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Variable Speed Circulators

try2hard Member Posts: 26
I'm trying to better understand the pressure differential settings for variable speed circulators like the Grundfos Alpha and Taco Viridian products. I've used an Alpha before in a simply system but we used the AutoAdapt feature and it worked well. After checking out the Viridian, I see they offer two pressure modes - Constant pressure and Proportional pressure, mentioning that the first is better for zone valves and the second for TRV systems.

I'm not quite understanding the difference. I was thinking about flow rate for something like a radiant manifold with 8 circuits. When only one loop was calling for heat, you may only need 1 GPM, while needing 8 GPM with all loops calling.


  • Zman
    Zman Member Posts: 7,607
    Constant pressure is just that. It provides constant pressure to the system. Constant pressure works well when there is very little resistance in the distribution piping. Systems where the distribution occurs in the boiler room right after the circ work well with constant pressure.

    In systems where there is significant resistance in the distribution piping like TRV's or remote zone valve systems, proportional pressure is appropriate. It provides a little more pressure all the time and tapers proportionally in order to always provide enough force to overcome the resistance in the distribution piping.

    It sounds like your system would work well with constant pressure. I have found that auto adapt sometimes has trouble detecting very small zones.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • try2hard
    try2hard Member Posts: 26
    @Zman Thanks for the great explanation; that makes sense. So the pump is really seeing the pressure "differential" change across the manifold loop as actuators/zone valves open and close.

    Do you have any preference between the Grundfos Alpha II and Taco Viridian circs?
  • Zman
    Zman Member Posts: 7,607
    I only have personal experience with the Alpha. I like like them.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 22,481
    There are a lot of choices for ECM style circs now, depends on what color you like :)

    Alpha is available in a 1 and 2 version now, a basic, or more featured version. I think the 2 comes with an insulation shell. Millions of Alphas in service, built in Fresno, CA.

    Wilo probably pioneered the US market, one of the first to offer full function small size ECMs. Looks like the popular Yonos is finally arriving , a small size circ with a few different versions including a PWM model. It's been a very popular OEM circulator in Europe.

    Armstrong has some dry rotor style ECM which takes the magnetite issue out of the equation. AquaMotion is another brand making inroads.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Dave H_2
    Dave H_2 Member Posts: 560
    With the Taco 00e series, there are several circs offered to best fit your business and customers (the Viridian name has been discontinued).
    The first difference in the 00e series compared to the standard PSC 00 circs is out of the box running full speed is almost half the power consumption for doing the same amount of work. 80 watts (007) to 44 watts (00e)

    The VR 1816 gives you the most versatility for a wide range of applications and you just aren't sure of the system parameters. The VR1816 has three modes, fixed speed, constant pressure mode and proportional pressure mode.
    The fixed speed is basically a volume dial, turn it to the speed you want it to operate at and it will stay at the speed, never changing speed. Great for zone pumping systems where each circ is designated to a zone.

    The second mode is Constant Pressure. The setting you have there is maintaining a constant discharge pressure of either 5, 10, or 15 foot of head. Great for open/close zone valves. As zone valves open and close, the circ will either speed up or slow down based upon the number of zones while keeping the discharge pressure the same.

    The third mode is the proportional pressure mode. Very similar to the constant discharge pressure mode but the curve is proportional instead of flat. Great for three way zone valves, thermostatic radiator valves or any proportional valve (it doesn't just open or close but modulates flow) This will also send just the right amount of heat to the zones.

    Now we jump into the 0015e3 and the 007e.
    The 0015e3 has two constant discharge pressure settings and one full speed setting. Low and medium setting is 5 and 10 foot of constant discharge pressure respectively and the high setting is full speed.
    The 007e is set at 10 foot of head constant discharge pressure. Could you use a CP circ for a zone pump system, definitely. It will find the point of operation needed and follow the flat curve and never change speed. If used in a zone valve system, it will change speeds as the zone valves open and close.

    They are all based upon the same platform but each one has the features that fit your projects and customer base. Make you choice and have the features you want and ones that you dont want or ever need.

    Dave H.
    Dave H