Sabbath controller for a hot water tank

Abstract

A water heating control system has a tank for holding a volume of water heated by a heater and having a hot water outlet and a cold water inlet connected to a main water supply whereby hot water removed from the hot water outlet is replenished with cold water. A temperature sensor provides a temperature signal indicative of water temperature in the tank, and a control unit monitors the water temperature based on the temperature signal and is responsive to selection of a Sabbath mode of operation for periodically actuating and de-actuating the heater while maintaining an average water temperature to less than a permitted preset threshold. In Sabbath mode the control unit closes a shut off valve connected to the water inlet when the heater is actuated and opens the shut off valve when the heater is not actuated.

Claims

1. A water heating control system comprising: a tank for holding a volume of water, said tank having a hot water outlet and a cold water inlet connected to a main water supply whereby hot water removed from the hot water outlet is replenished with cold water, a temperature sensor for providing a temperature signal indicative of water temperature in the tank, a heater for heating the water in the tank, a control unit that monitors the water temperature based on the temperature signal and is responsive to selection of a Sabbath mode of operation for periodically actuating and de-actuating the heater while maintaining an average water temperature to less than a permitted preset threshold, a flowmeter for producing a flow signal when water is drawn from the tank, and a controllable shut off valve connected to the water inlet; wherein when set to the Sabbath mode, the control unit is configured to close the shut off valve when the heater is actuated and to open the shut off valve when the heater is not actuated, and wherein the control unit is responsive to said flow signal for disabling the heater when water is drawn from the tank.

2. The water heating control system according to claim 1, further comprising a water pump coupled between the water outlet and the water inlet for re-circulating water in the tank.

3. The water heating control system according to claim 2, wherein the control unit is configured to activate the water pump when the heater is actuated.

4. The water heating control system according to claim 2, wherein the control unit is configured to activate the water pump constantly according to a preset duty cycle.

5. The water heating control system according to claim 1, wherein the control unit has a standby battery backup for retaining user settings in case of an electrical power failure.

6. The water heating control system according to claim 1, further including an override switch, operation of which during Sabbath mode causes the control unit to open the shut-off valve for a predetermined time.

7. The water heating control system according to claim 1, further including a mode selector for manually selecting regular use or Sabbath use.

8. The water heating control system according to claim 1, further including a programmable clock that automatically activates and deactivates Sabbath use based on a calendrical data relating to start and end times of the Sabbath.

9. A control unit for a water heating system, wherein: the water heating system comprises: a tank for holding a volume of water, said tank having a hot water outlet and a cold water inlet connected to a main water supply whereby hot water removed from the hot water outlet is replenished with cold water, a temperature sensor for providing a temperature signal indicative of water temperature in the tank, a heater for heating the water in the tank, and a controllable shut off valve connected to the water inlet; wherein the control unit comprises: a sensor input for coupling to the temperature sensor, a valve control output for coupling to the shut off valve, and a controller configured to monitor the water temperature based on the temperature signal and being responsive to a Sabbath mode of operation for periodically actuating and de-actuating the heater while maintaining an average water temperature to less than a permitted preset threshold, and for closing the shut off valve when the heater is actuated and for opening the shut off valve when the heater is not actuated.

10. The control unit according to claim 9, wherein the controller is responsive to a flow signal produced by a flowmeter for disabling the heater when water is drawn from the tank.

11. The control unit according to claim 9, wherein the controller is configured to operate a water pump for circulating water in the tank when the heater is actuated.

12. The water heating controller according to claim 9, wherein the control unit is configured to activate a water-pump constantly according to a preset duty cycle.

13. The control unit according to claim 9, wherein the controller has a standby battery backup for retaining user settings in case of an electrical power failure.

14. The control unit according to claim 9, further including an override switch, operation of which during Sabbath mode causes the control unit to open the shut-off valve for a predetermined time.

15. A water heating control system comprising: a tank for holding a volume of water, said tank having a hot water outlet and a cold water inlet connected to a main water supply whereby hot water removed from the hot water outlet is replenished with cold water, a temperature sensor for providing a temperature signal indicative of water temperature in the tank, a heater for heating the water in the tank, a water pump coupled between the water outlet and the water inlet for re-circulating water in the tank, a control unit that monitors the water temperature based on the temperature signal and is responsive to selection of a Sabbath mode of operation for periodically actuating and de-actuating the heater while maintaining an average water temperature to less than a permitted preset threshold, and a controllable shut off valve connected to the water inlet; wherein when set to the Sabbath mode, the control unit is configured to close the shut off valve when the heater is actuated and to open the shut off valve when the heater is not actuated.

16. The water heating control system according to claim 15, wherein the control unit is configured to activate the water pump when the heater is actuated.

17. The water heating control system according to claim 15, wherein the control unit is configured to activate the water pump constantly according to a preset duty cycle.

18. The water heating control system according to claim 15, further including an override switch, operation of which during Sabbath mode causes the control unit to open the shut-off valve for a predetermined time.

19. The water heating control system according to claim 15, further including a programmable clock that automatically activates and deactivates Sabbath use based on a calendrical data relating to start and end times of the Sabbath.

20. A water heating control system comprising: a tank for holding a volume of water, said tank having a hot water outlet and a cold water inlet connected to a main water supply whereby hot water removed from the hot water outlet is replenished with cold water, a temperature sensor for providing a temperature signal indicative of water temperature in the tank, a heater for heating the water in the tank, a control unit that monitors the water temperature based on the temperature signal and is responsive to selection of a Sabbath mode of operation for periodically actuating and de-actuating the heater while maintaining an average water temperature to less than a permitted preset threshold, a controllable shut off valve connected to the water inlet, and an override switch, operation of which during Sabbath mode causes the control unit to open the shut-off valve for a predetermined time; wherein when set to the Sabbath mode, the control unit is configured to close the shut off valve when the heater is actuated and to open the shut off valve when the heater is not actuated.

