Mono-fow heat loops.

kjs

We are working on a new (2 years old) heating system for a multi-unit building. Each building has 4 apartments. Each apartment has its own boiler and indirect water heater and one zone for 8-10 rooms in each apartment. All heating loops were designed by an engineer to be 3/4" mono-flow loops with drops to each baseboard of 1/2". All the mono-flow mains run in the ceiling of the basement apartment. In two buildings two rooms (baseboards)in the basement apartments will not heat up. The problem has been going on since the first winter the building was running. The installer tried to bleed air from baseboards with coin vents (installed on supply side of baseboard 8' below the mono-flow mains). We have installed purge stations in the baseboards to try to avoid cutting sheetrock ceilings, the baseboards still don't get hot. We are now convinced the installer didn't install directional tees?? Is it possible to have diractional tees and have the baseboards not get any hot water? They are in the middle of the run. Is a 3/4" main big enough for 8-10 baseboards??

Brad White_203

Uh Oh

According to Bell and Gossett literature, there should be no more than two tees on a circuit

Brad White_203

Uh Oh

According to Bell and Gossett literature, there should be no more than one (or was it two?) 3/4" x 1/2" tee on a circuit and only on the return side at that. In other words, no drop applications or high branch head applications, I assume.

If you had one 3/4" branch per ROOM, I would say fine. But a system like you describe, I would have used a one-inch main which allows me the rational use of the right number of branch fittings.

It is not an air problem, it is a pressure drop and flow problem. There may be either no such fittings or two many, from what I can tell.

kjs

Mono-flow

Brad,
The system has several design flaws. I was afraid that the 3/4" main was not big enough. We also installed a spiro-vent on the supply main they had an air scoop on the return. If the problem is not air as you described, I don't know how to fix it without major sheetrock damage.
The amazing part is that I obtained a copy of the the engineered plans (from the engineer) that specified all this. It is hard to fault the installer when it seems the design was wrong. What are the advantages to a mono-flow over reverse return or even loop in a single zone application?? Thanks I think for your comment.

Brad White_202

Monoflow

I have a saying in my office (consulting engineers), which I give to my drafters and designers: "Follow my mark-ups to the letter and you will never make a mistake. *I* may make a huge mistake in giving you bad information but *you* the drafter, will not be the one making it." Enough about that, I made my point.

The advantage of Monoflow is a savings of material, that single main going around the floor doing the work of two pipes.

Monoflow has the advantage over single-pipe (series-loop), in that individual radiators can have control valves without much affecting rooms upstream or downstream of it.

The series loop method shares a disadvantage with Monoflow in that the water temperature is progressively diluted as it heads toward the last radiator.

Each of these systems, properly designed, would compensate for this using larger radiators selected for the diminished water temperatures.

Reverse-return works if all of the emitters have the same pressure drop, to be self-balancing.

A possible solution although not cheap, would be to split the loops and use home-run pex to each radiator, assuming that you can isolate the branches. The remaining main might work for one or two rooms tops, that I can see.

Mind you, I do not have the heat losses nor layout, so take all of these as general comments.

joe_94

Valve on monoflow rad

Brad, So where it happens that the the first radiator on my upstairs monoflo zone is too big [ergo, too hot for small room despite my best efforts], you are saying I can throttle it down some with a valve...and not seriously affect the downstream rooms?
Mains in basement are one inch. Risers are half inch.
Heck, I was about to box it in with moveable shutter panels.
joe

Brad White_203

Essentially, yes.

I had a monoflow system for years with TRV's on cast iron radiators and it worked great.

There is another facet to this, that if you remove a radiator from the loop that you reconnect the supply to the return because to not do that would impede main flow.

I suppose the effect of a lot of valves closing would do the same thing, but you know what? If there was a difference, I never noticed it. I just figured the pump was riding it's curve and if flow was low, so was the load.

tccoggs_2

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