US20140352339A1

US20140352339A1 - Heat pump system having a high pressure trip controller

Info

Publication number: US20140352339A1
Application number: US13/908,884
Authority: US
Inventors: Rakesh Goel; Eric Berg; Pete Hrejsa
Original assignee: Lennox Industries Inc
Current assignee: Lennox Industries Inc
Priority date: 2013-06-03
Filing date: 2013-06-03
Publication date: 2014-12-04
Also published as: CA2844949A1

Abstract

One aspect presents a heat pump system controller that includes a control board a microprocessor located on and electrically coupled to the control board, and a memory coupled to the microprocessor and located on and electrically coupled to the control board. The memory has a program stored thereon that is configured to relate a temperature received from a liquid refrigeration line temperature sensor with a pressure of a compressor of a heat pump system and change an airflow rate of an indoor blower/heat exchange (ID) system of a heat pump (HP) system to avoid a shutdown of the HP system that occurs when the compressor reaches a trip pressure of the compressor.

Description

TECHNICAL FIELD

This application is directed to heat ventilation air conditioning (HVAC) heat pump systems.

BACKGROUND

Heat pump (HP) systems have gained wide commercial use since their first introduction into the HVAC market because of their operational efficiency and energy savings, and it is this efficiency and energy savings that appeals to consumers and is most often the deciding fact that causes them to choose HPs over conventional HVAC furnace systems. During the winter, a HP system transfers heat from the outdoor air heat exchanger to an indoor heat exchanger where the heat is used to heat the interior of the residence or building. The consumer uses a thermostat to select a temperature set-point for the interior. The HP then operates, using heat transferred from the outside, to warm the indoor air to achieve the set-point. As a result, the consumer enjoys a heating capability, while saving energy. Though auxiliary heating systems, such as electric or gas furnaces can be used in conjunction with the HP, this is typically done only for a brief period of time in order to achieve the set-point in extremely cold conditions.

SUMMARY

One embodiment of the present disclosure is a HP system that comprises an indoor blower/heat exchanger system (ID) system, an outdoor fan/heat exchanger and compressor (OD) system that are fluidly coupled together by a liquid refrigerant line. A liquid refrigeration line temperature sensor is coupled to the liquid refrigeration line and configured to provide a temperature of the liquid refrigeration line to the heat pump system. A controller is coupled to the liquid refrigeration line temperature sensor and configured to relate a temperature received from the liquid refrigeration line temperature sensor with a pressure of the compressor and change an airflow rate of the ID system to avoid a shutdown of the HP system that occurs when the compressor reaches a trip pressure of the compressor.
Another embodiment of the present disclosure is a heat pump system controller. This embodiment comprises a control board, a microprocessor located on and electrically coupled to the control board, and a memory coupled to the microprocessor and located on and electrically coupled to the control board. The memory has a program stored thereon that is configured to relate a temperature received from a liquid refrigeration line temperature sensor with a pressure of a compressor of a heat pump system and change an airflow rate of an indoor blower/heat exchange (ID) system of a heat pump (HP) system to avoid a shutdown of the HP system that occurs when the compressor reaches a trip pressure of the compressor.
Another embodiment presents a computer program product, comprising a non-transitory computer usable medium having a computer readable program code embodied therein, said computer readable program code adapted to be executed to implement a method of measuring and managing an indoor airflow rate of a heat pump system. The method comprises relating a temperature received from a liquid refrigeration line temperature sensor of a heat pump system with a pressure of a compressor of the heat pump system, and changing an airflow rate of an indoor blower/heat exchange (ID) system of the heat pump (HP) system to avoid a shutdown of the HP system when the compressor reaches a trip pressure of the compressor.

BRIEF DESCRIPTION

Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph showing the relationship between indoor discharge air temperature and OD ambient temperature for normal HP indoor airflow rate and comfort indoor airflow rate;

FIG. 2 is a graph showing the relationship between discharge pressure and indoor airflow rate at various outdoor ambient temperatures, where at low airflow rates, discharge pressure exceeds system high pressure limit;

FIG. 3 is a graph showing high correlation between discharge pressure and liquid line temperature with change in indoor airflow rate;

FIG. 4 illustrates a block diagram of an example HP system in which the enhanced controller of the disclosure may be implemented;

FIG. 5 shows a schematic of a layout diagram of an embodiment of the enhanced controller circuit board;

FIG. 6 presents a flow diagram of an example operation of a HP unit having the comfort controller associated therewith.

