TEV & EEV

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TEV & EEV. 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. - PowerPoint PPT Presentation

Transcript of TEV & EEV

Diapositiva 1*
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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.
TEV
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.
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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.
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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.
BALANCE
TEV
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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
Refrigeration capacity [W]
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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.
Why an EEV?
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The wide range of operation at various differential pressures and the precision terms of control allows significant energy savings.
Why an EEV?
From 20 to 35% energy saving
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What are the characteristics of Uniflair EEV?
1) Compatibility with all types of refrigerants and a very wide capacity range:
Logistic: drastically reduce the number of models of EEV that are used in the various units;
Control range: they work in a very large range of operating conditions;
Energy saving: an increase of around 2% in efficiency can be expected for each °C decrease in condensing temperature. (the compressors controlled in ON-OFF mode have reduced ON times, while those with capacity control or inverter control operate at a lower rate for the same capacity).
2) Precision in the modulation of the refrigerant flow (thanks to the long stroke of the nozzle):
Stable and precise superheat set point control;
If a bi-directional EEV is used in a reverse-cycle heat pump, only one EEV; needs to be installed instead of the two TEVs in the traditional solution.
3) Microprocessor control:
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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.
EEV System
The E2V, E3V and E4V series electronic expansion valves cover
a range of cooling capacities from 1 kW to 250 kW.
E2V
Large rangeability (15 mm stroke);
High-level materials;
Mechanical precision;
Bi-directional mounting;
Equipercentage flowrate;
The E3V and E4V valves completes the range of electronic expansion valves for medium–large capacity air-conditioning units:
Same reliable design and materials of E2V;
Up to 250 kW;
Bi-directional mounting;
Operating specifications of E2V
Maximum Operating Pressure (MOP)
up to 42 bars
Maximum Operating DP (MOPD)
Refrigerant temperature
-30T50°C (-22T122°F)
E2V stator Two pole low voltage stator (2 phases - 24 polar shoes)
Phase current
450 mA
Drive frequency
50 Hz
Phase resistance
Index of protection
Step angle
LOW SUPERHEATING
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BI-DIRECTIONAL MOUNTING
PIN LENGTH
This gives a good compromise between theoretical and mechanical resolution:
- Precise refrigerant modulation
the single step has no effect on refrigerant flow
EEV
TEV
PROPORTIONAL MODULATION
Axial movement of the pin gives perfect linearity in refrigerant flow.
Refrigerant flow (kg/h)
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The control of the electronic valve can be divided into two categories:
Superheat control with reference to the corresponding set point.
Control of unit safety with protections:
they are activated only if the pressure or temperature reach dangerous values that can be set by the user.
Control Features
Superheating Control Parameters
The superheat control function involves calculating the position of the valve based on the measure of the superheating and the corresponding set point.
Valve opening at start-up
Valve opening at start-up:
Defines the percentage of opening steps that the valve will reach immediately and before to start the superheating control. It should be set as near as possible the normal working position.
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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.
Superheating Control Parameters
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.
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Superheating Control Parameters
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.
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Superheating Control Parameters
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):
PID - integral time:
It’s defined by the parameter Ti. The integral action is related to time and makes the valve move in proportion to how far the superheat temperature is away from the set point.
The higher the difference, the more intense the integral action; the lower the integration time (Ti), the more intense the integral action.
The integral action is required to ensure that the superheat reaches the set point. Without this, in fact, the proportional action alone may stabilise the superheat at a value different respect to the set-point.
PID - derivative time:
It’s defined by the parameter Td. The derivative action is related to the speed with which the superheat varies, that is, the instant-by-instant gradient of superheat variation.
This action tends to contrast sudden variations in the superheat, bringing forward the corrective action; the effect is more intense the higher the time Td.
Superheating Control Parameters
The software that manages the valve includes 4 protection functions:
1. LowSH (low superheat) protection:
It acts quickly to close the valve in the event where the superheat is too low, to prevent the return of liquid to the compressor.
2. MOP (high evaporation temperature) protection:
It acts moderately to close the valve and limit the evaporation temperature if this reaches excessive values, so as to prevent the compressor from stopping due to thermal overload.
Protection Control Parameters
3. LOP (low evaporation temperature) protection:
It acts quickly to open the valve when the evaporation temperature is too low, to prevent the compressor from stopping due to low pressure.
