Problems With 1951 Monoflow Hybrid System
Greetings Everyone
I recently moved into a 1951 Cape that has an unusual monoflow-like hydronic system. The system is on a single thermostat and is supposed to heat both floors of the house, with one loop in the basement and risers going to the bathroom and two bedrooms upstairs. Each room has circular-fin baseboard convectors with coin valves in the elbows.
The boiler is a 2016 Energy Kinetics System 2000 Frontier and hot water storage tank. This is my first time with an EK boiler, and I have to say, I'm impressed. The recovery time for domestic hot water is under five minutes for the full tank, and the fuel consumption is incredibly low.
The system was always 1 1/2" copper with cast monoflow T's on the returns, but as the photos and diagram will show, it's not a typical monoflow setup. Starting around last month, when the weather began to cool off, I noticed that a run of baseboard in the dining room and a run of baseboard in the second bedroom upstairs were ice cold. They never got any hot water. When the boiler was serviced mid-October, the tech spent several hours trying to troubleshoot the problem, and drained nearly a half-gallon of water from the coin valves in both respective rooms to no avail. No air came out, and not hot water ever made it there, either.
- Is the boiler pumping in the wrong direction? I've followed the arrow on the circulator and coordinated it with the arrow on the T's, and they all line up, so it seems like the water is moving in the right direction.
- Are the T's clogged with debris?
- In one area, as the diagram shows, a return is actually coming into a regular T instead of a monoflow T. Would this disrupt the entire system?
I am stumped!
Comments
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Are there balancing valves to balance the flow between the 2 halves of the split loop?
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Is the convector element pitched toward the bleeder? they are likely airbound somehow, unless it is all aranged so that the air can rise to the bleeder, water could be flowing from the side that the air is not in.
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Hello Smith19,
Monoflow systems require a certain fluid velocity to work correctly, to create the needed pressure differential at the monoflow tees. Assuming it worked correctly before, could the circulator have diminished flow or the zone valve is not opening fully.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
It requires a certain velocity, but it isn't so much creating a pressure difference, it is creating enough flow that some of it wants to take the higher resistance path.
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@Smith19 , you could close the bypass valve to about 45° degrees (it's near the T&P gauge). This will create more flow out to the zone vs through the bypass. We do usually like to see a dedicated primary loop circulator on mono flow tee systems to ensure the head and flow required to service the zones, although you would need some re-piping to make that work. As @mattmia2 commented, split loop flow balancing (and air removal) can be challenging.
Roger
President
Energy Kinetics, Inc.
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"The invention of the monoflo tee is what makes this system work. It creates a pressure change large enough to make the water flow up or down into the radiation and back into the main loop pipe around the basement."
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
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The rad that says "Dead" without a Monoflo tee in the return will never work without a Monoflo on the return or put a separate pump on it.
The one that says "upstairs dead" doesn't say weather it has a Monoflo on the return but it needs one.
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Because it is tapped in at 2 different points in the loop the resistance of the loop in between probably will act the similar to the restrictor in the monoflo tee.
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There was absolutely no air at all. Not a fizzle. And he drained it for several minutes continuously.
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if the air can't get to the bleeder you'll never get it out.
i feel like i had this same conversation a year ago. that one turned out to be a combination of one of the monoflo tees was backwards and the balance wasn't set between the halves of the split loop.
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The one that is called out with "no monoflow" T is indeed the only one like that, every other return has a monoflow.
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Hello Smith19,
As the system is now, did if ever completely work correctly? If so what has changed ? Something must be different for it to just stop working. No other work was done prior to the failure ?
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
From my experiences w mono flow system and issues if the tee s are placed as in your diagram the individual loops would need balancing valves on them due to the fact that the placement of the tees in relationship to 90 s and other convectors make it difficult for it to operate within the basic design of the system being there’s added resistance of other fittings and tees and between each individual heating element . Either repipe it and maintain the correct distances and placement and use mono flows on both sides when in doubt or a large convector but usually it’s one tee for 1 st floor convector and 2 for 2 nd floor and convectors below the main . If that’s all to much then just gets a nice mainifold and do a home run system w 1/2 pex or better yet some pex Al pex way better o2 barrier and be done throw some actuator heads and now you have some zoning and a way to balance flow to each convector . And if in the future you want to add heat some where else as long as you have extra ports on the manifold your pretty much set just run more pex and install what every heating elements you desire .
peace and good luck clammyR.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating
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Thanks for all the comments.
I for sure have major flow issues. Closed the DHW bypass, briefly got heat to the offending baseboards, but it was short lived. When the bypass was opened, I got the most insane air noises I've ever heard. A whole litany of problems have started, too:
- Loud circulator (Taco 007, which some say is too weak for monoflow)
- An additional baseboard convector is slowly going cold
- Safety valve is lifting, pissing water onto the floor. A LOT came out last night
- Nagging (tiny) oil leak at the burner. This is likely unrelated but just as annoying. The burner is also short cycling like crazy.
