circulator and 1 pipe monoflo tee system

Jon2018

Hi all, curious about my monoflo system and the circulator.

If you have a pump in there and lets say its called pump A, as long as it gives you a delta T return of 20 degrees does it mean you are good to go?

Out of curiosity I'm going to start doing all the calculations, but just wanted to ask the question.

One other reason that I ask is all thought the downstairs convectors get pretty hot, seems that some of the second floor ones are not as hot, wondering if its just piping heat loss occurring inside the wall of the first floor before it gets to the second floor convector

hot_rod

Is this an existing system? You should have, or may need a few balance valves to adjust the various branches and emitters.

Cast iron radiators by chance? if so they could have TRVs added for more temperature control and balance.

It takes quite a few steps to design a diverter T system properly.

Start with a room by room heatloss calculation to see if you have proper amount or size of heat emitters.

Select a supply temperature and temperature drop. ex. 180/ 20°

The average SWT is used to select emitter size to the heatload of every room, from the load calc you performed. 180 plus 160 divided by 2 is the AWT or 170•

Calculate flow rate required to move the load at your selected ∆

Then size the piping mains and branches for those loads.

With all the piping info, measure all the piping and fittings, then a pressure drop is calculated calculated, size a circulator, using a pump curve. A diverter tee, depending on the size, is about equivalent to 17 feet of pipe, by the way that needs to be in the piping equivalent length calculation.

Ideally you generate a system curve over the pump curve, select a circulator where the system curve crosses the pump curve about the middle 1/3, called the "knee" of the curve.

Jon2018

Thanks Hot Rod, I'm gathering up my info and will report back further. Hopefully over the weekend I can get much of this info gathered up.
To answer some questions.

Yes 50 year old Taco venturi/monoflo system. So, from the boiler 1 1/4" supply line (boiler is in back part of the house) so basically the 1 1/4" main goes to the front of the house, then branches left and right to 1" lines, then just above the boiler comes back into a 1 1/4" return.

The house has in wall convectors.

hot_rod

Depending on how deep into it you want to get? maybe a few balance valve additions.

It considered a single loop system but emitters are also in series, so the first ones off the main see the hottest SWT, temperature drops as it supplies downstream emitters. If you add some long runs that piping loss also comes into play.

If it has the original boiler it was probably sized large enough or oversized if building upgrades have been made?

Perhaps there are some valves at the convectors? The old timers that understood diverter T systems often cover the bases.

Paul48

@hot rod
I'm pretty sure I've asked this before, but, how do you use TRV's on a monoflow system? Won't that dead end a branch?

hot_rod

I've never done one personally but the valve would just shut down or regulate the emitter as I see it.
Freeze protection could be a concern with piping in the walls if you close off completely. Most TRV have a winter position on the knob.

Modern Hydronics shows 3 or 4 way to pipe these systems including one drawing with a subassembly where a series of rads are controlled by one TRV, or a tee and TRV for each heat emitter.

And as expected plenty of math to calculate flow rate and temperature drop throughout the loop.

Paul48

We've always been told that if you remove a radiator from a monoflow system, you can't just cap the pipes. My concern would be that the TRV would effectively act like a capped pipe.

hot_rod

If you cap one off the pressure drop of the loop goes up, the system should be recalculated to assure you still have adequate flow. Here are a couple articles on design of diverter t systems.

https://www.pmmag.com/articles/84791-diversionary-tactics

You are correct B&G suggest removing the tee when removing a radiator or emitter, or connecting the tees with blank pipe.

40 K, 4 gpm load lets say 3 of 4 TRVs close, all requiring 1 gpm. One remains opens, the load is now 1 gpm, all going thru the run of the diverter tees. So the circ just needs to move 1 gpm thru the tees to meet the demand of 1 heat emitter. Pressure drop increases but flow rate required goes down. Would the circulator just shift up curve? The system curve shifts and crosses the pump curve in a different point. Maybe the system needs a reverse ∆P circulator

These type of systems have been used with both manual hand wheel valves and TRVs, it must be workable.

Paul48

I've got to admit......I've read the old documents about calculating head with the monoflow tees, and the number of tees and their orientation for more or less flow. I can only compare it to looking in the engine compartment of a new automobile, and thinking you're going to do some work in that. I honestly think that if I bought a house that had a monoflow system in it, I'd cut it out and re-plumb it.

lchmb

I redid the monoflow system at my parents house and the even heat cannot be beat. As far as trv's, the old school of thought was the radiators had to have full flow. As Paul mentioned, if you removed a radiator you tied it back into it's return so full flow was maintained around the loop. With that said I've seen hundreds with branches capped off. The only big thing with this type of system is flow. Need to move a lot of water. As far as the initial issue with 2nd floor radiators..you probably have air in them. With the system off, increase boiler pressure while bleeding the radiator on the 2nd floor. It may be you need to run a little higher in pressure to maintain pressure up there..

hot_rod

The biggest complaint we hear at HH, is purging them adequately after a drain down. I suppose a lot of high psi flow, maybe direct from the homes water pressure?

