Refrigeration
Another use of the term occurs in industrial refrigeration, specifically vapor-compression refrigeration. Normally, the economiser concept is applied when a particular design or feature on the refrigeration cycle, allows a reduction either in the amount of energy used from the power grid; in the size of the components (basically the gas compressor’s nominal capacity) used to produce refrigeration, or both. For example, for a walk-in freezer that is kept at -20°F, the main refrigeration components would include: an evaporator coil (a dense arrangement of pipes containing refrigerant and thin metal fins used to remove heat from inside the freezer), fans to blow air over the coil and around the box, an air-cooled condensing unit sited outdoors, and valves and piping. The condensing unit would include a compressor and a coil and fans to exchange heat with the ambient air.
An economiser display takes advantage of the fact that refrigeration systems have increasing efficiencies at increasing pressures and temperatures. The power the gas compressor needs is strongly correlated to both the ratio and the difference, between the discharge and the suction pressures (as well as to other features like the refrigerant’s heat capacity and the type of compressor). Low temperature systems such as freezers move less fluid in same volumes. That means the compressor’s pumping is less efficient on low temperature systems. This phenomenon is notorious when taking in account that the evaporation temperature for a walk-in freezer at -20°F may be around -35°F. Systems with economisers aim to produce part of the refrigeration work on high pressures, condition in which gas compressors are normally more efficient. Depending of the application, this technology either allows smaller compression capacities to be able to supply enough pressure and flow for a system that normally would require bigger compressors; increases the capacity of a system that without economiser would produce less refrigeration, or allows the system to produce the same amount of refrigeration using less power.
The economiser concept is linked to subcooling as the condensed liquid line temperature is usually higher than that on the evaporator, making it a good place to apply the notion of increasing efficiencies. Recalling the walk-in freezer example, the normal temperature of the liquid line in that system is around 60°F or even higher (it varies depending on the condensing temperature). That condition is by far less hostile to produce refrigeration, than the evaporator at -35°F.
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