Review on the HVAC System Modeling Types and the Shortcomings of Their Application

The modeling of the heating, ventilation, and air conditioning (HVAC) system is a prominent topic because of its relationship with energy savings and environmental, economical, and technological issues. The modeling of the HVAC system is concerned with the indoor thermal sensation, which is related to the modeling of building, air handling unit (AHU) equipments, and indoor thermal processes. Until now, many HVAC system modeling approaches are made available, and the techniques have become quite mature. But there are some shortcomings in application and integration methods for the different types of the HVAC model. The application and integration processes will act to accumulate the defective characteristics for both AHU equipments and building models such as nonlinear, pure lag time, high thermal inertia, uncertain disturbance factors, large-scale systems, and constraints. This paper shows types of the HVAC model and the advantages and disadvantages for each application of them, and it finds out that the gray-box type is the best one to represent the indoor thermal comfort. But its application fails at the integration method where its response deviated to unreal behavior. 1. Introduction The HVAC system modeling implies to the modeling of building, indoor, outdoor, and air handling unit (AHU) equipments. It is normally difficult for one HVAC system model to be completely comprehensive. Therefore, it is possible to divide the comprehensive model into submodels which may be appropriate in some instances. The key to any successful indoor thermal analysis or representation lies in the accuracy of the model of the indoor conditioned space within building and AHU equipments. The simple hand-calculation methods were available to find out the cooling/heating load until the advent of computer simulation programs for the HVAC systems in the mid 1960s. The first simulation method attempted was to imitate physical conditions by treating the variable time as the independent [1]. Most of the earliest simulation methods were based on the white-box or mathematical (physical) models, which are preferred over other models such as the black-box and the gray-box models because they are easy to analyze even though they are more complex than others [2]. 1.1. The Mathematical Model of the HVAC System There are two types of the white-box or the mathematical model: the lumped and the distributed parameters. The main advantage of the lumped parameter model is that it is much easier to solve than the distributed model. The mathematical models are very popular for the HVAC systems