Circulator speed on my outdoor wood boiler.

rico7467

I currently have a 1/3 hp taco circulator installed on my outdoor wood boiler. Is there a way to determine I'd I need to partially close a valve to throttle it back so the water isn't returning so fast or does it not matter how fast it returns to the boiler?

Jamie Hall

Some of our hydronics folks will chime in on this, but as a first cut... there are various degrees of fancy you could get on this, but my inclination would be to look at the delta T between in and out, and the final temperature, and set the flow rate to get the values which you want in the rest of the system.

hot_rod

Is this an un-pressurized type OWF by chance? Is one pump flowing the OWF and the entire distribution in the building?
What are the piping runs between OWF and house?

The pump SHOULD be sized to provide the BTU or flow rate the distribution system connected to it requires.

Often times those OWF have grossly oversized pumps due to undersized piping between the building and the OWF.

If it is an un-pressurized system you may have issues with that pump as you have little if any positive suction head, just the water level in the OWF. The higher the temperature in the OWF, the closer you are to cavitating that pump. At 180- 190 operating temperatures you'd like to have 4 psi or more on that pump. So about 9' of water above the pump location.

Is it giving you problems? Air noise, lack of sufficient heat? Or just curious?

rico7467

It's an unpressurized system with 175 feet supply of 1 1/4" that goes into a manifold and supplies two runs at 30 feet each of 1" into water to air heat exchangers in my airhandler then ditto on the return side. It's a mahoning 200 multi-fuel unit of 75000 to 150000 btu

Ironman

What's the model of the Taco circulator?

hot_rod

rico7467 said:

It's an unpressurized system with 175 feet supply of 1 1/4" that goes into a manifold and supplies two runs at 30 feet each of 1" into water to air heat exchangers in my airhandler then ditto on the return side. It's a mahoning 200 multi-fuel unit of 75000 to 150000 btu

I hope the 175' is round trip, not each way?

Generally a standard efficiency OWF run around 45- 50% efficient, so you may get 75,000 in wood fired mode? Not sure how that matches the load of you building.

If it is 175 feet, with a few valves and fittings a Taco 0011 would be plenty of pump, for 75K should move around 15 gpm.

Maybe in the gas or oil mode you may get more output, not sure why it is rated 75- 150?

Taco does build a pump specific to OWF, maybe a coated or bronze version of one of their pumps?

What do you have?

rico7467

350' round trip on the 1 1/4" underground pex and 60' round trip of 1" pex to each heat exchanger and my manifolds consist of 1 1/4" copper. The unit gas the option to burn #2 oil 1 1/2 gph nozzle which would produce 150000 btu and burns wood plus has shaker grates for coal so that's probably why it is 75,000-150,000. The unit holds around 300 gallon of water

rico7467

<img src="https://us.v-cdn.net/5021738/uploads/FileUpload/f3/cf6bf159b6b7cf27f13ae46652ea9e.png" /><img src="https://us.v-cdn.net/5021738/uploads/FileUpload/f3/cf6bf159b6b7cf27f13ae46652ea9e.png" /><img src="https://us.v-cdn.net/5021738/uploads/FileUpload/f3/cf6bf159b6b7cf27f13ae46652ea9e.png" />

hot_rod

Even on oil you need to assume an efficiency number. I;m not an oil expert, but with a dual fuel devise a wild guess 80% on oil. So 150 x 80% = 120,000 actual output. plus any altitude de-rate.

What needs to happen is you calculate all the components in the circuit and come up with a EL equivalent length to arrive at a head number. I use a sim program for that.

Every fitting, valve, heat exchanger, length of every pipe, etc. Only with that number, or a close estimate can you get an answer, to accurately size and select a pump. .

Or the trial and error pump sizing method that it sounds like you are under taking.

Is the system running? Are you having issues, or just trying to confirm someone else pump choice?

rico7467

System is running and going on the second season now. I usually burn would but I did burn coal when the Temps dropped real low last year because it seemed to last longer to allow me to only hav ed to load my unit twice daily. My water typically leaved at 180 and returns around 160-170

njtommy

I would imagine it's a Taco wb2400 pump?

hot_rod

That is the pump Taco suggests for OWF use. Stainless version would be best for an open system.

I see it has pressure ports in the body, nice feature. You could use those to check actual pump performance.

I hope Steve T from Taco is watching.

Ironman

Typically, a 20 - 30* Delta T (differential) will work fine with fan coils or AHUs. You don't want to drop below 150* in the boiler or flue gas condensation will occur.
I would definitely use the 2400 series circulator as Taco does not recommend using their wet rotor circs on unpressurized wood boilers.