CA2324669A1

CA2324669A1 - Element control within a hot water tank

Info

Publication number: CA2324669A1
Application number: CA002324669A
Authority: CA
Inventors: Nizar Ladha; Nazir Dosani
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-10-30
Filing date: 2000-10-30
Publication date: 2002-04-30

Abstract

A standard domestic electric water heater comprises a cylindrical tank having an upper immersion heating element to heat the upper 1/3 of the tank and a lower immersion heating element to heat the remainder (2/3) of the tank.

A programmable thermostat to control the lower immersion element according to a preset schedule or input power level.

Description

APPI,1(''ANT~~_ NAZIR DOSANI and NIZAR LADHA
T1T1,F~v Element Control Within A Hot Water Tank APP1.TC'.ANT~: NAZIR DOSANI and NIZAR LADHA
TTTT,F: Element Control Within A Hot Water Tank Field of Invention This invention relates to standard electric water heaters. In particular, this invention relates to a method and apparatus for controlling the lower immersion (electric) element.
Background of the Invention Maintaining a balance between a customer's needs for hot water and a electric utility's power 1o generation capability is a major problem.
Various methods have been proposed to control the energy used by electric hot water tanks.
Typically the hot water usage is highest during the morning and evening, at other times, the requirement for hot water is low.
Dosani et al. (Patent number EP0647365) shows a 2o method of controlling both elements within a tank.
The controller is made complex as both the temperature and power to the element is controlled.
Described herein is a simpler method which is to insert a power switch between input power and lower immersion element to control the lower immersion element, leaving the top immersion element to work normally.

This simple method, according to Ontario Hydro report of 1995-2005 Ontario Hydro Generation Mix Forecast" saves 1754 Kg/yr of Co2, averaged for 60ga1 and 80ga1 tanks.
Reference:
17. Incremental Energy Production - April, 1995 Forecast; ref. Banty Tezazu, Electricity Exchange, OH.
l0 18. Fossil Emissions, Ash production and Used Fuel Production: 1995 Fossil Business Report.
19. TSP: 1990 ratio of particulate emission to coal ash production - 8202 Mg/836000 Mg -0.009811.
Summarv of the Invention The present invention thus provides a programmable thermostat for controlling lower immersion 2o element(s~ within a electric hot water tank having a power supply for activating upper and lower elements according to pre-stored time schedule.
The present invention further provides a programmable thermostat for controlling a water heater having a power supply for activating upper and lower elements coupled to a temperature sensor associated with each element, the thermostat including a voltage monitoring circuit connected to the power supply and being capable of being programmed to switch from a consumption mode, in which the thermostat deactivates the water heater when water in the heater reaches a consumption temperature, and a shift mode, in which the thermostat deactivates the lower immersed element within the water heater in response to an increase or decrease in the power supply voltage beyond a pre-selected level.
The present invention further provides means for storing data within the programmable thermostat, which sets the consumption temperature, 'shift' mode time, input power level and the number of elements to control. The stored data can be active for a period of time (minutes, hours or any other time unit), and different stored data can be active for each time period. The length of each time period can also be programmed.
The present invention further provides means for communication to re-program the data stored within the programmable thermostat.
The present invention further provides means of controlling a mixing valve to deliver pre-mixed hot and cold water, at required temperature, to the dispensing fixture.

The present invention further provides a programmable thermostat for a water heater having at least two heating elements for heating water in the water tank, and switching means for activating each heating element independently, fault detection means for determining whether an activated heating element is functional, and means for activating an alternate heating element if the activated heating element is not functional.
to Brief Description of the Drawings In drawings which illustrate by way of example only a preferred embodiment of the present invention, Figure 1 is a block diagram of one embodiment of the present invention; and Detailed Description of the Invention Figure 1 illustrates the block diagram of the programmable thermostat system including the wiring diagram.
The water heater 10 is provided with upper and lower heating elements 35, 45 respectively, detachably connected to sealed receptacles (not shown) built into the wall of tank 10. A

