Coupling CFD and building energy modelling to optimize the operation of a large open office space for occupant comfort

Large open spaces are popular nowadays in office buildings. However, occupants often complain too cold and/or too warm in large open spaces. It remains a challenge to control the operation of air-conditioning systems to provide occupant comfort in a large open space due to the ununiform distribution of internal heat gains and occupancy. Previous studies using CFD tools or building energy modelling tools alone did not solve the combined problem of the distributive temperature field in the space and the cooling demand from multiple terminal units. This study proposed to divide the large space into multiple subzone areas based on the layout of the terminal cooling equipment and the distribution of internal heat gains and occupancy. Then a coupling of FLUENT simulation with EnergyPlus building energy simulation is used to compute the optimal thermostat setpoint for each subzone to ensure uniform occupant comfort in the large space. EnergyPlus computes the interior wall surface temperatures and terminal unit supply air flowrate of each subzone, which are passed to the CFD simulations as boundary conditions; while FLUENT computes the temperature and PMV field, as well as airflow rates across the virtual partition walls between two adjacent subzones, which are passed to EnergyPlus for consideration as inter-zone air flow. A case study using an open office space in Hong Kong is conducted to demonstrate the validity of the methodology. Different temperature setpoints were computed for the subzones that achieved uniform occupant thermal comfort while reducing energy use due to avoiding overcooling of the occupied surrounding. The results indicated that the coupling method can effectively provide a thermally comfortable environment with less energy use in large open office served by multiple terminal units.