1. Field of the Invention
This invention relates to a method and control apparatus for a heating or cooling system using an energy source which can be cyclically switched on and off. More specifically, the present invention is directed to a room temperature control apparatus and method utilizing a thermostat control of an energy source.
2. Description of the Prior Art
Several methods are well-known for controlling the heat supply or cooling of buildings and rooms in a fashion where energy is saved and simultaneously the room temperature is kept substantially constant. With one of those methods in a heating control, the temperature of a hot water supply is controlled dependent on the outside temperature of the room or building, and in the individual rooms radiator thermostats are provided which control the heat supplied by the hot water to the respective rooms dependent on the temperature setting of the thermostat. The temperature of the hot water supply is changed by either cyclically switching a hot water heating burner on and off or by continuously adjusting a hot and cold water mixing valve. In both cases, the room temperature sensor does not directly control the heat source, e.g., the burner, but the temperature sensor can only either supply the heat generated by the heat source to the room or can interrupt the heat supply to a room dependent on the heat demand. Such a temperature control of the supply water dependent on outside temperature does not take into consideration several factors which influence the heat demand, e.g., the thermal isolation and the heat storage capacity of the building, the influence of incident sunshine, the cooling effect of strong wind or rain as well as all those influences which depend on the utilization of the room, such as the opening and closing of windows, the opening and closing of radiator valves, changes of the setpoint of other room thermostats, night setback, the heat generation of electrical apparatus and lamps, as well as the occupation of the room with a few or many people. Such a temperature control of the supply water therefore cannot achieve an optimum usage of the energy of the fuel supplied to the burner.
In other known heating systems, the burner or another source of heat is directly switched on and off by a room thermostat which is located in the most important room of the building, i.e., in the case of a home or dwelling it is usually located in the living room. When the burner is switched on, it runs at full heating capacity, even if only a small temperature difference between the set point and the actual value has to be overcome. In this case, the burner runs only for a short period of time. This, however, means that in the case of small heat demand the burner is seldom switched on and then only for very short time intervals. Since some time elapses until the heat energy generated by the burner has heated up in the heat exchanger the heat supply medium, in most cases hot water, and this medium reaches the room where the thermostat is located and the thermostat can sense an increase of the room temperature above the preset set point and then can switch off the burner, excess heating energy is generated which actually is not required. One conventional attempt to overcome this deficiency uses a room thermostat with a so-called thermal feedback or heat anticipator where, when the thermostat is switched on, an electrical resistor increases the ambient temperature of the temperature sensor in the thermostat before the room temperature itself really increases. The result of this measure is not wholly satisfactory in many cases because the time delay between a switching on of the burner and the start of heating up of the room depends essentially on the kind and dimensioning of the heating installation and also on the volume of the room. In particular, with long piping between the burner or the boiler and the living room, completely satisfactory temperature control and energy use efficiency results cannot be achieved.
Furthermore, European Pat. No. 012,936 describes a method for optimizing the energy consumption in a building by measuring the period of time which the heating installation requires for heating up the building from a low night temperature to a higher room temperature at the beginning of the occupation time of the building. This measured period of time is then used in connection with the building outside temperature for calculating the heat up time required on the next morning.
Finally, German Pat. No. 1,615,500 shows an apparatus for automatically controlling the charging system of a storage heating installation. The heat storing system is charged through a predetermined time interval during the night hours, while during the day the stored heat is discharged to the room which has to be heated by means of a fan which is controlled by a room thermostat. In order to avoid an unnecessary loss of heat, the storage system is to be charged each time only with such an amount of heat as will most probably be required for the next day. For this purpose, switching means are provided which switch on the charging device during the night hours for such a period of time which depends on the operating time of the fan during the preceding day. This operating time of the fan can be calculated easily by summing the contact closure time intervals of the room thermostat.