Work it out.
Calculators
District heating output from flow and cooling
Q = m·c·ΔT
Tank volume (vertical cylinder)
Geometry
Ohm's law and electric power
Ohm's law
Test pressure for pressure testing a pipeline
DS 469 / AT-vejledning B.4.2
Legionella safety margin for hot water
DS 439 / Sundhedsstyrelsens legionella-vejledning
Water hardness: °dH to mg/l and mmol/l
Hårdhedsskala (°dH) – dansk vandværkspraksis
Pressure: bar to metres of water column
Fysik: p = ρ·g·h
The pump's hydraulic power
Grundfos Ecademy – hydraulisk pumpeeffekt
Natural gas: consumption to energy content and cost
Energinet – nedre brændværdi 11 kWh/m³
Wood pellets: quantity for energy content
Biobrændselsforeningen – brændværdi træpiller
Water loss in the distribution network (NRW)
DANVA / Miljøstyrelsens vandtabs-benchmarking
District heating: cooling bonus or penalty
Eksempel: afkølingstarif — 1% pr. °C (motivationstarif)
Boiler efficiency
Termodynamik: η = P_afgivet / P_indfyret
Voltage drop in a copper cable
DS/HD 60364-5-52 anneks G (via elinstallationsbekendtgørelsen) / kobbers resistivitet
Short-circuit current (simplified)
Forenklet kortslutningsberegning (jf. DS/EN 60909-princip)
Short circuit at the end of a supply cable
DS/EN 60909-0: voltage factor c_min = 0.95 and conductors at 80 °C · technical annex: short-circuit power and cable sizing
Transformer: rated current and short-circuit current
IEC 60076-1 and -5 (short-circuit voltage uk) · technical annex: transformer stations and short-circuit power
Cable on reel: length and weight
Geometric drum formula (layers × turns × mean circumference) · technical appendix: choice of cable and material for task
Tools that work in all subjects
Whatever your programme is called, these tools calculate the same — Pythagoras, area, percentages and units are not tied to one trade.
- Pythagorasa² + b² = c²Find the missing side, set out a right angle, check whether a room is square, and find the space diagonal.
- Area and perimeterm²Rectangle, triangle, trapezium, circle and composite shapes — area and perimeter.
- Volume and surface aream³ · lBox, cylinder, cone, sphere, pyramid, prism, pipe and frustum — also in litres.
- Percent%Percentage of, how many per cent, percentage change, discount and VAT.
- Scale and ratios1 : 50From drawing to reality, area and volume to scale, the rule of three and dividing in a ratio.
- Unit convertermm ↔ mFrom mm to km, Pa to bar and kB to GB — with the unit staircase.
- Time calculations and the clockt : minTime between two clock times, add time, and 1.75 h = 1 h 45 min for the timesheet.
- Slope and fall% · ° · 1:xFall from level to level, in per cent, per mille, degrees and mm per metre — and the height difference.
- Material consumption including wastem² + %Boards, paint, battens at c/c spacing and packs — for a composite surface or a whole room, with waste.