A comprehensive vehicle thermal analysis needs to examine in detail the interaction between every single thermal system involved in the heating process. In order to accurately predict the thermophysical behaviour of the total system during vehicle warm-up the use of simulation methods is recommended. This paper deals with the contradictory requirement of improving the energy-efficient heat-up behaviour of the passenger compartment without disregarding comfort and safety aspects. Hence, the thermal interaction between heat exchanger, electrical auxiliary heater, air ducts and passenger compartment will be discussed. In order to evaluate the effect of different heating strategies on passenger comfort, a passenger compartment model is used which predicts not only temperature developments but also humidity as a function of time. The predictions generated by the model were validated by extensive tests in a climatic wind tunnel. Within this paper a new model of a comprehensive HVAC-system is presented which is able to calculate temperature and relative air humidity developments in a passenger compartment. The model generates reliable assertions on the effect of different heating strategies. By implementing a windshield model all kinds of air control strategies such as minimizing the air flow through the defrost vents can be evaluated. The positive effect of this air routing strategy is shown. Furthermore, the effect of an increased recirculation rate in order to accelerate the heating of the passenger compartment is pointed out. By combining both measures the best results regarding heat-up behaviour is achieved. Based on the knowledge generated by the presented numerical investigations it is recommended to control the recirculation flap position not right from the beginning in order to lower the risk of condensation water on the inner surface of the windshield. There is no significant difference between OAC (outside air control) and OAC+R strategy in the temperature development at the early stage of the test. In OAC+R mode the transferred heat quantity within the heater core is reduced by an average of 25 % compared to the basis strategy. As a result the engine warm-up time is reduced. This leads to less fuel consumption and exhaust gas emissions. In spite of that a significant increase in mean air temperature level in OAC+R mode was achieved at the same time.
Numerical investigation of energy-efficient heat-up strategies considering a comprehensive HVAC-system
2011
14 Seiten, 12 Bilder, 1 Tabelle, 4 Quellen
Conference paper
English
Fahrzeugraum , Erwärmung , Thermoanalyse , Fahrkomfort , Fahrzeugsicherheit , Wärmetauscher , Fahrzeugbeheizung , Zusatzheizgerät , Luftkanal , Luftfeuchte , Zeitabhängigkeit , numerische Modellierung , Windkanalprüfung , Luftstrom , Regelungsstrategie , Umgebungstemperatur , Heizungssteuerung und -regelung , Simulation
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