US20160018154A1 - Sensor for coil defrost in a refrigeration system evaporator - Google Patents

Sensor for coil defrost in a refrigeration system evaporator Download PDF

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Publication number
US20160018154A1
US20160018154A1 US14/705,781 US201514705781A US2016018154A1 US 20160018154 A1 US20160018154 A1 US 20160018154A1 US 201514705781 A US201514705781 A US 201514705781A US 2016018154 A1 US2016018154 A1 US 2016018154A1
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United States
Prior art keywords
pipe
refrigerant
rods
evaporator
another
Prior art date
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Abandoned
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US14/705,781
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English (en)
Inventor
Greg Derosier
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Evapco Inc
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Evapco Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Evapco Inc filed Critical Evapco Inc
Priority to CA2947437A priority Critical patent/CA2947437A1/fr
Priority to US14/705,781 priority patent/US20160018154A1/en
Priority to MX2016014539A priority patent/MX2016014539A/es
Priority to PCT/US2015/029528 priority patent/WO2015171809A1/fr
Publication of US20160018154A1 publication Critical patent/US20160018154A1/en
Assigned to EVAPCO, INC. reassignment EVAPCO, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: DEROSIER, Greg
Abandoned legal-status Critical Current

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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
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • 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
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
    • F25D21/02—Detecting the presence of frost or condensate
    • 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
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
    • F25D21/002—Defroster control
    • F25D21/006—Defroster control with electronic control circuits
    • 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
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
    • F25D21/06—Removing frost
    • 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
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/11—Sensor to detect if defrost is necessary
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/226—Construction of measuring vessels; Electrodes therefor

