Grundfos 15-58fc versus Grunfos 15-55

[MrEd]

Anyone able to compare a Grundfos 15-58FC running on high, versus a 15-55 also running on high?

I have a two 15-58s, both always set on high, running in series on my "simplified pressurized system", and have been wanting two buy a 3rd pump to keep on the shelf for when one of the installed ones die (which will be at the coldest part of the year, in the middle of the night, on a long-weekend of course)...

my plan was to buy another 15-58 which has served me well (about $75). However this new deltaP pump caught my eye at the plumbing supply shop. It costs more (about $250), but supposedly modulates its own speed according to pressure, so the less zones opened, the lower the pump would push, and the more zones open, the harder it would push...seems neat. I could replace on of my 15-58s with this one, and keep the extra for backup purposes...

But, how does the max capacity of the 15-58 set to high, compared to the max power on the 15-55? (I am no expert, but they seem comparable)

Also, anyone know if this thing will actually turn automatically off when all zones are closed? and then back on again when a zone opens up? If so, that would be sweet and simplify some of my other control logic...

Thanks

 

[Jim K in PA]

You can compare the pump curves for them and see that they are nearly identical. Check the US Grundfos web site (I found them wiht a little google-ing).

Patriot Supply has the 15-55 for $230.

 

[chuck172]

Ed, Have you considedthe taco delta T pump with the “simplified pressurized system”.
I think it might work well as the load pump.

 

[MrEd]

How would one decide between a delta-T and a delta-P...both seem to want to solve the same problem, but in a different way?

 

[chuck172]

I'm thinking the delta t pump would offer variable resistance to the boiler pump, as the heating zones rise in temperature, and divert some hot water to storage.

 

[chuck172]

Are there any other opinions on whether a delta t or delta p pump would work better as the heating load pump with the “simplified pressurized system”.?

 

[MrEd]

I *think* the delta P would work better for me, the way my system is setup, I have a 15-58 at my wood boiler and another 15-58 (about 50 feet away), just before the distribution pipes that are controlled by 6 zone valves. The delta-P caught my attention, because rarely, if ever, are all 6 zones calling for heat, so the pump could ratchet down as zone valves close off (I'd still like to know if it will close off completely if all zones are shut).

I don't see how a delta-T would work in my scenario...but maybe I just don't see something obvious.

 

[chuck172]

Mr. Ed, Isn't your second pump, (load pump) turned on or off by the end switches of the zone valves?

 

[MrEd]

Mr. Ed, Isn't your second pump, (load pump) turned on or off by the end switches of the zone valves?

Yes, I was wondering if one of these delta-P's was actually smart enough to turn itself all the way off when no zones were open - I suspect not.

 

[deerefanatic]

If you run pump power through the end switches, it will!

 

[in hot water]

yes the Grundfos Alphas will shut down to a 4W draw (no flow) condition when all the zone valves close. That may be less current draw and operating expense than a transformer and relay box to use the end switches. I think that small current draw keeps the microprocessor and digital displays powered??

Some installers use the end switch to switch 120V, watch the rating of the switch and electrical codes when used that way. That takes transformer loss out of the equasion.

hr

 

[chuck172]

But is there a preference to whether a delta t or delta p pump be used as the heating load pump when there are two pumps in series as in the "simplified pressurized system"?

 

[in hot water]

Delta T and delta p are two completely different functions. Delta p changes pump speed as the flow through zones or loops change. I'm not sure how it would behave in and out of series with another circ. Unless you need periods of double the head, there really isn't a good reason to have pumps in series. It's too hard to define or predict a system curve or OP.

Here is an example of pumps in series in a drainback solar, notice how the pump curve and the system curve move around with one or both running. This example shows two circs in series to fill a drainback solar, then shut one down when the siphon is established. a bit different than a closed loop system like yours, but it shows the relationship of pumps in series and how the curves are influenced.

Inn your system the intent isn't to double the head, but to flow different loops, so when they both run you will see higher velocities if nothing else in the circuit changed, like the pressure drop (head).

Delta t would modulate based on temperature wherever you attach the sensors. Sometimes that function is used to maintain a fixed supply, like injection mixing. Sometimes the sensor is used on the return to a boiler to maintain a proper temperature. Maybe two delta t pumps with sensors carefully placed would modulate together? I don't see how either fits your piping other than to use the Alpha to reduce power consumption when it is running. No harm in trying, but how would you gauge any advantages other than power used for fluid moved.

The series with Alpha question may be one to ask a Grundfos engineer.

hr

 

[chuck172]

"Inn your system the intent isn’t to double the head, but to flow different loops, so when they both run you will see higher velocities if nothing else in the circuit changed, like the pressure drop (head)."
That's exactly my intent. I'm thinking as the heating zones satisfy, the load pump would slow down, either by pressure or temperature, while the boiler pump speed would remain constant. Thereby pushing more flow to storage, less to the load.
The wood boilern would be less prone to idle.
Tarm (Bioheat) uses a termovar diverting valve for this application.