Double Riser on Discharge?

[jogas]

We're installing a Carrier chiller with an air-cooled condenser. The Carrier rep said we needed a double riser on the discharge line due to unloading and the condenser being 10+ feet above the chiller. System is 134a. I do not have the models, just heard about it at our shop.
Anyone heard of this?
jogas

[core]

Years back I piped a McQuay chiller the same way. Four compressors and the discharge manifold teed off to two lines.

The evap. cooler was about 10 feet above the compressors. The only mistake we made was not putting isolation valves in, recovering all 600 lb’s was a nightmare when you had a small leak to fix.


Core

[viceman]

for oil return at reduced load.

[scott123]

Do yourself a favor and purchase a good refrigerant piping guideline. Trane makes a very good one. I can't tell you how many calls I've been on where the new/old equipment wasn't piped correctly and it was a nightmare for the contractor to straiten out.

For the situation you describe, and double riser is recommended.

[jogas]

I am well aware of double risers as used for capacity controlled systems to provide a hi and low capacity line riser. I just don't ever remember seeing a double riser discharge line. I usually expect to see a p-trap at the bottom and an inverted p trap at the top. I remember a hi-rise building with a Carrier chiller that ran 5 stories up and no double riser (R-22). Just p-traps.
I really thought this double suction discharge was for 134A only.
jogas

[hvacpope]

the single riser wont allow for the +/- 1000fpm velocity at minimum load,you could use an oil separator instead of the double riser set-up.