Airflow conversion
Convert volumetric airflow between cubic feet per minute and litres per second.
1 CFM = 0.4719 L/s
Q (L/s) = Q (CFM) × 0.4719
Q (CFM) = Q (L/s) × 2.1189
Q (CFM) = Q (L/s) × 2.1189
BEI 5.5 / TECHNICAL REFERENCE
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A searchable collection of fundamental equations, unit relationships and concise technical notes across HVAC, plumbing and mechanical engineering. Use these references to support learning and preliminary checks—not as a substitute for project-specific design.
Air changes per hour
Relates room volume, air-change rate and volumetric airflow.
Q = ACH × V / 3600
Q in m³/s; V in m³; ACH in h⁻¹. For m³/h, use Q = ACH × V. Outdoor-air requirements must be determined separately using applicable standards and occupancy criteria.
Sensible heat transfer
Estimate sensible heat transfer for a moving air stream when mass flow and temperature difference are known.
Q̇ = ṁ × cₚ × ΔT
Q̇ in W; ṁ in kg/s; cₚ in J/(kg·K); ΔT in K or °C difference. This is not a complete room cooling-load method.
Average pipe velocity
Calculate average velocity from volumetric flow rate and internal pipe area.
v = Q / A = 4Q / (πD²)
Use Q in m³/s and internal diameter D in m to obtain v in m/s. Do not substitute nominal pipe size for actual internal diameter.
Rectangular tank volume
Determine gross geometric volume of a rectangular tank.
V = L × W × H
Dimensions in metres produce volume in m³. Convert using 1 m³ = 1,000 L. Excludes freeboard, dead storage and unusable volume.
Volumetric flow rate
Relates average velocity to the cross-sectional area of a full-flow pipe.
Q = A × v
For circular pipe, A = πD²/4. This equation alone is not a drainage sizing or partially-full pipe model.
Reynolds number
Dimensionless ratio used to characterize inertial and viscous effects in internal flow.
Re = ρvD / μ
ρ in kg/m³; v in m/s; D in m; μ in Pa·s. Flow-regime thresholds depend on geometry and conditions; transitional flow should not be treated as a sharp universal boundary.
Pump system head
Conceptual sum of static, friction, minor-loss and pressure head components.
Hₜ = Hₛ + H𝒻 + Hₘ + Δp/(ρg)
Use consistent units and system boundaries. Actual pump selection also requires the system curve, flow requirement, fluid properties, efficiency and manufacturer performance data.
Darcy–Weisbach equation
Estimate straight-pipe friction head for steady, full-pipe flow.
h𝒻 = f (L/D) (v²/2g)
f is the Darcy friction factor. Confirm whether a supplied factor is Darcy or Fanning. Fittings and valves require additional minor-loss treatment.
Pressure head
Express pressure difference as an equivalent column height of fluid.
hₚ = Δp / (ρg)
Δp in Pa; ρ in kg/m³; g in m/s². The result is metres of the specified fluid, not automatically metres of water.
Mechanical power
For translational motion, power is the rate of doing work.
P = F × v
P in W when force F is in N and velocity v is in m/s. For rotating shafts, P = Tω, where T is torque in N·m and ω is angular speed in rad/s.
Temperature relationships
Convert temperature values and distinguish absolute temperature from temperature difference.
K = °C + 273.15
°F = (°C × 9/5) + 32
°F = (°C × 9/5) + 32
A temperature difference of 1°C equals a difference of 1 K. Absolute temperatures require the offset.
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QUICK TOOL / UNIT CONVERSION
Convert common engineering units.
A small utility for common conversions. Select a conversion type and enter a value.
100 CFM = 47.1947 L/s
Reference factors used: 1 CFM = 0.471947 L/s; 1 m³ = 1,000 L; 1 refrigeration ton = 3.51685 kW; 1 kPa = 1,000 Pa. Results are rounded for display.
Engineering use notice. These references are educational aids and preliminary calculation support. They are not a substitute for applicable Philippine laws and codes, project specifications, manufacturer data, verified design criteria, or review by a qualified professional. Confirm units, assumptions, fluid properties, boundary conditions and safety factors before applying any result to real work. No code-compliance claim is made by this page.