HEAT PUMP WATER HEATER

Abstract

A heat pump water heater employing a thermostatic mixing valve integrated with the water lines carrying water from a water tank to a heat pump and then back to the water tank to achieve one pass technology to heat the water quickly and to achieve rapid recovery time without the use of supplemental heating sources.

Claims

1. A heat pump water heater to be used with a pressurized water tank, said heat pump water heater comprising a heat pump, refrigerant piping, water piping, a heat exchanger, a thermostatic mixing valve, and a circulating pump, wherein the heat pump is configured to transfer heat energy to refrigerant circulated within the refrigerant piping, the water piping is comprised of inflow piping, outflow piping, and circulation piping, wherein the circulation piping is interposed between the inflow piping and the outflow piping, the inflow piping is connected to a lower portion of the water tank and configured to allow water to pass out of the water tank and into the circulation piping, and the outflow piping is connected to an upper portion of the water tank and configured to allow water to pass out of the circulation piping and into the water tank, a portion of the refrigerant piping and a portion of the circulation piping are integrated with the heat exchanger, such that heat energy from the refrigerant contained within the refrigerant piping is transferred to water contained within the circulation piping via the heat exchanger, the thermostatic mixing valve is located at a junction of the inflow piping and the circulation piping, with the inflow piping connected to a cold water inlet of the thermostatic mixing valve, one end of the circulation piping connected to a hot water inlet of the thermostatic mixing valve, and another end of the circulation piping connected to a mixed water outlet of the thermostatic mixing valve, the circulating pump is located inline of the circulation piping between the mixed water outlet of the thermostatic mixing valve and the heat exchanger and is configured to circulate water contained within the water piping, and the outflow piping is connected to the circulation piping by a T-junction located at a location between the heat exchanger and the hot water inlet of the thermostatic mixing valve; whereby the thermostatic mixing valve is configured to allow a variable quantity of water, including no water, to flow from the water tank to the heat exchanger, and to allow a variable quantity of water within the circulation piping to flow to the heat exchanger.

2. The heat pump water heater of claim 1 wherein the thermostatic mixing valve is adjustable to accommodate a desired temperature of the water contained within the circulation piping.

3. The heat pump water heater of claim 1 wherein the thermostatic mixing valve has a closed state and an opened state, whereby when the thermostatic mixing valve is in the closed state no water enters the circulation piping through the cold water inlet of the thermostatic mixing valve, and when the thermostatic mixing valve is in the opened state water enters the circulation piping through the cold water inlet of the thermostatic mixing valve.

4. The heat pump water heater of claim 3 wherein the heat pump water heater has a priming cycle, whereby during the priming cycle the thermostatic mixing valve is in the closed state, the heat pump is activated, and the circulating pump is activated, such that the heat pump causes heat energy to be transferred to the refrigerant in the refrigerant piping, and the circulating pump causes water located within the circulation piping to circulate within the circulation piping and to flow through the heat exchanger to absorb heat energy from the refrigerant.

5. The heat pump water heater of claim 3 wherein the heat pump water heater has an operating cycle, whereby during the operating cycle the thermostatic mixing valve is in the opened state, the heat pump is activated, and the circulating pump is activated, such that water flows from the water tank through the inflow piping into the circulation piping, the heat pump causes heat energy to be transferred to the refrigerant in the refrigerant piping, the circulating pump causes water located within the circulation piping to circulate within the circulation piping and to flow through the heat exchanger to absorb heat energy from the refrigerant, and water flows into the water tank through the outflow piping.

6. The heat pump water heater of claim 1 wherein the heat pump water heater further comprises a temperature probe located within the water tank proximate to a bottom of the water tank.

7. The heat pump water heater of claim 6 wherein the thermostatic mixing valve has an opened state, whereby when the thermostatic mixing valve is in the opened state water enters the circulation piping through the cold water inlet of the thermostatic mixing valve; the heat pump water heater has an operating cycle, whereby during the operating cycle the thermostatic mixing valve is in the opened state, the heat pump is activated, and the circulating pump is activated, such that water flows from the water tank through the inflow piping into the circulation piping, the heat pump causes heat energy to be transferred to the refrigerant in the refrigerant piping, the circulating pump causes water located within the circulation piping to circulate within the circulation piping and to flow through the heat exchanger to absorb heat energy from the refrigerant, and water flows into the water tank through the outflow piping; and the temperature probe determines the temperature of the water located in the water tank at the bottom of the water tank, and activates the operating cycle of the heat pump water heater when said temperature of said water is below a desired temperature, and deactivates the operating cycle of the heat pump water heater when said temperature of said water reaches the desired temperature.

