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

8 System and functionality integration 90
environment temperature, leading to a higher cabin temperature in winter and a colder
on hot days (see Figure 8.4).
The advantage of an indirect setting is that the adaption is based on measurements
and established comfort calculation instead of a simple relation with the ambient air
temperature. This should cause less need to change the settings and thus less distraction.
The air flow towards the passenger can also be adapted using the ���� variable. Persons
very sensible to air flow can reduce the direct draught in this way.
As examples three special modes are presented here: Recirculation-, defrost- and
precondition-modes. Recirculation is desired in case of odours entering the car from
outside, for example when driving through a tunnel. Here a switch is used to force air
recirculation. This is realised with changed boundaries by setting the lower boundary for
the recirculated air percentage ������� to 100%. A sensor in the air inlet could automatically
activate this mode if needed.
Defrosting the windscreen might have to be available manually if the glass is iced
and fast heating up of the window is desired. In this case again changing the boundaries
gives the desired result. All air needs to go to the defrost outlets, which is done by setting
the maximum air fraction to the feet ����� to zero. A high air flow is desired in order to
bring in heat fast and give a high heat transfer. Therefore, the air flow minimum is set to
a higher value (e.g. half the maximum) and the minimum temperature is raised. Finally,
there is an increased fogging risk with full recirculation. This is avoided by guaranteeing
a minimum of fresh air and by setting the upper bound for ������� to a value below 100%,
for example 50%.
The last mode, preconditioning, is used to heat (or cool) the car before starting
a journey. With a remote control this can be activated just like auxiliary heating in
conventional cars. To achieve this it would be sufficient to start the automatic climate
control, but in order to be more efficient and faster it is useful to modify the weights. Air
quality is not regarded at this point of time, since no human is in the car. This allows
the algorithm to use full recirculation all the time, making heating and cooling efficient.
Moreover, the thermal comfort can be favoured in comparison to the fogging affinity since
no water sources are in the car. Less aggressive heating of the windscreen gives lower heat
losses through the glass.