Seven Attributes of Highly Efficient Ice Making
Vogt Ice is well known for very efficient ice making machines but it’s really no secret how we do it. By understanding that efficient ice making requires moving and storing energy efficiently, we can share proven attributes that can help make your ice machine operate as efficiently as possible.
Attribute 1. The most efficient machines operate with relatively high evaporator suction temperature and lots of ice making surface area.
Vogt Tube Ice and Turbo Plate ice machines typically operate with a suction temperature of about 15F and 5F respectively. They have lots of surface area for ice building at these relatively efficient ice building temperatures. Conversely ice machines that operate below 0F evap. temp. operate much less efficiently. For a customer needing a 90 ton per day ice machine we recently compared two systems. One would operate at an evap. temp of -25F. The other would operate at 0F evap. temp. The low evaporating temperature ice maker would be smaller, but it would require a large refrigeration system with a 450 HP(336 KW) compressor. The system operating at 0F evap. temp. would have more ice machine surface area and only would require only a 280 HP (~209 KW) compressor. Operating 350 full days per year with an average electric cost of $0.12/ KWH the difference in energy costs alone is a whopping $ 128,000 per year! It makes sense to pay more for the bigger ice machine. In this case the energy savings alone more than make up the cost difference in the first several months.
Attribute 2: The ice machine refrigeration is designed to work with the refrigerant in it.
Particularly for “retrofit” refrigerants, often replacing R-22, customer’s lament that the replacement refrigerant is not nearly as efficient as the old refrigerant. Most often it’s that the old system is not designed to work with the new refrigerant. Not only do refrigerants have to perform in their optimum relevant temperature range but they must also remove latent heat as they boil in the evaporator. Some pick up more latent heat per lb. than others. To move the same amount of energy or heat, a compressor will have to move more gas for a lower latent heat refrigerant than a higher latent heat refrigerant. When correctly designed for the refrigerant even low latent heat refrigerants can be used very efficiently. High efficiency screw compressors can move high gas volumes efficiently and should be considered, particularly for many of the newest classes of refrigerants.
Attribute 3: Thin ice can generally be made more efficiently than thick ice.
Relative to stainless steel, ice conducts heat poorly. Ice making efficiency drops off as ice thickness exceeds 3/8” or so. Some ice-on-tube thermal energy storage designs specify ice to be built to over 2” thick. The outer ice builds slowly. And when cooling from the ice is needed, the ice also melts relatively slowly too. If not properly designed, responsiveness to demand could be an issue with these “thick ice” systems.
Attribute 4: Incoming water temperature is kept cool. Pre-chill water before making ice.
In many parts of the world it’s not uncommon for summertime incoming water to exceed 85F. In these cases a water pre-chiller, operating with an efficient 28F or so evaporating temperature, can be very cost effective. The pre-chiller should reduce the incoming water temperature to about 55F ahead of the ice machine. This can also increase overall ice productivity too.
Attribute 5: Ice is quickly released, with uniform heat (hot gas) distribution, not just hotter gas.
This gets a bit into the “science and art” of ice making machines but only the ice at the very surface of the evaporator needs to get slightly above freezing to cause the ice to release. The better the heat distribution across the whole surface area the less hot gas is required. Less heat means quicker cycles and more ice production too.
Atrribute 6: The ice machine system is adjusted to accommodate the season.
Ice machines, like HVAC systems, are spec’d to operate at design conditions that are expected to be the hottest and harshest times of the year. When not requiring “peak” ice making performance, save energy by adjusting the ice maker settings for a higher evaporating temperature and longer cycle times.
Attribute 7: Systems that are well maintained work better.
Though regular maintenance seems obvious, Vogt and Turbo ice machines are so reliable and so robust that good maintenance is sometimes taken too much for granted. To avoid damage to your ice machine always check to assure that during harvest (defrost) all ice releases, that there are no obstructions, that all valves and thermostats work well and that the machine is kept very clean. Like that bottle of water forgotten in the freezer, as water crystalizes to ice it can generate tremendous pressure, distorting plastic bottles and breaking glass ones. Ice can crush ship hulls if the ships are left without protection in a freezing harbor. Ice’s expansion forces are readily controlled in a well maintained ice machine. Without maintenance and over time, ice can damage any machine.
We’ve picked up these “Attributes” over many years of building Vogt Tube Ice and Turbo plate ice machines and by listening to what our customers say about them.
Feel free to share any comments about your own experiences or tips of the trade that you have picked up too.