TEMPERATURE REGULATING SYSTEM AND METHOD OF DEICING THE TEMPERATURE REGULATING SYSTEM

[0001] This disclosure is generally related to systems for heating and/or cooling, and more particularly to deicing of systems for heating and/or cooling.

[0002] Systems including an evaporator may be employed to provide heating and/or cooling operations, e.g., in the case of a heat pump or air conditioning system. A continued need exists to improve the efficiency and effectiveness of such systems.

[0003] In some aspects, this disclosure describes system for heating and/or cooling, such as, e.g., a heat pump or air conditioning system, and methods for operating the same. The systems include an evaporator which may be susceptible to icing during operation, and a sensor located on the evaporator, e.g., on the evaporator coil. The system may also include a control and icing detection module configured to detect the presence of actual icing of the evaporator during temperature regulating operation based on the output of the sensor. Upon detecting the icing of the evaporator, the control and icing detection module may initiate an operation to deice the evaporator. For example, to deice the evaporator, the control and icing detection module may control the system to reduce power to the compressor, which results in an increase in the temperature of the evaporator. As another example, the control and icing detection module may control the system to reverse the cycle to inverse the heat flow in the system, which again increases the temperature of the evaporator. Other suitable deicing operations are contemplated and are not limited to the above deicing methods. In some examples, the control and icing detection module may also determine when deicing of the evaporator is complete based on the output of the sensor and terminate the deicing operation based on the determination.

[0004] In one example, the disclosure relates to a temperature regulating system (e.g., a heating and/or cooling system), the system comprising temperature regulating device including a hot side and a cold side; and an icing sensor disposed on the cold side and which provides an output which changes based on a condition of the cold side; wherein the system is configured to detect, via the output of the icing sensor, icing of the cold side during a temperature regulating operation, and initiate deicing of the cold side based on the detection of the icing of the cold side.

[0005] In another example, the disclosure relates to a method of operating a temperature regulating system, the method comprising detecting, via an output of an icing sensor disposed on a cold side of a temperature regulating device and of which provides the output which changes based on a condition of the cold side, icing of the cold side during a temperature regulating operation; and initiating deicing of the cold side based on the detection of the icing of the cold side.

[0006] In another example, the disclosure relates to a temperature regulating system, the system comprising means for detecting, via an output of an icing sensor disposed on a cold side of a temperature regulating device and of which provides the output which changes based on a condition of the cold side, icing of the cold side during a temperature regulating operation; and means for initiating deicing of the cold side based on the detection of the icing of the cold side.

[0007] The details of one or more examples and techniques of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.

[0015] The drawings are not necessarily drawn to scale. Like reference numbers indicate like features, although variations between like features may exist in the various examples.

[0016] As noted above, in some aspects, this disclosure relates to a temperature regulating system for heating and/or cooling, such as, e.g., a heat pump system or air conditioning system, and methods for operating the same. FIG. 1 is a schematic diagram illustrating an exemplary temperature regulating device 70 including an icing sensor 20. Temperature regulating system 70 includes a heat transfer device 76 with cold side 72 and hot side 74. As shown in the example of FIG. 1, during a temperature regulating operation, heat transfer device 76 may receive heat through cold side 72 and then output the heat via hot side 74. In such a configuration, heat is transferred from a low temperature environment to a heated environment by heat transfer device 76. For temperature regulation through the transfer of heat, heat transfer device 76 may employ a vapor-compression cycle, e.g., including evaporation and condensation of cooling media (such as a refrigerator, air conditioning unit, or heat pump). Additionally, heat transfer device 76 may be a Peltier-based systems, e.g., that uses thermoelectric cooling or “Seebeck principle”) or operate on similar principles such as magnetic refrigeration.

[0017] In each case, temperature regulating device including heat transfer device 76 that transfers heat from one environment to another may be prone to condensed water and icing on cold side 72, e.g., due to the reduced saturation of water in air during cooling. To provide efficient heat transfer from the environment through cold side 72, large interface areas are desirable. However, icing of cold side 72 may reduce the interface area, thus reducing the heat transfer and reducing the efficiency of temperature regulating device 70.