KISS is what they are all about, but with TRVs added it should be a sweet,, comfortable, controllable but often a misunderstood piping method. I suspect some poorly modified versions are out there like any other piping method.

Jon2018

Hi all, still working on my measurement and getting my calculations in older.

When measuring the pipe run do you also measure each line that comes off the main and goes to the convectors?

In my case I have the 1 1/4" mian, which branches off to 1" for the left and right of the house. The monoflo tees are 1 1/4" x 1/2" , so I would measure the 1/2 pipe going and returning to each convector?

Paul48

I don't understand your description of your system. In it's purest form, a monoflow system consists of a main loop, that comes from the boiler and returns to the boiler. The tees are placed along the main to feed each emitter. You seem to be describing series branches off the main, by way of the monoflow tees?

JUGHNE

Split loop with supply going to end of house (no taps on this) then splits (left & right) into 2 loops with monoflow tees. Has 2 returns to the boiler. Make sense?

Paul48

" 1" for the left and right of the house. The monoflo tees are 1 1/4" x 1/2"

Nope

JUGHNE

He did say a single return of 1 1/4.......but needs the "Pocket Rocket" to be sure.

Jon2018

Hi I probably didn't describe the layout good in words. I attached a pic.

JUGHNE

So 1" X 1/2" monoflow tees.
Are they actually connected for the baths, living and family rooms as drawn? Tee for one unit in between the tees for another?

HomerJSmith

Off hand, I would think you would have to balance your two zones even tho you have a generous supply & return.

Peter_26

Just curious OP. Those your a system have a wye style dual valve fitting just before the main supply branches off into the two 1” for each zone?

Jon2018

Hi Jughne. Yes correct 1" x 1/2" tees. Each convector has one (1"x 1/2") tee off the 1" line. The drawing was just laid out like that for my purpose of measuring my runs, and where each convector was. It's basically my working drawing to capture all my info to do calculations. So, really the each convector in the 1" line has its regular tee, then monoflo, then the next one starts down the line. It is not as pictured in the diagram, meaning it does not go regular tee, then another regular tee then a monoflo then another monoflo. If I understood your question correctly


HomerJSmith...yeah HotRod was saying the same thing, but I was still gathering some info on the system. One thing though how do you balance since whether left or right 1" line, each line has on it a monoflo that goes to the first floor, then the second floor. Just like it's picture in the drawing.

Peter below are the pics of the wye. The first is the one that comes off the 1 1/4" line and splits to the 1" for the left and right side of the house. The second is just above the boiler where the 1" lines come back together on the return side and go to 1 1/4" line right into the boiler.

Jon2018

HOTROD, thanks for posting the link to that article, its was a good read.

Jon2018

Hi all gather some info, and something just doesn't seem right to me as far as the head needed. I attached my calcs.

Jon2018

Paul48

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

Page 18 gives the equivalent length of monoflow tees. That, and all fittings have to be taken into consideration.

Jon2018

The 50% in the formula should have already taken that into account and then some. If I add in more footage for the monoflo then would be another 18 X 23ft per monoflo thats another 414 ft plus the 419ft I already calculated. That's oer 800ft.

That can't be right

Paul48

I would argue that formula should not be used. The head loss for 1" and 1.25" pipe is readily available. There are equivalent length charts for all the fittings you have.

Jon2018

Ok, I'll do some more reading from the Caleffi site you posted and redo some numbers.

Leonard

Dumb question but what is 20 deg delta T ..... temp diff water inlet to outlet of furnace?

Paul48

You don't pump based on the DOE capacity of the boiler. You pump to the requirements of the emitters. Have you figured out how you're going to get the proper flow in each direction, where the pipe splits to 1"?

Leonard

OK figured out 20 deg deltas T is temp drop across the heat emitter.

Jonn2018

Hi all...been away from this thread for a bit. Anyways, redid some calcs and still show me that I need a pretty good head for this monoflo system to work. I'm still up around 25 lbs. All in all system works ok, but I think the second floor does not get as hot as first floor.
Any suggestions? The pump in the system now is a 15-58, My delta T according to my thermocouple meter is just about 20 degrees.

Since this is a single loop would be hard to install balance valve on this system. I would have to put balance valves all over the place

Peter_26

I think you would want to install balance valves, one for each loop, right after the 1 1/4" supply splits or right before the 1" loops merge back into the 1 1/4" return, one valve per loop. Check for valves at the convectors like suggested by "hot rod".

Maybe the upstairs doesn't heat up as well because you have air in that part of the system?

Do you have any pics of the system? What pressure is the system working at?

Jonn2018

The system was bleed out thoroughly, at the boiler and at each convector a few times, so I'm confident about no air.

The boiler pressure is 17 lbs, the expansion tanks is set at the same.

Not sure what the balance valves would accomplish as far as second floor goes as this is a monoflo system and in those same 1" lines it feeds the first and second floors. Now balancing between the left 1" pipe configuration and right 1" pipe configuration is something I could do, but that would be an expensive ordeal wouldn't it?