Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B41/00—Fluid-circulation arrangements
  • F25B41/30—Expansion means; Dispositions thereof
  • F25B41/31—Expansion valves
  • F25B41/34—Expansion valves with the valve member being actuated by electric means, e.g. by piezoelectric actuators
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2341/00—Details of ejectors not being used as compression device; Details of flow restrictors or expansion valves
  • F25B2341/06—Details of flow restrictors or expansion valves
  • F25B2341/068—Expansion valves combined with a sensor
  • F25B2341/0681—Expansion valves combined with a sensor the sensor is heated
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2600/00—Control issues
  • F25B2600/21—Refrigerant outlet evaporator temperature
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
  • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Definitions

• This invention relates to improvements in control ⁇ ling the operation of a thermostatic expansion valve used for metering refrigerant into the evaporator coil of a refrigeration system. More particularly, this invention relates to methods and apparatus for adding heat to the thermostatic expansion valve remote fluid- charged bulb for improving the operation of the valve and for correcting the superheat adjustment of the valve under adverse operating conditions.
• Thermostatic expansion valves have long been used in refrigeration flow control to control or meter the flow of liquid refrigerant into the evaporator coil. Because of its high efficiency and its ready adaptability to any type of refrigeration application, the thermosta- tic expansion valve is probably the most widely used refrigerant flow control at the present time.
• the operation of the thermostatic expansion valve is based on maintaining a constant degree of suction line super ⁇ heat at the evaporator outlet, permitting the valve to keep the evaporator filled with refrigerant under all conditions of system loading.
• the characteristic operation of the thermostatic expansion valve results from the interaction of three independent forces, i.e.: (1) the evaporator pressure, (2) the spring pressure of an internally adjustable spring, and (3) the pressure exerted by the saturated liquid-vapor mixture in the
• OMPI valve remote fluid-charged bulb The forces of (1) and (2) are balanced against (3).
• the forces generated by the fluid-charged bulb result from the heating of the remote bulb clamped to the suction line at the outlet of the evaporator coil due to the superheat of the refrigerant vapor leaving the evaporator coil.
• thermosatic expansion valves fail at low ambient temperatures or when one or more of the following conditions exist:
• the basic problem is that the superheat adjustment of the thermostatic expan- sion valve is a function of the capacity of the valve. Therefore, a solution to the problem is to introduce a control method which is not functionally related to the capacity of the valve. Adding heat to the remote fluid-charged bulb of the thermostatic expansion valve results in improving the control of the expansion valve. Controlling the heat applied to the bulb pro ⁇ vides a technique for correcting the superheat adjust ⁇ ment of the valve.
• thermosta ⁇ tic valve is used to control the diversion of hot gas from the hot gas side of the condenser to the evaporator ' inlet line in a refrigeration system. This gas is diverted to the evaporator to raise the temperature of the evaporator and reduce ..the capacity of the system. This technique is often used in automo ⁇ bile air conditioning or other refrigeration systems where the compressor speed of the system is unrelated to refrigerator or air conditioning load requirements.
• the thermostatic valve has a fluid-charged bulb that is placed in the air flow path through the evaporator coil. As the air temperature rises, the bulb is heated and throttles the operation of the valve to decrease the quantity of hot gas diverted into the evaporator.
• valve in automobile air conditioning systems an operator adjusted means for controlling the tempera ⁇ ture of the conditioned air is necessary, and an opera ⁇ tor adjusted means of heating the valve remote bulb is disclosed to control the operation of the valve and hence the hot gas diverted into the evaporator.
• the valve is not used in the capacity of an expansion valve to meter refrigerant into the evapora ⁇ tor coil of the system, the control of which in a thermostatic expansion valve is dependent on the super ⁇ heat across the evaporator coil.
• the disclosed device does not control the heat applied to the bulb by means of the cooling capacity of the refrigerant itself, nor can it function to correct the superheat adjustment of a thermostatic expansion valve independent of a pressure drop across the valve.
• U.S. Patent No. 2,735,272 discloses a liquid level control device for establishing a desired maximum level of liquid in a container, and is particularly suited for establishing a predetermined level of liquid refri ⁇ gerant in a tank supplying the evaporator unit in a refrigeration system.
