Energy content per pound of water returning to the boiler.
Total electricity generated minus auxiliary loads.
Net Heat Rate:–
Thermal Efficiency:–
Total Heat Input:–
function calculateHeatRate() {
// 1. Get input values
var flow = parseFloat(document.getElementById("steamFlow").value);
var hSteam = parseFloat(document.getElementById("steamEnthalpy").value);
var hFeed = parseFloat(document.getElementById("feedwaterEnthalpy").value);
var powerKW = parseFloat(document.getElementById("powerOutput").value);
// 2. Validate inputs
if (isNaN(flow) || isNaN(hSteam) || isNaN(hFeed) || isNaN(powerKW)) {
alert("Please enter valid numerical values for all fields.");
return;
}
if (powerKW <= 0) {
alert("Power output must be greater than zero.");
return;
}
if (hSteam <= hFeed) {
alert("Main Steam Enthalpy must be greater than Feedwater Enthalpy.");
return;
}
// 3. Perform Calculations
// Heat Input (Q) = Mass Flow * (H_steam – H_feedwater)
// Result is in BTU/hr
var heatInputBTUHr = flow * (hSteam – hFeed);
// Heat Rate = Heat Input (BTU/hr) / Power Output (kW)
// Result is in BTU/kWh
var heatRate = heatInputBTUHr / powerKW;
// Thermal Efficiency (%) = 3412.14 / Heat Rate * 100
// (3412.14 is the BTU equivalent of 1 kWh)
var efficiency = (3412.14 / heatRate) * 100;
// Convert Heat Input to MMBtu/hr for easier reading (Million BTUs)
var heatInputMMBtu = heatInputBTUHr / 1000000;
// 4. Display Results
var resultDiv = document.getElementById("resultSection");
resultDiv.style.display = "block";
document.getElementById("resHeatRate").innerText = heatRate.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0}) + " BTU/kWh";
document.getElementById("resEfficiency").innerText = efficiency.toFixed(2) + "%";
document.getElementById("resHeatInput").innerText = heatInputMMBtu.toFixed(2) + " MMBtu/hr";
}
Understanding Steam Turbine Heat Rate
In power generation thermodynamics, the Heat Rate is the primary metric used to evaluate the efficiency of a steam turbine and the associated thermal power plant. Unlike "efficiency" where a higher percentage is better, Heat Rate measures the energy input required to produce one unit of electrical output. Therefore, a lower Heat Rate indicates a more efficient system.
The calculation is fundamentally an expression of the Rankine cycle's performance. It determines how many British Thermal Units (BTU) of thermal energy from the fuel or steam are consumed to generate one kilowatt-hour (kWh) of electricity.
The Formula
The Net Plant Heat Rate (NPHR) is calculated using the following logical steps based on the conservation of energy:
Heat Input (BTU/hr): This is the energy absorbed by the working fluid (water/steam). It is calculated as: Mass Flow × (Main Steam Enthalpy - Feedwater Enthalpy)
Heat Rate (BTU/kWh): This normalizes the input over the electrical output: Heat Input (BTU/hr) / Net Power Output (kW)
Thermal Efficiency (%): This converts the heat rate into a percentage: (3412.14 / Heat Rate) × 100
Input Parameters Explained
To get an accurate calculation, precise thermodynamic properties are required:
Main Steam Flow (lb/hr): The mass of steam flowing into the high-pressure turbine inlet per hour.
Main Steam Enthalpy (BTU/lb): The total heat content of the steam entering the turbine. This is a function of pressure and temperature (e.g., steam at 2400 psig and 1000°F has a specific enthalpy found in steam tables).
Feedwater Enthalpy (BTU/lb): The heat content of the water returning to the boiler or steam generator. This energy represents what the cycle "recycles," reducing the new heat needed.
Net Power Output (kW): The electrical power supplied to the grid. For "Net" heat rate, this should subtract the plant's internal auxiliary power usage (pumps, fans, lighting).
Typical Values
Heat rates vary significantly based on the technology and age of the power plant:
Nuclear Power Plant: 10,000 – 10,500 BTU/kWh (Lower thermal efficiency due to lower steam temperatures).
Why Use a Heat Rate Calculator?
Power plant operators and performance engineers use these calculations daily to monitor degradation in the turbine blades, condenser performance issues, or boiler inefficiencies. An increase in Heat Rate (e.g., rising from 9,500 to 9,800 BTU/kWh) signals a problem that increases fuel costs and emissions.