Definitions

  • This invention relates primarily to industrial or commercial refrigeration systems. Specifically, this invention relates to systems for detecting an accumulation of frost on an evaporator and initiating a defrost cycle when the accumulation of frost reaches unacceptable levels.
  • frost detection systems such as those shown in U.S. Pat. Nos. 4,045,971 and 4,232,528, employ photoelectric sensors to detect the level of frost buildup on an evaporator coil.
  • the system in U.S. Pat. No. 4,831,833 uses an air velocity sensor in the air flow path to determine whether defrost should be initiated.
  • Another prior art system senses the differences in air temperature on each side of the evaporator in the refrigerated space as well as the temperature of the refrigerant leaving the evaporator.
  • the data from the sensors is processed to determine if there is a frost buildup requiring the initiation of the defrost cycle.
  • timed defrost systems The problem with prior art timed defrost systems is that the amount of water vapor in the air in the refrigerated area varies depending on a number of factors. Some of these factors include the humidity in the environment surrounding the space being cooled, the number of times the access door to the refrigerated area is opened, and the duration of such openings. The temperature in the area being cooled, the temperature of the evaporator, the velocity of the air passing through the evaporator and the evaporation of water from items stored in the cooled area, are all factors that also affect the rate of frost buildup. Usually, timed defrost systems must be set for the severe conditions when frost will accumulate most rapidly. When conditions are not so severe, there are unnecessary defrost cycles which waste energy and cost money. Conversely, if the timer is set for modest conditions, and actual conditions are more severe, then defrost cycles could be delayed beyond when they are needed thereby compromising system performance.
  • frost detection systems that rely on photoelectric sensors, such as that disclosed in the '971 patent, are only capable of sensing frost at a particular location on an evaporator.
  • frost buildup is not always regular or uniform, frost may build at locations away from the photoelectric sensor and not be detected. This will cause the evaporator to operate inefficiently because defrosting may be needed even though it is not detected due to the location of the sensors.
  • frost may build up near the sensor to a greater extent than at other locations causing defrost to be initiated when it is not needed.
  • Another deficiency of such systems is that they may not detect the buildup of transparent, clear ice.
  • the system in the '833 patent suffers from similar location-dependent deficiencies.
  • the inventors determined that there exists a need for a frost detection system that is more accurate, reliable and less expensive to implement than existing systems and which is unaffected by changes in the system due to changes in system components, or age or loss of refrigerant.
  • overfeed evaporator coil In an overfeed evaporator coil, more liquid is introduced into the coil than is evaporated by the coil. The excess liquid is called overfeed, which returns to the low pressure side accumulator. By overfeeding the evaporator, the inner surface is kept thoroughly wetted and thus achieves optimum heat transfer.
  • the ratio of liquid refrigerant to evaporated refrigerant in the vapor phase is referred to as the liquid mass ratio.
  • the liquid mass ratio is measured with a suitable sensor, including but not limited to a void fraction sensor. The sensor produces an output signal that is reflective of the amount of liquid in the refrigerant flow stream.
  • the sensor and its control system can measure a first or initial or full defrost liquid mass ratio, and use that ratio as the starting point for determining the trigger point for a defrost cycle.
  • the liquid mass ratio increases.
  • a control will signal that defrost of the coil is required.
  • the system can initiate defrost automatically upon receipt of such signal, or can be configured to alert a system operator to manually authorize system defrost.
  • the control system may optionally measure the liquid mass ratio, compare it to a first/initial liquid mass ratio and/or to a previous full defrost liquid mass ratio, and optionally use the new ratio, or optionally an average of prior full defrost liquid mass ratios, to use as the starting point for determining the trigger point for the next defrost cycle.
  • the system can be dynamic as it constantly adjusts to actual site and system conditions, and thus takes into account such factors as the age and possible loss of refrigerant.
  • the control system can also use input from the liquid mass ratio sensor to detect if an evaporator is operating at an optimum overfeed rate. The overfeed rate may not be optimum due to liquid feed valve settings or a reduction in heat transfer unrelated to frost on the coil.
  • a frost detection system for an evaporator which senses frost buildup by measuring the liquid mass ratio in or exiting from the evaporator coil.
  • a liquid mass ratio sensor is located in the evaporator coil.
  • a liquid mass ratio sensor is located between the evaporator coil and the compressor.
  • a frost detection system that need not take into account changes in the operating characteristics of the refrigeration equipment due to aging.
  • the frost detection system may be provided with a device that measures the heat load of the system, for example the air temperature into the coil relative to coil saturation temperature or the total flow rate of refrigerant (both liquid and vapor), and the heat load information is used to adjust the defrost point for specific liquid mass ratios detected by the liquid mass ratio sensor.
