sensing comprises sensing the minimum rate of temperature change of an inlet temperature at the inlet of the heat exchanger or an outlet temperature at the outlet of the heat exchanger.

The method of aspect 27, wherein sensing the minimum rate of temperature change of the inlet temperature or the outlet temperature is performed for a duration that is shorter than another duration when the pre-defined condition of the minimum temporal flow condition is not satisfied.

The method of aspect 28, wherein sensing the minimum rate of temperature change comprises sensing a temperature difference of 15°F to 20°F over the duration.

The method of aspect 24, wherein the sensing step comprises sensing a minimum temporal flow condition of the water supply.

The method of aspect 1, wherein the method of heating water in the tankless water heating appliance includes heating the water supply in response to a minimum user demand for the water supply established by detecting a flow draw for a predetermined draw duration, wherein the sensing step comprises sensing a minimum temporal flow condition of the water supply, and the activating step comprises activation of the burner to fire to transfer heat to the water supply contained in the heat exchanger when the flow of the water supply exceeds the minimum temporal flow condition, and the deactivating step comprises deactivating the burner to terminate the transfer of heat to the water supply contained in the heat exchanger, thereby triggering monitoring for the pre-defined condition of the water supply.

The method of aspect 31, further comprising activating a recirculation pump to deliver the water supply for heating.

The method of aspect 31, further comprising activating a recirculation pump, the burner, or a combination thereof when the flow draw is detected. The method of aspect 31, wherein the sensing step further comprises sensing the minimum temporal flow condition of the water supply, based on a number of pulses per second detected by a flow meter.

The method of aspect 31, wherein the sensing step includes sensing a minimum rate of temperature change of the inlet temperature.

The method of aspect 31, wherein the sensing step includes detecting a decrease in an inlet temperature or an outlet temperature.

The method of aspect 31, further comprising activating one or more of a recirculation pump and the burner, when a signal indicative of flow decreases, the inlet temperature decreases, the minimum rate of temperature change of the inlet temperature is detected, or a combination thereof.

A tankless water heating appliance configured to heat water in conditions of low water flow or no water flow, the tankless water heating appliance comprising: a heat exchanger configured to transfer heat to the water from a heat source when the water is contained in the heat exchanger; at least one sensor configured to sense a pre-defined condition of the water, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water; and a controller configured to: calculate a pulse fire duration for the heat source based on at least one of (i) a target temperature change (°F) of the water upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof; receive, from the at least one sensor, a signal indicating when the predefined condition is sensed; and when the pre-defined condition is sensed: activate the burner to fire for the pulse fire duration to transfer heat to the water contained in the heat exchanger, and deactivate the burner to terminate the transfer of heat to the water contained in the heat exchanger after the pulse fire duration is elapsed; and monitor for the pre-defined condition of the water, such that when the pre-defined condition is sensed again: activate the burner to fire for another pulse fire duration to again transfer heat to the water contained in the heat exchanger, and deactivate the burner to again terminate the transfer of heat to the water contained in the heat exchanger after the another pulse fire duration is elapsed.

The tankless water heating appliance of aspect 38, wherein the controller is configured to calculate the pulse fire duration according to the following equation:

Pulse fire duration (s)<x(Target Temp Change (°F)xVolume (gal)xDensity of Water (lbs/gal))/(Minimum Rated Heating Capacity (BTU/hr))x3600 s

The tankless water heating appliance of aspect 38, wherein when the at least one sensor is configured to sense the temperature indicative of a water temperature of the water supply, the at least one sensor is configured to detect at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

The tankless water heating appliance of aspect 38, wherein the target temperature change is in a range between 1°F to 49°F, and the target temperature change is based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

The tankless water heating appliance of aspect 41, wherein the target temperature change is in a range between 5°F to 40°F and the target temperature change is based on at least one of the inlet temperature at the inlet of the heat exchanger and the outlet temperature at the outlet of the heat exchanger.

The tankless water heating appliance of aspect 38, wherein the at least one sensor is configured to sense the minimum temporal flow condition of the water supply based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

The tankless water heating appliance of aspect 38, wherein the at least one sensor is configured to sense the minimum temporal flow condition of the water supply using a flow detector configured to sense flow of the water supply.

