Patent Publication Number: US-10782040-B2

Title: Heat pump system with fault detection

Description:
TECHNICAL FIELD 
     The present disclosure pertains to a Heating, Ventilation, and/or Air Conditioning (HVAC) system for a building. More particularly, the present disclosure pertains to fault detection in heat pump systems. 
     BACKGROUND 
     Heating, Ventilation, and/or Air Conditioning (HVAC) systems are often used to control the comfort level within a building or other structure. Such HVAC systems typically include an HVAC controller that controls various HVAC components of the HVAC system in order to affect and/or control one or more environmental conditions within the building. In many cases, the HVAC controller is disposed within the building and provides control signals to various HVAC components of the HVAC system. Improvements in the hardware, user experience, and functionality of such HVAC controllers, including remote sensor devices, would be desirable. 
     SUMMARY 
     The disclosure is directed to an HVAC system that includes fault detection. In a particular example of the disclosure, a system includes an indoor heat exchange coil and an outdoor heat exchange coil. The system includes an expansion valve and a compressor that compresses the refrigerant for delivery to one of the indoor heat exchange coil or the outdoor heat exchange coil, depending on whether there is a call for heat or a call for cooling within the building. The system may include a compressor discharge refrigerant temperature sensor that provides an indication of a temperature of the refrigerant exiting the compressor as well as an outdoor air temperature source for obtaining a measure of outdoor air temperature. A controller is operatively coupled to the compressor discharge refrigerant temperature sensor and the outdoor air temperature source and is configured to identify a difference between a temperature indicative of the temperature of the compressed refrigerant at or near the output of the compressor of the compressor and the measure of outdoor air temperature source. The controller is configured to identify a change in the identified difference over time and report a fault when the change in the difference exceeds a threshold. 
     In another example of the disclosure, a method is disclosed for detecting a fault in an HVAC system of a building in which the HVAC system includes a refrigerant loop with an indoor heat exchange coil, an outdoor heat exchange coil, an expansion valve and a compressor that compresses a refrigerant for delivery to one of the indoor heat exchange coil and the outdoor heat exchange coil. The method includes repeatedly sampling a temperature indicative of a temperature of the compressed refrigerant at or near an output of the compressor before the compressed refrigerant reaches any of the indoor heat exchange coil or the outdoor heat exchange coil, wherein each sample is taken with the temperature indicative of the temperature of the compressed refrigerant at or near an output of the compressor is stable. An outdoor air temperature is obtained. An average of a difference between each of the sampled temperatures indicative of the temperature of the compressed refrigerant at or near the output of the compressor and a corresponding outdoor air temperature is identified over a period of time. The method includes identifying a change in the identified average difference over time, and reporting a fault when the change in the average difference exceeds a threshold. 
     In another example of the disclosure, the server includes an input/output, a memory, and a processor that is operatively coupled to the input/output and to the memory. The processor is configured to store in the memory a plurality of temperatures each indicative of a temperature of a compressed refrigerant at or near an output of a compressor before the compressed refrigerant reaches any of an indoor heat exchange coil or an outdoor heat exchange coil of a remote HVAC system. The processor stores in the memory an outdoor air temperature that corresponds to each of the stored plurality of temperatures and identifies an average of a difference between each of the stored temperatures indicative of the temperature of the compressed refrigerant at or near the output of the compressor and the corresponding outdoor air temperature over a period of time. The processor identifies a change in the identified average difference over time, and outputs an alert via the input/output when the change in the average difference exceeds a threshold. 
     The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify some of these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments of the disclosure in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of an illustrative HVAC monitoring system in which a plurality of HVAC systems operating in a plurality of buildings are monitored; 
         FIG. 2  is a schematic diagram of an illustrative HVAC control system; 
         FIG. 3  is a schematic diagram of an illustrative HVAC control system; 
         FIG. 4  is a schematic structural diagram of a server forming a portion of the embodying the present disclosure; 
         FIG. 5  is a flow diagram showing an illustrative fault detection method; and 
         FIG. 6  shows a compressor with an output tube and a compressor discharge refrigerant temperature sensor thermally coupled to the output tube. 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular illustrative embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
     DESCRIPTION 
     The following description should be read with reference to the drawings wherein like reference numerals indicate like elements. The drawings, which are not necessarily to scale, are not intended to limit the scope of the disclosure. In some of the figures, elements not believed necessary to an understanding of relationships among illustrated components may have been omitted for clarity. 
