Abstract:
A heat pump water heater has a tank portion, an electric heating structure for adding electrical heat to water stored in the tank, and a heat pump for adding refrigerant heat to the tank water. A control system associated with the water heater has three user-selectable heating modes for heating the tank water during a given heating demand cycle—a first mode that initially heats the tank water with refrigerant heat while the electric heat is locked out for a first predetermined period before supplementing the refrigerant heat if necessary, a second mode similar to the first mode but with a longer electric heat lockout period, and a third mode in which only the electric heat is utilized to satisfy a tank water heating demand. Illustratively, the heat pump is disposed in a compact component arrangement on the top end of the water heater tank.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of the filing date of provisional U.S. patent application No. 61/276,110 filed Sep. 8, 2009. The entire disclosure of the provisional application is hereby incorporated herein by this reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention generally relates to liquid heating apparatus and, in a representatively illustrated embodiment thereof, more particularly relates to a specially designed heat pump water heater and associated control system. 
         [0003]    In the past, various proposals have been made for operatively coupling a heat pump to an electric water heater to controllably add refrigerant heat to the water stored in the tank portion of the water heater during water heating demand cycles. Since the coefficient of performance of a heat pump is considerably better than the coefficient of performance of the electric resistance type heating structure of an electric water heater, this use of a heat pump provides an opportunity to substantially reduce the operating cost of an electric water heater to which it is operatively coupled, with the electric heating structure being available as a supplemental water heating mechanism should the heat pump fail or need heating supplementation. 
         [0004]    As is well known in the water heater art, there is a tradeoff between the heating cost effectiveness of a heat pump and the more rapid water heating capability of an electric heating element. In conventionally constructed heat pump water heaters the user typically has little if any ability to selectively adjust the relationship between water heating cost effectiveness and water heating rapidity in the water heater to suit varying operating environments and hot water demand situations. An additional need that exists in the heat pump water heater area is the need for improvements in the placement and component arrangement of the heat pump portion of the water heater. It is to these needs that the present invention is primarily directed. 
       SUMMARY OF THE INVENTION 
       [0005]    In carrying out principles of the present invention, in accordance with a representatively illustrated embodiment thereof, liquid heating apparatus is provided that comprises first apparatus operative to transfer refrigerant heat to a liquid, second apparatus operative to transfer electrical heat to the liquid, and a control system. The liquid heating apparatus illustratively includes an electric water heater having a tank for storing water to be heated, the first apparatus illustratively includes a refrigerant circuit structure, preferably a heat pump, operatively coupled to the electric water heater, and the second apparatus illustratively includes an electric resistance type heating structure extending through an interior portion of the tank. 
         [0006]    According to an aspect of the overall invention, the control system may have a heating mode operative, in a heating cycle initiated in response to a sensed demand for liquid heating, to initially utilize the first apparatus, at the start of the heating cycle, to transfer refrigerant heat to the liquid while preventing operation of the second apparatus for a predetermined lockout period, thereafter utilize the second apparatus to supplement the refrigerant heating of the liquid with electrical heating thereof if the heating demand has not been satisfied by the previous refrigerant heating of the liquid, and then terminate the operation of both the first heating apparatus and the second heating apparatus at the end of the heating cycle when the demand for liquid heating is satisfied. The lockout of the second apparatus during each heating cycle in this heating mode is illustratively initiated only at the start of such heating cycle. 
         [0007]    According to other aspects of the overall invention, the first apparatus may include a water circuit coupled to the tank and having a pump operative to draw water from a bottom portion of the tank and return the water to a top portion of the tank, the first apparatus may include a compressor, and the control system may be operative, if necessary, to utilize the second apparatus to heat the liquid to a predetermined minimum temperature prior to permitting operation of the compressor. 
         [0008]    According to a further aspect of the overall invention, the control system may be operative to control the first apparatus and the second apparatus in either one of user-selectable first and second heating modes. The first heating mode, when selected, is operative in response a sensed demand for liquid heating to initially utilize the first apparatus to transfer refrigerant heat to the liquid, while preventing operation of the second apparatus for a predetermined first lockout period, and thereafter utilize the second apparatus to supplement the refrigerant heating of the liquid with electrical heating thereof if the heating demand has not been satisfied by the previous refrigerant heating of the liquid. 
