Login
EnergyPlus models follow fundamental heat balance principles very closely in almost all aspects of the program. However, the simulation of building surface constructions has relied on a transfer function transformation carried over from BLAST. This has all the usual restrictions of a transformation-based solution: constant properties, and fixed values of some parameters. As the energy analysis field moves toward simulating more advanced constructions, such as phase change materials (PCM), it becomes necessary to step back from transformations to more fundamental forms. This paper describes the development of an implicit finite difference thermal model of building surfaces that has been incorporated into EnergyPlus. The model simulates the performance of PCM’s using an enthalpy or heat content formulation so energy accounting is accurate, and the phase change enthalpy is included fully. The model also permits modeling temperature dependent thermal conductivity. The complete multilayer construction capability of EnergyPlus is retained, so simulations can be done with the PCM in any location within the surface structure. Because of the short time steps used in the finite difference solution algorithm, the zone time step can be reduced to correspond with the one minute minimum time step used by the integrated system in EnergyPlus. Examples showing the effect of using PCM’s in various locations within a wall construction, and examples of the annual energy performance changes caused by such materials are presented.
Follow us:
