Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
EnergyPlus is a tightly coupled simulation engine that uses iteration between zones, air systems, water systems, and on-site power generation. EnergyPlus is performing an iterative solution between the simulation domains in order to provide more accurate results. In EnergyPlus, the predicted load in the space is not passed to the air system, but is instead an input to a predictor/corrector algorithm that allows the zone to float for cases where the system does not exactly meet the space load. This is useful for simulating passive technologies such as radiant systems, buildings with demand limiting controls, undersized systems, and systems that properly modulate the flow on and off. The heat balance in the space is then used to compute the correct space temperature, which in turn, informs occupant comfort and surface temperatures. This coupled approach to simulation also shows up in central plant simulation, where the instantaneous fluid temperatures are calculated and then affect the air system by limiting capacity, affecting zone conditions. The iterative approach in EnergyPlus is a major contribution to longer runtimes, however coupling these simulation domains together is key in providing engineers with a tool that better simulates a wide variety of best-practice and cutting-edge technologies.
