flow control for 2 zones

leonz · May 2022

As the coal stoker heating season is over I want to fix or at least realistically think about what I need for parts to obtain the parts needed for our heating system.

I am using the Bell +Gossett NRF25 circulator which is set at speed one which is 12 gallons per minute. I have a spare circulator if needed.

The boiler has 34 gallons of water in it. The system has 54 gallons+- of water in it.

The house has 225 feet+- of 3/4 fin tube baseboard.

The piping was changed and set up as continuous one zone when the original hand fed boiler was installed in 1982 and the home has on thermostat for the entire home.

I have the original B+G boiler bypass that was installed with the coal stoker in 2015 that is closed and I guess I could use that one for the shorter loop feeding 4 gallons per minute through that part of the house and purchase another one for the longer heating loop feeding it 4 gallons per minute to make better use of the hot water heat being supplied by the coal stoker.

The bypass valve would have to be unsoldered and then resoldered into place and the bypass capped off.

Option two would be to leave the original bypass in place and install 2 new ones on both loops and set them at 4 gallons per minute and open the first one to 4 gallons per minute and recirculate 4 gallons per minute back to the boiler sump splitting the flow 3 ways between the two loops and the boiler bypass.

The water flow comes out of the top boiler pumping away and is reduced to one inch after the circulator and then enters a one inch Tee and the flow is further reduced to 3/4 to the 2 heating loops and returns to the boiler sump in 3/4" soldered copper.

I do not have to worry about the coal fire going out because the hold fire timer keeps the fire going if there is no heat call during the 30 minute timer cycle.

The house is poorly insulated and I know I lose heat but I figure the better way to do this is to regulate the flow especially during the very cold periods when I use a lot of coal to heat the place.

Our wonderful NYS home weatherization program will not help us because our roof leaks and they will not do anything for us because we need a new roof.

Option three would be to install one new boiler bypass valve; set it at 4 gallons per minute and install a new 8 gallon per minute circulator with an internal check valve in the isolation valve and keep the original bypass valve shut off and call it quits.
(This may be the simplest option as the boiler would only exchange 480 gallons per hour of regulated water flow with 4 gallons per minute going through each loop rather than 720 gallons per hour with an unbalanced flow, as Dan says be the ball in the pipe and think about how and where the water is flowing.

Your thoughts on this are most welcome as I have no idea how crazy this coming winter is going to be.

As much as I want to install a New Horizons rectangular insulated 495 gallon steel tank for additional thermal mass I cannot do it so I have to depend on the 54 gallons of water in the existing system with the heating loops, the steel compression tank and the boiler volume making my 54 gallons of thermal mass.

Jamie Hall · May 2022

I guess two questions to sort of get the ball rolling here. First, what temperature are you running coming out of the coal boiler? And related, what is the present delta T coming back? Remembering that the average temperature of the water in the fin tube will determine the heat output, and that flow rate and delta T are inversely related.

Second question is what are you trying to accomplish here? What problem are you trying to solve? Uneven heat? If that's it, splitting into two zones will certainly help, but you don't need more pumps to do that -- you'd just need a couple of balancing valves to control the relative flow in the two zones.

Can you tell us what it is you are trying to achieve here? That will help us to help.

leonz · May 2022

Hello Jamie,

(All my experience has involved hydraulics, hydraulic valves and hydraulic cylinders)

Yes, it is an uneven heat issue especially when the wind kicks up since the north facing walls are poorly insulated. I start out the heating season with 150 low 170 high and when it gets colder I raise the high limit to 180 and the low limit to 160.

I have seen the water in the return to boiler sump line drop to 120 or less degrees when the weather is really bad and cold.

I was more worried about keeping the 12 G.P.M. circulator in the system and its being too large and causing cavitation issues with my trying or wanting to keep 4 G.P.M. flowing through each loop as the baseboard is 3/4 copper.

Is using two boiler bypass valves set at 4 G.P.M. and leaving the NRF25 set at 12 gallons per minute overkill for this??

The reason I ask is because the dump zone temperature (which is the heating loop) is set at 190 and I would not want to damage the valves.

Thanks much,

Leon

leonz · May 2022

I guess I could use 2 3/4 NPT B+G circuit setters with threaded to sweat copper fittings then and not worry about it anymore.

These specific 3/4" NPT B+G circuit setters (117415LF) are $122.50 from Supply House as of today.

hot_rod · May 2022

A drawing of what you have may help. Really, you should have thermostatic return valves, especially you you are seeing 120F return temps

Jamie Hall · May 2022

Well, your big B&G is a bit of overkill, but that's not really a problem, except it may use more electricity than something newer might. You won't have trouble with cavitation, so long as the pump is pumping away from your compression tank.

What I would suggest is yes, two zones -- one for the area which gets cold when the breezes blow, and the other for the rest. But -- instead of two pumps, use two zone valves and get another thermostat, one to control each zone. This is not a big deal. Then each system will get the heat it needs.

You actually need more flow -- not less -- as your return temperatures are too low, and you may have trouble with corrosion in your boiler on the fire side, from condensation in there.

I confess to being a bit concerned about there not being a proper dump zone or tank; one really can't regard the heating system as one. I honestly do not regard a solid fuel boiler (wood or coal) without one as being truly safe, but if you have a very reliable and fail safe way to completely kill the draught on the fire, I suppose... Also, you should have a T and P relief valve, not just a pressure relief valve.

hot_rod · May 2022

225’ of fin tube as one circuit? Is so you need to split that loop, or the end of the loop will be fairly cool water
You want to look at the temperature leaving, and returning. Sound like you are supplying 180 and have 120 coming back? Is so that is another indicator of an excessive circuit length If it us all 3/4 tube, I doubt you are moving 12 gpm, 5 maybe 6 gpm with that pump on the circuit I think you are describing

Splitting the loop will slow more flow and also higher average temperature in the two loops for more output

Sane with hydraulics when the lines cannot handle the flow the pump produces

GroundUp · May 2022

You're not moving anywhere near 12 gpm with an NRF-25 on speed 1 unless that loop is 1-1/2"+ in diameter and pretty short.

flow control for 2 zones

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