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geothermal/radiant floor control ?

bill_8 Member Posts: 15
I have a geothermal system and am using two elec hot waters piped in parallel as storage. Nine zones radiant floor using AL plates. System works superbly. The heat pump has a freeze protection relay that turns pump off (manual reset needed)in the event earth loop leaving water temp is below 32 degrees. I would like to use the water heaters as emergency backup heat in the event the heat pump leaving water temp gets below say 34 degrees so that temp can be made more quickly to prevent freeze lockout. Once water temp is reached (about 122 degrees) the heat pump turns off and the temp in the earth loop leaving line rises rapidly and that could be used to turn off elec water heaters. A strap on thermistor type sensor with an accurate aquastat seems to be the way to go. It has been very cold here and I can sometimes trip the freezestat (not easy) by going no mix to the zone pumps and turning on all zone pumps at once. at 34 degrees leaving temp with the elec water heaters on the system can make temp before tripping the freezestat.

the tekmar 150 with the 071 sensor looks like it would handle this. any thoughts?

another option would be to turn up main mixing valve (more mix) based on earth loop leaving temp to reduce amount of cooler water coming into storage tanks. This would still keep somewhat warmer water circulating in system without actually shutting down a zone. A fellow contractor suggested a circ relay with priority control (built my own circ relay) but this would be the same as shutting down zones and for the majority of time would not be necessary. not quite sure how to accomplish second scenario....turning on elec heaters seems to be simplest thing to do.

any ideas? thanx, bill


  • mike terry
    mike terry Member Posts: 33

    If I understand this correctly,the earthloop is closed with 2 water heaters side by side and there is an evaporator in this loop.compressor moves heat from earth loop to radiant loop via some sorta heat exchanger. seems to me , since your not running any glycol in earthloop( my assumption) and 32 is your saftey cutout.looks like you be better off to put 2 more water heaters on the radiant side and put the heat where you want it and cut out the middleman(compressor)
    You must be reaching the point where the structure is loosing more heat than you can put in with a loop temp of 33degrees. are there any strainers or anything that could be slowing down the flow rate thru your evaporator? that could cause low compressor suction pressures along with the lower temps....just some thoughts good luck
  • Glenn Harrison
    Glenn Harrison Member Posts: 405
    Is your loop a well \"loop\" or a true Geothermal Loop.

    If your unit is connected to a geothermal loop with the pipes in the ground, you should be able to run that unit down to about 15º to 20º. To do this you would need to have the loop freeze protected, usually with methanol, and then there should be a set-up switch in the unit to tell the electronics that you are hooked up to a freeze protected loop so it will shut off at a lower temp.

    Glenn Harrison Residential Service Tech

    Althoff Industries Inc. Mechanical and Electrical Contractors

    Crystal Lake, Illinois
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