The tankless water heating appliance of aspect 38, wherein the heat exchanger comprises a coiled conduit having a plurality of rotations.

The tankless water heating appliance of aspect 45, wherein the coiled conduit of the heat exchanger comprises at least 17 rotations.

The tankless water heating appliance of aspect 45, wherein the coiled conduit of the heat exchanger comprises an uncoiled length of at least 40 feet.

The tankless water heating appliance of aspect 45, wherein the coiled conduit of the heat exchanger includes a cross-sectional area of the coiled conduit of at least 0.8 square inches. The tankless water heating appliance of aspect 45, wherein the coiled conduit of the heat exchanger includes a volume capacity of 0.3 to 2.0 gallons.

The tankless water heating appliance of aspect 49, wherein the coiled conduit of the heat exchanger includes the volume capacity of 0.4 to 0.7 gallons.

The tankless water heating appliance of aspect 38, wherein the heat source has a minimum heating capacity from 11,000 BTU/hr to 26,000 BTU/hr.

The tankless water heating appliance of aspect 51, wherein the heat source has the minimum heating capacity from 16,000 BTU/hr to 20,000 BTU/hr.

The tankless water heating appliance of aspect 38, wherein the pulse fire duration is between 5 seconds to 35 seconds.

The tankless water heating appliance of aspect 53, wherein the pulse fire duration is between 10 seconds to 30 seconds.

The tankless water heating appliance of aspect 38, wherein the tankless water heating appliance is configured to heat water without the need for the heat source being other than a burner.

The tankless water heating appliance of aspect 38, wherein the tankless water heating appliance is configured to avoid freezing of the water contained in the heat exchanger, wherein the at least one sensor is configured to sense a temperature indicative of a minimum water temperature of the water supply upstream of, downstream of, or within the heat exchanger, and the heat source is configured to transfer heat to the water contained in the heat exchanger, thereby avoiding the freezing of the water in the heat exchanger of the tankless water heating appliance.

The tankless water heating appliance of aspect 56, wherein the tankless water heating appliance is configured to avoid freezing of the water without activating a pump for the purpose of avoiding the freezing of the water.

The tankless water heating appliance of aspect 56, wherein the at least one sensor is configured to detect at least one of an inlet temperature at the inlet of the heat exchanger and an outlet temperature at the outlet of the heat exchanger.

The tankless water heating appliance of aspect 56, wherein the heat source is configured to transfer heat to the water contained in the heat exchanger for the pulse fire duration.

The tankless water heating appliance of aspect 59, wherein the at least one sensor is configured to detect a rate of temperature change of the outlet temperature, prior to the end of the pulse fire duration.

The tankless water heating appliance of aspect 60, wherein when the rate of temperature change of the outlet temperature exceeds a predetermined rate of temperature change prior to the end of the pulse fire duration, the controller is configured to deactivate the heat source to terminate the transfer of heat to the water contained in the heat exchanger.

The tankless water heating appliance of aspect 56, wherein the heat source comprises a burner.

The tankless water heating appliance of aspect 56, wherein the heat source comprises at least one heating element.

The tankless water heating appliance of aspect 38, wherein the tankless water heating appliance avoids overheating of the water contained in the heat exchanger, wherein the at least one sensor is configured to sense a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger, and the heat source is configured to transfer heat to the water contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance.

The tankless water heating appliance of aspect 64, wherein the tankless water heating appliance avoids overheating of the water without activating a recirculation pump for the purpose of avoiding the overheating of the water.

The tankless water heating appliance of aspect 64, wherein the at least one sensor is configured to sense the minimum rate of temperature change of an inlet temperature at the inlet of the heat exchanger or an outlet temperature at the outlet of the heat exchanger.

The tankless water heating appliance of aspect 66, wherein the at least one sensor is configured to sense the minimum rate of temperature change of the inlet temperature or the outlet temperature, for a duration that is shorter than another duration when water is not heated in conditions of low water flow or no water flow.

The tankless water heating appliance of aspect 67, wherein the at least one sensor is configured to sense the minimum rate of temperature change in a range between 15°F to 20°F over the duration.

The tankless water heating appliance of aspect 64, wherein the at least one sensor is configured to sense a minimum temporal flow condition of the water.

