Originally posted by ipabrewer
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Does your glycol temp stay near 28F when you're cooling two fermenters and crashing one? If the glycol reservoir temp goes up to 33-35 or higher, then that's your problem...the chiller is under-sized. I've been told recently by a refrigeration guy that as a rule of thumb, I shouldn't expect to get closer than 10F to the glycol temp across any heat exchange boundary. I think that's a bit conservative, but since your vessels aren't highly insulated, maybe closer to the reality for you.
The way he explained it (he was talking about a specific refrigerant that was in the chiller): A Freon evaporator temperature of 18F means the glycol is at 28F and whatever you're cooling, a fermenter or walk-in, is a minimum 38F. Trying to do better than that will take a LONG time, because the heat transfer rate is proportional to the difference in temperature. The close the temp difference, the less heat flows. This doesn't include counter-flow heat exchangers, which are way more efficient because they maximize the "delta-T" between the hot and cold side.
So, measure the temperature of the glycol where it enters the fermenter under load. That should tell you a lot.
Regards,
Mike
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