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Ice Machines – Cuber, Flaker & Nugget Basics
There are several types of ice machines, but in this article, we will focus on cuber style and flaker or nugget style. Both types produce ice, but the process of freezing and harvesting is a little different. The application in which the ice will be used will determine what style of machine is needed. I primarily work with restaurants and hospitals, so my article will be geared in that direction.
Let’s start by simplifying the ice-making process. If we take water and circulate it over an evaporator that is below freezing, we will at some point start to freeze that water. Once our ice has formed, we then harvest the ice and start our process again. That’s about as simple as it gets.
The steps to make ice seem simple: take water and freeze it. However, it’s not that simple. Making ice cubes is actually a pretty complicated process, with several critical steps that must be met for the process to work correctly. The first step starts with properly cleaning the water that will be made into the ice to remove any impurities. Water itself naturally contains minerals, and those minerals are an ice machine's worst enemy. The minerals lead to calcium buildup, which causes issues with the ice machine. A quality ice machine install will have a high-quality water filtration system installed. That system must be sized properly and have the appropriate filters inside that are chosen after a water quality test has been performed. Once we have properly filtered water, we bring the water into a reservoir inside the machine, and the water waits until the machine is ready to make ice.
Among all the ice machine manufacturers, there are several methods that the machine will tell itself that the ice storage bin is low on ice and to turn on. The most common methods are a thermostat or some sort of mechanical control that is actuated by ice buildup, subsequently telling the machine that the ice is low and it’s time to turn on.
Cuber-style ice machines
Assuming the machine is ready to turn on, most brands of ice machines will start in a pre-chill, which means that we cool the evaporator with no water running over it. That is done to try and prevent slush from forming. Then, using a water pump, the machine will start to circulate the water over the evaporator. That water will continually run over the evaporator and down into the sump, and then it will be pumped over the evaporator again. Each time it passes over the evaporator, the water will get colder and colder. Eventually, a little bit of the water will start to freeze to the evaporator plate, and this process will repeatedly continue until the ice is the proper thickness. Many methods can determine the thickness, including a thickness sensor, water level monitoring, or a timer. Once it’s time to harvest the ice, the most popular method is to introduce hot refrigerant from the discharge of the compressor into the evaporator and subsequently melt the ice off the evaporator from the inside out. While this happens, a little bit of water runs over the cubes to assist in dropping the cubes off the evaporator. A timer in the circuit board usually terminates the harvest cycle. Each manufacturer has its own unique way of making and harvesting the ice. With all cuber-style ice machines, the harvest cycle depends entirely on maintaining an adequate high-side pressure, as their defrost depends entirely on it. When the machine is self-contained and located indoors, it's not too hard to maintain the proper head pressure because the building will likely be conditioned. However, on remote systems where the condenser is located outside, we utilize head pressure control valves (headmasters) to back up the refrigerant in the condenser and reduce the condensing capacity of the condenser. That will subsequently raise the head pressure.
Flaker or Nugget-style Ice machines
These machines have a unique way of making ice. They utilize a round cylinder evaporator with an auger inside of it that is turned by a high-torque gear motor. The auger sits directly in the center of the evaporator with less than 1/16th of an inch clearance on either side. The auger is always spinning, and it has the shape of a corkscrew. The machine will have a water reservoir that supplies water to the evaporator whenever it gets low. The machine will start to freeze the water, and as it becomes ice, the continually turning auger will force the ice up to the top of the evaporator and out of a nozzle that will shape the ice into the desired style (crushed, flaked, or nugget). It is important to notice that with this style of ice machine, the harvest cycle happens when the ice gets thick enough for the auger to scrape it off; it both freezes and harvests the ice at the same time.
P.S. – We have a new podcast out on ice machines HERE. Enjoy!
P.P.S. – If you want to read more about Chris's HVAC work in restaurants, he also wrote this article about HVAC fire safety in restaurants.