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Earth Tube Labyrinth

asked 2015-09-01 16:44:37 -0600

g.maia gravatar image

updated 2015-09-01 22:46:17 -0600

Has anyone tried to model Earth tubes in energy plus? Specifically I have buried ductwork bringing tempered air into my AHUs. Energy plus has a 'ZoneEarthtube' object but this won't serve my AHUs. Anyone have a clever idea? Thanks for your help in advance.

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answered 2015-09-02 14:45:12 -0600

updated 2015-09-02 14:49:34 -0600

One possible solution would be to use the EMS manager to set the Outdoor Air System Node conditions at every timestep to the assumed 'tempered air' conditions.

Page 23 of The Book of Erl (EnergyPlus Application Guide for EMS) details this EMS actuator and actually suggests to 'make use of a separate model, outside of EnergyPlus, for some unique type of component (such as a labyrinth or earth-tube) that preconditions outdoor air; the results of that model could be fed into the air system model in EnergyPlus using these actuators.'

I'm not particularly savvy with EMS myself, but you may be able to calculate the assumed tempered air conditions, at each timestep, from the actual model using EMS sensors and some custom EMS logic. Alternatively, you could do some pre-processing as suggested above and feed it a custom schedule.

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This link to an esp-r paper may be helpful: Earth tube to air heat exchange

Chris Jones gravatar image Chris Jones  ( 2015-09-02 15:28:56 -0600 )edit
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answered 2016-08-04 12:52:51 -0600

JasonK gravatar image

I was looking for the same information and found that I had answered this question in the EnergyPlus_Support listserve several years ago. Here is the code from version 5, should be pretty much the same:

I have found it easier to run two simulations. The first one simulates the earth-tube only and then outputs the hourly dry bulb and wet bulb temperatures to a .csv file The second simulation utilizes EMS routines to replace the dry bulb and wet bulb hourly temperatures in the weather file with those found in the .csv output file but only for the outdoor air intake node... See code below: (note this was done with v.5 so there may be some updating that you need to do for v6)

EnergyManagementSystem:Sensor, Earth_Tube_DB_Sched, !Name EarthTubeDBSch, ! Output:Variable Index Key Name Schedule Value; ! Output:Variable or Output:Meter Name

EnergyManagementSystem:Sensor, Earth_Tube_WB_Sched, !Name EarthTubeWBSch, ! Output:Variable Index Key Name Schedule Value; ! Output:Variable or Output:Meter Name

EnergyManagementSystem:Actuator, ET_OADB_Override, ! Name DOAS Outside Air Inlet, ! Component Name Outdoor Air System Node, ! Component Type Drybulb Temperature; ! Control Variable

EnergyManagementSystem:Actuator, ET_OAWB_Override, ! Name DOAS Outside Air Inlet, ! Component Name Outdoor Air System Node, ! Component Type Wetbulb Temperature; ! Control Variable

EnergyManagementSystem:Program, SchedOA, ! Name SET ET_OADB_Override = Earth_Tube_DB_Sched, SET ET_OAWB_Override = Earth_Tube_WB_Sched;

EnergyManagementSystem:ProgramCallingManager, Schedule OA, ! Name AfterPredictorBeforeHVACManagers, ! EnergyPlus Model Calling Point SchedOA; ! Program Name 1

Output:EnergyManagementSystem, Verbose, Verbose, Verbose;

Schedule:File, EarthTubeDBSch, !- Name Any Number, !- ScheduleType W:\M\CALC\ETDB.csv, !- Name of File 1, !- Column Number 0, !- Rows to Skip at Top 8760, !- Number of Hours of Data Comma; !- Column Separator

Schedule:File, EarthTubeWBSch, !- Name Any Number, !- ScheduleType W:\M\CALC\ETWB.csv, !- Name of File 1, !- Column Number 0, !- Rows to Skip at Top 8760, !- Number of Hours of Data Comma; !- Column Separator

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Asked: 2015-09-01 16:44:37 -0600

Seen: 366 times

Last updated: Sep 02 '15