Extended Surface Air Coolers for Industrial Plants • the Con
Extended Surface Air Coolers for Industrial Plants • the Contractors Perspective (2009)-In view of the very large range of evaporator coil geometries, coil material combinations, coil defrost methods and circuiting options available on the market, the industrial refrigeration contractor often faces difficulties deciding which evaporator design to use for a certain application. Often selections are based on rules of thumb, e.g., an allowance of a certain number of square feet of coil surface area per pound of product. Considering the fact that coil material selections, choice of refrigerant, coil circuiting and coil geometry can influence heat transmission coefficients (u-values) by up to a factor of three or more, such an approach can lead to very poor results in practice. Other issues are relative humidity and dehydration of the refrigerated space. There are thousands of practical applications where the quality and shelf life of the products stored or chilled are directly influenced by the equilibrium relative humidity inside the room in question. Yet often extended surface air coolers are selected with geometries to suit the manufacturer and not the application. Frequently, the result is a squat coil when the coil should have been shallow and with large face area. The performance impact of fouling both on the inside, but also on the outside surfaces of cooling coils is often not highlighted sufficiently by manufacturers. Extended surface air cooling coils featuring comparatively high-heat transmission coefficients (u-values) in clean condition generally display a more rapid performance deterioration as a function of increasing fouling than an equivalent coil with lower heat transmission coefficient in clean condition. It is often not in the commercial interest of coil manufacturers to disclose this information, yet it can be of crucial importance to the refrigeration plant designer. It is commonly known that cooling coil performance increases as a function of increasing face velocity. What is not normally available from manufacturers is optimization of face velocities for maximum plant energy efficiency. This is the contractor’s problem and the tools that the contractor needs to perform this task are often not readily available. This paper will show a range of practical performance comparisons between various coil geometries, coil materials, circuiting options, refrigerant choices, flow patterns and refrigerant feed options. These performance comparisons will have one thing in common namely the software used to perform them. The comparisons therefore represent relative information valuable to the contractor because it is information not readily available from extended surface cooling coil manufacturers under normal circumstances.
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