  • a frost detection system that is more accurate, reliable and less expensive to implement that existing systems.
  • a method for controlling and/or initiating the defrost cycle of an evaporator having the following steps: detecting a first capacitance between charged plates situated in the coil of an evaporator, or downstream of the coil; detecting a second capacitance between the charged plates; and initiating a defrost cycle when a difference between the first capacitance and the second capacitance equals or exceeds a predetermined amount.
  • the predetermined amount may be changed according to operator preference.
  • the difference between said first capacitance and said second capacitance corresponds to a difference in volumes of fluid passing between said charged plates.
  • the first capacitance is determined when said evaporator has little or no frost.
  • an apparatus for initiating coil defrost in an evaporator including a refrigerant evaporating heat exchange coil and a sensor for detecting the ratio of liquid refrigerant to refrigerant in a vapor phase.
  • Said sensor may be located in said coil, or between said coil and a condenser of said evaporator, more particularly between said coil and a compressor of said evaporator, and more particularly between said coil and a separator of said evaporator.
  • the refrigerant evaporating heat exchange coil is in a liquid overfeed evaporator.
  • an apparatus for initiating coil defrost in a refrigeration system including a refrigerant evaporating heat exchange coil and a liquid mass ratio sensor located in the coil, or downstream of said coil, wherein said liquid mass ratio sensor is a capacitance sensor.
  • the liquid mass ratio sensor may include a plurality (two or more) of spaced apart conductive elements conductively connected to a current source.
  • the sensor detects changes in capacitance due to changes in the amount of liquid between the spaced apart conductive elements.
  • the liquid mass ratio sensor is a parallel plate sensor.
  • the liquid mass ratio sensor is made of parallel plates configured to receive a charge, and where the sensor is configured to take capacitance readings that reflect a volume of liquid passing between the plates of the sensor.
  • the conductive elements may take the form of coils, cylinders, or other shapes.
  • the conductive elements of the sensor may be in the form of parallel concentric cylinders.
  • a first part of the capacitance sensor is the metal wall of the pipe through which the refrigerant is passing, and a second part of the capacitance sensor is an electrode situated in the interior of the pipe.
  • the internal electrode portion of the sensor consists of a plurality of parallel metal rods covered in an insulating material such as PTFE (Teflon). The rods are electrically connected together on one end. An electrical connection is made to an external electronics unit through an insulating pressure tight fitting.
  • the parallel rods are arranged in an arc spaced a radial distance from the inside pipe surface by insulating spacers located at each end of the rods.
  • the parallel rods are arranged in a plane across the interior space of the pipe.
  • the spacers and rods allow for free liquid flow under the rods (between the rods and the inside surface of the pipe).
  • the rods and the metallic pipe make a capacitive type sensor that is responsive to the amount of refrigerant flowing between the rods and pipe wall.
  • FIG. 1 shows a perspective view of a sensor according to an embodiment of the invention.
  • FIG. 2 shows an end view of the sensor shown in FIG. 1 .
  • FIG. 3 shows a cross-sectional view of the sensor shown in FIGS. 1 and 2 .
  • FIG. 4 is a representation of a refrigerant evaporating cooling system having a sensor according to an embodiment of the invention.
  • FIG. 5 shows an end view of a capacitance sensor electrode according to an embodiment of the invention.
  • FIG. 6 shows a cut-away perspective view of a capacitance sensor electrode according to the embodiment shown in FIG. 5 .
  • FIG. 7 shows a side perspective view of the capacitance sensor electrode shown in FIGS. 5 and 6 , removed from the pipe.
  • FIG. 8 shows an end view of a capacitance sensor electrode according to a different embodiment of the invention.
  • FIG. 9 shows a cut-away perspective view of a capacitance sensor electrode according to the embodiment shown in FIG. 8 .
  • FIG. 10 shows a side perspective view of the capacitance sensor electrode shown in FIGS. 8 and 9 , removed from the pipe.
  • FIG. 1 shows a sensor 2 according to one embodiment of the invention.
  • the sensor shown in FIG. 1 works on the basis of capacitance change due to the amount of liquid refrigerant between two charged plates. As mentioned above, this is only one embodiment of the invention according to which the amount of liquid refrigerant in the coil or leaving the coil may be determined according to any number of known methods.
  • the capacitance sensor includes charged plates in the form of concentric cylinders, 6 and 8 , see FIGS. 2 and 3 .
  • the sensor shown in FIGS. 1-3 is a 2-inch HBDX-SAM-Mark void fraction sensor (in gas-liquid two-phase flow, the void fraction is defined as the fraction of the flow-channel volume that is occupied by the gas phase or, alternatively, as the fraction of the cross-sectional area of the channel that is occupied by the gas phase).
  • the HBDX-SAM-Mark sensor may be purchased from HB Products of Denmark, but any sensor that detects capacitance change between charged elements due to changes in the amount of liquid between them can be used according to the capacitance detection embodiment of the invention.
  • Cylinder 6 is held in the refrigerant flow path of cylinder 8 (which may also serve as the sensor housing) by stacks 12 .
  • Stacks 12 are conductively connected to charged cylinders 6 and 8 .
  • the capacitance change which is very small, is detected by a sophisticated electronic circuit 18 and then output in a useable signal to control system 20 .
