circulator pump - Single speed vs 3-speed vs variable

hal1000

Is there any downside in getting a 3 speed or variable speed circulator pump over a single speed?

Brewbeer

One possible downside is the new circulator may not be the right one for your application. Need to know more about the system to select the correct circulator.

Rich_49

Single speed PSC circs rarely meet the needs of any system without loads of accessories that may or may not be spec'd correctly . 3 speed circs are a bit more versatile in that you have 3 performance curves to work with , odds are better of having the right size circ Xs 3 . VS circs are best . Just look at the performance curves to insure they have the capability to do the job

hal1000

What are symptoms that a circulator is undersized? Oversized?

NY_Rob

What is your intended use for the pump?
CH, DHW, etc...?

Gordy

Before assessment of circulator sizing. You need to know the flow rates the system needs. From that system head loss calculations need to be done. Only then can you properly size a circulator.

It could be entirely possible that a happy medium need be chosen if the system piping can not manage the flow rates needed.

Is the system zoned?
If so are zone valves, or are circulators used?

Symptoms of over sized circulator is velocity noise, low delta.

Symptoms of undersized circulator trapped air, high deltas, boiler shutting down on high limit.

Just a few. It depends on what the circulator needs to be doing in the system.

PSC
3 speed
Delta t
Delta p
VS

They all have a place

hot_rod

I think any circulator replacement or upgrade should warrant a properly sized ECM. Some versions , like the B&G Varios which have a 7 speed selector have a very wide performance range.

Gordy

hot rod said:

I think any circulator replacement or upgrade should warrant a properly sized ECM. Some versions , like the B&G Varios which have a 7 speed selector have a very wide performance range.

Ecm selection is getting better, but there are still a lot of voids to Be filled that older systems have. Especially single zoned higher flow, and head systems. They are making progress.

hal1000

@Gordy
Is the system zoned? No. I have 1 circulator that flows into 2 loops. There are no zone valves and only 1 thermostat...each loop spans both floors - one loop is for the south half, one loop is for the north half.

I believe my current delta is 10F. I've never heard any noise from the pipes. Each season, I do get some air in the top radiators.

Gordy

What is your goal in circulator replacement. If things are working fine?

Gordy

I see you have another thread going. Which sounds like a balancing issue. Increasing flow may, or may not help. Could make things worse. I would try balancing rads as suggested. See how that works. If not maybe splitting the two loops, and installing a smaller circ on each.

hal1000

@Gordy Could one boiler serve 2 loops and 2 circulators? All on one zone? How would that be piped? My current system is one circulator flowing into the boiler.

Boiler -> supply pipe --> splits into 2 supplies --> comes back as 2 returns --> joins to 1 return --> expansion tank --> 1 circulator --> boiler

Gordy

Sure it would be two zones so a second thermostat would be needed, and a zone controller.

Gordy

I would try the balancing first however. Another option would be one circulator with two zone valves. The circulator would be a ECM delta p variety, or your existing with a differential bypass.

hal1000

@Gordy I see. So 2 thermostats, 2 zone valves, 2 circulators. Most likely, I would set both thermostats to the same temperature. Each zone would span 2 floors (north vs south halves)...it seems like a lot of work to ensure the loops both get adequate flow..

As you mentioned, balancing each radiator individually is one idea..any other ideas ?

Gordy

It would be either or. One circ two zone valves, or two circulators.

Gordy

With a 10 delta your getting good flow. How are you measuring delta, and where?

Brewbeer

Can you post photos of the piping in the vicinity of the circulator and where it splits into two loops, and of the radiators with the valves?