     All numbers are herein assumed to be modified by the term “about”, unless the content clearly dictates otherwise. The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include the plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is contemplated that the feature, structure, or characteristic may be applied to other embodiments whether or not explicitly described unless clearly stated to the contrary. 
     The present disclosure is directed generally at building automation systems. Building automation systems are systems that control one or more operations of a building. Building automation systems can include HVAC systems, security systems, fire suppression systems, energy management systems and other systems. While HVAC systems with HVAC controllers are used as an example below, it should be recognized that the concepts disclosed herein can be applied to building automation systems more generally.  FIG. 1  shows a system  1  that includes a number of buildings including a BLDG 1 labeled as 5a, a BLDG 2 labeled as 5b through a BLDG N labeled as 5n. It will be appreciated that there may be any number of different buildings. At least some of the buildings 5a, 5b through 5n, collectively referred to as buildings 5, may represent individual residences such as homes, townhouses, condominiums, apartments, and the like. In some instances, at least some of the buildings 5 may be larger structures such as office buildings, retail buildings, and university buildings, for example. 
     Each of the buildings 5 has an HVAC system. For illustration purposes, the BLDG 1 that is labeled as 5a includes an HVAC system  100   a , the BLDG 2 that is labeled as 5b includes an HVAC system  100   b , and the BLDG N that is labeled as 5n includes an HVAC system  100   n . It will be appreciated that some of the HVAC systems  100   a ,  100   b  through  100   n , collectively referred to as HVAC systems  100 , may include a variety of different heat, cooling and ventilation equipment. In some cases, at least some of the HVAC systems  100  may be forced air systems that utilize furnaces for heating and a separate air conditioning system for cooling. At least some of the HVAC systems  100  may be configured to utilize a heat pump system, in which the thermal properties of a refrigerant being expanded from a liquid to a gas, or being compressed from a gas to a liquid, are utilized in transferring heat between an environment outside of the building  100  and an interior of the building  100 . When heating is called for, the refrigerant releases heat within an indoor air coil. Conversely, when cooling is called for, the refrigerant releases heat within an outdoor air coil (much like a traditional air conditioning unit). 
     In some cases, HVAC systems such as the HVAC systems  100  may be monitored. The HVAC systems  100  may be monitored and/or remotely controlled in order to improve energy efficiency, for example. The HVAC systems  100  may be adjusted from afar. For example, a homeowner may want to change a temperature set point for their residence, or they may wish to confirm that their system is running properly. In some cases, the HVAC systems  100  may be monitored in order to ensure that each of the HVAC systems  100  are running efficiently and are not showing any signs of a loss of efficiency. Accordingly, in some cases the system  1  includes a network  6  and a server  7 , where the network  6  provides for communication between the server  7  and each of the HVAC systems  100 . In some cases, the HVAC systems  100  may periodically provide data such as but not limited to temperature data to the server  7  via the network  6 . In some cases, this temperature data may be useful in recognizing potential issues with the performance of one of the HVAC systems  100  early on, before equipment failure becomes an issue. 
     While the network  6  is schematically shown as a single element, it will be appreciated that the network  6  is intended to represent any number of distinct communication networks. For example, the network  6  may represent the Internet. The network  6  may be a local area network (LAN) or a wide area network (WAN). In some cases, the network  6  may represent a fiber optic network. The network  6  may provide a wireless access point and/or host a network host device that is part of the HVAC system  100 . 
