By, Doug Carruthers
For every geothermal ground loop design, there is a load dominant mode and a length dominant mode. The load dominant mode is the one that will transfer the largest amount of energy to/from the loopfield while the length dominant mode is the one which requires the largest amount of pipe in the ground to transfer that energy based on designer specified entering water temperatures. Most of the time, they are the same, but not always.
When the temperature of the fluid entering the heat pump and the deep earth temperature (DET) get closer together, the amount of pipe needed to transfer heat increases. So, in some system designs, it is possible that the load dominant mode will require shorter loop lengths.
In our latest update we have made it clearer when there is a difference between load dominance and length dominance in a design. On screen, we independently flag the load dominant and length dominant modes when they are different. And, in the reports, your dominance flags have been reworded for clarity.
For those that are really paying attention, fixed length mode works the same as it ever did and only considers load dominance. The reason for this is that Fixed Length Mode is a reverse calculation of EWTs and without adding an obscene amount of overhead (not to mention a false sense of accuracy), it isn’t always possible to obtain exactly equal heating and cooling lengths. So, even when the load dominant mode’s length is shorter, it is assumed that either fixed length mode did not converge on a real solution (which LoopLink flags as an error) or the difference between the two lengths is insignificant with respect to installed performance.