Newbie with some basic questions

Discussion in 'Geothermal Heat Pump Applications' started by Don L, Jan 17, 2015.

  1. Don L

    Don L New Member

    We just moved in to a 2007 built house in northern Minnesota. It is single story 3200 SF timber frame home with a 4 ft crawl space beneath; where the majority of the utilities are located. The home has an open loop geothermal system with both an in-floor radiant distribution as well as a forced air distribution system. The forced air portion has a propane furnace backup and it also serves as the air conditioner. The geothermal system has two FHP heat exchangers.

    I am totally new to geothermal so I don’t know exactly how the system works. It appears there is a single thermostat that controls the forced air distribution and six other thermostats that apparently control zones for the in-floor distribution system. The prior owners told us they rarely if ever turned on the in-floor system except one remote bedroom zone.

    The domestic water heater is off peak electric however there are two 1/2” copper lines entering it near the bottom and I believe they are coming from the geothermal heat exchanger. There is another water heater in the heated garage and I believe this one is just a storage tank for the in-floor system.

    We have been in the house only 2 weeks now and since I know very little, I turned off all in-floor zones and relied totally on the forced air distribution. The weather was quite nasty, getting to -20 F several days but the house stayed nice and warm at the set 71F temp. I am now going to try turning off the forced air portion and rely only on the in-floor distribution to see what happens for the next few days.

    My question are pretty basic, so please bear with me:

    • Is this called a “dual stage, dual fuel GSHP system?
    • Obviously, I want to avoid use of the propane as the fuel source as much as possible. What is the most efficient distribution system, the forced air or in-floor?
    • How should I set the thermostats to operate? Both systems at the same set point or one a few degrees lower than the other?
    • Anyone have experience with the Nest thermostat? Would that be of any value on this system? If so, which one the forced air or one of the in-floor zones?
    Thanks in advance.
     
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'm not sure about the label; dual stage describes systems whose compressors have two capacity steps, typically 2/3 and full power. Dual fuel sounds accurate given you have propane backup.

    It is hard to state which, forced air or forced water is more efficient without knowing quite a lot more about your own system; impossible, really. The only way you'd know for sure would be to submeter all system elements with a TED (The Energy Detective) or similar system and then collect data in both modes. Don't forget to normalize the data for degree-days.

    In theory in-floor radiant CAN be more efficient if executed perfectly, but that's a tall order.

    I personally feel NEST and similar thermostats are over-hyped. A tight building envelope coupled with careful automatic setbacks should suffice, but that's just my opinion.
     
  3. Tamar

    Tamar Member Forum Leader

    Don, I take it the previous owners were not the people who installed the geothermal? I cannot believe someone would go to the expense of putting in a 6 zone radiant/hydronic system and then rarely use it. It will be interesting to hear how your test of "radiant only" goes.
     

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