• the disclosed liquid level control device utilizes a heater coil to heat the remote bulb of a thermostatic expansion valve metering refrigerant into an evaporator header tank to maintain a desired refrigerant level in the tank.
• a low output heating element is used to heat a specially designed valve remote fluid-charged bulb.
• Heating the bulb maintains the valve open until the cold liquid refri ⁇ gerant level reaches the bulb location and cools the bulb at a rate faster than the low output heating element can heat the bulb. Coding the bulb closes the valve and establishes the liquid level at the location of the bulb.
• the heater element is built into the remote bulb and is not adapted for attachment externally to the bulb alone where the bulb has been clamped in a heat exchange relationship with the re ⁇ frigerant line..
• the disclosed control does not suggest correction or adjustment of the superheat of the valve measured across the evaporator coil, since the disclosed device functions only in connection with controlling the liquid level of a liquid refriger ⁇ ant.
• the present invention remedies the problems of the prior art by providing in one embodiment of the invention an improved control for a thermostatic expansion valve metering refrigerant fluid into a refrigeration system evaporator coil, having heating means for applying heat to the expansion valve fluid-charged bulb that has been clamped in a direct heat exchange relationship to the refrigerant line near the outlet of the evaporator coil, and a thermal conductor mounted on the bulb in a heat exchange relationship therewith and cooperating with the heating means for transferring heat directly to the bulb at a rate less than the cooling rate of the liquid refrigerant present in the line at the bulb location.
• apparatus for improving the superheat control of a thermostatic expansion valve metering refrigerant into a refrigeration system evaporator coil having a superheat setting means for establishing a required superheat, superheat determination means for measuring the superheat of the valve across the evapo ⁇ rator coil, differential means for comparing the measured superheat with the established superheat, and heating means cooperating with the differential means for apply ⁇ ing heat to the fluid-charged bulb of the valve when the measured superheat exceeds the established super ⁇ heat.
• a heating control means may also be included to control the heating means for increasing the rate of heating by the heating means when the measured super ⁇ heat exceeds the required superheat, and for decreasing the rate of heating by the heating means when the required superheat exceeds the measured superheat.
• one primary feature of the present invention is to provide a means of improving the control of a thermostatic expansion valve independent of the pressure drop across the valve by adding heat to the valve fluid-charged bulb.
• Another feature of the present invention is to provide a means of improving the superheat control of a thermostatic expansion valve to control the valve independent of the pressure drop across the valve by adding heat to the valve fluid-charged bulb when the measured superheat across the evaporator coil exceeds an established superheat.
• CMPI Still another feature of the present invention is to provide a means of controlling the rate of application of heat to the valve fluid-charged bulb in response to the differences in the measured superheat and the established superheat.
• Figure 1 is a schematic representation of a con- ventional refrigeration system employing the present invention for adding heat to the fluid-charged bulb of the thermostatic expansion valve.
• Figure 2 is a ' schematic representation of one embodiment of the invention for controlling superheat of a thermosatic expansion valve.
• Figure 3 is a schematic representation of a second embodiment of the invention for controlling superheat of a thermostatic expansion valve.
• Figure 4 is a graphical representation of the
• Figure 5 is an enlarged fragmentary view of the mounting of the valve fluid-charged bulb on the suction line and the mounting of the heating means and thermal conductor on the bulb.
• Figure 6 is a vertical cross-sectional view of the heating means, bulb and suction line taken along line 6-6 of Figure 5.
• FIG. 1 a simplified schematic representation of a typical refrigeration system 10 is shown having a compressor 12 and condenser coil 14 for condensing the compressed refrigerating fluid from a vapor state to a liquid state.
• a conventional thermo ⁇ static expansion valve 18 receives the condensed liquid refrigerant from the condenser coil through tubing 16.
• the expansion valve 18 controls or meters the flow of liquid refrigerant into the evaporator coil through tubing 20 where the cold liquid refriger ⁇ ant is vaporized by heat exchange with the refrigera ⁇ tion load (not shown) .
• the refrigerant in the vapor state returns through suction line tubing 24 to the compressor 12 for compression and recycling in the closed loop refrigeration system.
• the expansion valve 18 is a conventional thermosta ⁇ tic expansion valve which functions to maintain a con ⁇ stant degree of superheated refrigerant vapor in the suction line 24 as the vapor exits the evaporator coil 22.