     Depending upon the application and/or where the HVAC user is located, remote access and/or control of the HVAC systems  100  may be provided over the network  6 . A variety of mobile wireless devices may be used to access and/or control the HVAC systems  100  from a remote location over the network  6  including, but not limited to, mobile phones including smart phones, PDAs, tablet computers, laptop or personal computers, wireless network-enabled key fobs, e-Readers and the like. 
     In some cases, the HVAC system  100   s  may be programmed to communicate over the network  6  with an external web service hosted by the server  7 . While schematically shown as a single element, the server  7  may instead include one or more external web servers. The server  7  may be considered as providing data collection and data analysis. A non-limiting example of an external web service is Honeywell&#39;s Light Commercial Building System (LCBS)™ web service. The HVAC systems  100  may be configured to upload selected data (e.g. fault detection) via the network  6  so that the data may be collected, stored and analyzed on the external web server  7 . In some cases, the data may be indicative of the performance of the HVAC systems  100 . 
       FIG. 2  is a schematic diagram of one of the HVAC systems  100 . The illustrated HVAC system  100  includes an indoor heat exchange coil  10 , an outdoor heat exchange coil  12 , and a compressor  14  that may compress the refrigerant for delivery to one of the indoor heat exchange coil  10  or the outdoor heat exchange coil  12 . A reversing valve  16  is configured to direct the compressed refrigerant to the indoor heat exchange coil  10  when there is a call for heat and to direct the compressed refrigerant to the outdoor heat exchange coil  12  when there is a call for cooling. The compressed refrigerant will give off heat as it expands from a liquid to a gas while passing through either of the indoor heat exchange coil  10  or the outdoor heat exchange coil  12 . A controller  15  is operatively coupled to the compressor  14  and is operably coupled to the reversing valve  16  via an electrical connection  27  so that the controller  15  can control operation of the reversing valve  16  in order to direct the compressed refrigerant in a desired direction. The HVAC system  100  includes an expansion valve  20  that is configured to allow for a pressure drop of the compressed refrigerant in order to allow the compressed refrigerant to expand from liquid to vapor within either the indoor heat exchange coil  10  or the outdoor heat exchange coil  12 . The HVAC system  100  also includes refrigerant conduits that fluidly couple the components in the HVAC system  100 . For example, a refrigerant conduit  21  fluidly couples the outdoor heat exchange coil  12  with the expansion valve  20 . A refrigerant conduit  22  fluidly couples the expansion valve  20  with the indoor heat exchange coil  10 . A refrigerant conduit  23  fluidly couples the indoor heat exchange coil  10  with the reversing valve  16 . A refrigerant conduit  21  fluidly couples the outdoor heat exchange coil  12  with the reversing valve  16 . A pair of refrigerant conduits  25  and  26  fluidly couple the compressor  14  with the reversing valve  16  such that fluid flow can continue in a loop, regardless of whether the compressed refrigerant is being directed to the indoor heat exchange coil  10  or the outdoor heat exchange coil  12 . 
     As soon as the HVAC system  100  switches from a cooling mode to a heating mode, it now functions as a heat pump. The compressor  14  may deliver the compressed refrigerant to the outdoor heat exchange coil  12 . The controller  15  may be used to switch the reversing valve  16  to change the direction of flow of the refrigerant there through via an electrical connection  27 . The refrigerant may pass through the outdoor heat exchange coil  12  and through the expansion valve  20  via the refrigerant conduit  21  and through the indoor heat exchange coil  10  via the refrigerant conduit  22  and back to the input to the compressor  14  as indicated by the refrigerant conduit  25 . The expansion valve  20  removes pressure from the liquid refrigerant to allow expansion or change of state from a liquid to a vapor in the outdoor heat exchange coil  12 . 
