Technical Fundamentals and Applied Technology
Core concepts
Building-services engineering requires fluency in Ohm's law (U = I·R), electrical power (P = U·I, three-phase P = √3·U·I·cos φ), and protective measures (Schutzklassen, FI/RCD 30 mA, TN-S vs. TT systems). Know basic hydraulics: pressure, flow, pump curves, and the relationship between Druckverlust and pipe diameter. Understand heat output Q = ṁ·c·ΔT and COP for heat pumps. Familiarity with ÖNORM EN 12831 (heating load) and ÖNORM B 2538 helps.
Traps
Questions mix single-phase and three-phase formulas, or forget cos φ. Another trap: assuming a larger RCD trip current is acceptable - 30 mA is standard for socket circuits. Watch units: kW vs. kWh vs. kJ.
Worked example
Three-phase motor: U = 400 V, I = 10 A, cos φ = 0.85. P = √3 × 400 × 10 × 0.85 ≈ 5,889 W ≈ 5.9 kW. Rule of thumb: without cos φ you overestimate power by ~15% at 0.85.
Rule of thumb
For water heating: Q [kW] = flow [l/s] × 4.19 × ΔT [K].