The tankless water heating appliance of aspect 38, wherein the tankless water heating appliance heats the water in response to a minimum user demand for the water established by detecting a flow draw for a predetermined draw duration, wherein the at least one sensor is configured to sense a minimum temporal flow condition of the water, and the heat source is configured to transfer heat to the water contained in the heat exchanger when the flow of the water exceeds the minimum temporal flow condition, and the heat source is deactivated to terminate the transfer of heat to the water contained in the heat exchanger, thereby triggering the controller to monitor for the pre-defined condition of the water.

The tankless water heating appliance of aspect 70, further comprising a recirculation pump configured to deliver the water for heating.

The tankless water heating appliance of aspect 70, wherein the controller is configured to activate a recirculation pump, the heat source, or a combination thereof when the flow draw is detected.

The tankless water heating appliance of aspect 70, wherein the at least one sensor is configured to sense the minimum temporal flow condition of the water, based on a number of pulses per second detected by a flow meter.

The tankless water heating appliance of aspect 70, wherein the at least one sensor is configured to sense a minimum rate of temperature change of the inlet temperature.

The tankless water heating appliance of aspect 70, wherein the at least one sensor is configured to detect a decrease in an inlet temperature or an outlet temperature.

The tankless water heating appliance of aspect 70, wherein the controller is configured to activate one or more of a recirculation pump and the heat source, when a number of pulses per second detected by a flow meter decreases, the inlet temperature decreases, the minimum rate of temperature change of the inlet temperature is detected, or a combination thereof.

A tankless water heating appliance configured to heat water in conditions of low water flow or no water flow, the tankless water heating appliance comprising: a heat exchanger configured to transfer heat to the water from a heat source when the water is contained in the heat exchanger; at least one sensor configured to sense a pre-defined condition of the water, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water; and a controller configured to: calculate a pulse fire duration for the heat source based on at least one of (i) a target temperature change (°F) of the water upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof; receive, from the at least one sensor, a signal indicating when the predefined condition is sensed; and when the pre-defined condition is sensed: activate the burner to fire for the pulse fire duration to transfer heat to the water contained in the heat exchanger, and deactivate the burner to terminate the transfer of heat to the water contained in the heat exchanger after the pulse fire duration is elapsed; and monitor for the pre-defined condition of the water, such that when the pre-defined condition is sensed again: activate the burner to fire for another pulse fire duration to again transfer heat to the water contained in the heat exchanger, and deactivate the burner to again terminate the transfer of heat to the water contained in the heat exchanger after the another pulse fire duration is elapsed; and wherein the heat exchanger comprises a coiled conduit shaving a plurality of rotations extending between an inlet of the heat exchanger and an outlet of the heat exchanger, the number of plurality of rotations being selected to increase the volume of the water to be heated in the coiled conduit of the heat exchanger.

The tankless water heating appliance of aspect 77, the plurality of rotations including at least 17 rotations, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

The tankless water heating appliance of aspect 77, the plurality of coils having a capacity of at least 0.5 gallons for the water to be heated in the coiled conduit between the inlet and the outlet, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

The tankless water heating appliance of aspect 77, the plurality of coils including a conduit having an uncoiled length of at least 40 feet, a cross-sectional area of at least 0.8 square inches, or an uncoiled length of at least 40 feet and a cross- sectional area of at least 0.8 square inches, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims, and any combination of any features of any of the embodiments herein may be made, without departing from the invention.

Claims

What is Claimed:

1. A method of heating water in a tankless water heating appliance in conditions of low water flow or no water flow, the method comprising: introducing a water supply into a heat exchanger configured to transfer heat to the water supply from a burner when the water supply is contained in the heat exchanger; determining a pulse fire duration for the burner based on at least one of (i) a target temperature change (°F) of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water supply contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof; sensing a pre-defined condition of the water supply, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water supply; when the pre-defined condition is sensed, activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger, and deactivating the burner to terminate the transfer of heat to the water supply contained in the heat exchanger after the pulse fire duration is elapsed; and monitoring for the pre-defined condition of the water supply, such that when the pre-defined condition is sensed again, activating the burner to fire for another pulse fire duration to again transfer heat to the water supply contained in the heat exchanger, and deactivating the burner to again terminate the transfer of heat to the water supply contained in the heat exchanger after the another pulse fire duration is elapsed.

