I have the b23a-20 (20 plate) and I have been able to chill from boiling to 65 degrees in one pass with my pump running usually between 2/3 and 3 quarter power (Usually use my 12v topsflo which is only like 12L per minute.) Anyway it takes less than 5 minutes to cool 5.5 gallons so I'm curious whats different in your setup? warmer water?
LOL, definitely not warmer water, I'm in Ottawa, Canada.
I don't want to derail the OP's thread too much, so I'll just quickly describe my setup. I used to just run the wort from the kettle through the chiller in a single pass, and then straight into the fermenter, as you described. When I used tap water with my IC in a camping cooler ice bath as a "pre-chiller," this would get me to pitching temps in a single pass in just a few minutes, as you described.
The problem I was having is that I'm using a HopStopper on my kettle outlet port (basically a pickup tube enshrouded in a Frisbee-shaped pouch of fine stainless mesh) to keep trub and hop matter from going into my chiller. When pumping wort from the kettle, through the chiller and into the fermenter, I was losing suction in my pickup tube once the wort level got low enough to expose the HopStopper. The issue was that the HopStopper was blocking so much trub that wort was unable to flow through its mesh and to the pickup tube as fast as the pump was sucking it out.
So I'd lose suction, the pump would lose prime, and because of physics I was never able to get the pump to prime again. It doesn't produce suction, so once you've lost the siphon, you're done. This was happening every time, no matter how much I slowed the flow as the wort level dropped. I was left with at least a gallon of perfectly good wort in my kettle that I had no way of safely getting into my fermenter.
Keep in mind, it was still piping hot, as it hadn't been chilled yet, so I couldn't just rack it over with an autosiphon. I couldn't just pour it into the fermenter because I was a) worried about contamination from the upper edges of the kettle as it poured, and b) it constituted enough almost-boiling hot wort to significantly raise the temperature of the rest of the wort already in the fermenter.
That's why now I just recirculate the wort back into the kettle, so the HopStopper is continuously submerged during the entire process and I can run the chiller with the valve almost fully open. Once the wort is at pitching temperature, I simply rack it over to the fermenter with a plain old autosiphon, allowing me to get every last drop of wort from my kettle.
Note that I said *almost* fully open. I still have to constrain the flow a little bit to avoid cavitation in the hose leading from the kettle to the chiller as the HopStopper gets caked with trub. In some batches, depending on the grain bill, I've had to constrain the wort flow, while simultaneously continuously scraping trub off the submerged HopStopper screen with a sanitized spoon. I suspect this constriction, combined with the switch from tap water to ice water at 100°F, probably accounts for my slightly longer chilling time. Admittedly, in the winter, I've learned I don't actually need to switch to the ice water. The tap water is cold enough to get me all the way down to 65° F easily, so I've taken to only using the ice water in the summer.
