Monoflo Conversion Advice

Peter_26

Hello again,

I am looking for some advice or suggestions on a heating system conversion from single-pipe monoflo to either a home run or extended copper manifold system. The current system is piped as a split loop in a ranch home. I have already purchased replacement panel radiators based on a heatloss calculation with the help of HeatCAD. The panel radiators are oversized a bit for future changes.

I am honestly leaning towards the extended copper manifold piping option where I can reuse the 1" copper used on the split loops and not have to worry about routing 1/2" pex all the way back to the manifold which will be in close proximity to the boiler. Seems like an easier option and cuts down on the need for a larger amount of pex and not to mention having to secure all the pex. In a homerun setup, the runs, 8 of them, would range from 65' to about 15'. With the extended the runs would be from approximetely 17' down to 10'.

What are the pros and cons of an extended manifold vs a home run system other than what I have pointed out?

Should I add 2 isolation valves to each circuit or would the panel radiator valves with built in shutoff be enough to facilitate purging and service?


Any suggestions or advice would be greatly appreciated,

Thanks,
Pete.

mattmia2

Another option would be to leave one side connected to the current loop and run one home run piece of pex to each emitter and use the current monoflow loop as the return.

EBEBRATT-Ed

I agree that running everything in a home run with pex can be messy looking. But that's just me and old timer who likes copper.

If it was me I would leave the split loop as is just remove the mono flow tees and splice it back together. Since the mono flows are usually on the return you will still have your supply pipe to each panel radiator.

You can put valves in the basement that would be my choice.

I am assuming your supply pipe goes to the other end of the building and then splits before feeding the radiation

I would then start a new return at the boiler then split it and run the return in copper. This will give you reverse return which will be more self balancing. I would run the new return in copper and then you could use pex for the return branches. But that is just one way.


Take the BTU of the new rads and divide it by 10,000. That will give you the gpm you need for each rad.

Pipe size
1/2"=1.5gpm
3/4"=4 gpm
1"=8 gpm
1 1/4"=14 gpm

Pex you may have to upsize the gpms are usually less than copper


Another way would be (and I don't know how many rads you have). would be to use the copper to feed "remote manifolds". Manifolds can give you zone control if you get manifolds with valves on them.

mattmia2

A note about running it in pex, most likely each individual emitter won't need more than 1/2" and there are various racks to run parallel runs back to the manifold. Some ells can make it a lot neater.

Peter_26

Thanks @mattmia2 that’s a good idea, but my problem with that is that I would like to finish the basement at some point and the pipes would need to be removed. That’s why I planned on routing the runs along the steel beam that runs down the center of the basement and tucking them in the floor joist bays if homerun. If I go extended, just run supply and return on either side of steel beam and run pex tucked into the bays from each to panel radiators. The basement clearance is not that great and I’m going to need the space. 

The panel radiators supply and return will be connected from the bottom on one side. 

I would love to leave it as is, but I’m trying to plan for a future partial or full finished basement and trying to update for better efficiency with lower SWT. Getting all the ideas and suggestions will help me immensely. 

Thanks 

Big Ed_4

It would be simpler if you run home run if using the radiators thermostats .. You can use the nonoflow supply but you would also need the radiator diverters ... Use an auto circulator rather then a pressure bypass . Reverse return the radiator connections on the manifold .. I would use at least one manifold with shutoffs just incase you need for bleeding . I would also recommend a outdoor reset for comfort and a outdoor thermostat to turn on the heating zone ..

Peter_26

@EBEBRATT-Ed, that is also another good idea, the main issue would be future basement finishing. There will only be 8 radiators, well there are also 2 circuits (basement and garage), which I haven’t really given much thought too yet on how to incorporate them into the updated system piping. The garage is attached and the temperature requirement is not as crucial and for the basement I am thinking of warmboard or something similar. The main floor room with highest heatloss will only need .6 gpm, so 1/2” pex will be more than enough. I’ve even thought of going with 3/8” pex, but that would require more pumping power. The basement and garage would both also be below 1.5 gom each, so 1/2” would be enough. 

