I am just guessing.
In all heat exchangers of this class, earth tube, etc., a table is used for the ground temperature. There were many choices to be made. The slab program can be used to investigate the different conditions.
For the vertical tubes, the unwanted ground effect may be reduced by insulation. I.e. use heat insulated pipes for some connections.
If the flow rate is low, the temperature of the air at the exit end of the pipe is not the deep ground temperature, but the surface ground temperature. This may be what you are observing.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, eric wang <shaojieworld2005@...> wrote:
> I modeled the GSHP system in Chicago. After exporting the variables as listed below, I found that the supplementary heater uses lots of electric power on 01/27 06:00:00. That reduced the efficiency of the GSHP system. Also, the VERTICAL GROUND HEAT EXCHANGER:Ground Heat Exchanger Outlet Temp is very low (1.033 degree C) from 01/26 20:00:00 to 01/27 05:00:00. I am not sure what causes the low water temperature from the ground loop. Can you help me out?
> Zone/Sys Sensible Load to Heating Setpoint Predicted [W](Hourly)
> WAHP SUPP HEATING COIL:Heating Coil Electric Power [W](Hourly)
> VERTICAL GROUND HEAT EXCHANGER:Ground Heat Exchanger Outlet Temp[C](Hourly)
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