S
temperature sensor 30, 40, such as a thermistor, are located immediately adjacent to each of the upper and lower heating elements 35, 45.
In a conventional water heater the upper and lower elements 35, 45 are controlled by a thermostat through a conventional flip-flop circuit which alternately activates one or the other of the elements 35, 45 according to the temperature sensed 1o by the temperature sensors 30, 40 associated with each element. Typically the upper element 35 is activated first, to heat water in the upper portion of the tank 10, and during other periods the lower element 45 is activated to bring the remaining water in the tank 10 up to the preset consumption temperature desired by the user, which is generally between 50 and 60 degree C.
The upper element 35 is activated first, as it 2o heats a smaller portion (1/3) of tank 10 and thus provides the user with hot water in shorter time.
The present invention in a preferred embodiment utilizes a programmable thermostat 25, illustrated in Figure 1, to control the activation of the heating elements 35 and 45. The thermostat 25 is connected to the temperature sensors 30 and 40 through a flip-flop circuit in micro-controller 70, and most of the time operates in a consumption mode, activating and deactivating the heating elements 35 and 45 in the conventional fashion.
According to the invention the thermostat 25 includes means for switching from consumption mode to a shift mode. In one preferred embodiment a timer circuit regularly switches the thermostat 25 to the shift mode at predetermined intervals.
According to another preferred embodiment of the invention, the thermostat 25 is provided with a voltage sensor circuit 50 which continually monitors the supply voltage. The thermostat 25 is programmed to detect an increase or decrease in the supply voltage beyond a preset level, which may be about 7o beyond the nominal supply voltage, and to respond to such a voltage swing by switching to the shift mode. The shift mode is active only when the voltage is beyond the preset value.
According to another preferred embodiment of the invention, the thermostat 25 is provided with a voltage sensor circuit 50 which continually monitors the supply voltage. The thermostat 25 is programmed to detect an increase or decrease in the supply voltage beyond a preset level, which may be about 7o beyond the nominal supply voltage, and to respond to such a voltage swing by switching to the shift mode. The length of the shift mode is controlled by the timer circuit.
During the shift mode:
The flip-flop circuit in micro-controller 70 is circumvented. The thermostat 25 deactivates the lower element 45 to To prevent water at higher then consumption temperature, if pre-set, during consumption cycle, from reaching a dispensing fixture, a mixing valve 65, within the distribution system, is controlled by stepper motor 67 to pre-mix cold water and hot water from outlet 75, to reduce the temperature of water within the distribution system.
Temperature sensor 85, as shown in figure 1, is used to set the ratio of cold water mixed with hot water from outlet 75 to reduce the temperature of water within the distribution system.
In another embodiment the invention may be designed to allow for selectively activating the shift mode when a brownout condition detected by voltage sensing circuit 50. Brownout condition occurs when the line voltage drops due over demand from electric customers. Shift mode active for the duration of the brownout condition.

g In another embodiment the invention, timer circuit within thermostat 25 can be activated to time the shift cycle if required. When the timer signals that the shift cycle is complete, the thermostat 25 automatically switches back to the consumption mode.
Use of lower consumption temperature during peak electrical demand time, can help the electrical utility by lowering the demand and by setting higher consumption or normal consumption temperature during other times can ensure the user does not run out of hot water.
To meet the demands of the electrical utility and the user the following parameters have to be set for each time period which may be minutes, hours or any other time period:
1. Consumption temperature:
Temperature of hot water supplied to the user at outlet 85.
2. Shift interval:
If using timer to activate shift cycle then specify the time between the shift cycle.
3. Voltage swings:

Over voltage or under voltage to start/stop the shift cycle.
4. Voltage swing duration:
Length of time that the voltage must change for the programmable thermostat to recognize the change.
6. Duration of each cycle:
to Different consumption cycles and shift cycles can be programmed into the programmable thermostat, each cycle can have different control parameters (e. g.
consumption temperature can be different in each consumption cycle). The time of the cycle is entered here, the time can be in minutes, hours or any other time unit.
The time periods and the parameters can be 2o programmed into the programmable thermostat remotely or by a keypad (not shown) either by the user or the electrical utility company.
In a first embodiment, in the event that the micro-controller 70 activates a heating element 35 or 45, and after a short delay the temperature sensed by its associated sensor 30 or 40 does not rise, the micro-controller 70 will automatically switch the flip-flop circuit to deactivate that element and activate the other of the heating elements 35, 45 as backup. For example, if the temperature sensor 30 senses a temperature below the set temperature, the micro-controller 70 will activate the heating element 35 to raise the temperature of water in the upper portion of the tank 10 to set the temperature. If the element 35 does not respond, a fault condition is assumed and the micro-controller 70 will activate the element 45 automatically. A warning light may be provided to notify the user of the faulty element 35, and also the electrical utility company can be notified of the fault via the remote communication means.
For this monitoring function the micro-controller 70 includes a temperature monitoring circuit, not shown, which monitors the status of the heating element 35 or 45 at all times when an element is activated. In one preferred embodiment this is 2o accomplished by monitoring the temperature of the heating elements 35, 45 through the temperature sensor 30, 40 as described above. This monitoring circuit is subject to a time delay of 10 to 20 seconds after activation of the element, to prevent a "failed element" reading immediately after the power to element is switched on, while the element is still cool. Following this delay the micro-controller 70 reads the temperature sensors or 40 as an analog to digital convertor (ADC) count from the associated heating element 35 or 45.
The ADC output changes proportionately with the thermistor output, so that at any time when the element 35 or 45 is activated, after the initial delay, if the temperature detected by the associated sensor 30 or 40 does not increase then the micro-controller 70 will switch the flip-flop circuit to activate the other of the heating elements 35, 45 (or an auxiliary element, if provided). The micro-controller 70 can time stamp the failed element and record the information for a technician, and also display an alarm for the user and also call the local electrical utility company with fault indication.
To further enhance the thermostat 25, the heating elements are deactivated when ever the temperature sensors are shorted or opened by the user in an attempt to get more hot water or water at a higher 2o temperature.
It is advantageous to provide a programmable thermostat 25, which can be programmed locally or by remote means to lower the maximum temperature setting during periods when local utility anticipates peak power demand, to promote load shifting. This allows the elements 35, 45 to off for a longer periods of time. The programming can include alternate settings for weekends, vacations and intermittent uses (such as summer cottage), with an optional override switch accessible to the power utility company or the user.
It will be understood that, although various features of the invention have been described with respect to one or another of the embodiments of the invention, the features and embodiments of the invention may be combined or used in conjunction to with other features and embodiments of the inventions as described and illustrated herein.
Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to these particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalents of the specific embodiments and features that have been described and illustrated herein.
A preferred embodiment of the invention having thus been described by way of example only, it will be apparent to those skilled in the art that modifications and adaptations may be made without departing from the scope of invention, as set out in the appended claims.