  • the sensor may include additional concentric cylinder 4 , held in the refrigerant flow path of cylinder 8 by supports 10 , and capacitance changes between cylinders 4 and 6 , between cylinders 4 and 8 , or between cylinders 4 , 6 and 8 may be used to compare changes in the amount of liquid between them over time.
  • a first part of the capacitance sensor is the metal wall of the pipe through which the refrigerant is passing, and a second part of the capacitance sensor is an electrode 22 situated in the interior of the pipe.
  • the internal electrode portion 22 of the sensor consists of an array of a plurality of parallel metal rods 24 covered in an insulating material such as PTFE (Teflon) supported in support elements 26 .
  • support elements 26 are plastic, and the surface of the support elements 26 that face the rods define a plurality of recesses 25 configured to receive and hold the rod ends in fixed and spaced positions.
  • the support elements may be held together by a connecting rod 29 connecting the support elements and drawing them together, either by threading through a threaded hole 31 in the supports, or by passing through a hole in the supports into a threaded nut, or by any other known method.
  • the rods are electrically connected together at one end.
  • the rods may be solid or they may be hollow.
  • the rods may have a cylindrical cross section, as shown in FIG. 5 , or they may have a cross-section having a different shape, including square, elliptical, pentagonal, hexagonal, etc.
  • the rods may be arranged in an arc proximate to the inside surface of the pipe as shown in FIG. 5 , or they may be arranged in a plane across the interior space of the pipe as shown in FIGS. 5-7 .
  • the diameter of the rods in the embodiment shown in FIG. 5 is 0.1875 inches, and the radial distance between the centerline of the metal portion of the rod and the inside of the pipe is about 0.375 inches.
  • the spacing between the rods and the pipe affects sensitivity, flow thickness measurement, and sensor output range.
  • a closer rod-to-wall distance increases sensitivity but can affect the flow stream if the liquid impacts the sensor structure, and can also decrease sensor output range with thicker liquids.
  • Preferred spacing between the centerline of the rod and the inside surface of the pipe is considered to be between 0.1 inches and 0.5 inches, with more preferred spacing at 0.25 inches to 0.45 inches, and most preferred spacing at 0.35 inches to 0.375 inches.
  • Other spacing between rods and pipe surface may be used according to different sensitivity, liquid thicknesses, and sensor output range considerations and requirements.
  • the rods 24 shown in FIG. 5 have a length of about 10.5 inches, but they may be of any convenient length. Longer rods make the capacitor plate area higher, which in turn increases the sensitivity of the sensor.
  • the number of rods shown in FIG. 5 was selected to cover about a third of the circumference of the pipe in which they are situated.
  • the rods are electrically connected to an external electronics unit with insulated wires 27 through an insulating pressure tight fitting 30 .
  • the parallel rods of FIG. 5 are spaced a radial distance from the inside pipe surface by insulating spacers 28 located at each end of the rods. The spacers and rods allow for free liquid flow under the rods (between the rods and the inside surface of the pipe). Together, the rods and the metallic pipe make a capacitive type sensor that is responsive to the amount of refrigerant flowing between the rods and pipe wall.
  • FIGS. 8-10 show an alternative embodiment of the invention according to which the rods are arranged in a plane across the internal space of the pipe.
  • FIGS. 8-10 show a larger number of smaller diameter pipes, according to another embodiment of the invention.
  • the liquid mass ratio sensor of the invention may be placed in the coil of the evaporator 14 (see FIG. 4 ), or it may be placed downstream of the evaporator, for example at location 16 .
  • the sensor orientation may be vertical, horizontal or some other angle. Whatever the orientation, the sensor is preferably exposed to the liquid and vapor flow in the evaporator or downstream of the evaporator, and the sensor response is reflective of actual changes in the amount of liquid refrigerant evaporated.
  • the user may select a particular sensor output for defrost initiation depending on the cost of initiating a defrost cycle (cost of system down-time) relative to the savings gained through capacity increase as a result of defrost.
  • the selected point for defrost initiation may vary with evaporator application and to user sensitivity to cost and/or efficiency. It is estimated that the capacity reduction (loss of cooling power/efficiency) due to frost effects can range from 5% to 25% or more.
  • the system of the invention may be set to initiate a defrost cycle when the sensor detects a change in the liquid mass ratio of 5%, 10%, 15%, 20% or more, which may correspond to reductions in capacity of anywhere from 5% to 25%.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Defrosting Systems (AREA)
US14/705,781 2014-05-06 2015-05-06 Sensor for coil defrost in a refrigeration system evaporator Abandoned US20160018154A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
CA2947437A CA2947437A1 (fr) 2014-05-06 2015-05-06 Capteur de serpentin de degivrage dans un evaporateur de systeme de refrigeration
US14/705,781 US20160018154A1 (en) 2014-05-06 2015-05-06 Sensor for coil defrost in a refrigeration system evaporator
MX2016014539A MX2016014539A (es) 2014-05-06 2015-05-06 Sensor para la descongelacion de bobina en un evaporador de sistema de refrigeracion.
PCT/US2015/029528 WO2015171809A1 (fr) 2014-05-06 2015-05-06 Capteur de serpentin de dégivrage dans un évaporateur de système de réfrigération