         [0009]    The second heating mode, when selected, is operative in response a sensed demand for liquid heating to initially utilize the first apparatus to transfer refrigerant heat to the liquid, while preventing operation of the second apparatus for a predetermined second lockout period of a different magnitude than the first lockout period, and thereafter utilizing the second apparatus to supplement the refrigerant heating of the liquid with electrical heating thereof if the heating demand has not been satisfied by the previous refrigerant heating of the liquid. 
         [0010]    The control system may be additionally operative to control the first apparatus and the second apparatus in a third user-selectable heating mode which, when selected, is operative for only a predetermined time period to utilize only the second apparatus to transfer electric heat to the liquid in response to a sensed demand for liquid heating, the control system, after the expiration of the predetermined time period, automatically selecting one of the first and second heating modes for use in satisfying a sensed liquid heating demand. 
         [0011]    According to a further aspect of the overall invention, the control system may be operative to control the first apparatus and the second apparatus in either one of user-selectable first and second heating modes. The first heating mode, when selected, is operative to utilize the first apparatus and, if needed, the second apparatus to transfer heat to the liquid in response to a sensed demand for liquid heating. The second heating mode, when selected, is operative, for only a predetermined time period, to utilize only the second apparatus to transfer heat to the liquid in response to a sensed demand for liquid heating, the control system, after the expiration of the predetermined time period, automatically selecting the first heating mode for use in satisfying a sensed liquid heating demand. 
         [0012]    According to another aspect of the overall invention, the control system is operative to receive a desired liquid heating temperature set point input by a user of the liquid heating apparatus, and having a user-selectable heating mode which, in response to a sensed demand for liquid heating, initially utilizes the first apparatus to transfer refrigerant heat to the liquid, while preventing operation of the second apparatus for a predetermined first lockout period, and then utilizes the second apparatus to supplement the refrigerant heating of the liquid with electrical heating thereof if the heating demand has not been satisfied by the previous refrigerant heating of the liquid. If the user-input temperature set point is equal to or greater than a predetermined magnitude, the control system is automatically operative to implement a second heating mode similar to said first heating mode but having a predetermined second lockout period greater than the first lockout period. 
         [0013]    In accordance with yet another aspect of the overall invention, water heating apparatus is provided comprising an electric water heater having a tank for storing water to be heated, and an electric heating element extending through an interior portion of the tank and operative to add electric heat to water therein. A refrigerant circuit structure has sequentially connected in series therein a compressor, a condenser coil operative to receive a throughflow of tank water to be heated by refrigerant passing through the condenser coil, an expansion valve, and an evaporator coil with an associated evaporator fan. The evaporator coil forms an outer wall portion of a plenum structure within the interior of which the compressor is disposed, the evaporator fan being operative, during operation of the refrigerant circuit structure, to flow air through the interior of the plenum structure and then outwardly through the evaporator coil, to thereby transfer heat from the fan and the compressor to the evaporator. 
         [0014]    The water heating apparatus further comprises a water circuit extending between the tank and the condenser coil and having connected therein a pump operative to sequentially flow water from the tank, through the condenser coil and then back into the tank, and a control system operative to utilize the refrigerant circuit structure and the electric heating element to maintain a predetermined water temperature in the tank. 
         [0015]    Preferably, the control system has a user-selectable heating mode operative in a given heating cycle to sequentially operate the refrigerant circuit structure and then operate the electric heating element, if necessary, to supplement the water heating of the refrigerant circuit structure. Illustratively, the tank has an upper end, and the refrigerant circuit structure is a heat pump disposed on the upper end of the tank. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic diagram of the water heater and control system; 
           [0017]      FIG. 2  is a partially cut away perspective view of the water heater; and 
           [0018]      FIGS. 3A and 3B  combinatively form a schematic flow diagram illustrating various control techniques utilized in conjunction with the water heater and associated control system. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Turning first to  FIGS. 1 and 2 , liquid heating apparatus representatively embodying principles of the present invention is designated generally by the reference numeral  10  and illustratively includes an electric water heater  12 , a refrigerant circuit illustratively in the form of a heat pump  14 , and a specially designed control system  16 . 
