Grundfoss Alpha Pump Auto setting

JPL

What is the Alpha Pump really doing when in Auto setting? The literature says it finds some optimized setting, but how is it doing that? Is it trying to maintain a constant head? Also, what happens if your system curve does not go through the Auto zone region on the Grundfoss pump curve diagram?

I have three zones (on zone valves off a manifold). As different zones open and close the GPM readings on the pump change…that makes sense. But I took the pump's GPM readings with different zones open and the pump set at each of hi/med/low speeds, 6/9/12 ft heads, and Auto. Can't make much sense out of it, especially when I compare it to my system curves.

P.S. - I installed all new piping so I have accurate pipe measurements and fitting counts throughout. I calculated the system curves based on the equations in John Siegenthaler's book. That was a tedious process so wouldn't surprise me if my curves are wrong 🙄. Still curious, though, what the pump is really doing in Auto Mode and whether that it better than just setting it at Medium speed and leaving it.

Thanks!

hot_rod

https://forum.heatinghelp.com/discussion/200272/grundfoss-alpha-pump-auto-setting

There are a bunch of training modules in the e academy

https://www.grundfos.com/us/learn/ecademy/all-courses/alpha-and-upse-circulators-for-residential-heating/constant-pressure-autoadapt--alpha-#:~:text=With%20an%20ALPHA%20pump%2C%20when,the%20condition%20of%20the%20valves.

kenjohnson

I am not a professional but I have some practical observations on Grundfos Alpha "Auto" setting, mainly because I had the same question that you have. I run the Alpha in a radiant floor heating system fed by a geothermal heat pump with a buffer tank.

What I have observed is that the Alpha pump in Auto mode will stay at the constant pressure setting 1 unless it detects that it needs to go higher. I think it assumes that if zones are cycling open and closed and/or flow goes very low at times then Auto will stay at constant pressure setting 1.

If the pump is running flat out (all zones open continuously for days on end) then the Alpha Auto mode will increase the gpm, presumably by increasing to constant pressure setting 2 (I have seen this happen at my house).

If you have an outdoor reset (ODR) on your boiler water temperature (as I do), then the trick is to just keep adjusting the ODR settings until the circulated water temperature is just warm enough to keep the house warm but not so warm that a zone(s) cycles off. Then, wait a few days and the Alpha should increase the gpm in Auto mode.

If you don't have an ODR and just want more overall gpm flow in your system, then just set it to constant pressure setting 2.

Unless you have the Alpha pump connected to an on/off switch (doesn't pump when a zone is closed) don't use the constant speed mode.

Overall, I think the Alpha is pretty smart in how it decides to adjust water flow. Having said that, I think constant pressure 1 is a little too low to be optimized (overall) for my comfort and system efficiency and I find that constant pressure 2 works a little better to optimize the buffer tank water temperature (I can set the ODR a little differently to result in a slightly less warm water temperature - a plus for efficiency with my geothermal heat pump), and constant pressure 2 only uses modestly more electricity (just a little more compared to the efficiency savings I probably get by running my geothermal system a couple of degrees less warm).

I have also seen the professionals post that the constant pressure 2 setting seems to be the sweet spot for this pump. I wouldn't disagree with any professional who said "I just set this to constant pressure 2 and that minimizes call backs or complaints."

JPL

Bob, Ken… Thanks for your help! I went through the training modules for the Grundfoss Alpha pumps and that did help me understand the basics. Unfortunately, those modules discuss the newer pumps which have three Auto Adapt settings (constant curve, constant pressure, and proportional pressure). My pump is an older Alpha 2 which only has one Auto Adapt setting, along with 3 speed settings (hi/med/low) and 3 constant head settings (6', 9', 12'). I'm guessing the Auto Adapt mode on my pump is the proportional pressure? At any rate, since I have zone valves, I think I agree with Ken that best bet is to select a constant head setting and be done with it. I'm not sure how accurate the GPM readings on the pump are. I'm reading 9 GPM @ 6' head and 11 GPM @ 9' head. My total heat load is 7 GPM, so I'm thinking I am good at the 6' setting. Maybe kick it up to 9' when it gets really cold out and the system is running a lot. Appreciate your guys' help!!!

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