plumbing for multiple WF 7 Series HPs+flow centers on common ground loop

Discussion in 'General Discussions' started by gsmith22, Nov 12, 2019.

  1. gsmith22

    gsmith22 Member

    Not sure I have a problem or not but wanted a confirmation on how interior loop plumbing should be set up:

    I have two Waterfurnace 7 Series Heat pumps (4 ton unit for downstairs zone and 3 ton unit for upstairs zone). Each HP has its own flow center; each flow center has a single variable speed circulator pump (Grundfos Magna GEO 32-140 in each). Both flow centers are plumbed together into a single interior HDPE header pipe that runs outside to the common closed ground loop.

    During initial installation, the installer had plumbed Johnson Controls modulating valves supplied by Waterfurnace on the output side of each heat pump and wired them into the HP control board on the same terminals as the signal for the flow center pumps. This didn't work - the modulating valves didn't modulate and the flow center pumps ran at maximum regardless of whether the HPs were calling for flow or not. I didn't understand why a modulating valve would be needed with variable speed pumping anyway and suggested just check valves in their place (on the outflow side of the HPs) so that backwards flow/short circuiting when only one of the flow centers was running would be prevented through the non-running HP. Installer didn't understand it either, talked with Waterfurnace tech who told them they aren't needed, and decided my suggestion was the correct way to move forward. He removed the modulating valves and instead installed check valves on the output side of each heat pump. This seemingly cured everything: each circulator pump is only on when its respective HP is on and each circulator pump revs up and down according to its respective HP stage. Everything seemed okay.

    But I got this nagging feeling: why would Waterfurnace provide modulating valves (knowing I have 7 series units with variable speed flow centers on a closed loop) if they weren't necessary? In looking at the interior flow path through the HPs, it got me thinking too that if one HP/flow center is running, although the check valves on the HP outflow sides prevent backwards flow, what stops forward flow through the non running HP if only one is running? Would the combination of the pressure drop through the non-running HP and non-running flow center pump act as a blockage to essentially stop forward flow through the non-running circuit? Wondering if those modulating valves need to be placed on the inflow side of the HP to stop forward flow through a non-running HP? If so, were on the control board do they get wired as the installer showed me there didn't seem to be a place for them - only the variable speed pump signal wires. Curious as to what others have done/have installed for multi HP system each with own flow center on common ground loop. Thanks in advance.
  2. gsmith22

    gsmith22 Member

    geo-flo's website has a nice diagram of the plumbing layout I am describing:

    Diagram has 5 heat pumps and I only have 2 but otherwise the layout is the same. They show both a check valve (B1/B2) as well as a modulating valve (C1/C2). I understand why the check valve is needed so you don't get reverse flow, but is the modulating valve (really an on/off valve) needed to stop forward flow through a non-running HP. thanks
  3. wing

    wing Member

    Are you able to measure pressure drop across the non operating heat pumps ?

    If there is no pressure drop, then the flow rate is zero or very small.

    I suppose in abundance of caution you could also install a zone valve on each heat pump circuit that only opens when the pump is operating.
  4. gsmith22

    gsmith22 Member

    After I wrote the first two posts, I realized that measuring flow across the non-running heat pump while the other heat pump was running would remove any doubt about what is going on. I haven't done it yet, but I am planning on measuring flow in the non-running heat pump while I cycle the stages of the other running heat pump (uptick and downtick thermostat to get it to speed up and down) just to make sure low, medium, and high flow situations all work the same. Then switch running/non-running heat pumps and do the same test again. My gut says I am going to get very small amounts of flow (or maybe no measurable flow) in the non-running heat pump (say 1 to 5% of the flow in the running heat pump). That probably means the running flow center works slightly more than it should with one heat pump running (flow lost to non running circuit). That same gut feeling tells me I am still better off with that situation than installing a zone valve on each heat pump that creates a flow restriction even when fully open. Then I would have to figure out how to open and close the zone valve as the AXB board seems to be able to only control a variable speed pump or a zone valve but not both at the same time. I'll take the variable speed pump over the zone valve. :) Low flow situations when the HPs are at stages 1 or 2 are probably the only situations where you might have one running and the other not anyway so my proposed experiment is probably really on applicable to the first several stages of the HPs. I can't envision the situation where the downstairs zone needs the HP at 6 and the upstairs is off (or vice versa).