         [0020]    Water heater  12  has a vertically elongated cylindrical storage tank  18  for holding a quantity (representatively fifty gallons) of water to be heated. The tank  18  has a side-mounted cold water inlet  20  adjacent its lower end for receiving pressurized cold water from a source thereof, and a side-mounted hot water outlet  22  adjacent its upper end through which heated water may be periodically delivered, on demand, to hot water-utilizing fixtures such as sinks, bathtubs, showers, dishwashers and the like. Upper and lower electrical resistance heating elements  24 , 26  respectively extend through upper and lower interior portions of the tank  18 . An upper tank thermistor  28  senses an upper tank water temperature, and a lower tank thermistor  30  senses a lower tank water temperature. 
         [0021]    With continuing reference to  FIGS. 1 and 2 , the heat pump  14  (which may alternatively be another type of refrigerant circuit structure) includes a refrigerant piping circuit  32  in which a compressor  34 , a condenser coil  36 , an expansion valve  38  and an evaporator coil  40  having an associated evaporator fan  42  are connected in series as schematically depicted in  FIG. 1 . During operation of the heat pump  14 , the compressor  34  forces refrigerant from its outlet through the piping circuit  32  sequentially through a first flow passage  44  in the condenser coil  36 , the expansion valve  38 , the evaporator coil  40  and back into the inlet of the compressor  34 . 
         [0022]    A second flow passage  46  (see  FIG. 1 ) extends through the condenser coil  36  and is in thermal communication with the first condenser coil flow passage  44 . A water pump  48  has its inlet coupled to a lower interior end portion of the tank  18  by a pipe  50 , and its outlet coupled to the inlet of the condenser coil flow passage  46 . The outlet of the flow passage  46  is coupled to an upper interior end portion of the tank  18  by a pipe  52 . Accordingly, during operation of the heat pump compressor  34  and the water pump  48 , heat from compressed refrigerant traversing the condenser coil passage  44  is transferred to water being pumped from the tank  18  through the condenser coil passage  46  and back to the tank  18  via the pipes  50  and  52  to thereby transfer refrigerant heat to the tank water. 
         [0023]    A thermistor  54  senses the ambient temperature; a thermistor  56  senses the compressor discharge temperature; a thermistor  58  senses the evaporator coil inlet temperature; a thermistor  60  senses the evaporator coil suction temperature; and a thermistor  62  senses the condenser coil water discharge temperature. While the above-mentioned temperature sensing devices are representatively thermistors, it will be readily apparent to those of skill in this particular art that various other types of temperature sensors could alternatively be utilized without departing from principles of the present invention. 
         [0024]    As shown in  FIG. 2 , the heat pump  14  is representatively mounted on the upper end of the water heater tank  18 , with the evaporator coil  40  having a partially annular configuration which, in conjunction with associated top and side wall structures (removed in  FIG. 2  for purposes of illustrative clarity) bounds a plenum  63  disposed on the upper end of the tank  18 . The compressor  34  and the condenser coil  36  are disposed within the plenum  63 . The evaporator fan structure  42  is centrally disposed on the top side of the annularly curved evaporator coil  40  and is operative to flow ambient air downwardly into the plenum  63  and then horizontally outwardly through the evaporator coil  40 . This unique arrangement of the components of the heat pump  14  advantageously increases its operating efficiency by transferring both fan heat and compressor heat to the evaporator coil  40  via air being forced through the plenum  63  by the fan  42 . Of course, the heat pump  14  could be mounted on the water heater  12  in a different manner, or be positioned remotely therefrom, if desired. 
         [0025]    Referring again to  FIG. 1 , the control system  16  includes a microprocessor  64  preprogrammed to provide the water heater  12  and the heat pump  14  with a variety of subsequently described operational modes and control sequences that provide the water heating apparatus  10  with desirably enhanced operational flexibility and efficiency. Control system  16  also includes a user input touchpad input panel  66  that may be conveniently mounted on the exterior of the water heater tank  18  at a suitable location thereon. 
