Abstract
This paper presents an enhanced vertical ground heat exchanger (GHE) model for whole-building energy simulation (WBES). WBES programs generally have computational constraints that affect the development and implementation of component simulation sub-models. WBES programs require models that execute quickly and efficiently due to how the programs are utilized by design engineers. WBES programs also require models to be formulated so their performance can be determined from boundary conditions set by upstream components and environmental conditions. The GHE model developed during this work utilizes an existing response factor model and extends its capabilities to accurately and robustly simulate at timesteps that are shorter than the GHE transit time. This was accomplished by developing a simplified dynamic borehole model and then exercising that model to generate exiting fluid temperature response factors. This approach blends numerical and analytical modeling methods. The existing response factor models are then extended to incorporate the exiting fluid temperature response factor to provide a better estimate of the GHE exiting fluid temperature at short simulation timesteps.
Highlights
Whole-building energy simulation (WBES) programs, such as EnergyPlus R [1] and TRNSYS [2], use equipment-loop simulation algorithms that pass component entering and exiting conditions flow-wise from up-stream components to down-stream components
A chiller model that has a minimum required flow rate may require that all other components on the loop run at its minimum flow rate, even though they could be operated at a lower flow rate
Direct numerical models that fully discretize the spatial domain using finite-volume or finite-element methods are useful for providing detailed results for model validation, but are not useful in the context of ground heat exchanger (GHE) modeling for WBES due to the excessive simulation time and inputs required to run such a model
Summary
Whole-building energy simulation (WBES) programs, such as EnergyPlus R [1] and TRNSYS [2], use equipment-loop simulation algorithms that pass component (e.g., pumps, boilers, chillers, heat exchangers, etc.) entering and exiting conditions (e.g., flow rates, temperatures, humidity ratios, etc.) flow-wise from up-stream components to down-stream components. These components are generally connected in a loop so that every component on the loop is in some way connected to every other component on the loop. Historical WBES GHE models have relied on third-party libraries or software tools to provide input data for the simulation To avoid this additional burden on the modeler, the model developed here must be able to operate in a standalone manner
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