Master's Thesis Tobias Czarnecki


Development of an experimental environment and measurements for the evaluation of different defrosting methods for air chillers

Icing of the evaporator in a refrigeration cycle leads to an impairment of the transferred heat flow
and the system efficiency. The frosted heat exchangermust therefore be defrosted fromtime to time.
Electrical and hot gas defrosting methods are used in practice.
In order to study these strategies in more detail an experimental setup of a refrigeration circuit with
replaceable air cooler is modified. Sensors installed in the refrigeration cycle allow the evaluation of
the energy balance of all components of the refrigerant circuit.
An existing scale system for measuring the mass of the ice within the air cooler is optimized. A
concept for a mobile setup to study different samples will be created and developed. A calibration
method for the optimized scale system will be developed and implemented into the programmable
logic controller (PLC). The aim is to measure the time-varying amount of ice and condensation in
the air chiller in normal cooling or defrosting mode. Also the effect on the change of center of gravity
(2D) of the air cooler will be analyzed. The reading of sensor data is automated and will be carried
out by the PLC.
For the refrigeration cycle, a control concept is software-designed and implemented by a Beckhoff
PLC. The PLC enables fully automated operation of the refrigeration cycle by user default, the reading
of all sensors and the display of measured values. A software-governed system protection, including
function test is also provided in the PLC. If necessary, an adjustment of the control parameters
will be carried out.
After commissioning of the entire system, an air cooler is measured in a climate chamber under
different boundary conditions. In addition to the evaluation of the measurement results carried out
an evaluation of the measurements in terms of their reproducibility and an estimate of the measurement
error is made.