Circulator Question for Single Pump and Multiple Zones

lsayre · Post by **lsayre** » Sat. Mar. 22, 2014 3:30 pm

I've calculated that each of my 4 roughly equal length zones when looked at independently has about 7.2 ft. of head. And also that to deliver the full 100,000 output BTU's of my Coal Gun requires a flow of 10 GPM (at 20 degrees of temperature drop).

What I can't seem to fully get my head around is the requirement of the pump when all 4 zones are open at once. Is the entire systems head still only 7.2 ft. at that juncture, or is it something else? I believe the head of the system remains at 7.2 ft., but I'll need an expert to confirm (or correct) this.

lsayre · Post by **lsayre** » Sun. Mar. 23, 2014 5:34 am

I've answered my own question. Each zone opening up effectively expands the diameter of the pipe that the water is circulating through, thus dropping the resistance to flow, and causing the flow rate (GPM's) to increase. This moves the intersection of the combined zones head loss downward on the pumps curve.

Conclusion: The overall systems head does not remain constant or go up as more zones open, but rather it decreases as more zone valves open.

By the time my 4 x 3/4" diameter pipe zones are open the water is flowing through an effective 1.5" diameter pipe.

I've also re-calculated the head loss for my single longest zone loop at 8.4 ft.

Post by **Lightning** » Sun. Mar. 23, 2014 4:49 pm

lsayre wrote:Conclusion: The overall systems head does not remain constant or go up as more zones open, but rather it decreases as more zone valves open.

I agree that more zones open would decrease flow resistance which would allow faster turnover of the water thru the boiler.

Yanche · Post by **Yanche** » Sun. Mar. 23, 2014 9:33 pm

I agree also. But what will also happen is the flow rate in each zone will be reduced and less heat delivered to that zone as more and more zones are active. One can calculate the resistance in each zone individually. Then when multiple zones are operating it's like parallel resistors (electric circuit analogy). Determining the flow in each zone is possible but is it's more involved.

My preferred design is to use multiple zone pumps not zone valves.

Sting · Post by **Sting** » Mon. Mar. 24, 2014 7:01 am

Plumbers zone with pumps

Heating guys zone with valves

Its all works !

Gforks · Post by **Gforks** » Mon. Mar. 24, 2014 1:15 pm

Which is the better solution?

waldo lemieux · Post by **waldo lemieux** » Mon. Mar. 24, 2014 1:36 pm

Are you a plumber or a heating guy?

Carbon12 · Post by **Carbon12** » Mon. Mar. 24, 2014 1:46 pm

A general rule is, the more zones/feet of radiation, the more likely individual circulator pumps will work best, so,....it depends.

lsayre · Post by **lsayre** » Mon. Mar. 24, 2014 2:40 pm

My house has been set up for a single circulator and 4 zone valves since it was first made in 1964. it has gone through an oil boiler phase, a resistance boiler phase, and now a coal boiler phase, and all have worked well with a single circulator and zone valves.

whistlenut · Post by **whistlenut** » Mon. Mar. 24, 2014 3:16 pm

Keep a spare circ on hand(gaskets also), a 5/8" and 11/16" open end/ box end. Penetrating oil the bolts NOW unless they were anti-seized when installed. Shut off flanges or valves in place? Keep a spare zone valve head on hand, also.

As to circs or zone valves; depends........many system are hybrids with both. They are both very effective, but if the 'one circ' fails......with no replacement handy......on a twenty below evening.......

Gonna be a costly error on your part.

Sting · Post by **Sting** » Mon. Mar. 24, 2014 3:22 pm

Carbon12 wrote:A general rule is,....it depends.

Carbon12 · Post by **Carbon12** » Mon. Mar. 24, 2014 5:39 pm

@ Sting:

I seriously thought about not adding that,.....I didn't want to steal your thunder!

I guess I did, however.

lsayre · Post by **lsayre** » Mon. Mar. 24, 2014 6:00 pm

whistlenut wrote:Keep a spare circ on hand(gaskets also), a 5/8" and 11/16" open end/ box end. Penetrating oil the bolts NOW unless they were anti-seized when installed. Shut off flanges or valves in place? Keep a spare zone valve head on hand, also.

As to circs or zone valves; depends........many system are hybrids with both. They are both very effective, but if the 'one circ' fails......with no replacement handy......on a twenty below evening.......

Gonna be a costly error on your part.

I have a new in box circulator, a complete new zone valve, and a new zone valve control head on stand-by.

My previous circulator (B&G NRF-22) was 11 years old when I replaced it as part of the entire system makeover I did when installing the coal boiler. It had no issues, but I replaced it anyway.

Sting · Post by **Sting** » Mon. Mar. 24, 2014 6:48 pm

Carbon12 wrote:@ Sting:

I seriously thought about not adding that,.....I didn't want to steal your thunder! I guess I did, however.

Imitation is the sincerest form of flattery

oilman · Post by **oilman** » Mon. Mar. 24, 2014 9:17 pm

Have you looked at the Grundfos Alpha pump? I have been using them on multiple ZV systems. It is a variable speed circ.