     The reversing valve  16  may have a first position in which the compressor  14  delivers the compressed refrigerant to the outdoor heat exchange coil  12  via the refrigerant conduit  24 . The refrigerant may pass through the outdoor heat exchange coil  12  through the refrigerant conduit  21  to the expansion valve  20  and through the refrigerant conduit  22  to the indoor heat exchange coil  10  and back through the refrigerant conduit  25  to the compressor  14 . The reversing valve  16  may have a second position in which the compressor  14  may deliver the compressed refrigerant via the refrigerant conduit  26  to the indoor heat exchange coil  10  via the refrigerant conduit  23 . The refrigerant may flow through indoor heat exchange coil  10  through the refrigerant conduit  22  to the expansion valve  20  through the refrigerant conduit  21  to the outdoor heat exchange coil  12  and back to an input to the compressor  14 . This flow may be configured to provide a vapor compression system into which both cooling during warm ambient temperatures, indicated by solid arrows  21   b - 24   b , and heating during cold ambient periods, indicated by dashed arrows  21 - 24   a , is accomplished. Such a vapor compression system with a reversing valve  16  is commonly referred to as a heat pump. 
     If heating is being demanded, then the compressed hot refrigerant from the compressor  14  may be routed through the reversing valve  16  via the refrigerant conduit  26  toward the indoor heat exchange coil  10  via the refrigerant conduit  23  as shown in arrow  23   a  where its heat is given up to heat indoor air. When a heat pump is in heating mode, the pump is moving heat from outdoor air into an interior of the building  5  by moving outdoor air across the same outdoor heat exchange coil  12  that is now in heating mode. The compressed gas changes to a liquid in the indoor heat exchange coil  10 , which is now acting as a condenser. As a result, the indoor heat exchange coil  10  gives off heat to the air flowing there across, as shown by arrows  22   a  and  21   a . The flow of the liquid refrigerant from the indoor heat exchange coil  10  expands inside of outdoor heat exchange coil  12 . The outdoor heat exchange coil  12  absorbs heat from the air flowing across there, therefore discharging cool air to the outside. The vapor in the outdoor heat exchange coil  12  flows via arrow  24   a  through the reversing valve  16  in to the compressor  14  as indicated by the refrigerant in conduit  25 . The refrigerant is then compressed again by the compressor  14  and the cycle repeats. 
     Conversely, if cooling of the building  5  is desired, the controller  15  activates the compressor  14  and the high pressure hot refrigerant from the compressor  14  is routed through the refrigerant in conduit  26  to the reversing valve  16  to the outdoor heat exchange coil  12  in a direction indicated by the arrow  24   b  where the refrigerant is cooled for subsequent use indoors to cool the building  5 . It may take some time after the compressor  14  is activated for the temperature of the compressed refrigerant at or near the output of the compressor  14  to reach a stable temperature. When the high liquid refrigerant is condensed to a liquid and subcools, it passes from the outdoor heat exchange coil  12  in a direction indicated by the arrows  21   b  and  22   b  to the indoor heat exchange coil  10 . The cycle repeats as the refrigerant conduit  23 . Through the reversing valve  16  and returns to the compressor  14  via the refrigerant conduit  25 . 
     The controller  15  may be used to automatically change from heating to cooling, control and process algorithms, set a program schedule, provide remote access, diagnostics and protection, fault detection and protection, wired or wireless connection to a wall-mounted thermostat. A built-in fault detection system may be included to provide warnings and alerts to an end user and, if necessary, shut down the system. Remote access may also be provided through a remote control. 
     The controller  15  may be configured to identify the difference between the temperatures indicative of the temperature of the compressed refrigerant at or near the output of the compressor  14  and the measure of outdoor air temperature only after the compressed refrigerant at or near the output of the compressor  14  has reached a stable temperature. The compressed refrigerant at or near the output of the compressor  14  may reach a stable temperature when a rate of change of the temperature of the compressed refrigerant at or near the output of the compressor  14  may be below a rate threshold. 
     A compressor discharge refrigerant temperature sensor  30  may sense a temperature indicative of a temperature of the compressed refrigerant at or near an output of the compressor  14  before the compressed refrigerant reaches any of the indoor heat exchange coil  10  or the outdoor heat exchange coil  12 . An outdoor air temperature sensor  32  may provide a measure of the outdoor air temperature. Measured temperatures may include outdoor air temperature, return air temperature, liquid line temperature, suction line temperature, fan motor temperature and such. 
