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July 2002 [updated March 2003] By Mike Sherer Summer puts peak demand on ice and icemakers. Here are a few tips on how to spec a machine that runs cool and smooth as a Jamaican rum punch. Murphy’s Law corollary: Your icemaker will break when you need it most—when it’s hot outside and customers are thirsty. Summer’s heat puts peak demand on icemakers, meaning more than a few older machines will give up the ghost. Recent advances have improved icemakers to get more out of them—more efficiency, longer life, fewer service requirements and easier maintenance over time. When specifying an icemaker, however, the basics still apply. Choose Your Weapon First, you have to decide what kind of ice you want. While ice comes in all sorts of shapes and sizes, there are two basic types of ice—cubes and flakes. Each is made by a different type of machine. Cubers make individual ice cubes or slabs of cubes in batches. The ice may literally be in cube shape, or in a variation of a solid shape. Water is circulated over an evaporator where it freezes until cubes are fully formed. Then the cubes are harvested and moved to storage. Flake ice machines produce ice continuously, usually in a barrel-shaped evaporator. An auger inside the evaporator scrapes ice off the sides into a storage bin. Some machines compress flake ice into “nuggets,” which resemble ice cubes. More detail on your ice options is included in a sidebar here. Check it out and begin narrowing your definition of specifically what you’re looking for. There’s actually a whole world out there devoted just to which ice works for what uses. How Much? Next, you’ll need to calculate how much of the chilly stuff you need. Add up how much you presently use, taking into account use in both the front and back of the house. For new applications there are some general rules of thumb you can use to calculate production needs. An average restaurant, for example, will use about 1.5 lbs. of ice for each meal sold. A bar or cocktail lounge will use about twice that per seat. For beverage service, figure half the volume of the cup for ice. If you use a 16-oz. cup, for example, plan on 8 oz. of ice. Keeping a salad bar chilled takes about 35 lbs. per cubic foot. Hotels should plan on about 5 lbs. of ice per guest per day. Hospitals use about 10 lbs. per patient. Rules, of course, are made to be broken. Some of you may have a catering operation that will use ice for beverage service and for keeping food chilled. Hospital employees use a lot of ice in addition to that used for patients. A cocktail lounge with a raw bar will need ice for seafood displays. Also figure peak demands. Weekends often are busier than weekdays. Rush periods are heavier than the your daily average calculations would suggest, which will impact sizing the bin as much or more than sizing the icemaker for production. Take seasonality and holidays into account. If you’re up north, your summers might well draw heavier traffic. If you’re in the south, traffic might slow down during summer, but then the heat will create a noticeable extra load on your machines. Production Efficiency Production capacity depends on internal engineering matters, of course, but also on the temperature of the water coming into the machine and the ambient temperature around the machine. The warmer the temperature of both water and air, the longer it takes to make ice. To compare apples to apples, get production numbers from the Air-Conditioning & Refrigeration Institute at www.ari.org. ARI rates production capacity of icemakers using 70&Mac251;F inlet water and operating in an ambient temperature of 90&Mac251;F. After you’ve calibrated yourself on those standardized test figures, you can do some interpolation based on the manufacturers’ own data grids at varying temps to estimate how temperature changes will change production. ARI’s ratings also will give you a good idea of an icemaker’s energy efficiency. The ratings indicate how much energy in kilowatt hours a machine uses to produce 100 lbs. of ice. Just as important, they also indicate how many gallons of water the machine uses to make the same amount of ice. With the cost of water usage and sewer access rising in most areas of the country, more efficient machines can save big money. Compressors, Evaps & Condensers The major components of any icemaker, as many of you grizzled types know, are the compressor, condenser, evaporator and water distribution system. Skipping the harvest cycle for the moment, in a nutshell you’ve got a pump and two heat-exchange areas. The compressor drives liquid refrigerant toward the evaporator, which is like a radiator offering a lot of heat-transfer area where the refrigerant draws heat out of the water to be frozen. As it draws that heat, the refrigerant evaporates into a gas. The gas then pumps through the system to the condenser, another heat-exchange area with a large transfer area. There, the refrigerant, still in a hot gas state, sheds the thermal energy to the outside atmosphere, condensing back into a fluid and returning through the pump to begin the cycle again. The compressor is the workhorse of the machine. It’s likely to burn out and quit before any other part on an icemaker. You can extend compressor life two key ways: make sure the condenser is clean and cooling well, and buy a machine with enough production capacity so the compressor isn’t constantly running to keep up with demand. Next up: The evaporator is the heart of an icemaker. Its design and construction dictate the size and shape of ice cubes and influence efficiency. Evaporators must be rustproof since they’re constantly exposed to water. Most are constructed of copper with tin or nickel plating. Some machines use stainless evaporators. Copper does a better job of conducting heat than stainless, but must be plated to prevent it from corroding and contaminating the ice. The plating must be thick