Grundfos Circulation Pump Specs

flat_twin · December 2016

Hello, Need some help with circulating pump specs please. My Weil Mclain Eco 110 boiler with a single zone has a Grundfos 3 speed circulation pump. Here is the pdf for the pump. http://s3.supplyhouse.com/product_files/59896341-submittal.pdf

The graph for this pump shows the specs for each of the three speeds. Am I interpreting the chart right if I say the low speed setting is good for up to 14 ft of head at 10 gpm? And the middle speed is good for up to 18 ft of head at 13.75 gpm?

Figuring head...
This is a cast iron hot water radiator system with 2.5 in supply pipes as the two main branches. These break down to 1.25 in. pipes supplying individual radiators. The longest loop is 108' (boiler to farthest radiator and back to boiler). Twelve feet from the boiler on this same branch there are two side legs. One is a 6' run of 1.25 pipe to another radiator. The other is a 12' run to the one and only upstairs radiator. I did not include those two radiators and related pipe lengths when I figured the head. Should I include them or only the furthest length of pipe and radiator? Not sure if I should consider them in series since they are much closer to the boiler and not at the end of the furthest pipe run.
Only looking at the longest loop and not the side legs I'm using the loop length x 1.5 x .04 method.

108 x 1.5 x .04 is 6.48 ft of head.

With the range of 3 to 10 gpm specified by Weil Mclain and the 6.48 ft of head in my system, the Grundfos pump should be on the low setting if I'm looking at the Grundfos chart correctly.

I read that low velocity can introduce air problems into the boiler water. How low? Any danger of that with the pump running on low speed? Any harm in running the pump on the middle speed even though it exceeds the recommended velocity? I noticed no difference in the return water temperatures between the low or middle pump speed. I expected to see a smaller delta at the middle speed but that didn't happen.

Thank you!
Mark
(retired telco tech with a new found interest in hydronics)

Paul48 · December 2016

When reading the pump curve, as the head requirement goes up, the flow goes down. On low, at 14 ft hd the pump is dead-headed and there is zero flow. What year was the house built and is piping original?

flat_twin · December 2016

Hi Paul,
OK, on the chart I see 14 ft hd is at the zero gpm mark or "deadhead" as you mentioned. This is where I wasn't sure if I was reading the chart correctly. So with that in mind, if I have the pump speed on low and 6.5 hd ft is correct, my velocity is now 4 gpm? And if the pump is on the middle setting and 6.5 hd ft is correct, I have 8-9 gpm? Sounds like the middle setting is the place to be. The installer went back and forth between the middle and high setting but eventually left it on high. I felt like he came to that decision based on erring on the side of more is better. When I read the max gpm WM recommends is 10
I started looking into doing the math myself.

The house was built in 1850 (two story federal style stick frame with modern widows, siding, doors) and has been in our family since the mid 1960's. The heating system was likely installed in the 1930's. Radiators are 23" tall with six vertical pipes per section. I found a btu output calculator on boiler.net and figured 105k btu potential. The cast iron piping is original. The only copper is near the boiler to connect to existing cast iron.
We just got natural gas and replaced the old fuel oil boiler in November. Our heating contractor has always done a good job maintaining the fuel oil boiler so we had them install the NG boiler. Rather than repair the masonry chimney and install a liner we opted to spend that money and a bit more for a modcon boiler with direct venting. Our installer felt the 70k btu Eco boiler would be insufficient so they installed the Eco 110. The old fuel oil boiler was rated at 110k btu. I don't know what the nozzle size was.
As I picked the installer's brain during the installation I could see I'd have to educate myself to get the modcon dialed in to take advantage of it's outdoor reset and condensing abilities. I've done a ton of reading trying to get a good overview of my simple system.

My own calculations are...
1900 sq ft. house with 74k btu heat loss.
Total radiator output with 180 degree water is 101k btu

Boiler is set at max 130 / min 85 water temperature. Outdoor reset allows max water temp at -5 degrees outside and min water temp at 60 degrees outside. Good performance so far with minimal (almost none) cycling at 71 degree thermostat setting. If it's extremely windy I'm OK with the indoor temp sagging a bit or if the sun is strong the boiler may cycle more often. Today at 32 degrees outside the boiler water is 104 degrees.

