WATER HEATER WITH PROGRAMMABLE LOW TEMPERATURE MODE

Abstract

The temperature in a water tank (e.g., a residential water tank) is monitored, and a controller switches between a high temperature mode of operation and a low temperature mode of operation (e.g., based on a daily or weekly program). During the low temperature mode of operation, the controller generates signals to selectively activate a water heater to keep the water's temperature within a first range of values, (e.g., between 105 and 113° F). During the high temperature mode of operation, the controller generates signals that cause the water heater to heat the water to a temperature that is above the first range of values. This arrangement may be used for saving energy by operating in the low temperature mode at night and during those parts of the day when nobody is home, and by operating in the high temperature mode in the morning and evening when the demand for hot water is typically high. This arrangement is also well-suited for day-care centers and nursing homes, in which case the low temperature mode is used to reduce the risk of scalding. It is also useful in the homes of people who wish to avoid violating a religious injunction that prohibits heating liquids beyond a threshold temperature on the Sabbath.

Description

BACKGROUND

Conventional water heaters for residential and mixed use buildings typically keep the water in the tank between about 140-150°, and a thermostat is usually used to control the water temperature. (Note that all temperatures mentioned herein are specified in degrees Fahrenheit.) However, since thermostats do not provide a high a degree of accuracy, the water temperature can often fluctuate by up to 10° before the heating system switches on. In many cases, the inaccurate nature of the temperature control in conventional water heaters is not a problem, because the user can compensate for temperature variations by mixing in more or less cold water at the tap. In other cases, e.g., when small children or infirm adults may be using the hot water, the 140-150° temperature posses a potential risk of scalding the user. This risk can be eliminated by reducing the temperature of the water in the tank at all times (e.g., to 110°). However, keeping the temperature that low makes it very likely that the users will run out of hot water during high demand periods (e.g., in the morning, when many members of the household may be showering). Moreover, for low temperature operation, the large fluctuations of conventional temperature controls becomes more of an issue, since a 10° increase would increase the risk of scalding, and a 10° decrease would cause the users to run out of hot water during high demand periods.

SUMMARY

A controller monitors the temperature of water in a tank and switches between a high temperature mode of operation and a low temperature mode of operation based on time. During the low temperature mode of operation, the controller generates signals to selectively activate a water heater to keep the water's temperature within a first range of values (most preferably within a 4° or 6° subset of the 105°-113° F. range). During the high temperature mode of operation, the controller generates signals that cause the water heater to heat the water to a temperature that is above the first range of values.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a gas-fired water heater with a controller that is configured to provide a high temperature mode of operation and a low temperature mode of operation.

FIG. 2 is a schematic diagram of an alternative temperature control circuit for the system shown in FIG. 1.

FIG. 3 is a pictorial representation of the FIG. 1 embodiment, with the controller mounted on the water tank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a gas-fired water heater that has a high temperature mode of operation and a low temperature mode of operation. The water heater maintains accurate control over the water temperature in the low temperature mode of operation. The water heater uses a programmable controller/timer for switching between the high temperature and the low temperature modes at regular intervals. Note that the invention is described herein in the context of a gas-fired heater. However, the present invention is not limited to gas-fired heaters, and may be used with other types of water heating systems (e.g., electric and oil-fired water heaters) to provide similar results.

A water tank 30 of any conventional construction may be used. One example of a suitable water tank is the Bradford White M-I series of upright residential gas water heaters. The water in the water tank 30 is heated by a gas burner 45 which is configured with a suitable valve 46 to control the flow of gas from the gas supply 48 into the burner 45. One example of a suitable gas valve is the Robertshaw 722 series. The gas burner 45 and valve 46 are hooked up to the gas supply 48 using conventional techniques that are well known to persons skilled in the relevant art. A gas ignition controller 40 is hooked up to valve 46, also using conventional techniques that are well known to persons skilled in the relevant art. One example of a suitable gas ignition controller is the Robertshaw 780 series. Taken together, the ignition controller 40, the valve 46, and the burner 45 are configured so that an electrical input signal to the ignition controller 40 provides control over the flow of gas through the valve 46 into the burner 45 in order to heat the water 32 in the tank 30.

