US20120060827A1

US20120060827A1 - Control for a tankless water heater used with a solar water heating system

Info

Publication number: US20120060827A1
Application number: US13/042,076
Authority: US
Inventors: John Joseph Roetker
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2011-03-07
Filing date: 2011-03-07
Publication date: 2012-03-15

Abstract

A tankless water heating auxiliary system for a solar water heating system, includes a solar collector; a tankless water heater auxiliary system; an insulated water storage tank storing the potable water; a heat exchange system for heating stored water; and piping for connecting the collector, the storage tank and the heat exchanger in fluid communication. A first sensor is connected to and located adjacent the storage tank for sensing the temperature of the stored water at an outlet of the tank. A method for controlling initiation of heating in a tankless water heater auxiliary system, includes monitoring operation of a tankless water heater; measuring water flow using a water flow sensor to determine if water flow rate exceeds a use determined flow rate; implementing a control time delay into the tankless water heater to purge water from the heater and sense the inlet water supply temperature; measuring the water temperature using a heat exchanger outgoing thermistor; comparing the temperature measured by the thermistor to a predetermined temperature; and initiating a combustion sequence if the temperature measured by the outgoing themistor is less than the predetermined temperature.

Description

BACKGROUND OF THE DISCLOSURE

The disclosure relates to a control for a tankless water heater serving as an auxiliary heater for a solar water heating system.
Solar water heating systems are made up of components that collect solar energy, transfer the energy to the potable water via a heat exchanger, store the thermal energy, control system operations, deliver hot water where it is needed, and protect the system against freezing. Components can be combined in a variety of ways, but these six basic functions must be met, although some systems are simple enough that passive physics provide the control and motive forces to drive the fluids and heat transfer in the system. The systems also typically include an auxiliary heating system for when the solar heating is insufficient to meet hot water usage.
Solar water heating systems can generally be described using the following four terms: direct or indirect and passive or active. Direct systems heat the potable water directly through solar exposure. These systems are typically used in regions with little freeze risk since the potable water is used as the heat transfer fluid and therefore exposed to temperature outside of conditioned space. Indirect systems use a secondary heat transfer fluid to collect and transfer the solar energy to the potable water. The heat transfer fluids used are typically freeze resistant and these systems are better suited for cooler climates. Passive systems use the differential density created by the thermal gradient of the water or heat transfer fluid to move fluids in the system and accumulate heated potable water for usage. Active systems employ pumps to circulate the water or heat transfer fluid for the purpose of heat exchange. Several different system configurations are currently used based on these concepts. Solar water heating systems are capable of heating water to high temperatures, commonly up to 160° F. or higher. The system typically uses a thermostatic mixing valve (TMV) to temper the water to a selected level such as 110° F. to 140° F., to reduce the burn risk of the water as well as increase the energy storage capacity of the water storage tank.
Solar water heating systems typically employ one or more water storage tanks to contain the solar energy collected over the sunlit hours. Since the solar energy resource is not synchronized with the hot water usage, the energy storage function is an essential part of the system. During periods when the solar resource is insufficient to meet water usage, such as during cloudy weather conditions or during high hot water demand, an auxiliary heating system is needed to supply hot water. Several options exist for electric or gas auxiliary heating systems. Typically, a conventional electric or gas storage water heater can be combined in series with the solar water storage tank. Since this approach requires two storage tanks, significant floor space is needed to accommodate the arrangement. Single tank electric systems exist employing a large single tank, which thermostatically operate a resistance heater to heat the upper portion of the tank while the solar system provides heat to the lower portion of the tank. A gas tankless water heater can serve as a more compact gas auxiliary heater coupled with a solar water storage tank. The tankless water heater can either be mounted to the storage tank or in close proximity to the tank.
Tankless water heaters, also known as instantaneous or on demand water heaters, serve as inline heater exchangers which raise supplied water from the local supply temperature to a user selected set temperature level, usually in the range from 110° F. to 140° F. Tankless systems have negligible water storage capacity, typically less than 2 gallons. Heating is accomplished using high output, fixed level or variable gas burners, ranging from 50,000 BTU/hr to 200,000 BTU/hr, or electric resistance heaters ranging from 5,000 to 9,500 watts. Gas systems are most common due to the high energy requirement needed to create the desired temperature rise at flow rates needed to service a typical residence or light commercial application.
Tankless water heaters have previously been coupled with solar heated storage water tanks, serving as an auxiliary. The arrangement can be configured with the solar heated storage tank supplying water to a heated water circulation loop, which circulates heated water to usage locations with a continuously running or thermostatically controlled pump. The temperature of the circulation loop is maintained by the operation of the tankless unit, while the solar heated supply water feeds the system with water that requires a minimal temperature lift prior to usage. This configuration typically utilizes a small, 2- to 5-gallon, storage tank near the usage location to level the outlet water temperature. While this system supplies a consistent and immediate supply of heated water, it consumes excessive energy to maintain the circulation loop temperature and requires additional equipment at the time of installation.
The typical tankless water heater operation control method, whether gas or electric, senses the initiation of inlet water flow triggering a heating even independent of the upcoming water temperature to the unit. When cold water is being supplied to the tankless unit, this method provides the best heating performance with an appropriate level of efficiency. The conventional tankless operation control does not make provision for incoming water supply, previously heated at or above the set tankless units point, and as a result needless heating evens are initiated consuming unneeded energy and increasing the number of heating system operating cycles contributing to a shortened life of the equipment.
A conventional way of providing an on-demand supply of hot water to various plumbing fixtures is to use a tankless or “instantaneous” water heater in which water is flowed through a high heat input heat exchanger, without appreciable water storage capacity, so as to provide only as much hot water as needed by the open fixture(s). Where higher hot water flow rates than the instantaneous water heater can provide at the desired heated temperature are required, it has been conventional practice to connect a storage tank to the instantaneous water heater, in series, to supplement the hot water delivery capability of the instantaneous water heater with pre-heated storage tank water.
Thus, it is considered desirable to provide an improved tankless water heater control when used as an auxiliary with a solar water heating system, which overcomes the above-mentioned deficiencies and others while providing a better and more advantageous overall result.

