CA2198641A1 - Thermal storage controller with auto-power setting - Google Patents

Abstract

In a method for controlling the power consumption of an electrical load a switching device for controlling the supply of power to the load is responsive to time left to charge the load and the current temperature of the load. In the preferred embodiment a power calculation is made using 'time left to charge the load' and 'current temperature of the load' as inputs to formula:
Auto Power setting = (Thermal energy required / Time to charge)*100 In this fashion, the power supplied to the load is the minimum power required to reach the required temperature within the given time period.

Description

-- 2 1 '3~641 Field of Invention This invention relates to control of electrical loads. In particular, this invention relates to a method and apparatus for calculating and setting to the minimum required power that is supplied to an electrical load through the 5 power supply mains.

Back~round of the Invention Electrical power utilities typically face regular cycles of power usage 10 requirements. Peak usage periods occur generally at predictable times during business hours, while the lowest power demand occurs late at night. Meeting energy demands during peak periods, and disposing of excess electrical energy during low demands, has long been a problem facing electrical utilities.
Controller devices have previously been developed in attempts to shift power demands from on-peak periods to off-peak periods. Such prior art power controller devices have controlled the amount of power used by an appliance according to pre-stored 'power settings', as taught by Kent Hartig 20 et al. (U.S. Patent number 5,168,170) and PCT/CA93/00288 patented by the inventors, or the appliances are simply turned off.

Using pre-stored 'power setting' meets the needs of the electrical utility company but may not always meet the needs of the customer.

6 4 ~

The problem with pre-stored 'power setting' is that an appliance such as hot water tank, thermal storage heaters, or battery chargers may not regain the full energy potential as the loses may have been higher during the previous scheduled time period.

To satisfy both the electrical utility company and the customer, a pre-stored schedule with an adjustable 'power setting' has to be used to ensure that the customer's appliance reaches the full energy storage potential at the lowest possible setting so as not to over-load the electrical distribution o system.

The present invention overcomes this disadvantage by providing a controller with greater versatility and higher efficiency in the control and utilization of electrical devices. The present invention in a preferred 5 embodiment includes temperature sensing of the load to adjust the amount of power delivered to the electrical device and a real time clock to calculate the 'time left' within the current pre-stored time period.

The present invention further reduces the peak demand charges by 2 o using the minimum calculated power over a period of time.

The present invention further reduces the 'Time Of Use' charges by ensuring the appliance is fully charged with thermal energy within a time period, which has a lower 'Time Of Use' rate.

-2 1 ~864 1 The invention further provides the Utility Company with an advantage in that the energy usage for a given time period is fixed and therefor the 'standby' power for the time period can be reduced and the excess power can be sold off.

Using power control concept, patented by the inventors under PCT/CA93/00288 titled "Power controller device", the controller adjusts the power setting and thus the output power based on auto-power calculation.

0 The 'power setting' is calculated in real time based on the following formula:

Power setting = (Thermal energy required / Time to charge)* 100 Where:
Power setting Percentage of total output power.
Thermal energy required Degrees for hot water tank, kWh for ETS and battery chargers.
Time to charge Time left to charge the appliance in minutes.

Summary of the Invention The present invention thus provides a controller device comprising a power input means for receiving input power from an electrical power source, 2 5 a power output means for delivering output power to a load at a calculated 2 ! 9~64 i power level, a power reduction means electrically associated with the power input means and the power output means operable to reduce the maximum output power by discreet intervals, control means for controlling the power reduction means, and memory means for recording predetermined periods of 5 time.

Brief Description of the Drawin~s 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 thermal storage controller with auto-power setting in accordance with the present invention; and Figure 2 is a block diagram of a standard North American hot water tank.

Figure 3 is a schematic diagram of the power supply, voltage detection and reset circuitry 1;

2 o Figure 4 is a schematic diagram of the load switching circuitry 1;

Figure 5 is a schematic diagram of the temperature sensor and stepper motor driver circuitry 1;

2 5 Figure 6 is a schematic diagram of the microprocessor circuitry 1 and;

Figure 7 is a graph indicating the energy required to charge the appliance and the actual energy delivered to the appliance.

Detailed Descrintion of the Invention For illustration purposes, specific embodiments of the invention will be described in association with a standard electrically heated domestic hot water delivery system having two immersed elements. Other modification of 10 the invention for use with other thermal storage appliances will be obvious to one skilled in the art.

