We float condensing pressure
Today many companies claim that to save energy they
float condensing pressure of the refrigeration plants. Essentially, during
summer operation the condensing pressure will float itself based on fluctuation
of the wet bulb temperature and refrigeration loads. To save energy, this
pressure should be floated at optimum level to minimize high side (compressors +
condensers) power use. The compressor and condenser capacities should be
matched. When the refrigeration load and compressor capacity is reduced,
condenser capacity should be reduced as well.
When should the condensing pressure be floated?
Floating should be done during periods of warm weather.
However, when weather is hot, majority of the refrigeration plants will have
maximum refrigeration load and all condensers will operate at full capacity (no
floating). The refrigeration plants with significant and frequent fluctuation of
the refrigeration loads will benefit the most from floating condensing pressure.
During the periods of cool weather, the refrigeration plants will be operated at
minimum condensing pressure (no floating). I think that periods of warm (not
hot) weather is the best time to float condensing pressure. However, evaporative
condensers should not be undersized, otherwise they will run at full capacity
and the refrigeration plant will never reach an optimum condensing pressure.
How
great are the savings of floating condensing pressure?
Floating condensing pressure does not save compressor
energy, but it saves condenser energy. The condenser energy is not significant
and typically in the range of 8-10% of total refrigeration plant energy use. My
research has shown that properly floated condensing pressure will save 15-20% of
condenser energy use. This means that these energy savings will be in the rage
of 1-2% of total refrigeration plant energy use.