Some hydronic system designers cling to certain system piping configurations — even when existing projects using those configurations have produced problems.
One incorrect piping layout I’ve seen repeated many times could be described as a “morphing” of primary/secondary piping, and a classic header-type multi-zone distribution system. I’ve seen it as installed hardware, and in neatly prepared CAD drawings created by professional engineers. The latest rendition of this problematic piping layout recently popped up in an e-mail sent to me for review.