• Such a thermostatic expansion valve 18 typi-
• CMFI cally includes a remote fluid-charged bulb 26 which is attached in a thermal heat exchange relationship to the suction line 24 near the outlet from evaporator coil 22 by means of a clamp or strap 25...
• the bulb 26 is heated to the same temperature as the refrigerant in suction line 24 which vaporizes some of the liquid in the bulb 26.
• the pressure exerted by the saturated liquid-vapor mixture in the remote bulb 26 is communi ⁇ cated to the expansion valve 18 through a capillary tube 27.
• the characteristic operation of the thermo ⁇ static expansion valve results from the interaction of three forces: (1) the evaporator pressure and (2) the pressure exerted by an internal and adjustable valve spring acting against (3) the pressure exerted by the liquid-vapor mixture of the remote bulb.
• the superheat setting of valve 18 determines how much of the evapo ⁇ rator coil 22 surface will be utilized. A low superheat setting utilizes a greater percentage of the evaporator coil 21 surface.
• the superheat control 30 is shown for adding heat to the remote bulb 26 as will be here ⁇ inafter explained in greater detail.
• the present invention provides an improved con ⁇ trol for a thermostatic expansion valve 18 metering refrigerant fluid into an evaporator coil 22 by provid- i ng a heating means (control circuit 38 and heater 40) for applying heat to the fluid charged bulb 26 clamped in a direct heat exchange relationship to the suction line 24 near the outlet of the evaporator coil 22.
• the heating means includes a heater 40 which may con ⁇ veniently be a resistive heater coil housed in a suitable houseing or container 44, such as a case of epoxy resin or the like.
• a clip 42 of thermally con ⁇ ducting material cooperates with the heater 40 and is adapted for mounting directly on the remote bulb 26 for applying heat directly to the bulb.
• the heat applied to bulb 26 causes the expansion valve 18 to open for increasing the quantity of refrig ⁇ erant metered into the evaporator coil 22.
• the thermal conducting clip 42 limits the transfer of heat from heater 40 to the bulb 26 at a rate less than the coolirig rate of the liquid refrigerant present in the line 24 at the bulb location.
• the rapid cooling of bulb 26 by the liquid refrigerant in suction line 24 will rapidly overcome the heating effect applied by the heating means through thermal conductor 42 and rapidly cause the valve 18 to decrease the quantity of refrigerant metered into the evaporation coil 22.
• De ⁇ creasing the quantity of refrigerant admitted into evaporator coil 22 prevents further liquid refrigerant from reaching the remote bulb ' 26 location on suction line 24.
• the rate of cooling of bulb 26 is decreased until the quantity of heat applied by the heating means again effects the liquidvapor mixture pressure exerted by bulb 26 on valve 18 to open the valve and increase the quantity of refrigerant metered into evap ⁇ orator coil 22.
• control 30 includes appa ⁇ ratus for improving the superheat control of a thermo ⁇ static expansion valve 18 metering refrigerant into an evaporator coil 22, including a circuit 38 for receiving superheat temperature information from temperature sens ⁇ ing devices 32 and 34, attached to the inlet line 20 of evaporator 22 and to the suction line 24 adjacent remote bulb 26 and the outlet of evaporator 22, re- spectively.
• Devices 32 and 34 may conveniently be attached to the refrigerant lines 20 and 24 by means of clips or straps 36.
• Temperature information from temperature sensing probes 32 and 34 is applied to control circuit 38 through conductors 33 and 35, re- spectively.
• Control circuit 38 utilizes the superheat temperature information received from probes 32 and 34 to control a heating means 40 mounted in a heat exchange relationship to remote bulb 26 for heating the bulb. Such heating permits controlling the superheat sensed by bulb 26 for correcting the superheat adjustment of valve 18 'without changing the mechanical superheat setting of the thermostatic expansion valve.
• heating means 40 may be mounted directly on the bulb 26 by means of a thermally conducting member 42.
• the clip or thermal conductor member 42 may con ⁇ veniently be a metal clip that surrounds the heater coil 40 and has a pair of descending spring-clip legs 42* .