[0018] As shown, icing sensor 20 is disposed on cold side 72. As will be described below, the output of icing sensor may change as a function of the condition of cold side. For example, the output of the icing sensor (e.g., in terms of impedance or resistance) may be indicative of icing at one or more portions of cold side 72 during operation. Based on the detection, system 70 may initiate an operation to deice cold side 72.

[0019] For ease of illustration, examples of system 70 are generally described herein being configured as a heat pump or an air conditioning system such as system 10 below which use a vapor-compression cycle. However, temperature regulating system 70 may also be a temperature regulating system that does not employ a vapor-compression cycle to regulate temperature. An example temperature regulating systems that do not employ a vapor-compression cycle includes Peltier-based systems, e.g., that uses thermoelectric cooling and including a hot side and cold side.

[0020] The market for air conditioning and heat pump systems is growing rapidly. Worldwide power consumption from air conditioning systems and heat pump systems are increasing due to the increasing number of units. Thus, it may be desirable to increase the efficiency of the units, e.g., to minimize the power consumed by operation of the systems.

[0021] One source of inefficiency in heating and cooling systems is icing of the evaporator during operation of the system, particularly in relatively high humidity environments. When icing occurs, at least one of frost or ice form on at least a portion of the surface of the evaporator, such as the coil surface, from moisture present in environment and/or leaking refrigerant. For example, the evaporator of heat pumps (which typically operate in environments with high humidity and temperatures close to zero degrees Celsius at the evaporator) may naturally begin to ice-up at temperatures near zero degrees Celsius. Similarly, air conditioners may ice-up for various reasons, including lack of refrigerant, dirty filter or evaporator coil, low outdoor temperature, leaks in the evaporator coil, and the like. In the case of leaking refrigerant, there may be a higher likelihood of the evaporator icing as more of the refrigerant charge is depleted, along with reduced cooling capacity of the system. As another example, increasing the efficiency of a system by exchanging a refrigerant (e.g., changing from R22 to higher efficiency R438) reduces the evaporator temperature thus increasing the susceptibility of the evaporator to icing during operation.

[0022] Such icing may be an efficiency limiting issue even in well maintained systems. One technique of air source heat pump icing removal is a reverse-cycle defrost/deice operation. During the reverse-cycle defrost/deice operation, the heat pump runs in a cooling mode by reversing a normal heating mode. This increases the temperature of the evaporator to remove the frost/ice from the evaporator surface. Another deicing technique includes electrically heating the evaporator, e.g., via one or more heating coils on or near the evaporator.

[0023] However, while such techniques may adequately deice the evaporator, the techniques consume more energy than necessary in most cases due to the lack of ability to accurately detect the presence of icing during operation. For example, heating and cooling systems may be configured to initiate deicing operations only on a periodic basis, e.g., based on a duty cycle or when environmental conditions are such that icing may be likely, without regard to whether icing is actually present on the evaporator during operation. Moreover, such systems may not include any sensory feedback indicating if and when the evaporator has been adequately deiced following initiation of the deicing operation. Rather, for example, the system may be configured to perform the deicing operation for a set period of time, e.g., passed on experimental data, regardless of whether or not the overall deicing operation was actually successful in deicing the evaporator. Such a technique may cause the system to perform the deicing operation longer than necessary or may not be successful in deicing the evaporator during the deicing operation, both of which reduce the operation efficiency of the system.

