Single Stage & Two Stage Glycol Assisted Heat Exchangers

Wort chillers are typically plate and frame heat exchangers (PFHX). These are recuperative, indirect heat exchangers that use countercurrent flow to transfer heat between fluids. The plates in PFHXs are stainless steel both for sanitary purposes and because of its high thermal conductivity. The PFHX design provides a large amount of plate surface area with a compact footprint, making it a highly efficient and affordable solution for exchanging heat between two or more fluids.

In brewery applications, the media that would pass through the heat exchanger would be beer wort and water. If applicable, a propylene glycol solution would be used in the second stage of a two-stage PFHX cooling system. The wort produced in the brewing process is approximately 200 °F and needs to be cooled down to fermentable temperatures (~70 °F) before being transferred into the fermentation vessels. This cooling process is typically called “knocking out the wort.”

In the case of a single-stage PFHX, ground or city water is used to cool down the wort to fermentable temperatures. Two-stage systems are required where ground water temperatures are close to or above the desired knock out temperature, as a colder glycol solution is then needed to cool the wort the rest of the way.

In a two-stage system, the wort will move through the first chamber or stage in the heat exchanger with a majority of the heat transferring to the water. The wort will then channel to the second stage of the PFHX, where process glycol will absorb the remaining heat from the wort.

The flow of glycol entering the PFHX can be controlled manually or with an electric flow control valve. For manual control a diaphragm or globe valve is best, because the glycol can be metered in more finite increments (as compared to a ball valve). The manual valve would be installed in-line on the glycol supply side of the heat exchanger, and would then be opened or closed manually based on the desired leaving temp of the product.

For electric flow control, an actuated ball valve with a modulating function (as opposed to simple on/off control) can be installed in-line on the supply. An external signal from a temperature controller modulates the valve open and closed in varying degrees. This modulating control signal sent by the temperature controller is based on an input from a temperature sensor, which detects the wort temperature leaving the PFHX. The temperature controller compares this sensed wort temperature to the target set point, and adjusts the glycol flow control valve position accordingly.