Circulator for mono-flo system

gpjazz

I figured I'd start a new thread in regards to circulator sizing. So I'm sorry for the duplicate. But this is in reference to another thread about auto air bleeders…

The reason I asked this to begin with is because a customer says they have to bleed radiators all the time and they were asking about automatic air vents.

But I've found out more info and I don't think it's an air problem at all. This home has a mono-flo system and it does not seem to be circulating thru all of the radiators. I do not believe there is an air lock anywhere. This is a ranch style home with a full basement. The system fill pressure is about 15 psi cold. It just does not seem as though the circulator is moving the water properly.

Which brings me to my next question…

How is a circulator pump sized for mono-flo ? I have not dealt with mono-flo systems much at all, so I'm not extremely familiar with them. I realize there has got to be some restriction created thru the mono-flo tees. But how much ?? There are some radiators fed with 1/2" and some fed with 3/4".

I still need to go back and figure out the total length of piping and count up all the radiators. I do know that this system is a single zone with 1 1/4" copper mains. The main supply from boiler is 1 1/4", then splits and makes two separate loops around the basement , and then back to the return. The main returns coming back to boiler are also 1 1/4" copper. There are also ball valves on each of the supply mains to adjust flow to each of loops. The circulator is currently installed on the return line near boiler, and it is also "pumping away" from the expansion tank. Again, I'm thinking that the current circulator is just not sized correctly.

So how do I determine what circulator is required for this type of mono-flo system ?

How do I calculate everything?

Thank you for any advice

SuperTech

For starters it would be a big help if let us know what circulator is there right now, but I highly doubt the problem is an undersized circulator. I've seen plenty of homes with 1-14" monoflo tees work fine with a Taco 007 or Grundfos 15-58. It's more likely that it's not installed properly or you have an air problem. Pictures of the boiler and the piping make it a lot easier for us to help you.

Big Ed_4

Hi volume with low head is what you want . B&G 100 was commonly used , three speed circulator on high brings you in range…

hot_rod

There are a few steps involved to get an exact pressure drop for the diverter tee circuit. A sketch of the system is a good starting point. This B&G sheet takes you through the calculation steps.

They are not so easy to bleed and that seems to be the most common no heat call.

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108121-Selection%20Guide.pdf

This EL equivalent length chart converts the MonoFlo tees, and other fittings in the piping into feet of pipe. So see that each 1-1/4 tee is equal to 25' of copper tube for EL

Chapter 11 in Modern Hydronic Heating & Cooling takes you through the steps also. basically turning all the branch subassemblies into one "resistance" number. So with the flow requirement in GPM for the ayatem, and the pressure drop number, that is the correct way to select a circulator.

Use the blue "system curve" you developed and lay it over a pump curve. Where the pump curve and system curve cross is the actual OP operating point of the system

Here are the steps for a simple fin tube circuit with typical components.

A 5 gpm flow in this 100' circuit would be 4.93' head

Here is a Grundfos 26-99 pump curve.

I added a 007 and the Grundfos 15-58 3 speeds onto the chart. The 007 is a higher flow, lower head, flat curve circ compared to the 15-58.

Mid curve they are similar performance, but the 15-58 is higher head. Which may be needed if you calculate a high pressure drop circuit.

So IF you really want to define your circuit, you have some math to do. Probably more often without knowing or defining the circuit, technicians just try to pump there way out of low heat conditions. 3 or multi-speed circulators give you more wiggle room for the trial and error method :)

Oversizing the circ possibly pushes rouge air bubbles out of the air locked circuits. Mission accomplished!

Steve Minnich

@hot_rod The most thorough and accurate response you’ll ever see for the OP’’s question.