• Determination of BHE energy production

    Hi all,

    I’m working on the efficiency of a BHE system and my goal is to determine the total energy produced by the BHEs throughout the simulation timeframe. However, I’m not sure if I’m using the proper selections or methods to get the total energy produced by the system.

    I have extracted data from FEFLOW using the Period-Budget Panel, but I’m not sure if my data is accurate. I followed these steps to get the energy output data;
    - I recorded a dac file of a 20 year run and opened the dac file.
    - The edge selection for the BHEs were converted to 3D nodal selection, and selected. Note that I have selected the entire length of the BHEs (90m), as well as each BHE in the model.
        I am unsure if this is the correct selection.
    - In the Period Budget Panel I used the “Domain of Interest” (DOI) drop-down I chose “Current Node Selection”.
    - I then exported the results (FEFLOW creates a txt file that is opened in Excel).

    The exported file gives energy rate and total cumulative energy for all BCs (Dirichlet, Nuemann, etc.), however only Point-Source BCs have any data since only the BHEs were selected. Fields with data are as follows;
    - Point-Source BCs
    - Storage Capture/Release
    - Imbalance

    Right now I’m only really looking at the Point-Source BCs In and Out values, which FEFLOW help documents label as a Heat Nodal Sink/Source Boundary Condition. As per FEFLOW help “… [i]inflows are considered as negative, outflows as positive. Thus a sink/source boundary condition with a positive sign means extraction of thermal energy from the ground, a negative sign is used for injecting energy[/i].” so I am assuming my Point Source In is heat injected into the ground (when the system is cooling) and Point Source Out is heat extracted, and to get the total energy I would need to add the two together (i.e. Point Source In + Out = Total)

    I have kept the Storage Capture/Release and Imbalance data, but I’m not sure how or if I should include it in any energy calculations. If you have any insight, I would greatly appreciate the help.

    Thank you
  • How to determine heat rate transfer for a Heat-Transfer BC?

    I am building a 3D model and plan to have a Heat-Transfer BC that will go on the surface layer and simulate monthly average temperature of the ground and I'm having some trouble. The documentation says in addition to a reference temperature (which I have) and an in/out transfer rate, however I'm not sure how to set this up the transfer rate parameter.

    The documentation states that the transfer rate is thermal conductivity divided by the thickness (? = ?/d), but the “thickness” parameter is not defined. My model has four different layers, each with different thermal conductivities and thickness's, so I'm not sure what value to use.
    When determining the transfer rate, would I use the thickness of each layer as my thickness value? Or should I use the overall thickness of the model for each layer (i.e. if 1st layer is 10m thick, use 10m. If the 2nd layer is 5m thick, use 15m, etc.)?

    Thanks in advance
  • Selective Discritization


    I am currently making a 3D model that includes a basement of a building in the overall model area. I need to have the walls of the building finely discretized so they have 3 layers of elements within 0.5m, but only to a depth of 3m (the depth the building’s basement). However, the depth of my model needs to be at least 130m (I will be adding BHEs eventually), and having such high discretization all the way down to 130m generates far too many nodes and elements which is too much for my system to handle.

    I am wondering if there is a way to selectively discretize only the layers or slices that make up the top 3m of the model, leaving the lower layers with fewer elements/nodes.  I do have a shapefile for the walls themselves (as well as the interior of the building, excluding the width of the walls), if that helps in any way. I did see previous posts that suggested using TetGen for re-meshing around points, however I’m not sure that would apply to my issue.

    Thanks in advance,