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TEV & EEV PowerPoint Presentation

TEV & EEV

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TEV & EEV

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  1. TEV & EEV

  2. TEV All air conditioning units commonly use a traditional thermostatic expansion valve (TEV) as the expansion device: this is the standard component fitted with a sensor bulb and, in more recent models, a pressure fitting for external compensation. TEV has a number of characteristics that, in many aspects, limit the versatility of the installation and the performance that could be achieved.

  3. TEV BULB REGULATING SCREW EXTERNAL EQUALIZATION TO EVAPORATOR LIQUID LINE

  4. TEV A thermostatic expansion valve is built up around a thermostatic element separated from the valve body by a diaphragm. A capillary tube connects the element to a bulb and a valve body with valve seat and a spring. The bulb is usually charged with the same operating refrigerant.

  5. TEV TEV meters the flow of liquid refrigerant entering the evaporator at a rate that matches the amount of refrigerant being boiled off in the evaporator. This is it's main purpose but like all the other metering devices it also provides a pressure drop in the system, separating the high pressure side of the system from the low pressure side, thus allowing low pressure refrigerant to absorb heat onto it's self. The valve itself has 3 forces that act upon each other to accomplish this task: P1  Bulb pressure acting on the upper surface of the diaphragm, in the valve opening direction. P2  Evaporating pressure acting on the underside of the diaphragm, in the valve closing direction. P3  Spring pressure acts on the underside of the diaphragm, in the valve closing direction, and is used to set the superheating.

  6. TEV The external pressure equalization is used when the evaporator creates a large pressure drop (plate evaporators, coil evaporator with a capillary distributor). In this case, the pressure P2 is not affected by the pressure drop, therefore the balance of the diaphragm is more stable. EXTERNAL EQUALIZATION NO EQUALIZATION BALANCE

  7. TEV To keep the superheating at 8 °C, the regulating screw has to be adjusted to create the pressure P3

  8. TEV A = SS = Static Superheat B = OS = Opening Superheat C = SH = SS + OS =TotalSuperheat Example: Static superheat SS=4°C (factory setting). Opening superheat OS=4°C. The opening superheat is 4°C, i.e. the point from which the valve begins to open up to nominal capacity. Opening superheat is determined by the design and cannot be changed. Total superheat: SH = SS + OS = 4 + 4 = 8 °C Total superheat SH can be changed by changing SS (by using the regulating screw). For a good selection of the valve, the residual capacity must be 20% of the total capacity valve completely open residual capacity Nominal capacity Refrigeration capacity [W] Superheating [°C]

  9. Whyan EEV? The main advantages concerning the efficiency of an electronic expansion valve (EEV) compared with the TEV are, basically, in three items: Quicker response time for changes, stable superheat in the whole range of operation conditions, both for full as well as part load operation. The improvement on the COP is highly significant. The more the operation conditions vary, the more the advantages of EEV get measurable.

  10. Whyan EEV? From 20 to 35% energy saving The wide range of operation at various differential pressures and the precision terms of control allows significant energy savings. The EEV permits the operation of the unit at significantly low condensing pressures: in fact the only limits are the minimum ΔP compatible with the compressor used and outside temperature.

  11. Whyan EEV? • What are the characteristicsofUniflair EEV? • 1) Compatibilitywithalltypesofrefrigerants and a very wide capacityrange: • Logistic: drastically reduce the numberofmodelsof EEV that are used in the variousunits; • Controlrange: they work in a verylargerangeofoperatingconditions; • Energy saving: anincreaseofaround 2% in efficiency can beexpectedforeach °C decrease in condensing temperature. (the compressorscontrolled in ON-OFF mode havereduced ON times, whilethosewithcapacitycontrol or inverter control operate at a lower rate for the samecapacity). • 2) Precision in the modulationof the refrigerant flow (thanksto the long strokeof the nozzle): • Stable and precise superheat set pointcontrol; • If a bi-directional EEV isused in a reverse-cycleheatpump, onlyone EEV; needstobeinstalledinsteadof the twoTEVs in the traditionalsolution. • 3) Microprocessorcontrol: • MOP (maximumoperatingpressure); • LOP (lowestoperatingpressure); • HiTcond and Lownoise.

  12. EEV System EEV is a servo-controlled and electro-mechanic device which expands the flow of refrigerant in a variable manner, using commonly a pressure sensor and a temperature sensor (corresponding to the pressure fitting for compensation and the sensor bulb in the TEV). Both these sensors are fitted to the evaporator outlet, and the measurements are read and processed by a controller that decides the best degree of opening of the valve in real-time.

