Tank-tankless water heater

Abstract

A tank-tankless water heater includes primary and secondary heat exchangers, and a combustor for the production of flue gases. In operation, water is first heated as the water and flue gases flow through primary heat exchanger. The water flows into the tank where it is stored and again heated as the flue gases flow through the secondary heat exchanger. A pump moves the water from the secondary heat exchanger, through the primary heat exchanger, and back to the secondary heat exchanger for storage as needed to maintain the stored water at a desired temperature. Water is drawn from the secondary heat exchanger during initial demand to provide a ready source of hot water, and the hot water supply is maintained by the primary heat exchanger during sustained hot water draws. The primary heat exchanger may include a temperature or temperature differential control system.

What is claimed is: 
     
         1 . A tank-tankless water heater comprising:
 a combustor for the production of hot flue gases;   a primary heat exchanger including a core and a flue gas flow path; and   a secondary heat exchanger including a tank and at least one flue;   wherein flue gases flow from the combustor through the flue gas flow path and then through the at least one flue;   wherein water to be heated first flows through the core, then into the tank where the water is stored, and then flows out of the tank for use upon demand; and   wherein heat is transferred from the flue gases to the water first as the water flows through the core and the flue gases flow through the flue gas flow path, and again as the water is stored in the tank and the flue gases flow through the at least one flue.   
     
     
         2 . The water heater of  claim 1 , wherein the primary heat exchanger includes a primary water inlet that delivers water to be heated to the core, and a primary water outlet that delivers heated water from the core to the tank; and wherein the primary heat exchanger is a temperature controlled heat exchanger having a flow control valve operable to selectively restrict flow of water through the core to achieve a desired water temperature at the primary water outlet. 
     
     
         3 . The water heater of  claim 1 , wherein the primary heat exchanger includes a primary water inlet that delivers water to be heated to the core, and a primary water outlet that delivers heated water from the core to the tank; and wherein the primary heat exchanger is a temperature differential controlled heat exchanger in which the temperature of water flowing through the core from the primary water inlet to the primary water outlet is raised a substantially fixed amount. 
     
     
         4 . The water heater of  claim 1 , further comprising a water pump communicating between the tank and the core and operable to move water from the tank, through the core, and back to the tank, to heat the water and raise the temperature of water in the tank. 
     
     
         5 . The water heater of  claim 4 , wherein the water pump is operable to move water from a bottom portion of the tank, then through the core, and then to a top portion of the tank. 
     
     
         6 . The water heater of  claim 4 , wherein the water pump is operable to move water from a top portion of the tank, then through the core, and then to a bottom portion of the tank. 
     
     
         7 . The water heater of  claim 4 , further comprising a temperature sensor sensing water temperature in the tank, the temperature sensor activating the water pump in response to the water temperature in the tank falling below a set point temperature. 
     
     
         8 . The water heater of  claim 1 , further comprising a flow activation controller operable to initiate operation of the combustor in response to water flow through the core. 
     
     
         9 . The water heater of  claim 1 , further comprising a water flow circuit operable, in response to a performance draw of hot water from the tank, to draw hot water from the tank at a first temperature, mix the hot water with cold water to produce reduced temperature water at a temperature lower than the first temperature, flow the reduced temperature water through the primary heat exchanger to produce reheated water at a second temperature substantially equal to the first temperature, and returning the reheated water to the tank. 
     
     
         10 . The water heater of  claim 1 , wherein the primary heat exchanger includes a primary water inlet and a primary water outlet; wherein the secondary heat exchanger includes a secondary water inlet communicating with the primary water outlet for receiving hot water from the primary heat exchanger, a secondary water outlet through which hot water flows out of the tank for use upon demand, and a two-way port; the water heater further comprising a tee communicating between the primary water inlet and the two-way port, and adapted to communicate with a source of cold water; wherein upon demand replacement cold water from the source of cold water replaces hot water drawn from the tank; and wherein at least some of the replacement cold water flows through the two-way port into the tank without flowing through the primary heat exchanger. 
     
     
         11 . The water heater of  claim 10 , further comprising a temperature sensor generating a signal in response to water temperature in the tank falling below a set point during continued flow of water out of the tank for use; a water pump; and a controller activating the pump in response to receiving the signal to direct an increased amount of cold water from the tee to the primary water inlet and thereby reduce the amount of cold water entering the tank through the two-way port. 
     
     
         12 . The water heater of  claim 10 , further comprising a temperature sensor generating a signal in response to water temperature in the tank falling below a set point during continued flow of water out of the tank for use; and a controller restricting cold water flow through the two-way port into the tank in response to receiving the signal, to increase an amount of cold water flowing through the primary heat exchanger prior to entering the tank after the signal is generated. 
     
