I'm testing out a new Inkbord 308 temperature controller for the first time with a chest freezer. I tested it out first by just cooling some wort prior to pitching any yeast, and I am having problems with it overcooling. Wort started at ~75F, and I set the temp to 54 overnight, but it overcooled to 46. It took the whole day with the top open to warm back up to 54. Ambient temperature outside the freezer for the day was 65-70 but will go as low as 50 at night. The controller can control a heater but I don't have one and I'm wondering if I can get away without a heater wrap.
Perhaps in retrospect, this isn't too surprising -- it takes a lot of energy and time to cool the wort, so by the time the wort hits temperature, the temperature difference between the wort and inside the freezer has become quite large and the residual "cold" can further cool the wort. Probe is taped to the side of a plastic carboy, with small towell insulating the probe.
I recognize that the fermentation itself will generate some heat to counteract some overcooling, but my question is if it's enough to prevent overcooling. Or do I need to spring for a heater wrap? How can I make it work with just a freezer for cooling? I've also tried keeping the top propped open, with limited luck (wort at 54, changed set temp to 53, and it overcooled to 51, even during a warm day (~70F).