Technology for Improving the Energy Efficiency and Increasing the Capacity of Ice Makers

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Various Excerpts From the 28 Page Federal Technology Alert

About the Technology

A waste chill recovery (WCR) heat exchanger could be applied to any ice maker to improve its energy efficiency. The WCR device is basically a type of "shell and tube" heat exchanger that precools makeup water being charged to the ice maker with cold waste water being discharged from the ice maker. A simplified, generic flow diagram of the concept is shown in Figure 1. Relatively warm makeup water flows through the tube while the near-freezing waste water flows around the tube within the shell of the heat exchanger. Heat is transferred from the makeup water to the discharge water, which lowers the temperature of the water charged to the ice maker's reservoir. As a result, the amount of heat that must be removed from the water by the ice maker's refrigeration system is reduced along with the electricity required to drive the refrigeration system.

Other Benefits

Lowering the initial water temperature in the ice maker's reservoir reduces the time required to cool the water to the freezing point, which reduces the entire ice making and harvesting cycle. In fact, the increased production rate may be the most valuable impact to users with inadequate ice-making capacity who may otherwise be forced to buy supplemental ice, purchase a supplemental refrigeration unit, or buy an additional ice maker. In addition, reducing the cooling load on the ice maker should result in less "wear and tear", resulting in lower maintenance costs and longer equipment life.

Where to Apply

The previous section described and discussed the key factors affecting the cost-effective application of WCR heat exchangers to ice makers. The bulleted items listed below summarize the key favorable conditions that will most likely result in a cost-effective application. Not all of these conditions necessarily need to exist for an application to be cost-effective. Cost-effectiveness depends on the specific values of the variables identified in equations 1-7. Still, if the majority of these conditions do not exist, it is unlikely a WCR heat exchanger will be cost-effective.
  • The annual demand for ice is relatively high, generally greater than 30% of its annual production capacity, if operated continuously throughout the year.
  • The ice maker operates in a "purge" mode to charge and discharge its water reservoir.
  • The average annual makeup water temperature is relatively high, generally greater than
  • The ice maker's condenser is located indoors.
  • The electricity rate is relatively high, generally greater than $0.08/kWh.
Field Experience

The WCR technology is successfully being used in a wide range of commercial applications--hotels, restaurants, convenience stores, and schools. Although few ice machines are separately metered, all the sites we spoke with indicated an observable decrease in cycle time indicating a lowering of inlet water temperature. Where test measurements were performed, the WCR technology reduced inlet water temperature an average of 15.2 F or 21.9%. The cycle times were reduced by, 2.1 minutes, on average, or 18.1%.}
 
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