Refrigeration: Ice Makers
More than 1.2 million ice makers are operated in restaurants, hospitals, hotels, and other commercial facilities in the United States. Together they consume more than 9.4 billion kilowatt-hours (kWh) of electricity each year and rack up more than US$800 million in annual electricity bills. The energy efficiency of new ice makers has improved considerably over the past decade, and there are now many efficient models to choose from, some of which provide substantial energy savings with little or no incremental cost over less-efficient models—a win-win situation. With new state and federal standards coming into effect, the number and diversity of energy-efficient ice makers will continue to increase.
Types of ice. Ice machines produce a variety of ice for a range of applications. The choices are cube, flake, crushed, and nugget.
- Cube ice is clear and comes in various shapes—rectangular, crescent, pillow-shaped, pure cube, or other regular shapes. The largest dimension is about 1.25 inches (3.18 centimeters). Pieces of cube ice range in weight from 1/6 to 1/2 ounce (4.8 to 14.0 grams) and contain minimal amounts of liquid water. More than 80 percent of ice machines sold in the U.S. make cube ice.
- Flake ice comes in chips or flakes that contain up to 20 percent liquid water. Flake ice tends to conform to the surface of items that rest on it and is typically used in supermarket display cases, on fishing boats, or anywhere food needs to be preserved for short periods. Flake ice may also occasionally be used in soft drinks.
- Crushed ice consists of small, irregular pieces made by crushing larger chunks of ice. Its primary use is for keeping drinks cool.
- Ice nuggets, made by extruding and freezing slushy flake ice into small pieces, are also used primarily to cool drinks.
For more about types of ice and the machines that make them, see Chapters 34 and 47 of the American Society of Heating, Refrigerating and Air-Conditioning Engineers' (ASHRAE's) 2006 ASHRAE Handbook—Refrigeration. Information about ASHRAE publications is available at www.ashrae.org.
Types of machines. Ice machines may be mounted above a storage bin or integrated with an attached insulated bin—a style known as a self-contained unit (Figure 1). Integrated units are the simplest to install but usually come with a fixed capacity. The capacity of nonintegrated units can be increased by stacking additional ice makers on top of the first machine or by placing a second machine next to the first on top of a larger bin.
Ice makers are also classified as batch or continuous in operation. Batch models tend to produce ice that is purer than its source water, because the freezing process separates out the impurities. In continuous units, chemicals tend to remix in an ice/water combination. Controls for batch ice makers are more complicated—they must end the freezing process at the proper time to start a thawing cycle, and resume the freezing process after the ice has been harvested.
Types of condenser. Ice makers are available with three different types of condenser:
- Air-cooledice makers use the most energy but are less expensive than water-cooled models. They also use less water. Their energy use per 100 pounds (45 kilograms) of ice ranges from 4.6 kWh (for machines making 1,500 pounds of ice per day) to 20.4 kWh (for self-contained machines making 50 pounds of ice per day).
- Water-cooled models are more efficient than air-cooled units. Their energy use per 100 pounds of ice ranges from 3.4 kWh (for machines making 1,800 pounds of ice per day) to 10.5 kWh (for self-contained machines making 150 pounds of ice per day). There is no addition to air-conditioning loads, because the heat removed in making the ice is discharged outside the building.
- Remote air-cooled condensers transfer the heat generated by the ice-making process outside of the building. Like water-cooled units, they reject heat outside of conditioned spaces and therefore do not increase air-conditioning loads. Their energy use per 100 pounds of ice ranges from 4.2 kWh (for machines making 1,650 pounds of ice per day) to 8.8 kWh (for machines making 400 pounds of ice per day). They also reduce noise levels inside by up to 75 percent, but there are extra installation costs for running lines to a remote location.
