TEMPERATURE CONTROL SYSTEM OF GAS-FIRED WATER HEATER

A temperature control system of a gas-fired water heater includes a cold water pipe connected to one side of a heat exchanger and a hot water pipe connected to another side of the heat exchanger. A circulation pump is mounted to a water return pipe, which has two ends respectively connected to the hot water pipe and the heat exchanger to direct and return hot water from the hot water pipe back to the heat exchanger. When a hot water faucet is opened to activate a combustion operation of the gas-fired water heater, the circulation pump is set in continuous operation to pump water from the water return pipe for returning back to the heat exchanger, so that the returned hot water can be mixed, in the heat exchanger, with cold water supplied through the cold water pipe in order to achieve a set temperature.

(a) TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a temperature control system, and more particularly to a temperature control system of a gas-fired water heater that involves a circulation pump for continuously pumping return water through a return water pipe into a heat exchanger.

(b) DESCRIPTION OF THE PRIOR ART

Referring toFIG. 3, a known tankless or hybrid water heater (involving a fire-tube heat exchanger) comprises, structurally, a cold water pipe91and a hot water pipe92arranged and connected to two sides of a heat exchanger90with a mixing valve93connected between the cold water pipe91and the hot water pipe92and an adjustment valve94mounted to the cold water pipe91in order to achieve a desired set temperature of hot water. An internal temperature of the known heat exchanger90is generally set at a level higher than the desired set temperature of hot water. (For example, the hot water set temperature is 50° C., and the temperature of the heat exchanger90is set at 70° C.) The mixing valve93(such as a stepping motor controlled valve) conducts hot water that is fed to the hot water pipe92by the heat exchanger90to mix with the cold water supplied through the cold water pipe91in order to achieve the precise set level of temperature.

Referring toFIG. 4, some of the known water heaters are provided with a pump95, and a 2-way valve96is provided for temperature control. The purpose of the pump95is to eliminate or remove latent heat that is generated after the combustion operation of the heat exchanger90is shut down (namely the hot water faucet is closed).

The known water heaters suffer at least the following drawbacks:

(1) The heat exchanger90has to bear a relatively high thermal stress because a great temperature difference exists between a water inlet port (connected with the cold water pipe91) and the water outlet port (connected to the hot water pipe92) of the heat exchanger90.

(2) Because of thermal inertia and thermal impact, the service life of the heat exchanger90is shortened.

(3) Due to latent heat of the heat exchanger90, there are severe issues of excessively high and low temperatures.

(4) Loading applied to the mixing valve93and the 2-way valve96is heavy for they have to constantly adjust to accommodate different flow rates.

Thus, it is necessary for improvement of the known temperature control mechanism of water heaters.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a temperature control system of a gas-fired water heater that involves a circulation pump for continuously pumping water to return through a return water pipe back into a heat exchanger in order to constantly keep the temperature of the heat exchangers the same as a set temperature.

To achieve the above objective, the present invention comprises a heat exchanger, a cold water pipe, a hot water pipe, and a circulation pump, wherein the heat exchanger heats and converts cold water into hot water. The cold water pipe is connected to one side of the heat exchanger to supply cold water into the heat exchanger. The hot water pipe is connected to another side of the heat exchanger to output hot water generated by the heat exchanger. The circulation pump is mounted to a water return pipe. The water return pipe has two ends that are respectively connected to the hot water pipe and the heat exchanger to direct and return hot water from the hot water pipe back into the heat exchanger.

The present invention is provided with a circulation pump that takes the place of the traditionally used mixing valve and adjustment valve. When a hot water faucet is opened to activate a combustion operation of the gas-fired water heater, the circulation pump is constantly kept in operation to pump and return the hot water from the hot water pipe through the water return pipe, as returned water, back into the heat exchanger. At the same time, the cold water pipe supplies cold water into the heat exchanger so that the returned hot water and the cold water are mixed in the heat exchanger for preheating for the purpose of reaching a set temperature and making temperature control stable, without excessively high or excessively low temperature. The temperature of the heat exchanger can be always kept at the same level as the set temperature. The heat exchanger does not cause any issue of latent heat.

When the hot water faucet is closed to thus shut down the combustion operation of the gas-fired water heater, the circulation pump40is periodically set into operation at a fixed or variable interval in order to generate a water flow that helps reduce generation and accumulation of scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS. 1 and 2, a temperature control system of a gas-fired water heater according to a preferred embodiment of the present invention comprises a heat exchanger10, a cold water pipe20, a hot water pipe30, and a circulation pump40. Details will be provided below:

The heat exchanger10is operable to heat and convert cold water into hot water with an operation principle that is commonly known and will be not repeated herein.

The cold water pipe20is connected to one side of the heat exchanger10to supply cold water to the heat exchanger10.

The hot water pipe30is connected to another side of the heat exchanger10to output hot water generated by the heat exchanger10.

