4378 -- A Model for Simulating the Performance of a Shallow Pond as a Supplemental Heat Rejecter with Closed-Loop Ground-Source Heat Pump Systems PDF

Commercial buildings and institutions are generally cooling- dominated and therefore reject more heat to a ground-loop heat exchanger than they extract over the annual cycle. This paper describes the development, validation, and use of a design and simulation tool for modeling the performance of a shallow pond as a supplemental heat rejecter in ground-source heat pump systems. The model has been developed in the TRNSYS modeling environment and can therefore be coupled to other GSHP system component models for short time step (hourly or less) system analyses. The model has been validated by comparing simulation results to experimental data collected from two test ponds. The solution scheme involves a lumped-capacitance approach, and the resulting first-order differential equation describing the overall energy balance on the pond is solved numerically. An example application is presented to demonstrate the use of the model as well as the viability of the use of shallow ponds as supplemental heat rejecters in GSHP systems. Through this example, it is shown that ground-loop heat exchanger size can be significantly decreased by incorporating a shallow pond into a GSHP system.

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