Design of an Automatic Control Algorithm for Energy-Efficient ...

4 Control strategy
The main goal of this thesis is to design a control strategy that fulfils the control objectives
described in Chapter 2 in the best possible way.
4.1 Existing control structures
As pointed out in Section 1.1 most of the automatic “climate” control systems include only
automatic temperature control. These controllers are often quite simple in order to require
less powerful computing hardware. A simple hand-tuned relation between ambient, cabin
and outlet temperature is used. Linearly to the output temperature the fan speed is set.
Static rules are implemented to handle situations when for example the coolant is too
cold. This approach does only partially reflect comfort (by a fixed temperature) and does
not reduce energy consumption if possible.
An approach based on a CO2 sensor [3] only uses full recirculation or fresh air,
but not a mixture of both. It also does not include other objectives than the air qual-
ity. Another automatic defog control by Wang et al. (2004) [22] simply overrides the
normal control. The integration into a control system is done by Jung, Lee and Jang
[23], but apart from a PID-estimator in the fog-detection no details are given. In general
these developments focus on single parts of the control, but not on an all-encompassing
approach.
Information about the core algorithms difficult to obtain, since they are mostly kept
as business secrets. One published approach by Wang et al. [24] uses an energy balance
model and look-up tables to determine the required outlet air flow and its temperature
to maintain a comfortable cabin. To this a transient part used to heat up (or cool down)
the cabin is added. In this way a simple model based control is implemented. However,