2. The method of claim 1, wherein the step of determining the pulse fire duration for the burner includes determining the pulse fire duration according to the following equation:

3. The method of claim 1, wherein the step of sensing the pre-defined condition of the water suppiy includes sensing the temperature indicative of a water temperature of the water supply, and sensing the temperature indicative of the water temperature of the water supply comprises sensing at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

4. The method of claim 1, wherein the target temperature change of the water supply upstream of, downstream of, or within the heat exchanger includes a range between 1°F to 49°F and is detected based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

5. The method of claim 4, wherein the target temperature change of the water suppiy upstream of, downstream of, or within the heat exchanger includes a range between 5°F to 40°F and is detected based on at least one of the inlet temperature at the inlet of the heat exchanger and the outlet temperature at the outlet of the heat exchanger.

6. The method of claim 1, wherein the step of sensing the pre-defined condition of the water supply includes sensing the minimum temporal flow condition of the water supply based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

7. The method of claim 1, wherein the step of sensing the pre-defined condition of the water supply includes sensing the minimum temporal flow condition of the water supply using a flow detector configured to sense flow of the water supply.

8. The method of claim 1, wherein step of introducing the water supply includes introducing the water supply into a plurality of rotations of a coiled conduit of the heat exchanger.

9. The method of claim 8, wherein step of introducing the water supply includes introducing the water supply into at least 17 rotations of the coiled conduit.

10. The method of claim 8, wherein step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into an uncoiled length of the coiled conduit of at least 40 feet.

11. The method of claim 8, wherein step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into a cross-sectional area of the coiled conduit of at least 0.8 square inches.

12. The method of claim 8, wherein the step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into a volume capacity of 0.3 to 2.0 gallons.

13. The method of claim 12, wherein the step of introducing the water supply into the plurality of rotations of the coiled conduit of the heat exchanger includes introducing the water supply into the volume capacity of 0.4 to 0.7 gallons.

14. The method of claim 1, wherein the step of activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger includes activating a minimum heating capacity from 11,000 BTU/hr to 26,000 BTU/hr.

15. The method of claim 14, wherein the step of activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger includes activating the minimum heating capacity from 13,000 BTU/hr to 20,000 BTU/hr.

16. The method of claim 1, wherein the step of activating the burner to fire for the pulse fire duration includes activating the burner for 5 seconds to 35 seconds.

17. The method of claim 16, wherein the step of activating the burner to fire for the pulse fire duration includes activating the burner for 10 seconds to 30 seconds.

18. The method of claim 1, wherein the heating of the water supply in the tankless water heating appliance is performed without the need for a heat source other than the burner.

19. The method of claim 1, wherein the method of heating water in the tankless water heating appliance avoids freezing of the water supply contained in the heat exchanger, wherein the step of sensing the pre-defined condition of the water supply includes sensing a temperature indicative of a minimum water temperature of the water supply upstream of, downstream of, or within the heat exchanger, and the step of activating the burner to fire for the pulse fire duration to transfer heat to the water supply contained in the heat exchanger includes pulsed activation of the burner to fire such that heat is transferred to the water supply contained in the heat exchanger, thereby avoiding the freezing of the water supply in the heat exchanger of the tankless water heating appliance.

20. The method of claim 19, wherein the method avoids freezing of the water supply without activating a pump for the purpose of avoiding the freezing of the water supply.

21. The method of claim 19, wherein the sensing step comprises sensing at least one of an inlet temperature at the inlet of the heat exchanger and an outlet temperature at the outlet of the heat exchanger.

22. The method of claim 19, wherein the activating step comprises poised activation of the burner to fire for the pulse fire duration.

23. The method of claim 19, wherein the sensing step comprises sensing a rate of temperature change of the outlet temperature, prior to the end of the pulse fire duration.

24. The method of claim 23, wherein when the rate of temperature change of the outlet temperature exceeds a predetermined rate of temperature change prior to the end of the pulse fire duration, the method comprises deactivating the burner to terminate the transfer of heat to the water supply contained in the heat exchanger.

25. The method of claim 1, wherein the method of heating water in the tankless water heating appliance avoids overheating of the water supply contained in the heat exchanger, wherein the sensing step comprises sensing a temperature indicative of a water temperature of the water supply upstream of, downstream of, or within the heat exchanger, and the activating step comprises pulsed activation of the burner to fire to transfer heat to the water supply contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance.

