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.