HEAT PUMP APPARATUS AND HEAT PUMP CONTROL METHOD

Abstract

A heat pump apparatus is provided and includes an outdoor unit, an indoor unit in communication with the outdoor unit, and a control unit in communication with the outdoor unit and the indoor unit. The indoor unit includes a heat exchange housing for heating inlet air, a plurality of temperature sensors to detect and measure temperature of the inlet air and heated air at various positions in the indoor unit, and a control unit to control heat pump operations. The heat exchange housing includes a heat exchanger, a blower, and a heater unit. The control unit includes a processor and a memory, and is configured to perform operations to control a heating operation of the heat pump apparatus based on a calculated temperature of the heated air passing the heat exchanger.

Description

TECHNICAL FIELD

The present disclosure relates to a heat pump apparatus and heat pump control method.

BACKGROUND ART

Heat pump apparatuses or systems, including a heat pump and a heater, have been known to simultaneously operate the heat pump and the heater to obtain, for example, a desired target room temperature (i.e., an indoor unit outlet air temperature). Heaters used in such systems have been known to be provided with safety devices (such as temperature sensors, pressure sensors, and/or limit switches) that not only prevent the room temperature from becoming too high, but also prevent the temperature of an indoor unit of the system from exceeding an acceptable operating temperature range. Based on monitoring of room temperature and/or operating temperature, the safety devices help control operation of the heat pump and heater thereby protecting the safety of the heat pump apparatus while maintaining the desired room temperature.

CITATION LIST

Patent Literature

• Patent Literature 1: U.S. Pat. No. 11,609,021

SUMMARY OF THE DISCLOSURE

Technical Problem

While known heat pump apparatuses attempt to adequately protect component parts and avoid safety hazards when temperatures become too high, there is a risk that heaters and safety devices will not work as intended due to repeated use during normal operations and/or high temperature exposure. For example, when the temperature of the heat pump is sufficiently high and when the heater is turned ON, a limit switch connected to the heater is operated to turn OFF the heater to protect the components and maintain a desired room temperature while avoiding safety hazards. When the heat pump is turned OFF, the heat-exchange temperature of the air drops, the limit switch is operated again, and the heater is turned ON again. Such a control operation causes the heater and the limit switch to repeatedly turn ON/OFF to maintain the appropriate temperature. With such a repeated ON/OFF operation cycle, durability and reliability of the heater and safety devices becomes unsatisfactory for normal operations of the heat pump apparatus.

Solution to Problem

There is, therefore, a need for a protection requirement to satisfy the safety and proper operation (and durability) of the safety device, as well as the heater, during the useable life of the heat pump apparatus system. Accordingly, in the present disclosure, embodiments of a heat pump apparatus and a heat pump control method are provided to control the use or activity of the safety device(s) and heater(s) during normal heat pump operation. Limiting use of the safety device(s) and heater(s) during normal operation prevents degradation of component durability and reliability during the useful life of the heat pump apparatus while accurately controlling room temperature within a safe and comfortable range. By avoiding operation of the safety device(s) and heater(s) during normal heat pump operations, the intended life cycle of the safety devices can be maintained, and repair and/or replacement of the component parts can be prevented.

In embodiments, the heat pump apparatus may include an outdoor unit and an indoor unit in communication with the outdoor unit. The indoor unit may include a heat exchange housing for heating inlet air and a plurality of temperature sensors to detect and measure temperature of the inlet air and heated air at various positions in the indoor unit. The heat exchange housing may include a heat exchanger, a blower, and a heater unit. The heat pump apparatus may further include a control unit that includes a processor and a memory, and is configured to perform operations to control a heating operation of the heat pump apparatus based on a calculated temperature of the heated air passing the heat exchanger.

In embodiments, the control unit may be configured to perform operations including detecting a temperature of the inlet air, and determining a difference between the temperature of the inlet air and a set temperature stored in the memory. When the difference between the temperature of the inlet air and the set temperature is not greater than or equal to a predetermined temperature stored in the memory, the control unit prevents a heating element contained in the heater unit from heating during a heat pump heating operation.

In other embodiments, the control unit may be configured to perform operations including detecting a temperature of the inlet air, and determining a difference between the temperature of the inlet air and a preset inlet air temperature value stored in the memory. When the difference between the temperature of the inlet air and the preset inlet air temperature value is greater than or equal to a predetermined temperature stored in the memory, the processor further detects a high pressure conversion temperature from a temperature sensor of the outdoor unit, calculates a heat exchanger outlet air temperature, and determines whether or not to perform heat pump heating with the heater unit based on the calculated heat exchanger outlet air temperature.

