Electric resistance heating devices – Heating devices – Tank or container type liquid heater
Reexamination Certificate
1999-06-23
2001-03-27
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Tank or container type liquid heater
C392S449000, C392S498000
Reexamination Certificate
active
06208806
ABSTRACT:
This invention relates to control of domestic electric water heaters.
Electric heating appliances are major consumers of electric power and power utilities have attempted to address the problem of controlling peak demand by encouraging off peak heating of such appliances with reduced tariffs. However this often leads to the inconvenience of hot water or heating not being available when it is needed. A consequence has been that consumers switch from using electric power to a more demand responsive energy source such as gas for hot water and space heating.
One means of dealing with this problem has been for the power utilities to develop a more demand responsive distribution system. This usually entails using high frequency signals sent over the power lines to activate or deactivate heaters at individual sites. Examples of this approach are disclosed in Canadian patent 1203568, U.S. Pat. No. 4,888,495 and WO95/22190. U.S. Pat. No. 4,540,875 addresses the control of space heating demand by sensing ambient temperature at a central control point and high frequency signals are superimposed on the normal power line voltage to provide operating instructions to the individual space heaters. Difficulty has been encountered in sending high frequency signals over power lines because of noise interference. U.S. Pat. No. 4,264,960 addressed this problem by using telephone lines to send signals to power substations which then send signals over power lines to remote appliances. U.S. Pat. No. 5,732,193 discloses a behavioristic method of monitoring power usage to accumulate an historical record of power use and then use this data to achieve load leveling for the power utility. These attempts have all aimed at better control of demand from the power utility's perspective by control from the power utility.
The other approach has been to address control from the consumer's perspective by providing control of power consumption at the heater depending on its energy need. These attempts all try to utilize the cheaper off-peak power without compromising the need for instant heating or hot water. U.S. Pat. No. 4,568,821 provides a display and control panel located inside the home and senses the temperature of the water in the hot water tank to enable the consumer to choose the most economical means of obtaining the needed hot water. Most attempts of this kind have tried to automate the switching decisions. U.S. Pat. No. 4,948,948 discloses a water tank with heating elements of different power ratings disposed at different heights in the tank and a timer switches on the elements individually at the most economical time for each element depending on the power utilities tariff.
Another approach based on timer control at the tank is to sense the tank temperature and switch on the heating elements to reheat the tank to a predetermined temperature. Australian specification 33728/84 discloses a tank with several thermostats and several heating elements of different power ratings. Depending on the temperature gradient of the tank as sensed by the thermostats an appropriate element is chosen so that the tank can reach the specified temperature during the allocated off peak period. Thus a tank with only a small heating demand will use the low power element and the higher power rated element will be switched on if the heat demand is high. French patent 2552210 utilizes a timer, a thermostat and an element in a water heater and is arranged so that if the water temperature is above a certain value the heating element is not switched on. U.S. Pat. No. 4,998,024 utilizes a programmable controller for water heaters which is programmed with data relating to optimum periods for heating based on historical data for the seasons and weekdays, weekends and holidays. These systems are still dependent on operating within a preset time period and do little to alleviate the problem of all electric, water or space heaters being switched on at the same time. French patent 2465389 discloses a storage heater control which senses the temperature and the temperature setting of the heater. An electric circuit responsive to this data is connected to the power line and acts to delay the switching on of the heater in response to signal received over the power line.
It is an object of this invention to provide a water or space heater with a controller which improves the economy and/or convenience of these heaters for the consumer and at the same time allow the power utilities to smooth out the demand curve.
BRIEF DESCRIPTION OF THE INVENTION
To this end the present invention provides an electric water heater which includes
a) a water tank
b) an electric heating element disposed within said tank
c) a cold water inlet into said tank
d) a hot water outlet from said tank
e) optionally at least one thermostat in said tank or a water meter connected to said inlet or outlet to measure the amount of water used
f) a calendar/clock and timer connected to said element
g) a memory store connected to said water meter and said timer clock to record daily readings of
i) optionally, the average temperature of the tank or the amount of water used in the period from one heating period to the next
ii) the power used or the time required to heat the water in the tank to the desired temperature
and store the readings for a predetermined number of preceding days
h) a programmable means programmed to analyze the readings in the memory store and calculate for each day the time duration required to bring the water to the desired temperature
i) said memory store including power load curve data collected from the power generator appropriate to the day of week and season and
j) said programmable means being programmed to match the required heating duration to a low cost portion of the load curve.
The prior art water tanks did not attempt to calculate the duration of time required to bring the water in the tank to the desired temperature. Further the prior art tank controllers did not store historical data to enable such a calculation to be made. It is possible to obtain an approximate estimate of the time of heating from a number of different data readings. Any one of power used, time of heating, lowest temperature of tank, amount of water used or entering tank, can be used as the basis of a calculation in combination with the known volume of the tank and the rating of the heating element(s). The accuracy of such a calculation can be improved using statistical analysis of stored historical data.
In contrast to the prior art which monitored electric power usage only, or used thermostats to monitor water temperature and power requirements, this invention preferably monitors water usage and heating duration for an individual water heater to establish an historical daily behavior pattern for the tank. By monitoring water usage and statistically analyzing this over a set preceding period and combining this with a similar analysis of heating durations, an accurate assessment of the required heating duration for each day can be calculated. By combining heating duration data with meter readings of water passing into or out of the tank, variations in the performance of the heater, due to seasonal conditions or factors affecting efficiency, can be better accommodated than relying on temperature measurements of water in the tank.
By programming into the controller appropriate averaged load curve data from the power utility, the controller, by accessing the calendar, can match the required heating duration against a low in the load curve most appropriate to the day and season. As a preferred minimum, six different 24 hour load curves would be stored in the controllers memory namely weekdays and weekends for summer and winter and autumn/spring where the latter seasons can be treated as the same. A greater number of these data sets can be used to achieve finer tolerances in load leveling by the power utility. Usually the major low period in the power load curve is overnight, but there is sometimes a smaller low period during the day [9 am to 6 pm]. Thi
Aquabeat Pty Ltd.
Campbell Thor
Connolly Bove Dodge & Hutz
Walberg Teresa
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