Simscape Refrigerant Loop Product - sherpa-eng.com · A refrigerant loop has 4 main intensive states: the high and low pressure, ... MIL/SIL/HIL - Comparison simulated data with tests

Simscape Refrigerant Loop Product

SHERPA ENGINEERING

12 avenue de Verdun 92250 LA GARENNE COLOMBES FRANCE

Tél. (33) 01.47.82.08.23 - Fax (33) 01.47.82.00.96

SA au capital de 412.400 € - APE : 7112B- SIRET : 413 367 228 00033

Aims

The product is an easy to use simscape simulator with simple GUI or HMI allowing to define:

- the different configurations of the physical system

- the different operating modes: start, stop, load variation

- the different defaults or dysfunctions: defaults on sensor, actuator, components

- the steady state or dynamic scenario to run in open or closed loop

- A quick start with the data of just a nominal point

- A possibility to do an automatic scaling of the model

R: this Matlab/Simulink/Simscape open model and simulator can be easily modified or customized by the

user to define its specific simulator.

Operating principles

The objective of refrigerant loop is to produce cooling thermal power that is transferred to air or water

with a good performance whatever the environmental conditions and to protect the components.

A refrigerant loop has 4 main intensive states: the high and low pressure, the condenser sub cooling and

the evaporator overheat.

The high pressure balance depends on the interaction between the compressor mass flow rate capacity

and the capacity of condenser which reduces the volumetric mass flowrate.

The low pressure balance depends on the interaction between the evaporator which generates

superheated refrigerant mass flow rate and the compressor capacity that removes the mass flowrate.

The condenser sub-cooling protects the expansion valve against chocking by expansion of vapor. It

depends on the refrigerant mass in the system and mainly in the condenser. This sub-cooling is set up

during the loop filling. It varies not too much during the operating point and depends on the condenser

energy balance. A bottle allows to maintain the cycle during refrigerant life leakages


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The evaporator superheat protects the compressor against liquid bubbles expansion. It depends on the

energy balance in the evaporator. It is generally controlled by thermostatic valve or maintained by

accumulator.

As the COP (coefficient of performance) of the loop is function of the thermodynamic cycle and the

intensive variables, it is necessary to control these 4 main intensive states.

The dynamic control allows to master the 4 intensive variables (pressure, temperature) and the extensive

variables (mass flow rate) which are linked by the component characteristics.

Therefore, it is necessary to have 5 main actuators:

- the speed of the compressor that acts on the extensive mass flow rate or the compressor capacity

if the speed is constrained,

- the expansion valve that sets up the evaporator superheat

- the refrigerant mass that maintains a sub-cooling at the valve input.

- The condenser air mass flow rate that acts upon the high pressure

- The evaporator air mass flow rate that acts upon the low pressure.

As these actuators act in some limits, it is obviously important to have a consistent component static sizing

to obtain the required cooling power in critical conditions.

Simulator usages

- Parametric study and computation of parametric table for steady state points: definition of

mapping of inputs or parameters

- Dynamic simulation in nominal/degradation/failures conditions

- Easy loop sizing, mainly for condenser and evaporator.

- Validation tests: MIL/SIL/HIL

- Comparison simulated data with tests data (real tests, reference)

- Energy optimization

- Pre calibration of controlled laws

The simulator functions:

- Pre-processor to define the scenario, the parameters and the initial states

- Component sizing functionalities

- Auto sizing scaling: the intensive variables are unchanged but all the extensive variables are scaled.

- Post-processor to visualize the results:

on line plot of thermodynamic diagram

This model can be integrated in higher level model, for example in Air loop model.


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Refrigerant cold loop physical description

Elements of the cold loop are:

− Volumetric compressor

fixed capacity: the mass flow rate is function only of the speed of the compressor.

variable capacity; in this case the capacity can be internally manipulated (control of low pressure) or

externally (control of the outlet evaporator air temperature). The efficiency constitutive laws depend

on the compressor capacity.