The decision to turn on the burner 45 or turn off the burner 45 is made by a controller 20, which sends appropriate electrical signals to the ignition controller 40 to control the flow of gas into the burner 45. More specifically, when the controller 20 receives information indicating that the temperature of the water 32 in the tank 30 is too low, the controller 20 sends appropriate electrical signals to the ignition controller 40 which will, in turn, cause the burner 45 to turn on, thereby raising the temperature of the water 32. If the controller 20 receives information indicating that the temperature of the water 32 in the tank 30 is at or above the desired temperature at any given moment, the controller 20 turns off the signal to the ignition controller 40, which causes the valve 46 to turn off so that the burner 45 will stop heating the water 32 in the tank 30.

The controller 20 receives information about the temperature of the water 32 from a temperature probe 25. The temperature-sensing portion of the probe 25 is in thermal contact with the water 32 in the tank 30. For the application described below, the water temperature must be sensed with a higher degree of accuracy than in conventional water heaters. Accordingly, the temperature probe 25 must be designed to provide relatively high accuracy. One preferred approach for implementing a temperature probe with sufficiently high accuracy is to use a thermistor such as the Invensys-Robertshaw 54584-006. Alternative temperature sensors that can provide sufficient accuracy include RTDs and integrated circuit temperature sensors, such as the LM34 analog temperature sensor or the LM92 digital temperature sensor, both made by National Semiconductor. The latter can sense temperatures between 60 and 120° F. to an accuracy of less than 1° F.

The interface between the temperature probe 25 and the controller 20 will depend on the particular sensor technology that is selected for use in the temperature probe 25. However, for any given sensor technology, the interface between the controller 20 and the temperature probe 25 is preferable implemented using conventional techniques that are well known to persons skilled in the relevant art. Based on the signals arriving from the temperature probe 25, the controller 20 obtains information about the temperature of the water 32 in the tank 30. The controller 20 using this information to decide whether or not to turn on the burner 45 by sending appropriate control signals to the ignition controller 40. Circumstances when the controller 20 turns the burner 45 on or off are described below.

One useful application for the dual-mode water heater depicted in FIG. 1 would be a day care center in mixed-use building. At night and in the morning, when the residents will likely be taking showers and using a lot of hot water, the controller 20 selects the high temperature mode and maintains the temperature of the water in the tank at about 140°. This is accomplished by reading the signals arriving from the temperature sensor 25 to sense the temperature of the water in the tank 30, and sending appropriate signals to the ignition controller 40 to turn the burner 45 on or off The temperature monitoring via the sensor 25 may be done constantly or periodically, but in the latter case it should be done often enough so that the temperature cannot change too much between measurements, based on to the thermal inertia of the water in the tank 30.

When the controller 20 recognizes that it is time for the day care center to open (e.g., based on a time schedule that has been programmed into the controller 20), the controller 20 sets the system to operate in the low temperature mode. Optionally, the switch to the low temperature mode is programmed to occur an interval of time before the lower temperature water is actually required, since the tank will not cool instantly as soon as the mode is switched. For example, if the day care center opens at 8 AM, the controller may be programmed to switch to the low temperature mode a half hour in advance of that time, at 7:30 AM. The temperature will drop between 7:30 and 8 as hot water is drawn out of the tank (by ordinary use of hot water) and replaced by incoming cold water.

Optionally, after the low temperature mode has been selected, hot water may be drained from the tank under control of the controller 20 in order to rapidly reduce the temperature of the water to the desired level. One way to accomplish this is by having the controller 20 send appropriate signals to an electrically operated valve (not shown) that draws hot water from any hot water pipe that is fed by the tank 30. Of course, appropriate plumbing must be provided between the hot water supply, the valve, and an appropriate drain.

A suitable program of operation for the controller 20 for use in a day care center that operates on weekdays only is set forth in Table 1 below.

TABLE 1
Day	5:00 AM-7:30 AM	7:30 AM-6:00 PM	6:00 PM-5:00 AM
Sunday	140°	140°	140°
Monday	140°	110°	140°
Tuesday	140°	110°	140°
Wed-	140°	110°	140°
nesday
Thurs-	140°	110°	140°
day
Friday	140°	110°	140°
Satur-	140°	140°	140°
day

Another useful application for the dual-mode water heater depicted in FIG. 1 would be in residential homes. In the evening and in the morning, when the residents will likely be taking showers and using a lot of hot water, the controller selects the high temperature mode and maintains the temperature of the water in the tank at a desired high temperature (e.g., 130°). At night and during portions of the day when nobody is home, the temperature may be set to a desired low temperature (e.g., 90°) in order to save energy. Temperature control is implemented in the same way as in the day care application discussed above, except that the timing of the transitions and the temperature set points are different. A suitable program of operation for the controller 20 for achieving energy savings in residential homes is set forth in Table 2 below.

