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

4 Control strategy 42
gain through radiation) which can be seen as the disturbance on the (simplified) model.
Through humidity observation it can identify the total amount of water emitted by the
passengers and even try to estimate the number of persons in the car. On the windscreen
the disturbances through rain and sun can be calculated.
When these disturbances to the ideal system are known (or approximately known),
they lead to an improved prediction of the system and thereby to improved control. The
controller will have reduced stationary errors and react faster.
Another task is to estimate the CO2 concentration in the cabin. Usually no sensor
which would allow to control the amount of recirculation without impairing air quality is
available. However, the concentration of carbon dioxide can be simulated based on the
(estimated) number of persons and the amount of recirculated air. Even if the result is
not accurate, it gives qualitative information about the air indicating when to stop using
recirculation.
4.5 The working point optimiser
Optimisation of the HVAC-system set-points has been done in buildings in various ways
as seen in Section 4.2.
This concept of optimisation will be adapted for the use in a car. Computational
power is available today in more compact and energy efficient units making them suitable
for vehicle applications where they are already used for entertainment. The comfort
demand is less strict as in a building, as no one expects a car to have perfect comfortable
climate from the first minute. Moreover, the system mostly is not safety critical. A cabin
temperature which is some degrees above or below the ideal temperature or slightly cold
feet will not present a safety risk. Only the windscreen fogging remains to be prevented.
The timescale of the controlled systems in a car still is in the range of seconds (cf. Section
3.1.5) and permits the use of a more complex and computation time consuming algorithm.
The objectives, presented in Chapter 2, are mostly the same as in a building. They
contain mathematically complex expressions like in the thermal comfort calculation. The
optimiser has to find the best compromise between them.
As result a set-point for the HVAC-control is given defining the air blown into the