This was found by our friends at Gleason Steam and we have all come across problems just like this one during inspections. |
This particular air handler has four rows of stacked coils, all of which have experienced recurring failures and diminished heat transfer. One of the four identical coils is highlighted here. Proper steam coil installation will ensure maximized heat transfer and avoid damage caused by corrosion, water hammer, and freezing. Here is what’s wrong.
Very simply:
• Incorrect steam trap elevation: To maintain pressure differential across the steam trap when the steam supply is off, the trap must be mounted at least 14" below the coil outlet. Result - Back-up of condensate into the steam coil.
• Incorrect steam trap style: Float & Thermostatic (F&T) steam traps are recommended for all low and medium pressure coil applications. Result - Possible back-up of condensate into the steam coil and build-up of non-condensable gases.
• Improper reduction of pipe size at coil outlet: Piping must be the same size from the coil outlet connection to the steam trap. Result - Back-up of condensate into the steam coil.
• Unsupported piping on outlet side of coil: Piping must be supported independently of the coil. Thermal expansion and contraction stresses on coil headers must be considered. Result - Damage to the coil.
• Lack of swing joint or flexible connectors: Flexible connectors must be used to avoid placing expansion and contraction stresses on coil headers. Result - Damage to the coil.
• Insufficient pipe diameter downstream of steam trap: To account for flash steam volume, pipe diameter of the steam trap outlet piping should be increased by one pipe size. Result - Decreased pressure drop across the trap and condensate backed-up into the steam coil.
• Lack of subcooled temperature indication upstream of (non-modulating) steam trap: Continual monitoring of saturated temperature upstream of the steam traps between scheduled testing intervals is critical to ensure proper evacuation of condensate. Result - Failed steam traps will not be detected, backing up condensate into the steam coil.
• Lack of vacuum breaker: The reduction of volume - due to condensing steam - can create a negative pressure, not allowing condensate to be evacuated. Result - Back-up of condensate into the steam coil.
• Lack of automatic air vent: Air and other non-condensable gases are insulators and must be continuously evacuated from the steam coils. (Steam traps cannot be counted on to do this sufficiently.) Result - Diminished heat transfer.
This is my observation with a lot of these problems.
You can not totally place blame on the installers because most of the time they are just following a cookie cutter drawing from the company building the system. But operators and maintenance techs should pay attention when doing rounds. Not every construction tradesman knows the proper steam trap to use or where to place a gauge, but when problems come up, take your time to thoroughly look at the system. Do not be rushed by management and eliminate all defects found.
Until next time,
Mike
And thanks to Gleason Steam.
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