Claims

1. A programmable thermostat for controlling a water heater with temperature sensor associated with it, comprising a temperature monitoring circuit coupled to the temperature sensors, the thermostat being capable of being programmed to switch from a consumption mode, in which the thermostat deactivates the water heater when water in the water heater reaches a first consumption temperature, and a shift mode, in which the thermostat deactivates the lower immersed heating element within water heater.

2. The programmable thermostat of claim 1 including means for monitoring the power supply.

3. The programmable thermostat of claim 2 wherein the thermostat switches between a consumption mode, in which the thermostat deactivates the water heater when water in the water heater reaches a first consumption temperature, and a shift mode, in which the thermostat deactivates the lower heating element in response to change in the voltage of the power supply.

4. The programmable thermostat of claim 3 wherein the change is an over voltage interval.

5. The programmable thermostat of claim 3 wherein the change is an under voltage interval.

6. The thermostat of claim 1 including a timer circuit.

7. The thermostat of claim 6 wherein the thermostat periodically switches between a consumption mode, in which a thermostat deactivates the water heater when water in the water heater reaches a first consumption temperature, and a shift mode, in which the thermostat deactivates the lower immersed heating element within water heater.

8. The thermostat of claim 1 wherein a temperature sensor is associated with a heating element and the thermostat responsive to a temperature sensor for activating the heating element.

9. The thermostat of claim 1 including switching means for activating each heating element independently, fault detection means for determining whether an activated heating element is functional, and means for activating an alternate heating element if the activated heating element is not functional.

10. The thermostat of claim 1 in which the thermostat is programmable.

11. The thermostat of claim 10 in which the thermostat is remotely programmable.

12. The thermostat of claim 10 in which the thermostat is programmable using a removable keypad.

13. The thermostat of claim 10 including the means for programming;
a. Consumption temperature, b. Shift interval, c. Voltage swings, d. Voltage swing duration, and e. Duration of each cycle,

14. The programmable thermostat of claim 1 including the means of monitoring the temperature sensor.

15. The programmable thermostat of claim 14 wherein the water heater is deactivated in response to shorted temperature sensor.

16. The programmable thermostat of claim 14 wherein the water heater is deactivated in response to opened temperature sensor.

17. The programmable thermostat of claim 1 including the means of controlling a mixing valve.

18. The programmable thermostat of claim 17 wherein the mixing valve controls the ratio of cold water mixed with hot water to reduce the water temperature at a dispensing fixture.

19. A programmable thermostat for a water heater, comprising a. switching means for activating each heating element independently, b. fault detection means for determining whether an activated heating element is functional, and c. means for activating an alternate heating element if the activated heating element is not functional.

20. The programmable thermostat of claim 19 wherein the fault detection means comprises a temperature sensor associated with the activated heating element.

21. The programmable thermostat of claim 20 including means for delaying activation of the fault detection means for a preset interval after activation of the activated heating element.

22. The programmable thermostat of claim 19 wherein the alternate heating element is provided with fault detection means.