How to set up proper steam condensate piping
All steam condensate systems for commercial, industrial, and any other application need to have proper piping. 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. If it is, the system won’t be able to control the temperature. 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 set point.
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 pressure drops below the back pressure, the heater will stall. The sensor sees a drop in temperature and begins to open the steam valve so both steam and condensate will begin to flow again.
This process causes the water temperature to increase and the valve to close. The high temperature 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 over 39 years of industry experience. He began his career with Cummins-Wagner as a sales engineer. In 1994, Richard started Environmental Air Products (EAP), an HVAC air side division for Cummins-Wagner. As General Manager of EAP, he defined EAP’s purpose and goals to expand on Cummins-Wagner’s market segment. In 2000, he was asked to manage the Engineered Services Group (E3). E3 is responsible for providing technical support to the engineering community. In addition, Richard provides training and educational seminars to external and internal clients to further develop their professional growth. Richard is also a member of ASHRAE, ASPE and CASHE.