SUMMARY OF THE DISCLOSURE

According to one aspect of the disclosure, a tankless water heating auxiliary system for a solar water heating system, includes a solar collector; a tankless water heater auxiliary system; an insulated water storage tank storing potable water; a heat exchange system for heating stored water; piping for connecting the collector, the storage tank and heat exchanger in fluid communication; and a first sensor connected to and located adjacent the storage tank for sensing the temperature of the stored water at an outlet of the tank.
According to another aspect of the disclosure, a method for controlling initiation of heating in a tankless water heater auxiliary system, includes: monitoring operation of a tankless water heater; measuring water flow using a water flow sensor to determine if water flow rate exceeds a use determined flow rate; implementing a control time delay into the tankless water heater to purge water from the heater and sense the inlet water supply temperature; measuring the water temperature using a heat exchanger outgoing thermistor; comparing the temperature measured by the thermistor to a predetermined temperature; and initiating a combustion sequence if the temperature measured by the outgoing themistor is less than the predetermined temperature.
Another aspect of the disclosure is a solar water heater system employing a tankless, (instantaneous) inline heater as an auxiliary which is controlled using a sensor configuration which determines the stored water temperature as a condition for initiating the powering or combustion sequence for the auxiliary heater. The sensor configuration eliminates needless cycling of auxiliary systems and reduces energy consumption.
Another aspect of the disclosure is to place an auxiliary control sensor at the outlet or top of the solar water storage tank which senses the water delivered to the tankless auxiliary and prevent needless powering of the auxiliary power system. This solution would reduce energy consumption and reduce the number of operation cycles of the auxiliary, improving reliability.
Another aspect of the disclosure is reduced energy consumption in the range of $20-$40 annually and a reduction in the number of operation cycles, improving system reliability.
Another aspect of the disclosure is a stored/delivered water temperature sensor which determines heating requirements for the series combination of a heat pump water heater storage tank and an instantaneous water heater.
Still other aspects of the disclosure will become apparent after a reading and understanding of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the solar water heater tank and tankless auxiliary system in accordance with a preferred embodiment of the disclosure;

