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  1. #27
    Join Date
    Jun 2008
    Posts
    47

    Cool reverse-return?

    I don't mean to hijack this thread, but can you define "Reverse Return" wells?

    We are positioning 7 wells (separated into three loops.... our hvac and driller agreed this was best for the install)...

    3 are at 300ft, separated 20ft
    2 are at 225 ft separated 20ft
    2 are at 225 ft separated 20ft

    There are 3 sets of lines coming into basement. does reverse-return define how they are connected to the manifold coming to / from the house?

  2. #28
    Join Date
    Aug 2008
    Posts
    40

    Only one question

    What are the water temps in and out of the unit? Temps and Delta T speak volumes about well field.

    a0128958 your temp seems high for entering. Delta T should be 10 degrees.
    Last edited by Jarredsdad; 08-03-2008 at 06:18 PM.

  3. #29
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    Reverse return is a parallel piping configuration that attempts to self balance the flow through the parallel circuits - in this case the wells.

    It's hard to describe without an illistration, I would suggest googling it. Any one who installs any form of hydronic equipment should be able to show you a quick sketch of a reverse return system. Plenty of info on the wild wild web....

    In a small set-up like yours it will likely not be needed. We always design our well fields reverse return - but we are usually envolved with 20 or 100 or 200 ton systems...

  4. #30
    Join Date
    Aug 2008
    Posts
    40
    In a reverse return the first loop to get water is the last to return and the last to get water is the first to return. Diagram here:
    http://www.majorgeothermal.com/PDFs/Manifolding/Long%20Header%20Vertical%205%20Port.pdf

    Any IGSHPA certified installer will disign his/her loops with reverse return, don't want to do all that work and end up with a "locked" hole.

    http://www.igshpa.okstate.edu/index.htm

    http://www.igshpa.okstate.edu/pdf_fi...h_vol1_no3.pdf

  5. #31
    Join Date
    Aug 2006
    Location
    Dallas (Plano), TX
    Posts
    168
    Quote Originally Posted by Jarredsdad View Post

    a0128958 your temp seems high for entering. Delta T should be 10 degrees.
    I agree, but don't know why.

    My EWT at the moment ranges from 76 - 84F, depending on time of day and/or amount of heat being rejected (about 750 KBTU per day, at about a 30 - 82 KBTU/hr rate). Here's a chart that clearly illustrates the wide EWT swing over each day: http://welserver.com/WEL0043/EnteringWaterTemps.gif

    My 'deep earth' temp is 68 for my vertical loop - 8 wells, each at 300' deep, 1" HDPE U-Tube pipe, normal grout.

    My flow is 14 - 21 gpm with DeltaT ranging from 4.5 - 5.

    My KBTU/hr is pretty accurately measured, BTW.

    Many thanks,

    Bill

  6. #32
    Join Date
    Aug 2008
    Posts
    40
    That's a chart alright.

    Don't doubt your Kw figures.

    76 and 84 are high with a 68 deep temp. Wonder how deep the header pipes are.

    Where do you get your flow stats from? Flow meter or pressure drop to feet of head to gpm?

    7 gpm swing with 8 degree swing. Are you sure your not pushing air around in the loop? Did you witness a good flush and purge at install?

    Last questions are. Do you have valves at in inlet and outlet of the unit? Are they full flow ball valves? Are they wide open? Or did the installer put in a CV valve at yhe coil outlet to maintain cosnstant flow?

  7. #33
    Join Date
    Aug 2006
    Location
    Dallas (Plano), TX
    Posts
    168
    Quote Originally Posted by Jarredsdad View Post

    76 and 84 are high with a 68 deep temp. Wonder how deep the header pipes are.

    Where do you get your flow stats from? Flow meter or pressure drop to feet of head to gpm?

    7 gpm swing with 8 degree swing. Are you sure your not pushing air around in the loop? Did you witness a good flush and purge at install?