enough and applied properly so it doesn’t chip or flake. Most evaporators are mounted vertically inside the icemaker cabinet. Water is pumped over the top of the evaporator and flows down, slowly freezing until each cube compartment is filled. Excess water flows into a sump where it is recirculated until the freezing cycle is over. Sediment and minerals collect at the bottom of the sump and are purged after a certain number of cycles. A few icemakers use horizontally mounted evaporators. In these machines, water is sprayed from below into the evaporator’s compartments and frozen. The advantage, say manufacturers, is that sediment and scale have less chance of freezing onto the evaporator, resulting in a better ice cube. Location, Location, Location Where you plan to put an icemaker and its components will impact performance and efficiency. Three basic component setups are offered by most makers and for most models: self-contained air-cooled units, self-contained water-cooled units and remote air-cooled units. And two companies, one in 1999 and one this year, have introduced new technologies that allow a fourth option—putting both the compressor and condenser on the remote pad. (See the sidebar on page 43.) Self-contained air-cooled ice machines, as the name implies, can be plunked down anywhere you have access to water and electricity. They’re the basic choice in many cases, cost-effective and relatively simple. But because their condensers, compressors and fans are right there, they generate heat and noise on the spot, so you might not want to locate them too near customer service areas. The heat they put out also will add to your HVAC load. You’ll usually find water-cooled versions in large operations such as hotels or casinos where water already is used in the HVAC system. Water-cooled icemakers typically come with a higher price tag and use a lot of water, but they’re more energy efficient than other designs. Some areas of the country have restrictions on water use, prohibiting water-cooled icemakers. Remote air-cooled icemakers put the condenser on a remote pad, usually rooftop. The main advantages are improved cooling in most climates, which translates into less stress on the system and some energy advantages. The tradeoff? Installation costs are significantly higher than for self-contained machines. Noise is partially reduced, but the compressor is still with the unit. Most icemakers run hot gas through the evaporator to harvest ice. The compressor has to be close by to prevent the system from slugging liquid refrigerant. So remote units still locate the compressor and fan motor inside the icemaker cabinet. This leaves the noise in the maker, a problem that only worsened when the industry switched to more environmentally friendly R-404a from CFC refrigerants. The new refrigerant tends to foam when heated, making compressor noise even louder. As for the fourth category: A new type of remote package puts the compressor and fan motor on the pad, rooftop or otherwise, right along with the condenser. That moves all the heat and noise outside. To sidestep the inherent problems of trying to pipe hot gas long distances to the evaporator for harvest cycling, these units instead use cooler vapor from the refrigerant accumulator. As the vapor releases its heat energy to loosen the ice from the evaporator, it returns to liquid state. These units are ideal in operations that use self-serve beverage dispensers or anywhere icemakers are close to customers and need to be quiet. Before leaving the topic of location, also think of where you use ice when you consider the type and location of an icemaker. If you have to transport large quantities of ice some distance to another area of the operation, you may want to buy two smaller icemakers rather than one large machine. One place you definitely shouldn’t locate an icemaker is anywhere near a bakery or pizza prep area. Yeast likes the moist conditions inside icemakers and creates a slimy mess. Filters & Other Goodies An icemaker’s three worst enemies are sediment, scale and chlorine. Sediment and scale can build up on parts like the evaporator and water nozzles, cutting efficiency and potentially causing machines to go down. Chlorine affects the taste of ice and can corrode stainless surfaces in the machine. Chemicals and minerals also can stain and pit the nickel plating on an evaporator. Most icemakers can be equipped with water filters. Ask for a water quality report from your water company to determine whether you should filter your water, and what type of filter you need to deal with the local contaminants. Several models come with self-cleaning systems. In some cases, all you have to do is load de-scaling or sanitizing solution in the machine and push a button. The icemaker automatically cycles the solution through the machine, purges it and begins a new ice-making cycle. Some have optional timers that automatically clean the icemaker after a certain number of cycles. Another nemesis of icemakers: airborne microorganisms. Some new machines have plastic parts impregnated with antimicrobial compounds that inhibit growth of these microorganisms. One maker provides a device that releases chlorine dioxide gas into the icemaker cabinet. None of these systems are intended to replace manually cleaning on a regular schedule, of course. But they offer an additional safety element. So there’s the short course on icemakers. Now your real work begins. And remember, when you’re torn between your capital-budget spreadsheet and lifecycle costing, quality may tag your capital budget for a little more, but it usually pays for itself in the long run by reducing operating expenses. The New, The Different The wheels just keep turning in foodservice. You find a new need (or apply more pressure about an old one), and the factories start noodling. Check out some recent developments in icemakers: |
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