In additional embodiments, the control unit may be configured to perform operations including detecting a temperature of the inlet air, detecting a high pressure conversion temperature from a temperature sensor of the outdoor unit, calculating a heat exchanger outlet air temperature, and comparing the calculated heat exchanger outlet air temperature to a preset heat exchanger outlet air temperature value stored in the memory. When the calculated heat exchanger outlet air temperature is greater than or equal to the preset heat exchanger outlet air temperature value stored in the memory, the control unit prevents a heating element contained in the heater unit from heating during a heat pump heating operation.

In embodiments, when the calculated heat exchanger outlet air temperature is less than or equal to preset heat exchanger outlet air temperature value stored in the memory, the control unit may further compare an amount of time that has passed since a last operation of the heating element to a preset amount of time stored in the memory such that if the amount of time since the last operation of the heating element exceeds the preset amount of time, the control unit controls the heat pump apparatus to perform heat pump heating with the heater element, and if the amount of time since the last operation of the heating element does not exceed the preset amount of time, the control unit prevents the heating element from heating during a heat pump heating operation.

In embodiments, the calculated heat exchange outlet air temperature may be represented by the formula:

$\mathrm{Tw}2=\mathrm{Tk}-\left(\left(\mathrm{Tk}-T_{w1}\right)/\exp \left(\mathrm{KA}/\left(c\rho Q/3600\right)\right)\right),$

• • c Specific heat of inlet air
  • ρ Density of outlet air
  • Q Air volume
  • Tw1 Inlet air temperature
  • Tw2 Outlet air temperature
  • K Heat passing rate of heat exchanger
  • A Heat transfer area of heat exchanger (fin surface area)
  • Tk Condensing temperature of heat exchanger

In embodiments, the preset heat exchanger outlet air temperature value stored in the memory may be set to a predetermined range.

In embodiments the heater unit may include a heater element, a relay that controls the ON/OFF of the heater element, and a safety device that turns OFF the heater element when a temperature of air flowing from the heat exchanger exceeds a predetermined range. When the calculated heat exchanger outlet air temperature is within the predetermined range, the safety device is prevented from being triggered.

In embodiments, the control unit may perform one or more of the above identified operations in a heat pump heating control method.

Advantageous Effects of Invention

According to the present disclosure, safety devices can be prevented from being used during normal heat pump operation. When safety devices are not operational during normal heat pump operation, degradation of component durability and reliability can be prevented while accurately controlling room temperature within a safe and comfortable range.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a refrigerant circuit diagram for a heat pump apparatus according to a non-limiting embodiment of the present disclosure.

FIG. 2A illustrates a cross-sectional view schematic of components of an indoor unit and an outdoor unit of the heat pump apparatus according to non-limiting embodiments of the present disclosure.

FIG. 2B illustrates a perspective view of a heater unit provided to an indoor unit of the heat pump apparatus according to non-limiting embodiments of the present disclosure.

FIG. 3 illustrates a system-level structural diagram of the heat pump apparatus according to non-limiting embodiments of the present disclosure.

FIG. 4 illustrates a flow chart of a heating operation of the heat pump apparatus according to non-limiting embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

In view of the foregoing, the present disclosure, through one or more of its various aspects, embodiments and/or specific features or sub-components, is thus intended to bring out one or more of the advantages as specifically noted below. In particular, preferred embodiments of a heat pump apparatus and heat pump control method will be explained in detail below with reference to the accompanying drawings. The technology of the present disclosure, however, is not limited to the embodiments. Additionally, methods described herein are illustrative examples, and as such are not intended to require or imply that any particular process of any embodiment be performed in the order presented. Words such as “thereafter,” “then,” “next,” etc. are not intended to limit the order of the processes, and these words are instead used to guide the reader through the description of the methods. Further, any reference to claim elements in the singular, for example, using the articles “a,” “an” or “the”, is not to be construed as limiting the element to the singular.

