Baseline
To
estimate potential energy savings of the refrigeration plant, we should compare
plant energy use at improved set points to plant energy use at baseline set
points. To get correct estimation, real life baseline set points should be
chosen. Sometimes people claim that they can save 40 - 50% of energy use. Is it
possible? Yes. If we choose baseline condensing pressure of 180 psig for all
year around operation, 40 - 50% of total energy savings can be achieved. Did you
see any ammonia refrigeration plant operating at 180 psig of condensing pressure
all year around? I did not. If we compare energy use at real life average
condensing pressure of 130 psig to energy use at optimum condensing pressure,
total energy savings for the same plant will be in the range of 10 - 20%.
Today many companies are focused on floating condensing
pressure. How much energy can be saved by floating condensing
pressure?
Example.
Wet
bulb temperature of ambient air changes from 60°F to 65°F. To maximize energy
savings, condensing pressure should be floated from 120 psig to 130 psig by
following the fluctuation of the wet bulb temperature. To estimate potential
energy savings, we should compare energy use at optimum floating condensing
pressure to energy use at baseline condensing pressure. This plant can have 2
baseline condensing pressures of 120 psig and 150 psig. If baseline condensing
pressure is 120 psig, energy savings will be 2%. If baseline condensing pressure
is 150 psig, energy savings will be 12%. Today, when many companies are focused
on energy savings, majority of the refrigeration plants will have baseline
condensing pressure of 120psig. It means that operation of these plants are
close to the optimum (at wet bulb temperature of 60 - 65 degF) and floating
condensing pressure will give you 2% of energy savings. You can get the same
energy savings by lowering minimum condensing pressure by 5 psig, but you do not
need sophisticated and expensive PLC for this action as floating condensing
pressure is required.
To
estimate real life energy savings, real life baseline set points should be
chosen.