Thermodynamics Simulation

Heat pump simulation with TIL Suite

System

This CO2 cycle represents a typical air-to-water heat pump for a building. The heat pump has a tube bundle heat exchanger on the high pressure side as gas cooler. The gas cooler heats the water for the building. On the low-pressure side there is a finned tube heat exchanger which is used as an evaporator. The evaporator is located outside the building and absorbs the heat from the ambient air. This heat pump also has an internal heat exchanger, which is realised in the model by two pipes and a heat connection.

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Simulation

The system can be simulated over different periods of time. Since the environmental conditions are constant in this example, a stationary state is established quite quickly (after 200 seconds). The state variables of CO2, such as pressure, temperature and enthalpy, change in the cycle and can be evaluated in the simulation results. Instead of constant ambient conditions, varying boundary conditions can be applied or measurement data can be read in.

Results

Pressure and enthalpy of CO2 can best be shown in a p-h-diagram. In this example we have visualized the simulation result with our software DaVE. The figure in the p-h-diagram illustrates the thermodynamic cycle, with points 1 to 6 corresponding to the sensor points (ph) of the model. The CO2 transfers heat to the water from measuring point 1 to 2, whereby the pressure remains constantly high, but the temperature in the supercritical area drops continuously. On the low-pressure side from point 4 to 5, the CO2 absorbs heat from the ambient air.

Ventilation system simulation with TIL Suite

System

This model of a ventilation system consists of component models for fans, heat recovery, adiabatic recooler, droplet separators, coolers, dehumidifiers, air heaters and steam humidifiers. The conditioning of the supply air to a preset temperature and humidity can be simulated in detail. In addition to different boundary conditions (weather data) on the outside, further models for the interaction with buildings can be coupled on the supply air side. The individual components and the volume flow rate can be freely configured according to the specific application. Furthermore, single components can be switched on and off.

Simulation

The ventilation system was tested under variable operating conditions by continuously varying the temperature and humidity for the outside air and the desired supply air conditions. The component models each act depending on the local air state and condition the air flow according to their physical mode of operation. Integrated controllers allow different air conditions, such as those that occur in summer and winter, to be simulated without further user intervention. It is also possible to test and compare different control concepts.

Results

The state variables of the supply and exhaust air path are visualised in the hx-diagram. The temperature and humidity of the supply air always remain within the comfort zone in the case under investigation. The first half of the video refers to the winter case, with cold and dry outside air. The temperature and humidity of the extract air drops considerably in the heat exchanger and heats the supply air accordingly. The supply air is then brought to the desired temperature and humidity level by the heater and humidifier. In summer, the adiabatic recooler is active so that the supply air can be cooled down more in the heat exchanger. The exhaust air now changes not only the temperature but also the humidity. For conditioning the supply air, all components are temporarily active.

Battery cooling simulation with TIL Suite

System

This is a model of an electric car with an attached cooling circuit. The cooling circuit connects battery, vehicle interior and surroundings, pumps and fans ensure appropriate circulation. In cool ambient temperatures, the waste heat from the battery can be used to heat the interior (upper heat exchanger). At high temperatures in summer, the three-way valve is switched over and the battery is cooled against the outside air (lower heat exchanger). The heat output of the battery results from the given driving profile.

Simulation

The simulation can be used to support the dimensioning of the heat exchangers and control of the pumps and fans. In the present case the cooling of the battery is investigated on a summer day with a constant air temperature of 25°C. The cooling is done against the outside air, the three-way valve is consequently switched to the lower circuit. As a speed profile an HFET driving cycle with an average speed of approx. 50 km/h over a total distance of 50 km has been simulated.

Results

The battery provides the necessary power to accelerate the vehicle according to the driving cycle. The waste heat generated in the process heats the battery. Despite active cooling against the ambient air, the battery temperature continues to rise and exceeds the limit temperature of 40 °C after 30 minutes. Since the temperature of the cooling water is very close to the battery temperature, the limiting factor is the heat transfer to the environment. This heat exchanger must be dimensioned considerably larger to allow sufficient cooling.