TABLE 2
Day	6-8 AM	8 AM-5 PM	5-11 PM	11 PM-6 AM
Sunday	130°	130°	130°	90°
Monday	130°	90°	130°	90°
Tuesday	130°	90°	130°	90°
Wednesday	130°	90°	130°	90°
Thursday	130°	90°	130°	90°
Friday	130°	90°	130°	90°
Saturday	130°	130°	130°	90°

A third example of a suitable application for the dual-mode water heater depicted in FIG. 1 would be for use in the homes of people who observe the Jewish law that prohibits heating liquids beyond a certain threshold temperature on the Sabbath. Many Jewish legal authorities that were contacted by the inventor maintain that the threshold temperature is 113° F., and others maintain that the threshold temperature is as low as 106° F. However, all these authorities agree that heating liquids on Sabbath is not prohibited by Jewish law when the liquid is not heated beyond the threshold temperature.

In a conventional water heater, when the water temperature is set at about 140°, when a person draws hot water from the tank, cold water flows into the tank via the cold water inlet pipe. When that cold water mixes with the hot water that is already present in the tank, its temperature will be raised above the threshold, which would violate the prohibition of heating liquids on the Sabbath. To avoid this, some observant Jews refrain from using hot water on the Sabbath, so that the incoming cold water is never heated beyond the threshold temperature.

If, however, the hot water that is contained in the tank is always kept at or below 112°, which is below the threshold temperature according to the aforementioned Jewish legal authorities, when the cold water flows into the tank via the cold water inlet pipe, it will not be heated past the threshold temperature. Under these circumstances, Jewish law permits people to draw hot water out of the tank on Sabbath, even though cold water will flow into the hot water tank as the hot water leaves.

Thus, for this application, the controller 20 is programmed to switch into the low temperature mode of operation about one hour before Sabbath (to provide a period of cool-down time), and to switch back to the normal high temperature mode when Sabbath is over. In the embodiment described above with rapid cooling, that time can be reduced. Since the Jewish Sabbath starts at sundown on Friday evening and lasts until the stars come out on Saturday night, and since the sun sets at different times during the year, a suitable program for the controller 20 for automatically entering the low temperature mode before Sabbath begins is shown in Table 3:

	TABLE 3
		start low temp. mode	end low temp mode.
	Month	Friday at	Saturday at
	January	3:30 PM	5:30 PM
	February	4:00 PM	6:00 PM
	March	4:30 PM	6:30 PM
	April	5:00 PM	7:00 PM
	May	5:30 PM	7:30 PM
	June	6:00 PM	8:00 PM
	July	6:00 PM	8:00 PM
	August	5:30 PM	7:30 PM
	September	4:30 PM	7:00 PM
	October	4:00 PM	6:30 PM
	November	3:30 PM	6:00 PM
	December	3:00 PM	5:30 PM

Preferably, the controller is programmed to make suitable adjustments in regions that observe daylight savings time, to adjust for the changed time of sunset.

Alternatively, instead of roughly estimating the time when Sabbath begins based on the month, a more precise start time for switching to the low temperature mode can be determined based on the date. The controller 20 can obtain knowledge of the date by keeping track of time after being set once by the user in any conventional manner. In alternative embodiments, an appropriate receiver (not shown) that receives the atomic clock signals broadcast by the National Institute of Standards and Technology in Boulder, Colorado, may be added so the system to determine the date and time. The controller 20 would then determine the correct time to switch modes based on the expected time of sunset on the day in question (e.g., by using an appropriate look-up table indexed by the date).

Optionally, a Jewish calendar may be programmed into the controller 20, and the controller may be programmed to select the low temperature mode during those Jewish holidays when similar prohibitions on heating water are applicable.