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Need to figure out the expansion tank or water leaking in thing. new water will bring in more air which will make things air bound again.
isn't there a zone valve or separate circulator that stops flow to the hx for dhw when there is no dhw call?
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Closing the bypass valve completely doesn't allow the system manager to shut down the burner and can cause the boiler to overheat (popping the relief valve and noise in the circulator) and possibly cause steaming. I would strongly recommend you pipe this primary secondary (which we recommend for high volume and monoflow systems) and increase the pump to 010 or equivalent. Doing a proper circulator sizing is the best way to make sure you get the correct flow for you distribution system but an 010 would most likely work. The 007 most likely can't move the water against the resistance of the monoflow system. If shutting the bypass down allowed heat to flow then the circulator is borderline.
John Ringel Energy Kinetics2 -
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Just thinking, you might check the pre-charge on that Domestic hot water expansion tank that appears to be in use as the expansion tank for the boiler system??? The factory pre-charge on that tank is 40 psi and may relate to why you are now having blow-off issues. If by chance it is water logged, that air ended up out in the system as an air lock on your highest circuits. A replacment tank with shutoff valve might be advised so you can avoid draining the system to replace a bad tank. A 3/4 to 1/2" thread adapter will allow the use of a Webstone tank fill and drain valve that will permit connection to a conventional boiler tank with 1/2" threads.
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On closer inspection I may be wrong on that Watts tank. Perhaps is is on a DHW line and not with the boiler. But where is the system expansion tank and is it waterlogged?
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Ah, at last it seems to be hiding behind the boiler along with another TACO pump. The original boiler may have had an old low head high volume B&G pump that would work with the monoflo tees. The smaller TACO likely does not have the high volume of the old pump and as others have said may do better with the higher head and volume TACO replacement.
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The question i would have is how fast was the water being bled from the bleeders? and are there shut off valves on each of the 2 lines going to the convector?
Water in this case can take the path of least resistance. Bleeding slow can pull water from one side rather than the other giving the appearance of no air. This can be fixed by hopefully shutting off one valve supplying the section in question, bleeding it vigorously, shutting off the other, opening the first, repeat the bleeding.
If this isn't possible due to lack of valves, I've dropped the pressure on the system to zero at the point of the convector, removing the bleeder, install make shift piping with a ball valve and coil of 3/8 copper. Ive dumped it in sinks out windows into showers where ever. The point is the full flow of water and start stop action using ball valve can usually free up air from both pipes involves. Once complete drop the pressure at the unit to zero again and replace the bleeder.
Robert W.
Energy Kinetics
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Monoflo systems usually don't have valves on emitters because of the added resistance.
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This is super helpful, thank you!
Sums it up well. I have some major circulation issues.
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Incorrect. The white expansion tank is purely for DHW use, as you can see it is piped into the EK plate style heat exchanger and actually hangs from the cold water supply. I see your point though. Both expansion tanks have been checked.
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It seems more and more like a flow problem. Lots of techs really seem to think this is air related, but after what's been discussed here, and seeing that I have a Taco 007, I don't think I'm moving enough water. And that's one Taco 007 for a three bedroom house.
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You are entirely correct.
The only way to fix this system is to take the advice of John Ringel of EK and pipe the system Primary/Secondary with a larger pump for the system. The size of the pump is dependent on three things:
- How many monoflo tees are utilized?
- What is the size of the copper piping used on the main run(s) around the building?
- How long, in feet, is the main run around the building?
Also, you are going to need TWO monoflo tees for each of the rads upstairs that refuse to heat.
I would also recommend to flow in ONE DIRECTION only. The tee that directs the flow in two directions cuts the flow rate in half. Not on a monoflo system!!
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There are plenty of split loop monoflo systems. it works if you do the math right and have balancing valves to balance the flow between the 2 halves.
unless there is some flow restriction with the boiler, it will be trickier to get it right, but if you figure the resistance of the loops and the boiler and use that to size a pump to get enough flow through that resistance it should work without changing it to primary secondary. Primary secondary will be more tolerant of errors.
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It depends on the pipe sizing. If he has a 1" loop, it is certainly possible to get a sufficient flow rate from the pump and than split that in half (give or take). But, if it is 3/4", the resulting flow rate out of the pump will be barely sufficient (even with a large pump) and then you are going to split that in half……………good luck with that!
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As @jringel , others, and I mentioned before, the correct way to pipe this is with a primary secondary loop, even though it has 1 1/2" copper tubing.
A good way to make this system work as well as possible is to make the split loop a primary/secondary loop (connect the supply and return and inject into it with a 0010 or equal as the primary loop circulator). If possible, cut the "dead" zone out and make it its own zone fed with a zone circulator (this has to branch off in the tee before the 007 on the Frontier, it cannot be zoned with a circulator in the location that the zone valves are typically located after the 007). Add valves so each half of the loop can be balanced and purged; similar for the "dead zone" (whether the system is upgraded to primary/secondary or not as balancing and purging are the path to success here). If this is of interest, @jringel or I can post the piping and wiring diagram for this type of primary/secondary system.
Best,
Roger
President
Energy Kinetics, Inc.1
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