The 2nd Generation introduced the external, “shell and tube” chiller evaporator. Although commonly used on higher temperature air conditioning systems, the manufacturers were hesitant to approve them for this lower temperature application due to risk of freeze up.
Although the heat exchange ability improved, a new challenge surfaced. They were unable to supply enough glycol flow to the Fermenters. The flow was limited to what could be pushed through the chiller evaporator, often less than optimum for the expanding brewery.
The 2nd generation design also made it a challenge to control the flow of refrigerant to the evaporator. As the number of Fermenters calling for cooling fluctuated, the flow through the evaporator would change, sometimes dramatically. As the flow decreases, the amount of heat exchange in the evaporator decreases, the refrigerant control valve (TXV) must adjust accordingly- often an impossible task.
Many of the challenges have been overcome with improved system design and operating controls. Today you will still find a number of systems manufactured in this “2nd Generation” design, operating quite effectively and reliably. The optimum application for these systems is a constant, steady load with little fluctuation.
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