**Estimation of potential energy
savings**

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Many companies promise to end users to save a lot of
energy. Very often they give you exaggerated numbers. To make a right decision
you should have correct information about potential energy savings. How to get
this information? First you should ask these companies to estimate potential
energy savings. Second you should check all numbers in this estimation. These
numbers should be based on real life operation. I will give couple examples how
to estimate potential energy savings.

**Example 1.
**Very often evaporators of the
refrigeration plants are over defrosted. How to estimate energy saved by
eliminating one defrost cycle of one evaporator?

Assume that we have 20 TR evaporator and it has 30
minute or 0.5 hour hot gas supply for the defrosting. Efficiency of hot gas
defrosting is very low. Assume that our evaporator has hot gas defrost
efficiency of 10%. It means that 10% of energy supplied by hot gas will go to
melt the frost. 90% of this energy will be released into refrigerated room as
parasitic refrigeration load. Typically, hot gas supply for the defrost is 1.5
times greater that refrigerant evaporation during cooling mode. For our
evaporator, heat released into refrigerated room during one defrost cycle will
be 20 x 1.5 x 0.5 x 0.9 = 13.5 TR. Assume that energy efficiency of the
refrigeration plant is 2.5 BHP/TR. For mentioned evaporator elimination of one
defrost cycle will save 13.5 x 2.5 x 0.7457 = 25.2 KW
energy.

**Example 2.
**During winter operation,** **lowering condensing pressure can save
a lot of energy. Estimation of these potential energy savings can be done based
on engineering data from compressor manufacturer. Assume that we have compressor
Frick RWB-II-134 and it is 100% loaded. Condensing pressure is 151.7 psig and
suction pressure is 23.8 psig. At these operating conditions mentioned
compressor has refrigeration capacity of 233.8 TR and energy use of 264.9 BHP.
Compressor energy efficiency (energy use per unit of refrigeration) will be
264.9/233.8 = 1.133 BHP/TR. Assume that condensing pressure was reduced to 125.8
psig. At these operating conditions refrigeration capacity will be 240.2 TR and
energy use will be 228.7 BHP. Energy efficiency will be 228.7/240.2 = 0.952
BHP/TR. Condensing pressure was reduced by 151.7 - 125.8 = 25.9 psig. This
pressure drop has improved compressor energy efficiency by 1.133 - 0.952 = 0.181
BHP/TR. Reduction of condensing pressure from 151.7 psig to 125.9 psig will save
240.2 x 0.181 x 0.7457 = 32.4 KW energy.

These are two simple examples. However, these
estimations can be more complicated. Ask your energy efficiency adviser to help
you with complicated estimations. Correct estimations can give you real life
numbers and they will be very helpful to make right decision.

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