• the upper portion of member 42 and heating coil 40 may conveniently be cast into an epoxy resin block or body 44 for providing a degree of insulation for coil 40 and member 42 and a means for storing heat.
• the spring-clip legs 42* are clipped over the body of bulb 26 to provide a direct heat exchange relationship with bulb 26, but not with the refrigeration suction line 24 to which the bulb is shown clamped by clamp 25.
• the clip 42 may be constructed of any suitable thermally conducting material but sized to limit the heat transfer from heater 40 to bulb 26 to a rate less than the cooling rate of- the refrigerant present in suction line 24 at the bulb 26 location.
• the temperature probes 32 and 34 may be any appropriate temperature responsive sensing means that will detect temperature and generate an electrical signal representative thereof, such as a temperature responsive diode or a thermistor.
• the temperature sensing devices 32 and 34 are shown as temperature responsive diodes (32 and 34) having their cathodes connected in parallel to ground potential through conductor " 46.
• the anode of the inlet diode 32 is connected through conductor 33, biasing resistor 50 and conductor 52 to a source of positive Voltage (+V) .
• the anode of the outlet diode 34 is connected through conductor 35, resistors 48 and 49 and conductor 52 to a source of positive voltage (+V) in parallel with diode 32.
• the resistor 49 acts as a biasing resistor for diode 34
• resistor 48 is a resistor that functions as a superheat setting means for establishing a required superheat for the valve 18.
• Resistors 48 and 49 comprise a voltage level establishing means or a voltage divider network.
• the anode of diode 32 is also connected through conductors 33 and 55 as one input to a differential amplifier 56.
• the anode of diode 34 is also connected through conductor 35, resistor 48 and conductor 53 as a second input to amplifier 56.
• the output of amplifier 56 is applied through conductor 57 to an integrating circuit 58.
• a variable voltage signal output from integrator 58 is applied through conductor 59 to a voltage controlled oscillator (VCO) 60.
• VCO voltage controlled oscillator
• the variable voltage input signal to oscillator 60 causes the oscillator to generate a variable frequency output signal the frequency of which increases or decreases in a functional relationship to the increase or decrease in voltage of the received integrator signal.
• the oscillator output signals are applied through conductor 61 as an input to a conventional pulse gener ⁇ ating circuit 62.
• Pulse circuit 62 receives the var ⁇ iable frequency output signals from oscillator 60 and generates in response thereto a series of voltage pulses for application to the heating means 40 through
• Heating means 40 may be., any desired thermal energy source such as a resistive heating element as hereinabove described. Of course, other suitable thermal energy sources may be utilized.
• the temperature responsive diodes 32 and 34 detect the refrigerant temperature at their respective locations on the refrigerant lines 20 (inlet) and 24 (outlet) of the evaporator coil 22. Since the refrigerant vapor will be superheated as it leaves evaporator coil 22 through suction line 24, and the refrigerant will be in its liquid (cold) state as it enters coil 22 through line 20, the difference in voltage at the anodes of diodes 32 and 34 will be an approximate measure of the super ⁇ heat of the refrigerant at the outlet of the evaporator coil 22. Diodes 32 and 34 respond to temperature by increasing conduction as the temperature rises, there ⁇ fore, as the temperature increases the voltage across the diodes decreases.
• the voltage signal level produced at the anode of diode 32, and applied to amplifier 56 via conductor 55, will also generally always be higher than the voltage signal level appearing at the anode of diode 34.
• voltage setting means 48 when voltage setting means 48 is set for a required superheat setting, the series addition of the anode voltage appearing on conductor 35 and the voltage drop on the leg of resistor 48 combine to produce a third voltage signal applied as the second signal input to amplifier 56 through con- ductor 53.
• the differential amplifier 56 compares the voltage signals applied as inputs and generates an output signal (Vy) representative of the differences in the input signals (i.e., the superheat).
• Vy an output signal representative of the differences in the input signals (i.e., the superheat).
• the V ⁇ output signal will be positive or negative depending on whether the irst ' voltage signal from diode 32 (inlet) applied through conductor 55 to amplifier 56 exceeds or is less than the combined third signal from diode 34 (outlet) and voltage divider 48 applied through conductor 53 to amplifier 56.
• the voltage signal on input 55 to amplifier 56 exceeds the voltage signal on input 53
• the measured superheat exceeds the required super ⁇ heat.
