What is a steam coil?

What exactly is a steam coil?

Are you making the most of your investment in a steam system? For ages, steam has been employed as a heat transmission medium. It is still a popular choice for commercial heating and a variety of industrial uses today. Yet, in our experience, the industry's understanding of steam and steam equipment is inconsistent, and we hope to assist clear things up in the following areas.

Several types of steam coils

Standard steam coils (single-pass and multiple-pass)

Steam distributing coils (single-pass)

Standard Steam Coils

A standard steam coil, often known as a steam coil, is a type of heat exchanger that uses steam to heat air or another gas. Steam enters the coil by an intake header and is dispersed throughout the coil in a series of tubes similar to those seen on most coils.

The thermal energy emitted by a steam coil's fin surface is absorbed by air as it travels across it. The heated air then mixes with downstream air, elevating its temperature to the temperature specified by the application.

Single-Pass Standard Steam Coils

This is the more adaptable of the two steam coil designs. They are less difficult and are usually the first choice. The following are some essential facts concerning single pass standard steam coils:

Single-pass steam coils have a steam inlet header on one end and a condensate exit header on the other end of the heat exchanger.

Steam coils are often one, two, or three rows in length. The steam makes a single run through the coil's straight tubes, arriving at the steam intake header and exiting at the other end at the outlet header.

For non-modulating (constant volume and temperature) steam applications, single-pass steam coils are the most prevalent design. They can be installed horizontally or vertically, as seen below. When installed horizontally, the tubes should be tilted in case arrangement to ensure proper condensate drainage.

Steam should be distributed as uniformly as possible into the coil's circuits in all steam coils. To prevent uneven loading, this design will frequently include orifice stubs or a baffle inside the input header.

Single-pass designs are commonly used in applications with inlet air temperatures above freezing. But, when mounted vertically, this design gives great freeze resistance. To reap this benefit, we recommend limiting coil finned lengths under 72 inches and steam pressures at 5 PSIG or higher.

Multi-Pass Standard Steam Coils

Multiple-pass steam coils are often utilized in applications where having the connections on the same end of the coil is advantageous.

Multiple-pass designs are often utilized only when:

a. The usage of a single-pass design is prohibited due to spatial constraints or another cause.

b. The application requires more than two rows, and all rows must be contained within a single case.

Consistent steam pressure and temperature are especially important when employing multiple-pass steam coils in sub-freezing temperatures. This is due, in part, to the longer circuit lengths seen in multiple-pass designs, which, when combined with the fact that these designs cannot be sloped, can impede condensate drainage and increase the likelihood of freezing.

Steam Distributing Coils

Because of its header construction, steam dispersing coils are more sophisticated than ordinary counterparts. Steam dispersing (SD) coils, also known as "tube inside a tube" coils, have headers that consist of a smaller tube encased in a larger one.

The tube-in-tube design is intended to allow for more uniform dispersion of steam from the outer tube into the rest of the coil. Its design also leads to more uniform air temperature coming off the coil, allowing for better temperature control in low or variable steam pressure situations.

Steam Distribution Coils with a Single Pass

Single-pass steam distributing coils, like ordinary steam coils, have connections on opposing sides of the heat exchanger.