To compare among the condenser technologies, machines manufactured in 2007 making approximately 800 pounds of ice per day average the following energy use per 100 pounds of ice:
- Air-cooled ice makers: 5.8 kWh
- Water-cooled ice makers: 4.7 kWh
- Remote air-cooled ice makers: 5.8 kWh
These efficiencies represent an approximately 10 percent improvement versus 800-pound-capacity ice makers manufactured in 2002. A typical commercial ice maker lasts 7 to 10 years.
Types of bins. Ice-storage bins are available in a range of sizes, usually with a full-width door that allows users access to the ice. Bins are usually sized to hold 10 to 12 hours worth of ice production. Larger bins are available for such applications as supermarket displays for which ice is only changed once or twice a week. Sealed, sanitary units are also available, but they're much more expensive than standard units. They are often used in hospitals, motels, and restaurants, and for any operations in which ice comes in direct contact with food or drink.
Water heat recuperation. Some ice makers direct the incoming water behind the evaporator plate or over the ice to use the heat of the incoming water to assist in the ice-harvesting process. This step also serves to prechill the incoming water and cuts energy use significantly.
Water treatment system. Ice makers can be run directly from tap water supplies, but some applications may require additional water treatment. In general, if the total chemical content of the incoming water is greater than 400 parts per million, auxiliary water treatment is recommended.
Self-cleaning systems. A relatively new option among ice makers is the self-cleaning machine. Typically, ice makers are cleaned and sanitized every two to six weeks, which requires emptying the bin of ice, adding cleaning solution, switching the controls to a cleaning mode that circulates the cleaning solution through the machine, and then producing enough ice to be sure the machine is cleared of the solution. Self-cleaning models automate most of these steps.
Energy-efficient units. The Consortium for Energy Efficiency (CEE) has created voluntary standards for commercial ice maker energy and water efficiency. These can be found, along with a list of ice makers that meet the standards, on the CEE web site at www.cee1.org. The sample calculation in Table 1 shows estimated energy savings from hypothetical ice makers that meet each of the CEE efficiency tiers compared with a baseline standard ice maker.
This sample calculation can be used to estimate a simple payback period. However, in some cases, high-efficiency ice makers have little or no incremental cost versus less-efficient models. For example, a search for air-cooled ice makers with approximately 1,200 pounds of capacity showed that a model meeting CEE Tier 1 standards was the most expensive, US$120 (2 percent) more than a baseline model, whereas models meeting the Tier 2 and Tier 3 standards cost US$250 (3 percent) and US$350 (5 percent) less than the baseline model, respectively.
Ice-making capacity and energy efficiency are only two of many features to look for, and there are several manufacturers. It is important to find an ice maker and manufacturer or dealer that best meet your needs. Just remember that it pays to shop around. A win-win situation—lower initial cost and lower energy costs—is possible.
Determine required capacity. Determining the required capacity of an ice-making machine is based on rules of thumb developed over years of experience. Manufacturers provide sizing guidelines to help users pick the most economical combination of ice maker and storage bin. The guidelines are based on the type and size of the application. For example, an ice maker for soft drinks in a fast food restaurant might be expected to be in service seven days a week at its average level of ice production and might have to produce ice at a peak rate of 150 percent of average for two of those days. Under those conditions, the machine should be sized to provide 0.25 to 0.5 pounds (0.11 to 0.23 kilograms) per customer.
Pick a machine with the right capacity. Oversizing an ice maker can increase energy consumption due to excessive standby losses. On the other hand, larger ice makers generally are more efficient (they consume less energy per unit of ice) than smaller ones. It is important to pick a unit that most closely matches your quantity requirements. Ice machines are designated by the amount of ice that they can produce in a 24-hour period, under reference conditions of 70º Fahrenheit (F, 21º Celsius [C]) ambient temperature and 50ºF (10ºC) inlet water temperature. Typical sizes are 250, 400, 500, 650, 800, 1,000, 1,200, and 1,400 pounds per 24 hours, but machines are available that make several tons of ice per day. Actual capacity varies with both ambient temperature and water temperature. Manufacturers usually recommend using the capacity listed at the test conditions used by the Air-Conditioning and Refrigeration Institute (ARI): 90ºF (32ºC) ambient air and 70ºF (21ºC) water. Selecting equipment based on the capacity at those conditions will ensure that adequate ice can be produced under most conditions encountered in operation.