DETAILED DESCRIPTION

As noted above, HP units have gained wide use and are popular with consumers because they can reduce energy costs by using the heat in outdoor air to heat the space of an indoor structure, such as a residence or business. Though these HP units are typically very efficient in operation and energy savings, there is a drawback. The drawback is that the airflow from the blower of the indoor unit may feel cooler to an occupant than airflow from a HVAC furnace system that uses a gas or electric furnace to heat the air. Thus, the cooler register air from the HP system can make the occupant feel uncomfortably cool during the heating cycle.
To address this problem, the HP unit, as disclosed herein, includes a controller that is configured to run under a comfort mode function wherein the airflow from an indoor HVAC system is controlled in such a way as to make the airflow feel warmer to the user. When activated, this controller causes the airflow rate to decrease, which increases the temperature of the airflow. The resulting higher temperature airflow allows the occupant to feel warmer and more comfortable than when the unit runs in a normal operating mode, during which the airflow may feel cooler to the occupant.
In one embodiment, the controller includes a coded data table that relates indoor discharge air temperature as a function of outdoor ambient temperature, as illustrated in FIG. 1. The coded data can be obtained by testing the HP unit with which the controller is intended to be used, or using computer modeling software for that particular HP unit. In another embodiment, the data may be calculated in real-time. Where the data is obtained through actual test data, the HP unit is tested at various outdoor ambient temperatures and airflow rates to achieve a relationship between indoor discharge air temperature and the outdoor ambient temperature and compressor discharge pressures.
As seen in FIG. 1, the dashed line represents an HP unit's typical or normal indoor airflow rate operation, while the solid line represents the HP unit's comfort airflow rate operation as modified by the controller. The testing establishes that the overall indoor discharge temperature can be increased when operating the HP unit at lower airflow rates. With this disclosure, it is recognized, however, that as the airflow rate, decreases, the compressor discharge pressure also increases, as seen in FIG. 2. In fact, if the controller drives the airflow rate too low, the discharge pressure of the compressor increases to such an extent as to trip the compressor's pressure switch, which turns the HP unit off. If the pressure switch is tripped more than a predetermined number of times, the HP unit shuts down, and if this shutdown event occurs, the user must call a service technician to restore operation of the HP unit. This is an inconvenience to the user that the present disclosure addresses.
The embodiments of the controller of the present disclosure provide a controller that is coupled to a liquid refrigeration fluid line temperature sensor and is configured to prevent a shutdown of the compressor that occurs when it reaches predetermined, excessive discharge pressures. Using temperature data received from the temperature sensor, the controller may gradually increase the airflow rate, which, in turn, decreases the discharge pressure of the compressor to avoid a shutdown. Alternatively, the controller may be configured to automatically de-activate and return to a normal operation mode, which would also decrease the discharge of the compressor, and thereby, avoid a shutdown. Thus, the controller may either cause a decrease in the indoor flow rate to warm the discharged air, or it may increase the indoor airflow rate to prevent the compressor from reaching excessive trip pressures.
With the present disclosure, it has been recognized that a strong correlation exists between the liquid refrigeration line temperature of the HP system and the discharge pressure of the compressor, as illustrated in FIG. 3. Based upon this recognition, the controller can be configured to obtain a temperature reading from a temperature sensor positioned on the liquid refrigeration line and provide temperature data that would relate closely to the compressor discharge pressure for a given compressor. For example, in FIG. 3, if the liquid refrigeration line temperature is 120° F., the compressor discharge pressure may be 600 psig, which may be close or at most shut-down pressures, and if the liquid refrigeration line temperature is 90° F., the compressor discharge pressure may be a relatively safe 450 psig operating pressure. With the recognition of this correlation, the control algorithm, embodiments of which are discussed below, can determine when a trip pressure is near or is reached. In response to this condition, the controller responds by increasing the airflow rate of the HP unit, which decreases the compressor's discharge pressure, thereby avoiding activation of the HP units' pressure trip switch.
