Instructions for Coils

Steam Coils

Application Recommendations:

Satisfactory operation and service life are best ensured when coils are installed with proper piping, trap, and support arrangement. The following notes and figure 1 (page 15) are recommended for the coil unit installation and operation.

General:

1.Provide separate supports and hangers for the unit and the piping.

2.Be certain that adequate piping flexibility is provided. Stresses resulting form expansion of closely coupled piping and coil arrangement can cause serious damage.

3.Standard steam coils are pitched in the casings when installed for horizontal air flow. The CASING MUST BE LEVEL after the unit is installed for proper condensate drainage. If condensate is not removed the coil will suffer from water hammering and will have a shortened life. On vertical air flow applications, the coils must be pitched when installed.

4.Do not reduce pipe size at the coil return connection. Carry return connection size through the dirt pocket, making the reduction at the branch leading to the trap.

5.It is recommended that vacuum breakers be installed on all applications to prevent retaining condensate in the coil. Generally, the vacuum breaker is to be connected between the coil inlet and the return main. The vacuum breaker should be open to the atmosphere and the trap design should allow venting of large quantities of air.

6.Do not drip supply mains through the coil.

7.Do not attempt to lift condensate when using modulating or on-off control.

8.Do not reduce the pipe size leaving the coil.

Traps:

1.Size traps in accordance with the manufacturer’s recommendations. Be certain that the required pressure differential will always be available. DO NOT UNDERSIZE.

2.Float and thermostatic or bucket traps are recommended for low pressure steam. On high pressure systems, bucket traps are normally recommended. The thermostatic traps should be used only for air venting.

3.Bucket traps are recommended for use with on-off control only.

4.Locate traps at least 12 inches below the coil return connection.

Controls:

1.On high pressure installations, a two-position steam valve with a face and bypass arrangement is preferred where modulating control is required.

2.Modulating valves must be size properly. DO NOT UNDERSIZE.

Freezing Conditions (Entering air below 35oF):

1.5 PSI steam must be supplied to the coil at all times.

2.Provision should always be made to thoroughly mix fresh air and return air before it enters the coil on return air units. Also, temperature control elements must be properly located to obtain true air mixture temperatures.

3.As additional protection against freeze-up, the trap should be installed sufficiently far below the coil to provide an adequate hydrostatic head to ensure removal of condensate during an interruption in the steam pressure. Estimate 3 feet for each 1 PSI of trap differential required.

4.On start up, admit steam to coil ten minutes before admitting outdoor air.

5.Provision must be made to close fresh air dampers if steam supply pressure falls below minimum specified.