Patent Publication Number: US-2019178545-A1

Title: Heating, ventilating, air conditioning, and refrigeration system with mass flow stabilization

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to heating, ventilating, air conditioning, and refrigeration (HVAC-R) systems. In particular, this invention relates to an improved HVAC-R system structure and an improved method of controlling an expansion valve in an HVAC-R system to achieve improved cooing of an evaporator. 
     In a conventional HVAC-R system, an expansion valve is controlled based on the superheat. Superheat control is achieved using pressure sensor and a temperature sensor to measure HVAC-R system fluid pressure and temperature, respectively. Superheat is then calculated for a particular refrigerant using the measured temperature and pressure, and controlled by causing the superheat to move to a target superheat value by adjusting the pressure and temperature using any of a group of known open-loop or closed-loop algorithms. 
     Superheat is a function of pressure and temperature, and is conventionally calculated using pressure-temperature (P-T) charts that map a saturation temperature at a particular pressure. The values of the saturation temperatures at particular pressures may vary with different refrigerants. These values for saturation temperature and a temperature of the refrigerant are typically measured at an outlet of an evaporator in the conventional HVAC-R system, and are typically used to calculate superheat. 
     Typical HVAC-R systems in which a refrigerant fluid mass flow rate exiting the condenser is relatively stable tend to be more efficient than similar HVAC-R systems in which the refrigerant fluid mass flow rate exiting the condenser is unstable. 
     Thus, it would be desirable to provide an improved HVAC-R system structure and an improved method of controlling the expansion valve by stabilizing the refrigerant fluid mass flow rate exiting the condenser and then controlling the superheat at the outlet of the evaporator. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved structure and an improved method of controlling the expansion valve in an HVAC-R system. 
     In one embodiment the heating, ventilating, air conditioning, and refrigeration (HVAC-R) system includes an evaporator, a compressor, a condenser, an expansion device between the condenser and the evaporator, a superheat controller between the evaporator and the compressor, and a mass flow meter between the condenser and the expansion device. The superheat controller is configured to measure refrigerant fluid pressure and temperature and calculate superheat therefrom, to receive and analyze a mass flow rate of the refrigerant fluid traveling out of the condenser and measured by the mass flow meter, and further configured to provide a control signal to the expansion device. 
     Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a block diagram of a first embodiment of an HVAC-R system according to the invention. 
         FIG. 2  is a block diagram of a second embodiment of an HVAC-R system according to the invention. 
         FIG. 3  is a perspective view of the universal superheat controller illustrated in  FIGS. 1 and 2 . 
         FIG. 4  is a cross sectional view of the universal superheat controller illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , there is illustrated at  10  a block diagram of a first embodiment of a HVAC-R system in accordance with this invention. Other than an improved superheat processor  22  of a superheat controller  20  and a mass flow meter  24 , the illustrated HVAC-R system  10  is, in large measure, conventional in the art and is intended merely to illustrate one environment in which this invention may be used. Thus, the scope of this invention is not intended to be limited for use with the specific structure for the HVAC-R system  10  illustrated in  FIG. 1  or with refrigeration systems in general. On the contrary, as will become apparent below, this invention may be used in any desired environment for the purposes described below. 
     As is well known in the art, the HVAC-R system  10  circulates a refrigerant through a closed circuit, where it is sequentially subjected to compression, condensation, expansion, and evaporation. The circulating refrigerant removes heat from one area (thereby cooling that area) and expels the heat in another area. 
     To accomplish this, the illustrated HVAC-R system  10  includes an evaporator  12 , such as an evaporator coil. The evaporator  12  may be conventional in the art and is adapted to receive a relatively low pressure liquid refrigerant at an inlet thereof. A relatively warm fluid, such as air, may be caused to flow over the evaporator  12 , causing the relatively low pressure liquid refrigerant flowing in the evaporator  12  to expand, absorb heat from the refrigerant fluid flowing over the evaporator  12 , and evaporate within the evaporator  12 . The relatively low pressure liquid refrigerant entering into the inlet of the evaporator  12  is thus changed to a relatively low pressure refrigerant gas exiting from an outlet of the evaporator  12 . 