[0024] In accordance with some examples of the disclosure, a temperature regulating system may include an icing sensor that allows the system to monitor for the presence of icing on the surface of an evaporator surface (or other cold side surface), during heating and cooling operations. Using such an icing sensor, the system may monitor for icing of the evaporator (or other cold side surface) and initiate deicing of the evaporator (or other cold side surface) upon detection of icing. In this manner, the system may be able to actively monitor for icing of the evaporator (or other cold side surface) and intelligently initiate deicing of the evaporator (or other cold side surface) when appropriate, e.g., rather than based on some preset duty cycle. Additionally, in some examples, the system may continue monitor for the presence of icing on the evaporator (or other cold side surface) using the icing sensor while the system is operating to deice the evaporator (or other cold side surface). Once the system determines, using the icing sensor, that the evaporator (or other cold side surface) has been adequately deiced, the deicing may be terminated and heating and/or cooling operations may be resumed.

[0025] FIG. 2 is a schematic diagram illustrating an example temperature regulating system 10 including an icing sensor 20. As shown, system 10 includes a compressor 12, a condenser 14, an expansion valve 16, an evaporator 18, and an engine 22, all of which are in fluid communication with each other to allow for a refrigerant to flow throughout system 10 during heating and/or cooling operations along flow path 34. In general, system 10 may operate to move heat from a colder environment to a warmer environment using mechanical work. While examples of the disclosure are primarily described with regard to system 10 being configured as a heat pump or an air conditioning system, examples of system 10 are not limited as such. For example, system 10 may be configured as a refrigeration system (e.g., as in the case of a refrigerator), a freezing system (e.g., as in the case of a freezer), a reversible heat pump, or any other heating or cooling system including an evaporator that may be susceptible to icing during operation. Moreover, as noted above with regard to FIG. 1, system 10 may be a temperature regulating system that does not employ a vapor-compression cycle to regulate temperature. The temperature regulating system may include a hot side and a cold side (e.g., the cold side in system 10 may include evaporator 18 and the hot side may include condenser 14). Temperature regulating systems that do not employ a vapor-compression cycle include Peltier-based systems.

[0026] In the case of performing a heating operation as a heat pump, system 10 may be configured to remove heat from a cooler environment to heat a warmer environment. The refrigerant, in its gaseous state, is pressurized and circulated through the system 10 by compressor 12 which is driven by engine 22. On the discharge side of compressor 12, the hot and highly pressurized vapor refrigerant is cooled in condenser 14, until it condenses into a high pressure, moderate temperature liquid. Heat is released during the cooling process into the internal environment to be heated. The condensed refrigerant then passes through a pressure-lowering device, which in the example of FIG. 2 is shown as expansion valve 16. In other cases, the pressuring lowering device may be a capillary tube, a work-extracting device such as a turbine, or other suitable device. The low pressure liquid refrigerant then enters evaporator 18, in which the fluid absorbs heat and boils. The refrigerant then returns to the compressor 12 and the cycle is repeated. The process is similar in the case of a cooling operation, except that the condenser 14 is external to the environment to be cooled and the evaporator 18 is located internal to the environment to be cooled. In the case of a heating operation, the evaporator 18 is located external to the environment to be heated and the condenser 14 is located internal to the environment to be heated.

[0027] In each case, evaporator 18 is susceptible to icing during the heating or cooling operation of system 10 during which time frost or ice may form on one or more surfaces of evaporator 18 during operation. For example, frost or ice may form on one or more locations on the external surface of the cooling coil of the evaporator 18, e.g., due to the presence of moisture and low temperature of the evaporator coil surface. As noted above, the icing of evaporator 18 may decrease the efficiency of the heating or cooling operation of system 10 and may decrease the operation life span of system 10.

[0028] As shown in FIG. 2, system 10 includes icing sensor 20 disposed on evaporator 18 and which detects an icing condition thereof. During a temperature regulating operation, the output of sensor 20 via and output signal may be monitored by control and icing detection module 24 to detect the presence of icing of evaporator 18. In addition to detecting the icing of evaporator 18, control and icing detection module 24 may control the operation of system 10, e.g., during a heating or a cooling operation. For example, control and icing detection module 24 may control the power and direction of engine 22 which drives compressor 12 during operation as well as other operation parameters of system 10. Additionally, the control and icing detection module 24 may continue to monitor for the presence of icing on the evaporator using the icing sensor 20 while the system is operating to deice the evaporator. Once the control and icing detection module 24 determines, via the output of sensor 20, that the evaporator 18 has been adequately deiced, the control and icing detection module 24 may terminate the deicing operation and may resume the heating and/or cooling operations.

