The present invention relates generally to a control arrangement for a water heating system particularly a system in which a conventional water heater provided with its own conventional heating element is used, and a system in which an alternate source of heat, that may be a solar collector panel or another typeof heat source, is provided, with the entire system being controlled in a programmed manner that substantially increases the efficiency of the system and permits a variety of alternative modes of operation that can accommodate the use of the system by users having a variety of lifestyles.
In its simplest form, a conventional water heater used in a residence or the like includes a heating element, such as an electrical element or a gas heating unit, which is thermostatically controlled to heat the water stored in the water heater when it is below a predetermined desired temperature. It is well-known that such conventional systems necessarily involve high energy costs, and some efforts have been made to modify these systems to reduce energy costs. One familiar example is the use of a timer that may be set to energize the water heater heating elements only during "off-peak" hours when the costs of electrical energy is reduced, but these arrangements have several disadvantages, such as not having hot water readily available during certain time periods when it may be needed by the user.
It is also known that solar collectors can be used to heat water to reduce energy costs by utilizing solar energy as a partial alternative to the more expensive conventional heating elements. Some of these known systems include a heat storage material, usually in the form of a phase change material, which acts to store heat obtained from a solar collector, and this stored heat is made available through a control system to heat the water. For example, in Abhat U.S. Pat. No. 4,131,158 a temperature responsive control system is provided in which water from a well or public water supply is heated by stored solar energy when the temperature of the stored solar energy is greater than the temperature of the water. Other solar systems utilizing the benefits of a phase change material to store solar energy are disclosed in Lindner U.S. Pat. No. 4,371,029 and Hepp U.S. Pat. No. 3,986,919.
In solar systems of types generally described above, some attention has been given to a control for increasing the efficiency of the system by shutting down the circulation of the fluid from the collector to the heat storage unit when the temperature in the solar panel liquid circuit is less than the temperature in the storage vessel. Examples of control systems of this general type are disclosed in U.S. Pat. Nos. 4,191,166, Jaarem, Buckley 4,399,807 and Kirts 4,339,930.
Finally, in co-pending U.S. patent application Ser. No. 765,141, filed Aug. 13, 1985, an improved control arrangement is provided which includes a first control for disenabling the pump for the potable water in the water heater fluid circuit when the temperature of the potable water reaches a predetermined maximum temperature, and a second control operates independently of the first control to disenable the pump in the solar heated fluid circuit to disenable such pump whenever the temperature of the fluid in the solar fluid circuit is equal to or less than the temperature of the phase change material, or when the temperature of the phase change material reaches a predetermined maximum temperature.
While all of the foregoing control arrangements provide internal, usually automatic, controls for utilizing alternate energy sources such as a solar energy to augment the heating of water in water systems and the like, none of them permit any significant variation in the control of the overall system by the user of the system, and none of these provide an adequate arrangement by which the user can program the system to operate in different modes depending on the particular circumstances and needs of the user of the system.