  13. Carel EEV Range The E2V, E3V and E4V series electronic expansion valves cover a range of cooling capacities from 1 kW to 250 kW. E2V

  14. EEV TechnicalFeatures • The best features of the E2V are: • Large rangeability (15 mm stroke); • High-level materials; • Mechanicalprecision; • One code forall the refrigerants; • Bi-directionalmounting; • Up to 50 kW; • Equipercentageflowrate; • The E3V and E4V valves completes the rangeof electronic expansionvalvesformedium–largecapacityair-conditioningunits: • Samereliable design and materialsofE2V; • Up to 250 kW; • Inspectionporthole (E4V); • Separated body for easy maintenance; • Bi-directionalmounting;

  15. TechnicalFeaturesof the E2V

  16. TechnicalFeaturesof the E2V LOW SUPERHEATING The superheating value can be lowered by decreasing the set point to the desired value: this feature of EEV control does not involve the risk of swings that are typical of a TEV.

  17. TechnicalFeaturesof the E2V BI-DIRECTIONAL MOUNTING

  18. EEV TEV TechnicalFeaturesof the E2V PIN LENGTH TEV usually has a pin about 1 mm long; E2V has 480 steps on a 15 mm pin. This gives a good compromise between theoretical and mechanical resolution: - Precise refrigerant modulation - Wide capacity modulation range With thousands of steps on few millimeters the single step has no effect on refrigerant flow

  19. TechnicalFeaturesof the E2V PROPORTIONAL MODULATION Axial movement of the pin gives perfect linearity in refrigerant flow. Refrigerant flow (kg/h) Valve opening (%)

  20. ControlFeatures • The controlof the electronic valve can bedividedintotwocategories: • Superheatcontrolwithreferenceto the corresponding set point. • Controlofunitsafetywithprotections: • they are activatedonlyif the pressure or temperature reachdangerousvaluesthat can be set by the user.

  21. SuperheatingControlParameters The superheatcontrolfunctioninvolvescalculating the position of the valve based on the measureof the superheating and the corresponding set point. Valve opening at start-up Superheatset-point PID - proportionalgain PID - integraltime PID - derivativetime • Valve opening at start-up: • Definesthe percentageof opening stepsthat the valve willreachimmediately and beforeto start the superheatingcontrol. Itshouldbe set asnearaspossible the normalworking position. • As aninitialapproximation, it can bedeterminedbycalculating the ratiobetween the coolingcapacityof the evaporator and the coolingcapacityof the valve. A 10 kW valve installed on a 5 kW evaporatorwillpresumably operate at 50 % opening.

  22. SuperheatingControlParameters 2. Superheat set-point: A low SH set point ensures better efficiency of the evaporator, a lower air or water temperature and the temperature control set point is reached more easily. Nonetheless, instability may be created in the system, with wider swings in the superheat and the return of liquid to the compressor. A high SH set point ensures greater system stability and less or negligible swings in the superheat. Nonetheless, this may penalise the efficiency of the evaporator and prevent the temperature control set point from being reached. • PID - proportional gain: • It’s defined by the parameter K. The proportional action opens or closes the valve whenever the superheat increases or decreases of 1°C. • Consequently, the higher the value of K, the faster the reaction of the valve to variate the superheating. The proportional action is fundamental, as it affects the speed of the valve response, however it only considers the variation in the superheat, and not the corresponding set point. • Therefore if the superheat does not vary significantly, the valve will essentially remain steady and the superheat set point may not be reached.

  23. SuperheatingControlParameters The advised range is given by the formula : Max Steps: the maximum regulation steps; QCIRC : the capacity in kW of the cooling circuit in normal operating conditions; QEEV: the capacity in kW of the EEV in the same conditions. In the event that multiple operating conditions exist which are noticeably different (cooling capacity, Te, Tc), it is necessary to use an average Kp from those which are calculated by the formula or from the tests carried out in different conditions generally favouring low values and reducing the integral protection terms (LOW, SH. MOP…)

  24. SuperheatingControlParameters If valves made by other manufacturers are used, the same recommended parameters can be used initially, modifying the “Proportional gain” based on the maximum number of control steps for the valve installed. Example of adapting the proportional gain for the different valves: Reference  CAREL E2V (480 maximum control steps): SPORLAN SEI - 1, (1596 steps): ALCO EX-5 (750 steps):

  25. SuperheatingControlParameters • PID - integraltime: • It’s definedby the parameterTi. The integralactionisrelatedtotime and makes the valve move in proportiontohow far the superheat temperature isawayfrom the set point. • The higher the difference, the more intense the integralaction; the lower the integrationtime (Ti), the more intense the integralaction. • The integralactionisrequiredtoensurethat the superheat reaches the set point. Withoutthis, in fact, the proportionalaction alone maystabilise the superheat at a valuedifferentrespectto the set-point. • PID - derivative time: • It’s definedby the parameterTd. The derivative actionisrelatedto the speedwithwhich the superheat varies, thatis, the instant-by-instantgradientof superheat variation. • Thisactiontendstocontrastsuddenvariations in the superheat,bringingforward the correctiveaction; the effectis more intense the higher the timeTd.