[0029] As shown, control and icing detection module 24 may include processor 36. Processor 36 may include any one or more microprocessors, controllers, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and discrete logic circuitry. The functions attributed to processors and control and icing detection module 24 described herein, including processor 36, may be provided by a hardware device and embodied as software, firmware, hardware, or any combination thereof. Although not shown, control and icing detection module 24 may also include a memory, which may include any volatile or non-volatile media, such as a random access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. The memory may store computer-readable instructions that, when executed by processor 36, cause system 10 to perform various functions described herein. The memory may be considered, in some examples, a non-transitory computer-readable storage medium comprising instructions that cause one or more processors, such as, e.g., processor 36, to implement one or more of the example techniques described in this disclosure. The term “non-transitory” may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term “non-transitory” should not be interpreted to mean that the memory is non-movable. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in RAM).

[0030] FIG. 3 is a block flow diagram illustrating an example technique which may be employed to detect the presence of icing of an evaporator during temperature regulating operation, and initiate deicing based on the detection. For ease of illustration, the example of FIG. 3 is described with regard to system 10. However, other heating or cooling systems with configurations different than system 10 may also employ such techniques. Further, the example technique of FIG. 3 is described primarily as being carried out under the control of processor 36. However, configurations are not limited as such. For example, multiple processors may be employed to carry out all or portions of the example of FIG. 3. The detection of icing based on the output of icing sensor 20 may be performed in some examples without employing a processor.

[0031] As shown in FIG. 3, processor 36 may detect the presence of icing on evaporator 18 using icing sensor 20 during temperature regulating operation of system 10 (30). As noted above, the icing of evaporator 18 may include the formation of frost or ice on one or more portions of evaporator during operation. For example, frost or ice may form on the surface of one or more portions of the coil of evaporator. Icing sensor 20 may be physically located on the surface of evaporator and may take the form of a single sensor or multiple sensors located at multiple locations on evaporator 18. Example locations for sensor 20 to be disposed on evaporator 18 include the surface of the radiator of evaporator, between cooling fins of evaporator 18, or any other portion one which frost or ice may form during temperature regulation operation. The location of icing sensor 20 on evaporator 18 may be such that sensor 20 is in physical contact with the frost or ice formed on the surface of evaporator 18.

[0032] Icing sensor 20 may be configured such that a characteristic signal of sensor 20, when interrogated by processor 36, varies or otherwise indicates whether or not icing is present at the location of sensor 20 on evaporator 18. Thus, processor 36 may continually or periodically monitor the characteristic output of icing sensor 20 during operation of system 10 for heating or cooling to detect the icing of evaporator 18. The output of icing sensor 20 may change based on a condition of the evaporator including changing based on whether or not icing in present on evaporator 18.

[0033] In one example, icing sensor 20 may be configured as one or more of the exemplary sensors configured to detect icing described in U.S. patent application Ser. No. 14/023,094, filed Sep. 10, 2013, the entire of content of which is incorporated herein by reference. For example, icing sensor 20 may take the form on a conductive polymer structure located on the surface of evaporator 18. Processor 36 may detect the presence of ice or frost on the surface of evaporator 18 where icing sensor 20 is located based on the capacitance, impedance or other spectroscopy of the conductive polymer structure sensed via the output of icing sensor 20.

[0034] In one exemplary embodiment, as described in U.S. patent application Ser. No. 14/023,094, icing sensor 20 may include a first element. Processor 36 may be coupled to the first element and configured to receive a signal from the first element related to a characteristic to analyze the signal to detect a condition such as icing. The first element can be electrically conductive. In some examples, the first element can comprise a conductive polymer, a sputtered metal, a wire, a coating or a thin film. The signal can be spectrally analyzed by processor 36 to detect the condition. The first element can form a capacitor, and the characteristic can be a capacitance. Alternatively, the characteristic can comprise impedance. Further still, the first element can comprise a resistor, and the characteristic can comprise a resistance. Processor 36 may be configured to periodically sample the first element to receive the signal or continuously receive the signal.

