This simulation model demonstrates how a HVAC system featuring different operating modes (cool down, heat pump mode) can be realized in one simulation model.
To combine both conditioning modes in one simulation model, it is necessary to split the system into two branches. Therefore the system consists of two condensers and two evaporators.
Basically there are two ways to select the conditioning mode:
The mode itself can be chosen in the Simulation parameter window.Usable from release: KULI 9.1-0.01
Phase change material can store a high amount of energy due to its very high thermal inertia. This energy can e.g. used for a fast engine warm-up, to provide cooling performance in the HVAC system (evaporator) while no compressor is available, …
The high amount of enthalpy for the phase change is modeled by changing the point masses cp value (thermal capacity) during the melting / solidification process.
The heat transfer to the PCM element depends on the amount of mass flow. By adding an additional medium component and a calculation controller, a speed / volume flow dependency can be modeled.Usable from release: KULI 9.1-0.01
One possibility to set a target temperature in the cabin for a fixed displacement compressors is to control the compressors RPM.
This example demonstrates how a subsystem including several calculation controllers can easily be added to an existing HVAC simulation system.
By adjusting the compressor RPM, the performance of the compressor is controlled. This controlling strategy is included in a subsystem which mainly consists of calculation controllers.
As a necessary input, the user has to define a required cabin temperature and the upper and lower limit for the compressor RPM. The calibration coefficient is a kind of RPM offset for the controller, used in each simulation time step.
If the average cabin temperature exceeds the upper temperature limit plus the temperature tolerance, the max. RPM of the compressor is used.
In all other cases the RPM is reduced or increased by the calibration coefficient. Due to the change of the RPM in each simulation time step, a smooth control characteristic is created.Usable from release: KULI 13.1
This subsystem takes care that the cabin temperature is kept between specified borders and if the temperature in the cabin is reached, then the entire AC circuit is turned off. Additionally the inertia of evaporator is taken also into account.
This simulation features a control system in which is the cabin temperature kept in specific borders by turning on and turning off the entire AC systems.
When the AC system compressor is turned off and the air still flows through an evaporator the inertia of the evaporator causes the air to cool itself by rejecting heat and at the same time warming the evaporator until it reaches the ambient temperature. In order to take this phenomenon into account, this system was created.
Also in this case is the transient behavior of an evaporator simulated by a point masses. In order to reach a smoother outlet temperature curve a heat conduction coefficient is positioned between the evaporator air side point mass and the evaporator refrigerant side point mass.Usable from release: KULI 9.1-0.01
KULI software for energy management optimization gives you the opportunity to efficiently investigate different concepts for EV/HEV batteries.
A possible concept is a nickel metal hydride battery which can be cooled by passenger cabin air.
Input data loosely based on Honda Insight
The Subsystem can be used for the calculation of the operating distance of a vehicle. Basically it can directly be used for electric vehicles, but with slight modification also for conventional combustion engines.
The calculation is done in every time step. Due to the fact that the Operating distance is based on averaged values, the accuracy of the result increases with the amount of simulation steps.
Necessary input values are:
The gearbox delivers a significant amount of heat to the gearbox oil, depending on the efficiency of the gearbox in the current operating conditions. This model demonstrates how the amount of heat can be calculated and put into the appropriate locations in the circuits.
The central element is an efficiency map, based on gear, torque, rpm, and temperature. The conversion from mean eff. pressure to torque is included with the help of calculation controllers. The heat of the gearbox is put into a point mass in an oil circuit. The point mass is also connected to another point mass via a heat conduction component with which it is possible to consider the heat transfer to the ambient.Usable from release: KULI 8.0-1.04
The COM interface, developed by Microsoft®, provides a standardized interface for programs to communicate with each other. KULI components has a set of built-in COM commands, which allows external programs to create KULI component files.
The part of KULI components that allows to save component files is implemented as a dynamic link library (DLL). This KuliCompInterface.dll can be called by any other application that supports COM. The current example is a simple demonstration of the KULI compinterface. An Excel datasheet for KULI input of a radiator component has an integrated button that allows to store the data directly as an *.kulirad-file.Usable from release: KULI 8.0-1.04
Only transient simulation allows using the full potential of computer aided engineering regarding component sizing & packaging.
For the simulation of realistic temperature profiles the thermal capacities of the engine should be considered.