[Configuration of Heat Pump Apparatus]

FIG. 1 is a diagram illustrating a heat pump apparatus 1 according to the present disclosure. The heat pump apparatus 1 is configured to heat and/or cool interior spaces. The heat pump apparatus 1 includes an outdoor unit 2 and an indoor unit 3. The outdoor unit 2 is connected to the indoor unit 3 by refrigerant pipes 4, 5. A compressor (not shown) is provided to control flow of the refrigerant into and out of the indoor unit 3. During a heating operation, the compressor compresses the refrigerant and discharges the same from the outdoor unit 2 into the indoor unit 3. As will be discussed in detail below, the outdoor unit 2 is also electrically connected to the indoor unit 3 to carry out the heat pump control operation.

As shown in FIG. 2A and FIG. 4, the outdoor unit 2 includes a high-pressure conversion temperature sensor 70 that detects an outside temperature (T_out) of the refrigerant in the refrigerant pipe 2.

The indoor unit 3 includes a heat exchange housing 20. The heat exchange housing 20 includes an inlet opening 22 to permit the inlet air having an inlet air temperature to pass into the heat exchange housing 20 and an outlet opening 24 to permit conditioned heated air to flow out of the indoor unit 3 and through one or more ducts (not shown) toward one or more interior rooms to be heated to or maintained at a desired temperature.

The heat exchange housing 20 includes a heat exchanger 40, a blower 50 (or fan), and a heater unit 60. As shown in FIG. 2A, the heat exchanger 40 includes temperature sensors 42 and 44. Temperature sensor 42 detects and measures the inlet air temperature (T_xi) of the inlet air flowing into the heat exchanger 40 from the inlet opening 22. Temperature sensor 44 detects and measures a temperature (T_x) of the heat exchanger 40. In embodiments, a temperature sensor 42 is provided toward an entrance of the heat exchange housing 20 to detect and measure the inlet air temperature (T_xi) of the inlet air flowing into the heat exchange housing 20. In embodiments, the temperature (T_x) detected by the temperature sensor 44 is at least one of the temperature of a section of the refrigerant pipe 4 disposed in the heat exchanger 40 and/or a frame 46 of the heat exchanger 40 supporting the refrigerant pipe 4 and heat transfer function.

As shown in FIG. 2B, the heater unit 60 includes a heater element 62, a safety device 64 (such as a limit switch) electrically connected to the heater element 62, and a contactor relay 66 electrically connected to the safety device 64 and the heater element 62. The limit switch 64 is configured to detect and measure a temperature of the heater element 62. In embodiments, the safety device 64 is a bimetal-type limit switch. Contactor relay 66 is mounted to a mounting plate 68 at a heater inlet side of the heater unit 60 separated and spaced from the heater element 62 and the safety device 64. The blower 50 is provided between the heat exchanger 40 and the heater unit 60 to direct flow of the heated air from the heat exchanger 40 to the heater unit 60 and across the heater element 62.

During a heating operation, compressed refrigerant from refrigerant pipe 4 flows through the heat exchanger 40, and inlet air (at the inlet air temperature (T_xi)), entering the indoor unit 3 through the inlet opening 22, flows over a heat exchange section of the refrigerant pipe 4 in the heat exchange housing 20 such that heat from the refrigerant pipe 4 is transferred to the inlet air and the inlet air is conditioned to become heated air which then flows through the heat exchange housing 20 toward the outlet opening 24 via the blower 50. The blower 50 blows the heated air past heater element 62 of the heater unit 60 for further heating (when ON) as the air exits the heat exchange housing 20 through the outlet opening 24, which then, as described above, directs the flow of heated air into the interior space at the desired temperature via the one or more ducts.

As shown in FIGS. 2A and 3, the indoor unit 3 further includes a control unit 200 that includes a central processing unit (CPU) 210, a storage unit 220, and a communication unit 230. The CPU 210, including a memory and a processor, is configured to execute a control program to carry out the heating operations of the heat pump apparatus 1. The storage unit 220 includes a memory and stores the control program to carry out the operation of the heat pump apparatus 1. The storage unit 220 also stores detection values that correspond to detection signals from various temperature sensors provided throughout the heat pump apparatus 1, as well as preset settings information (e.g., control specifications) and/or input from a terminal (such as a thermostat interface) regarding the heating operation.

It is noted that any processor described herein may be a general-purpose processor or may be part of an application specific integrated circuit (ASIC). The disclosed processors may also be microprocessors, microcomputers, processor chips, controllers, microcontrollers, digital signal processors (DSP), programmable logic devices logical circuits including programmable gate arrays (PGA) such as a field programmable gate array (FPGA), or other types of circuit that includes discrete gate and/or transistor logic. Additionally, any processor described herein may include multiple processors, parallel processors, or both. Multiple processors may be included in, or coupled to, a single device or multiple devices.

