Calculate Gross and Net Heat Rate and Thermal Efficiency
Megawatts (MW)
Megawatts (MW)
Mass per Hour (lbs/hr)
Energy per Mass (Btu/lb)
Net Power Output:–
Total Heat Input:–
Net Plant Heat Rate (NPHR):–
Thermal Efficiency:–
function calculateHeatRate() {
// 1. Get Input Values
var grossMW = parseFloat(document.getElementById('phr_gross_gen').value);
var auxMW = parseFloat(document.getElementById('phr_aux_power').value);
var fuelFlow = parseFloat(document.getElementById('phr_fuel_flow').value);
var hhv = parseFloat(document.getElementById('phr_hhv').value);
// 2. Validation
if (isNaN(grossMW) || isNaN(auxMW) || isNaN(fuelFlow) || isNaN(hhv)) {
alert("Please enter valid numerical values for all fields.");
return;
}
if (auxMW >= grossMW) {
alert("Auxiliary power cannot exceed or equal Gross Generation.");
return;
}
// 3. Calculation Logic
// Calculate Net Power in MW and convert to kW (1 MW = 1000 kW)
var netMW = grossMW – auxMW;
var netKW = netMW * 1000;
// Calculate Total Heat Input per hour (Btu/hr)
// Formula: Flow (lbs/hr) * HHV (Btu/lb)
var heatInputBtuHr = fuelFlow * hhv;
// Calculate Heat Rate (Btu/kWh)
// Formula: Total Heat Input (Btu/hr) / Net Power Output (kW)
var heatRate = heatInputBtuHr / netKW;
// Calculate Thermal Efficiency (%)
// Constant 3412.14 is the thermal equivalent of 1 kWh in Btu
var efficiency = (3412.14 / heatRate) * 100;
// 4. Formatting and Display
document.getElementById('phr_res_net_power').innerHTML = netMW.toFixed(2) + " MW";
// Format large numbers with commas
document.getElementById('phr_res_heat_input').innerHTML = heatInputBtuHr.toLocaleString('en-US', {maximumFractionDigits: 0}) + " Btu/hr";
document.getElementById('phr_res_heat_rate').innerHTML = heatRate.toLocaleString('en-US', {maximumFractionDigits: 0}) + " Btu/kWh";
document.getElementById('phr_res_efficiency').innerHTML = efficiency.toFixed(2) + "%";
// Show result div
document.getElementById('phr_results_area').style.display = "block";
}
Understanding Plant Heat Rate
In the power generation industry, the Heat Rate is the metric used to measure the thermal efficiency of a power plant. Unlike "efficiency" percentages where a higher number is better, Heat Rate measures how much fuel energy is required to produce 1 unit of electricity. Therefore, a lower Heat Rate represents higher efficiency.
How is Heat Rate Calculated?
The calculation determines the thermal energy input relative to the electrical energy output. The standard engineering formula for Net Plant Heat Rate (NPHR) is:
Heat Rate (Btu/kWh) = [Fuel Flow (lbs/hr) × Heating Value (Btu/lb)] / Net Generation (kW)
Key Components:
Gross Generation: The total electricity produced by the generator terminals.
Auxiliary Power (House Load): The electricity consumed by the plant's own pumps, fans, and lighting. This must be subtracted to find the Net Generation.
Heating Value (HHV): The energy density of the fuel used (e.g., Coal, Natural Gas, Diesel).
Converting Heat Rate to Efficiency
To convert the Heat Rate into a standard percentage efficiency, we use the thermal equivalent of electrical energy. One kilowatt-hour (kWh) of electricity is physically equivalent to 3,412 British Thermal Units (Btu).
Thermal Efficiency (%) = 3412 / Heat Rate × 100
Typical Industry Benchmarks
Different technologies have different expected heat rates:
Combined Cycle Gas Turbine (CCGT): ~6,000 to 7,000 Btu/kWh (Very Efficient)
Supercritical Coal Plant: ~8,800 to 9,500 Btu/kWh
Subcritical Coal Plant: ~9,500 to 10,500 Btu/kWh
Simple Cycle Gas Turbine (Peaker): ~9,500 to 11,000 Btu/kWh
Monitoring heat rate is crucial for power plant economics. As fuel is the largest operating cost, even a minor reduction in heat rate (improvement in efficiency) can result in significant financial savings and reduced carbon emissions per megawatt produced.