         [0026]    In the representatively illustrated form thereof, the touchpad  66  has disposed on the face thereof up and down temperature setting arrows  68 , 70  which may be pressed by a user to increase or decrease the selected desired tank water temperature setting. To the right of the arrows  68 , 70  is a vertical column of temperature setting indicating lights  72 , 74 , 76 , 78 , 80 , 82  that respectively correspond to six user-selected water temperature settings having magnitudes that increase vertically from indicating light  72  to indicating light  82 . Thus, for example, if the user wants to select a “normal” water temperature to be maintained in the tank  18  the user simply presses one of the temperature setting arrows  68 , 70  one or more times until the indicating light  76  is illuminated, indicating that a “normal” tank water temperature setting has been selected. 
         [0027]    At the lower end of the touchpad  66  are four mode selection areas  84 , 86 , 88  and  90  which may be pressed by a user to select manners in which the water heating apparatus  10  will function. These touchpad areas  84 , 86 , 88 , 90  respectively correspond to an “energy saver” mode, a “normal” mode, an “off” mode, and an “electric heat only” mode. Pressing the “energy saver” area  84  illuminates a corresponding indicating light  84   a  on the touchpad  66 , pressing the “normal” area  86  illuminates a corresponding indicating light  86   a  on the touchpad  66 , and pressing the “electric heat only” area  90  illuminates a corresponding indicating light  90   a  on the touchpad  66 . 
         [0028]    As will be subsequently described in greater detail herein, the energy saver mode of the control system  16  assists the water heater  12  in obtaining maximum efficiency. The normal mode, on the other hand, is geared to maximizing the performance of the water heater  12  while still providing good energy savings. Each of these two modes, in a predetermined, somewhat different manner, first utilizes heat pump energy (in the form of refrigerant heat) to raise the water heater tank temperature before additionally utilizing electric heat if needed to fulfill a water heating demand. When selected, the electric heat only mode utilizes only electric heat to meet water heating demands, but is automatically limited to a set operational time period built into the control system. Upon expiration of this time period, the control system automatically returns the water heater to its previously selected normal or energy saver mode. 
         [0029]    Turning now to the flow chart of  FIGS. 3A and 3B , the modes and operational sequences of the water heater  12 , carried out by the control system  16 , will be more fully described. With initial reference to  FIG. 3A , the water heating apparatus  10  is initially powered up at the start step  92  (by user selection of the energy saver, normal or electric heat only mode) after which a transfer is made to pre-warm test step  94 . At step  94  a query is made as to whether the lower tank temperature (as sensed by thermistor  30 ) is less than a predetermined temperature (representatively 70° F.) and the upper tank temperature (as sensed by the thermistor  28 ) is less than or equal to a predetermined temperature (representatively 75° F.). 
         [0030]    If both of these sensed temperature conditions are met, the control system  16  effects a transfer to step  96  at which a pre-warm cycle is initiated to heat the tank water to a predetermined minimum temperature (representatively 80° F.) to protect the compressor  34 , at its subsequent start-up, by assuring that its initial discharge temperature (as measured by thermistor  56 ) is sufficiently high to prevent damage to the compressor  34 . In response to the pre-warm cycle being initiated at step  96 , the control system  16  energizes the water pump  48  at high speed, and energizes both of the electric heating elements  24  and  26 . A transfer is then made to step  98  at which a query is made as to whether the sensed lower tank temperature is equal to or greater than its predetermined minimum temperature. While the answer to this query is negative, the tank water temperature continues to be monitored at step  98  until the query answer becomes positive, at which point the electric heat is de-energized at step  100  and a subsequent transfer is made to step  102 . 
         [0031]    At step  102  a query is made as to whether the tank water needs heat. If it does not, the control system  16  maintains the operational sequence at step  102  until it is determined at such step that the tank water does need heat from the water heating apparatus  10 , at which point a transfer is made to step  104 . At step  104  a query is made as to which operational mode (i.e., the energy saver mode, the normal mode or the electric heat only mode) has been selected. If the energy saver mode has been selected a transfer is made to step  106 . At step  106 , the heat pump  14  is started, to deliver refrigerant heat (via the circulation of water through pump  48 ) to the tank water, and electric heat is locked out for a predetermined delay period (representatively 45 minutes). 