The memories as described herein may be random access memory (RAM), read only memory (ROM), flash memory, electrically programmable read only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or any other form of storage medium known in the art. Memories may be volatile or non-volatile, secure and/or encrypted, unsecure and/or unencrypted.

The communication unit 230 (via, e.g., wired connection, short-range wireless devices, wireless networked devices) communicates with a control unit 300 (configured in a complementary manner to that of the control unit 200) of the outdoor unit 2 and the various sensors to request/receive information for the CPU 210 to carry out the heating operation. The CPU 210 receives detection results acquired by the various temperature sensors and acquires control signals from the same. Based on the received detection results and control signals, the CPU 210, as will be described below, performs temperature control of the heat pump apparatus 1. In embodiments, the control unit 200 and the control unit 300 are printed control circuit boards.

As shown in FIG. 3, the CPU 210 receives from the temperature sensor 42 the inlet air temperature (Txi) of the air flowing into the heat exchange housing 20 from the inlet opening 22. The CPU 210 also receives from the temperature sensor 44 the temperature (T_x) of the heat exchanger 40. The CPU 210 further receives from an outdoor refrigerant temperature sensor (or the high-pressure conversion temperature sensor) 70 provided at the outdoor unit 2 the high pressure conversion temperature (Tout) of the refrigerant flowing towards the heat exchanger 40 housed in the indoor unit 3. The CPU 210 is connected to the heater unit 60 via heater element 66 to command the heater element 62 to energize.

As shown in FIG. 2, the safety device 64 is provided at the mounting plate 68 and connected to the heater element 62. The relay 66 connects to both the heater element 62 and the safety device 64. In embodiments, a backup safety device 64a, also connected to relay 66, may also be provided at the mounting plate 68 attached to the heater element 62.

FIG. 4 illustrates a flowchart that represents the heating operation carried out by execution of the program by the CPU 210 to control the heating operation of the heat pump apparatus 1.

In S101, the CPU 210 detects the inlet air temperature (Txi) from the temperature sensor 42 entering into the heat exchange housing 20. In S103, the CPU 210 determines if there is a difference between the detected inlet air temperature (Txi) and a set temperature value (Ts) stored in the storage unit 220. In embodiments, the set temperature value (Ts) is a predetermined target temperature or demand temperature received from a terminal having a user interface (e.g., thermostat, tablet/mobile phone application). If the difference between the detected inlet air temperature (Txi) and the set temperature value (Ts) is not greater than or equal to a predetermined threshold temperature value (Tpv) within a range of predetermined temperature values, in S105, the CPU 210 determines that the heating unit 60 should not perform operations and that the heating operation should be carried out by heat pump operation only. In other words, in S105, the CPU 210 disables operation of heater element 62 and only performs a heat pump heating operation via the heat exchanger 40 and blower 50.

To carry out this operation, CPU 210 is electrically connected to the heater element 62. When the difference between the detected inlet air temperature (Txi) and the set temperature value (Ts) is less than the predetermined threshold temperature value (Tpv), the relay 66 controls the circuit to prevent operation of the heater element 62.

If, on the other hand, the difference between the detected inlet air temperature (T_xi) and the set temperature value (T_s) is greater than or equal to the predetermined threshold temperature value (Tpv) within the predetermined temperature value range, in S107, the CPU 210 detects the inlet air temperature (T_xi) of the air entering into the heat exchange housing 20 and the high pressure conversion temperature (T_out) of the refrigerant pipe flowing from the outdoor unit 2 into the heat exchanger 40. At S109, the CPU 210 calculates (through a temperature prediction calculation method) a predicted heat exchanger outlet air temperature (T_w2). The predicted heat exchanger outlet air temperature (T_w2) is calculated by the CPU 210 to determine whether operating conditions warrant operation of the heater unit 60, i.e., whether the heater unit 60 should be ON or OFF for a given heating operation. By controlling an actual heat exchange outlet air temperature (To), the number of repeated operations of the heater unit 60 and the safety device 64 can be prevented.

(Prediction method of heat-exchange outlet air temperature) The CPU 210 performs the predicted heat exchanger outlet air temperature calculation method to calculate the predicted heat exchanger outlet air temperature (T_w2).