    Last questions are. Do you have valves at in inlet and outlet of the unit? Are they full flow ball valves? Are they wide open? Or did the installer put in a CV valve at yhe coil outlet to maintain cosnstant flow?
    I believe the 68° deep earth temp is what it would be only if heat wasn't being dumped into the earth. In my case, at the moment, I'm dumping about 650 KBTU/day, or about 20 MBTU/month, into the earth.

    Header pipes to connect up the 8 wells (spaced 20' or more apart) are at about 5 feet deep.

    Flow stats come from pressure drop across coax heat exchanger / looking up resulting flow from WaterFurnace tables. Pressure gage is 3.5" high accuracy.

    The 7 gpm swing was a summary statement due to having 2 GSHP units hooked up to one vertical loop. In actuality, it's a very constant flow, depending on unit operation:
    3 ton unit alone = 14 gpm
    5 ton unit alone = 21
    3 & 5 ton units together = 11 + 19

    I didn't witness flush/purge at install time. I do have SpiroTop air release valves at the highest point of each EWT connection.

    I don't have valves at the GSHP inlets/outlets (see http://www.pbase.com/neukranz/image/84286044 - 5 ton unit ).

    I do have fully open ball valves at the pump inlets/outlets (see http://www.pbase.com/neukranz/image/84286046 - 5 ton pumps). Check valves are also here.

    Many thanks!

    Best regards,

    Bill

  8. #34
    Join Date
    Aug 2008
    Posts
    40

    WoW

    Bill, all I can say is Ouch.

    IMO your install is not correct.

    You have no way to regulate water flow through the water coil. Your just pumping through and not taking advantage of the earth heat transfer.

    If you have the install manuals you may see what the manufacturer recommends for EWT and Delta tee. Rule of thumb is 10 degrees, which is from a long convoluted formula Florida Heat Pump used to have years ago. Basically, when you were all done the end result was 10 degrees Delta T.

    Some, like McGuay, want 12 to 14 degrees.

    To affirm, don't belive me. Ask this guy, http://www.igshpa.okstate.edu/pdf_fi...h_vol1_no3.pdf. Haven't talked to him in, gee 5 years, so make the email full of facts as I expect he's pretty busy.

    Another Geo rule is 3 gpm per ton. You're over that.

    Lastly, Bill, I am not some new member who thinks he knows, I know I know.

    I was IGSHPA cert, only need the ED to troubleshoot. Did do warranty repair for Florida Heat Pump with a blank check to fix the system. Long story there, but personally satisfactory because Joe Homeowner thought I wanted his money Not so Joe, I'm here to fix it and you own zero.

    Chris

  9. #35
    Join Date
    Aug 2006
    Location
    Dallas (Plano), TX
    Posts
    168
    Quote Originally Posted by Jarredsdad View Post

    ... You have no way to regulate water flow through the water coil. Your just pumping through and not taking advantage of the earth heat transfer.

    If you have the install manuals you may see what the manufacturer recommends for EWT and Delta tee. Rule of thumb is 10 degrees ...

    Another Geo rule is 3 gpm per ton. You're over that.

    Chris
    Chris, your time/effort to respond is much appreciated.

    I'm going to pursue the link you provided - this is very helpful. Thanks.

    For my actual installation, perhaps I can find someone who can:
    - model my borehole field characteristics and determine if my EWT can be optimized as a function of slower water flow (thus improving EER);
    - figure out what pumps could then be substituted for my existing Grundfos (UP 26-116) pumps;
    - install the pumps.

    Published WaterFurnace spec is about 8.8F DeltaT at 75F EWT, regardless of 3 or 5 ton unit (1st stage). (Flow is spec'd at 8 gpm for 3 ton unit, and 14 for 5 ton unit.)

    This isn't far from your stated above 10 DeltaT rule-of-thumb.

    And indeed, WF's published flow rate specs for my units are at about 3 gpm/ton (2nd stage), as you note above as another rule-of-thumb.

    Thanks too for the note on your qualifications - I'm sure other professionals here, and those asking questions, will substantially benefit from your knowledge and skills.

    Best regards,

    Bill

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