     Software logic in the controller  15  may look at sensor data gathered by the communicating controls at periodic intervals to determine the moving average of the maximum difference between the compressor discharge refrigerant temperature as indicated by the compressor discharge refrigerant temperature sensor  30  and the outdoor air temperature as indicated by the outdoor air temperature sensor  32  when the compressor  14  is running and either comparing against a known good value determined during maintenance or looking for a change past a threshold over time. In some cases, the software logic that looks at the sensor data, and determines whether there has been an undesired change in the moving average of the maximum difference between the compressor discharge refrigerant temperature as indicated by the compressor discharge refrigerant temperature sensor  30  and the outdoor air temperature as indicated by the outdoor air temperature sensor  32  may instead reside within the server  7 . 
     The controller  15  may further be configured to identify a moving average of the maximum difference between the temperature indicative of the temperature of the compressed refrigerant at or near the output of the compressor  14  as indicated by the compressor discharge refrigerant temperature sensor  30  and the measure of the outdoor air temperature as indicated by the outdoor air temperature  32 . Over time the controller  15  may identify a change in the identified difference and report a fault when the change in the difference exceeds a threshold. The threshold may be a user-programmable threshold. In some cases, the threshold is programmed by the factory. In some instances, the threshold may indicate a temperature difference that is greater than 10 degrees F. The period of time may be at or around 10 minutes, as an example. 
     In some cases, an increase in the average maximum difference between the compressor discharge refrigerant temperature sensor  30  and the outdoor air temperature sensor  32  may mean that the compressor  14  is working harder than normal. Over time, this can result in a loss of energy efficiency as well as a possible reduction in the longevity of the equipment. This can also indicate that possible repairs or maintenance may be required. In addition, the average maximum difference between the compressor discharge refrigerant temperature sensor  30  and the outdoor air temperature sensor  32  may be normalized by adjusting for changes in outdoor wet bulb temperature which influences the efficiency of the condenser heat transfer and thus the compressor working temperature. 
     The HVAC system  100  may further include a room thermostat  42  which is configured to monitor and control a temperature within a space in which the room thermostat  42  is deployed. In some cases, the room thermostat  42  may be operably coupled to the outdoor air temperature source  31  as well as to the network  6 . The room thermostat  42  may include a unique identifier, such as an electronic serial number, an IP address, and/or combinations thereof, which identifies the room thermostat  42  to the network  6 . In some cases, the controller  15  may be implemented by the room thermostat  42  that is disposed within the building  5  and that is configured to thermostatically control the HVAC system  100  of the building  5 . In some cases, the controller  15  may be implemented within the server  7 . 
     The room thermostat  42  may be operably coupled with a weather service  8  may be operably coupled to the room thermostat  42  via the network  6 . The weather service  8  may be configured to receive local weather data including outdoor temperature, outdoor humidity, a solar load, wind speed, weather alerts and/or warnings, as examples. The information provided by the weather service  8  come from the National Weather Service, for example, although this is not required 
       FIG. 3  show a schematic diagram illustrative of an HVAC system  100   a  that lacks the reversing valve  16 . In this configuration, the HVAC system  100   a  may operate as an air conditioning unit. For both a split air conditioning unit and a split heat pump there are two refrigerant lines connecting the units, one containing condensed liquid refrigerant and the other containing vapor refrigerant. When cooling of the building  5  is being demanded, the controller  15  activates the compressor  14 . The high pressure hot refrigerant from the compressor  14  is routed through the refrigerant in the conduit  24  to the outdoor heat exchange coil  12  as indicated by the arrow  24   b  where the refrigerant gives up heat and is cooled for subsequent use indoors to cool the building  5 . It may take some time after the compressor  14  is activated for the temperature of the compressed refrigerant at or near the output of the compressor  14  to reach a stable temperature. 
