chweber
07-02-2009, 02:51 PM
Dear Fellow Members:
I have a small dual temp Zero-Zone rack, R404a. Quite a nice system. However, I have a problem, or think I do: The receiver liquid level reads zero when all circuits are calling. Seems like it' s just low on gas. But when the largest circuit (14-door LT case) goes into hot-gas defrost the receiver liquid level rises to about 50% (This is for summer mode. In split-mode the rec liquid level reaches 75%.) After it comes out of defrost the receiver liquid level plummets back down to zero and we get liquid level alarms. Only one LT circuit goes into defrost at any one time. I don't want to add too much more ***** because of the high spike during defrost. The liquid-level gauge appears to be functioning OK: It is a Rochester gauge and the analog dial agrees well with the electrical output. Also, on this receiver 10% of liquid level corresponds roughly to 24lbs 404a.
For the record, on the day we were seeing this liquid level "instability," we had 58F ambient, head pressure on fan cycling approx. 175 psig. System runs fine otherwise.
The questions I have are:
1. Can the largest circuit's evaporators (3 LT evaps for 14 doors. Each LT door approx 1600 BTUH.) really contain (by my estimate anyway) 120 lbs of ***** that is backing up into the (flow-through) receiver during hot-gas defrost? Or is there something else going on?
2. Could the receiver be somewhat undersized? Receiver capacity I estimate to be 250-300 lbs.
3. We typically try to charge rack systems like these with 20% liquid level with all systems calling. But that would appear to get us to at least a 95% receiver liquid level during defrost in split mode. Is there a better way to charge these systems?
Other data: Rack has 6 scroll compressors. Rack capacity approx. 110MBTUH. Glass door merchandisers, total 81 doors.
I have been a member for a while and appreciate all the hard work and helpfulness of the experts on this site.
Thanks much, Chris
I have a small dual temp Zero-Zone rack, R404a. Quite a nice system. However, I have a problem, or think I do: The receiver liquid level reads zero when all circuits are calling. Seems like it' s just low on gas. But when the largest circuit (14-door LT case) goes into hot-gas defrost the receiver liquid level rises to about 50% (This is for summer mode. In split-mode the rec liquid level reaches 75%.) After it comes out of defrost the receiver liquid level plummets back down to zero and we get liquid level alarms. Only one LT circuit goes into defrost at any one time. I don't want to add too much more ***** because of the high spike during defrost. The liquid-level gauge appears to be functioning OK: It is a Rochester gauge and the analog dial agrees well with the electrical output. Also, on this receiver 10% of liquid level corresponds roughly to 24lbs 404a.
For the record, on the day we were seeing this liquid level "instability," we had 58F ambient, head pressure on fan cycling approx. 175 psig. System runs fine otherwise.
The questions I have are:
1. Can the largest circuit's evaporators (3 LT evaps for 14 doors. Each LT door approx 1600 BTUH.) really contain (by my estimate anyway) 120 lbs of ***** that is backing up into the (flow-through) receiver during hot-gas defrost? Or is there something else going on?
2. Could the receiver be somewhat undersized? Receiver capacity I estimate to be 250-300 lbs.
3. We typically try to charge rack systems like these with 20% liquid level with all systems calling. But that would appear to get us to at least a 95% receiver liquid level during defrost in split mode. Is there a better way to charge these systems?
Other data: Rack has 6 scroll compressors. Rack capacity approx. 110MBTUH. Glass door merchandisers, total 81 doors.
I have been a member for a while and appreciate all the hard work and helpfulness of the experts on this site.
Thanks much, Chris