Bachelor's thesis Arno Eggert

 

Experimental investigation and evaluation of air diffusers of various geometries

Active chilled beams are increasingly used as ventilating and air-conditioning components in indoor
air-conditioning. Active chilled beams use a central conditioned flow of fresh air (primary air)
to generate a decentralized forced circulation of room air (secondary air). Inside the active chilled
beam the secondary air which is aspirated by entrainment effects is mixed with the primary air and
then released back into the room (supply air). Through integrated heat exchangers thermal load
can be fed to or discharged from the secondary air. An active chilled beams circulation behaviour
is described by the entrainment rate. The rate of circulated secondary air to fed primary air cannot
be calculated at the moment. Especially geometric influences (nozzles, wall contour, installations)
as well as operating influences (primary flowrate) are currently not displayable. Therefore, complex
and time-intensive experiments are still necessary to determine aerodynamic behaviour.
This expenditure of time is now supposed to be minimalized by an improved measuring technique
and automated controlling during measurements. For examination of prototypes and serial devices
considering entrainment behaviour there was no suitable experimental environment at the EBC so
far. For exact measurements of primary and secondary air volume flow rate, a test bench with automated
control was planned, set up and put into operation. Volume flow rates are determined by calibrated
orifices according to the differential pressure approach. The secondary volume flow rate is
set through suitable influx covers, which cause a possibly commutated and velocity-homogeneous
flow as well as through the continuing control of the zero-pressure. The developed test bench enables
reproducible measurements with high accuracy and allows the evaluation of different active
chilled beams considering their entrainment behaviour.
This thesis introduces the planning, set up and commissioning of the test bench for active chilled
beams. The development of an entrainment cover and a differential pressure based control for
zero-pressure adjustment are presented.The influencing variables on measurement uncertainties
are discussed and their impact on the measuring data is pointed out. The thesis concludes with the
presentation of the measurement results in formof characteristic entrainment curves.