Commonly Used Heat Unit Conversions for Boilers

Common thermal units include kW/MW, kcal/h, t/h (evaporation rate), BHP, RT, etc. The following is the unit conversion relationship of these units.

​​I. Boiler Capacity Units​​

1. ​​Evaporation Capacity (Steam Boilers)​​
   • ​​Definition​​: Mass of steam produced per hour, denoted as ​​D​​.
   • ​​Units​​: Tonnes per hour (​​t/h​​) or kilograms per hour (kg/h).
   • ​​Rated Evaporation​​: Design steam output under specified fuel/parameters (nameplate value).
2. ​​Heat Supply Capacity (Hot Water Boilers)​​
   • ​​Definition​​: Effective heat output per hour, denoted as ​​Q​​.
   • ​​Units​​: Megawatts (​​MW​​), kilowatts (kW), or 10⁴ kcal/h.

​​II. Common Thermal Units​​

1. ​​Kilocalorie (kcal)​​
   • ​​Definition​​: Heat required to raise 1 kg of water by 1°C (≈ 4.18 kJ).
   • ​​Application​​: Widely used in China for boiler heat load (e.g., “600,000 kcal/h boiler”).
2. ​​Megawatt/Kilowatt (MW/kW)​​
   • ​​Definition​​: International standard power units (1 MW = 1,000 kW).
   • ​​Application​​: Rated power for hot water boilers and large power plants.
3. ​​Boiler Horsepower (BHP)​​
   • ​​Definition​​: Capacity to evaporate ​​34.5 lb/h​​ (≈15.65 kg/h) of water at 212°F (100°C).
   • ​​Application​​: Labeling for imported boilers (often marked as ​​at 212°F​​).
4. ​​British Thermal Unit (BTU)​​
   • ​​Definition​​: Heat required to raise 1 lb of water by 1°F (≈ 1,055 J).
   • ​​Application​​: Fuel calorific value and emissions in North American boilers.

​III. Core Conversion Relationships​​

Key equivalents for low-pressure saturated steam boilers:

​​Note​​: The 1 t/h = 0.7 MW benchmark may vary ±5% due to steam parameters (pressure, temperature).

​​IV. Boiler Horsepower (BHP) Details​​

Critical clarifications for imported equipment:

• ​​vs. Mechanical Horsepower (HP)​​:
  • 1 Mechanical HP = 0.745 kW (for motors/pumps).
  • 1 BHP = 9.81 kW (thermal boilers).
• ​​BHP → Evaporation​​:
  • 1 BHP = 0.01565 t/h (steam).

  Derivation: Evaporating 34.5 lb water requires ≈ 34.5 × 970 BTU (latent heat) ≈ 33,465 BTU/h ≈ 9.81 kW.

​​V. Application Notes​​

1. ​​Unit Labeling Differences​​:
   • ​​Domestic Boilers (China)​​: Directly labeled in ​​t/h​​ or ​​MW​​.
   • ​​Imported Boilers​​: May use ​​BHP​​ or ​​”at 212°F”​​; convert via 1 BHP ≈ 15.65 kg/h.
2. ​​Efficiency and Corrections​​:
   • Theoretical conversions assume ​​saturated steam, low-pressure boilers​​. For superheated steam or higher pressures, correct outputs using enthalpy values.
   • Boiler efficiency (η) affects output:
     • Gas boilers: η ≈ 82–87%.
     • Coal-fired boilers: η ≈ 75–80%.
3. ​​Design Recommendations​​:
   • Prioritize ​​SI units (MW/kW)​​ to avoid confusion. Verify ​​BHP​​ meaning for imported equipment.
   • Hot water boiler sizing: 1 MW ≈ 1.43 t/h steam equivalent, covering ~12,000 m² residential heating (at 60 W/m²).

​​Summary​​

Boiler units center on ​​evaporation (t/h)​​ and ​​heat supply (MW)​​, supplemented by ​​kcal​​ and ​​BHP​​. Key conversions:

• ​​1 t/h = 0.7 MW = 600,000 kcal/h ≈ 71.3 BHP​​;
• ​​1 BHP = 9.81 kW ≈ 15.65 kg/h evaporation​​.
  Always validate units against steam parameters, efficiency, and regional standards to prevent design errors.