HYDRONIC PIPING

[trashcanman]

Anybody ever hear of a "Modified Header System"? I ran across it in an HVAC handbook (by Arthur Bell). It warns not to use it as it causes operational problems. Says it does not work. What does it look like? Just curious.

 

[RossABQ]

I have the book; can you give the page where the reference appears?

 

[trashcanman]

Page 154, C.3.c.2). Only thing I can think of is a header that is not the same diameter for the full length.

 

[quark]

We call them as increasing (for return) and decreasing (for supply) headers. Conceptually, you can maintain constant pressure drop across each unit, but you have limitation with the commercially available pipe sizes. Reversed return header is an option in that case.

I am not aware of any operational problems and there should not be any.

 

[RossABQ]

The book has an error in it. If you read the preceding paragraphs where he describes untized and manifolded systems, he has the advantages/disadvantages swapped in the cited paragraph.

If a unitized system has dedicated pumps for each chiller/boiler, and a manifolded system has all pumps connected to a manifold that in turn feeds multiple chillers/boilers, the "modified manifold" would be where some boilers/chillers have a dedicated pump and some don't. You can see the problems if one pump has to be used for one chiller, but multiple (manifolded) pumps can serve another chiller. There are redundancy issues for one thing. If all chillers/boilers are not the same capacity, you need to use a unitized system or some hybrid like a "modified manifold" system but have the appropriate controls.