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Normalized Energy Cost

 

A normalized energy cost is annual energy cost divided by a measure that is able to account for variations in the factors that influence energy costs. Normalized costs are typically expressed in dollars per pound of product, kWh per pound of product, kWh per cubic foot of refrigerated space and etc.  These costs allow managers and operating engineers to compare their operating costs on an apple to apple basis with previous years or with other plants.

The purpose of a refrigeration plant is to handle the refrigeration loads. There are several types of loads on a refrigeration system, including product load, infiltration load, envelope heat gain, internal loads, and other parasitic loads as defrost. These loads will vary over time in response to a number of factors. In process-driven plants, refrigeration loads are directly influenced by product temperature and product rate. Variation of different products can also affect the loads. In refrigeration plants that serve refrigerated rooms, loads will depend on entering product temperatures, weather and product turnover. Operating procedures, such as defrosting or door management in refrigerated rooms, may have impact on the load. Finally, for many plants weather is an important factor.

Weather influences loads by a combination of ambient heat gains and air infiltration. Weather-dependent loads are significant for the freezers, coolers, refrigerated docks and refrigerated production rooms. Weather has a limited effect on the loads for many food processing and industrial process cooling plants. In these cases, the load is primary determined by the initial and final temperatures of the product and by production rate.

Normalized energy costs can be a useful tool to evaluate energy savings of the refrigeration plant. These costs can be compared before and after implementation of the energy saving measures. However, to get correct results the influence of parasitic refrigeration loads should be minimize or these loads should be kept at a constant level. During the tests, variation of the weather should be minimal.   

 

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