What cooling is and how it works

What cooling is and how it works

June 10, 2024

At Tanktemp we believe that if you want something to work right, then you need to understand how it works.  

We don't make beer, wine, hemp oil, or spirits; we make chillers. Just like you, there is a lot of math and skill that goes into making our product, not to mention the secret recipes. We know one of the most important factors in your process is cooling liquid; and that’s where we come in. But what is cooling, exactly? To answer that, we first have to talk about thermodynamics.

Thermodynamics is very simple in theory. You can’t create COLD, you can only move thermal energy (heat) from one location to another. That is what we do, we move the thermal energy from your product to another location, usually the ambient air, to cool the product down. 

Here’s how it works 

Refrigerant flows through a compressor, raising the pressure of the refrigerant to a point where its temperature is above ambient air. Once it’s hot enough the refrigerant flows through the condenser, where it condenses from a vapor to a liquid, letting off heat in the process of phase change. The released heat is what makes the condenser hot. After the condenser, the refrigerant goes through the expansion valve, where it experiences a pressure drop, this pressure drop causes the refrigerant to flash into a low pressure/low temperature vapor. Finally, the refrigerant goes to the heat exchanger where the cold refrigerant flows through one tube and glycol through the other. They never actually touch or mix, but the metal between them does. The refrigerant draws thermal energy from the glycol in the heat exchanger which causes the refrigerant to vaporize. The vaporized refrigerant goes back to the compressor to restart the cycle as well as the glycol. 

More technical? OK. 

Let’s talk about the 3 Laws of Thermodynamics and how they apply to chillers. 

Thermodynamics describes the movement of heat in nature and has three basic rules:

  • Energy cannot be created or destroyed, it can only be moved or changed form.
    • The only way to cool an object down is to remove the thermal energy from it. This requires the ability to move the thermal energy to a different location or object, or change the state of the original object (phase change) in a way that requires energy to do so. 
      • We use refrigerants, glycol, and air for this. The chillers we build are called air cooled units vs liquid cooled. 
    • Pressure can be used to aid in the transformation of an object, (Or working fluid) from one state to another. We use refrigerant and compression for this.  
  • Energy must flow from a higher state to a lower state. In other words, heat will always be transferred from a warmer object to a cooler object.
    • Refrigerant chills the glycol and glycol is sent out to the tanks, the tank transfers the heat to the glycol. The heated glycol releases the heat back to the refrigerant, and then the refrigerant releases it via fans to the air. 
      • A steady supply of cool air is needed for this transfer. 
  • As a system moves toward Absolute Zero, the entropy of the system approaches a constant value. 
    • In other words, the colder something becomes, the less change it is able to go through. The less heat the product has the harder it is to remove it.  
    • Absolute Zero refers to the point at which atoms stop moving and is defined on the Kelvin scale as 0 K (not 0 degrees K). This point is physically impossible to reach, at -459.67°F (-273.15°C) and nothing can be colder than Absolute Zero. Any object above this temperature still contains heat due to the atoms having energy. So technically, there is no such thing as cold. 

This provides a very basic approach to thermodynamics and how cooling works. The main thing to remember is that removing the heat from a tank does not simply involve pumping cold glycol into the tank, it is a sophisticated process of removing and transferring the heat elsewhere. 

What your chiller needs from you  

  • Air flow: Keep at least 24” clear around the entire unit to allow for fresh air, the cooler the better. Then unrestricted air flow in front of the unit so it doesn't recycle that heat it just removed back into the air flow.  
  • Clean air coils: These should be cleaned annually. 
  • Refrigerant: Low refrigerant levels don't allow for the correct pressures inside the unit to remove the heat. 
  • The correct glycol mixture and levels: The fastest way to kill a chiller is to have your glycol mixture off. Glycol is a food-grade antifreeze. Inside the heat exchanger it will be up to 15F colder than the temperature you set on your chiller controller. If your glycol is not strong enough to keep it from freezing, ice will start to form in the heat exchanger. When ice forms, it first creates an insulator between the refrigeration side of the heat exchanger and the glycol side and reduces or stops the heat transfer.

