Meaning of G-function data sets (Ln + G-function)

asked 2021-03-19 15:27:57 -0500

Jim Dirkes's avatar

updated 2021-04-01 11:01:30 -0500

Using EnergyPlus, we're modeling a borefield that uses a proprietary tubing (Gi-4 from Geothermal Innovations) that has very different geometry than typical U-tubes. Prior to this, we've used "typical" g-function data sets in the GroundHeatExchanger:ResponseFactors object which matched the borefield size.

For this model, we want to make sure we're representing the proprietary ground heat exchange properly, so we asked the manufacturer for their g-factors. They graciously sent a data sheet with a single g-factor - and our previous models have had 30-80 sets of Ln and g-factor values.

Frankly, I'm planning to try to absorb the Engineering Reference discussion on g-functions, but it looks pretty painful, so I'm asking two questions in hopes of experiencing less pain:

1) What is the purpose and difference between each of the multiple sets of Ln / G-function values?

2) Is there a simpler way to model a borefield that, for example, can use the manufacturer's calculated (single) g-function?

Thanks in advance.

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