[0035] In some examples, the first element may be integrated with a second element. The second element can be used as a heating element to provide the heat and the first element can be used as a sensing element to sense the characteristic. The first and second elements can be used as heating and sensing elements to provide the heat and to sense the characteristic. In some examples, processor 36 may be configured to deice evaporator with the heat of second element upon detecting the presence of icing on evaporator by the first element of sensor 20.

[0036] Other example configurations of sensor 20 may also be employed. For example, sensor 20. Sensor 20 may be fabricated in the form of probe station measurement MEMS structure, packaged MEMS structure in SMD packaging, interdigital electrode structures, e.g., made of conductive polymer, or other suitable form. Sensor 20 may be fabricated using any suitable technique including printed circuit board technology or flexible printed circuit board technology. Sensor 20 may be fabricated separately from that of evaporator 18 and then applied on the surface of evaporator or integrally formed during the fabrication of evaporator 18.

[0037] FIG. 8 is a schematic diagram illustrating an example icing sensor 20 in the form of interdigital electrode 80. Electrode 80 includes first conductive portion 82 and second conductive portion 84 formed on substrate 86. First and second conductive portions 82 and 84 may be formed of a conductive material, such as, e.g., a conductive polymer, a sputtered metal, or a metal wire. As shown, first and second conductive portions 82 and 84 are separated by gap 88 on surface of substrate 86. To measure impedance, a current may be conducted between first portion 82 and second portion 84. Based on the configuration of electrode 80, the measured impedance or other output signal may vary based on whether or not icing is present on the surface of evaporator 18 at the location at which electrode 80 is disposed. Electrode 80 is just one example of a configuration that may be employed to form icing sensor 20, and other configurations are contemplated which also allow icing sensor 20 to function as described herein.

[0038] FIG. 4 is a schematic diagram illustrating example circuitry 40 indicating the signal path that may be used to analyze the output of icing sensor 20, e.g., to detect the presence of icing in the manner described herein. As shown, circuitry includes digital-to-analog converter (DAC) 42, first analog-to-digital converter (ADC1) 44, second analog-to-digital converter (ADC2) 46, signal processing module 48, icing sensor 20, and reference “shunt” 52. DAC 42 may generate a periodic signal (e.g. sine wave) which is applied to sensor 20. Example frequencies of the signals range from 1 kHz to several hundred kHz. The current which flows through sensor 20 also flows through a second element (reference “shunt” 52) with known impedance. Thus, the current can be calculated from the voltage measurement of second analog-to-digital converter 46. Due to the serial connection shown in FIG. 4, the current through icing sensor 20 and reference 52 is the same, and the impedance of icing sensor 20 can be calculated from the voltage measurement of first analog-to-digital converter 44. The synchronous sampling of the two analog-to-digital converters in the configuration of FIG. 4 may be advantageous, e.g., as compared to asynchronous sampling. In particular, unlike that of synchronous sampling, asynchronous sampling may indicate an incorrect complex impedance because of the relatively high frequencies and the complex impedance associated with the system. Other circuitry and analysis techniques may include those examples described in U.S. patent application Ser. No. 14/023,094, filed Sep. 10, 2013. Other suitable examples may be employed to allow systems 10 and 70 to function as described herein.

[0039] As shown in FIG. 3, upon detecting the presence of icing of evaporator using sensor 20 (30), processor 36 may initiate an operation configured to deice evaporator (32). For example, the operation may cause any ice or frost on the surface of evaporator 18 to melt and/or evaporate. In some examples, processor 36 may reduce the power supplied to compressor 12 and/or motor 22. Reducing the power results in an increase in the temperature of the evaporator to melt ice present on the surface of evaporator 18. In this case, system 10 may continue heating or cooling operation during the deicing of the evaporator albeit at a lower power.

