Direct Return/Reverse Return:

icesailor

I always understood (Iperhaps improperly) that a "true" reverse return (first out, last back) was a far better way to pipe unusual loads than a direct return (first out, first back) because the reverse return balanced the system better and you avoided the problem of the water wanting to take the path of least resistance and short cycle through the first loop. That the extra pipe was worth it. I've gone to great pains to always do this. I have done this with multi-zone systems with series looped baseboard mixed with other stuff for as lond as I can remember.

I was looking at a Califfi manual on zoning the other day and realized that all these high teck piping diagrams with all these home run connections going to return manifolds are drawn and probably installed as direct returns. Why aren't they piped backwards so they are reverse returns? Or did I miss something that is new and the old is now out the window?

I'm just curious.

Charlie from wmass

You missed nothing

My take on it is the manifolds are so short they negate the pressure loss when planning them. Reverse return is best no matter what the price point sales are doing.

Mark Eatherton

The rule of hand...

Kind of like the rule of thumb, but BIGGER :-)



I always tell my students, that if they have more than 5 circuits on a manifold, this it is best to pipe it reverse return. If less than 5, then it doesn't really make that big of a difference, Also, it is CRITICAL that all pressure drops be approximately the same, otherwise even reverse return will get out of balance.



Also, with a lot of todays manifolds, they come with flow meters and balancing valves that make balancing flow a snap!!



TImes, they are a changin'....



ME

hot_rod

Balancing

The next Caleffi i-dronics, issue #8 will be on balancing. I think you will learn some interesting things about reverse return and it's ability to "self balance". I sure did.



A lot of research went into the topic. Stay tuned.



hr

icesailor

Reverse Return:

I already knew of the ability of "reverse return" to self correct.That's why I always do it when needed. I don't even give it a thought about it. I'm piping up a job with all fan coils. One zone has three floor units. The first one is 30' developed, out and back. The last one is 80' developed, round trip. The middle one is 60'. Run in 1/2" HePEX, that's a lot of restriction I would need to dial into a manifold. 3/4" reverse return seems to me to be cheaper on material and drilling. Plus, I get a full 3/4" right to the floor units. I have 7 fan coils to connect in 3 zones. The thought of connecting 14 home runs makes my head ache. Connecting 6 sooths it.

I don't want to be in competition for the ugliest system next year.

Charlie from wmass

My opinion on home run systems

it they are for less than stellar labor who can not properly lay out proper sized pipe. There are often articles about extended manifolds to save money as an alternative to home runs. You know how to do it right. Just because it is in the latest trade magazine does not make it better, faster or easier. Often it is just one more way to move money from the labor column to the material column, I eat better off the labor column and my wholesaler eats better off the material column.

Alk

Direct and reverse return combined

Hi everyone,

I'm trying to design a cooling system with 15 identical compartment units of 450,000BTU/Hr and one MUA unit (2,250,000BTU/Hr) all tied up to the same 800Ton chiller.  Because of the difference in cooling loads I was thinking to tie up the 15 compartment units using reverse return piping, and the MUA unit using direct return piping and a balancing valve. What are your thoughts about this? Thanks.