Rhode Island Changing to a variable speed pump

Discussion in 'General Discussions' started by ChrisJ, Mar 3, 2016.

  1. ChrisJ

    ChrisJ Active Member Forum Leader

    Utility rm005.jpg View attachment 1635 I have a single speed B & G pump on my non-pressurized loop. See picture.

    Is it possible, or even worth it, to replace it with a variable speed ECM pump?

    I can't buy from Phoenix, not a contractor, but I can buy a Wilo Stratus pump.

    ChrisJ View attachment 1635
    Last edited: Mar 4, 2016
  2. geoxne

    geoxne Active Member Forum Leader

    Changing to a vs pump only makes sense if you have multiple HPs or if you have a variable speed or staging HP that has an internal controller that can control the pump.
  3. Stickman

    Stickman Active Member Forum Leader

    Posted in error - sorry
  4. ChrisJ

    ChrisJ Active Member Forum Leader

    Do any 2 stage HPs come with an internal controller that you know of?

    I am replacing a combination heat pump, I may end up with multiple heat pumps. If that's the case could the pump be swapped out and still use the tank, valves ect.

  5. geoxne

    geoxne Active Member Forum Leader

    I do not know of any combination HP that controls a VS pump except the CM Trilogy and it comes with its own internal pump.
  6. ChrisJ

    ChrisJ Active Member Forum Leader

    I am replacing the combination unit with a water to air HP to heat and cool the main floor. The basement and garage have radiant in the slab, I will add a water to water HP if funds allow, to heat the basement and garage.

    In the picture is my existing non-pressurized pump and tank setup. I know I would need motorized valves, check valves, some kind of controller to operate them. Just wondering if I can reuse what I have and just swap the pumps.

  7. geoxne

    geoxne Active Member Forum Leader

    No need for check valves with zone valves.

    No need for controller. The VS pump should have an internal constant pressure controller. The HPs will open zone valve when running. An isolated end switch on the zone valve will enable the pump. That's the easy part.

    The hard part (if you dont know how) is to calculate the Ft/Hd at the appropriate gpm for the total system to size the pump and set the constant pressure to operate at. This means measuring (or knowing) the length, size and type of every pipe and fitting in the system including ground loops and how they are connected; HP pressure drop; and zone valve Cv.
  8. geoxne

    geoxne Active Member Forum Leader

    Also, you shouldn't just assume the loop field will carry the new equipment.
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    If Phoenix does not sell to you, order a B&D canister and bold on a Wilo Stratos.

    Waterfurnace ABC board also controls a VS circulator pump. Via a PWM signal.

    Yes, be aware that you are not adding a significant load your loop field has trouble with, and also make sure it is able to handle any additional flow.
  10. geoxne

    geoxne Active Member Forum Leader

    I believe you could swap out the pump with your setup. You will have to check flange to flange and bolt dimensions for fitment.
    Doc meant to say WF advanced AXB control but it is not available in a combination air/hydro radiant unit.
    ChrisJ, one could argue that your existing loop field supports the load and flow of the existing combo unit and you would not be adding any additional load. However, you will have to accommodate for the flow of the installed capacity of 2 HPs running at the same time.

    Your first decision should be whether you are going to install multiple HPs (now or future)-
    If you are, then use a constant pressure VS pump with zone valves.
    If not, I do not see the ROI on a VS pump unless it is a variable speed HP. If you are committed to a VS pump on a single HP it should be one with an internal vs control or you will have to add an external control vs pump controller.
    Last edited: Mar 5, 2016
  11. geoxne

    geoxne Active Member Forum Leader

  12. ChrisJ

    ChrisJ Active Member Forum Leader

    Thanks geoxne and Doc,

    The loop field is 5 trenches 200', 1" straight pipe. 1.25" supply and return, reverse return headers.

    The 4 ton combo unit has dual compressors, so 3 stages of heat + aux, main level air heat very rarely left first stage. The size of the unit was more driven by the ability to make on demand DHW. Walkout basement and drive under garage has radiant in slab. 3800 sq ft heated space.

    This winter we have only had air heat, radiant was emptied of water and DHW has been supplied by a HPHW heater for a little over a year. Both water to water heat exchangers have been bypassed due to refrigerant leaks.

    2 years of parts changes and recharges We have decided to just get a new water to air heat pump. I have a plan to make DIY solar thermal panels to heat the garage. The basement can be heated with a little bleeding from the main air heat.

    So it doesn't sound like the electricity saved by having a vs ecm loop pump is worth the $1100 or so price of the pump, unless I do go with a separate water to water next to the water to water.

    Again Thanks, ChrisJ
    Last edited: Mar 7, 2016

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