<Prediction Formula of Heat-Exchange Outlet Air Temperature>

First, the predicted heat exchange outlet temperature (T_w2) is determined based on the following relationship defined between a condensing load and a heating capacity of the heat pump apparatus 1:

• • Condensing load (Φk)=Heating capacity (Φh), where
    • Φk=KA((T_w2−T_w1)/In((Tk−T_w1)/(Tk−T_w2))); and
    • Φh=cρQ(T_w2−T_w1)

Symbol	Item	Symbol	Item
Φh	Heating capacity	Φk	Condensing load
c	Specific heat of inlet air	K	Heat passing rate of heat exchanger
ρ	Density of outlet air	A	Heat transfer area of heat exchanger
			(fin surface area)
Q	Air volume	Tk	Condensing temperature of heat
			exchanger
Tw1	Inlet air temperature
Tw2	Outlet air temperature

According to the formula, the outlet air temperature T_w2 is equal to the predicted heat exchange outlet air temperature. Thus, the predicted heat exchange outlet air temperature (T_w2) is represented by:

$T_{w2}=\mathrm{Tk}-\left(\left(\mathrm{Tk}-T_{w1}\right)/\exp \left(\mathrm{KA}/\left(c\rho Q/3600\right)\right)\right)$

In order for the CPU 210 to calculate the predicted heat exchange outlet air temperature (T_w2) certain parameters are set in the storage 220 or detected by one or more of the various sensors to be received by the CPU 210 for processing during the heating operation. In this regard, indoor unit 3 parameters obtained by sensors for calculation of the formula include heat-exchange inlet air temperature (T_w1/Txi) and heat exchanger condensing temperature (Tk) values.

Other parameters in the calculation formula are also fixed values stored in the storage 220.

It is noted that with long pipe systems, the sensor 42 of the indoor unit 3 inlet 22 may have a more accurate condensing temperature (T_k) than the high-pressure saturation temperature (T_out) of the outdoor unit 2 sensor 70 because the refrigerant enters the indoor unit 3 in two phases and can account for pressure reductions due to pipe pressure damage.

As a result, in embodiments, the condensing temperature (T_k) in the formula adopts the lower of the high-pressure saturation temperature (T_out) or the condensing temperature (T_k) of the heating heat-exchange inlet at inlet opening 22.

Based on the above parameters, the predicted heat exchanger outlet temperatures calculated by the CPU 210 should be maintained within an acceptable range of the actual measured outlet air temperature (Txo). This, in turn, allows the CPU 210 to accurately control operation of the heat pump and/or heater unit 60 and prevent the use of the safety devices during normal operating conditions, as well as overuse of the heater unit 60.

With the predicted heat exchange outlet air temperature (T_w2) calculated, the CPU 210 continues execution of the control program at S111. At S111, the CPU 210 determines whether the calculated temperature (T_w2) is less than or equal to a set heat exchange outlet air temperature value (Tsx). In embodiments, the set heat exchanger outlet temperature (Tsx) is an upper limit of an acceptable operational temperature or temperature range. If the calculated temperature (T_w2) is not less than or equal to the set heat exchange outlet air temperature value (Tsx), in S113, the CPU 210 determines that the heating operation should be carried out by the heat pump only. In other words, the CPU 210 disables operation of heater element 62 and only performs heat pump heating operation via the heat exchanger 40 and the blower 50 (without additional heating from the heater unit 60). Put another way, at S111 the CPU 210 judges whether the heater unit 60 operation is possible based on the calculated temperature (T_w2). If the calculated temperature (T_w2) is too high then operation of the heater unit 60 is prevented.

If, on the other hand, the calculated temperature (T_w2) is less than or equal to the set heat exchange outlet air temperature value (Tsx), in S115, the CPU 210 further determines whether a predetermined amount of time (t_set) has passed since the heater unit 60 was last operated (or turned ON). In embodiments, the preset amount of time is a cycle time of the relay 66 that delays operation of the heater unit 60 to determine whether the conditions for such operation are satisfied. If the predetermined amount of time (t_set) has not passed, then the CPU 210, in S117, maintains the disabled operation state of heater unit 60 and only performs heat pump heating. This prevents the repeated ON/OFF situation for the heater element 62 and enhances the life-span of both the relay 66 and the heater unit 60. If, on the other hand, it is determined that the predetermined amount of time (t_set) has expired, the CPU 210, in S119, performs the heating operation of the heat pump apparatus 1 utilizing both the heat pump and the heater unit 60. Thus, in S115, it is judged whether the heater operation is possible based on, not only the predicted heat exchange outlet air temperature (T_w2), but also the relay cycle time of replay 66. By managing the cycle time, the CPU 210 prevents overuse of the relay 66 which is used for heater element 62 ON/OFF control and prevents use of the safety device 64 during normal operation of the heat pump apparatus 1.

