Block-oriented Models for Transient HVAC Simulations

An improved block-oriented simulation methodology of vehicle air conditioning systems has been developed, based on dynamic and thermodynamic formulations of automotive components. The method applied considers any system as dynamic and the steady-state as a particular condition reached during transient states. Therefore it is necessary for every component of the system to define the dynamic laws, the dynamic constants and to impose the initial conditions. A few examples of modeled components are described in order to show the consistency of the thermodynamic differential approach and input/output relations between subsystems. An alternative approach of experimental look-up tables with respect to the thermodynamic differential method has also been applied, whenever it was convenient in terms of calculation improvements. The model, although mono-dimensional, is able to describe different non-stationary behaviors in typical HVAC (Heating, Ventilating, and Air-Conditioning) applications: warm-up, cool-down, transient thermodynamic effects in air ducts and more. The model is currently being used during pre-development and development phases to dimension HVAC systems. This article is focused on describing warm-up models: a comparison between simulations and experimental data is shown for different cases, in order to underline the effects of different components and boundary conditions. The model abilities in predicting the system behavior and the methodology approach are discussed: model sensitivity with respect to different heating sources, airblowers, heat-exchangers and additional heaters (PTC) are taken into account, while changing wind tunnel boundary conditions.