26. The method of claim 25, wherein the method avoids overheating of the water supply without activating a recirculation pump for the purpose of avoiding the overheating of the water supply.

27. The method of claim 25, wherein step of sensing comprises sensing the minimum rate of temperature change of an inlet temperature at the inlet of the heat exchanger or an outlet temperature at the outlet of the heat exchanger.

28. The method of claim 27 , wherein sensing the minimum rate of temperature change of the inlet temperature or the outlet temperature is performed for a duration that is shorter than another duration when the pre-defined condition of the minimum temporal flow condition is not satisfied.

29. The method of claim 28, wherein sensing the minimum rate of temperature change comprises sensing a temperature difference of 15°F to 20°F over the duration.

30. The method of claim 24, wherein the sensing step comprises sensing a minimum temporal flow condition of the water supply.

31. The method of claim 1, wherein the method of heating water in the tankless water heating appliance includes heating the water supply in response to a minimum user demand for the water supply established by detecting a flow draw for a predetermined draw duration, wherein the sensing step comprises sensing a minimum temporal flow condition of the water supply, and the activating step comprises activation of the burner to fire to transfer heat to the water supply contained in the heat exchanger when the flow of the water supply exceeds the minimum temporal flow condition, and the deactivating step comprises deactivating the burner to terminate the transfer of heat to the water supply contained in the heat exchanger, thereby triggering monitoring for the pre-defined condition of the water supply.

32. The method of claim 31, further comprising activating a recirculation pump to deliver the water supply for heating.

33. The method of claim 31, further comprising activating a recirculation pump, the burner, or a combination thereof when the flow draw is detected.

34. The method of claim 31, wherein the sensing step further comprises sensing the minimum temporal flow condition of the water supply, based on a number of pulses per second detected by a flow meter.

35. The method of claim 31, wherein the sensing step includes sensing a minimum rate of temperature change of the inlet temperature.

36. The method of claim 31, wherein the sensing step includes detecting a decrease in an inlet temperature or an outlet temperature.

37. The method of claim 31, further comprising activating one or more of a recirculation pump and the burner, when a signal indicative of flow decreases, the inlet temperature decreases, the minimum rate of temperature change of the inlet temperature is detected, or a combination thereof.

38. A tankless water heating appliance configured to heat water in conditions of low water flow or no water flow, the tankless water heating appliance comprising: a heat exchanger configured to transfer heat to the water from a heat source when the water is contained in the heat exchanger; at least one sensor configured to sense a pre-defined condition of the water, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water; and a controller configured to: calculate a pulse fire duration for the heat source based on at least one of (i) a target temperature change (°F) of the water upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof; receive, from the at least one sensor, a signal indicating when the predefined condition is sensed; and when the pre-defined condition is sensed: activate the burner to fire for the pulse fire duration to transfer heat to the water contained in the heat exchanger, and deactivate the burner to terminate the transfer of heat to the water contained in the heat exchanger after the pulse fire duration is elapsed; and monitor for the pre-defined condition of the water, such that when the pre-defined condition is sensed again: activate the burner to fire for another pulse fire duration to again transfer heat to the water contained in the heat exchanger, and deactivate the burner to again terminate the transfer of heat to the water contained in the heat exchanger after the another pulse fire duration is elapsed.

39. The tankless water heating appliance of claim 38, wherein the controller is configured to calculate the pulse fire duration according to the following equation:

40. The tankless water heating appliance of claim 38, wherein when the at least one sensor is configured to sense the temperature indicative of a water temperature of the water supply, the at least one sensor is configured to detect at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

41. The tankless water heating appliance of claim 38, wherein the target temperature change is in a range between 1°F to 49°F, and the target temperature change is based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

42. The tankless water heating appliance of claim 41, wherein the target temperature change is in a range between 5°F to 40°F and the target temperature change is based on at least one of the inlet temperature at the inlet of the heat exchanger and the outlet temperature at the outlet of the heat exchanger.

43. The tankless water heating appliance of claim 38, wherein the at least one sensor is configured to sense the minimum temporal flow condition of the water supply based on at least one of an inlet temperature at an inlet of the heat exchanger and an outlet temperature at an outlet of the heat exchanger.

