I have drawn this simple piping. It is similar to what I will have in my system. My question is about monoflow tee's. The drawing shows two tee's that I have highlighted in green. Should these tee's be Monoflow or standard?

Standard. If you put monoflows in, you will get flow through whether the pump is running or not. Monoflows will force flow through.

Also, those tees should be installed close together.

I believe that would be considered an injection circuit. The following are the main rules for injection circuits. The last one is really only critical for injecting into low temp circuits.

1. There shall be at least 6 pipe diameters of straight pipe prior to the “T” fittings.
2. There shall be no more than 4 pipe diameters between the “T” fittings.
3. There shall be a minimum of 12 inches of drop on the injection loop to create a thermal trap to prevent convective heat transfer.

Monoflow Tees are typically used on kickspace heaters where you don't want the entire flow of the circuit being bottlenecked by a small pipe diameter device.

Unlike injection circuits, with Monoflow T circuits you always want to make sure you have at least 12" between them.

This message has been edited. Last edited by: Neophyte,

Neo- I'm not quite sure you got the picture straight. That is a HX in the piping diagram. So, unless by injection you mean injected into a HX your interpretation is a bit off. Thanks for your reply anyway.

Guest- thats for the info. You confirmed my "gut feelings." I guess need reassurance on sme of my decisions untill I design and build more systems. Trying to lean on one's own can be difficult. This board and its arcives (man I hope we get those back) are an excellant reasource for me. I have been to some HVAC web-sites, and to be honest I was begining to dislike the industry as a whole. The are some real jack-a$$e$ out there. This board has renewed my interest and trust of people in this field. I am considering a carrer change to this type of work. Thanks Rad-net, keep up the good work.

Neo,

Monoflows are old school, designed for one pipe systems. They worked well when trying to keep labor and material costs down and were used a lot on radiators and fin tube. Not too popular today (at least in my parts).

I can see where they would work well on a retrofit with a kickspace heater though.

Pexster,

I got the picture straight but I guess the way I worded it is confusing. I realize it is not a variable speed injection mixing circuit but it would follow the same rules since they are both forms of primary/secondary circuits. The fact that it is a heat exchanger does not make a huge difference. Just out of curiousity, what is the heat exchanger circuit being used for?

You have a one pipe monoflow circuit depicted in your picture. That is, the supply to and return from the heat exchanger are attached to the same pipe, as opposed to a 2-pipe direct return or 2-pipe reverse return.

If you did not have a circulator "injecting" water to the heat exchanger off of the supply line, then you would need monoflow Tees to divert the water. I believe monoflow Tees are also referred to as Venturi Tees or Diversion Tees. Since you have a circulator pump "injecting" the water, you don't require a monoflow Tee. If you did have a monoflow Tee, you would not need the circulator but you would need a way to control the flow.

The first two rules of primary/secondary circuits as stated in my previous post should apply to this circuit. As Guest stated, the tees should be close together as it prevents ghost flow. Also, the second rule is important as well. If you have an elbow too close to the Tee, then you have turbulent water running through the tees, which will prevent the uncoupling of the primary and secondary circuits. This means that flow through the primary circuit will cause flow through the secondary circuit. With all of that said, any unwanted flow may not be a huge problem in your case since your pump on the other side of the heat exchanger will be off.

I should also make one note as to the second rule. A "rule of thumb" for the straight pipe is a minimum of 6 pipe diameters on either side as I stated. A more accurate rule would be to have a minimum of 8 pipe diameters on the upstream side and a minimum of 4 pipe diameters on the downstream side.

As guest stated, monoflow Tees are commonly used on one pipe monoflow circuits. They are used to create a bypass loop, which is usually attached to a radiator, convector, baseboard or kickspace heater. They are also commonly used in one pipe series loops where one of the devices may present a large pressure drop. For instance, in my house I have a one pipe series loop feeding through several baseboards with 3/4" pipe. In this series loop, I also have a kickspace heater (1/2" piping) that can present as much as a 2.6 ft pressure drop. Therefore, rather than feed the entire circuit through this device, a monoflow Tee circuit was installed off of the 3/4" piping to divert some of the flow to the kickspace heater.

Knowing what I know now, I would have had my installer pipe this kickspace heater differently. I should have had him pipe it on a seperate loop down to the basement. It would have given me better flexibility with the circuit.

This message has been edited. Last edited by: Neophyte,