Controlling the temperature with a high degree of accuracy is particularly important in the first and third applications described above, especially in the low-temperature mode of operation. For example, in the context of a daycare center, if the water is 10° too hot while the daycare center is opened, it would increase the risk of accidentally scalding, and temperatures above 113° are problematic for the Jewish Sabbath. (Note that for those users who choose to comply with a lower threshold temperature, such as 106°, all the relevant temperature values set forth herein must be adjusted accordingly). Conversely, if the water temperature drops too far (e.g., to 100°), it may not be hot enough for the user's desired use (e.g. washing hands or doing dishes), especially during periods of high demand. Accordingly, the controller 20 should make appropriate and timely adjustments to minimize the temperature fluctuations, preferably to within a 6° F. range, and more preferably to within a 4° range (e.g., to manage the temperature fluctuations within the tank 30 so that it always stays between 105° and 111°, or more preferably between 107° and 111°).

In the embodiment illustrated in FIG. 1, the controller 20 turns the burner 45 on and off as required in both the low temperature mode and the high temperature mode by sending appropriate signals to the ignition controller 40. Thus, the controller 20 has direct control over the burner 45 in both the low temperature and the high temperature modes. In an alternative embodiment, the controller 20 retains direct control over the burner 45 in low temperature mode, but passes responsibility for controlling the temperature to another device (e.g., a conventional thermostat) in the high temperature mode where accuracy is less important. This may be accomplished as shown in FIG. 2, for example, by having the controller 20′ selectively actuate a relay 90 to connect a thermostat 92 to the control input of the ignition controller 40 in high temperature mode, and to connect the control output of the controller 20 to the ignition controller 40 in low temperature mode. In that case, the controller 20′ would have direct control over the burner 45 in low temperature mode, but would have indirect control over the burner in the high temperature mode (by letting the thermostat bring the temperature up to a range that is higher than the temperatures associated with the low temperature mode).

FIG. 3 shows how the system can be physically connected to a water heater. A control panel 80 is shown mounted to the body of the water heater 30 at a convenient height. The control panel 80 preferably houses the controller 20 (shown in FIG. 1), as well as a display and buttons for implementing a user interface, which may be implemented in any of a variety of ways that will be apparent to persons skilled in the relevant arts. For example, a user interface similar to those used for programmable air conditioning thermostats may be used, preferably including a digital display that displays the current temperature of the water in the tank and/or the temperature setting. The control panel 80 may be mounted to the tank's wall using any suitable approach including but not limited to screws, glues, magnets, straps that surround the tank, etc. A magnetic mount may make it easier to install the above-described embodiments in retrofits of existing tanks. Preferably, the control panel 80 is relatively small and as lightweight to facilitate easy mounting.

The tank 30 has a utility compartment 82, which may be used to house the gas ignition controller. In electric heat embodiments, the utility compartment 82 may be used to house components like a controller power module, a transformer, a heating element control switch, and the connection to the temperature probe. Optionally, a cover for the utility compartment 82 may be shaped to accommodate the control cable connection, and the power module may be fixed to the cover itself to simplify the installation and retrofitting of existing tanks. A cable 84 connects the control panel 80 to the components housed in the utility compartment 82. Optionally, the cable 84 may be coiled to simplify installation onto different sized tanks or at other locations that may be preferred by the user.

Claims

1. A water heating apparatus comprising: a tank for holding a volume of water; a temperature sensor configured to be in thermal contact with the water and produce an output signal that is accurately indicative of the water's temperature; means for heating the water in the tank; and a controller that monitors the water's temperature based on the output signal and selects, based on the passage of time, either a high temperature mode of operation or a low temperature mode of operation, wherein in the low temperature mode, the controller, based on the output signal, generates signals to selectively activate the means for heating so as to keep the water's temperature within a first range of values, and wherein, in the high temperature mode, the controller generates signals that cause the means for heating to heat the water to a temperature that is above the first range of values.

2. The water heating apparatus of claim 1, wherein the temperature sensor comprises a thermistor.

3. The water heating apparatus of claim 1, wherein the temperature sensor is implemented in an integrated circuit.

4. The water heating apparatus of claim 1, wherein the means for heating comprises a gas burner, and wherein the controller comprises a gas ignition controller that is operatively connected to the gas burner.

5. The water heating apparatus of claim 1, wherein the tank has a capacity of at least 30 gallons.

6. The water heating apparatus of claim 1, wherein the controller is programmed to cycle between the low temperature mode and the high temperature mode based on the time of day and a user-programmed setting.

