Delta-P Circulator and Differential Pressure Bypass Valve

gotgas

This is a follow-up to this thread.

The question is this: with a continuous runs delta-P circulator, what type of bypass valve would be appropriate to provide flow what the circulator is running on idle (7 watts)? Would if be something like this?

We have a system with no thermostats, but 12 hydronic radiators that have mechanical thermostats. When they are open, the pump (linked here) ramps up to provide flow. When they are all closed, it still runs at a low flow. We need to provide somewhere for that flow to go.

One idea was is to run one of the returns back to the supply before the pump, and set the thermostat to always be 20% open at minimum. That loop will always be open and allowing minimal flow. We could do that with one of the towel rack radiators, so they always have a little warmth. The other is the bypass valve.

What do you think about these ideas? I appreciate any input. Thanks much.

Ironman

A delta P circulator needs no bypass.

The 7 watts that appear periodically is the circulator ATTEMPTING to produce flow in case any of the TRVs are open.

What you’re proposing would be counter productive to the pump’s logic, waste energy and short cycle the boiler.

gotgas

Ironman said:

A delta P circulator needs no bypass.

The 7 watts that appear periodically is the circulator ATTEMPTING to produce flow in case any of the TRVs are open.

What you’re proposing would be counter productive to the pump’s logic, waste energy and short cycle the boiler.

If you are correct, I think that is great. That is how I thought it operated but I have been told that it runs continuously all the time and therefore needs some method for flow. If you have a moment, would you take a look at the pump that I linked and let me know if based on the literature of that pump it needs continuous flow?

And the thread I linked above, the consensus seems to be that it needs to have continuous flow. I was prepared to address that but I would like it much better if we can eliminate the bypass.

hot_rod

I don’t think you want a bypass, here is the installation manual schematic 

Good question for Taco

EBEBRATT-Ed

according to the diagram @hot_rod posted no bypass is needed. I would like a bypass, but I am old school. If the pump is slow enough at idle so it can't cavitate and cause any damage it should be fine

hot_rod

I carved a couple pump volutes out of plastic for some Grundfos 15-55 Alphas demos

Under a no flow condition 0 gpm, 3 W it spins very slowly, Id guess a few 100 rpm

I can deadhead this for hours, maybe even over night, I doubt it will boil, flash, or get even warm enough to have any concern

A bypass in a delta P function kinda defeats the purpose of a delta p function?

The bypass is parasitic and will just spin the circ faster than it needs to,  for no apparent value?

hot_rod

https://www.grundfos.com/content/dam/global/page-assets/learn/ecademy/pdfs/module-7-grundfos-autoadapt-autoadapt-in-depth-master.pdf

This does a good job of explaining how the circulators work and Auto Adapt
This is the Alpha 2 15-55, , newer versions like the Alpha 15-58, are even more refined

gotgas

I was away for a few days but wanted to respond. Thanks for all the input. Hot rod, here is what we have currently.

gotgas

We left those two unions on the end of the loop to install the bypass. However if I do not need it I would rather not do that. I could also install the bypass but have it turned up so it would only function in an overpressure event. Should we close that Loop, leave it open, or install the bypass? If we do not have to spi  the circulator 24/7, then I would like to avoid doing that.

hot_rod

No need if you are running a ∆P mode. I think you want to turn the pump motor down?

I ran the demo I showed a few posts up overnight and the fluid never got above room temperature. About 12 oz of water in the pump and piping. So no issue with the circ running against closed zone valves. In the correct mode