       FIG. 4  is a schematic diagram of the server  7 . The server  7  may include an input/output  50 , a processor  52  and a memory  54 . The memory  54  may store a plurality of outdoor air temperatures that are received via the input/output  50  from the building  5 . The memory  54  may be used to store any desired information, such as algorithms, set points, schedule times, diagnostic limits, such as for example, differential pressure limits, delta T limits, and the like. The memory  54  may be any suitable storage device including, but not limited to RAM, ROM, EPROM, flash memory, a hard drive and/or the like. The input/output  50  may include a wireless transceiver for wirelessly sending and/or receiving signals over a wireless network  6 . In some cases, the input/output  50  may be in communication with a wired or wireless router or gateway for connecting to the network  6 , but this is not required. 
     In some cases the processor  54  may store information within the memory  52 . The processor  54  may include a microprocessor, microcontroller, or such. The processor  52  may be operatively coupled to the input/output  50  and the memory  54 . The processor  52  is configured to receive the input/output  50  and store in the memory  54  a plurality of temperatures each indicative of a temperature of a compressed refrigerant at or near an output of the compressor  14  before the compressed refrigerant reaches any of the indoor heat exchange coil  10  or the outdoor heat exchange coil  12 . Each of the plurality of temperatures may be taken when the temperature indicative of the temperature of the compressed refrigerant at or near an output of the compressor  14  is stable. The processor  52  may identify an average of a difference between each of the stored temperatures indicative of the temperature of the compressed refrigerant at or near the output of the compressor  14  and the corresponding outdoor air temperature over a period of time. This time may be approximately 10 minutes. Further, processor  52  may identify a change in the identified average difference over time and output an alert via the input/output  50  when the change in the average difference exceeds a threshold. The alert may be provided to a contractor that is responsible for maintaining remote HVAC system  100 . This alert may be configured to appear on a contractor&#39;s alert page display, dashboard, pad, tablet, smartphone, laptop or an office computer via a wire/and or wireless connection. The alert may be reporting of an event record. An event may pertain to a threshold of some kind that has been crossed. An alert may be either a sensed value going outside a specific bound or an analytic value exceeding a specified bound. 
     The outdoor air temperatures that correspond to each of the stored plurality of temperatures may be received from a remote weather service  8  via the input/output  50 . The outdoor air temperature may be normalized by adjusting for changes an outdoor wet bulb temperature. 
       FIG. 5  is a flow diagram showing a method  500  for detecting a fault in an HVAC system such as but not limited to the HVAC system  100  described above. The method  500  may include repeatedly sampling a temperature indicative of the compressed refrigerant at or near an output of the compressor before the compressed refrigerant reaches either the indoor heat exchange coil  10  or the outdoor heat exchange coil  12  as indicated at block  510 . In some cases, each sample may be taken when the temperature is indicative of the temperature of the compressed refrigerant at or near an output of the compressor is stable. The compressed refrigerant at or near the compressor  14  may be considered to be stable when a rate of change of the temperature of the compressed refrigerant at or near the output of the compressor  14  is below a rate threshold, for example. 
     An outdoor air temperature may be obtained from the outdoor air temperature sensor  32 , as indicated at block  520 . An average of a difference between each of the sampled temperatures indicative of the temperature of the compressed refrigerant at or near the output of the compressor and a corresponding outdoor air temperature over a period of time may be identified, as indicated at block  530 . A change in the identified average difference may be identified over time, as indicated at block  540 . A fault may be reported when the change in the average difference exceeds a threshold, as indicated at block  550 . 
       FIG. 6  shows the compressor  14  with an output tube  60  and the compressor discharge refrigerant temperature sensor  30  thermally coupled to the output tube  60 . The compressor discharge refrigerant temperature sensor  30  may be thermally coupled to the output tube  60  within a distance “d” of four inches or less from an outer housing  62  of the compressor  14 . 
     Those skilled in the art will recognize that the present disclosure may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, the scope of legal protection given to this disclosure can only be determined by studying the following claims.