     
         13 . The water heater of  claim 10 , further comprising means for increasing the flow of cold water from the tee to the primary water inlet and decreasing the flow of cold water from the tee to the two-way port; wherein cold water is introduced to a bottom portion of the tank through the two-way port; and wherein water is introduced to a top portion of the tank from the primary heat exchanger. 
     
     
         14 . The water heater of  claim 1 , further comprising:
 a first sensor coupled to a lower portion of the tank for generating a first signal indicative of water temperature within the lower portion of the tank;   a second sensor coupled to an upper portion of the tank for generating a second signal indicative of water temperature within the upper portion of the tank;   a two-way port communicating with the lower portion of the tank;   a cold water supply line communicating with both the primary water inlet and the two-way port;   a proportional valve communicating between the cold water supply line and the two-way port; and   a water pump communicating between the cold water supply line and the primary heat exchanger;   wherein cold water flows into the tank through the two-way port during initial performance draw of hot water from the tank;   wherein the water pump is energized in response to the first sensor generating the first signal, such that a portion of cold water from the cold water supply line flows through the primary heat exchanger before reaching the tank; and   wherein the proportional valve restricts flow of cold water through the two-way port in response to the second sensor generating the second signal.   
     
     
         15 . The water heater of  claim 14 , further comprising a flow sensor monitoring the flow of hot water during a performance draw; wherein the flow sensor causes the proportional valve to increase the flow of cold water through the two-way valve in response to the performance draw ending. 
     
     
         16 . The water heater of  claim 14 , wherein the pump draws water from the tank through the two-way port, flows the water through the primary heat exchanger where the water is reheated, and returns the reheated water to the tank in the absence of a performance draw in response to at least one of the first and second signals being generated. 
     
     
         17 . The water heater of  claim 1 , wherein the at least one flue extends between a top portion and bottom portion of the tank; and wherein flue gases flow up through the at least one flue from the bottom portion to the top portion of the tank. 
     
     
         18 . The water heater of  claim 1 , wherein the at least one flue extends between a top portion and bottom portion of the tank; and wherein flue gases flow down through the at least one flue from the top portion to the bottom portion of the tank. 
     
     
         19 . The water heater of  claim 1 , wherein the primary heat exchanger is substantially entirely within the tank of the secondary heat exchanger. 
     
     
         20 . A method of heating water, comprising the steps of:
 (a) providing a primary heat exchanger having a core and a flue gas flow path;   (b) providing a secondary heat exchanger including a tank and at least one flue;   (c) producing hot flue gases;   (d) moving the flue gases through the flue gas flow path and then through the at least one flue;   (e) flowing water to be heated first through the core, then into the tank;   (f) heating the water first in the primary heat exchanger as the water flows through the core and the flue gases flow through the flue gas flow path; and   (g) after heating the water in the primary heat exchanger, storing the water in the tank and heating the water in the tank as the flue gases flow through the at least one flue.   
     
     
         21 . The method of  claim 20 , further comprising sensing a temperature of the water stored in the tank and moving water from the tank, through the core, and back to the tank to reheat the water stored in the tank in response to the water temperature in the tank falling below a set point temperature. 
     
     
         22 . The method of  claim 20 , wherein step (f) includes selectively restricting the flow of water through the core to achieve a desired temperature of water flowing out of the primary heat exchanger. 
     
     
         23 . The method of  claim 22 , wherein step (e) includes introducing water from the core into a top portion of the tank. 
     
     
         24 . The method of  claim 20 , wherein step (f) includes raising the temperature of water flowing through the core a fixed amount. 
     
     
         25 . The method of  claim 24 , wherein step (e) includes introducing water from the core into a bottom portion of the tank. 
     
     
         26 . The method of  claim 24 , further comprising the steps of (h) providing hot water from a top portion of the tank to a user; and (i) in response to step (h), moving hot water at a first temperature out of the top portion of the tank, mixing the hot water with cold water to create reduced temperature water, flowing the reduced temperature water through the core to create reheated water having a second temperature substantially equal to the first temperature, and introducing the reheated water into the bottom portion of the tank. 
     
     
         27 . The method of  claim 20 , further comprising (h) providing hot water from a top portion of the tank to a user; (i) in response to step (h), bypassing the primary heat exchanger to direct cold water directly into a bottom portion of the tank to replace water flowing out of the tank; (j) monitoring water temperature in the tank; and (k) diverting a portion of the cold water from flowing directly into the bottom portion of the tank, and flowing the diverted cold water through the primary heat exchanger and then into a top portion of the tank in response to water temperature in the tank being below a cut-out temperature. 
     
     
         28 . The method of  claim 20 , wherein step (d) includes transferring sufficient heat from the flue gases to the water in the secondary heat exchanger to create condensation of water vapors in the flue gases in the at least one flue.