Bleeding Baseboard MonoFlow system

Robert_25

STEVEusaPA said:

Usually when it’s one monoflow tee it’s on the return. Water wants to short circuit thru the non monoflow loop.
But @Robert_25 gave you right info for simple balancing.
Where’s the expansion tank and what type?

The monoflow system I ripped out of my house had the diverter tees in either location (some were on radiator supply, most were on radiator return). Taco's literature (page 3 from link below) shows that putting the venturi fitting on the supply side will increase flow through the radiator. I am not sure how much of a difference in flow it makes, but it might be worthwhile if the radiator is large.

http://www.taco-hvac.com/uploads/FAQ_attachments/venturi_fittings.pdf

seth1066

Robert_25 said:

Make sure the valve marked by X2 is fully open, and close X1. Turn the heat on and let the circulator run for a few minutes to see if your monoflow loop gets hot. If it does, slowly open the X1 valve until the "other loop" gets hot also. At that point you should have a balanced system. You can verify by letting everything cool off, and then turning the heat on - both loops should get hot.

Ok, the valve design makes it a little difficult to gauge the position. There is only 1/4 turn to full off. I started at full off and heat got into the monoflow side of the system, better than it has since the install.

Next, the valve was moved to about a 1/4 open and heat got into the the two non-mono radiators. At about 1/2 open still good, but then the boiler got to its set cut off temp of 181* and shut down, coming back on at 176. Then it continued to cycle at these temps even with the non-mono side at full open.

*The boiler has a Hydrostat controller and its high temp was set to 170 and the low to 160. When the digital readout was 181, the mechanical gauge was at 170.

At the start, the water pressure was at just under 20, so I let some in to 25 and it stayed there throughout.

My wild guess is that there should be more flow. I don't know if this news helps, but rooting around a box the installers left I found the original pump, a Taco 007-F4. Here are the spec differences (which seemed to be only the GPM)--

Original Circulator
Taco 007-F4
Max Head (Ft): 10
Head Range (ft.): 0-10
Max Flow (GPM): 23
Flow Range (GPM): 0-23
Max Pressure (PSI): 125

Current Circulator
TACO 007e2f2
Max Head (Ft): 10
Head Range (ft.): 0-10
Max Flow (GPM): 16
Flow Range: 0-16 GPM
Max Pressure (PSI): 125

mattmia2

If it heats both sections with x1 most of the way closed then leave it like that. You won't need much flow to heat that standard loop. What kind of valve is it, is it a globe or ball valve? I hope it isn't a gate valve, those will get damaged over time if you try to use them for throttling. The opening size of a ball valve is very much not a linear relationship with the handle position.

If there isn't enough flow in the monoflow loop to pull the water through the emitters then the heat from the boiler doesn't have any place to go other than the small conventional loop so the burner will shut down on high limit.

seth1066

Not sure of the type:

seth1066

mattmia2 said:

If there isn't enough flow in the monoflow loop to pull the water through the emitters then the heat from the boiler doesn't have any place to go other than the small conventional loop so the burner will shut down on high limit.

That's what I'm thinking. Is the difference in the pumps of 16 GPM vs. 23 GPM enough to effect a sufficient increase in the flow? Both have the same head range.

The valve was wide open for the past two seasons with low to mediocre heat to the monoflow loop. My thinking now was before, the boiler was starting and stopping due to temp limits, not the thermostat. I'm pretty sure that's not the case; the ambient temp would reach to where the thermostat was set (the room with two radiators in the non-mono loop is 8 feet from the thermostat).

mattmia2

That is some sort of ball valve. Some ball valves have specially shaped holes in the ball and orifice plates to make them more linear but I don't think that is one of them.

The real answer here is to zone the conventional and monoflow loops separately either with 2 ciculators or zone valves, especially if the types of emitters in each zone are different, but you can make it work a lot better than it currently does with a balancing valve(you would need the balancing valve anyhow if you zone it with zone valves). Globe valves are better for balancing because they are more linear. If you do a heat loss calculation for the conventional loop you can get a better idea of what the output needs to be and from that you can figure out what the minimum flow is that it needs.

seth1066

mattmia2 said:

That is some sort of ball valve. Some ball valves have specially shaped holes in the ball and orifice plates to make them more linear but I don't think that is one of them.

It's a 90 degree turn with a wrench to go from full on to full off, which would make it a pia as a balance valve. I don't know what they were there for (its twin is on the mono loop), but are now used in conjunction with the two added purge valves.

EBEBRATT-Ed

@seth1066

That is a gas cock not the greatest for balancing.

I am glad you have flow.


Try this test but you probably should have a digital thermometer with two probes. Let the boiler go cold and then start the heat up.

What your looking for is 15-20 degrees difference between supply and return temp. The supply temp on both loops will be the same. Try to balance the system to get both return temps the same, the same temp coming back from both loops Then before the system shuts down see if you have 15-20 degrees between the supply and return.

If your higher than a 20 degree TD you need more flow...bigger pump

seth1066

Robert_25 said:

STEVEusaPA said:

Usually when it’s one monoflow tee it’s on the return. Water wants to short circuit thru the non monoflow loop.
But @Robert_25 gave you right info for simple balancing.
Where’s the expansion tank and what type?

The monoflow system I ripped out of my house had the diverter tees in either location (some were on radiator supply, most were on radiator return). Taco's literature (page 3 from link below) shows that putting the venturi fitting on the supply side will increase flow through the radiator. I am not sure how much of a difference in flow it makes, but it might be worthwhile if the radiator is large.

http://www.taco-hvac.com/uploads/FAQ_attachments/venturi_fittings.pdf

The monoflow part of this system utilizes two monoflow Tees per baseboard unit. As you know, the first is shaped (not sure if it is a venturi design, but I think not) to force water to the radiator and the second creates a low pressure to facilitate it to flow out, probably a venturi shape like the TACO. My wild guess is it would take a much stronger flow for a system to operate with a single Tee per unit.

seth1066

Thanks to everyone that commented and gave your expertise; I learned a lot. If you remember, my diagnosis was the replacement pump, the TACO 007E, was the only thing different in the system; nothing had been changed. The Columbia boiler was an exact duplicate to the one that it replaced with the exception of the old style monster expansion tank that was exchanged for a bladder model.

Because I didn't have the specs on the original pump, I had wondered what specs the pump would need for this system. I found the old pump, a TACO F4. This pump was superseded by the TACO F5.

The balancing suggestion did help to get flow to the monoflow supply side, but not enough to flow through the monoflow radiators. The system would overheat and cut off; not enough cooler water coming in from the return. EBEBRATT-Ed had it right, more flow needed.

I installed a TACO F5 from SupplyHouse.com for $106 and the system is back to it's old self. I will play with the balance that EBEBRATT-Ed suggested to fine tune the temps between the the non-mono and mono circuits.

Again, thanks to EBEBRATT-Ed and everyone for your knowledge and expertise.