Master's Thesis Jan Wilmes

Examination and Analysis of Membrane Based Enthalpy Exchangers in Air Conditioning

In the present thesis an enthalpy exchanger is researched experimentally. It is examined, if the operating
conditions influence the transfer behaviour of the enthalpy exchanger.
Target of the research therefore is the sensible and the latent transfer coefficient as well as the sensible
and latent effectiveness. Concurrently a model is tested for its fitting with the test results. The
model describes the sensible and latent transfer coefficient as empirical equations of a dimensionless
temperature and a dimensionless humidity respectively.
A quantity depending on temperature and a quantity depending on humidity are varied as factors.
The difference between the thermodynamic mean temperatures of the outdoor airstream and the
extract airstream is used as the temperature depending factor. The mean value of the logarithmic
mean humidity of the outdoor airstream and the extract air stream is used as the humidity depending
factor.
Furthermore, on both outlet sides of the enthalpy exchanger, which are the supply air side and the
exhaust air side, 5 temperature sensors are installed to measure a temperature profile. The 5 sensors
are located in the form of a cross. The objective of this investigation is to detect inhomogeneity in
the temperature profiles and to find a mean temperature of each side for further research.
To supply the enthalpy exchanger with a well-defined outdoor airstream and extract airstream, two
air handling units are used. Both air handling units provide the possibility to humidify, heat and
cool the airstream. However, just the air handling unit conditioning the outdoor air stream contains
a vent and a sorption drier.
The test object is a crossflow enthalpy exchanger with a maximum airflow rate of 400 m/h. It is
installed in test a container to guarantee repeatable air stream conditions.
This thesis proves a dependency between the sensible transfer coefficient and the researched factors.
Furthermore, it is demonstrated that the mean humidity has no influence on the latent transfer
coefficient.
This thesis does not provide a verified dependency between the latent transfer coefficient and the
difference between thermodynamicmean temperatures.
The model of the transfer coefficient, as described in this thesis, does not show a satisfying fitting
concerning the sensible terms. However, the model for the latent transfer coefficient shows a good
fitting towards concerning themeasured values.
The measured temperature profile shows a significant inhomogeneity at the outlet sides of the exchanger.
In this thesis it was not possible to identify all impacting parameters on this profile unambiguously