Virginia 1st winter of geothermal heat & cast iron radiators - $51/month

Discussion in 'Geothermal Heat Pump Testimonials' started by frankz, Apr 21, 2016.

  1. frankz

    frankz New Member

    With warm weather forecast for the rest of April, heating season here in central Virginia is pretty much over, so here’s a tally of the first winter’s performance of our 3-ton geothermal heating system with cast iron radiators (see welserver.com/WEL0961 for description of the system). Overall, the results were better than I expected, $267 for the whole winter, or about $51/month for the 5-month period Nov-Mar. Although we have solar panels, geo cost is calculated as if I bought all the power from the grid. Geodata2016.png

    I’m pretty confident of these numbers, which are based on welserver data. kWh values were calculated from a Hall effect current sensor on the line to the heat pump, and include the flow center and circulation pumps. The sensor was calibrated against an electromechanical residential electric meter using a resistive load (space heater), so if anything the kWh values are probably overestimated by a few percent due to power factor. I did not have the welserver set up in October, but degree-days as well as electric bill was almost the same as November, so I assumed the same kWh. Needless to say, I am very happy with the results. I was hoping to come in under $400, but I never thought it would be closer to $200! If I’d installed a gas boiler instead, I’d be paying $204/year just for the connection, never mind the gas. The only caveat is that this does not include hot water.

    We did not have a single problem with the system all winter, and we never needed backup heat from the oil-fired boiler. The coldest night was St. Valentine’s day when it dipped to 11°F, and you can see that the radiator temperature was maxing out at about 117°, but even then the system wasn’t running continuously, so it looks like it could have handled a few degrees colder than that. Performance of the loops was outstanding, the absolute lowest EST reading was 45°.

    HeatingSystemr.png

    Even so, I can think of a few tweaks that might squeeze a little more efficiency from the system. I should probably put a delay relay on one of the ECM circulators just to flush the last few gallons of hot water from the heat exchanger into the radiators at the end of each cycle. Also, when the unit is running at first stage, deltaT for the loop is only 4.5°, so I might save a bit by running just one of the flow center pumps on first stage. The thermostat is currently set to trigger second stage if setpoint isn’t reached within 40 min, but I’m thinking it might be better to just set second stage to come on at a certain outdoor temperature, say 32°, so that it would never come on in milder weather. Also on tap for the summer is even more insulating, e.g., the ceiling joists are only a little over half full of rock wool so that could use some improvement. More importantly, we just signed the contract for another 4 kW of grid-tied solar panels, which should be enough to cover both heat and A/C and will bring us pretty close to being energy self-sufficient and carbon-neutral.
     
  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I love happy endings. I have fought for years that cast iron emitters will not work with geo.

    Mark
     
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    What kind of pumps do you use? model number?

    No new 3 ton system should have a 2 pump flow center!
     
  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Why not?
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Because a customer should not having to pay for the running costs of 2 pumps when 1 will do the job....
     
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Oh Great Carnack, I agree, but how do you know that is the case?
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

     
  8. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Why would you want to do this? Not sure if that adds anything.
     
  9. frankz

    frankz New Member

    My thought was, for maximum COP you'd always want the lowest possible radiator temperature that would maintain setpoint. You can see from the WEL data that radiator temp is much more variable in milder weather. It always runs long enough to go into 2nd stage. If I blocked out 2nd stage, the radiator temp would rise more gradually, heat would have more time to disperse through the room, and the max radiator temperature would be lower. Probably not a big effect though, admittedly.
     
  10. frankz

    frankz New Member

    The flow center pumps are Grundfos UP26 99F. The flow center was chosen by the loop contractor but in retrospect they do seem like a bit of overkill to me. He told me as a general rule about an 8° deltaT is optimal. With pumps on the lowest setting it's close to that on 2nd stage but only 4.5° on 1st stage. But it's no problem running just one pump, right?
     
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    But it's no problem running just one pump, right?

    Right
     
  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Ideally you want to take one pump out but you can also try to disable one of them by disconnecting it. Your system COP will go up by 10-15% by not using one of the pumps.
    You would also benefit from an outdoor reset which throttles back your supply temps on warmer weather, which will significantly effect your COP.
    Your system like will run more effective in 2nd stage than in 1st stage, given that your pumping power remains the same. In other words, your parasitic loss with the pumps running will be the same, but the free energy harvested will be less in 1st stage. So proportionally you are using more pumping power per BTU delivered in 1st stage than in 2nd stage, which negatively effects your COP.
     
  13. Olas

    Olas New Member

    Hi, You will have to excuse my lack of knowledge and with the best effort to understand it all the post and subsequent posts do go over my head a bit. I have nearly had our 30kw ground source heat pump commissioned with the ground loop full and the buffer tank ready to be heated. It runs on 3 10kw pumps 1800m of 2 meter deep loop. The majority of the property I will have underfloor heating. All UF in the solid floors 190 square meters (basement) and 2//3 of the ground floor timber and 1/3 of the 1st floor. It is a big building. It is a renovation and I am simply cannot put underfloor in some rooms so I think I will go for cast iron Rads. My questions is this. Did you and should I oversize the rads if they are cast iron with the same calculation if they were steel or do I need to oversize at all. I have the wattage required for the rooms of course. I can't size at the manufacturers Delta 50 figures of course as my flow temp is lover than that at more like delta 35 or 50 degrees. Any help would be very much appreciated. Thank you. If you need any more info hopefully I can provide it.
    regards,
     
  14. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Olaf, maybe start a new thread.

    But if building new, I'd look at fan convectors (Myson) vs. radiators. The bonus being you can get air conditioning out of them as well.
     
  15. Olas

    Olas New Member

    Hi, yea really don't need air con and anpwriod property so they wouldn't really look the part.
     
  16. Olas

    Olas New Member

    Sorry thanks for your reply and I've taken your advice and put it on a new thread. Thank you.
     

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