The present invention relates to heating systems, and more specifically to a heat recovery system for boiler and domestic water.
Conventionally, the cold water supply line is fed to a boiler tankless coil where the cold domestic water is heated by the boiler water and released to be used in hot water fixtures of a house. The boiler water, on the other hand, when returned from the house heating units or house radiating system, returns to the boiler through a water circulator. After being reheated, the boiler water is forced back into the house heating units.
A major disadvantage of the conventional arrangement is that feeding cold water to the boiler tankless coil reduces the efficiency of the boiler since the boiler must heat the cold water from approximately 40.degree.-50.degree. F. to approximately 120.degree.-180.degree. F. Although requiring a great input of heat for this purpose, a great deal of the boiler heat escapes through the stack with the flue gases without the heat being retrieved.
In addition to reducing the efficiency of the boiler for heating the boiler water, prior art systems which only utilized an internal boiler tankless coil were also deficient in providing sufficient quantities of domestic water for bathing, using major appliance, etc. It frequently occurs that the capacity of the boiler tankless coil is insufficient for producing sufficient quantities of domestic hot water or heating such water sufficiently rapidly to provide the desired quantities.
In U.S. Pat. No. 2,189,749, which discloses a water heater, suggests the use of a supplemental heating unit using flue gases passing through an envelope filled with boiler water through which a coil for domestic water passes. However, the arrangement described requires that the flue gases be forced from the heating boiler down into and through the supplemental heating unit. Such an arrangement is not recommended for many reasons. Firstly, it causes back pressure on the system as heated gases rise to be vented. Also, the excess pressure can cause relief-type devices to blow off which can soot up an entire dwelling. Further, with the arrangement in the patent, using a tube and baffle design, soot will collect if the oil burner is not running to peak performance. Additionally, the disclosed device utilizes a damper operated by an actuating rod, and the damper could carbonize and that sends heat causing the butterfly to malfunction. This could also cause back pressure which may result in a release of soot in the premises.
U.S. Pat. No. 2,554,338 is for a water heater and uses an auxiliary water heating tank inside the furnace with a pipe coaxial with the flue leading to a tank surrounding the flue. However, the two auxiliary hot water tanks which are disclosed are disposed directly in coal which is transferring heat to the domestic water. Using oil as a fuel and placing the auxiliary hot water tanks in the flames of a oil fired boiler would cause many problems, form soot, smoke and in most cases, could not fit into conventional boilers used today. Furthermore, to install domestic water lines through the smoke pipe and have gases pass through a domestic water tank is not practical as it gravitates to the tank and must be heated to move the water. For these reasons, the water heater disclosed in this patent could not be applied to today's conventional oil heating units.
A furnace system for heating air and water is disclosed in U.S. Pat. No. 2,827,893. This system provides a water heater in the exhaust flue in conjunction with a circulation system and a forced air heating system. A summer and winter changeover is used to eliminate the use of the separate water heater in winter and using cold water in the coils in the summer to aid cooling of a building. However, the use of a coil to extract heat from a hot air unit or heat exchanger is very inefficient since the heat is being taken from the home heating air. The use of a separate circulator disclosed in this patent to move water is an additional problem for those who service the unit. Further, the coil is restrictive both to the flow of hot air which is rising and the return air. The patent also discloses the use of a storage tank and expansion tank. However, the use of these is not practical since there are too many parts to be installed. The use of a unit of this type, which is complex, along with a hot water heater is not at all practical as it offers no saving utilizing such a system. The disclosed system merely retards heat flow in the unit and takes heat from it as well.
An energy recovery and storage system is also disclosed in U.S. Pat. No. 4,037,786. This patent teaches an arrangement which provides a heat recovery and storage system utilizing heat transfer pipes and circulating water from a storage tank or heat sink in response to sensors responding to water temperature and flue gas temperature. However, the use of transfer heating rods to heat domestic water is inefficient as the heat only strikes the surface area of those rods. Additionally, the use of a hot water heater and storage tank is costly for the operation of the hot water heater and the extra boost given to it by the energy recovery and storage system is grossly inefficient. The use of a storage tank along with the hot water heater is not practical for the space needed to install such a unit.
In U.S. Pat. No. 3,896,992 there is disclosed a heat recovery system for space heating and for potable water heating. This system provides a heat recovery coil and a flue that may alternately provide additional heat to the heating system or provide preheating of the domestic hot water system. However, the coil inside the flue pipe will restrict flue gas and reduce draft causing soot conditions. Also, dismantling the flue pipe for cleaning can create a substantial problem. Further, the water pre-heater tank along with the disclosed pressure gauge and pressure relief valve all require additional space. The disclosed system is extremely elaborate, too costly and impractical.