Description

DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 depicts a schematic drawing of one embodiment of the heat pump water heater of the present invention.

[0022] FIG. 2 depicts a water line piping diagram of the device of the present invention.

[0023] FIG. 3A depicts a prior art embodiment of a heat pump water heater wherein water from the water tank is pumped through a heat exchanger to obtain heat energy created by a heat pump.

[0024] FIG. 3B depicts another prior art embodiment of a heat pump water heater wherein refrigerant heated by a heat pump is circulated through piping surrounding the water tank, thereby heating the water in the water tank through conduction through the walls of the water tank.

[0025] FIG. 3C depicts yet another prior art embodiment of a heat pump water heater wherein refrigerant heated by a heat pump is circulated through piping immersed within the water tank, thereby heating the water in the water tank through direct conduction.

[0026] FIG. 4 is a graph depicting the temperature of water in the water tank over various periods of time as hot water is used domestically.

[0027] FIG. 5 depicts a generic thermostatic mixing valve.

DETAILED DESCRIPTION OF THE INVENTION

[0028] During operation, cold water flows out of the bottom 12 of the water tank 10 into inflow piping 140 of the water piping 130 and through the thermostatic mixing valve 180 (which is adjusted to a desired temperature) and then to the heat pump 110 for heating; and heated water flows out of the heat pump 110 through outflow piping 150 of the water piping 130 into the top 14 of the water tank 10, either to replenish the hot water in the tank 10 or for immediate domestic consumption. See FIG. 1.

[0029] (A). During the initial priming of the heat pump 110, the cold water inlet 182 of the thermostatic mixing valve 180 is closed off to the inflow piping 140 of the water piping 130. Water already in the circulation piping 160 is pumped by the circulating pump 190 through the circulation piping 160 through the heat exchanger 170, where it receives heat energy produced by the heat pump 110 and delivered through the refrigerant piping 120 to the heat exchanger 170. The partially heated water then passes through the T-junction 162 and continues through the circulation piping 160 back to the thermostatic mixing valve 180. (Water does not flow out of the circulation piping 160 through the outflow piping 150 of the water piping 130 during this step because the outflow piping 150 is connected to the top 14 of the pressurized water tank 10. Since the cold water inlet 182 of the thermostatic mixing valve 180 is closed to the inflow piping 140, water is not flowing out of the water tank 10 and the water tank 10 remains fully pressurized, preventing more water from entering the tank 10 via the outflow piping 150. Alternatively, if there is call for hot water, the tank 10 remains pressurized by the corresponding inflow of water into the water tank 10 from the external water supply, again preventing water from flowing through the outflow piping 150.) If the water within the circulation piping 160 has not yet reached a sufficiently warm temperature, the cold water inlet 182 of the thermostatic mixing valve 180 remains closed and the water repeats this circuit through the circulation piping 160 as described above, with each repetition adding more heat energy to the water and thus eventually raising the temperature of the water in the circulation piping 160 to the desired temperature.

[0030] (B). Once the water in the circulation piping 160 reaches the desired temperature, the cold water inlet 182 of the thermostatic mixing valve 180 begins to open, letting cold water from the bottom 12 of the water tank 10 into the circulation piping 160 through the inflow piping 140. Because water from the water tank 10 is now flowing into the circulation piping 160, a corresponding amount of heated water in the circulation piping 160 flows out of the circulation piping 160 through the outflow piping 150 into the top 14 of the water tank 10; this water is already at the desired temperature. The thermostatic mixing valve 180 controls the amount of the flow of the cold water into the circulation piping 160. Water already in the circulation piping 160 that had been heated to the desired temperature during the priming phase but which did not flow back to the water tank 10 through the outflow piping 150 remains in the circulation piping 160 and enters the hot water inlet 184 of the thermostatic mixing valve 180, to be mixed with the cold water and then returned to the heat exchanger 170 through the mixed water outlet 186 of the thermostatic mixing valve 180. This combined hot and cold water flowing through the circulation piping 160 is much closer to the desired temperature, and the heat exchanger 170 can easily bring it up to the desired temperature. Cold water entering the circulation piping 160 through the inflow piping 140 during this phase is therefore heated to the desired temperature in fewer passes through the heat exchanger 170, even in as few as a single pass. If too much cold water enters through the inflow piping 140, or if the heat exchanger 170 does not bring the water to the desired temperature in a single pass, the thermostatic mixing valve 180 closes off access through its cold water inlet 182 (or restricts entry of water to some degree) and the process reverts back to operation as described in phase (A), above.

