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# Earth tube - Multiple tubes in E+

Hey, I understand that the earth tube system in energy plus is a single linear tube, but there are many installation which are designed like the one in the image below.

Is it possible to simulate them in the energy plus instead of the traditional linear system.

Regards, Prethvi Raj, Building Performance Analyst, TRAJECT 361.

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I may be missing the point here, and if so would gladly be educated, but I would imagine this would be set up in a way that the inlet air would be forced to travel along each of the interconnecting pipes to maximise the effective contact area between the air and the ground i.e. the header pipes would be blocked at specified points to force air through the full length of the pipe network. If it wasn't configured like that I would imagine the air would simply short-circuit through one of the larger header pipes which wouldn't give much heat transfer surface area (and there would be no point in the interconnecting pipework)?

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Hey, I'm sorry for not uploading a clear picture, I hope this image has more clarity.

( 2020-06-12 03:34:43 -0600 )edit

Unfortunately, EnergyPlus only allows ZoneEarthTube objects to take outdoor air and supply it to a zone -- you cannot specify that the outlet of one earth tube is the inlet for another earth tube.

If we focus on your picture, then it appears that there are two wider pipes with a larger radius connected to four narrower pipes with a smaller radius. If you are concerned with accurately modeling the different heat transfer processes between these two types of pipes and the surrounding soil, you could represent each type of pipe with a ZoneEarthTube object. You would then set the Pipe Radius to the proper radius of each type of pipe, and then set Pipe Length equal to the TOTAL length you want to represent (2x the length of each wider pipe, 4x the length of each narrower pipe). The problem with this approach is that you wouldn't capture the impact of air leaving the first wider pipe, entering the four narrower pipes, and then entering the second wider pipe -- EnergyPlus assumes that each type of pipe has outdoor air entering them and then supplying air at the end to a zone. It doesn't look like there are any EMS actuators available to override earth tube behavior, either.

An alternative is to combine all of these pipe segments into one earth tube in the model. You would use the same total length of all pipe segments, but enter a radius so that the total exterior pipe surface area in the model is equal to the sum of the exterior pipe area for all segments.

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