VS Pumping with Modulating Valves

Discussion in 'General Discussions' started by geoxne, Sep 21, 2016.

  1. geoxne

    geoxne Active Member Forum Leader

    I am in the process of specifying equipment for a job with multiple WF Series 7 units. I understand the value of reducing pump power with a central VS pump, low head piping and zone valves with multiple units.

    My question is, with multiple Series 7 VS units, does it make sense to use modulating valves at each unit for efficiency? Or am I just creating more head for the central VS pump, thus negating any assumed gain while flowing at less than full rate?
     
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    You should get rid of the central VS pump. Multiple VS pumps will interfere with one another - they can get stuck "searching" for the right flow.

    So if each circuit has a VS pump (the built-in 7 one), you don't need valves - just check valves to ensure no short-circuiting.
     
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I am designing all my multi heat pump systems with central VS pump. The ones with WF series 7 we use modulating valves, although I use modulating Belimo valves and not the Johnson Control valves Waterfurnace supplies for lesser pressured drop at higher compressor stages, and for the single or dual stage HP I use motorized non-modulating valves. The valves work well with the PWM signal from the 7 series. I did one job with 2 heat pumps and the 32-140 on each heat pump, and regretted it. For me, central VS is the way to go. I use 2 VS in parallel for redundancy if I have multi family projects.
    To answer your question: the valves close down and restricts the flow to the point that the central VS revs down, thus still saving energy. The closing never goes below 25%, thus the head pressure is really never that high that it would render the VS inefficient. The power consumption comes more from the GPM than the ft/hd.

    Couple important points:

    1) I use exclusively Wilo Stratos. They can be set for variable pressure and constant pressure, and can serve as master-slave if you wire them together, so they talk to each other.
    2) The design is so if one fails, the other one can carry the whole load, otherwise they run at 50% max.
    3) Key is the pressure drop design for the header and the in house distribution system so the heat pumps are naturally balanced.


    The variable pressure setting is more tricky and requires a skillful design of the loop field, but will result in an ultra efficient pumping solution. The idea behind is that at low pumping requirement or part load, the pressure drop of the loop field goes towards zero, thus you can significantly reduce ft/hd and still pump the same amount of fluid through the heat pump. Thus restricting the flow can be your friend, if you design is correct, and you program the pump and the valve accordingly. The key is the open the valve more at lower comp stage since your ft/hd might be very low at variable pressure setting.

    Here is a system with 29 heat pumps (single and dual speed) with (2) central VS. The only reason for 2 pumps again is redundancy.

    http://welserver.com/WEL0714/

    PM me and I can send you the designs for central VS and WF 7 series. Not very different, just with modulating valves on there. How many 7 series? What is the size? We built about 10 systems last year with central VS and multi HPs, 3 of them were with multiple WF 7 series. They run like a charm that way, and the energy usage of the central VS was ridiculous low.
     
  4. geoxne

    geoxne Active Member Forum Leader

    The Series 7 has no built-in pump available unlike ClimateMaster. Waterfurnace does not control a VS pump on DeltaT either. It can control an individual unit VS pump (or Mod Valve) based on a Min/Max % setting in configuration and the output% is calculated and output to VS pump depending on what the compressor speed is.

    I would certainly not get rid of the central VS pump set to run on constant pressure with on/off. My question remains does a Mod Valve do anything for me or will a simple on/off valve work as well?

    Edit: Doc answered my question while I was typing. Thanks!
     
    Last edited: Sep 21, 2016
  5. ChrisJ

    ChrisJ Active Member Forum Leader

    You guys posted at about the same time...
     
  6. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Geoxne,

    Yeh. Makes sense now. Didn't read it that way to begin with.
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    on/off valve would waste a lot of pumping power with the 7 series, the energy consumption is much more dictated by the gpm than the ft/hd.

    John Manning has some sweet setups with single and dual VS flow centers.
    http://phoenixflowcenters.com/phoenixStore/index.php?cPath=37&osCsid=rfhsttuicnk

    If you don't use too many HPs his GV zone controller makes sense too, to shut of the central pump completely when no HP is running.
    If you are going that route, check the variable pressure setting vs the constant pressure. It can save an additional 50-75% pumping power in part load, but requires higher percentage opening settings at the lower end of the range for the modulating valves.
     
    Last edited: Sep 21, 2016
  8. geoxne

    geoxne Active Member Forum Leader

    I see now. Even though the modulating valve is "restricting" flow, the central VS pump set to constant pressure will "see" the head increasing and turn down to a lower RPM autonomously to maintain constant pressure. It was the "restricting flow" that I was getting stuck on, as I was taught never to do such.
    I agree wholeheartedly. I use them exclusively for multiple unit closed loop systems and highly recommend them. His design input and innovation is worth the price of admission. I was converted 5 years ago and I am still amazed to see how well the systems work. The non pressurized system performs rock solid with never a call back, while efficiently pumping only what the system needs.
     