4. HITCond (high condensing temperature, optional) protection:
It can only be enabled if the controller measures the condensing pressure/temperature. It acts moderately to close the valve if the condensing temperature reaches excessive values to prevent the compressor from stopping due to high pressure.
Protection Control Parameters
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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.
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):
Settings Guide
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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.
Dimensions
Positioning the valve
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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!
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
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.
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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.
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Evaporator pressure transducer
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.).
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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.
Electrical valve connections
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Pay attention to the polarity: contact number 4 is wider than the others so don’t force, otherwise the valve will not open correctly.
Electrical valve connections
User interface for programming the parameters;
Local network connection (tLAN, pLAN, RS485 supervisor).
If the driver is not compatible with the pLAN or tLAN, the driver must operate in stand-alone mode, activating and deactivating the control of the valve based on the status of the digital input:
digital input open: the driver closes the valve and deactivates control;
digital input closed: the driver opens the valve and starts control.
EVD Family Drivers
EVD4 Driver
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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.
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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.
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EVD4 User Interface
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.
4-pin connector
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;
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• check the box containing the value of the parameter;
• click the right mouse button;
• set the new value;
• Press ENTER.
To reverse the value of a digital parameter (red or green rectangle):
• check the box containing the value of the parameter;
• click the right mouse button.
Meaning of the red or green rectangle:
- GREEN = FALSE or OFF or 0 or DISABLED, in relation to the meaning of the reference parameter;
RED = TRUE or ON or 1 or ENABLED, in relation to the meaning of the reference parameter.
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EFFECT OF K
Increasing the value of the proportional gain, increases the reactivity of the valve, to the limit where this may cause instability and not reach the set point with precision. This depends on the ratio between the circuit capacity and the valve capacity, and on the maximum number of valve control steps.
Proportional action
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The proportional action follows the logic whereby the greater the error, instant by instant, the more intense the action on the process so as to bring the controlled variable to the desired value.
Proportional action
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Example with three different values of K applied to the controller.
Higher values of K grant a quicker reaction, but create swings, lower values grant slower reactions and more difficulties reaching the SH set-point.
Proportional action
EFFECT OF Ti
Increasing the value of the integral time Ti, the valve reaches the set point more slowly but avoids excessive swings. This depends on the type of evaporator and the inertia of the circuit.
Integral action
The integral action is used to guarantee that the error is null in steady state. Indeed, the integral action is not zero if there is no error; quite the opposite, if for example the error remains stable, it continues to increase linearly, following the principle whereby “until the controlled variable decides to move in the
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The integral action, by definition, does not make “jumps” and therefore is the slowest to react. Indeed, it has almost no effect during the initial transient periods: these periods are dominated by the other two actions. To define the integral time, the P+I actions are considered.
Integral Action
Proportional Action
Ti integral time:
increasing “C”, the action made from “A” will be slow and precise.
Integral action
EFFECT OF TD
Increasing the value of the derivative time TD decreases swings, however there may be fluctuations around the set point.
Derivative action
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The derivative action “tries to understand where the error is going and how fast it is moving” and reacts as a consequence; the parameter TD determines how far into the future the prediction is made.
The derivative action is the fastest to react (including to measurement noise, unfortunately) and it is only helpful if the prediction is good, that is, if TD is not too high compared to the temporal changes in the error: the difference can be seen by examining cases A and B in the figure.
Derivative action
EEV Tester
EEV tester can perform three types of tests on stepper motor electronic expansion valve:
1) Measurement of motor windings resistance:
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EEV Tester
EEV tester can perform three types of tests on stepper motor electronic expansion valve:
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EEV Tester
EEV tester can perform three types of tests on stepper motor electronic expansion valve:
2) Forced opening or closing of the valve:
Opening
Closing
EEV Position
With this parameter, the regulation function of the EVDriver (AUTO setting) is…