7. The water heating apparatus of claim 6, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

8. The water heating apparatus of claim 7, wherein the lower limit of the first range of values is at least 105° F.

9. An apparatus comprising: a temperature sensor configured to be in thermal contact with water in a tank and produce an output signal that is accurately indicative of the water's temperature; and a controller configured to monitor the water's temperature based on the output signal and select, based on the passage of time, either a high temperature mode of operation or a low temperature mode of operation, wherein in the low temperature mode, the controller, based on the output signal, generates signals to selectively activate a water heater to keep the water's temperature within a first range of values, and wherein, in the high temperature mode, the controller generates signals that cause the water heater to heat the water to a temperature that is above the first range of values.

10. The apparatus of claim 9, wherein the temperature sensor comprises a thermistor.

11. The apparatus of claim 9, wherein the temperature sensor is implemented in an integrated circuit.

12. The apparatus of claim 9, wherein the controller is programmed to cycle between the low temperature mode and the high temperature mode based on the time of day and a user-programmed setting.

13. The apparatus of claim 12, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

14. The apparatus of claim 13, wherein the lower limit of the first range of values is at least 105° F.

15. A method of controlling the temperature of water in a tank comprising the steps of: monitoring the temperature of the water in the tank; switching, based on the passage of time, between a high temperature mode of operation and a low temperature mode of operation; generating, during the low temperature mode, signals to selectively activate a water heater to keep the water's temperature within a first range of values; and generating, during the high temperature mode, signals that cause the water heater to heat the water to a temperature that is above the first range of values.

16. The method of claim 15, wherein the switching step comprises switching between the high temperature mode and the low temperature mode based on the time of day and a user-programmed setting.

17. The method of claim 16, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

18. The method of claim 17, wherein the lower limit of the first range of values is at least 105° F.

19. A water heating apparatus comprising: a tank for holding a volume of water; a temperature sensor configured to be in thermal contact with the water and produce an output signal that is accurately indicative of the water's temperature; means for heating the water in the tank; and a controller that monitors the water's temperature based on the output signal and recognizes when the Jewish Sabbath occurs based on the passage of time or receipt of a time-dependent signal, wherein the controller, based on the output signal, selectively activates the means for heating to keep the water's temperature within a first range of values during the Jewish Sabbath, and wherein the controller controls the means for heating so that water is heated to a temperature that is above the first range of values during at least some other times.

20. The water heating apparatus of claim 19, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

21. The water heating apparatus of claim 20, wherein the lower limit of the first range of values is at least 105° F.

22. The water heating apparatus of claim 19, wherein the controller recognizes when Jewish holidays occur based on the passage of time or receipt of a time-dependent signal, and wherein the controller, based on the output signal, selectively activates the means for heating to keep the water's temperature within the first range of values during Jewish holidays.

23. The water heating apparatus of claim 22, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

24. The water heating apparatus of claim 23, wherein the lower limit of the first range of values is at least 105° F.

25. An apparatus comprising: a temperature sensor configured to be in thermal contact with water in a tank and produce an output signal that is accurately indicative of the water's temperature; and a controller that monitors the water's temperature based on the output signal and recognizes when the Jewish Sabbath occurs based on the passage of time or receipt of a time-dependent signal, wherein the controller, based on the output signal, selectively activates a water heater to keep the water's temperature within a first range of values during the Jewish Sabbath, and to heat the water to a temperature that is above the first range of values during at least some other times.

26. The apparatus of claim 25, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

27. The apparatus of claim 26, wherein the lower limit of the first range of values is at least 105° F.

28. The apparatus of claim 25, wherein the controller recognizes when Jewish holidays occur based on the passage of time or receipt of a time-dependent signal, and wherein the controller, based on the output signal, selectively activates the means for heating to keep the water's temperature within the first range of values during Jewish holidays.

29. The apparatus of claim 28, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

30. The apparatus of claim 29, wherein the lower limit of the first range of values is at least 105° F.

31. A method comprising: accurately sensing the temperature of water in a tank; recognizing when the Jewish Sabbath occurs; and selectively activating a water heater to keep the water's temperature within a first range of values during the Jewish Sabbath, and to heat the water to a temperature that is above the first range of values during at least some other times.

32. The method of claim 31, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

33. The method of claim 32, wherein the lower limit of the first range of values is at least 105° F.

34. The method of claim 31, further comprising the steps of: recognizing when Jewish holidays occur; and selectively activating the water heater to keep the water's temperature within the first range of values during the Jewish holidays.

35. The method of claim 34, wherein the first range of values has a range of 6° F. or less, and the upper limit of the first range of values is below 113° F.

36. The method of claim 35, wherein the lower limit of the first range of values is at least 105° F.