Applications Claiming Priority (2)

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US201461989080P 2014-05-06 2014-05-06
US14/705,781 US20160018154A1 (en) 2014-05-06 2015-05-06 Sensor for coil defrost in a refrigeration system evaporator

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CA (1) CA2947437A1 (fr)
MX (1) MX2016014539A (fr)
WO (1) WO2015171809A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160172606A1 (en) * 2013-07-31 2016-06-16 Basf Se Luminescent diaza-monoaza-and benzimidazole metal carbene complexes for use in electronic devices such as oleds
CN107490607A (zh) * 2017-06-29 2017-12-19 芯海科技（深圳）股份有限公司 一种利用蒸发管作为电极的凝霜传感器
US11035594B2 (en) 2016-12-12 2021-06-15 Evapco, Inc. Low charge packaged ammonia refrigeration system with evaporative condenser

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US4347709A (en) * 1981-01-19 1982-09-07 Honeywell Inc. Demand defrost sensor
US6264898B1 (en) * 1997-11-19 2001-07-24 The Titan Corporation Pulsed corona discharge apparatus
US8146421B2 (en) * 2008-02-08 2012-04-03 Pulstone Technologies, LLC Method and apparatus for sensing levels of insoluble fluids
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US9188381B2 (en) * 2013-03-21 2015-11-17 Evapco, Inc. Method and apparatus for initiating coil defrost in a refrigeration system evaporator
US9429352B2 (en) * 2012-02-28 2016-08-30 Lg Electronics Inc. Air conditioner and method of controlling the same

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US4347709A (en) * 1981-01-19 1982-09-07 Honeywell Inc. Demand defrost sensor
US6264898B1 (en) * 1997-11-19 2001-07-24 The Titan Corporation Pulsed corona discharge apparatus
US8146421B2 (en) * 2008-02-08 2012-04-03 Pulstone Technologies, LLC Method and apparatus for sensing levels of insoluble fluids
US20130031921A1 (en) * 2010-05-26 2013-02-07 Mitsubishi Electric Corporation Refrigerating and air-conditioning apparatus
WO2012062329A1 (fr) * 2010-11-12 2012-05-18 Hb Products A/S Système ou procédé pour mesurer la phase d'un fluide frigorigène dans un système de réfrigération
US20170131012A1 (en) * 2010-11-12 2017-05-11 HP Products A/S System or method for measuring the phase of ammonia in a cooling system
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160172606A1 (en) * 2013-07-31 2016-06-16 Basf Se Luminescent diaza-monoaza-and benzimidazole metal carbene complexes for use in electronic devices such as oleds
US11035594B2 (en) 2016-12-12 2021-06-15 Evapco, Inc. Low charge packaged ammonia refrigeration system with evaporative condenser
CN107490607A (zh) * 2017-06-29 2017-12-19 芯海科技（深圳）股份有限公司 一种利用蒸发管作为电极的凝霜传感器

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MX2016014539A (es) 2017-08-22
CA2947437A1 (fr) 2015-11-12

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