− Condenser:

-with integrated or separated bottle.

-Refrigerant side: 3 zones (overheating, condensation, sub-cooling)

-Air side: wet or dry air

R: the void rate is not taken into account

− Evaporator :

The functioning of evaporator depends much on the air humidity. Therefore, we consider dry or wet

regime to assess the right cooling thermal power. There are several zones:

- 2 zones for refrigerant: evaporation and overheating

-2 zones air side: wet or dry air.

− Expansion valve:

Several options are existing:

Thermostatic valve: the opening area depends of output evaporator temperature and

corrections of Text.

Controlled valve: the section is controlled to have a defined overheat law at evaporator

output to protect the compressor.


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Fixed valve: the section is fixed

Elements of the air subsystem

- Condenser fan

- Evaporator fan

All these super elements have been developed from the simscape library elements

Simulator structure

The simulator is composed of modular blocks:

1 – Block of protocols or scenarios management

2 – Block of defaults

3 – Control block of pressure, temperature or power

4 – Sensors block: leakages, sensors defaults, actuators blocking, components degradation

5 – System synoptic with on line numeric and graphic results

6- Results storage and pre-defined plotting:

7 – excel data import/export

Cold loop with one Air Evaporator

Cold loop with two parallel evaporator ( air or water)


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Protocol block

Choice of simulation mode:

- Sizing: search of functional or dimensional parameters

- Steady state computation for one point or for a mapping of N points

- Dynamic simulation

Choice of open/ closed loop options

Choice of environmental conditions

Choice of configuration options

Following is an example of cockpit:


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Default Block

This block defines the defaults applied to components, to sensors or actuators:

blockage, bias, degradation


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Control Block

This block implements the control of

- Compressor: speed or capacity to realize the low pressure objective

Ncp or Vol_Cp as P_LP=set point

- Valve section to realize the evaporator superheat

Va as OVH_Ev=set point

- Condenser fan to control the high pressure max

Vfan as P_HP < max

Sensor block

- Real or virtual sensor.

Synoptic Block

- Numeric values of all properties in all system plans

- On line or off line graphic diagrams and plots


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Condenser map : it gives all the parameters and values of components

- geometric , functional internal/external fluids parameters , exchanger parameters

- air and refrigerant values

-Refrigerant Cycle

- Air diagram


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- Power balance

Plots:

Protocol: variation of compressor speed and inlet temperature evaporator 1


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Control Valve and compressor

Points 1 to 8


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Similitude : auto scaling of factor 100.


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Data Import/Export

Parameters import and results export between matlab and excel.

All the cases of parametric table are defined in excel sheet and the results are exported in excel file.

Refrigerant Package

Basic Professional

Library

Volumetric Compressor,

controlled or fixed valve,

equivalent condenser

evaporator dry and wet air

bottle

+ Compressor (pistons, scroll, palet)

+ Thermostatic valve

+ condenser 3 zones

+ evaporator 2 zones (air or water)

+ accumulator

Model

User functional parameter law,

basic architecture (one evaporator line)

Dry air diagram

basic documentation

Nominal

Theoretical laws for coefficient

Two evaporator lines

Wet Air diagram

Complete documentation

+ Degradation and defaults


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Simulator Limited protocols

No identification

Energy and mass balance

No Excel link

Thermodynamic diagram off line

Basic synoptic

Extended protocol

Components identification

Advanced Graphic

Excel link

thermodynamic diagram on line

Detailed synoptic

Price

Prices (Keuros) Basic Professional

Library 2 5

Standard Model 3 5

Standard Simulator 6 10

Training / day 1.5 2.

Technical Assistance / day 0.8 0.8

Specification of work On demand On demand

Documents

Simscape Refrigerant Loop Product - sherpa-eng.com · A refrigerant loop has 4 main intensive states: the high and low pressure, ... MIL/SIL/HIL - Comparison simulated data with tests