Surface Heat Exchange

Owned by Kester Scandrett
Last updated: 18 Nov, 2016
2 min read

The Surface Heat Exchange tab contains the Main Heat Exchange Options and is where the user sets the Surface Heat Exchange Sub-model as shown in Figure 1. This drop down list now contains six options, one more than previous versions of the EFDC_Explorer Modeling System. The user will note that the Settings button is no longer provided. These settings have been moved to more appropriate places, adjacent to the option that requires these setting to simplify the modeling process. Only settings which are relevant are now provided in the Surface Heat Transfer Coefficient Frame and in the Light Extinction Coefficients frame, depending on which option is selected.  For example, if sediments are not being simulated the Light Extinction for TSS is hidden as not applicable.

The options for the Surface Heat Exchange Sub-model are now:

  • No Atmospheric Linkage
  • Full Heat Balance (Legacy)
  • External Equilibrium Temperature
  • Constant Equilibrium Temperature Coefficient
  • Equilibrium Temperature (CE-QUAL-W2 Method)
  • Full Heat Balance with Variable Extinction Coefficient

These  options are described further below.

Note that to activate the heat sub-model in EFDC, the temperature constituent must be activated (Active Modules | Sub-Model Computational Options | Details). The ASER.INP file must be used for all of the thermal sub-models to compute the surface and bottom heat exchange processes. Also, depending on whether the current model is EFDC_GVC or EFDC+, the EFDC_Explorer form will have different options shown in the Main Heat Exchange Options frame.

Figure 1  Surface Heat Exchange Options.

The Full Heat Balance with Variable Extinction Coefficient option was added in EE8.2 and provides the user with the option of allowing light extinction to be dependent on the total suspended solids in the water column, thereby making light extinction temporally and spatially varying.  The extinction factors are determined on a cell by cell basis for each time step based on TSS, and if the water quality model is active, based on POM, DOM and Chlorophyll-a as well.

With this option the user may also set the evaporative and convective heat transfers to be impacted by the wind speed. The user should select the appropriate check box for the Vary with Wind Speed option, and then ensure a correct setting for the heat transfer coefficient for each option.