As shown in Figure 1, in one embodiment, the present invention comprises a Thermal storage controller with auto-power setting, shown generally as 10, for controlling the power consumed by a resistive load device, such as a water heater 2 (shown in figure 2) of the type described in U.S. Patent No.
5,115,491. The power controller device 10 comprises an input power means 12, an output means 14, a power reduction means 16 and a control means 18.

2 o The input power means 12, illustrated schematically in figure 3, is capable of receiving input power from an alternating current power source (not shown).
This could be any alternating current power source, including a standard wall plug as found in any residential building and which derives power from the local electrical utility.

6 2 1 '~ 64 ~
The output power means 14 is capable of providing output power from the device 10 to a resistive load device such as a water heater, baseboard heater, brick heater, battery charger or the like. It will be appreciated that the resistive load device could be any electrical device, which exhibits power 5 consumption characteristics similar to that of a resistor. The controller can also be used in similar fashion to control a reactive load, such as an air conditioner compressor.

As shown in Figure 1, the device further comprises power reduction means 16 10 electrically associated with both the power input means 12 and the power output means 14. The power reduction means 16is operable to reduce the output power going to the load device by discrete intervals.

Figure 3 illustrates the power input means comprising a power supply circuit including a bridge rectifier 50. The microprocessor 18is stimulated to energize the power output means 14 by a opto-isolator.

Figure 4 illustrates the output power means 14 for the controller illustrated inFigure 1, comprising switching circuits 14a, 14b for each of the upper and 2 o lower resistance heating elements 3 and 4 in the water heater 2. A low current (100 mA) opto-isolator 56 signaled by the microprocessor 18 switches a heavy duty TRIAC 58 which controls the output power to load 2.

Figure 6 illustrates the microprocessor 18 and its associated clock circuitry 2 5 1 8a and e2prom memory 20.

2i~'~6~1 Figure 7 illustrates graphically the amount of energy required to charge the appliance, indicated by the dashed line A and the energy delivered over time as indicated by the solid line C. Line B and D are assumed 'pre-stored' power 5 settings from other controllers.

Most local utility companies can usually predict when the on-peak and off-peak periods will occur. Therefore, the desired temperatures and time intervals can be recorded in the memory means 20.

The controller device 10 comprises memory means 20 upon which the desired output temperature for a plurality of predetermined time interval can be recorded. The duration of the interval can vary, such as from 10 seconds to several hours, and different intervals can be selected for different times of the 5 day, weekends, holidays etc.

The following are recorded in the memory means 20:
1. The date and duration of each time interval for the various settings of temperature levels, including week days, weekends, public holidays and 2 o desired vacation days;
2. Temperature levels for each time interval, for each load being controlled;

3. The steps or increment of power level increase/reduction;

4. An address for remote addressing;

2 5 The power reduction means 16 reduces the power to any resistive load device 2'1 'j~6~

from the maximum output level to a lower output level through conventional means such as "cycle stealing", which entails periodically elimin~ting half cycles or full cycles from the alternating current being supplied to the resistive load device. In this way, both the power consumed by the load and 5 the power supplied by the alternating current source are reduced, thereby resulting in a net reduction and savings in power consumption.

Control means 18 controls the power reduction means 16. In a preferred embodiment, the control means 18 comprises a microprocessor running in 0 real time. In this way, the control means 18 selectively directs the power reduction means 16 to deliver power at different power output levels for different time interval as calculated by microprocessor 18.

The power reduction means 16 reduces the output power level delivered to resistive load device 2 by discrete intervals.

In the preferred embodiment, when the voltage detection circuit 15 in Figure 3 senses a resumption of supply power above the preset minimum after a brownout or blackout, the brownout and blackout sensor means 24 sends a 2 o signal S3 to the control means 18. In response to signal S3, the control means 18 will deliver power to a resistive load in gradually increasing increments (of10% in the preferred embodiment) rather than immediately increasing the output power to preset output level, a so-called 'soft-start'. This helps to prevent "fly-back", which is a condition that occurs after a blackout, 2 5 brownout or activation of large loads when all the loads begin to draw power ~ 1 9~64 l simultaneously, creating a power surge which overloads the system and can cause another brownout or blackout.

Under normal operations, before activating the electrical load, the 'soft-start'5 process is always used to ensure the 'fly-back' effect does not compromise the electrical distribution system.

At a pre-set time before de-activating the electrical load, control means 18, starts to reduce power in gradually decreasing steps, a so-called "soft-end".
0 This again helps to prevent "fly-back" effects.

