Refrigerant vertical risers height restrictions 1

[rossc]

Commonly manufacturers (of DX split systems) appear to indicate that the height of a vertical refrigerant risers can be installed as long as a trap in installed for every, say 25 feet, of vertical rise BUT then state in that there is a restriction on the vertical rise of only 20 feet, no traps to extend this height, flat out 20 feet only. Why state for a riser "every 25 feet install a trap" if the riser can only be 20 foot max. to start?

There are a lot of split systems out there that are installed, operating and breaking this rule.

 

[BronYrAur]

I don't have a direct answer to your question, but I do know that Trane has changed it recommendations. For example, they no longer require traps and double-suction risers on their new systems. I'm sure there is still a limit on the riser length, however. See

http://www.trane.com/commercial/library/vol274/en274.pdf

for more info.

 

[atlas06]

It is 50 feet in rise for most standard AC units from all major manufcaturers. Typically it is limited to 23 feet for small units such as SANYO, Friedrich.
However, Mitsubishi (Mr. Slim type units) indicate a height as much as 164 feet and a one way length of also 164 feet. It indicates a derating factor as you go beyond 25 feet.