Brewers in southern climates have a particular challenge chilling wort due to the elevated ground water temperature. Although 58F water is easily attainable in most of the country during the Fall/Winter/Spring brewing season, this is not usually the case in the South, particularly in the summer when cooling water temperatures can exceed 80F in the summer, making chilling wort to the ideal temperature (68F) impossible.
However, the incredible cooling capacity and efficiency of the Therminator chiller will allow chilling wort much closer to ground water temps, at faster rates, and using less water than any chiller on the market. Obviously, wort flow rate and wort outlet temperature are trade-offs. A good rule of thumb (assuming 5gpm of water flow) is that the Therminator will chill about 3-5oF above the cooling water temperature at moderate wort flow rates (about ¾-1gpm), and about 10oF above the cooling water temperature at higher wort flow rates (about 1.5-2 gpm). Chiller performance is not linear, so it is difficult to predict exact performance at conditions not shown in the graph above. Bear in mind that the performance graph is based on cooling the wort to 68F.
If your cooling water is still too warm to cool to your desired wort temperature, you will need to use an immersion chiller in an ice-bath in conjunction with your Therminator chiller to lower the cooling water temp the additional degrees. Simply place a 1/2" or 5/8" diameter copper coil in-line with the cooling water hose (prior to entering the chiller) and immerse the coil in an ice bath to "pre-chill" the cooling water temperature. Since the Therminator chiller is so fast, much less ice will be consumed in comparison to other chillers.
