Water heating appliances and space heating appliances have undergone significant changes over the last several years. In the past, fuel was relatively inexpensive and water heaters and space heaters were designed for maximum reliability, simplicity and long life with only a small emphasis placed on fuel efficiency. This set of priorities has changed with the rising price of fuel. Over the last several years, water heaters and space heating furnaces have been designed with a much greater emphasis placed on fuel efficiency. These heaters are generally more complex than their less efficient ancestors.
An additional development has been the combining of water heating and space heating functions in a single appliance. This combination was developed to improve overall efficiency of the total water heating and space heating function within a given home, commercial building or vehicle. Moreover, savings on the space occupied by these appliances and installation expenses have been achieved by the combination of the two essential appliances into one high efficiency unit.
One such high efficiency combined water and space heating appliance is described in U.S. Pat. No. 4,541,410 to Jatana, the disclosure of which is incorporated herein by reference. Jatana describes a heating apparatus in which air is mixed with fuel and introduced into a blower which moves the mixture under pressure into the burner of a closed combustion chamber. The combustion chamber is contained within a tank containing water. The products of combustion exit the combustion chamber and pass through a helical tube of several turns within the body of water. The heat of combustion is extracted from the products of combustion by conduction through the walls of the combustion chamber and the helical exhaust tube. A high efficiency water heater results. The heated water from the water heater is also used to heat the air of a home or building by piping the hot water to a heat exchanger contained within the ducts of the home ventilation system. While this apparatus provides a highly efficient water and air heater, certain problems remain.
In order to maximize efficiency, the Jatana heater draws combustion air from outside of the home or building being heated. This requires piping or ducts from outside the building to the heater. Such piping or ducts are unique to each building in which the appliance is installed. Air to be mixed for combustion must be drawn through these ducts, and, due to variations in the length of the ducts, turns within the ducts and the like, the resistance of each individual installation to the flow of air will be different. This often requires that valves governing the air supplied to the furnace and gas supplied to the furnace be professionally and individually adjusted for each installation. Any changes in the resistance of the ducts to the flow of air caused by the introduction of foreign objects into the ducts, denting of the ducts or the like after adjustment may cause a change in the ratio of air to fuel in the heater, negatively effecting efficiency.
The burner in the Jatana device is a cylindrically shaped screen contained within a cylindrical combustion chamber. It has been found that the introduction of the air and fuel mixture into this burner under pressure sometimes results in a swirling circumferential motion leading to noisy operation.
In the Jatana unit and in many other high efficiency units several additional problems arise. Thus, air in excess of what is required for proper combustion of the fuel is often mixed with the fuel to be certain that the burner is never supplied with too little air, resulting in incomplete combustion.
Also, the burner of a high efficiency heater normally operates most efficiently at a given gas pressure and a specific energy input level. Variations in gas pressure and variations in energy input level cause reductions in efficiency. Therefore, the capacity, that is the input energy level, of a given furnace or heater cannot be easily adjusted while maintaining high efficiency.
Problems of stability sometimes arise. Conditions in the combustion chamber change because of high outside wind, changes in gas pressure and the like and result in "fast cycling" and other problems which negatively effect efficiency. "Fast cycling" is the rapid and repeated changing of the furnace from the on state to the off state. It is often noisy and inefficient.
The present invention contemplates a new and improved apparatus and method which overcomes all of the above referred to problems and others and provides a water and space heating appliance of high efficiency, reliability, stability and quality.