44. The tankless water heating appliance of claim 38, wherein the at least one sensor is configured to sense the minimum temporal flow condition of the water supply using a flow detector configured to sense flow of the water supply.

45. The tankless water heating appliance of claim 38, wherein the heat exchanger comprises a coiled conduit having a plurality of rotations.

46. The tankless water heating appliance of claim 45, wherein the coiled conduit of the heat exchanger comprises at least 17 rotations.

47. The tankless water heating appliance of claim 45, wherein the coiled conduit of the heat exchanger comprises an uncoiled length of at least 40 feet.

48. The tankless water heating appliance of claim 45, wherein the coiled conduit of the heat exchanger includes a cross-sectional area of the coiled conduit of at least 0.8 square inches.

49. The tankless water heating appliance of claim 45, wherein the coiled conduit of the heat exchanger includes a volume capacity of 0.3 to 2.0 gallons.

50. The tankless water heating appliance of claim 49, wherein the coiled conduit of the heat exchanger includes the volume capacity of 0.4 to 0.7 gallons.

51. The tankless water heating appliance of claim 38, wherein the heat source has a minimum heating capacity from 11,000 BTU/hr to 26,000 BTU/hr.

52. The tankless water heating appliance of claim 51, wherein the heat source has the minimum heating capacity from 16,000 BTU/hr to 20,000 BTU/hr.

53. The tankless water heating appliance of claim 38, wherein the pulse fire duration is between 5 seconds to 35 seconds.

54. The tankless water heating appliance of claim 53, wherein the pulse fire duration is between 10 seconds to 30 seconds.

55. The tankless water heating appliance of claim 38, wherein the tankless water heating appliance is configured to heat water without the need for the heat source being other than a burner.

56. The tankless water heating appliance of claim 38, wherein the tankless water heating appliance is configured to avoid freezing of the water contained in the heat exchanger, wherein the at least one sensor is configured to sense a temperature indicative of a minimum water temperature of the water supply upstream of, downstream of, or within the heat exchanger, and the heat source is configured to transfer heat to the water contained in the heat exchanger, thereby avoiding the freezing of the water in the heat exchanger of the tankless water heating appliance.

57. The tankless water heating appliance of claim 56, wherein the tankless water heating appliance is configured to avoid freezing of the water without activating a pump for the purpose of avoiding the freezing of the water.

58. The tankless water heating appliance of claim 56, wherein the at least one sensor is configured to detect at least one of an inlet temperature at the inlet of the heat exchanger and an outlet temperature at the outlet of the heat exchanger.

59. The tankless water heating appliance of claim 56, wherein the heat source is configured to transfer heat to the water contained in the heat exchanger for the pulse fire duration.

60. The tankless water heating appliance of claim 59, wherein the at least one sensor is configured to detect a rate of temperature change of the outlet temperature, prior to the end of the pulse fire duration.

61. The tankless water heating appliance of claim 60, wherein when the rate of temperature change of the outlet temperature exceeds a predetermined rate of temperature change prior to the end of the pulse fire duration, the controller is configured to deactivate the heat source to terminate the transfer of heat to the water contained in the heat exchanger.

62. The tankless water heating appliance of claim 56, wherein the heat source comprises a burner.

63. The tankless water heating appliance of claim 56, wherein the heat source comprises at least one heating element.

64. The tankless water heating appliance of claim 38, wherein the tankless water heating appliance avoids overheating of the water contained in the heat exchanger, wherein the at least one sensor is configured to sense a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger, and the heat source is configured to transfer heat to the water contained in the heat exchanger, thereby avoiding the overheating of the water supply in the heat exchanger of the tankless water heating appliance.

65. The tankless water heating appliance of claim 64, wherein the tankless water heating appliance avoids overheating of the water without activating a recirculation pump for the purpose of avoiding the overheating of the water.

66. The tankless water heating appliance of claim 64, wherein the at least one sensor is configured to sense the minimum rate of temperature change of an inlet temperature at the inlet of the heat exchanger or an outlet temperature at the outlet of the heat exchanger.

67. The tankless water heating appliance of claim 66, wherein the at least one sensor is configured to sense the minimum rate of temperature change of the inlet temperature or the outlet temperature, for a duration that is shorter than another duration when water is not heated in conditions of low water flow or no water flow.