The circulation pump40is mounted to a water return pipe50. The water return pipe50has two ends respectively connected to the hot water pipe30and the heat exchanger10to direct hot water from the hot water pipe30back to the heat exchanger10.

In an embodiment, the heat exchanger10comprises a water tank. The water tank has a capacity that is less than or equal to 10 gallons, this covering heat exchangers of the instantaneous heating type (which has no water storage at all) or fire tube type and hybrid type (which have a minor amount of water storage). For water storage greater than such a range may not achieve a uniform temperature inside the tank and may not be capable of effective control of temperature.

In an embodiment, the water return pipe50is connected to the hot water pipe30and the heat exchanger10to form an internal circulation. The connection between the water return pipe50and the heat exchanger10forms an inlet port of return water, which is not set at the same location as that of an inlet port of cold water formed of the connection between the cold water pipe20and the heat exchanger10.

In an embodiment, the heat exchanger10is combined with a combustion blower60, wherein the combustion blower60is connected to a fuel gas pipe61and the fuel gas pipe61comprises a fuel gas valve62, for supplying fuel gas to the heat exchanger10to serve as a combustion heat source.

The above provides a description to the components of the present invention and the assembly thereof. Examples of use, features, and advantages of the present invention will be illustrated below.

The present invention is applied to a circulation pump40to take the place of the traditionally used mixing value and adjustment valve. When a hot water faucet is opened to cause activation of a gas-fired water heater for combustion, the circulation pump40is constantly supplied with electrical power to continuously drive hot water from the hot water pipe30, through the water return pipe50, back into the heat exchanger10so as to achieve continuous circulation of the return water, and at the same time, the cold water pipe supplies cold water into the heat exchanger, so that the cold water is mixed with the return water in the heat exchanger10for pre-heating to reach a set temperature (for example a temperature of hot water being set at 50° C.). Temperature control in this way is stable so that no excessively high or excessively low temperature may occur. The temperature of the heat exchanger10can be constantly kept at the set temperature and no latent heat may occur in the heat exchanger10.

When the hot water faucet is closed to have the combustion operation of the gas-fired water heater shut down, the circulation pump40is periodically set into operation at a fixed or variable interval so that flowing water helps reduce accumulation and generation of scale.

The present invention possesses at least the following advantages:

(1) The temperature of the heat exchanger10is constantly kept the same as the set temperature.

(2) The heat exchanger10has no temperature hysteresis.

(3) The heat exchanger10has no latent heat so that the temperature at a hot water outlet is steady without excessively high or excessively low temperature thereby helping prevent burning caused by the latent heat of the heat exchanger10.

(4) The circulation pump40is kept in operation during a water heating operation and is set into operation periodically at a fixed or variable interval in a standby period of the heater. As such, the flowing water, when moving in the heat exchanger10, causes a water flow that helps reduce generation and accumulation of scale.

(5) The heat exchanger10has low thermal inertial and low thermal impact so that the service life can be extended.

(6) No mixing valve and adjustment valve are required so that the number of components can be reduced.

The following table provides a comparison of difference between the present invention and the conventional water heaters shown inFIGS. 3 and 4:

The Present InventionPrior Art Water Heaterspurpose ofto eliminate latent heatto provide internal or externalpumpcirculation mode (only onemode being available)principle(1) the hot water activated(1) for internal mode, theofand combusting and thepump being set into operationoperationpump kept in operationonly after combustion is shut(2) shutting down combustiondown in order to removeof the water heater, while thelatent heatpump set in periodic(2) for external mode, theoperationpump being arranged to(3) the pump being used onlyreplace a circulation pumpfor internal circulationinstalled in a hot water(4) the temperature of the heatcirculation pipe set up insideexchanger being equal to thea house in order to provide anset temperatureexternal circulation of hotwater(3) the temperature of theheat exchanger is alwaysslightly higher than the settemperature and would bemixed with cold water from abypass pipe (with a mixingvalve) to reach the settemperaturepurpose ofto balance the temperature ofnot suitable for temperaturepumpthe heat exchanger in order tocontrol (for the mixing valveinstal-control temperatureis the key component forlationtemperature control)waterwhich is a component otherwhich the same part as thecirculationthan or not a part of a coldcold water pipeand returnwater pipecom-ponentpurpose ofto provide two different(1) return water being notwatertemperature zones:used to control temperaturereturn(1) condensation efficiency of(2) after combustion is shutcom-flue gas is made higher anddown, the pump beingponentthe result of flue gasallowed to operate for fewcondensation is better, heatingseconds because the top ofefficiency being higherthe heat exchanger is(2) pre-heating of cold waterexcessively hot and the returnsupplied into the heatwater is used to remove a partexchanger in order to controlof the latent heat of the heatthe water tank temperature ofexchanger (this beingthe heat exchangerworkable for only the internal(3) completely eliminatingcirculation mode)latent heat, achievingtemperature control, free ofthermal stress, achievingextended life span(4) reducing the number ofcomponents