@mattmia2 I like the idea of the ells too, but I’m trying to keep the connections at a minimum. Thinking about that now it’s kind of funny that I am leaning towards an extended manifold that would require a slew of soldered tees and isolation valves 😂. That’s some food for thought. 

I would like to insulate the piping also and the homerun would add to the project significantly. The extended return wouldn’t be that bad. Also, the copper piping has a considerable amount of heatloss, well not really lost, but doesn’t get to where it’s needed most. I could practically turn off the basement loop and it would be warm in the basement with the boiler and the piping. 

Great suggestions and they get me me thinking. 

EBEBRATT-Ed

@Peter_26

I have asked about this issue and never got an answer:

How do you insulate PEX. It's not the same diameter OD as...........anything. We used it on chilled water once and it made a mess.

Can't use fiberglass because it's to rigid and armaflex isn't the right diameter

hot_rod

Also panel rads run 30 or wider delta T, so the piping can be 1/2 sometimes 3/8 Pex

Up to 3 rads could be in series if you use H valves with adjustable bypass built in to them 

Just do the math with the temperature drop. Reverse return with the 1@ copper is a good option.

mattmia2

Since it is a closed system you can also use black iron. That could be easier and less expensive if you are building your own manifold.

hot_rod

There are a few ways to pipe a reverse return, one more piping intensive.

Peter_26

@Big Ed_4 I definitely want to use TRVs and a ΔP circulator would make it much simpler. The current monoflow layout is not an option for the reasons described. ODR is something that I would like and I am trying to work that in with my cast iron boiler.

@EBEBRATT-Ed If you asked me the question I don't see it in the previous comments, but if you mean in general you are correct about the insulation, regardless I would use K-flex. There will be some space, but I would try ans seal the ends as best as I can when connecting them together to avoid air infiltration. I think something would be better than nothing in this case. Also, thinking about your suggestion on placing the isolation valves on both supply and return in the basement makes sense if I decide on the extended manifold. Thinking about it now it would be redundant to use radiator valves and isolation valves.

@hot_rod I used HDS2 Pipe Sizer and 3/8" pex is a good fit at a number of ΔT's and all while keeping the Reynolds number above 4000 if I decide on the homerun layout. Thanks for the piping diagrams. Although I don't like the idea of dismantling the current monoflo system because it works just fine, but since I'm changing the baseboard for panel radiators and other changes for possible future changes it definitely merits it to make things easier. The panel radiators in series is also a good option, I'm going to have to give that some thought also. It would definitely cut down on tubing and all I would need to do is drill a small hole in the floor joist to interconnect the rads from room to room. How would I calculate the flow requirement for 3 in series, just add the 3 individual flow requirements and pipe accordingly? The H valve adjustments would be an approximate setting for the flow of each rad?

@mattmia2 the extended manifold I was referring to is like the one below. It's been used in underfloor radiant. Instead of them being at one end they would be at the center of the basement running parallel to the steel I beam.

mattmia2

What you are calling an "extended manifold" is usually called a supply main or a return main depending on its function.

hot_rod

Peter_26 said:

@Big Ed_4 I definitely want to use TRVs and a ΔP circulator would make it much simpler. The current monoflow layout is not an option for the reasons described. ODR is something that I would like and I am trying to work that in with my cast iron boiler.

@EBEBRATT-Ed If you asked me the question I don't see it in the previous comments, but if you mean in general you are correct about the insulation, regardless I would use K-flex. There will be some space, but I would try ans seal the ends as best as I can when connecting them together to avoid air infiltration. I think something would be better than nothing in this case. Also, thinking about your suggestion on placing the isolation valves on both supply and return in the basement makes sense if I decide on the extended manifold. Thinking about it now it would be redundant to use radiator valves and isolation valves.