FIG. 2 shows the effect on discharge pressure when the indoor airflow in increased. The controller would engage this mode when the discharge pressure reached either the trip pressure or a pre-set discharge pressure, as related to a liquid refrigeration line temperature, that might be, for margin purposes, less than the actual trip pressure of the compressor, and at which the controller would cause the indoor airflow to increase, thereby decreasing discharge pressure, to avoid compressor shut-down.
As seen from FIG. 3, as the indoor airflow rate decreases, the discharge pressure increases. Thus, in one embodiment, the controller, when activated, will decrease the airflow rate in order to increase the temperature of the indoor airflow. However, if a temperature is received by the controller from the liquid refrigeration line temperature sensor that indicates that a trip pressure is close or has been achieved, the controller takes one of the two actions as noted above. The point at which the controller is either de-activated or begins increasing airflow, will depend on the unit or the desired amount of margin allowed for the known trip pressure.
FIG. 3 also shows discharge pressure being lower at low outdoor ambient temperatures, when compared with relative medium to high outdoor ambient temperatures that occur during times at which the HP unit would function in the heating mode. Also, as the outdoor ambient temperature decreases, the temperature of indoor airflow decreases. Thus, the indoor airflow rate can be further lowered at lower outdoor ambient temperatures without exceeding the high pressure limit. Because activation of the controller causes a lower indoor airflow rate at lower temperatures, the temperature of the indoor airflow will increase, thereby causing the user to feel warmer or more comfortable. The controller provides the advantages of making the user to feel warmer, thus more comfortable, while avoiding activating the trip pressure of the controller.
One embodiment of the controller as implemented in a HP system 400 is illustrated in FIG. 4. FIG. 4 illustrates a block diagram of an example of the HP system 400 in which a controller 405, as provided by embodiments described herein, may be used. Various embodiments of the controller 405 are discussed below. The HP system 400 comprises an outdoor (OD) system 410 that includes a heat exchanger 415, equipped with an outdoor fan 420, which in certain embodiments may be a conventional variable speed fan, a compressor 425, and an optional outdoor controller 430, coupled to the OD system 410. When present, the outdoor controller 430 may be coupled to the OD system 410 either wirelessly or by wire. For example, the outdoor controller 430 may be coupled to either the compressor 425 or the fan 420, or both. In the illustrated embodiment, the outdoor controller 430 is attached directly to the compressor 425 and is coupled to the compressor 425 by wire. If the outdoor controller 430 is not present, it may be controlled by an indoor thermostat.
The HP system 400 further includes an indoor (ID) system 435 that comprises an indoor heat exchanger 440, equipped with an indoor blower 445, which in certain embodiments, may be a conventional, variable speed blower, and an indoor system controller 450. The indoor system controller 450 may be coupled to the ID system 435 either wirelessly or by wire. For example, the indoor system controller 450 may be located on a housing (not shown) in which the blower 445 is contained and hard wired to the blower 445. Alternatively, the indoor system controller 450 may be remotely located from the blower 445 and be wirelessly connected to the blower 445. The indoor system controller 450 may also be optional to the system, and when it is not present, the indoor system 435 may be controlled by an indoor thermostat.
The HP system 400 further includes a liquid refrigeration line temperature sensor 455 that is coupled to the controller 405 for communications therewith. In one embodiment, the liquid refrigeration line temperature sensor 455 may be located on a refrigeration line that exits the heat exchanger 415. The liquid refrigeration line temperature sensor 455 may obtain a temperature reading by sensing the outer surface of the refrigeration tubing. In most cases this reading will be very close to the temperature of the liquid refrigerant within the tubing, given the good thermally conductivity of the refrigerant tubing to which the senor 455 is attached. However, in other embodiments, the temperature sensor 455 may be located at other locations on the liquid refrigeration line.
