Steam coils are heat exchangers mainly used for heating or cooling applications through the direct transfer of heat between steam and a water-based fluid such as air, water or a water-glycol mixture. They consist of a continuous coil of tubing through which steam flows and transfers heat to the surrounding fluid through conduction. Steam coils find widespread applications in heating and cooling systems for various industrial and commercial processes.

How Steam Coils Work

A Steam Coil works on the principle of heat conduction between two fluids separated by metal tubing. It consists of copper or stainless steel tubing, which is cleaned and degreased thoroughly before use. The tubing is then formed into coils with perfectly rounded bends to ensure maximum contact area for heat transfer. Steam at high pressure and temperature from a boiler enters one end of the coiled tubing. As the steam flows through the coils, it transfers its latent heat of condensation to the tubing walls. On the outside, a liquid like water or glycol-water mixture flows over or around the coils. The heat conducted through the tubing walls causes the temperature of this liquid to rise. When the heating process is complete, the condensed steam exits the coil along with any collected condensate. Thus, through direct contact heat transfer, the steam coil raises or lowers the temperature of the circulating fluid.

Applications

Steam coils find a wide range of applications for both heating and cooling purposes:

– HVAC Systems: They are extensively used as heating coils in air handlers, fan coil units, heat exchangers etc. of HVAC systems to heat incoming air or water.

– Industrial Processes: Steam coils provide process and equipment heating in food plants, dairies, laundries, pulp and paper mills, chemical plants and other process industries.

– Food Industries: They maintain temperatures required for pasteurization, sterilization, cooking, evaporating and drying in food and beverage production lines.

– Building Heating: Low pressure steam coils underneath radiators or convectors provide zone heating for buildings.

– Heat Recovery: In refrigeration plants, steam coils recover waste heat from compressor air-cooled condensers and oil coolers.

– Cooling Applications: For chilled water and glycol systems, steam coils act as cooling coils by circulating chilled fluids.

– Humidification: Steam injects moisture into air handler units to maintain optimum relative humidity levels.

Types of Steam Coils

Depending on mounting/configuration and fluid technology, steam coils can be classified as:

Wall Mounted Coils: Recessed or surface mounted on walls, they heat the air circulating around them in ducts or open areas.

In-Line Coils: Installed inside air handlers or AHUs in the air stream to heat incoming air evenly.

Fan Coil Units: Consist of one or more coil circuits installed in Fan Coil Units to condition spaces.

Wraparound Coils: Tend to wrap completely around the duct or equipment to maximize heat transfer area.

Tube-Within-Tube Coils: Inner steam tube surrounded by an outer fluid tube for higher efficiency.

Direct Contact Steam Injection Coils: Steam is injected directly into air stream to add humidity along with heat.

Non-Fouling Coils: Have specific internal geometries that prevent scale buildup in thermal power stations.

Design Considerations

Proper design of steam coils requires consideration of various factors like steam pressure, flow rate, temperature of circulating fluid, required heat output and space constraints. Key design aspects include:

– Coil Circuitry: Single, dual or multiple parallel circuits based on kW load and steam pressure.

– Tubing Size: Depends on steam pressure, volume flow and diameter-to-thickness ratio for strength.

– Finned Coils: Optional aluminium fins increase heat transfer surface area by 30-40%.

– Connections: Threaded, grooved, flanged or welding end connections for installation.

– Piping: Steam traps, valves, gaskets etc. are specified as per application.

– Housing: Galvanized/stainless sheet metal housing protects coil and piping assembly.

– Performance Testing: Coils undergo hydraulic tests and AHRI certification for ratings.

Steam Coil Maintenance

Proper maintenance is essential to ensure reliable performance of steam coils over their lifespan. Periodic tasks include:

– Cleaning: Removal of scale and dirt buildup on coils and inside tubing to avoid deterioration.

– Inspection: Checking for cracks, corrosion or mechanical damage to tubing, fins and housing.

– Trapping: Proper functioning, locating and replacing defective steam traps if any.

– Insulation: Maintaining insulation blanket over coils and steam supply lines.

– Water Treatment: Boiler water treatment checks hardness, alkalinity and prevents scaling.

– Record Keeping: Logging of process parameters, inspections and any maintenance tasks.

– Replacement: Timely replacing worn out components like gaskets, valves as necessary.

Steam coils provide highly efficient heat transfer from saturated steam for heating, cooling and humidification needs across multiple industries and commercial buildings. Correct design, installation and regular maintenance ensure prolonged, trouble-free performance of these workhorse heat exchangers. Effective utilization of waste heat streams through coils also boosts energy efficiency in thermal plants.

*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it.