The selection of a lower condensing head pressure is one of the best ways to reduce energy costs in an ammonia refrigeration system. The larger condenser saves money all year round; and, at the same time increasing the tons of refrigeration produced by the compressor. Therefore, more tons at a lower brake horsepower per ton of refrigeration produced.
Consider a typical high stage screw compressor operating at +12°F (25.6 psig) suction and discharging at various pressures. As the discharge pressure (CP) gets lower, the capacity of the compressor increases, and the BHP/TR (energy input per ton refrigeration) goes down. Therefore, in effect, it does more for less. The following graph show the relationship between condensing pressure and compressor performance /energy consumption for various condensing pressures.
Clearly, the above Graph A.1 shows that the lower the condensing pressure, the lower the energy consumption of the compressor power. The difference between 96°F (184.3 psig) and 82°F (143.7 psig) condensing pressure is approximately 20.6% lower energy consumption while at the same time increasing compressor capacity (TR) approximately 5.1 %. Thus, at peak condensing conditions, the larger condenser saves approximately 20% of the compressor energy costs while providing approximately 5% more capacity using the aforementioned example.
A larger condenser is a good investment. It allows the compressors to work less and thus lowering the energy consumption and extending the useful life of the refrigeration equipment. Larger condensers utilizes fewer fans and pumps during the cooler seasons of the year, and lasts longer than the marginally sized alternative. In most cases, the larger condenser will pay for itself in just a few years while benefiting the system owner for many years.
Watch our video and learn more about lowering condensing pressure and wet bulb control.