The HP system 400 further includes a thermostat 460, which, in certain embodiments may be the primary controller of the HP system 400. The thermostat 460 is preferably an intelligent thermostat that includes a microprocessor and memory with wireless communication capability and is of the type described in U.S. Patent Publication, No. 2010/0106925, application Ser. No. 12/603,512, which is incorporated herein by reference. The thermostat 460 is coupled to the outdoor controller 430 and the indoor controller 450 to form, in one embodiment, a fully communicating HP system, such that all of the controllers or sensors 405, 430, 450, 455, and 460 of the HP system 400 are able to communicate with each other, either by being connected by wire or wirelessly. In one embodiment, the thermostat 460 includes the controller 405 and further includes a program menu that allows a user to activate the controller 405 program by selecting the appropriate button or screen image displayed on the thermostat 460. In other embodiments, the controller 405 may be on the same board as the outdoor controller 430 or the indoor controller 450. Thus, the controller 405 may be located in various locations with respect to the HP system 400.
In general, the compressor 425 is configured to compress a refrigerant, to transfer the refrigerant to a discharge line 465, and, to receive the refrigerant from a suction line 470. The discharge line 465 fluidly connects the compressor 425 to the outdoor heat exchanger 415, and the suction line 470 fluidly connects the indoor heat exchanger 440 to the compressor 425 through a reversing valve 475. The reversing valve 475 has an input port 480 coupled to the discharge line 465, an output port 482 coupled to the suction line 470, a first reversing port 484 coupled to a transfer line 486 connected to the outdoor heat exchanger 415, and a second reversing port 490 coupled to a second transfer line 492 connected the indoor heat exchanger 440. As understood by those skilled in the art, the transfer lines 486, 492 allow for the reversal of the flow direction of the refrigerant by actuating the revering valve 475 to put the HP system 400 in a cooling mode or a heating mode. One skilled in the art would also appreciate that the HP system 400 could further include additional components, such as a connection line 494, distributors 496 and delivery tubes 498 or other components as needed to facilitate the functioning of the system.
FIG. 5 illustrates a schematic view of one embodiment of the controller 405. In this particular embodiment, the controller 405 includes a circuit wiring board 500 on which is located a microprocessor 505 that is electrically coupled to memory 510 and communication circuitry 515. The memory 510 may be a separate memory block on the circuit wiring board 500, as illustrated, or it may be contained within the microprocessor 505. The communication circuitry 515 is configured to allow the controller 405 to electronically communicate with other components of the HP system 400, either by a wireless connection or by a wired connection. The controller 405 may be a standalone component or it may be included within one of the other controllers previously discussed above. In one particular embodiment, the controller 405 will be included within the thermostat 460. In those embodiments where the controller 405 is a standalone unit, it will have the appropriate housing and user interface components associated with it.
The controller 405 is configured or programmed with an algorithm and data that relates a temperature received from the liquid refrigeration line temperature sensor with a pressure of the compressor and change an airflow rate of the ID system to avoid a shutdown of the HP system that occurs when the compressor reaches its trip pressure. The trip pressure is the pressure beyond which the unit should not be operated. Thus, in many instances, HP units will have trip pressure switches that will shut down the HP unit once a predetermined high pressure is reached. The high pressure limit can vary from one type of HP unit to the other. For example, the high pressure limit of a particular HP 4 ton unit may be 590 psig.
In one embodiment, the controller 405 is coupled to a conventional primary controller that is coupled to the ID system 435 (FIG. 5). The primary controller is configured to control an operation of the heat pump system 400 according to a temperature set-point. In one aspect of this embodiment, the primary controller is the thermostat 460 and the controller 405 is located within the thermostat 460.
In another embodiment, the controller 405 is programmed with data that relates the trip pressure of the compressor 425 with a temperature of the liquid refrigeration line, as obtained from the liquid refrigeration temperature sensor 435. This correlated data may be obtained either by testing different compressors at different readings of compressor discharge and liquid refrigeration line temperatures, or it may be obtained through computer modeling software. Once obtained, however, a liquid refrigeration line temperature at it relates to a trip pressure of a compressor can be achieved and used during HP system operation to avoid the compressor's shut-down.