@hot_rod I used HDS2 Pipe Sizer and 3/8" pex is a good fit at a number of ΔT's and all while keeping the Reynolds number above 4000 if I decide on the homerun layout. Thanks for the piping diagrams. Although I don't like the idea of dismantling the current monoflo system because it works just fine, but since I'm changing the baseboard for panel radiators and other changes for possible future changes it definitely merits it to make things easier. The panel radiators in series is also a good option, I'm going to have to give that some thought also. It would definitely cut down on tubing and all I would need to do is drill a small hole in the floor joist to interconnect the rads from room to room. How would I calculate the flow requirement for 3 in series, just add the 3 individual flow requirements and pipe accordingly? The H valve adjustments would be an approximate setting for the flow of each rad?

@mattmia2 the extended manifold I was referring to is like the one below. It's been used in underfloor radiant. Instead of them being at one end they would be at the center of the basement running parallel to the steel I beam.

yes, add the flow requirement of the series you intend. the bypass is adjustable for how much slips by.

Some info herehttps://www.caleffi.com/sites/default/files/file/01036_na.pdf

i like homerun best as each rd gets the flow and temperature it needs. Or combine manifold and series.

mattmia2

If they are in series you also have to account for the drop in water temp from the heat that the previous emitters have absorbed in sizing the subsequent emitters. It will be less of a factor with the bypass than if the full flow was through all of the emitters but it is still there.

hot_rod

mattmia2 said:

If they are in series you also have to account for the drop in water temp from the heat that the previous emitters have absorbed in sizing the subsequent emitters. It will be less of a factor with the bypass than if the full flow was through all of the emitters but it is still there.

In theory they should see about the same temperature, some piping loss, in series with a bypass H valve. It's more of a flow balance regulation.

Peter_26

@mattmia2 in Idronics 4 section 6. Manifold Configuration and Piping Options they refer to it as an extended manifold, so I went with that.

@hot_rod I am guessing that in order for rads to see just about the same temp depends on the adjustment of the bypass, which is not a straightforward adjustment. Is there a way to know the ratio of bypassed fluid to rad supply fluid?

So, do you guys think what I call the "extended manifold" with the 1" copper is feasible?

hot_rod

If you know what gpm each rad needs to cover the load you could do some number crunching. Would the three radiators be the exact same size? If so the 35% works out.  

You would need to define and analyze that entire circuit to get an exact preset

I would start at the factory default setting and trial and error the fine tuning. Are you using TRVs?

Peter_26

@hot_rod, no, if I decide to go with the 3 panel rads in series they will not be the same size. I think that complicates things. And that would be the case for another 3 rads I can series pipe and 2 rads I can series pipe also. I have a total of 8 panel rads.

Is the 35% the bypassed flow or the flow to the rad? Either way the bypassed water from the first rad would still be cooler when mixed with the return water from the radiator and subsequently to the second rad and same for the 3rd. A larger ΔT would make things even more complicated.

Yes, TRV's would be used, but even then it would probably entail a lot of tweaking of the bypass valve and considering different scenarios like what happens if the first rad's TRV closes and so and so forth. Yeah, I think that's making it look more complicated than just piping them individually.

hot_rod

Here is a look at 3 common piping methods. Yes in series you see some temperature drop. You are blending SWT with return with bypass H valves, so you wouldn't see a 36° drop, for example, as you would in series without the bypass. That blended temperature could be calculated.

Home run will eliminate or mitigate that. RR could also, IF all three rads were the same size and controlled as one group.

So the home run solves a few concerns. All get near identical SWT, different loop lengths would have some effect. Pressure drop will be minimized, and TRVs could be on each radiator, even if 3 were in one room, you would get individual control.

So these are the pros and cons of the 3 methods. Piping and labor hours is another discussion, and you may base your method on you "stuff" on hand

Peter_26

@hot_rod thanks for all the info! 

I will take all the suggestions and info into consideration and plan accordingly.