68. The tankless water heating appliance of claim 67, wherein the at least one sensor is configured to sense the minimum rate of temperature change in a range between 15°F to 20°F over the duration.

69. The tankless water heating appliance of claim 64, wherein the at least one sensor is configured to sense a minimum temporal flow condition of the water.

70. The tankless water heating appliance of claim 38, wherein the tankless water heating appliance heats the water in response to a minimum user demand for the water established by detecting a flow draw for a predetermined draw duration, wherein the at least one sensor is configured to sense a minimum temporal flow condition of the water, and the heat source is configured to transfer heat to the water contained in the heat exchanger when the flow of the water exceeds the minimum temporal flow condition, and the heat source is deactivated to terminate the transfer of heat to the water contained in the heat exchanger, thereby triggering the controller to monitor for the pre-defined condition of the water.

71. The tankless water heating appliance of claim 70, further comprising a recirculation pump configured to deliver the water for heating.

72. The tankless water heating appliance of claim 70, wherein the controller is configured to activate a recirculation pump, the heat source, or a combination thereof when the flow draw is detected.

73. The tankless water heating appliance of claim 70, wherein the at least one sensor is configured to sense the minimum temporal flow condition of the water, based on a number of pulses per second detected by a flow meter.

74. The tankless water heating appliance of claim 70, wherein the at least one sensor is configured to sense a minimum rate of temperature change of the inlet temperature.

75. The tankless water heating appliance of claim 70, wherein the at least one sensor is configured to detect a decrease in an inlet temperature or an outlet temperature.

76. The tankless water heating appliance of claim 70, wherein the controller is configured to activate one or more of a recirculation pump and the heat source, when a number of pulses per second detected by a flow meter decreases, the inlet temperature decreases, the minimum rate of temperature change of the inlet temperature is detected, or a combination thereof.

77. A tankless water heating appliance configured to heat water in conditions of low water flow or no water flow, the tankless water heating appliance comprising: a heat exchanger configured to transfer heat to the water from a heat source when the water is contained in the heat exchanger; at least one sensor configured to sense a pre-defined condition of the water, the pre-defined condition being selected from the group consisting of (i) a temperature indicative of a water temperature of the water upstream of, downstream of, or within the heat exchanger; (ii) a minimum rate of temperature change of the water supply upstream of, downstream of, or within the heat exchanger; and (iii) a minimum temporal flow condition of the water; and a controller configured to: calculate a pulse fire duration for the heat source based on at least one of (i) a target temperature change (°F) of the water upstream of, downstream of, or within the heat exchanger; (ii) a volume (gallons) of the water contained in the heat exchanger; (iii) a minimum rated heating capacity (BTU/hour); or a combination thereof; receive, from the at least one sensor, a signal indicating when the predefined condition is sensed; and when the pre-defined condition is sensed: activate the burner to fire for the pulse fire duration to transfer heat to the water contained in the heat exchanger, and deactivate the burner to terminate the transfer of heat to the water contained in the heat exchanger after the pulse fire duration is elapsed; and monitor for the pre-defined condition of the water, such that when the pre-defined condition is sensed again: activate the burner to fire for another pulse fire duration to again transfer heat to the water contained in the heat exchanger, and deactivate the burner to again terminate the transfer of heat to the water contained in the heat exchanger after the another pulse fire duration is elapsed; and wherein the heat exchanger comprises a coiled conduit shaving a plurality of rotations extending between an inlet of the heat exchanger and an outlet of the heat exchanger, the number of plurality of rotations being selected to increase the volume of the water to be heated in the coiled conduit of the heat exchanger.

78. The tankless water heating appliance of claim 77, the plurality of rotations including at least 17 rotations, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

79. The tankless water heating appliance of claim 77, the plurality of coils having a capacity of at least 0.5 gallons for the water to be heated in the coiled conduit between the inlet and the outlet, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.

80. The tankless water heating appliance of claim 77, the plurality of coils including a conduit having an uncoiled length of at least 40 feet, a cross-sectional area of at least 0.8 square inches, or an uncoiled length of at least 40 feet and a cross- sectional area of at least 0.8 square inches, thereby providing an increased volume of the water to be heated in the coiled conduit between the inlet and the outlet.