Heat pump water heater with external inlet tube   

FIELD OF THE INVENTION

The present subject matter relates generally to water heaters, and more particularly to a heat pump water heater with an improved inlet tube design.

BACKGROUND OF THE INVENTION

Conventional electric resistance water heaters include a tank defining a chamber for retention of water. A water inlet pipe connects to a cold water supply line and relatively cold water into the chamber. Typically, the inlet pipe (“dip tube”) extends internally from the top of the tank to a location adjacent to the bottom of the tank. Within the tank, electric resistance elements (typically two) heat the water, which is dispensed from an outlet pipe located adjacent to the top of the tank. As hot water is dispensed, cold water is introduced into the bottom of the tank. As the water is heated, in rises in the tank.

Heat pump water heaters are gaining broader acceptance as a more economic and ecologically-friendly alternative to electric water heaters. These systems utilize a condenser configured in a heat exchange relationship with the water storage tank, for example wrapped around the tank in a series of coils. During operation of the heat pump cycle, a refrigerant exits an evaporator as a superheated vapor and/or high quality vapor mixture. Upon exiting the evaporator, the refrigerant enters a compressor where the pressure and temperature increase and the refrigerant becomes a superheated vapor. The superheated vapor from the compressor enters the condenser (or gas cooler in a transcritical system), wherein the superheated vapor transfers energy to the water within a storage tank and returns to a saturated liquid and/or high quality liquid vapor mixture.

Water heater tank designs developed for electric water heaters are, however, not particularly efficient for heat pump water heaters. Accordingly, it would be desirable to provide a water heater tank that increases the efficiency of the heat pump cycle in a heat pump water heater.

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In a particular embodiment, a heat pump water heater system is provided with a water storage tank and a sealed heat pump cycle, which includes a compressor, a condenser/gas cooler, an evaporator, and a refrigerant. The condenser/gas cooler is disposed in a heat exchange relationship with at least a portion of the water storage tank for heating water within the tank. The tank further includes an outlet through which hot water is discharged, and a cold water inlet that is disposed to introduce cold water into the tank at a location of a bottommost portion of the condenser. With this configuration, cold water introduced into the tank is not pre-heated by hot water in the tank so as to enhance the thermodynamic cycle efficiency of the system by increasing the temperature range over which heat is rejected from the condenser/gas cooler.

The system may include an inlet pipe that is disposed externally of the tank and connected to the cold water inlet, which is disposed proximate to a bottom of the tank.

In a particular embodiment, the condenser/gas cooler is a coiled heat exchanger wrapped around the tank and having a refrigerant inlet disposed proximate to the cold water inlet and a refrigerant outlet disposed proximate to a top of the tank.

In still another embodiment, the system may include a generally horizontally disposed cold water discharge pipe within the tank connected to the cold water inlet and having outlets disposed along the length of the pipe. The outlets may be oriented towards a bottom of the tank.

The system may include a supplemental heat source, such as one or more supplemental electric resistive heating element within the tank.

The present invention also encompasses a water storage tank apparatus that is particularly suited for use in a heat pump water heater system. The tank apparatus includes a tank in which cold water introduced into the tank is heated and discharged as hot water. A refrigerant condenser/gas cooler is configured in a heat exchange relationship with at least a portion of the tank. The tank further includes an outlet through which hot water is discharged, and a cold water inlet that is disposed so as to introduce cold water into the tank at the location of a bottommost portion of the condenser/gas cooler.

The tank apparatus may include an inlet pipe that is disposed externally of the tank and connected to the cold water inlet, which is disposed proximate to a bottom of the tank.

In a particular embodiment, the condenser/gas cooler is a coiled heat exchanger wrapped around the tank and having a refrigerant inlet disposed proximate to the cold water inlet and a refrigerant outlet disposed proximate to a top of the tank.

In still another embodiment, the tank apparatus may include a generally horizontally disposed cold water discharge pipe within the tank connected to the cold water inlet and having outlets disposed along the length of the pipe. The outlets may be oriented towards a bottom of the tank.

