Design of an Automatic Control Algorithm for Energy-Efficient ...
Design of an Automatic Control Algorithm for Energy-Efficient ...
Design of an Automatic Control Algorithm for Energy-Efficient ...
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3 System description 26<br />
The maximum time const<strong>an</strong>t is easily identified to equal infinity. This is the case if no air<br />
is exch<strong>an</strong>ged with the environment <strong>an</strong>d nothing is ch<strong>an</strong>ging. Furthermore, the minimum<br />
values are found to be (neglecting the water mass in the air) ������ � ���� � �� � <strong>for</strong> the<br />
MUTE car. A much faster reaction is seen as no further “storage” exists apart from the<br />
air.<br />
For the windscreen temperature the ch<strong>an</strong>ging variables are the convection heat<br />
tr<strong>an</strong>sfer coefficients.<br />
��� � ������ ¡ ��� ¡ ��� ¡ ������<br />
������� � �������� ¡ ���<br />
(3.22)<br />
The highest time const<strong>an</strong>t is found with a st<strong>an</strong>ding car giving ������� � ��� �. Looking<br />
<strong>for</strong> the maximum, the estimation <strong>of</strong> ������� (equation 3.10) needs to be consulted with the<br />
maximum car speed (here 100 ��<br />
� is chosen). In this way a ������� <strong>of</strong> approximately ��<br />
seconds is obtained.<br />
These values are used <strong>for</strong> controller sample time considerations <strong>an</strong>d give <strong>an</strong> indi-<br />
cation what type <strong>of</strong> control c<strong>an</strong> be used. Due to the involved car parameter they will be<br />
different between car types. Moreover, some (as the infinity) will not occur in reality due<br />
to air leakages not considered here. Consequently some values might be higher th<strong>an</strong> in a<br />
real car. The calculations still give a rough estimation <strong>of</strong> the timescale in which ch<strong>an</strong>ges<br />
in the systems occur. The results show that these happen in the r<strong>an</strong>ge <strong>of</strong> several seconds.<br />
3.2 The HVAC-unit<br />
The HVAC-unit is the actor in the cars thermal system. It draws the air from the outside<br />
or the car cabin (recirculation), cools <strong>an</strong>d/or heats it up <strong>an</strong>d defines the way to blow it<br />
into the cabin. The heat sources (<strong>an</strong>d sinks) are regarded in the following Section 3.3 <strong>for</strong><br />
a heat pump system.<br />
For <strong>an</strong> HVAC-unit several types <strong>an</strong>d layouts exist. The most common type, the<br />
air mix type, is shown in Figure 3.4. The air is drawn by a f<strong>an</strong> from the outside or the<br />
car - chosen by the recirculation flap. Be<strong>for</strong>e flowing through the f<strong>an</strong>, a filter (not drawn<br />
in the picture) prevents dust <strong>an</strong>d other pollution from entering the car. The air passes
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