another heat delivery pipe thread

[mikeyny]

I was just wondering How much pipe diameter has to do with boiler performance when it is coming in from the outdoors. I know most folks have their pipes buried. I realize there are many different ways to insulate and bury, water proof and protect pipe coming in from an outdoor boiler, but what size is best? my system is 2 inch iron pipe well insulated above ground. Is 2 inch overkill. Is 3/4 too small. It must make a difference in the final performance for a system. The only reason mine is 2 inch is because it was free. The boiler manufacturers must have some recommendation as to what size is right for each system. Is there a simple rule of thumb??
Mike

 

[VeggieFarmer]

Mikeyny - I was talking with the Tarm guys today about this, and they recommended either 2" iron or a double run of 1" pex to link an outside boiler to a basement storage tank. Sounds like you're all set with the free iron.

 

[Willman]

Hi,Long time lurker here. First post of many to come I am sure. My question concerns the actual tapping of the boiler. What size is the Tarm ? My concern is my existing manifold and monoflow loop size. It is 1 1/4" How does one one inch pex loop keep the 1 1/4" fully charged ?
Will

 

[mikeyny]

the tapping on my older tarm are 1 and a quarter. It bush's up to 2 inch and I have no problem that i know of with flow.

 

[solarguy]

It's not a matter on the size of your connections, it's boils down to how many GPM can a specific pipe size accomadate at what velocity so as not to cause interior pipe erosion. Generally if you can be under 7' a second in velocity you'll be safe. The other factor that plays into the equation
is the fluid & friction loss thru a pipe. Is it 100% water or a gycol mixture, this effects friction loss thru pipe.

Personally I wouldn't recommend over 12 GPM thru 1" (120,000 BTU's per hr) but the charts do say you can do 25 GPM (250,000 BTU's per hr) thru 1" at 7' a second in velocity however you are out of the "normal design range". We try to engineer everything to be under 3.5' per second.

I think this is one of the reasons why so many OWB installations limp along, small diameter pipe and water flowing to quickly to transfer the heat.

 

[solarguy]

Made an oops...

I wouldn't exceed 5' a minute in velocity thru any size pipe for a heating application.
This would put 1" pipe at 17 GPM, 170,000 BTU's per hr.

 

[sled_mack]

Made an oops...

I wouldn't exceed 5' a minute in velocity thru any size pipe for a heating application.
This would put 1" pipe at 17 GPM, 170,000 BTU's per hr.

Please tell me you meant 5' per second?

 

[solarguy]

dam, I did mean seconds.

guess it's time to slap on the skis.......

 

[EricV]

The tappings on my Tarm 40 are 1 1/4".

 

[Bob Rohr]

/Pipe sizing depends on a few factors. The type of fluid, the temperature, delta T and acceptable velocities.

Typically we design around a 20 degree delta T, with water at 180F.

For continous use hydronic systems 4 feet per second is an industry standard. DHW pipe sizing will often use 8 FPS in their tables.

Oversizing the pipe will slow the speed of the fluid. Below 2 FPS the fluid will not carry the air along to purge. Target 4 FPS.

Here is a table based on 4 FPS, 20F delta T.

1" pex is commonly used in OWF piping. 7.5 is a safe flow rate for that tube or 75,000 BTU/ hr.

Some of the PAP, like Kitec has a larger id. Figure 10- 11 GPM through that tube, about the same as 1" copper tube.

Larger delta t would allow more heat to be moved. if you can design around a 40 delta t you can move twice the energy through the same size tube.

If you have a buffer tank for example and pull a mix down radiant temperature off that, a 40F delta T can be used.

I suspect most OWF installations with a 1" pex (one size fits all) and a high head Taco circ probably run some fairly high velocities. if the system is fitting free you may get away with that for some time.

hr

 

[Willman]

Thanks guys for the answers.Thread is copied into my hydronics folder for continued reference. I am in the planning stage for my boiler set up for next winter. A load of wood coming will be the first actual step to begin my project.
Will

 

[Eric Johnson]

Welcome to the Boiler Room, Will. What kind of boiler are you planning to get?

 

[Willman]

Hi Eric, I have been checking out all the gasifier boilers. So far no firm choices. I will keep reading all the threads. IMHO the piping, pumping (distribution), control and storage strategy is what makes or breaks an installation. I have some books by Dan Holohan that describe very well all things hydronic. The boiler is the big item though.

 

[Eric Johnson]

Good move with the Dan Holohan books.