The tank apparatus may include a supplement heat source, such as one or more supplemental electric resistive heating elements within the tank.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a diagram view of a conventional heat pump water heater system;

FIG. 2 is a view of an embodiment of a heat pump water storage tank in accordance with aspects of the invention;

FIG. 3 is a view of an alternative embodiment of a heat pump water storage tank in accordance with aspects of the invention; and

FIG. 4 is a diagram view of a heat pump water heater system incorporating still a further embodiment of a water storage tank in accordance with aspects of the invention.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

Referring now to the figures, FIG. 1 depicts a heat pump water heater (HPWH) system 100 that includes an evaporator 102, a compressor 130, a condenser 108, a throttling device 106, and at least one fan 104. The condenser 108 is assembled in a heat exchange relationship with the water storage tank 120 to heat the water within the tank. During operation of the heat pump cycle, a refrigerant exits the evaporator 102 as a fluid in the form of a superheated vapor and/or high quality vapor mixture. Upon exiting the evaporator 102, the refrigerant enters the compressor 130 wherein the pressure and temperature of the refrigerant are increased such that the refrigerant becomes a superheated vapor. The superheated vapor from the compressor 130 enters the condenser 108 wherein it transfers energy to the water within a storage tank 120 and condenses into a saturated liquid and/or high quality liquid vapor mixture. This high quality/saturated liquid vapor mixture exits the condenser 108 and travels through the throttling device 106. Upon exiting the throttling device 106, the pressure and temperature of the refrigerant drop at which time the refrigerant enters evaporator 102 and the cycle repeats itself.

In an alternate embodiment, the HPWH system 100 is a transcritical system wherein the refrigerant (typically CO2) has a low critical point and thus operates on a transcritical cycle wherein it evaporates in the subcritical region and rejects (transfers) heat at temperatures above the critical point in a “gas cooler” instead of a condenser. It should thus be appreciated that element 108 discussed herein may also be a gas cooler depending on the type of system.

The water storage tank 120 in the system 100 of FIG. 1 is a conventional design wherein a water inlet line 112 is provided for directing cold water to the bottom of the tank 120 via a dip tube 110 such that the water is preheated by the water in the tank before it discharges into the tank at the outlet of the dip tube 110.

The system 100 may also include supplemental electric heating elements 122 and 124 placed near the top and bottom of the water storage tank 120 to heat the water.

The heated water exits the tank 120 at exit 114 and flows to the residence or other place where heated water is desired. The system 100 may include a temperature sensor 126 positioned to sense the temperature of the water in the upper region of the tank and may also have additional temperature sensors placed at various locations for sensing other temperatures, such as heat pump condenser inlet and outlet temperatures, ambient temperature, etc.

The system 100 may also include a controller 152, equipped with a microprocessor, that determines which of the compressor 130, an upper electric resistance heater 122, and a lower electric resistance heater 124 shall be energized, and for how long, in order to heat the water within the water storage tank 120. The controller 152 may receive any manner of temperature readings (e.g., from sensor 126), flow signals, setpoints, and so forth, to implement its control functions.

FIGS. 2 and 3 depict embodiments of a water storage tank apparatus 220 in accordance with aspects of the invention, and FIG. 4 depicts yet another embodiment of a tank apparatus 220 installed within a heat pump water heater system 200. With respect to FIG. 4, it should be appreciated that the invention encompasses any manner of heat pump water heater system 200 that incorporates a water storage tank in accordance with aspects of the invention, and that the configuration of the system 200 depicted in FIG. 4 is for illustrative purposes only.

FIG. 2 depicts an embodiment of a water storage tank apparatus 220 that may be configured into any suitable heat pump water heater system 200 (FIG. 4). In the embodiment of FIG. 2, the storage tank apparatus 220 includes a tank 222 that may be surrounded by a shell component 224. Any manner of suitable thermal insulating material may be disposed within the space between the shell 224 and tank 222, as is well known in the art. The tank 222 includes a bottom 223 having a cold water inlet 232 disposed proximate thereto. The tank 222 receives cold water via the cold water inlet 232, heats the water, and discharges the water through a hot water outlet 230 proximate to a top portion of the tank 222.

