Refrigeration is the process of transferring heat from a hot substance or a space to a place where it is unobjectionable. This heat transfer can be achieved in multiple ways by using transfer media such as water, ice, ammonia or synthetic refrigerants. The refrigeration process provides an cold environment for many applications.
Refrigeration is not a new discovery or an isolated concept. The roots of refrigeration can be traced back to the 1600s. The original applications, dairy transportation and meat packing, were seen as early as 1867. However, DuPont Corp. transformed it into a commercial product with countless applications in 1920. The original refrigerant media was cold water and ice, but scientific advances and innovation have changed the media to sophisticated synthetic gases and liquids.
In order to better understand the refrigeration cooling process, it is important to understand the terminology used in the industry. Basic definitions include:
(also shown as ΔT or TD). TD is the temperature difference
between the coil or refrigerant temperature and the space air temperature. The
coil temperature commonly is referred to as the saturated suction temperature
Sensible Cooling. This
is the process of removing heat from an environment, resulting in a temperature
change (dry surface).
Latent Cooling. This is the process of
removing heat from an environment, resulting in a reduction in relative
humidity (wet surface).
- Ton. This is the refrigerating effect
equal to the melting of the 1 ton of ice in 24 hr, or 12,000 BTU/hr.
Refrigerant. This is
a liquid that can be changed to vapor, compressed and condensed back to a
liquid under safe operating conditions. The desired boiling point should be
obtainable at moderate pressures. Some commonly used refrigerants are R-717,
R-22 and R-134a.
- Coefficient of Performance (COP). This is the ratio of heating or cooling provided by a heat pump (or other refrigeration machine), to the energy consumed by the system, under designated operating conditions.
There are two operating conditions and methods of process cooling: cyclic and non-cyclic refrigeration. Cyclic refrigeration is described above. The difference between the two methods is that in non-cyclic refrigeration, the cold media does not return to the evaporator after it passes though the expansion valve. Single-cycle (non-cyclic) refrigeration can be visualized as a traveling cooler, where ice is used to keep a substance cool. Once the ice melts, to continue cooling, more ice must be added to replace the water. Most industrial applications use cyclic refrigeration for efficiency and cost considerations.
The two operating conditions are sensible and latent cooling. The difference between the two is the transfer media. In latent cooling, water is sprayed onto coils to increase the thermal coefficient. Sensible cooling is dry cooling where air is the heat transfer media. Latent cooling is more efficient because of water’s higher heat capacity.
Supporting Equipment and MaintenanceEvaporative condensers can be more effective if other products are used in series with these condensers. One solution is an ice thermal storage unit, where ice is created during non-peak times. The ice then is melted during the day to offset the peak load. The process results in cost savings and serves as an energy storage and backup in case of an emergency.
The maintenance requirements of process cooling equipment vary by manufacturer. Some manufacturers incorporate features into the standard design of products to simplify maintenance. For example, some manufacturers provide man-size access doors, extended bearing lubrication lines, premium efficiency motors and platforms. Other designs may incorporate the means to inspect and maintain critical components such as fill, coils and nozzles without entering or stopping the unit.
Designing for maintenance provides flexibility for the operators and lower maintained cost.
Sidebar:Many manufacturers provide efficient heat transfer products.
Explore the options to find the equipment that provides an edge.
Condensers with Axial Fans Improve Efficiency
For instance, one evaporative condenser design utilizes axial fans to minimize energy consumption. It also incorporates features to ensure ease of maintenance and efficient field assembly.
Another design uses coil technology (see figure) to increase efficiency and reduce energy consumption. The basic operational principle is the combined flow, where air and water travel in a parallel path in the coil section, minimizing scale-producing dry spots on the coil.
According to the manufacturer, the coil technology provides twice the contact surface between water and the coils when compared with the conventional counterflow technology. The amount of heat removal is directly related to the amount of surface area and the quality of interaction between air, water and the coils containing the refrigerant.
Because of the design, the spray water temperature in the condenser with the enhanced coil technology design is much colder than conventional technology. This helps the condenser remove more heat and reduces the probability of performance-robbing scale buildup on the coils.