    I have the Symphony monitoring from Waterfurnace on each heat pump that includes a flow meter on the inlet side of the HP. But the flow info is hidden behind the dealer firewall and I can't see it on the thermostats or owner web interface. I really don't understand what they are thinking by hiding this information. I get they don't want owners messing with settings and that is not my intention but its kind of infuriating that I paid for the Waterfurnace monitoring and I don't get to see all that is monitored. To top it off, I know they are using my data for their marketing literature because my installer was able to pull up all the units they have installed with monitoring and show me how they function including past energy use (which ultimately confirmed my pre-installation math that GSHP was the way to go and ditch the propane heat/ac units).

    If I can't figure out how to see the flow data, I'll have to get the instruments to use the pete's ports on the inlet and outlet side of the HPs to do this experiment. Anyone know how to get into the non-visible data on Symphony without the AID tool?
  5. SShaw

    SShaw Member

    You can see the flow data. Google "aurora weblink manual" and read the installation manual, especially pages 10-12, carefully.
    gsmith22 likes this.
  6. gsmith22

    gsmith22 Member

    thank you so much. I have that manual at home and must have not read that part very carefully while I was getting the AWL hooked into my wifi connection. I'll give local mode a try and see if I can test my flow theory. thanks again
  7. SShaw

    SShaw Member

    You're welcome. Let me know how it works for you. I find the "Performance Monitor" menu takes four or five minutes to show up. I'm not sure if that's an issue unique to my system or something normal.
  8. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Interesting discussion.

    If you want to use one variable speed circulator per 7 series, yes, check valves are the way to go. The modulating valves are thought for open loop designs. However, if we have more that (1) 7 series on one looptfield, we always use central pressure regulated variable speed pumps with modulating valves on each heat pump.

    Example diagram attached

    Attached Files:

  9. gsmith22

    gsmith22 Member

    local mode using a web browser essentially turned my laptop into an AID tool - thank you so much SShaw. I can confirm that the "performance monitoring" menu options do take several minutes to show up while the basic info is available once I connect to the AWL local wifi signal. I'm glad you pointed that out as I couldn't find the "flow" data initially until the performance stuff showed up. Per the sensor data, I don't have any flow in the non-running heat pump when the other heat pump is running (at various speeds) confirming check valves are all that is needed for a closed loop system with heat pumps plumbed in parallel and each heat pump having their own flow center.

    docjenser, I was strongly considering just one flow center with multiple heat pumps but I don't think my installer had done that previously (actually much of what I asked to be installed seemed to be a new thing for them) and I was worried about them understanding how the controls work. Ultimately I settled for the multi-flow center (one on each HP) approach with the idea that if all the flow centers had variable speed pumps, I wouldn't be too far behind the single central pressure regulated variable speed pump flow control from an efficiency standpoint. Weather it is an open loop system with modulating valves or a closed loop system with central pressure regulated variable speed pumps and modulating valves on each heat pump, how do you control both the modulating valves and variable speed pump? The AXB board seems to be able to control a VS pump or a modulating valve but not both which is what lead us to the check valve scenario.

    While in the local mode, I was able to see that both my loop pumps and blower fans for each HP are set to the Waterfurnace recommended defaults. The fan seems okay (G at 2, Low at 3, High at 9, and Aux at 10) but I think the variable speed loop pump for each HP is working way too hard at lower HP stages. They have it at 50% min and 100% max and I was getting ~12gpm for the 4 ton unit (alone) and ~14gpm for 3 ton unit (alone) running them between stages 1 to 3. This seems really high to me and its my understanding that 2.5 to 3gpm/ton is needed at full capacity only or do I have this wrong? The instruction guide manual for the AID tool discusses a way to set the min/max for each flow center but there was limited details on the process. Has anyone done this? Do I only need 2.5 to 3gpm/ton at full capacity or across all stages of the variable speed HP? I'd like to do this with my installer (I don't think they have any clue about this) and want to understand the process for configuring the min/max for each flow center (I guess the fan too if someone has a procedure/document). Anyone with any knowledge of how to commission these settings properly as opposed to just taking the Waterfurnace defaults?
  10. SShaw

    SShaw Member

    gsmith22, Good to hear your machine behaves like mine.

    The 7 Series installation manual gives the recommended flow rates on page 9. Recommended Min is 5 GPM for both the 3 ton and the 4 ton. Max is 12 GPM for the 3 ton and 15 GPM for the 4 ton.

    In the AID tool you can set the pump to Min and measure the flow rate through your loop. You can do the same for Max. You can also set the pump percentages for Min and Max. This lets you determine how to set the variable speed pump to achieve the recommended flow rates. The process is described on page 41 of the installation manual under AXB setup.

