Grundfos Magna3 - 1000 gal. storage help.

[tuolumne]

Vermont provides a $500 rebate on this pump and I picked one up to replace my failing 15-58. This is installed on an EKO-40 with 1000 of storage on system pressure. Right now the pump is in "Auto-adapt" mode and is clearly moving a lot more water at 40 watts than the old pump ever did. I've just started the boiler for the first time with this new pump.

The question(s): what settings can I use to maximize performance in the system noted above. Ideally, the pump will increase flow as the boiler heats up so that the boiler won't cut out the fan (190 degree set point). I am hopeful that I can achieve this, but the directions are confusing to me. Does anyone have some practical experience to share?

Thank you, Chad

 

[heaterman]

Which particular model do you have?

 

[DaveBP]

A schematic of your system will help a lot. You'll get more relevant answers that way and not so many shoot-from-the-hip rules of thumb.

A cellphone photo of a paper and pencil sketch is good enough.

 

[maple1]

Yowsers - 500 off? How much was the pump? They sure look cool if that counts.

Is this just to move water between boiler & storage? The 15-58 in my loading unit on low does that fine - I don't drive my storage up real high though. Doesn't see 180+ very often, 190 is really rare.

 

[tuolumne]

The pump is a 32-100. This pump is controlled by the boiler (on/off with a set temp.) I have a primary/secondary setup, with separate pumps. If no zones are calling this pump circulates to the storage tanks. If a zone is calling, the primary pump will pull off some water into the primary loop.

When it was new, I would leave the 15-58 on low speed when I was starting the boiler and flip it high when the temperature came up. This worked moderately well, but it lacked the flow capacity to prevent the boiler from idling some. As it aged, the pump stayed in high all of the time and the boiler has been cycling more, and occasionally giving me errors associated with high temps.

Ideally, the new pump could maintain a constant delta-T and do the speed changes automatically. I assume this would require connection with an independent thermometer. I am not sure what type is necessary, nor how it would communicate with the pump. The boiler also has a temperature gage wired in that is extra at this time. Also, it seems that the boiler controls themselves could be made to communicate this somehow. Right now I am playing with the manual adjustments to achieve the same result.

 

[ewdudley]

Vermont provides a $500 rebate on this pump and I picked one up to replace my failing 15-58. This is installed on an EKO-40 with 1000 of storage on system pressure. Right now the pump is in "Auto-adapt" mode and is clearly moving a lot more water at 40 watts than the old pump ever did. I've just started the boiler for the first time with this new pump.

With a $500 rebate you should probably get another one and put them in parallel, just to be sure.

 

[Floydian]

With a $500 rebate you should probably get another one and put them in parallel, just to be sure.

 

[tuolumne]

These last posts are not very helpful. Has anyone had practical experience with this pump? What kind of temperature sensor would work? Any recommendations for what delta-T to go for with an EKO-40 and 1000 gallons of storage?

 

[ewdudley]

These last posts are not very helpful. Has anyone had practical experience with this pump? What kind of temperature sensor would work? Any recommendations for what delta-T to go for with an EKO-40 and 1000 gallons of storage?

As suggested above, we need more information in order to provide any useful recommendations. How is your boiler-to-storage loop configured? Can you sketch a schematic? What are the pipe diameters and lengths? Is there a thermostatic mixing valve? What range of temperatures does the controller on the EKO offer for supply temperature control? Can you go ahead and use a smaller pump, sell the Magna. and pocket the difference without getting in trouble with the state of Vermont?

 

[maple1]

I think a 20° delta through the boiler is a pretty common figure. That's what I see with my 15-58 on low.

 

[Floydian]

These last posts are not very helpful.

Apologies, tuolumne.

That's a BIG pump you've got and I found EW's sarcastic comment to be quite funny.

It's kind of hard to imagine an installation that would require a pump that size with a 40Kw boiler. Even at 30 ft of head that thing will pump ~17 gpm! and I'm guessing you are well under 30 ft.

Btu/hr= gpm X 500 X T

So if you were pumping 10 gpm and seeing a 25 T through the boiler than 10 X 500 X 25 =125,000 btu/hr.

The Magna is probably pumping a LOT more gpm but to know this we need to know the head loss of your setup. In general, high flow and small delta T's are gonna cost you more in electricity than lower flows with larger delta T's.

Noah

 

[tuolumne]

Here is a diagram that I posted on this site way back. Things have functioned well this way since then; I have never added any backup system, and the 1000 gallons of storage satisfies our needs to be away for a long weekend in the winter.

The new pump may be oversized, but it is getting heat into the tanks way more efficiently than the old pump did in its best days. This may be a higher electrical consumption at times, but much less heat loss to the basement (important for summer burning) and up the chimney. The pump on "minimum" won't move enough water to keep the boiler from hot-cycling. On "normal" it sometimes consumes up to 175 watts which seems excessive. On my next burn I will try dialing it in at 10 gpm based on the above post to see what happens. I can watch the delta-T with my current thermometer placement, so I will perhaps just go for 20 degrees and try to pick a set gpm to achieve that.

 

[maple1]

I'm a bit puzzled on why so much pumping/wattage is needed to avoid 'hot cycling'. As mentioned, a 15-58 on low does my 40kw boiler fine - until my return temps start getting up there with a half-decent fire going. Which rarely happens. Then I might see 190 at top of boiler - but again very rare. Pretty well a constant 20° delta. What is your boiler return temp usually? Just wondering if the Danfoss is keeping that higher than it needs to be? Also wondering how far apart the boiler & storage are & size of piping. I'm not sure what a 15-58 on low pumping through a LK810 with storage right next to it via 1.25" pipe equals in gpm.

 

[cpeltier]

Are you sure the flow is not (partially) bypassing through the heating loop and heating loop pump when you are charging the tanks and the heating loop pump is idle?
To prevent a ghost flow you need to make sure there is some head in the heating loop to prevent unnecessary bypass with this piping arrangement.

 

[tuolumne]

Are you sure the flow is not (partially) bypassing through the heating loop and heating loop pump when you are charging the tanks and the heating loop pump is idle?
To prevent a ghost flow you need to make sure there is some head in the heating loop to prevent unnecessary bypass with this piping arrangement.

I am sure that flow is not going through the primary loop; there is a temperature gage that that makes that clear. I have about 36' of 1-1/4" pipe plus the two 500 gallon tanks to pass through on my storage loop. I also burn very dry wood. The 15-58 did not hot-cycle on high when the pump was working, but it always did on low.

I'll watch the return temperature better on the next burn.