  26. ProtectionControlParameters The software thatmanages the valve includes 4 protectionfunctions: 1. LowSH (low superheat) protection: Itactsquicklytoclose the valve in the eventwhere the superheatistoo low, toprevent the returnofliquidto the compressor. 2. MOP (high evaporation temperature) protection: Itactsmoderatelytoclose the valve and limit the evaporation temperature ifthisreachesexcessivevalues, so astoprevent the compressorfromstopping due tothermaloverload.

  27. ProtectionControlParameters 3. LOP (low evaporation temperature) protection: Itactsquicklyto open the valve when the evaporation temperature istoo low, toprevent the compressorfromstopping due to low pressure. 4. HITCond (high condensing temperature, optional) protection: It can onlybeenabledif the controller measures the condensingpressure/temperature. Itactsmoderatelytoclose the valve if the condensing temperature reachesexcessivevaluestoprevent the compressorfromstopping due to high pressure.

  28. Settings Guide As concerns the control parameters, the following general indications can be used as a guide: Proportional gain (from 3 to 30): Increasing the proportional gain K increases the reaction speed of the valve and is recommended if the system is particularly perturbed or to make superheat control faster. If high (>20), may cause swings and instability. Integral time (from 40 to 400 sec): Increasing the integration time Ti improves stability but makes the valve slower in reaching the superheat set point. If lowered (<40 sec) generates swings and instability. If the system is already perturbed, high values (>150 sec) are suggested so as to avoid creating further disturbance. Derivative time (from 0 to 10 sec): Increasing the derivative time Td improves the reactivity of the valve, in particular in perturbed systems, reducing the amplitude of swings in the superheat. If high, may in turn generate excess reactivity and consequently swings.

  29. Settings Guide Protector thresholds: The thresholds used for the 4 protectors should be set based on the features of the system being controlled. All are expressed as temperatures (°C):

  30. ExplodedView

  31. Dimensions If the valve is undersized, the performance of the system will be affected, as it will not be possible to reach the desired temperature and the superheat will generally be high or greater than the set point. If, on the other hand, the valve is oversized, the problems may involve system “swings” (there may be wide variations in temperature, pressure and superheat), and consequently poor efficiency, or alternatively there may be the return of liquid to the compressor.

  32. Positioning the valve Always install a filter dryer before the refrigerant inlet; if the installation is bi-directional (flow of refrigerant in both directions, reverse-cycle heat pumps), a bi-directional liquid/gas filter should be fitted on both expansion valve connections, or other solutions can be used, depending on the layout of the installation.

  33. Positioning the valve In no circumstances is upside-down installation allowed, that is, with the stator facing downwards.

  34. Welding the valve Unscrew the locking nut and remove the stator (winding). If necessary, remove the connector if inserted. Before starting welding, wrap the body of the valve (without the stator) in a wet rag, to avoid overheating the inside parts. When finished welding, replace the stator and tighten the valve-stator locking nut. NO!

  35. Positioning the probes The ideal position for both probes is immediately at the evaporator outlet, so as to be able to measure the effective refrigerant superheat. Superheating measurement

  36. Suction temperature probe The position of this probe is extremely important, as it determines the accuracy of the superheat value and the speed of response to variations in this. The probe should be installed after the evaporator outlet, in a straight and horizontal section. Comparing the section of pipe to the face of a clock, the probe must be positioned at 12 o’clock for pipes with a diameter less than 22 mm, and at 4.30 or 7.30 for pipes with a diameter greater than or equal to 22 mm.

  37. Suction temperature probe All precautions must be taken to maximize the thermal coupling between the pipe and probe, conductive paste on the point of contact between the probe and the pipe, fastening the probe with a clamp. The probe cable must be looped in the immediate vicinity of the probe and then secured by elastic band. Finally, the pipe-probe assembly should first be covered with aluminium tape, and then with thermal insulating material.