• the required superheat exceeds the measured superheat.
• V ⁇ p applied to integrator 58 are integrated and an integrator output voltage signal (Vj) is generated for application as an input to VCO 60.
• Vj integrator output voltage signal
• the voltage of the integrator output signal increases or decreases in a functional relationship to the differences beween the voltage inputs to amplifier 56 as hereinabove described. Accordingly, V ⁇ will increase in a functional relationship to the differences in the input signals to amplifier 56 when the measured superheat exceeds the required superheat, and will decrease in a functional relationship to the differences in the input signals to amplifier 56 when the required superheat exceeds the measured superheat.
• the integra- tor variable voltage signal Vj is applied to the VCO 60 as hereinabove described to produce output signals the frequency (fj) of which are functionally related to the voltage level of the input V j signals.
• the vari ⁇ able frequency voltage pulses generated by pulse gene- rator 62, as hereinabove described, are applied to heating means 40 for increasing or decreasing the rate of heating by the heater 40.
• the frequency of the voltage pulses from pulse genera ⁇ tor 62 will increase, thus increasing the rate of heating by heater 40 and adding heat to the remote bulb 26. Increased heating of bulb 26 will cause the valve 18 to open further to meter an increased quantity of cold liquid refrigerant into the evaporator coil 22, thus tending to decrease the measured superheat until it equals or is lower than the required superheat.
• the required superheat exceeds the measured super ⁇ heat across the evaporator coil 22
• the frequency of the voltage pulses from pulse generator 62 will de ⁇ crease, thus decreasing the rate of heating by heater 40 and applying less heat to the remote bulb 26. Applying less heat to bulb 26 will cause throttling of the valve 18 to meter a decreased quantity of cold liquid refrigerant into the evaporator coil 22, thus tending to increase the measured superheat until it equals or exceeds the required superheat.
• FIG. 3 a second simplified embodiment of the control circuit 38 is shown.
• the temperature sensing means 32 and 34 are arranged in electrical parallel with the voltage divider 48 and 49 disposed in series with diode 34 as hereinabove previously described. Since the function of the temperature sens ⁇ ing devices 32 and 34 and the voltage divider 48 and 49 are identical to the functions hereinabove described, no further description will be given here.
• the voltage signals from the temperature measuring circuit are applied as identical inputs to those hereinabove des-
• thermal mass 70 interposed in a heat exchange relation ⁇ ship between heating means 40 and the valve remote fluid charged bulb 26 for stabilizing the rate at which the heating means 40 applies heat to the bulb 26.
• Thermal mass 70 acts as a thermal integrator to stabilize the heating rate of bulb 26, rather than having a cut-on (heating) or cut-off (no heating) mode of operation.
• valve capacity vs. the superheat setting is shown in Figure 4 as curve 80 for a predetermined condenser line pressure and evaporator pressure.
• a preferred mechanical super ⁇ heat setting of 10° may provide approximate ⁇ ly 55% capacity of the valve.
• the capacity vs. superheat curve 80 is shifted to 80', and the 10° superheat setting will only yield a partially fed evaporator coil due to a reduction in capacity to 25% as shown at 84.
• the capacity (C) of the valve can be expressed as follows:
• curve 80 is the capacity of the valve 18 vs. the valve superheat with a 10° superheat setting shown as point 82, corresponding to a 55% valve capacity as hereinabove described.
• the curve 80 can be shifted to curve 86 (dotted line curve) and the required superheat may be lowered to 5° of superheat as shown at point 82' while retaining the same 55% valve capacity as previously described.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Control Of Temperature (AREA)
• Temperature-Responsive Valves (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

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ID=22161239

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Cited By (13)

Citations (6)

Family Cites Families (1)

• 1981
  • 1981-05-20 WO PCT/US1981/000682 patent/WO1982004142A1/en not_active Application Discontinuation
  • 1981-05-20 AU AU73218/81A patent/AU7321881A/en not_active Abandoned
  • 1981-05-20 JP JP50215381A patent/JPS58500771A/ja active Pending
  • 1981-05-20 EP EP19810901773 patent/EP0079331A4/en not_active Withdrawn

Patent Citations (6)

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