Extreme coldness. It’s what makes Duluth, Duluth. Our partisans (see: Emily) call it “pristine,” and “wild.” They say it makes them proud to live in Duluth. It makes them feel like they earned it.
As a relatively new Duluthian, whose brain hasn’t been through too many freeze-thaw cycles, I just call it “ridiculous.” It makes me feel brave…on the days when it doesn’t make me feel scared.
As a distiller, the cold is an inescapable physical reality. When it’s -30F outside, which is a regular operating condition in Duluth, mechanical systems work differently. The diesel in our distillery truck turns to jelly. The cold air in our chimney is too heavy for the hot exhaust gases from our boilers to fight through, so instead of rising, smoke just pours out into our mechanical room. That’s if the boiler isn’t too frozen to fire at all. In the winter of 2013 our boiler partially froze, and Canal Park Brewery’s boiler partially froze, and Bent Paddle Brewery’s boiler froze solid – all in the same week. It was one of those scary weeks.
The primary distiller’s downside to cold is that it slows barrel aging. This is part of why Kentucky Bourbon ages in 5 years but Scotch whisky takes 10. Whisky in Scotland basically takes the winter off from aging.
But mostly, for a distiller, cold is a good thing. Because distilling is about boiling and condensing, and the condensing takes cold. In Scotland, distilleries traditionally did their condensing with creek water. In the summer, when the surface water got too warm to do the job, they’d take a few months off. Between the whisky taking the winter off, and the distillers taking the summer off, it’s a wonder any whiskey ever got made!
Here in Duluth, we have cold water year round. Our tap water comes from Lake Superior, which is ridiculously cold. In the winter it comes out of the tap around 40 degrees. In the summer it runs around 50 degrees. So when we began, we began by using this cold water to do our condensing. This was an energy efficient choice, but not a water efficient choice. In the last year we’ve been using as much as 200,000 gallons of water a month, and while this is not at all an unusual amount for a distillery, it was not a resource use we felt good about. So when we came up with our strategic plan for 2015, we set a goal of reducing our water use by 50%.
Given Duluth’s extreme cold, you’d think cooling process water would give you an embarrassment of options. Over the last year, I’ve investigated many many options. I considered an open cooling loop to the lake. I considered a closed loop with a heat transfer coil in the lake. I considered a closed geothermal loop digging down from an old storm sewer under the distillery. I talked to engineers, to engineering professors, to engineering students, to geothermal contractors, to industry cooling contractors, and to process water experts. I called every imaginable resource, including the city, the utility company, non-profits that specialize in energy use reduction and making manufacturing more environmentally friendly. But, mostly they suggested solving the problem with electricity by mounting a big old electric chiller on the roof and calling it a day. This would mean running a big compressor all year long to create cold – in an atmosphere already overflowing with extreme coldness! This, interestingly, is the way almost all breweries do their cooling, even in cold places like Duluth.
But, this did not satisfy me. I did not want to reduce our water use by dramatically increasing our electricity use, particularly given that most of our regional electricity comes from coal.
So, I kept talking with people until, I found a couple folks willing to help. One is a process cooling specialist from Alabama, and the second is a civil engineer in Duluth. This is what we did (in case you’re interested):
Our cold process water runs through the condensers on the stills, and the fermenting equipment (more on our fermenting equipment – which we affectionately call “the brewery” – soon!). It comes out hot. This hot water runs over to our barrel room, and through a few refurbished fan coil units. These are basically just radiators with fans that we found in a basement, and they push some of the heat out of the water and into the room. This means the barrels get heated up during the day when the stills are running, and then cool off at night. In the winter it’s enough heat to keep them around room temperature instead of freezing. In the summer it’s enough to make the barrel room miserably hot. This diurnal variation is exactly what we want to facilitate whiskey aging.
Then that still-quite-warm water runs back over to the distillery and into a 2,000 gallon reservoir. From the reservoir, the water is pumped through a heat exchanger where it’s cooled off, and then back out to the distillery and brewery process. All in a nice closed loop.
Now the heat exchanger works by transferring the heat from the water to a second medium, which is glycol. The glycol (basically food-grade antifreeze, and a key ingredient in Fireball™, hehe) is pumped through the heat exchanger, and it takes on the heat from the water, before it runs up to a hybrid adiabatic cooler on the roof. What the heck is a hybrid adiabatic cooler, you ask? It is essentially just a giant radiator with a fan. Most of the year, given our extreme cold, that’s all it takes to shed the heat. In the summer, when the ambient temperature is higher than we want our process water to be, the cooler sprays water into the air as it passes through the radiator, allowing it to shed a couple extra degrees. That’s the “adiabatic” part. We benefit here from the fact that it stays pretty cool on the lake even in the middle of the summer, and it’s almost always windy up on our roof. The glycol leaves the cooler, well, cooler, and comes back down to the heat exchanger to take on some more heat from the water.
The water reservoir allows us to store cold, and to buffer changes in the temperature of the process water, which can really mess with the distilling process. By the end of the day, the reservoir will be pretty warm, but overnight it cools back down so in the morning we have nice cold water to start with. This allows us to run a smaller system than we otherwise would.
We’re still in the first month of operating this cooling system, so the numbers are still shaking out. I think we’ll have reduced our water use by about 90%. And we’re still getting the controls hammered out so it can efficiently regulate itself. In spite of everything we’ve done to anticipate the challenges, I’m sure we’ll have some problems to solve when it’s -30F next winter because there’s almost nothing that doesn’t freeze at -30. But at the very least, we can say we’re saving lots of water for the sturgeon and for the next bottle of gin.