     The outlet of the evaporator  12  communicates with an inlet of a compressor  14 . The compressor  14  may be conventional in the art and is adapted to compress the relatively low pressure refrigerant gas exiting from the evaporator  12  and to move such relatively low pressure refrigerant gas through the HVAC-R system  10  at a relatively high pressure. The relatively high pressure refrigerant gas is discharged from an outlet of the compressor  14  that communicates with an inlet of a condenser  16 . The condenser  16  may be conventional in the art and is configured to remove heat from the relatively high pressure refrigerant gas as it passes therethrough. As a result, the relatively high pressure refrigerant gas condenses and becomes a relatively high pressure refrigerant liquid. 
     The relatively high pressure refrigerant liquid then moves from an outlet of the condenser  16  to an inlet of an expansion device or valve. In the illustrated embodiment, the expansion device is a Modular Silicon Expansion Valve (MSEV)  18 , described below, that is configured to restrict the flow of refrigerant fluid therethrough. As a result, the relatively high pressure refrigerant liquid is changed to a relatively low pressure refrigerant liquid as it leaves the expansion device. The relatively low pressure refrigerant liquid is then returned to the inlet of the evaporator  12 , and the refrigeration cycle is repeated. 
     The illustrated embodiment of the HVAC-R system  10  additionally includes at least one external sensor, configured as a superheat controller (SHC)  20 , described below, and that communicates with the fluid line that provides fluid communication from the evaporator  12  to the compressor  14 . The illustrated embodiment of the HVAC-R system  10  also includes the mass flow meter  24 . The mass flow meter  24  may be conventional in the art and configured to measure the mass flow rate (the mass per unit time, e.g., kilograms per second) of refrigerant fluid traveling through the condenser  16 , and specifically measured at the outlet of the condenser  16 . The mass flow meter  24  reports mass flow rate data to the SHC  20  through a wire or cable  58 . Alternatively, the mass flow meter  24  may be connected to the SHC  20  by a wireless connection. 
     The SHC  20  is responsive to one or more properties of the refrigerant fluid in the fluid line (such as, for example, pressure measured by a pressure sensor portion  42 , and temperature measured by a temperature sensor portion  44 , both described below) and generates a signal that is representative of that or those properties to a controller or processor, such as a superheat processor  22  within the SHC  20 , also described below. In response to the signal from the SHC  20  (and, if desired, a target device  56  described below, and other non-illustrated sensors or other inputs), the superheat processor  22  generates a signal to control the operation of the MSEV  18  via a wire or cable  60 . Alternatively, the SHC  20  may be connected to the MSEV  18  by a wireless connection. 
     A second embodiment of the HVAC-R system in accordance with this invention is shown at  10 ′ in  FIG. 2  and includes a second embodiment of the SHC  20 ′. As shown in  FIG. 2 , the superheat processor  22 ′ may be mounted to the HVAC-R system  10 ′ external of the SHC  20 ′. The superheat processor  22 ′ is substantially identical to the superheat processor  22 , and will not be further described herein. The second embodiment of the HVAC-R system  10 ′ also includes the target device  56  configured as a temperature sensor and connected to the superheat processor  22 ,  22 ′ via a wire or cable  62 . Alternatively, the target device  56  may be connected to the superheat processor  22 ,  22 ′ by a wireless connection. The target device  56  that may also be configured as a plurality of temperature sensors, laptop and notebook computers, cell phones, memory cards, and any device or devices used in or with conventional end of the line test equipment. 
     MSEVs, such as the MSEV  18 , are electronically controlled, normally closed, and single flow directional valves, and may be used for refrigerant fluid mass flow control in conventional HVAC and HVAC-R applications. 
     The exemplary MSEV  18  illustrated in  FIGS. 1 and 2 , is a two-stage proportional control valve. The first stage is a microvalve (not shown) configured as a pilot valve to control a second stage spool valve (not shown). When the microvalve (not shown) receives a Pulse Width Modulation (PWM) signal from the superheat processor  22 ,  22 ′, the microvalve (not shown) modulates to change the pressure differential across the second stage spool valve (not shown). The spool valve (not shown) will move to balance the pressure differential, effectively changing an orifice opening of the MSEV  18  to control a desired amount of refrigerant flow. 