FIG. 2 is a flow chart illustrating the sequence of steps of the combustion sequence of the tankless auxiliary;

FIG. 3 is a control board for the system of FIG. 1; and

FIG. 4 is a flow chart illustrating a sequence of steps of the combustion sequence of the tankless auxiliary in accordance with another embodiment of the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a solar water heater supply system 10 in accordance with a preferred embodiment of the present disclosure is shown.
The system 10 includes a solar collector 12 which may be of conventional design which collects and provides heat to a heat transfer fluid that then transfers the heat from the collector 12 to water contained in a conventional insulated water heater storage tank 14 having a cold water inlet 16 near a bottom 17 of the tank and a hot water outlet 18 near a top 19 of the tank. A thermostatic mixing valve 20 is provided at a hot water outlet pipe 22 which mixes cold water from a cold water supply line 26 with the hot water from hot water line 22 to provide the user with water at the user selected water temperature.
Such mixing valves 20 are typically used in solar hot water heating systems because it is desirable to store water in the tank at temperatures which may be higher than that desired for use by the user, for increased energy storage. This is because solar energy is only available periodically over the course of a day, e.g., during daylight hours, and the intensity of the sunlight varies even during such hours, so in order to take the fullest advantage of the energy when it is available, the water in the heater storage tank may be allowed to reach a higher temperature than that desired by the user when turning on the hot water. For example, the maximum temperature for the water in the tank may be pre-set at a value on the order of 160° F., while the user may prefer a setting in the 110° F.-120° F. range. The mixing valve blends cold water as needed with the hot water to properly limit the temperature of the water from the water heater system to the temperature selected by the user, effectively increasing stored hot water capacity. Mixing valve 20 may be any one of many commercially available thermostatic mixing valves.
Referring to FIG. 1, cold water enters the tank 14 via cold water inlet 16. Cold water exits the tank via outlet 28 and enters pipe 30 and flows to the solar collector panel 12. The collector warms the water which then passes through warm water outlet pipe 31 to the tank 14 and enters the tank via inlet 32. Warm or hot water exits the tank via outlet 18 and pipe 22 to the tankless water heater 24 via inlet 54. The tank 14 is located in a conditioned space and is vertically close to the collector to reduce head pressure.
A control system determines when sufficient solar energy is available and controls system operation accordingly. A controller 77 is operative via an electrical wire connection to push fluid through the system. In the illustrative embodiment, the control system includes sensor 33, a thermistor sensor which can be band clamped to a copper fluid line at the top of the tank 14 to sense the temperature of the fluid in the line at that point. Alternatively, sensor 33 can be mounted inside the tank. Sensor 33 is connected via wire 35 to tankless heater 24 and controller 77. The power to energize the system under normal operating conditions is provided by an external power source such as a 120 volt ac power supply 34 (FIG. 3) from a utility company, or an integrated power source such as a photovoltaic cell collector. A reserve power supply, such as a battery, is preferably included to provide power to evacuate the heat transfer fluid from the system in the event of a failure of the primary power supply.
Pipe 31 extends out from a solar collection panel 12 which absorbs solar heat and is drawn to the hot water reservoir tank 14 via inlet 32. The warm water is removed from the warmest area of the upper portion 19 of the water tank through a warm water pipe 22 attached to upper portion of the hot water reservoir tank.
Hot water demand exceeding the stored volume of the tank is supplied by the tankless gas water heater. Alternatively, an electric pump operation could also be easily configured to provide electric only operation if gas prices become uncompetitive during all or a seasonal portion of the year. In this scenario, tankless units can simply be disabled.
The tankless, instantaneous inline heater 24 acts as an auxiliary and is controlled using a sensor configuration which determines the sorted water temperature, based on a user selected temperature level, as a condition for initiating the powering or combustion sequence for the auxiliary heater. The sensing eliminates needless cycling of auxiliary systems and reduced energy consumption.
The tankless water heater serves as an inline heater exchanger which raises supplied water from the local supply temperature to a user selected set temperature level, usually in the range from 110° F. to 140° F. The tankless system itself has negligible water storage capacity, typically less than 2 gallons. Heating is accomplished using high output, fixed level or variable gas burners, ranging from 50,000 BTU/hr to 200,000 BTU/hr, or electric resistance heaters ranging from 5,000 to 9,500 watts. Gas systems are preferred due to the high energy requirement needed to create the desired temperature rise at flow rates needed to service a typical residence or light commercial application.
Existing tankless water heater operation control methods, whether gas or electric, sense the initiation of inlet water flow triggering a heating even independent of the upcoming water temperature to the unit. When cold water is being supplied to the tankless unit, this method provides the best heating performance with an appropriate level of efficiency. Existing tankless operation controls do not make provision for incoming water supply, previously heated at or above the set tankless units point, and as a result needless heating evens are initiated consuming unneeded energy and increasing the number of heating system operating cycles contributing to a shortened life of the equipment.