In another embodiment, the controller 405 may be configured to change the airflow rate when the liquid refrigeration line temperature is less than a predetermined maximum temperature of the liquid refrigeration line. In an aspect of this embodiment, the predetermined maximum temperature indicates a pressure that is equal to or less than a trip pressure of said compressor 425. The maximum temperature, and thus the related pressure, can be chosen such that a cushion or an extra margin for error is configured into the controller to avoid getting too close to the trip pressure, thereby assuring that the actual trip pressure will not be reached during operation.
In yet another embodiment, the controller 405 is further configured to store a trip pressure that occurs during operation of the HP system 400. In one aspect of this embodiment, the controller 405 is further configured to read and store a temperature of the liquid refrigeration line upon the occurrence of the trip pressure and use that stored temperature as an indication of the trip pressure and regulate the airflow rate based on the stored temperature. In such embodiment, once the trip pressure has occurred and the pressure and related temperature has been stored in the memory of the controller, certain embodiments provide a controller that then operates the airflow pursuant to the actual stored numbers in place of the table. This embodiment allows for even a more accurate operation of the HP unit.
Accordingly, if the controller reduces the airflow in attempt to make the occupant feel warmer and the compressor discharge pressure gets too close or comes to stored value of the trip pressure as determined from the stored temperature, the controller will either increase the airflow to reduce the pressure or de-activate the function completely. Again, as with other embodiments, the controller may have a sub-routine that reduces the actual stored values for both the pressure and temperature and reduces them to provide for airflow reduction or de-activation at values just less than those stored to ensure that the trip pressure is not reached again.
In another embodiment, the controller 405 may be embodied as a series of operation instructions that direct the operation of the microprocessor 505 when initiated thereby. In one embodiment, the controller 405 is implemented in at least a portion of a memory 510 of the controller 405, such as a non-transitory computer readable medium of the controller 405. In such embodiments, the medium is a computer readable program code that is adapted to be executed to implement a method of measuring and managing an indoor airflow rate of the HP system 400. The method comprises relating a temperature received from a liquid refrigeration line temperature sensor of a heat pump system with a pressure of the compressor 425 of the HP system 400 and changing an airflow rate of the indoor blower/heat exchange (ID) system 435 of the HP system 400 to avoid a shutdown of the HP system 400 when the compressor 425 reaches a trip pressure.
FIG. 6, illustrates a flow chart of the operation of a one embodiment of the controller, as provided herein. At start, the controller queries the liquid refrigeration line temperature sensor to obtain a temperature reading. If the temperature reading is greater than maximum temperature allowed for safe discharge pressure operation of the HP unit, the controller will not engage the decreased airflow (i.e., comfort) function and indoor CFM will be equal the normal CFM of the HP system. If the temperature is less than the maximum temperature, the controller activates and begins running the comfort function to decrease the air flow until the temperature reading becomes greater than the mean or average temperature for the HP unit, at which time, the controller will decrease the airflow by some fraction, as follows:
Indoor airflow=comfort airflow+n*(normal airflow−comfort airflow), where n is some positive fractional number
If the temperature reading is less than the mean temperature, then the comfort function will continue to run until the temperature reading from the sensor becomes greater than a minimum temperature. If during this portion of the cycle, the liquid refrigeration line temperature becomes greater than the minimum temperature, then the controller will reduce the indoor airflow as follows:
Indoor airflow=comfort airflow+(n−x)*(normal airflow−comfort airflow), where x is some fractional number less than n
As long as the liquid refrigeration line temperature is less than the minimum temperature, the unit will continue to run in the comfort mode until the set-point programmed into the thermostat is achieved.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.