[0040] In another example, to initiate deicing, processor 36 may the control system 10 to reverse the cycle to inverse the heat flow in the system, e.g., by reversing the direction of engine 22. In such an operation, refrigerant may flow in the direction opposite to that of flow direction 34. Such inversion may again increase the temperature of evaporator 18 to melt or otherwise deice evaporator 18.

[0041] Additionally or alternatively, processor 36 may initiate thermoelectrical deicing of evaporator 18. For example, system 10 may include one or more electric heating coils proximate to the icing surface of evaporator 18. When icing is detected, processor 36 may activate the heating coils to increase the temperature of evaporator to melt or otherwise deice evaporator 18.

[0042] After initiating deicing (32), processor 36 may continue the deicing operation for any suitable amount of time. In some examples, processor 36 may continue to operate system 10 in a deicing mode for a preset period of time determined to be long enough to adequately deice evaporator 18, e.g., based on empirical data. Additionally or alternatively, as shown in FIG. 3, processor 32 may continue to monitor for the presence of icing on evaporator 18 using sensor 20 during the deicing operation (34). Processor 32 may continue the deicing operation until processor 32 determines evaporator 18 has been adequately deiced, e.g., when icing is determined to no longer be present on evaporator 18 using sensor 20, at which time processor 32 may terminate the deicing operation (36). Following termination of the deicing operation (36), system 10 may resume temperature regulating operation.

[0043] Various experiments were performed to evaluate the ability to detect the presence of icing on the surface of a component, such as, e.g., an evaporator, using one or more of the example sensors described herein. In general, testing indicated that it was possible to detect the present of icing.

[0044] FIGS. 5 and 6 are plots illustrating experimental results for detecting icing via an icing sensor based on measured impedance spectra. As noted above, icing of an evaporator may be detected based on measure impedance on the surface of an evaporator, e.g., using a circuitry configuration such as that shown in the example of FIG. 4. While note wishing to be bound by theory, water has a relatively large dielectric number (about 81) due to the polarity of the water molecule. In ice this dipole is in essence “frozen” so the changes in the impedance spectra are relatively large. Conversely, air has a relatively low dielectric number. Thus, it is possible to discriminate air, water and ice based on the measured impedance spectra. One method for measurement of a spectra may be Fourier analysis (FFT/DFT). By utilizing the configuration of FIG. 4, the analysis may be carried out in a timely and advantageous manner.

[0045] FIG. 5 is a plot illustrating an example impedance spectra for water, ice, and air. The spectra gives the values for Z(f_k) over the k discrete frequency points f_k, typically as a result of an FFT/DFT Transform. A transformation may be carried out according to the following:

$Y_i=A\times \frac{Z\left(f_{k+n}\right)}{Z\left(f_k\right)}t=1\dots k-n$

where n is a suitable integer and A is a normalization constant. FIG. 6 is a plot illustrating an example result of the transformation. Integration of these curves (or simple averaging) may give a reliable scalar value for the detection of ice and/or water based on the output of an icing sensor used to measure impedance on the surface of an evaporator.

[0046] FIG. 7 is a plot illustrating experimental results for detecting the presence of icing on an evaporator. In particular, FIG. 7 is a plot of time versus transformational parameter value representative of the spectral analysis of measured impedance on a surface measured during a time period during which icing occurred. The transformational parameter on the vertical axis was determined using the FFT/DFT Transform technique described above. As labeled, the results indicated that initially the sensor and surface were dry. Subsequently, condensation of water was detected on the surface based on the sensor output. Following the condensation of water, frost was detected on the surface and sensor based on the sensor output.

[0047] Various examples and techniques have been described. Aspects or features of examples described herein may be combined with any other aspect or feature described in another example. These described examples and other examples are within the scope of the following claims.