In this example the existing engine component from KULI drive is remodeled using the primitive components point mass and heat conduction. The engine can be modeled as two direct masses and two indirect masses.The direct masses are heated by combustion processes, and exchange heat with each other, the oil and the water circuit respectively, the ambient air and with the indirect masses. The indirect masses exchange heat via conduction with their respective direct mass only.Usable from release: KULI 8.0-1.04
In this example we will investigate, how to model a hybrid passenger car with KULI. We will especially focus on the electric components and their integration into the overall cooling system.
The aim of a decent fan control strategy is to provide adequate air flow for the cooling system at minimum fan power and noise.
The KULI controller objects enable to implement an arbitrary control strategy for system optimization.
In the subsystem Fan control the controlling information is set up. For comfortable use you can change the values for the temperatures for changing the fan stage and the fan stages itself in the inner circuit window.
Based on the fan (electrical or mechanical fan) the fan stage or the fan speed can be used as the controlled parameter. In the provided model an electrical fan switches on as the air temperature rises above 60°C and switches off as the temperature falls below 55°C. The transient aspect of the example is the hysteresis which can be modeled using a delay controller. For better system overview the control strategy is packed into a KULI subsystem.Usable from release: KULI 9.1-0.01
In the coolant circuit the thermostatic valve is one of the most important control units to maintain the system’s desired set point temperature. Due to its mechanical technology usually the thermostat has some delay in its reaction, which should be considered in transient cycle simulation. This example is based on the tutorial example ExEngine. The major modification is that it includes a more detailed model for the thermostat, placed in the subsystem “Thermostat”.
The main idea is that a fluid point mass models the wax element including the metal housing of the thermostat. This point mass is responsible for the hysteresis of the thermostat. The mass of the point mass can be adjusted to fit the current application; moreover, also the heat transfer coefficient from the coolant to the mass can be adjusted, even depending on the flow rate. A corresponding characteristic line is prepared (but contains only a single value in this demo example).
The temperature of the mass (i.e., of the wax element) is then taken into a characteristic line in which the lift opening (between 0 and 100%) of the thermostat is calculated. Based on this lift opening two fluid resistances are calculated that have opposite behavior: If the temperature is still low, then the resistance of the bypass will be low, the resistance of the exit to the radiator branch will be high. If the temperature is high, then it is vice versa.
The example is given for a thermostat working as a branch; the method would work in the same way for a thermostat working as a confluence.Usable from release: KULI 8.0-1.04
This subsystem models a viscous clutch via a point mass.
The warming up hystereses are defined via the following inputs:
Furthermore the transmission ratio from engine speed to the input speed of the viscous clutch is modeled via a constant factor. And the transmission from the clutch-input speed to the fan speed is modeled via a 3D-map (“fan_rpm”) dependent on the engagement Ratio.Usable from release: KULI 9.1-0.01
Charge air cooler tanks may have a big impact on the efficiency of the heat exchangers behind. A simple approach to model those effects in KULI is the use of area resistances to block the air flow in the area where the tanks of the charge air cooler are located.
The area resistances correspond to the size of the real -life tanks.To consider the high air resistance typically caused by the tanks a high pressure loss coefficient has to be set. To model the local impact regarding the heat exchanger surfaces the area resistances simply can be integrated to the cooling package using the KULI block function.Usable from release: KULI 8.0-1.04
The heater matrix uses coolant to warm the air that enters the passenger cabin. Of course, this can influence the behavior of the complete coolant water circuit. This example illustrates how to add a heater matrix to a System.
To take care of an additional heater matrix in an existing KULI cooling system one has to add a radiator component to the KULI system. On the fluid side it is integrated to a normal coolant circuit using branch and confluence components. On the air side it is necessary to use two parallel branches to simulate separate air paths for the engine cooling part and for the HVAC part. The example is based on the basic example “Ex_Fluid.scs” from the KULI installation setup.Usable from release: KULI 8.0-1.04
In the passenger compartment typically a certain comfort temperature is demanded. In concept phase where only a few data are available, KULI supports the engineer in finding the required evaporator cool load to achieve the design temperature.