[0031] (C). Once the water in the tank 10 (measured by a temperature probe located at a distance close to the bottom 12 of the tank 10) achieves the desired temperature (meaning, the entire tank 10 is filled with water at the desired temperature), the device turns off. As hot water is used from the tank 10, additional cold water enters the tank 10 at the bottom 12; the temperature probe detects the resulting drop in temperature at the bottom 12 of the tank 10 and restarts the device; the thermostatic mixing valve 180 controls whether the restart needs to go through phase (A) or whether it can immediately go into phase (B).

[0032] What has been described is a one pass system. The device is designed to quickly heat the water from the bottom 12 of the tank 10 while leaving the hot water at the top 14 of the tank 10 ready for immediate use. Due to heat stratification, the cold water entering the tank 10 will not be accessible for domestic hot water use. Moreover, if the outflow piping 150 of the device is piped to the hot-outlet of the water tank 10, the device will provide usable hot water instantly any time the heat pump water heater 100 is running. Given any amount of time to recover, the water tank 10 will be at least partially full of usable hot water. In typical conditions, 30-minutes after a complete draw-down of the tank 10, the device will have reheated fifteen gallons of water to 120? F., which is enough for a shower, while a prior art 120V heat pump water heater with integrated resistance heating will have a tank full of luke-warm water.

[0033] Integrated heat pump water heaters, when operating in heat pump only mode, are only able to add minimally heated water to the water tank. In order to get any water in the water tank up to a usable temperature (such as 105? F. or 125? F.), these systems have to heat the entire contents of the water tank. So, after a series of demanding hot water uses, such as multiple showers or a bath, there is no usable hot water available in the water tank for up to several hours. Lab performance testing supports this. A 240V water heater addresses this problem by placing a 4.5 kW resistance electric heating element in the upper ?-? of the water tank. This allows the water heater to heat just the top fifteen gallons of water (as opposed to forty-five or more) and this smaller volume can be raised to a hot, usable temperature in a shorter amount of time. However, a 120V water heater does not have this option. At that voltage, any resistance elements will be less than 900 W. That is insufficient power to raise the temperature of fifteen gallons of water quickly. Because the device of the present invention operates in one pass mode, it is able to effectively heat water contained in the tank 10 from the top 14 of the tank 10 down (by adding sufficiently heated water to the top 14 of the tank 10), which means hot water, at a usable temperature, is available more quickly than with an integrated heat pump water heater approach using only a 120V resistance heating element.

[0034] While the preferred embodiments of the present invention have been described, modifications can be made and other embodiments may be devised without departing from the spirit of the invention.

Example of Use

[0035] A prototype of the device of the present invention was installed in a real world environment to test its efficacy. The device was installed in the basement of a single family home with two adults and two children, ages three and six. The average temperature in the basement in February has been 47? F. Pex pipe and sharkbite fittings connect the device to a 40 gallon capacity electric water heater. The two-pole, 240V circuit breaker was switched off to the water heater, thereby disabling the resistance heating element and making the device of the present invention the sole source of heat. The device was plugged into the a 120V outlet on a 15 A breaker. The device draws up to 900 W momentarily during startup and averages about 700 W.

[0036] FIG. 4 displays a screen capture of the two primary temperature sensors on the water side of the device installed in the single family home from 6:00 PM to 3:00 AM on February 8th and 9th, 2022. At the time this graph was produced, the device was set to produce 120? F. minimum hot water. In the graph, one line 200 is the temperature of the water leaving the device. The other line 210 is the temperature of the water located low in the water tank, just 12 or so from the bottom. This low position is what determines when the device needs to operate. A lower temperature probe location means the device will activate and begin heating water after only 5-10 gallons of hot water is consumed. This ensures that the water tank is topped off and ready for a large demand at any time.

[0037] Just after 7 pm a bath was prepared for the three year old, and the six year old got in the shower in a separate bathroom. As cold water entered the tank from the municipal water supply, the temperature probe detected the cold water coming in to the bottom of the tank, which triggered the device to begin making hot water. The device responded by producing 120? F. water which was then sent to the hot water pipe, just outside the tank, and instantly consumed by the bath and shower. The contribution from the device was but a small fraction of the total flow going to the fixtures, with the majority of the hot water coming from the tank. Both shower and bath were as long as desired with no fluctuation in temperature. By 9 pm, the water in the lower portion of the tank was beginning to heat up, indicating that the tank was becoming heat soaked, just two hours after the heavy use. The sharp drop in temperature just after 9 pm occurred when an adult showered. Again, the temperature began recovering quickly, and within two hours the water in the bottom of the tank was already approaching 110? F. By just after 2 am, the water in the bottom of the tank reached its set point of 125? F. and the device tuned off.