How to set up proper steam condensate piping
All steam condensate systems for commercial, industrial, and any other applications need to have proper piping (see Figure 1). When a steam-to-water heater with a modulating control valve is used, the condensate from the float and thermostatic trap should not be lifted (see Figure 2), or else the system won’t be able to control the temperature. That’s because the pressure in the coil will be too low to push the condensate up to an overhead return.
When this happens, the heat from the condensate will transfer through the coil into the hot water, even though the controls have sensed the water is at or above its setpoint. When there is an overhead condensate return, provisions should be made for gravity to drain the condensate to a lower receiver and pump the condensate to the overhead return.
A heater is expected to operate with 15 PSIG at the inlet of the control valve. There is a 10-ft lift from the trap outlet to the overhead return. The 10-ft column of water exerts a back pressure on the trap outlet of 4.5 PSIG.
A typical pressure drop across a temperature control valve is 30% (about 4.5 PSIG) when fully open, so 10.5 PSIG is left to enter the coil. As the steam condenses in the coil, the pressure will continue to drop. When the it drops below the back pressure, the heater will stall. The sensor then will see a drop in temperature and begin to open the steam valve, so both steam and condensate can begin to flow again.
This process causes the water temperature to increase and the valve to close. The high temperature (HT) condensate will stop flowing, and the heat from the HT condensate will transfer to the domestic water side. This causes an uncontrolled temperature rise, possibly to unsafe levels.
Richard Goins has more than 39 years of industry experience. He began his career with Cummins-Wagner as a sales engineer. In 1994, he started Environmental Air Products (EAP), an HVAC division of Cummins-Wagner. As general manager of EAP, he defined the company’s purpose and goals to expand on Cummins-Wagner’s market segment. In 2000, he was asked to manage the Engineered Services Group (E3), which is responsible for providing technical support to the engineering community. In addition, Goins provides training and educational seminars to external and internal clients to further develop their professional growth. He is also a member of ASHRAE, ASPE, and CASHE. Edited by Jack Smith, content manager, CFE Media, Control Engineering, firstname.lastname@example.org.
- Steam condensate systems for commercial and industrial applications must have proper piping.
- A typical pressure drop across a temperature control valve is 30% when fully open.
- When the pressure drops below the back pressure, the heater will stall; the sensor then will see a drop in temperature and begin to open the steam valve, so steam and condensate can begin to flow again.
When was the last time your plant conducted a steam trap audit?