The current example represents a very basic configuration of an HVAC system. Air duct, blower and evaporator are simply modeled by heat flow sources, temperature- and mass flow targets with input based on rough assumptions. Using this model, the user can optimize the evaporator air outlet temperature such, that the evaporator cool load will lead to the desired cabin temperature.Usable from release: KULI 8.0-1.04
In the vehicle HVAC system air recirculation mode is used to reach a desired temperature faster and to prevent from bad outdoor smell. On the other hand passenger air quality may suffer from the recirculation. An approach to keep the advantage of recirculation but reduce its disadvantage is the use of mixed air.
The current example is based on “Ex_AC_cool_down_recirc.scs” from the KULI installation setup. Here, the user can set a proportion of fresh and recirculation air that will blow into the cabin.Usable from release: KULI 13.1
On the standard condenser test bench the refrigerant inlet and outlet conditions are fixed and the refrigerant mass flow is the test result. For plausibility checks or for calibration: The corresponding KULI model allows a virtual reproduction of the test bench situation.
The refrigerant condition can be defined by inlet-temperature,-pressure and outlet-subcooling value (à CND-Test_VariantEntryTemp.scs). The air inlet condition is fixed, the air flow can be varied to test for different operating points. The condenser test bench is packed to a subsystem and does not require the user’s attention in first instance. Test results like refrigerant mass flow, heat transfer and pressure loss are collected in another subsystem . Variants of the test bench model require inlet superheat instead of inlet temperature or mean pressure instead of inlet pressure as input (à CND-Test_VariantEntrySH.scs, CND-Test_VariantEntrySH(meanPressure).scs).Usable from release: KULI 14
In the passenger compartment typically a certain comfort temperature is demanded. A possible control strategy to reach comfort level is the use of a PID controller.
The input of the controller is the deviation of the actual temperature to the reference temperature of 22°C. The output value affects e.g. an electro heater with the purpose of minimizing the temperature gap.Usable from release: KULI 8.0-1.04
In real-life cooling packages there will be an non-uniform air flow distribution on heat exchangers, which can have a big effect on heat transfer rate. Using CFD results with KULI it is possible to consider this uneven air flow on heat exchangers.
In the KULI direct CFD interface method *.txt-files containing a velocity distribution from CFD calculation and *.txt-files for writing output like a temperature distribution have to be defined. Unlike the standard/variable resistance matrix method, the direct CFD interface does not require the preprocessing step of calculating a matrix of local resistance corrections. Also unlike the two other methods, here the influence of fans or cp-values on the system air flow are neglected, the system airflow is taken directly from the velocities of the CFD input file. The big benefit of this method is, that KULI can be directly integrated in CFD code, e.g. for iterative underhood computation.Usable from release: KULI 8.0-1.04
This example compares the thermal simulation of a truck cooling system and a simple driving simulation. This proceeding allows the evaluation of the coolant temperatures and the determination of the consumption for a defined driving cycle.
In the past few years hybrid vehicles have been in the center of automotive engineering efforts, in particular in the field of passenger cars. But hybrid powertrains will also be important for commercial trucks. This focus on hybrid vehicles leads to high demands on thermal management since the additional components in a hybrid vehicle need appropriate cooling or even heating.
Beside conventional tasks in energy management, KULI software provides excellent opportunities for the simulation of hybrid- and pure electric vehicles.
This example compares the influence in power consumption of a mid-sized electric car with and without preconditioning (e.g. during a connection with a charger is established).
An extended application of the refrigerant cycle is the use as a heat pump, where the evaporator is used as an auxiliary heater. KULI enables to perform quick analysis of heat pump concepts.
In the corresponding KULI model the real-life evaporator is set up as an KULI condenser-model and vice versa the real-life condenser is set up as an KULI evaporator-model. For investigations in very cold ambient temperatures, where refrigerant low pressure level might fall below ambient pressure an extended media property file of Refrigerant R134a is attached to the example. Sensors and actuators on the inner circuit sheet of KULI allow a good overview on system parameters and results.Usable from release: KULI 8.0-1.04
Especially in HVAC systems using CO2 as refrigerant the evaporator can be used as an auxiliary heater. This can be implemented by switching of the condenser which leads to a triangular process.
In the corresponding KULI model the condenser simply does not exist. For convergence of the calculation model the operation mode “Hot gas cycle mode” has to be activated in the refrigerant circuit definition.Usable from release: KULI 13.1