Question 1

How do I calculate torque from horsepower?

Accepted Answer

Torque (Nm) = Power (W) / Angular Velocity (rad/s), or Torque (lb·ft) = (HP × 5252) / RPM. For example, a 10 HP motor at 1750 RPM produces: T = (10 × 5252) / 1750 = 30 lb·ft = 40.7 Nm.

Question 2

How do I size an HVAC duct using the equal friction method?

Accepted Answer

The equal friction method maintains constant pressure loss per unit length (typically 0.1 in.w.g./100 ft or 0.8 Pa/m). Duct size is found from: Q = A × V, where Q is airflow (CFM or m³/h) and V is velocity (typically 1,000–2,500 FPM for supply air). Use our HVAC Duct Sizing Calculator for instant results per ASHRAE standards.

Question 3

What is the formula for pipe flow velocity?

Accepted Answer

Pipe flow velocity V = Q / A, where Q is volumetric flow rate (m³/s or GPM) and A is pipe cross-sectional area (m² or ft²). For a standard pipe: V = 4Q / (π × D²). Reynolds number Re = ρVD/μ determines flow regime (laminar <2300, turbulent >4000).

Question 4

How do you calculate bearing L10 life?

Accepted Answer

Bearing L10 life = (C/P)^p × (10⁶/60n) hours, where C is dynamic load rating (kN), P is equivalent dynamic bearing load (kN), p is 3 for ball bearings or 10/3 for roller bearings, and n is rotational speed (RPM). This gives the life at which 90% of bearings will survive.

Question 5

How do I calculate heat load for a room (HVAC)?

Accepted Answer

Heat load Q = U × A × ΔT for conduction through walls, plus solar gain, occupancy (75W sensible per person), lighting (10 W/m²) and equipment loads. Per ASHRAE, total cooling load = sensible + latent loads. Use our Heat Load Calculator for full Manual J-style calculations.

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