ARI publishes a directory called "Certified Automatic Commercial Ice-Cube Machines and Ice Storage Bins." Information about ARI publications is available at www.ari.org.
Pick a unit with an appropriate noise level. The noise level of ice makers is typically equal to that of a window air conditioner, which is acceptable for most applications. In some cases, lower levels may be desirable, and the buyer should ensure that the manufacturer can provide equipment that meets those requirements.
Pick a reliable unit. Most purchasers of ice-making machines choose them as much for reliability as for efficiency or first cost. Although reliability data for specific equipment are not available, you can make a sound choice by looking for equipment with the fewest moving parts and with controls that include diagnostic capabilities. In addition, two small machines rather than one large one can provide more availability.
Look for an easy-to-maintain model. Even the most reliable ice makers require a lot of maintenance if they are to last more than a few years. Regular cleaning and sanitation treatments are necessary for both the ice-storage and ice-making parts. Therefore, the best bet is to go with equipment that includes clear, simple installation and maintenance instructions and procedures.
Look at water costs in areas where water is expensive. A hundred pounds of ice is equal to about 12 gallons (45 liters) of water. The amount of water used to make that much ice varies widely, in the range of 13 to 35 gallons (49 to 132 liters). The extra water is used for melting and releasing the ice and for keeping the equipment operating smoothly and cleanly. Where water prices are average, water cost for ice making is less than 30 percent of the electricity cost. But in areas where water is expensive, water use may be an important consideration.
There is also a connection between water use and maintenance costs. Some self-cleaning machines use three times as much water as standard models, but they save on labor costs. Higher water consumption also reportedly improves overall machine reliability by keeping components such as the water pump free of scale and by keeping the evaporator clean. Unfortunately, no data are available precisely correlating water use and maintenance costs. If water costs are high in your area, ask equipment manufacturers about water-conserving options.
New U.S. federal and state standards will continue to push ice-maker efficiency upwards. Federal energy-efficiency requirements taking effect in 2010 will be the same as the current (voluntary) CEE Tier 1 standards. California's 2008 energy-efficiency standards for commercial ice makers are also the same as the current CEE Tier 1 standards (see Appliance Efficiency Regulations on the California Energy Commission web site, www.energy.ca.gov). Both the federal and California standards will include water-efficiency requirements. Canada is strengthening its ice maker standards in 2008 as well—see the Natural Resources Canada Office of Energy Efficiency web site, www.oee.nrcan.gc.ca, for more information.
Energy Star efficiency levels for ice makers go into effect January 1, 2008. These initial levels cover only air-cooled ice makers and those that make cube (not flake or nugget) ice. They mirror CEE Tier 2 standards for the specified machines. The Energy Star program has stated its intention to include flake and nugget machines once a test standard is available and adequate data are collected for deriving performance requirements. For more information, see the Energy Star web site: www.energystar.gov.
Several U.S. states offer incentives for ice-maker efficiency: California, New York, Vermont, and Wisconsin. Some U.S. and Canadian cities also offer ice-maker efficiency incentives, including Austin, Texas; Oakland, California; Las Vegas, Nevada; San Diego, California; Seattle, Washington; and Toronto, Ontario.
From a technological standpoint, ice makers are being designed with the ability to shut off automatically at specified times. This allows them to take advantage of off-peak energy consumption—for example, making ice at night and shutting off during the day. As an added benefit, ice-maker noise is reduced during daytime business hours. Incremental gains in ice-maker energy efficiency continue to be made as well, mostly from improvements to compressors, which consume more than 90 percent of the energy an ice maker uses.