Contrary to what you might think, the correct antifreeze mixture (55% water + 45% propylene glycol) always have to be used, also when the chiller is programmed only to produce water at positive temperatures (>2°C).
In fact, already when water is produced at 10°C (noticed by the glycol mixture thermostat) inside of the evaporator, where happens the thermal exchange between mixture and refrigerant gas R-404A, the temperature is approximately -1 °C.
If glycol is not used, the ice formation between the evaporator plates causes the decreasing of the thermal exchange and, most important, with the increase of volume causes damages and the break-up of the plates.