Referring now to FIG. 3, tankless auxiliary water heater 24 carries out operation of a heat exchanger 42 which has a burner 44. A remote control 46 can have various controlling elements or indicators, such as a hot water tension switch, a heating switch, a “burner on” indication light, a driving switch, a water temperature setter and a fluctuation switch and is connected to the system via a wire 48.
Referring to FIG. 2, a logic diagram of the tankless operation sequence is as follows. An inquiry 50 is made in which a water flow sensor 52 measures whether the flow from water inlet 54 is more than 2.4 liters per minute. If the answer is YES, additional remote tank sensor 33 on the tank 14 then measures the water temperature at the tank. An inquiry is made whether the temperature is less than 120° F. If the answer to inquiry 56 is NO, then the water flow sensor again measures water flow. If the answer is YES, then combustion fan 55 is turned on at step 58. This saves energy and starts up the flow event in the tankless heater. Thus, the tank is regulated even if the water is not 160° F. An inquiry 60 is made if the fan rotation is detected to be NORMAL. If the answer is YES, an initial check is made if normal at step 62. If YES, the ignition is turned on at step 64. Then, referring to step 72, the various solenoid valves are operated. Main solenoid valve 66, valves 67, 68, 69 and modulating valve 70 are operated at step 72 and allow gas into the system via inlet 73. An inquiry 74 is made as to whether the flame at burner 44 is detected to be greater than 1 μA. If YES, then hot water leaves the heater via outlet 76.
In a high temperature state, the solar hot water temperature detected with the temperature sensor is higher than the hot-water-supply preset temperature or undesired water temperature setter of the hot-water-supply remote control, a combustion signal is sent to the hot-water-supply controller to prevent combustion movement in the hot water supply system.
Referring to FIG. 3, a control board 77 for the tankless auxiliary water heater 24 of FIG. 1 is shown.
A heat exchanger outgoing thermistor 80 is used to measure hot water temperature at an outlet of heat exchanger 42. If water temperature reaches a predetermined limit, gas supply from gas inlet 73 is stopped. An overheat switch 82 is situated on the heat exchanger 42 to prevent gas supply to the heater such as when water temperature reaches a predetermined limit, such as 97° C. for a predetermined amount of time. A thermal fuse 84 is situated on the heat exchanger 42 to prevent electrical power supply to the heater such as when the temperature exceeds a predetermined limit such as 129° C.
The gas tankless control monitors the stored water temperature as a condition for initiating a heating operation. The control logic is the same as used by heat exchanger outgoing thermistor 80 with the addition of a logical “and” check of the remote temperature sensing thermistor 33 such as shown in FIG. 2.
The temperature of the outgoing hot water is constantly monitored by the water temperature thermistor 33 located near the outlet of the tank. If the outgoing water temperature reaches a temperature above the preset temperature such as 5° F. above the preset temperature, the burner 44 will automatically go out or be directed not to start based on the remote water temperature thermistor 33 sensed value. The temperature difference calibration is to be a user or factory input. The burner 44 will only ignite again once the outgoing hot water temperature falls below the preset temperature.
Sensing probe or thermistor 33 is placed directly on the storage tank 14, preferably adjacent to or on the top 19 of the tank. Alternately, sensor 33 can be placed inside the tank. Placement of the sensor directly on or inside the tank provides direct sensing of the intended supply water and negates the effect of water which has cooled in the piping between the storage tank and the instantaneous heater unit's inboard sensors. The “cool” volume of water in the piping may create a brief powering event which is quickly terminated when the “hot” stored water arrives from the solar storage tank. The remote sensing can be used in parallel with the existing heat exchanger sensor 80, which detected the heat exchanger temperature in addition to the existence of flow as a requirement for the initiation of heating power.
Gas utilities are always seeking energy efficient water heating solutions in order to receive “green” credits as well as an increasing consumer demand for these products. US gas/water/heater sales are 5 million units annually.
By placing the sensor 33 at the outlet or top of the solar water storage tank, needless powering of the auxiliary power system is prevented. This configuration reduces energy consumption and reduces the number of operation cycles of the auxiliary, improving reliability.
Referring to FIG. 4, another embodiment is described using a flow chart diagram. In this embodiment, a tankless auxiliary control mode allows the heating or combustion sequence to occur or be triggered by comparing the heat exchanger outgoing thermistor 80 temperature level relative to a user selected temperature level.
The response to this control input will only be active during a flow event. A time delay after the detection of water flow is needed in order to purge the water in the system and sense the inlet supply water temperature.
Specifically, referring now to FIG. 4, at step 90 the tankless auxiliary operation is monitored as previously described for FIGS. 1-3. Proceeding to inquiry 92, water flow sensor 52 measures the water flow rate from the water inlet 54. An inquiry is made as to whether the water flow detected is greater than a set flow level (e.g. such as 2.4 liters/minute). If the answer is YES, then step 94 is initiated, in which a delay logic is added for an “x” time interval, in which “x” time can be preset by the user. The time delay is needed after the detection of water flow in step 92 to purge the water in the system and sense the inlet supply water temperature.
Proceeding to inquiry 96, the heat exchanger outgoing or exit thermistor 80 temperature level is compared to a preset user temperature level, and an inquiry is made as to whether the heat exchanger outgoing thermistor temperature level is less than the set level. If the answer is YES, then the heating event or combustion logic is initiated as step 98, which is similar to the steps 58-74 described in FIG. 2.
The disclosure has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.