Design day for this area is 5 degrees. It's not unusual to dip into the -5 range during the winter.

hot_rod · December 2016

In pump lingo
Shutoff Head is that condition at the top of the curve
Run-Out is the point at the other end.

Ideally you want the pump operating in the middle 1/3 of the curve for best efficiency and pump life.

Some chose to define a system curve, which lies over the top of the pump curve. Where the two cross established the OP Operating Point
This is where the pump actually is running on the curve.

EBEBRATT-Ed · December 2016

with flows of 10-18 gpm the resistance of 2.5" pipe is almost non existant. Your looking for the one radiator and main loop combination that has the most resistance. Does the system heat well and are you able to balance the heat to the various radiators with so little flow??

If the house heats well on low speed and as long as the boiler has enough flow this will make the boiler condense which will improve efficiency.

what I would do;

Without a way to measure flow use this method.

Set the thermostat back on a day you plan to be home, let the house, boiler and piping cool down. Turn up the thermostat several degrees and the boiler should go to maximum input as long as it's input isn't limited by some setting.

Using a thermometer check and record the supply and return temperatures at each radiator. Circle the house and do this several times as the system comes up to temperature. If the boiler hits high limit while this is happening you may not have enough flow.

with a condensing boiler your looking for a TD of 30-40 degrees.

Adjust the pump speed until you get what you need.

Paul48 · December 2016

Is there an old expansion tank in the attic, or the piping from one that was there? I suspect you have a gravity conversion. Are your radiator valves in good working order? Speed 2 is right about where you need to be +/- a gallon or two. If the circ has trouble supplying the most remote radiator, that's where the radiator valves can help.

flat_twin · December 2016

Paul48 said:
Is there an old expansion tank in the attic, or the piping from one that was there? I suspect you have a gravity conversion. Are your radiator valves in good working order? Speed 2 is right about where you need to be +/- a gallon or two. If the circ has trouble supplying the most remote radiator, that's where the radiator valves can help.

No tank in the attic. There was an old expansion tank in the cellar near the boiler strapped up between the floor joists. It was large and had no diaphragm. I recall it was water logged one time and had to be bled. It was replaced in the 1990's with a small modern expansion tank. All the piping is in the cellar or crawl space except for the one small radiator on the 2nd floor and it's piping is visible. The boiler that was here in the mid 60's was a large coal boiler converted to fuel oil. I couldn't tell you if it had a circulation pump. The conversion couldn't have been that old because I remember there being an old coal bin in the corner of the cellar and there was still some coal in it!
There have been two smaller fuel oil boilers since then and now the NG modcon boiler. None of the distribution and return piping has been modified since the 60's.

The house is very comfortable everywhere. No complaints at all about that. There's never more than 1 degree variation from one room to the next. The room farthest from the boiler (the same one I used for figuring head) tends to be the one that's 1 degree warmer since the two radiators in that room have six more sections each over the two radiators in the same sized room directly above the boiler. Maybe it was built that way since it was so far away from the boiler? Again, no complaints since this is our living room where we spend our time in the evenings.

We've always appreciated having hot water heat over forced air but now it's even better with steady warm radiators and not the hot or cold radiators depending on when the boiler ran last.

If my head calculation is close enough I'm happy to leave the pump on the middle speed. If I'm off and it's actually less head then I'm still not overshooting the 10 gpm spec by much. If there's better way to figure head ft for a system like this, let me know.

Paul48 · December 2016

https://heatinghelp.com/systems-help-center/sizing-circulators-for-old-gravity-hot-water-heating-systems/

This may help some. As I said, I believe you are close on speed 2, based on this.

flat_twin · December 2016

Very good info there. Thanks for the link

flat_twin · December 2016

hot rod said:
In pump lingo
Shutoff Head is that condition at the top of the curve
Run-Out is the point at the other end.

Ideally you want the pump operating in the middle 1/3 of the curve for best efficiency and pump life.

Some chose to define a system curve, which lies over the top of the pump curve. Where the two cross established the OP Operating Point
This is where the pump actually is running on the curve.

I found this resource that shed some light on my question about operating point. Figure 5-6. I'll have to take this a little slower, my brain was starting to hurt! LOL!

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

Grundfos Circulation Pump Specs

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