Claims

What is claimed is:

1. A heat pump system, comprising:

an indoor blower/heat exchanger system (ID) system;

an outdoor fan/heat exchanger and compressor (OD) system;

said ID system and said OD system being fluidly coupled together by a liquid refrigerant line;

a liquid refrigeration line temperature sensor coupled to said liquid refrigeration line and configured to provide a temperature of said liquid refrigeration line to said heat pump system;

a controller coupled to said liquid refrigeration line temperature sensor and configured to relate a temperature received from said liquid refrigeration line temperature sensor with a pressure of said compressor and change an airflow rate of said ID system to avoid a shutdown of said HP system that occurs when said compressor reaches a trip pressure of said compressor.

2. The system of claim 1, wherein said controller is coupled to a primary controller coupled to said ID system, said primary controller configured to control an operation of said heat pump system according to a temperature set-point.

3. The system of claim 2, wherein said primary controller is a thermostat and said thermostat includes said controller.

4. The system of claim 1, wherein said controller is programmed with data relating said trip pressure of said compressor with a temperature of said liquid refrigeration line.

5. The system of claim 1, wherein said controller changes said airflow rate when said liquid refrigeration line temperature is less than a predetermined maximum temperature of said liquid refrigeration line.

6. The system of claim 5, wherein said predetermined maximum temperature indicates a trip pressure of said compressor.

7. The system of claim 1, wherein said controller is further configured to store a trip pressure that occurs during operation of said HP system.

8. The system of claim 7, wherein said controller is further configured to read and store a temperature of said liquid refrigeration line upon the occurrence of said trip pressure and use said stored temperature as an indication of said trip pressure and regulate said airflow rate based on said stored temperature.

9. The system of claim 1, wherein said controller is configured to increase or decrease an airflow of said ID system based on said temperature received from said liquid refrigeration line temperature sensor.

10. The system of claim 1, further comprising an indoor controller and an outdoor controller, wherein either or both of said indoor controller and outdoor controller is coupled to said controller.

11. A heat pump system controller, comprising:

a control board;

a microprocessor located on and electrically coupled to said control board; and

a memory coupled to said microprocessor and located on and electrically coupled to said control board and having a program stored thereon, said program configured to relate a temperature received from a liquid refrigeration line temperature sensor with a pressure of a compressor of a heat pump system and change an airflow rate of an indoor blower/heat exchange (ID) system of a heat pump (HP) system to avoid a shutdown of said HP system when said compressor reaches a trip pressure of said compressor.

12. The controller of claim 11, wherein the program configures said controller to cause said ID system to decrease an airflow rate of said ID system in response to a temperature received from a liquid refrigerant line temperature sensor.

13. The controller of claim 11, wherein said controller is coupleable to a primary controller of said HP system, said primary controller configured to control an operation of said ID system according to a temperature set-point.

14. The controller of claim 13, wherein said primary controller is a thermostat and said thermostat includes said controller.

15. The controller of claim 11, wherein said controller is programmed with data relating a trip pressure of said compressor to a temperature of a liquid refrigeration line of said HP system.

16. The controller of claim 11, wherein said controller is configured to decrease an airflow rate of said ID system when said liquid refrigeration line temperature is less than a predetermined maximum temperature of said liquid refrigeration line.

17. The controller of claim 16, wherein said predetermined maximum temperature indicates a pressure of said compressor that is equal to or less than a trip pressure of said compressor.

18. The controller of claim 11, wherein said controller is further configured to store a trip pressure that occurs during operation of said HP system.

19. The controller of claim 18, wherein said controller is further configured to read and store a temperature of said liquid refrigeration line upon the occurrence of said trip pressure and use said stored temperature as an indication of said trip pressure and regulate said airflow rate based on said stored temperature.

20. The controller of claim 19, wherein said controller is configured to increase or decrease an airflow of said ID system based on said temperature received from said liquid refrigeration line temperature sensor.

21. A computer program product, comprising a non-transitory computer usable medium having a computer readable program code embodied therein, said computer readable program code adapted to be executed to implement a method of measuring and managing an indoor airflow rate of a heat pump system, said method comprising:

relating a temperature received from a liquid refrigeration line temperature sensor of a heat pump system with a pressure of a compressor of said heat pump system; and

changing an airflow rate of an indoor blower/heat exchange (ID) system of said heat pump (HP) system to avoid a shutdown of said HP system when said compressor reaches a trip pressure of said compressor.