Grundfos Variable speed pumps F/SF/LC?

cloudd

I am using a 12 loop manifold (each loop is no greater than 300’ @ 1/2” HelioPEX pex)

Is there a specific style of variable speed pump I must use to combine with HelioPEX. Does it have to be stainless steel or cast iron? 

I am looking at a Grundfos alpha 2 15-55

What does the f/sf/lc. Refer to???

hot_rod

15-55 should be the correct size.
F= flanged
SF= stainless body, flanged
LC= line cord comes with a cord

If that is barrier pex, no need to use a stainless $$ circulator.

HomerJSmith

FLANGE/STAINLESS FLANGE/LINE CORD
Do you have thermo actuators on the manifold? No, if it is a closed sys, cast iron will do with barrier pex. 12 loops is a lot of flow at 1 GPM per loop=12 GPM. The supply and return pipe must be larger than 3/4" pipe. The maximum flow for 3/4" pipe is 4-5 GPM. How many thermostats?
If the loops are within 10% of each other you won't need balancing valves. I like Caleffi twist-flo manifolds. They have balancing gauges on them and are well engineered.
A ECM pump will save on electric energy usage.

It's all about how it is connected to the boiler.

GroundUp

12 loops at 300ft is too much for an Alpha 15-55. You don't need stainless or anything fancy, but for the extra $3 a year spent on electricity (while saving $150 on the pump itself), I'd change that Alpha out for a 15-58F or FC with the check valve removed- unless it's got actuators in which case I'd probably go to an Alpha 26-99. I've toyed with this and while I love the Alpha, anything more than 8-9 loops at 300ft on a 15-55 drags the flow rate down to an uncomfortable level of .2-.3 GPM per loop. I recently had to put an Alpha 15-55 in a 15 loop system at 250ft because an Alpha 26-99 was unavailable at the time, and the flow rate was hovering around .15 GPM per loop on constant speed 3. It heated the home, but very poorly until I was able to swap the 26-99 in its place.

hot_rod

Ideally you would know what gpm is required in the loops? That is based on the BTU/hr you are trying to move per loop.

The RadPad, which might be a bit conservative suggests . 6 gpm for 1/2" pex at 300' loop, 3.8' head.

.75 is workable on that 1/2 loop, so
12 loops X .75= 9 gpm
6' head at that .75 gpm.

This gives you @ 25 btu/ sq ft with tube 12" OC.
83° surface in a 70° ambient space temperature.

Based on RadPad calculations.

Pump curve attached. The 15-55 looks like it is in an ideal range, mid curve.

The Grundfos product selection site allows you to drop a pin on the pump curve and get results also.

Depending on the piping to and from the manifold, hopefully 1"

GroundUp

hot_rod said:

Ideally you would know what gpm is required in the loops? That is based on the BTU/hr you are trying to move per loop.

The RadPad, which might be a bit conservative suggests . 6 gpm for 1/2" pex at 300' loop, 3.8' head.

.75 is workable on that 1/2 loop, so
12 loops X .75= 9 gpm
6' head at that .75 gpm.

This gives you @ 25 btu/ sq ft with tube 12" OC.
83° surface in a 70° ambient space temperature.

Based on RadPad calculations.

Pump curve attached. The 15-55 looks like it is in an ideal range, mid curve.

The Grundfos product selection site allows you to drop a pin on the pump curve and get results also.

Depending on the piping to and from the manifold, hopefully 1"

Once again, "looks like" and "is" are very different things. Go ahead and try to pump even three 300ft loops of 1/2" pex with a 15-55 and you'll find out real fast that .75 GPM per loop is unattainable. Yes, the curve says otherwise but no, it's not going to happen. Perhaps due to the possibility that the head loss calcs we all use are not as linear as we think they are? As an extreme example, let's just say one single loop of 1/2" pex at 300ft long using pure water at 100*F. According to my calculator, 1.25 GPM is attainable at 17.7ft/hd, which also falls within the Alpha's performance curve. Those of us familiar with radiant know very well that this will never happen, despite the "facts" saying otherwise. This also means there's a possibility of those "facts" being false in other parts of the curve, does it not?

hot_rod

GroundUp said:

Ideally you would know what gpm is required in the loops? That is based on the BTU/hr you are trying to move per loop. The RadPad, which might be a bit conservative suggests . 6 gpm for 1/2" pex at 300' loop, 3.8' head. .75 is workable on that 1/2 loop, so 12 loops X .75= 9 gpm 6' head at that .75 gpm. This gives you @ 25 btu/ sq ft with tube 12" OC. 83° surface in a 70° ambient space temperature. Based on RadPad calculations. Pump curve attached. The 15-55 looks like it is in an ideal range, mid curve. The Grundfos product selection site allows you to drop a pin on the pump curve and get results also. Depending on the piping to and from the manifold, hopefully 1"

Once again, "looks like" and "is" are very different things. Go ahead and try to pump even three 300ft loops of 1/2" pex with a 15-55 and you'll find out real fast that .75 GPM per loop is unattainable. Yes, the curve says otherwise but no, it's not going to happen. Perhaps due to the possibility that the head loss calcs we all use are not as linear as we think they are? As an extreme example, let's just say one single loop of 1/2" pex at 300ft long using pure water at 100*F. According to my calculator, 1.25 GPM is attainable at 17.7ft/hd, which also falls within the Alpha's performance curve. Those of us familiar with radiant know very well that this will never happen, despite the "facts" saying otherwise. This also means there's a possibility of those "facts" being false in other parts of the curve, does it not?

So what is the purpose of pump curves? If the tube in fact presents that pressure drop, the circulator output is determined., measured or calculated.

Certainly kinks or fittings, sludge in the tube would change the flow.

The PPI website has tube pressure drop calculator, not related to hydronics or radiant specifically. it's just the measured and calculated data.

These tables are used for sizing domestic water flows, fire protection, lawn sprinkler, etc. These pressure drops are the same whether a circulator is used or the building water pressure is driving force.

I agree the jobsite reality may not match exactly, but there would be an underlying cause, if measured flow is not very close or exactly as the pressure drop charts, or pump curves indicate.

Here are a few examples, a 300' loop at 2.20 gpm, and at .75 gpm

In my shop I have 300' loops of 1/2'

With 3 loops open I get up about 1 gpm with a similar Alpha 25- 55 (Euro model)

Screenshot 2023-04-04 at 2.56.47 PM.png

Screenshot 2023-04-04 at 2.56.32 PM.png

Screenshot 2023-03-30 at 10.29.44 AM.png

Uploaded 2:37 pm175.44 KB

Screenshot 2023-03-30 at 10.29.44 AM.png

hot_rod

3- 1/2 loops @ 300'. New flow setters.

HomerJSmith

Bob, I was wondering why those flow setters were so discolored. They weren't cleanable?

hot_rod

HomerJSmith said:

Bob, I was wondering why those flow setters were so discolored. They weren't cleanable?

I have been draining and refilling my system a lot as
I change piping and components, so mostly rusty colored from the sep, pumps and expansion tank.
I’m going to try and soak them in some CLR. Really no way to take them apart to clean

cloudd

HomerJSmith said:

FLANGE/STAINLESS FLANGE/LINE CORD Do you have thermo actuators on the manifold? No, if it is a closed sys, cast iron will do with barrier pex. 12 loops is a lot of flow at 1 GPM per loop=12 GPM. The supply and return pipe must be larger than 3/4" pipe. The maximum flow for 3/4" pipe is 4-5 GPM. How many thermostats? If the loops are within 10% of each other you won't need balancing valves. I like Caleffi twist-flo manifolds. They have balancing gauges on them and are well engineered. A ECM pump will save on electric energy usage. It's all about how it is connected to the boiler.

-There will be thermal actuators
-1” oxygen barrier pex supply/return to the combi.
-it is a closed loop system
-6 thermostats 

Cast iron pumps are ok with thermal actuators correct?

GroundUp

Cast iron circs are okay with anything, as long as it's a closed loop system. The circ has no correlation to actuators.

HomerJSmith

An ECM pump is a perfect match for thermo actuators. Like electricity, the supply and return piping to the manifold gpm can be demanded off. That all 12 actuators opening at the same time would only occur at the coldest day in winter, probably less than 2% of the time.
1" supply and return, I think would be adequate. I think you would benefit using a Hydro Separator. I would use a Caleffi twist flow manifold so you could balance all the loops as to flow.
Pay particular attention to the wiring and current draw of the actuators to the thermostats, especially so if you are using wifi thermostats.

hot_rod

The Grundfos 15-58 Alpha or UPse would be the newest offerings and a little bit more power than a 15-55

The second number in Grundfos speak is max. head in decimeters.
15- 55(decimeters) = 18' at shutoff head
58= 19'

The new 15-58 Alpha has some really nice features, Auto Adapt is available in all modes now, so some extra adjustability.