Chiller killers

Ice 

Ice is the chiller killer. If enough ice forms in the heat exchanger it will crack the exchanger and has the potential to send glycol into the compressor after pumping all your refrigerant into the glycol. If this happens, it is normally more cost effective to replace the chiller than to fix it, as everything has to be replaced.  

Ambient Air temperature

The surrounding temperature affects how well the refrigeration system is able to cool the glycol. If the ambient temperature is hot, the system may not be as successful in lowering the temperature of the glycol or the refrigerant. Typically chillers are set to run up about 120F. When placing your chiller take into account the average ambient temperature, the added heat the system itself will expel, and any other factors that could add external heat (e.g. direct sunlight if the unit is outdoors).

De-super-heaters, venting, misting systems and swamp coolers can all be used to cool the air and thus lower the head pressure inside the chiller to keep it working.

 Lets keep your chiller from redlining and overheating. 

Call us we have a ton of tips and tricks, some are FREE! (503) 389-8818  

Settings 

One of the most common things we see as the ambient air temp goes up is groups setting the chiller to a colder temp. This is incorrect and opposite of what should be done.

If your chiller is not keeping up, turn it up a few degrees not down. In order to cool a tank you want the chiller to be set 5 degrees colder than your desired tank temperature. By doing this, you are increasing the efficiency of the chiller making it not work as hard to achieve the same result. Your effective range will increase, you will not overheat the unit, and your power bill will thank you.

Think of your car. 0-60 happens pretty quick, 60-120 takes longer. The resistance against the machine in both cases increases greatly, just like a car there is 4 times the energy exerted against the chiller at 120F. It is also where most units will trip on high head pressure or redline, and shut down. High-pressure is like the rev limiter on your car. 

For us science geeks here is the formula… ΔU = Q -W   internal energy = energy gained as heat - work. 

What that means. The harder you work the system the more heat it creates do to the work  thus working against our goal of removing heat.

Sizing

If your chiller isn’t keeping up, you may need more BTUs. See what you need here BTU audit. Redlining anything is never good for it. Overheating a unit will cause it to fail more often, and more catastrophically. And it always seems to fail when you need it most.   

Most chiller systems can be simply added to or upgraded 

Also oversized units are just as bad. You want something a little bigger than you need, but not grossly over-size. We can of course help with that. If you see your unit running for 5-10 minutes at a time, it wants more load. If it runs for about 30 minutes or longer then shuts down it is probably pretty close to being sized right. 

When a chiller is oversized it starts up and shuts down a lot more because it runs for only a short time to meet the thermostat setpoint. Then a few minutes later it comes on again and runs for a short time. Over the course of a day, an oversized chiller can have a lot more start-ups and shut-downs than a properly sized chiller. That means you'll probably be repairing it more often and replacing it sooner.

Lack of service

Hiring a technician once a year to service the unit is the best way to prolong the chiller’s life. The majority of our service calls are for chillers that are not regularly maintained. Preventative maintenance will save you in the long run. Annual service plans are well worth the money, and you can read more here. 

The chiller should also be cleaned regularly. A technician should clean the condenser coils, which can become dirty and pick up debris over time. An inspection should also include checking the fans and pumps, return, glycol brix, and refrigerant levels. 

Clogged coils reduce at least 10% of the BTU rating of the chiller and if left long enough can cause total loss of cooling. This is normally what we see that takes out the compressor. A $150 cleaning will save you on the power bill and the repair bill. 

You have the wrong type of chiller

Not having a unit rated to do the work you are asking it to do is more common than you might think. Not all chillers are made the same. Most, in fact, are not made for the temperatures that breweries, wineries or distilleries require 28F or below. Most equipment is designed to cool to 65F max. Different compressors use different gases and these gas and compressors run at different pressures. If your unit looks like an AC unit, odds are it isn't the right unit for our needs. 



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