A heat pump refrigerant condenser/gas cooler 226 is configured in a heat exchange relationship around at least a portion of the tank 222, depending on the particular configuration of the condenser/gas cooler 226. For example, the condenser/gas cooler 226 may be a planar or plate-like heat exchanger that is wrapped at least partially around the tank 222. In the illustrated embodiment, the condenser/gas cooler 226 is a coiled loop heat exchanger 228 having a plurality of tube coils wrapped around at least a portion of the tank 222. These coils may be disposed between the shell 224 and the tank 222, as depicted in FIG. 2.

In the embodiment of FIG. 2, refrigerant from a compressor 212 (FIG. 4) is introduced at a refrigerant inlet 240 to the condenser/gas cooler 226 at a location proximate to a top portion of the tank 222. The refrigerant circulates through the coils of the heat exchanger 228 and exits at a refrigerant outlet 242. Thus, in this particular configuration, the “hot” refrigerant is introduced at the top portion of the tank 222 and the “cold” refrigerant exits at a location proximate to the bottom 223 of the tank generally at a location corresponding to the cold water inlet 232.

In the embodiment of FIG. 3, the directional flow of the refrigerant through the coiled heat exchanger 228 is opposite of that depicted in FIG. 2. In other words, the “hot” refrigerant enters the coiled heat exchanger 228 at the refrigerant inlet 240 proximate to the bottom 223 of the tank generally at the location of the cold water inlet 232, and the “cold” refrigerant exits at the refrigerant outlet 242 generally proximate to the top portion of the tank. The configuration of FIG. 3 may be desired in that an even greater temperature gradient is defined in the tank, which may further enhance thermodynamic efficiency by allowing heat rejection from the condenser/gas cooler 226 across a wider temperature range, as compared to the embodiment of FIG. 2 wherein the initial “hot” refrigerant is exposed in an initial heat-exchange relationship with the relatively hotter water within the tank at the top portion of the tank 222.

Referring still to FIGS. 2 and 3, the cold water inlet 232 may be supplied with cold water via an inlet pipe 234 that is disposed alongside of the tank 222. It should be appreciated, however, that any manner of suitable piping arrangement may be utilized to conduct cold water into the tank at a location of the colder water inlet 232 generally proximate to the bottom portion of the tank 223.

The operative location of the cold water inlet 232 and the condenser/gas cooler 226 may vary relative to each other. In general, however, it is desired that the cold water be introduced into the tank at a location that generally corresponds to the lower portion of the coiled heat exchanger 228 (regardless of the directional flow of the refrigerant). It is not beneficial for a cold “slug” of water to settle at the bottom portion of the tank 222 without being sufficiently heated by the condenser 226. This situation would result in a relatively stagnate thermal layer of cold water at the bottom portion of the tank without necessarily improving the thermodynamic efficiency of the heat pump system.

Referring to FIG. 4, the embodiment of the water storage tank apparatus 220 includes a discharge pipe 236 connected to the cold water inlet 232. This discharge pipe includes any configuration of outlets 232 that serve to uniformly distribute the cold water introduced into the tank 222 across the diameter of the tank. The outlets 238 may be disposed so as to direct the cold water towards the bottom 223 of the tank so as to enhance thermal stratification within the tank.

The storage tank apparatus 220 in FIG. 4 also includes a supplemental heating source, such as one or more electric resistive heating elements 244, with one element 244 disposed proximate to the top portion of the tank and the other element 244 disposed proximate to a bottom portion of the tank 222. The use of supplement electric resistive heating elements in a heat pump hot water system is known in the art and need not be described in detail herein. In general, the heating elements 244 are activated by a controller 210 in situations wherein the demand of hot water placed on the system 200 exceeds the heating capability of the heat pump thermal cycle.

FIG. 4 further depicts the water storage tank apparatus 220 placed in a heat pump cycle utilizing a compressor 212, and evaporator 202, a fan 204, and a throttle device 206. The operation of these components is described above with respect to FIG. 1 and need not be repeated herein. The controller 210 may be configured with the compressor 212 and the resistive heating elements 244 and be responsive to any manner of input signals, such as temperature of water within the tank, flow of water out of the tank, thermostat set points, and the like, to coordinate operation of the system.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.