Diagnostic help please

Discussion in 'Vertical and Horizontal Loops' started by waterpirate, Aug 10, 2010.

  1. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I recently had a contractor shut down a loop field and convert to temporary open loop scenario due to a ewt of 94 and lwt of 100.6. The data I have collected is as follows based on initial design and open experiment.

    4 ton loop field= 4 3/4 200' bores in saturated sands and clay 20% grout
    waterfurnace ndh049 with 4 ducted zones
    cooling load 35,900/44,900
    heating load 35,000
    ewp 26.2
    lwp 23.8

    At an ewt of 94 the unit would only satisfy cooling load to a temp of 75-76 in house, loop temp continued to rise. Hvac repurged and verified no air lock or circ problem. I recomended that the unit be hooked up to a water line and see what happens. With an ewt of 65.5 which I think is due to pipe routing through the garage and a lwt of 76.2 the machine is satisfying the house load to a chilly 69-70.
    This is where my knowledge as the driller really falls short. I did get the cut sheet for said unit and found that at an ewt of 70 in high speed(second stage?) gives the unit a capacity of 53.1 and 37.2 in cooling. Am I correct in assuming that this may be the actual cooling load for the house since it works? At the ewt of 90 the cooling capacity is listed as 47.8 and 34.9 that would only cool to a temp 75-76. At the ewt of 90 the capacity of the unit appears to match the numbers provided but will not cool. I plan t excavate the manifold to ensure that backfill did not kink or damage a circuit and while I am there I plan to flow test also and compare numbers.
    Anybody see something jumping out that appears not kosher? Suggestions?
  2. Eric,

    What is missing from your posted data is flow info, flowcenter type, pressurized or non-pressurized system, antifreeze info, etc..

    I would suggest getting a handle on flow prior to proceeding with excavation.

    How and where was ewp 26.2 and lwp 23.8 measured? 2.4 PD ????
    Last edited: Aug 10, 2010
  3. Looby

    Looby Member Forum Leader

    What pressure units? ...psi or ftwc?

    ...static pressure is kinda low in either case,

    Last edited: Aug 10, 2010
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Pressureised system, water furnace flow center, 20% methanol, pressure readings were taken through the coil at unit via pt ports, A 2.4 psi pressure drop indicates what for this model waterfurnace?
    No comments on the load figures?
  5. Looby

    Looby Member Forum Leader

    That's very close to 10.0 gpm (+/- 0.25 gpm for each 0.1 psi error in delta_P).

    Interpolated from Envision Installation Manual, page 40.
    Last edited: Aug 10, 2010
  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    What jumped out at me is the radical change in house temp (75-->69 = 6 degrees) based on dropping the EWT from 90 to 65.

    A WF 049 unit is said to produce well over 40 kbtuh even with EWT 100+, although the 2.4 psig pressure drop indicates marginal flow for higher EWTs.

    System only loses 5-10% cooling capacity given stated change in EWT - that is not consistent with a 6 degree change in minimum indoor temp unless outdoor temp changed radically as well.

    The install manual isn't as good as the spec manual for these units which has many pages of btuh, psid, water temp, etc. I could email you that.

    Eric - maybe we can chat by phone and I can help you work through this issue and you can help me a bit on a pump issue we have discussed online.

    Try me Wednesday evening at ( PM'd phone number) if that time is convenient.
  7. GCI

    GCI Member

    Rambling thoughts here...

    High EWTs, low flow and low temperature rise across the coil are conflicting pieces of information. With lower flowrates, you should see a temperature rise in excess of 10 degrees.

    A 6 degree rise across the coil in cooling mode is low, especially with a 10 gpm flowrate. Strictly based on the lack of temperature rise in cooling, I would guess:

    1) the low voltage to the unit isn't wired properly (or the t-stat isn't set up for two stages of cooling) and it isn't kicking into high
    2) if controls aren't the issue, there may be another issue with the heat pump, possibly refrigerant charge

    It is unlikely that the heat pump would be able to pull room temps down to 69-70 in low speed and it is unlikely that the heat pump would be able to push the temp in excess of 90 degrees in first stage unless loopfield capacity is an issue... On that basis, check for a blocked loop.
    Last edited: Aug 12, 2010
  8. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader


    Thank you all for your comments and input, it is why this forum stands out in a crown of intra net forums.
    The hvac was sooooo sloooowwww to get me data it was infuriating. When the data finally did arrive it was incomplete. The "rubic's cube" peice of data arrived yesterday. The design was for 95/75 in cooling. We have seen a three week stretch that gave us 80 in the morning at 5am and over 100 by noon. We got a 3 day respite and then we went right back to 80/100. Given that peice of design data the unit is doing all it can at the design load. Run times have been around 18 to 20 hours a day with no recovery time for the loop field. My favorite addage " the load is what the load is"
    Many thanks to Curt who helped me get my brain wrapped around even more of the unit side dynamics in an effort to diagnose.
    Final word= the design was to tight to account for the 50 year heatwave. A local geo guy in business doing geo since the 70's said that he see's the design loads go up and down as they relate to recent wheather patterns since he began. The loads get tighter and tighter untill a fluke year occurs and then they snowball back to planning for a rainy day.

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