    Your installer should have done this for you, obviously. You will use a lot less energy when you get the pumps set properly. When my system is on H2/F4 the pump uses only 15W to flow 5.7 GPM. If the WF sensors can be believed, the COP is over 7.
  11. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You only have to control the modulating valves.
    The central pump regulates itself. You can set them for constant pressure, meaning when more heat pumps come online or the modulating valves open up more, The central pump recognizes the loss in back pressure and revs up accordingly.
    The art comes in when now the flow increases and the pressure drop of the loop field comes into play, with higher flow through it. Now you benefit from variable pressure setting, meaning the central pump automatically increases the pressure to overcome the added pressure drop in the loop field. Works like a charm once you master it, and you never go back to multiple pumps.

    So you simply dial in the flow you need with one or 2 heat pumps, set it to variable pressure, and watch it to rev up when more heat pumps come online. We are having 50-60 heat pumps on one flow center, it really works like a charm.
    The issue with the single pump for each heat pump design we had was the back flow trough the non engaged pumps, which you can cure with a check valve, which then soon or later fails, and then you are up and running looking for the flaw in the system.

    This is not currently streaming data, but you can see the general design/concept. 2 central pumps for redundancy.
  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Any reason you have the fan running at stage 4 when the compressor is running at stage 2?
  13. SShaw

    SShaw Member

    Not particularly. I have a 4T 7 Series. My installer set the fan for 2/3/9/10 (G/L/H/AUX) and I haven't changed it. I have an Intellizone2 zoning system with two zones. Basement and main level are on Zone1 and the upstairs is on Zone2. The system seems to bounce between H2/F4 and H6/F5 most of the time I don't think I've ever seen it in stage 1, which seems a bit odd.

    Speed 9 is supposed to be 1520 CFM, which would be close to the the typical recommended airflow of 1500 CFM for 4T so I left it. I'm open to adjusting things if it would improve performance.

    I measured COPs of 7.3 at H2/F4 and 5.5 at H6/F5, including the pump power, so it seems like the system is doing pretty well. I didn't turn off the DSH when making those measurements. I'm not sure how the DSH might have affected the measurement.
  14. gsmith22

    gsmith22 Member

    I'd be interested to know how to determine proper fan settings instead of Waterfurnace's defaults. If there is a methodology or document you can point me too, I'll be happy to do my own reading/research.

    How does the central pump regulate itself? Does it have its own controller separate from the AXB board? Its probably an issue with my installer but he couldn't figure out where to wire the pump low voltage signal wires with the modulating valves installed. Doesn't seem like it would be necessary anyway for my setup (only needing check valves on parallel pumps) but I'm curious how it works should I ever decide to ditch my current setup. I believe one of the 32-140 pumps could handle the full flow at system pressure drop but it would be close. I'll keep an eye on the check valves - wouldn't have suspected they would be "fragile" especially with the swing valves I have (plumbed horizontally at least).
  15. David Maynard

    David Maynard Renewable

    Hi gsmith22,
    You can follow these recommendations for adjusting fan settings using the AID Tool. You will need your installation manual or find it here
    Plug your AID Tool (if you don't have one, configuring the fan speeds will be considerably more difficult using SW-1) in the heatpump or Symphony. From the Main Menu, select ''Setup'', then ''ECM Speed Setup''. Select ''Yes'' you want to change. From there, you will have 4 different speeds to configure (G, L, H & AUX). Compare these speeds to page 17 of the installation manual and place them accordingly within the 048 (4 ton) zone of speed selections. Be advised, read the footnotes carefully. You might have to test out these speeds for performace, COP and noise from the air duct distribution system.
    Hope this helps.
  16. gsmith22

    gsmith22 Member

    thanks for the reply. I was aware of how to adjust the fan speeds. My question was more along the lines of why should fan speed 3 be configured with compressor speeds 1 and 2 (WF defaults) rather than say fan speed 1 or fan speed 2. Or say why is fan speed 9 set as the highest speed rather than something higher ( 10, 11, or 12 speeds). I am near positive the fan speed will directly relate to how much cooling and heating the unit can perform and I suspect lowering the fan speed will cause an increase in compressor wattage as it has to work harder to meet set point. So I have decided to leave this alone (for now). I could see where really low pressure drop duct layout may allow lower fan speeds and really high pressure drop ducts may force higher speeds. WF defaults are probably a happy medium. I have to think on this some more. In my system, the WF fan speed defaults result in fan wattage between 5 and 10% of the overall system wattage so its really just enhancements at the margins at this point anyway.

