Closed Feedwater Heater TTD & DCA Performance Calculator
Calculate feedwater heater Terminal Temperature Difference (TTD), Drain Cooler Approach (DCA), heat duty, and tube fouling diagnostics per HEI standards.
Extraction Steam & Drain Conditions
Feedwater Stream Flow & Temperatures
Diagnostic Health & Thermal Performance
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
What is Terminal Temperature Difference (TTD) in a feedwater heater?
TTD is defined as the saturation temperature of the condensing extraction steam minus the temperature of the feedwater exiting the heater tube bundle: TTD = Tsat - Tout. In condensing-only heaters, typical design TTD is 5°F (2.8°C). In heaters equipped with a desuperheating zone, TTD can approach 0°F or even negative values.
What does Drain Cooler Approach (DCA) signify?
DCA is the temperature difference between the drains (condensate) leaving the subcooler zone and the incoming cold feedwater entering the tube bundle: DCA = Tdrain - Tin. A normal design DCA is 10°F (5.5°C). High DCA values indicate failed liquid level controls, allowing live steam to blow through the subcooler.
How does degraded FWH performance impact overall power plant heat rate?
When an HP feedwater heater degrades by 5°C in TTD, the feedwater enters the economizer colder, requiring the boiler to fire significantly more fuel to produce rated steam. A disabled HP heater can degrade overall cycle heat rate by 1.5% to 3.0%, increasing annual fuel costs by hundreds of thousands of dollars.