     U.S. Pat. No. 9,140,613 discloses a superheat controller (SHC). The SHC disclosed therein is a single, self-contained, stand-alone device which contains all the sensors, electronics, and intelligence to automatically detect a fluid type, such as refrigerant, and report the superheat of multiple common fluid types used in residential, industrial, and scientific applications. U.S. Pat. No. 9,140,613 is incorporated herein in its entirety. 
       FIGS. 3 and 4  herein illustrate the SHC  20 , which is similar to the superheat controller disclosed in U.S. Pat. No. 9,140,613. The SHC  20 , like the HVAC-R system  10  described above, is in large measure, conventional in the art, and is intended merely to illustrate one device in which this invention may be used. Thus, the scope of this invention is not intended to be limited for use with the specific structure for the SHC  20  illustrated in  FIGS. 3 and 4  or with devices configured to detect and report superheat in a fluid system in general. On the contrary, as will become apparent below, this invention may be used in any desired device for the purposes described below. 
     As shown in  FIGS. 3 and 4 , the illustrated embodiment of the SHC  20  includes a housing  30  having a body  32 , a cover  34 , and a fluid inlet member  36 . The fluid inlet member  36  may be secured to the housing  30  by a mounting ring  37 . The mounting ring  37  attaches the fluid inlet member  36  to the housing  30  portion by a threaded connection. Alternatively, the mounting ring  37  may be attached to the fluid inlet member  36  by any desired method, such as by welding or press fitting. In the embodiment illustrated in  FIGS. 3 and 4 , the fluid inlet member  36  is a brass fitting having a centrally formed opening that defines a sealing surface  38 . 
     The SHC  20  includes an integrated pressure and temperature sensor  40  having pressure sensor portion  42  and a temperature sensor portion  44  mounted to a printed circuit board (PCB)  46 . The superheat processor  22 , a data-reporting or communication module  50 , and an Input/Output (IO) module  52  are also mounted to the PCB  46 . The IO module  52  is a physical hardware interface that accepts input power and reports data through available hard-wired interfaces, such as wires or cables  54 , to the superheat processor  22 . Target devices  56  that may be connected to the SHC  20  via the IO module  52  may include additional temperature sensors, laptop and notebook computers, cell phones, memory cards, and any device used in or with conventional end of the line test equipment. Alternatively, the target devices  56  may be connected to the communication module  50  by a wireless connection. 
     The superheat processor  22  is mounted to the PCB  46  and is a high-resolution, high-accuracy device that processes the input signals from the pressure and temperature sensor portions  42  and  44 , respectively, of the integrated pressure and temperature sensor  40 , detects the fluid type, calculates the superheat of the fluid, and provides an output that identifies the level of the calculated superheat. The superheat processor  22  may also be configured to provide other data, such as fluid temperature, fluid pressure, fluid type, relevant historical dates maintained in an onboard memory (such as alarm and on-off history), and other desired information. Advantageously, the superheat processor  22  maintains a high level of accuracy over a typical operating range of pressure and temperature after a one-time calibration. Non-limiting examples of suitable superheat processors include microcontrollers, Field Programmable Gate Arrays (FPGAs), and Application Specific Integrated Circuits (ASICs) with embedded and/or off-board memory and peripherals. 
     The mass flow rate of refrigerant fluid traveling out of the condenser  16  is measured by the mass flow meter  24  and provided to the superheat processor  22 ,  22 ′. Advantageously, the mass flow rate may be combined with pressure and temperature data from the pressure sensor portion  42  and the temperature sensor portion  44 , respectively, as feedback inputs to control the expansion valve, i.e., the MSEV  18 , of the HVAC-R system  10 . With the mass flow rate provided by the mass flow meter  24 , a control signal provided to the MSEV  18  by the superheat processor  22 ,  22 ′ may be weighted so as to maintain a stable or consistent fluid mass flow rate into the evaporator  12 . The improved HVAC-R system  10  may be especially useful in fluid systems that experience only small load changes over time, such as for example, closed door refrigerated display cases in grocery stores and the like. 
     The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.