In embodiments, in order to prevent the safety device 64 of the heater unit 60 from operating during normal operations, the heat exchange outlet air temperature (Txo) is maintained within a predetermined range. In this way, the outlet air temperature after passing through the heater unit 60 can be limited to an acceptable range which does not exceed a predetermined temperature. This, in turn, prevents the safety device 64 from being triggered.

The foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separately claimed subject matter.

The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. As such, the above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

1. A heat pump apparatus comprising: an outdoor unit;an indoor unit in communication with the outdoor unit that includes: a heat exchange housing for heating inlet air that includes: a heat exchanger;a blower; anda heater unit; anda plurality of temperature sensors to detect and measure temperature of the inlet air and heated air at various positions in the indoor unit; anda control unit that includes a processor and a memory, and is configured to perform operations to control a heating operation of the heat pump apparatus based on a calculated temperature of the heated air passing the heat exchanger.

2. The heat pump apparatus according to claim 1, wherein the control unit is configured to perform operations including:detecting a temperature of the inlet air;determining a difference between the temperature of the inlet air and a set temperature stored in the memory, whereinwhen the difference between the temperature of the inlet air and the set temperature is not greater than or equal to a predetermined temperature stored in the memory, the control unit prevents a heating element contained in the heater unit from heating during a heat pump heating operation.

3. The heat pump apparatus according to claim 1, wherein the control unit is configured to perform operations including:detecting a temperature of the inlet air;determining a difference between the temperature of the inlet air and a preset inlet air temperature value stored in the memory, whereinwhen the difference between the temperature of the inlet air and the preset inlet air temperature value is greater than or equal to a predetermined temperature stored in the memory, the processor further: detects a high pressure conversion temperature from a temperature sensor of the outdoor unit;calculates a heat exchanger outlet air temperature; anddetermines whether or not to perform heat pump heating with the heater unit based on the calculated heat exchanger outlet air temperature.

4. The heat pump apparatus according to claim 1, wherein the control unit is configured to perform operations including: detecting a temperature of the inlet air;detecting a high pressure conversion temperature from a temperature sensor of the outdoor unit;calculating a heat exchanger outlet air temperature; andcomparing the calculated heat exchanger outlet air temperature to a preset heat exchanger outlet air temperature value stored in the memory, whereinwhen the calculated heat exchanger outlet air temperature is greater than or equal to the preset heat exchanger outlet air temperature value stored in the memory, the control unit prevents a heating element contained in the heater unit from heating during a heat pump heating operation.

5. The heat pump apparatus according to claim 4, wherein when the calculated heat exchanger outlet air temperature is less than or equal to preset heat exchanger outlet air temperature value stored in the memory, the control unit further:compares an amount of time that has passed since a last operation of the heating element to a preset amount of time stored in the memory such that: if the amount of time since the last operation of the heating element exceeds the preset amount of time, the control unit controls the heat pump apparatus to perform heat pump heating with the heater element, andif the amount of time since the last operation of the heating element does not exceed the preset amount of time, the control unit prevents the heating element from heating during a heat pump heating operation.

6. The heat pump apparatus according to claim 4, wherein the calculated heat exchange outlet air temperature is represented by the formula:

7. The heat pump apparatus according to claim 4, wherein the preset heat exchanger outlet air temperature value stored in the memory is set to a predetermined range.

8. The heat pump apparatus according to claim 7, wherein the heater unit includes: a heater element;a relay that controls the ON/OFF of the heater element; anda safety device that turns OFF the heater element when a temperature of air flowing from the heat exchanger exceeds a predetermined range, andwhen the calculated heat exchanger outlet air temperature is within the predetermined range, the safety device is prevented from being triggered.

9. A heat pump heating control method for the heat pump apparatus according to claim 2, wherein the control unit performs the operations.

10. A heat pump heating control method for the heat pump apparatus according to claim 3, wherein the control unit performs the operations.

11. A heat pump heating control method for the heat pump apparatus according to claim 5, wherein the control unit performs the operations.

12. A heat pump heating control method for the heat pump apparatus according to claim 7, wherein the control unit performs the operations.