Figure 5 illustrates the temperature sensor means for the controller 10 illustrated in Figure 2. Each sensor comprises a thermistor 78 with an associated voltage detector. The microprocessor 18 is programmed with known voltage values corresponding to temperatures within the range of thermistors 78. Changes in temperature are thus detected, and if the temperature of the heated water drops the 'soft-start' process is activated for one or both heating elements 3, 4 (in response to signals from T3 and T4) in accordance with the preset output requirements for that time period.
In a preferred embodiment, when the temperature of the heated water reaches the set point (in response to signals from T3 and T4) in accordance with the preset output requirements for that time period the 'soft-end' process is activated before de-activating the heating elements.

' 4 In a preferred embodiment, within each time period that the elements are active, full power is supplied to each element alternatively and the time taken to raise the water temperature by one degree C is noted and recorded for each element (Tl~ctop for top element and Tl~cbottom for bottom element). This time 5 takes into account the size of element in kW, size of tank in liters, and the status of element (calcium build-up on the element affects the heating process).

The basic formula to calculate the auto-power is shown below:
10 Pauto = (Erequired / Tleft) * 100 The formula is modified for hot water tanks to take into account the size of tank in liters, size of elements in kW and the status of elements (as the amount of calcium build-up on the element affects the heating time):
5 Pauto= ((Tl~ctop(Tstop~ Ttop) + Tl~cbottom(Bstop~ Thottom)) / Tlength) * 100 The formula for Electrical Thermal Storage unit, taking into account the stand-by losses:
Pauto = (((Trequired - T~rcllmlll~qt~qd) +Tloss ) / Tlength) * 100 The formula can be further modified for Electrical Thermal Storage unit, to take into account the stand-by losses and the heat used by the dwelling during the charge period:
Pauto= (((Trequired--T~rGIlm~ t~d) + Tused+ Tloss) / Tlength) * 100 where:
Pauto Calculated power as a percentage of total power.
Erequired Total energy required by the appliance.
Tleft Time left to charge the appliance.
100 To get the percentage of total power.
Tl~ctop Time taken to change the temperature by 1~C at 100%
power for top element 3 in Figure 2.
Tstop Temperature in degrees centigrade required at element 3 in Figure 2.
0 Ttop Current temperature in degree centigrade at element 3 in Figure 2.
Tlocbottom Time taken to change the temperature by 1~C at 100%
power for bottom element 4 in Figure 2.
Bstop Temperature in degrees centigrade required at element 4 in Figure 2.
Tbottom Current temperature in degree centigrade at element 4 in Figure 2.
Tlength Length of time in minutes available to charge the appliance.
2 o Trequired Temperature required within Electrical Thermal Storage unit.
Taccumulated Temperature already accumulated within the Electrical Thermal Storage unit.
Tused Temperature used to heat the dwelling during the charge 2 5 period.

Tloss Standby losses as specified by the manufacturer.

Figure 7 illustrates the energy delivered to an appliance by the solid line C, as 5 calculated by control means 18. If 'pre-stored' power settings as indicated bysolid line B were used, as taught by Kent Hartig et al. (U.S. Patent number 5,168,170), the output power may be higher then solid line C in which case more energy is required from the Electrical Utility company in a given time period. If the 'pre-stored' power setting as indicated by solid line D, as taught 1 c by and PCT/CA93/00288 patented by the inventors, is lower then solid line C, the appliance does not reach the full energy storage potential.

The controller is remotely programmable by using various communication protocols or media. In the preferred embodiment of the invention when data is received by control means 18, in Figure 6 via COM1 and COM2 lines, the control means 18 stores the data in memory 20 for use by the program as pre-stored data.

A preferred embodiment of the invention having thus been described by way 2 o of example only, it will be apparent to those skilled in the art that modif1cations and adaptations may be made without departing from the scope of invention, as set out in the appended claims.

Claims (4)

1. A thermal storage controller with auto-power setting comprising:
a power input circuit for receiving input power from an electrical power source;
a output circuit for delivering output power to a load at a calculated power level;
a power adjustment circuit electrically associated with the power input circuit and the power output circuit operable to change the output power level of said power output circuit by discrete intervals;
a controller for controlling the power adjustment circuit, said controller including means for calculating the output power based on energy required by the load and the time left to charge the load.

2. The thermal storage controller with auto-power setting device defined in claim 1 wherein the power adjustment circuit changes the output power level in equal steps.

3. The thermal storage controller with auto-power setting device defined in claim 1 wherein when said power output circuit is reconnected to said load, said controller conditions said power output circuit to supply output power to said load in gradually increasing increments.

4. The thermal storage controller with auto-power setting device defined in claim 1 wherein said controller conditions said power output circuit to supply output power to said load in gradually decreasing intervals before said power output circuit is disconnected from said load.