The second generation introduced external “shell and tube” chiller evaporators. Although typically used in higher temperature air conditioning systems, manufacturers were hesitant to approve them for such lower temperature applications because of the risk of freezing.
Despite the improved heat exchange capability, new challenges surfaced. They were unable to provide sufficient glycol flow to the fermenter. The flow rate was limited to what could be pushed through the cooler evaporator, often not optimal for an expanding brewery.
The second generation design also made controlling the refrigerant flow to the evaporator a challenge. As the number of fermenters to be cooled fluctuates, the flow through the evaporator can change, sometimes dramatically. As the flow rate decreases, the amount of heat exchange in the evaporator also decreases and the refrigerant control valve (TXV) must be adjusted accordingly, often an impossible task.
Many of these challenges have been overcome with improvements in system design and operating controls. Today, you will still find some systems manufactured in this “second generation” design that operate quite efficiently and reliably. The best application for these systems is a constant, stable load with minimal fluctuations.
The Third Generation Chiller
Two-pump glycol design. The dual pump design simply provides a constant flow through the chiller evaporator at all times. Maximum evaporator efficiency is achieved at all times with a dedicated recirculation pump (pump 1). The dedicated process pump (pump 2) is specifically designed for the brewery load, and our flow is no longer limited to the portion that can be pushed through the chiller evaporator. Over the years, this design has been continually improved with the addition of a central baffle storage tank, improved pump operation, a high efficiency evaporator, and many other features and controls. Throughout its development there have been two main cooler system controls; a thermostat to control the temperature of the glycol solution and a flow switch to prevent freeze ups. The thermostat has evolved from a basic mechanical device to today’s microprocessor or PLC-based controller, which is actually a trend that predicts temperature loads and variations. In addition to superior temperature control, brewers require these controllers to provide remote monitoring and notification capabilities. Freeze protection has also shifted from mechanical paddle switches to refrigerant pressure monitors, highly accurate and reliable flow sensors and pump motor monitoring, providing unparalleled system protection.
Today’s systems offer compact, high-efficiency evaporators that provide very close approach temperatures (temperature difference between refrigerant and glycol) and provide reliable and long-lasting operation. The introduction of electronic expansion valves has helped to improve the operational efficiency and reliability of today’s systems. The biggest advancement is the total system control now offered. Customers no longer need to purchase brewery chiller systems from multiple suppliers and assemble them on site; today there are many chiller system manufacturers that offer a total package for any size facility.