Liquid heaters and vaporizers – Heat transmitter
Reexamination Certificate
1999-05-13
2001-01-09
Lazarus, Ira S. (Department: 3743)
Liquid heaters and vaporizers
Heat transmitter
C122S406100
Reexamination Certificate
active
06170440
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to combustion heaters for water, and more particularly to a booster utilizing an infrared burner for efficiently raising the temperature of water to a desired level for use by a downstream user, generally a commercial warewashing apparatus.
Commercial washing apparatuses, such as conveyor and door type model warewashing or dishwashing machines, generally require water at a temperature of between 120° and 160° F. during washing cycles. This water can generally be obtained cheaply and easily from the central hot water supply of most buildings. Furthermore, keeping the water at this temperature does not usually pose a problem since most warewashers are equipped with a supplemental heating source located in the wash water holding tank in order to keep the water within the desired temperature range for washing.
However, in order to comply with health regulations, warewashing systems that do not utilize a sodium hypochlorite sanitizing system or the like are required to sanitize the ware being washed with a rinse using a minimum of 180° F. water. Furthermore, the use of a 180° F. water rinse is desirable because it facilitates the drying of the ware, thereby decreasing the turnaround time necessary for reuse. This high temperature is generally out of the range available from most buildings central hot water source. Thus, in order to supply water at this desirable temperature, boosters have been employed to raise the temperature of the incoming water from between 110° and 140° F. to the required sanitizing temperature of 180° minimum.
For a typical application, the required water supply rate for a given booster can vary from between 60 to 400 gallons per hour and the required temperature increase can vary from 30° to as much as 80° F., depending on the temperature of the water received from the primary water supply. During busy periods the demand for this water can be quite large, thereby requiring that the booster be capable of continuously supplying a minimum of 180° water at the required final rinse flow rate. Additionally, in order to insure easy installation, equipment of this type is generally subject to certain dimensional restrictions. Typically, the booster will be required to fit under a counter height of approximately 34 inches and within a counter depth of between approximately 25 to 30 inches. Furthermore, a clearance of at least 6 inches is generally required underneath the equipment to facilitate the cleaning of the floor. Further adding to the design constraints for boosters of this type is the fact that they should be simple to operate and easy to maintain. Finally, in order to reduce operating costs, heat losses, other than to the water being heated, need to be kept to a minimum.
Electrically heated booster water heaters are available which generally meet the above requirements. These electric heaters have been attractive to consumers since their initial cost is relatively low and installation is relatively easy. However, heaters of this type are very expensive to operate. Other booster water heaters are known which utilize a blue-flame gas fired heater to supply hot water at the sanitizing temperature. There are many prior art patents for heaters of this type, including U.S. Pat. No. 3,160,145 which discloses a gas fired water heater having a blue flame gas burner at atmospheric pressure disposed below a horizontally mounted finned tube heat exchanger. Heaters of this type are not without problems, though. They are known to produce a noise known as “flame roar” while igniting which can be annoying and distracting to workers. Also, when used to supply sanitizing water at 180°, they are relatively inefficient since in many prior art designs more water is heated to the 180° temperature than is necessary and the remainder is then mixed with cold water to supply primary hot water at 140° to other sources.
Accordingly, boosters have been developed which use high efficiency infrared heaters to heat the water to the desired temperature. An infrared burner is a high efficiency gas burner which is fed an air/gas mixture of a specific concentration. The air/gas mixture flows onto a surface, otherwise known as the combustion surface, where it is ignited. The proportion of the air/gas mixture is preadjusted so that when the burner is ignited a burning zone is maintained at a set level above the combustion surface. Preferably, this burning zone is tuned by adjusting the gas/air flow rate and the back pressure such that burner performance and heat transfer are optimized. For example, U.S. Pat. No. 5,201,807 to Liljenberg et al. discloses the use of such an infrared burner in a water booster for a commercial warewasher. The Liljenberg invention includes a pump which continuously pumps water to be heated through a finned tube heat exchanger which is disposed in close proximity with the burner combustion surface.
SUMMARY OF THE INVENTION
In accordance with the present invention, a gas fired booster is provided which is very efficient, thereby reducing annual operating costs of the booster over prior systems. In particular, the gas fired booster of the present invention provides an infrared burner disposed within a heat exchanger which is substantially enclosed by a water storage tank. The gas fired burner of the present invention fits acceptably under a counter, as is generally required for such equipment, is easy to install and operate, and is inexpensive to maintain. In a preferred embodiment, the infrared burner includes a hollow tube which is covered by a woven ceramic fiber sleeve. An air/gas mixture is fed to the burner through the hollow tube and then through the interstices of the woven ceramic fiber sleeve where ignition occurs on a surface thereof. The burner is encircled by a heat exchanger, preferably of the coiled finned tube type, which is connected to a water inlet. Water flows through the heat exchanger thereby receiving heat from the burner before exiting to an outlet pipe which is connected to the holding tank. Preferably, the heat exchanger is surrounded by the holding tank and hot air and exhaust gases from the burner are allowed to permeate through the heat exchanger to contact the surrounding holding tank before being vented to the atmosphere.
The booster of the present invention is also provided with a pump for continuously circulating water from the holding tank through the exchanger coils to maintain the desired temperature. A temperature sensor is provided which monitors the temperature of the water continuously circulating through the heat exchanger. When a temperature below the desired temperature is sensed, the sensor signals the infrared burner to reignite. This process is repeated continuously while the booster is in an operating stage.
However, in a preferred embodiment, a timer or control loop is provided so that the pump continues to circulate water through the heat exchanger and holding tank for a period of time after the booster is shut down. This is done to avoid vaporizing water left in the heat exchanger, thereby increasing the life of the booster. The pump can continue to operate for a length of time which has been predetermined to sufficiently dissipate the heat from the burner or it can be shut down when the temperature sensor reads a temperature below a predetermined “safe” shutdown temperature.
In a preferred embodiment, the water holding tank completely encircles the primary heat exchanger and the infrared burner disposed within. This design further increases the energy efficiency of the booster by allowing the water in the holding tank to absorb any excess heat given off by the infrared burner that is not transferred to the water in the heat exchanger. Preferably, this tank is annular and insulated to further minimize heat losses. Additionally, in a preferred embodiment, an insulated plug is provided which seals off the end of the primary heat exchanger. This plug increases the efficiency of the booster by increasing the back pressure of the heated gases emanating from the burner and by
Grueser Thomas A.
Hoying Gary V.
Monnier Carla A.
Noren Doug W.
Noren Lars T.
Clarke Sara
Lazarus Ira S.
Premark FEG L.L.C.
Thomas Hine & Flory LLP
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