Model-based optimization can help improve the indoor thermal comfort and energy efficiency of Heating, Ventilation and Air Conditioning (HVAC) systems. The models used in previous optimization studies either omit the dynamic interaction between indoor airflow and HVAC or are too slow for model-based optimization. To address this limitation, we propose an optimization methodology using coupled simulation of the airflow and HVAC that captures the dynamics of both systems. We implement an optimization platform using the coupled models of a coarse grid Fast Fluid Dynamics model for indoor airflow and Modelica models for HVAC which is linked to the GenOpt optimization engine. Then, we demonstrate the new optimization platform by studying the optimal thermostat placement in a typical office room with a VAV terminal box in the design phase. After validating the model, we perform an optimization study, in which the VAV terminal box is dynamically controlled, and find that our optimization platform can determine the optimal location of thermostat to achieve either best thermal comfort or least energy consumption, or the combined. Finally, the time cost for performing such optimization study is about 6.2 hours, which is acceptable in the design phase.
Inhomogeneous airflow distribution is common in air-conditioned rooms, especially the large open spaces. To evaluate the thermal comfort of such space, or the control performance of the Heating, Ventilation, and Air Conditioning (HVAC) systems in an efficient way, one will need a fast prediction method to simulate the airflow and temperature distribution. This paper proposes a discrete state-space method, called state-space fluid dynamics (SFD), for the fast indoor airflow simulation. To handle time-varying velocity and temperature field, SFD converts all the governing equations of fluid dynamics into the form of a state-space model. Four typical cases are selected to evaluate both the accuracy and speed of SFD, compared with fast fluid dynamics (FFD), which is another fast airflow simulation program. Results show that SFD is capable of achieving faster-than-real-time airflow simulation with an accuracy similar to FFD. The computing time of SFD is longer than FFD when the time step size is the same. However, SFD can generally produce better results than FFD when the time step size is larger, which allows SFD run faster than FFD.
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