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Earth tube with Heat recovery in E+ or Design builder

asked 2020-06-05 04:25:03 -0500

Prethvi Raj gravatar image

updated 2020-06-05 08:16:05 -0500

Hey Team,

We are working with the Earth tube system as the major source of air intake into the building. But, I believe the earth tube works as a standalone system in the E+.

Is it possible to integrate it with the Heat recovery, before supplying the air into the zones ?

Please take a look at the attachment for the reference.

Regards, Prethvi, Building Performance Analyst, TRAJECT 361. C:\fakepath\Ventilation_unit_with_heat_pump_&_ground_heat_exchanger.png

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answered 2020-06-05 08:47:22 -0500

You are correct that the earth tube object in EnergyPlus is meant to be a standalone system that provides air directly to a zone. Most other HVAC components in EnergyPlus have inlet & outlet node settings that allow you to define where that component is located in the model, such as connecting the earth tube outlet air as the heat recovery inlet air. If you think that EnergyPlus should include this as a new feature, then you can make a comment in an existing feature request on Github where the EnergyPlus source code is hosted.

If you want to try a workaround, you could do the following:

  1. Run an initial simulation with the earth tube object and report the Earth Tube Zone Inlet Air Temperature and Earth Tube Zone Inlet Wet Bulb Temperature that leaves the earth tube as hourly or timestep frequency output variables.
  2. Create a modified EPW weather file that uses the air outputs from the first simulation as the outdoor air drybulb and wet-bulb. I would recommend using Elements to do this since it has psychrometric laws built in that prevent impossible air conditions (RH > 100%, e.g.).
  3. Run a second simulation that removes the earth tube object, has the heat recovery device with outdoor air -> air intake on one path and extract air -> exhaust air on the other (using node names from your linked diagram), and uses your modified EPW file from the previous step. Now, the "outdoor air" drybulb and webulb entering the heat recovery device before supplying air to the zone is the same as what would have been leaving the earth tube.
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Hey Aaron,

Thanks a lot. This is a smart work around for the simulation.

Is it possible to get the data for the temperature of the air before entering the heat recovery and after leaving them in the simulation.

Regards, Prethvi Raj.

Prethvi Raj gravatar image Prethvi Raj  ( 2020-06-06 02:05:52 -0500 )edit

You're welcome! Yes, EnergyPlus can provide output variables for System Node Temperature throughout HVAC systems, including inlet/outlet nodes of the heat exchanger's exhaust stream or intake stream.

Aaron Boranian gravatar image Aaron Boranian  ( 2020-06-07 07:39:05 -0500 )edit

answered 2020-06-09 02:20:52 -0500

Dave gravatar image

You mention that you are using DesignBuilder (which includes the earth tube component), so you could also consider using the EMS to connect the nodes and generate any additional outputs you need in Results Viewer. If you contact DesignBuilder's Support Desk with your question and relevant details they will confirm the best approach.

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Asked: 2020-06-05 04:25:03 -0500

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Last updated: Jun 09 '20