pump flow rates

maggiedog

Grundfos alpha2 15fc/lc flow rate on autoadapt mode only goes to 3 gpm. According to the chart with the head it has its capable of about 10 gpm. With below freezing temperatures (has outside sensor) and multiple zones calling for heat it does seem to me to be going high enough. Does this sound right? or is 3 gpm sufficient?
Triangle Tube boiler , in floor heat. 5,000 sq ft plus 800 sq ft heated floor in carport. if run in position III, it'll go to 6 gpm at 43 watts

SuperTech

The outdoor temperature has no effect on the circulator. Why are you so concerned about the flow? Is the system heating the space adequately?

maggiedog

Last night the system seemed to struggle to maintain temperature. I realize the outside temp is just factored in to set the target boiler temp, just didn’t realize these systems work on a much lower volume than I would have thought.

EBEBRATT-Ed

I doubt 3gpm is enough. What is the boiler btu output rating??
With radiant heat I would think 1 gpm may do 15,000-20,000 btus of boiler output. That's just a rough guess.
Example a boiler with a 75000 btu output would need 75000/15000 or 20000 would be 3.5-5 gpm

Gordy

One can not realistically properly answer the question with out knowing the details. As in boiler size, heat loss, emitter design flow rates, zoning, number of loops etc.

You can play with circ settings, and see if another setting works better. Usually if the boiler is not seeing enough flow it can lock out on high limit, or short cycle. I’m assuming that’s not an issue.

A 100k boiler should see 10 gpm for a 20 delta.

Typically radiant floors should see a 10 degree delta from supply to return on a loop. Higher flow can narrow the delta.

If you have flow meters a loop should be flowing in the .5 to .75 range roughly.

If you have a 10 loop manifold needing .5 gpm for each loop you need to have 5 gpm flowing to the manifold.

That’s a rough crash course.....

hot_rod

I would not trust those GPM readouts, I have measured errors of 80% on some, it mainly a calculated number. A flowmeter or balance valve would give you a true indication.

Zman

I don't think auto adapt works very with with radiant systems. I would run it on constant pressure 3 and see how it does.

On similar jobs of that size I have done, I have found the alpha 2 is not enough with everything open.

SuperJ

> @Zman said:
> I don't think auto adapt works very with with radiant systems. I would run it on constant pressure 3 and see how it does.
>
> On similar jobs of that size I have done, I have found the alpha 2 is not enough with everything open.

Agree with constant pressure 3, if it heats fine then try constant pressure 2. The pump is essentially limited to about 43 watts. You can get a wee bit more flow if you remove the check valve, if you don't need one for application.

Make a change and then give it a couple days before you make another. In slab radiant takes a while to stabilize.