Claims

What is claimed is:

1. A tankless water heating auxiliary system for a solar water heating system, comprising:

a solar collector;

a tankless water heater auxiliary system;

an insulated water storage tank storing potable water;

a heat exchange system for heating stored water;

piping for connecting said collector, said storage tank and said heat exchanger in fluid communication; and a

first sensor connected to and located adjacent said storage tank for sensing the temperature of the stored water at an outlet of said tank.

2. The tankless water heating auxiliary system of claim 1, further comprising a controller connected to said first sensor.

3. The tankless water heating auxiliary system of claim 2, wherein when said first sensor detects whether the water temperature in said storage tank is greater than or less than 120° F.

4. The tankless water heating auxiliary system of claim 3, wherein said first sensor is placed on a top surface of said tank.

5. The tankless water heating auxiliary system of claim 3, wherein said first sensor is placed inside of said tank.

6. The tankless water heating auxiliary system of claim 4, wherein said first sensor is connected to said tankless heater via wire.

7. The tankless water heating auxiliary system of claim 6, wherein said first sensor is operative to detect a temperature greater than a predetermined maximum reference water temperature.

8. The tankless water heating auxiliary system of claim 7, wherein when said first sensor detects a temperature below a predetermined maximum reference temperature, said burner is activated.

9. The tankless water heating auxiliary system of claim 7, wherein when first sensor detects a temperature above 120° F., said burner is not activated.

10. A method for controlling initiation of heating in a tankless water heater auxiliary system, comprising:

monitoring operation of a tankless water heater;

measuring water flow using a water flow sensor to determine if water flow rate exceeds a use determined flow rate;

implementing a control time delay into the tankless water heater to purge water from the heater and sense the inlet water supply temperature;

measuring the water temperature using a heat exchanger outgoing thermistor;

comparing the temperature measured by said thermistor to a predetermined temperature; and

initiating a combustion sequence if the temperature measured by said outgoing themistor is less than said predetermined temperature.