  9. geoxne

    geoxne Active Member Forum Leader

    The proposed system will have one NVV036 with Intellizone2 in the basement to serve the first floor and finished portions of basement, one NVH036 in loft attic space with Intellizone2 to serve the second floor and a NSW040 to provide basement slab warming and DHW with a Lochinvar SDT80 dual coil indirect. All mechanical spaces and ducting are inside the envelope.

    I have upsized my S&R piping to 1 1/4 HDPE for the 40' one way runs to the attic unit in an attempt to equalize pressure drop with short piping runs to basement units. I will use Hazen/Williams calculations for flow/head and Hardy Cross for multiple flow path iterations to size pipe and run lengths for units in the basement that are in close proximity to the flow center.
     
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I assume you are piping the dual coils in the tank together for the heat pump?

    A few things come to mind. We found that the LLT for the dual coil indirect tanks has to be about 10F higher than the water in the tank in order to transfer enough heat. A NSW gets on the edge at 130 LLT when you want the tank at 120 F. We use the new optiheat capable to go up to 150F LLT, and only cost marginally more, but provide much higher efficiency at 130F LLT. The operating envelope of the heat pump is simply much wider. Just a thought.

    The 1.25" line will help to balance the system to the attic.

    The NVV036 each have 12 gpm nominal flow at 14.7 ft/hd versus 10 gpm and 8.5 ft/hd for the NSW040 (if I am not mistaken), if you use belimo valves with a CV of 23 on the 7 series and a taco valve with a CV of 10 on the NSW, you have between 10 and 10.3 gpm balanced flow on each heat pump. Should work out nicely!
     
  11. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Any resistance in your areas to methanol through the building? We're getting spec'd PG throughout.

    Combined with a bunch of our climate demands on horizontal loopfield sizing, and we do end up with some headloss it is difficult to get away from.
     
  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    No issues with Methanol.
    I admit we are spoiled with methanol in terms of headloss.

    But I would put (2) Wilo Stratos in series for up to 80 ft/hd if I had to. What is the alternative? Putting dual pump in series on each heat pump?

    I would be radical in adding pipe, running more circuits in parallel and make the circuits shorter. Large header pipes, large CV valves. Starve the heat pump a bit. What ever I have to do to get the pressure drop down. To stay below 35-40ft total.
     
  13. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    So this is commercial work for us. With distributed heat pumps throughout the building - on the VS pump/valve setups as discussed above.

    The alternative for us is generally a hydraulic separator between the source and load that helps bring the headloss down to that <30' range.

    But now two pumps (or more). In the commercial world this makes the conventional guys rest easy as they tie in secondary support on the load side. The cooling towers being another push for the PG antifreeze. So one source pump going down doesn't take everything down basically.

    This is also so we have some flexibility. We are quoting jobs without the final drawings basically. We don't know where heat pumps are going in the commercial building, so we don't know final headloss. We can setup our loopfield irregardless of what is happening inside once we know our design loads (but not zoning).
     
  14. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    We usually design and also install our larger residential and commercial systems. So I spec everything anyway. I do not do jobs where a "conventional guy" needs to rest easy. I shy away from them. I like to see the loop around 15 ft/hd, and the inside also around 15ft/hd, for a total of 30 ft/hd, but that is with Methanol.
    I admit I did not have an application with a cooling tower yet, I usually just make the loop larger in cooling dominated scenarios. I do use parallel pumps for redundancy so one pump failure does not take the system down. The wilo stratos 3-40 run 120 gpm at 40ft/hd, or 160 ft/hd at 160 gpm, so that supports 50 tons. If I need more gpm I run another one parallel. The most I have seen are 8 Wilos in parallel for 400 tons at Skidmore college, one of John Manning's jobs.
    Pressure drop for me is not using things like balancing valves, secondly pumps, or valves with high CV, flowmeters, basically everything which restricts flow, running things in parallel, and using large enough pipe. But I can envision applications where it get trickier, especially with Glycol.
     
    Last edited: Sep 23, 2016
  15. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I need to go to the loo. Do I need to talk to john Manning?
     
  16. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You might learn something....
     
  17. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    KISS MY BISON.
     
  18. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    As always Mark....very professional.
     
  19. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I am no longer a pro. I am DIY.
     
  20. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Does this have anything to do with the Higgs Bison I read about earlier this week?
     

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