It all depends on the tap water temp. Plate chillers with the flows dialed in properly can get the output to a couple degrees warmer than the coolant temp. For example, my water is running 70F right now so the best I can hope for is about 73F in a direct pass to the fermenter. Recirculating back to the kettle works ok, but still, it's only going to come out of the plate somewhere between 70 and 73F no matter how cool you get the wort in the kettle.
It may seem silly and overcomplicated but another way to do this is to daisy chain two smaller plate chillers where the wort path runs in series on the way to the fermenter. The first chiller runs tap water where the output is routed back to the HLT or a bucket for clean up water. The second plate is fed by a small pond pump filled with icewater. The output is sent right back into the icewater bin. This is really beneficial if you like brewing lagers in the summer. With this setup, you can throttle the tap coolant back pretty slow so that the output is nice and hot for cleanup because the wort would still come out at near 100F. Once it's that low, it doesn't take much ice to drop to under 70.