         [0032]    A transfer is then made to step  108  where a query is made as to whether the tank water needs heat. If the tank water does not need heat, a transfer is made back to step  102  wherein the system waits until there is another call for tank water heating. If it is determined at step  108  that the tank water does need heat, a transfer is made to step  110  at which a query is made as to whether the previously set electric heat delay (or “lockout”) period set at step  106  has expired. If such delay period has not expired, the system continues to loop through steps  108 , 109  as indicated, until the delay period expires, at which point a transfer is made to step  112  (see  FIG. 3B ) at which point the electric heating of the tank water is initiated by energizing the upper electric heating element  24 . Next, at step  114  a query is made as to whether the tank water needs heat. If it does, the system stays at step  114  until the step  114  query answer becomes negative, at which point both refrigerant and electric heating of the tank water are terminated, and a transfer is made back to flow chart point  116  (see  FIG. 3A ). 
         [0033]    An adaptive mode, associated with the energy saver mode, is also preferably pre-programmed into the control system  16 . If, at step  106 , the user-selected tank water set point temperature is at or above a predetermined threshold magnitude (representatively, 130° F.), the adaptive mode is automatically initiated by the control system  16  in place of the energy saver mode to further increase the efficiency of the water heating apparatus  10 . When this adaptive mode is automatically initiated at step  106 , the electric heat delay period is set to a lesser time period (representatively 20 minutes) than in the energy saver mode, and a transfer is made to step  108  as previously described. 
         [0034]    If at step  104  in  FIG. 3A  it is determined that the normal mode has been selected by the user, a transfer is made to step  118  at which point the heat pump  14  is started, to deliver refrigerant heat to the tank water, and electric heat is locked out for a predetermined delay period (representatively 30 minutes). 
         [0035]    A transfer is then made to step  120  where a query is made as to whether the tank water needs heat. If the tank water does not need heat, a transfer is made back to step  102  wherein the system waits until there is another call for tank water heating. If it is determined at step  120  that the tank water does need heat, a transfer is made to step  122  at which a query is made as to whether the electric heat delay (or “lockout”) period set at step  118  has expired. If such delay period has not expired, the system continues to loop through steps  120 , 122  as indicated, until the delay period expires, at which point a transfer is made to step  124  (see  FIG. 3B ) at which the electric heating of the tank water is initiated by energizing the upper electric heating element  24 . Next, at step  126  a query is made as to whether the tank water needs heat. If it does, the system stays at step  126  until the step  126  query answer becomes negative, at which point both refrigerant and electric heating of the tank water are terminated, and a transfer is made back to flow chart point  116  (see  FIG. 3A ). 
         [0036]    A normal high temperature mode, associated with the normal mode, is also preferably pre-programmed into the control system  16 . If, at step  118 , the user-selected tank water set point temperature is at or above a predetermined threshold magnitude (representatively, 130° F.), the normal high temperature mode is automatically initiated by the control system  16  in place of the normal mode to further increase the efficiency of the water heating apparatus  10 . When this normal high temperature mode is automatically initiated at step  118 , the electric heat delay period is set to a lesser time (representatively 15 minutes) than in the normal mode, and a transfer is made to step  120  as previously described. 
         [0037]    If at step  104  in  FIG. 3A  it is determined that the electric heat only mode has been selected by the user, a transfer is made to step  128  at which point only the electric heat is energized (illustratively by energizing both of the upper and lower electric heating elements  24  and  26 ), without the heat pump  14  being utilized in this water heating mode. Preferably, also at step  128 , a timer is automatically set (representatively for a two week time period). At the next step  130  a query is made as to whether tank water heating is needed. If it is, the system remains at step  130  until the tank water heating demand is satisfied at which point a transfer is made back to step  102  to await another electric heat-only heating demand. After expiration of the previously set timer period, the system automatically reverts to the previously set energy saver or normal mode (or to the default energy saver mode if one of these two modes was not selected before the electric heat only mode was selected). Additionally, at any time during this automatically set timer period the user may manually reset the system to another heating mode if desired. 
         [0038]    The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.