All you need to know about compressor-powered wine cellaring cooling systems – Part 1
In a previous article, Alfred described the differences between cellaring in Europe and America (read here).
The main conclusions were the following:
The quality of European wine cellars is empirically recognized, notably for their stability in regards to temperature and high humidity rates during all of the different seasons.
On the other side of the ocean, the North American (and Asian) dream is to create wine cellars inside houses, where cooling systems and construction materials are used with properties that are not always fully adapted to what the ultimate goal is: stability, humidity and innate darkness of traditional cellars such as the ones found in Europe.
In this spirit of continuity, Alfred wanted to bolster its knowledge on various composing parts of this new type of wine cellar, as a goal to better serve and protect your valuable collection.
This week, we have opted to present the first part of an interview with Mr. Normand Brais, ex-professor at the École Polytechnique de Montréal
The second part of this interview will be presented next week, in another Alfred blog entry.
An artificial climate that dictates the aging process
Nowadays, the vast majority of wine enthusiasts control the temperature of their wine cellar with the help of a compressor-powered cooling system. The same mechanism is used at a smaller scale in various smaller version of wine cellars that are very close to simply being miniature fridges purposely designed for wine storage. No matter the size, the materials, the precision or the power of these various alternatives, they all share a common aspect that powers each and every one of these: the compression of a gas.
To further understand this type of system that presents itself as the new trend in modern wine cellars, Alfred has decided to interview an ex-professor of the École Polytechnique de Montréal, Mr. Normand Brais (mechanical engineer and doctorate in nuclear engineering)…
Alfred — Could you briefly explain the general functionalities of a compressor?
Compressor-based cooling systems are extremely old systems. These systems use a compressed gas to create cool. It is all quite simple: compressing the gas creates heat. This heat is then evacuated. The system then starts the process, but inversely (a process named decompression) that is brought through a tiny orifice. When the pressure of the gas diminishes, the opposing effect is created: the long awaited chill air!
The first cooling systems were invented during the 1800s by a very creative doctor from the South of the United-States who was looking for a way to treat his patients affected by the yellow fever. As you probably know, before the Civil War, the people from the South were getting their ice from Boston and various other regions in the North, something that they couldn’t do anymore during the war.
Thereby, this doctor had to create, on his own, the first cooling system by compressing air and sending it through a small orifice to create his own cool and, therefore, create his own ice to treat his patients! An interesting heritage from this part of history is the way used to measure the power of these cooling systems (fridges, air conditioning systems, etc.): it always references the total amount of ice that can be produced in 24 hours.
It is, as shown here, a very old system that has benefited from various improvements over the years. Today, instead of using air as a gas, freon is used – a sophisticated family of gas that offers better performances in terms of efficiency, temperature control and better withstands utilization pressure. This small change greatly simplified these machines that then became much cheaper to acquire.
Originally, compressors were quite useful to conserve meat, as an example. Indeed, in the old days, the various methods to conserve, other than salt and spices, were quite limited. It was found that bringing the meat to 3 or 4 °C (an even under the freezing point) was a great way to conserve food for much longer periods.
On the other hand, for wine, it is quite far from the ideal temperatures… as wine should be kept around 14 to 16 °C, which means that using a compressor in a wine cellar is basically asking for the machine to keep the temperature at a much higher point than what they were originally designed for, from 10 to 12 °C hotter, to be precise.
Therefore, we can conclude that compressor-based systems were adapted to fulfil different utilizations, notably for food conservation but also for air conditioning in houses and transportation (cars, buses, planes, etc.). It is then this same mechanism that is found in small wine cooling systems and air conditioning systems specifically designed for wine cellars?
It is always this same process with the compression of a gas and all of the following steps described earlier. In fact, to create the smallest devices possible, compressors specifically used in wine cellars were conceived to maintain their “cool element” at a temperature of 4-5 °C. This creates humidity, therefore creating a very dry environment which is evidently not something that is desired in a wine cellar.
Alfred — Why do defrost cycles happen? What occurs during these cycles?
This happens when the system is not fully adapted or programmed properly. It frequently happens that the “cool element” reaches a temperature inferior to 0 °C and in this case, the water turns to ice before condensation; this ice forms up around the mechanism and the system is then unable to create the heat with the air coming from the cellar. In this case, these systems have been programmed to inverse their cycles to thaw down the ice. This is the process that is described as a defrost cycle. In other words, this only happens when the system loses its control on its environment.
When referencing the smaller mechanisms found in smaller devices, this means that if this system was bigger, the compression would happen in a larger environment which would lead to a better control of the temperature? Is this accurate?
Indeed, this is possible. Theoretically, a compressor-powered cooling system could be adapted for wine cellars, with the “cool element” working at a hotter temperature – around 10 °C as an example. On the other hand, right now, the compressors produced on the market (99.9%) are all aimed at the fridge market. For this reason, almost nobody has followed the road to trying to improve and adapt these systems for wine cellars.
What we call the compression rate – the difference between the initial pressure and the final pressure of the compressor – should be, in reality, much smaller than the current systems. These compressors would be very different, which would also bring forth quite a big change on the mechanical side of things.
Would these compressors then be much larger?
It would not necessarily affect the size of these compressors, but more so the piece of the mechanism that creates the heat: the required surface would be much more larger to compensate for the temperature of the cooling fluid (freon) that would be higher. Just like in the current systems, we would have to choose only one temperature for this cooling fluid; it could not be changed after the initial choice.
It is for this reason that these systems must always function intermittently? To “deal” with this unique temperature?
Exactly. The temperature of the fluid is unique, which explains that when the mechanism activates, the system will aim to chill the cooling fluid to its temperature of 4 to 5 °C. When it intermittently stops, it is due to the fact that the cellar has reached the temperature programmed by the user, 14 °C as an example. This is what is commonly referenced as the “set point”.
In other words, if maintaining a cellar at 14 °C is the goal, the system will let the temperature reach 14 °C and then stop. It will then let the temperature rise in the cellar – 15 or 16 °C – and would then activate again to bring it back down to the “set point”: there is always this “dead zone” of 1 or 2 °C, no matter the system.
By using the analogy of a car, it is possible to better understand this process. As an example, it is possible to drive at a constant speed, but it is also possible to accelerate and decelerate constantly to maintain an overall desired speed. I had an aunt that was that kind of driver… it was not enjoyable at all, to say the least… (laughter)
The temperature is therefore never really at the “set point”. It keeps going up and down in every “dead zone” phase… What if the compressor didn’t function intermittently? Would the system cool down the wine cellar to around 4-5 °C?
Right on. By never shutting down and with no “set point”, all of the wine cellar would reach the temperature of the cooling fluid, which is around 4 to 5 °C, a temperature that is way too cold for wine. In fact, by definition, by only have one temperature for the cooling fluid, the system must function intermittently, which affects the stability of the temperature in the wine cellar.
This also means that everytime that heats enters the cellar (by various ways), this intermittent system will keep repeating its cycle over and over? Does this affect the overall lifespan of the compressor?
Indeed, everytime that the temperature rises rapidly in the cellar, the system will have to activate itself more frequently which will certainly accelerate its deterioration. No matter which mechanical system has to constantly turn on and off will have its lifespan directly affected by this unending repetition that will damage the mobile pieces, pieces that are needed for the system to function properly.
This is what marks the end of the first part of the interview. Do not miss the second part published next week on the Alfred blog!
Normand Brais: former teacher at l’École Polytechnique de Montréal, mechanical engineer, owner of a master degree in aerothermal and a doctorate in nuclear engineering.