    For anyone following this, I found some interesting patterns while adjusting the variable speed flow centers. With one unit off and one unit on (one flow center per unit, plumbed in parallel to common header), each flow center was adjusted - min speed could be set at about 20 to 25% to achieve the 5gpm minimum per WF for each unit and max speed could be set at about 60 to 65% to achieve the 12 or 15gpm max per WF for each unit. However, with both units running, I found that min speed had to be adjusted upward to 30% on each flow center. Each flow center pressurizes the common header creating a back pressure on the flow centers that they must overcome to have forward flow (check valves prevent backwards flow). When set to anything below 30%, I found the flow centers fought with each other and ended up with no or too little flow on one heat pump, even though they had over 5gpm with only one running. 30% on each allows each flow center to run alone (at more than 5gpm) and as well as together (at just above 5gpm). A similar thing was found at the max speed too. I had to put the 3 ton unit at 70% and the 4 ton unit at 75% and even then they were a little under the WF max flows. I've since done some reading on this and it is a "feature" of this layout. It seems that in addition to the check valves (to prevent backwards flow/short circuiting), you also have to have nearly the same pressure loss through each unit/piping as well as have the same size pumps or else the system probably wouldn't flow through one of the heat pumps. Idronics 5 has a nice writeup on this same situation for hydronic heating zoned via circulators (Figure 6-5).
    David Maynard likes this.
  17. David Maynard

    David Maynard Renewable

    Smith, I did some digging around and found the 7 Series Application Guide which goes into more detail with regards to ventilation than the actual instal manual. I would explain, but there's a lot of material to cover. I'll let you consult Page 15 of the attached PDF and give me your thoughts afterwards. I really hope this is helpful, because I don't what else to refer to if not. Let me know!

    Attached Files:

  18. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The energy needed to increase airflow in the air ducts increase as a square function, meaning twice as much flow requires 4 times the energy. a small reduction in the airflow can cause substantial savings in fan power, but only a small increase in compressor power. Fan setting of 1 usually leads to air coil icing in the A/C mode, you need at least set it a minimum of 2. High fan setting of 8 or higher lead to noise and unnecessary energy consumption and discomfort, without much increase in air flow. You only need fan setting of 9 or 10 for the aux heat, otherwise the heat elements burn out.

    In addition of what you are describing with individual circulation pumps for each heat pump (they start stealing flow from each other, and water flows the path of least resistance) makes me go with a central circulator which is pressure self regulated. The controller is internal and independent from the AXB board. The Wilo Stratos can be regulated via a 0-10 volt PWM signal from the ABC board, but the setup is different. The 0-10 V signal controls the modulating valve, which when closing down further and increases the back pressure in the pipes, which is recognized by the will pump, which causes it to rev down to keep the pressure constant. Pretty ingenious.
    Even better is the variable pressure setting, which increases the pressure during high system flow requirements. Only then the pressure drop of the loopfield becomes relevant. The heat pump need the same flow each (constant pressure), aka the same pressure, but when more of them are running and the flow increases in the loop field, the pressure drop in the loop field raises and requires more pressure from the pump, thus the pump can increase the pressure up to 100% more, in order to keep the flow rate to the heat pumps the same.

    And always keep in mind, to have 2 gym flow instead of 3 gpm is not the end of the world either.
  19. gsmith22

    gsmith22 Member

    David thank you for that document. The only way to access it seems to be from google and it isn't linked on waterfurnace's website which is odd. thank you for pointing it out. It provides a lot more about the operation of the compressor staging too - all very interesting.

    docjenser, yes, I didn't think about the friction loss of air in ducts and how that increases exponentially with speed (same as in water flow in loops) so there probably is some efficiency in lowering the fan speed slightly (say from 3 to 2 at the low end) without increasing compressor wattage. I obviously don't want to ice the coil. I was aware of the need for a particular fan speed for aux heat as that is pretty well documented in the installation manuals. I'm guessing the upper fan speed should be set to the room by room flow dictated in a manual J calculation? Based on the manual J calcs, I have a 3 ton unit for my upstairs zone which is oversized (smallest 7 series) so I am thinking its upper fan speed could really be lowered. The 4 ton unit for the downstairs is nearly perfectly sized so I am guessing its upper fan speed may need to be in the 7 to 8 range (its at 9/WF default). I'll play around with them. Thank you both in this quest to dial in the efficiency.

    Should a pump in my current flow center setup fail (hopefully in the distant future), I will strongly consider modifying the plumbing arrangement to take advantage of the single pressure regulated pump. What I have now is real good (say 95 out of 100) but clearly the central pressure regulated system would be a 100.
  20. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The upper fan speed is influenced by the airflow across the heat pump coil, nothing else. Run you units at stage 12 and check you delta T, if you are in the 25F range, you are doing fine. If not lower it. For the lower stage I would simply set it at stage 2. Most of the time I run it wit 2 as the low setting, and 6 or 7 as the high setting, and 9 or 10 for aux heat.

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