New York GeoStar Quote - Central NY

Discussion in 'Quotes and Proposals' started by TheBigYahi, Aug 1, 2018.

  1. TheBigYahi

    TheBigYahi New Member

    First off, thanks to the site for being a wealth of information for someone like me shopping for geothermal systems.

    I've been having a heck of a time getting call backs in my area, so I only have been able to get one quote so I would really appreciate feedback.

    We are taking advantage of the impending death of our central A/C unit to make the jump to geo. At the same time, we're investing in a community solar project (our panels, their farm, remote net metering) with the goal of going Net Zero.

    Contractor: A large home performance/HVAC company. Their website has several case studies on geothermal systems they've installed in my area.

    Inputs: 46 kbtu heat loss, 22 kbtu heat gain

    System:
    1 - 500' vertical loop with 1-1/2" pipe
    GeoStar Sycamore 5 ton (51 kbtu heat, WF Series 7 rebranded)
    GeoStar Ashton 2 ton for DHW using a 50 gallon State electric heater for storage
    GeoStar IntelliZone2 - 4 zones (basement, first floor, master bedroom, other bedrooms)
    Aurora Web Monitoring

    Net Price: $28k after NYSERDA grants and tax credits

    The original proposal called for a 4 ton unit, however its output is only 43 kbtu so with the variable compressor and loop pump I thought it prudent to upgrade to the 5 ton unit. The cost increase was small.

    I want to preface my questions with the fact that I want to trust the contractor, however they haven't been able to produce loop design numbers which gives me some pause. I've asked all of these questions to them, but while I await a response I would love to hear opinions.
    1. At 51 kbtu this is equivalent to a 4.25 ton unit and the resulting loop field is 117 ft/ton. The contractor claims that by going with 1-1/2" pipe the resulting increase in flow will negate the smaller loop field. I've read on here that heat transfer is independent of pipe diameter and larger sizes only help with minimizing pumping pressure.
    2. Although they share the same loop field, they claim the hot water unit will have no affect on performance due to the shorter duty cycle. My opinion is mixed on this. I know it's not prudent to size for the full 22 kbtu additional, but is it acceptable to ignore it completely?
    3. For the DHW system, the storage tank they specified doesn't have connections to act as a hydronic zone for the Ashton unit, just cold in and hot out. I can't really envision how it would work without 4 connections, cold water in, hot water out, hydronic in, hydronic out.
     
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Looks like they are using the GroundUp Geo design, which by itself is utterly solid (and has been field tested in many settings) and they use GeoStar equipment supplied by John Manning at Phoenix Energy Supply. He is one of the best designers in the Industry, and NYSERDA only gives rebates out after they check out the quality, meaning of your system is not performing the contractor is not getting paid the $10,000 from NYSERDA. The GroundUp design fits for every occasion within a certain parameter, since the variable speed unit is adapting.

    1) Larger pipe has slightly better heat transfer due to larger surface area. The key is the higher volume and the continuous draw without pulsing which makes the single borehole perform very well. It might drive the borehole temp further down, costing you a few % on efficiency during peak time, but the average seasonal temp is actually higher.

    2) You loop might go down to 25F when both units are running, and the variable speed runs at full capacity. Over all the system will be significantly more efficient. In addition the ground lacks behind (thermal inertia), and only drops to its coldest temp at the end of the heating season (March), however peak capacity is needed normally on the coldest days of the year, typically Jan or Feb, when the ground is still warmer. The borehole design is covering about 69,000 BTU/H heatloss in central NYS climate. We have a single 500ft experimental borehole covering 84,000 BTU/h heatloss load, pushing the boundaries further. So the ft/ton formula is going out off the window. I would not worry about it.

    3) Tank: Indeed you have to worry about that the w-w unit turns on, it will pull cold water through the tank and mix it with hot water on the top of the tank. I would be beneficial to have the water going into the heatpump from the tank to be taken from the bottom of the tank.

    PM me who the contractor is, I can talk to them (we are all friendly here), and I'll call John Manning. Maybe he knows something I don't.

    But overall your design has been proven to be very efficient. I would not worry.

    Check out GroundUpgeo.org
     
  3. ChrisJ

    ChrisJ Active Member Forum Leader

    My first system was a combo water to water and water to air system. It used a standard water heater for the storage tank.

    The drain had a "T" installed so water could be pulled from the bottom of the tank to the HP, then sent back to tank via a T in the cold water entering pipe.

    To me the main draw back is the ports on these tanks are only 3/4". If enough GPM can be sent through the heat exchanger I guess it doesn't matter.

    I also had a radiant storage tank set up similarly, except the water from the HP back to the tank went into the port for the pressure relief valve. That's how we got 4 connections
     
  4. TheBigYahi

    TheBigYahi New Member

    Thanks for the great replies. There was some misunderstanding and there is a heat pump loop through the water storage tank, which is what I expected. I have some questions about the control schemes which I’m going to ask the engineer about next week, otherwise I think we are good to go.
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The tank is controlled by a simple thermostat, which turns the w-w heatpump on when the tank temp drops below a certain level.
    The w-w and the w-a (water-air) heat pump talk to each other, since the w-a controls the variable speed circulator serving both heat pumps. As soon as the w-w wants to turn on, the w-a tells the variable speed loop field circulator to go to full speed as long as the w-w needs to make hot water.
     

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