Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
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.