21. The water heating control system according to claim 20, further including a programmable clock that automatically activates and deactivates Sabbath use based on a calendrical data relating to start and end times of the Sabbath.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic representation of a hot water tank heating system with a Sabbath controller according to an embodiment of the invention.

DETAILED DESCRIPTION

(3) Referring to FIG. 1 there is shown schematically a water heating control system 10 comprising a tank 11 for holding a volume of water. The tank 11 has a hot water outlet 12 and a cold water inlet 13 connected to a main water supply 14. Water in the tank 11 is heated by a heater 15 and water temperature is controlled by a control unit 16 in response to a temperature signal indicative of water temperature generated by a temperature sensor 17. The heater 15 is powered by an electrical supply 18 connected to the heater via terminals 19 and 20. The control unit has a mode selector 21 for selecting regular use or Sabbath use. It is noted that the mode selector 21 is shown schematically as a manual set-switch by way of example and illustration. In practice, it may be implemented by a fully automatic programmed timer that is responsive to calendrical data relating to the start and end times of the Sabbath according to time of year and geographical location for setting and terminating Sabbath mode. Such an arrangement is described at col. 5, line 35ff of U.S. Pat. No. 7,672,576 and in paragraph [0022] of US 2007/0051819. In Sabbath mode, water temperature is prevented from rising above a permitted preset threshold, which is typically slightly less than 40 C. During regular use, the water is heated normally in conventional manner. A controllable shut off valve 22 connected between the water inlet 13 and the main water supply 14. During normal use, the shut off valve 22 may be left open so that hot water drawn from the tank is constantly replenished by cold water from the main water supply.

(4) During Sabbath mode, the control unit 16 periodically actuates and de-actuates the heater 15 while maintaining an average water temperature to less than the permitted preset threshold. The control unit 16 is further configured to close the shut off valve 22 when the heater 15 is actuated and to open the shut off valve 22 otherwise, thus avoiding heating water while hot water is being drawn from the tank, when the heating is largely wasted. Preferably, this control feature is independent of whether regular or Shabbat mode is operational because during prolonged use of hot water, such as when taking a shower, there is simply inadequate time to heat cold water entering the tank to replenish the hot water drawn from the tank. Therefore, energy used to heat water during prolonged use of the tank is largely wasted. Likewise, in some embodiments, the control unit 16 may be configured to disable the heater 15 when water is drawn from the tank 11 through the water outlet 12 in order to avoid incoming cold water cooling down the hot water as it is actually being used. To this end, a flowmeter 23 is coupled to the water outlet 12 for producing a signal indicative of water flow that is fed to the control unit as shown by the dotted line. The flowmeter 23 could equally be coupled to the water inlet 12 in series with the shut off valve 22.

(5) Optionally, a water pump 24 may be coupled between the water outlet 12 and the water inlet 13 for re-circulating hot water in the tank. The temperature sensor 17, which may be a thermistor, is shown schematically inside the tank. But in practice, it is mounted inside a pipe through which the pump re-circulates the water from the hot to the cold side. It may also be mounted in thermal contact with an external wall of the tank via some heat sink compound to assure a good thermal contact. Hot water temperature measurement is subject to hysteresis and it can take many minutes of use before any substantive change in temperature is registered. By re-circulating hot water in the tank, the heated water mixes more quickly with the cold water and the temperature sensor 17 is able to produce a more accurate reading. In some embodiments, the pump 24 is actuated constantly in a preset duty cycle, such as 90 seconds on and 10 seconds off. However, the invention also contemplates controlled actuation of the pump 24 by the control unit 16 when the heater 15 is actuated, whereby water is circulated in the tank 11 only during heating. The control unit 16 may have a standby battery backup 25 for retaining user settings in case of an electrical power failure.

(6) As noted above, the control unit 16 is typically programmed to initiate Sabbath mode automatically based on the time of commencement of the Sabbath, which varies throughout the year and also according to geographical location. In practice, some contingency is built into the system so that Sabbath mode is initiated before the actual time when the Sabbath commences. The reason for this is twofold: first, particularly in the summer months when the astronomical time for Sabbath is late on Friday evening, many communities bring in the Sabbath earlier. The control unit 16 may be programmed to take this into account so as to safeguard against a Sabbath-observant user from inadvertently heating water above the permissible temperature after the local community has commenced the Sabbath. Secondly, it takes time for hot water in the tank to cool down and if hot water is drawn shortly after the commencement of the Sabbath prior to the water temperature having fallen to 40 C., the cold water that replaces this hot water may then be heated on the Sabbath to above 40 C. So it is desirable to allow the water temperature to settle down to 40 C. before the onset of the Sabbath regardless of the season.

(7) But this causes a potential problem since a user may arrive home before the onset of Sabbath and want a hot shower. If the control unit 16 is already in Sabbath mode and the water in the tank is above 40 C., the shut-off valve 22 will be closed and the user will be unable to take a shower. To alleviate this situation, an override switch 26 may be provided that causes the control unit 16 to open the shut-off valve 22 within a specified time window before the commencement of the Sabbath and thereby release hot water from the tank in the case where Sabbath mode is enabled and the temperature is over the permissible temperature. In some embodiments, the override switch 26 allows hot water to be released from the tank for a period of thirty minutes and will close again if the temperature is higher than permissible.

(8) It will be appreciated that the control unit 16 is easily adapted for connection to existing installations and to this end the appended claims include claims directed to the control unit per se.

(9) It will also be understood that while the invention is particularly useful for domestic applications, no such limitation is inherent and the invention may be used also for commercial applications, where it finds utility particularly related to those features that are not dependent or conditional on Sabbath use.