  38. Evaporatorpressuretransducer Ratiometric transducer needs 3 wires. Operating voltage is supplied to the drive circuit from a power supply, and the gain of the drive circuit is adjusted in accordance with variations in the operating voltage to make the drive signal and the output signal proportional to the operating voltage. The pressure transducer must be installed near the temperature probe on the top of the pipe. It can be positioned away from the point of temperature measurement only if the section of pipe that separates the two probes does not contain devices that alter the pressure (heat exchangers, flow indicators, valves, etc.).

  39. Electrical valve connections Completely insert the stator into the valve body and tighten the locking nut. Never leave the stator in place without the locking nut or with the nut partially unscrewed because water may infiltrate inside. Fit the cable with the co-moulded IP67 connector, connecting it to the stator and fastening it carefully with the screw provided. IP67 protection is not guaranteed if the screw is not properly secured. Connect the wires on the other end of the cable to the terminals on the driver, carefully following the instructions shown on the driver instruction sheet, and observing the correct sequence of the colours. If connected incorrectly, the valve may not move or may move in reverse compared to the direction controlled by the driver.

  40. Electrical valve connections Pay attention to the polarity: contact number 4 is wider than the others so don’t force, otherwise the valve will not open correctly.

  41. EVD Family Drivers • The EVD family driversmainlydifferasregards: • Typeofpressuretransducer(ratiometric or 4-20 mA); • User interface forprogramming the parameters; • Local network connection (tLAN, pLAN, RS485 supervisor). • If the driver isnotcompatiblewith the pLAN or tLAN, the driver must operate in stand-alone mode, activating and deactivating the controlof the valve based on the status of the digital input: • digital input open: the driver closes the valve and deactivatescontrol; • digital input closed: the driver opens the valve and startscontrol.

  42. EVD Family Drivers

  43. EVD4 Driver EVD4 driver can operate independently (stand alone), connected to a supervisor to control the fundamental parameters by RS485, or connected to the pCO or μC2 controllers by tLAN.

  44. EVD4 Driver

  45. EVD4 Driver NOT USED

  46. EVD4 Driver

  47. EVD4 Driver Because the EVD4 driver communicates with pCO boards by tLAN, the addressing of the driver is required in order to allow the main board to recognize the correct driver. For example, if a unit has 2 refrigerant circuits, 2 E2V valves and 2 EVD drivers will be required. The addressing of the driver is as it follows: Circuit 1  Driver address: 1 Circuit 2  Driver address: 2 By default, the factory driver address is set to 2; in this case, if a replacement of the driver of the first refrigerant circuit is necessary, the address must be changed to 1. EVD4 User Interface allows the changing of addresses and other parameters.

  48. EVD4 User Interface • The software used to install EVD4 UI is available in the following configurations: • “EVD4_UI Address”, to set the address of the EVD4; • “EVD4_UI Key”, to program the key; • “EVD4_UI Stand Alone” to program the stand-alone EVD4; • “EVD4_UI MCH2” to program the EVD4 with μC2; • “EVD4_U positioner” to use the EVD4 as a positioner with 4 to 20 mA or 0 to 10 V. • This box is used to set the Driver+Valve system configuration values. • These parameters should be set and checked before activating the unit.

  49. EVD4 User Interface 4-pin connector • Service serial port allows access to the functions of the EVD4 via PC. To access this connector: • 1) Remove the cover by levering it with a screwdriver on the central notch; • 2) Locate the white 4-pin connector and insert the special converter cable. • 3) Connect the USB cable to the PC; if the EVD4 is not powered by the 24 Vac line, it will take its power supply from the serial converter. • Start EVD4 User Interface. • This serial port can be connected and disconnected without needing to remove the USB cable from the PC. tLAN

  50. EVD4 User Interface Preparing the user interface: The program does not require installation; simply copy the entire contents of the distribution directory to the required location on the hard disk. The program cannot run from the CD as it requires write access to the configuration files. Open the IN\EVD400UI.INI file from the path where EVD4_UI.exe is located and make sure that the Paddr parameter is set to 1. Start the EVD4_UI program using the shortcut icon to the application and not the EVD4_UI.exe fi le, then press COM SETUP and set: • Port = COM address of the serial port used to connect the USB converter; • Baud Rate = 4800 • Parity = NO PARITY • Byte Size = 8 • Stop Bits = 1 Press SAVE. Now, if the converter is connected to an EVD4, image of the driver will be displayed in the top left and the EVD version window will show the following data: • Firmware rev. = firmware version of the EVD4 connected; • Param key rev. = parameter key version (for future use); • Hardware rev. = hardware version; • Network address = network address of the main serial port;