One of the most critical steps in brewing is cooling the wort from the kettle to a temperature suitable for yeast pitching. In most systems this is done with a cold liquor tank. A two-stage heat exchanger is a newer, more energy efficient and cost-effective automated solution.

We discussed in our last blog “How to take the heat off your craft brewing energy costs” how cooling wort is done through the knockout process. For knockout to recover heat in a stack condenser, all brewers need a certain amount of cold water.

To cool the water, cold glycol is needed through the use of a chiller and/or heat pump. A chiller uses refrigerant to remove heat from the glycol (let’s call the energy “E” in the diagram) and expels it by blowing out hot air into the environment. The chiller uses electricity to pump the refrigerant, pump the glycol, and blow the air across the hot coils. But for all the energy it takes for the chiller to do its job, it can move two to four times as much energy (E) out from the glycol. While refrigeration often gets a bad rap, it is important to understand that refrigeration can move a lot more heat than the energy the chiller uses. In breweries, in addition to cooling down water, you also need to heat wort. Doesn’t it seem like a waste to just throw out all that heat outdoors?

Once you have cold glycol, you can put it through another heat exchanger – one just like the “knockout” described above. If you pump the water from your tank through the heat exchanger and return it back to the tank, you can remove that same amount of heat (2E), and you will see that the temperature drops. This requires that a dedicated pump be available for pumping cold liquor through the heat exchanger and this adds costs and piping. One way to be energy efficient is to use a jacketed tank which circulates the glycol directly through a jacket surrounding the inner tank and is still insulated from the outside. Fewer pumps and less piping mean less energy is used and less energy escapes.

Now that you’ve removed a certain amount of heat (2E) from the city water that you put in your cold liquor tank, you can use it to knockout the wort. When you knockout with it, not only does it go back to the temperature it came in at (city water temp), but it actually goes even higher (4E). This additional heat is returned to the hot liquor tank for future use. So, with a heat exchanger and chiller, you can reduce heat from the wort and return it to the cold liquor tank and instead of losing that heat, return it to your hot liquor tank for additional

savings!

A single stage knockout can heat the cold water up to about 145°F, that’s about 3.5E.  But to do so you had to cool down the city water 2E to make cold liquor. To do that you consumed about 1E of electricity in the chiller. Instead of spending 1.5 E to heat up city water you only spent 1E, that 33% more efficient!

Remember the “two-stage knockout” we mentioned in the last blog? In a two-stage heat exchanger, the wort passes through two separate cooling stages in succession. Proportional valves are used to control the flow rate of the coolant through each stage. In Stage 1, city water is used as the coolant to initially cool the wort. In Stage 2, the glycol from your chiller is used as the coolant to cool the wort to the target fermentation temperature, e.g. 68°F.

Automating the proportional valves allows for precise control and minimization of energy usage. The system can automatically adjust the coolant flows in each stage to hold temperatures with little waste or overcooling. Using only a cold liquor tank, a large volume of water is required to cool the wort, and this water is often too much volume for the hot liquor tank. If your brewhouse also uses a stack condenser which is generating hot water during the boil, you may not have room for the hot water generated from knockout and have to dump it down the drain.

While a two-stage heat exchanger can use cold liquor and improve efficiency, it can go so far as not using cold liquor at all and only use city water. The short term load however can strain chiller capacity, risking inadequate cooling. Increasing the glycol reservoir size helps address this by acting as a “heat buffer.” The larger reservoir absorbs more heat from the wort allowing use of a smaller chiller while still handling the cooling requirements. The keys to energy efficiency are to make the reservoir large enough to sufficiently buffer the peak loads and insulate it well to prevent heat loss.

For breweries, a two-stage heat exchanger is a great choice for wort cooling. Automating coolant control boosts energy efficiency and heat recovery, reducing costs and environmental impact. By investing in innovative technologies like this, breweries will significantly improve sustainability and process returns. Stay tuned to learn more about how to do away with cold liquor and recover even more energy, keep chillers small, and brew tasty, more sustainable beer!