<https://www.inspectorsjournal.com/topic/7096-geothermal-closed-loop-system/#comment-54156>
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"OK, but the ice in the pic is on the outside of the pipe....I don't see the connection between that and the mixture being \"wrong\".          I'm not an expert on geothermal (more accurately, ground-source heat pump) HVAC systems but I know enough to take a stab at your question.     The unit in your pic contains the compressor and water-refrigerant heat exchanger of a split system. The AHU is somewhere off your picture, probably in the attic with the gas furnace. The top two lines coming out of the unit are for a heat assist loop for the hot water system. The bottom two lines are for the ground loop. The lines in the center are the hi/lo pressure refrigerant lines heading to the AHU.     Since this unit is located in the basement and not outdoors, ice on the outside of the lines means that the temperature of the fluid inside the lines has fallen below 32 degrees F. Some ground-source heat pump systems are designed for ground loop low temps above 32 and others for temps below.     If the system is designed to operate with a low temp above 32, then ice on either of the ground loop lines is a symptom of a problem.     If the system is designed to operate with a low temp below 32, the loop will have some antifreeze in it (as noted by energy star), and ice on the ground loop return line is to be expected. You can control it by putting insulation on the outside of the pipe where it is exposed to the humidity in the air.      Both of the ground loop lines in your pic have ice on them. Ice on the ground loop supply line (regardless of the low temp design value for the loop) is a problem. The supply line should be a fairly constant temp around 50-55 degrees, year-round. It shouldn't have ice on it. Ice on both lines means the temp of the entire ground loop has dropped below 32 degrees.     If you are getting ice on lines that should not ice up, it means that the ground loop cannot supply enough heat to keep up with the demand created by the equipment that is extracting the heat from it. The causes of that problem could be many: the ground loop could be too short, the ground loop could be too shallow below grade, there could be air or a blockage in the ground loop line, pump problems, incorrect refrigerant charge or valve problems in the compressor loop of the heat pump, etc. If the problem is not corrected the ground loop can freeze.     Digging up the loop can be an expensive repair....     Brandon \n"
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