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§ 16

Compressed air: what the leaks cost

How much of the compressor's power goes to leaks, and what does it cost?

Answer: Leaks in compressed air networks are among the largest energy wastes in workshops and production because they flow day and night and can't be heard in the noise. Measuring is easy: when no one is using compressed air (e.g. before morning shift) time how long the compressor runs loaded and unloaded. Everything it delivers then goes to leaks. The calculator finds the leakage share, leakage flow and what it costs in electricity per year. The figures are your own measurements and compressor's type plate.

Formula

Lækageandel = belastet tid ÷ (belastet tid + aflastet tid), målt når ingen bruger luft

Lækageflow = lækageandel × kompressorens ydelse

Elforbrug til lækager = lækageandel × belastet effekt × timer under tryk

Udgift = elforbrug × elpris

Symbols and units in the formula
SymbolMeaningUnit
t_belastetTime loaded in measurement (total)s
t_aflastetTime unloaded/stopped in measurement (total)s
kapacitetCompressor's capacity (type plate)m³/min
effektCompressor's consumed power, loadedkW
driftstimerHours per year when the network is under pressuretimer/år
elprisYour electricity pricekr./kWh
=Leaks' electricity bill per yearkr./år
=Leakage share of compressor capacity%
=Leakage flowm³/min
=Electricity consumption for leaks per yearkWh/år

Validity and source

Source
Idle method for leak measurement (Danish Energy Agency/SparEnergi: compressed air in businesses)

Does not apply when

  • Measure over at least 5–10 load and unload periods so the measurement doesn't depend on when you started the watch. A compressor also uses power unloaded (often 20–40 % of full load), and that part is not included here, so the figure is a conservative estimate. Frequency-controlled compressors cannot be measured this way: use the compressor's power measurement at idle instead.

Worked example

The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.

Substituted

  • Time loaded in measurement (total)90 s
  • Time unloaded/stopped in measurement (total)210 s
  • Compressor's capacity (type plate)3.20 m³/min
  • Compressor's consumed power, loaded22 kW
  • Hours per year when the network is under pressure4,500 timer/år
  • Your electricity price1.60 kr./kWh

Giver

  • Leaks' electricity bill per year47,520 kr./år
  • Leakage share of compressor capacity30.0 %
  • Leakage flow0.96 m³/min
  • Electricity consumption for leaks per year29,700 kWh/år

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Sådan bruger du den

I alle virksomheder med trykluft, fra autoværksteder til produktion. Lækager kan ikke høres i dagslarmen, men de koster strøm hele tiden. Målingen tager et kvarter før morgenskiftet og giver et tal, der overbeviser chefen.

Step by step

  1. Sørg for at alt udstyr er stoppet, men at nettet er under tryk.
  2. Tag tid på kompressoren over mindst 5 cyklusser: hvor længe den er belastet, og hvor længe den er aflastet eller stoppet.
  3. Læg tiderne sammen, og skriv dem ind.
  4. Skriv kompressorens ydelse og effekt fra typeskiltet, timer under tryk pr. år og elprisen.
  5. Aflæs lækageandelen og prisen. Find lækagerne med en ultralydsdetektor eller sæbevand.

Typical errors

  • At måle mens nogen bruger luft. Så bliver lækagen for høj.
  • At tage én enkelt cyklus. Mål over flere, og læg sammen.
  • At måle en frekvensstyret kompressor sådan. Den kører hele tiden, bare langsommere.

Examples from everyday life

Produktionsvirksomhed med 22 kW-kompressor

Før morgenskiftet kører kompressoren belastet i 90 s og aflastet i 210 s over fem cyklusser. Den yder 3,2 m³/min og trækker 22 kW. Nettet står under tryk 4.500 timer om året.

Time loaded in measurement (total)
90 s
Time unloaded/stopped in measurement (total)
210 s
Compressor's capacity (type plate)
3.2 m³/min
Compressor's consumed power, loaded
22 kW
Hours per year when the network is under pressure
4,500 timer/år
Your electricity price
1.6 kr./kWh

It means: Lækagerne æder 30 % af kompressoren, 0.96 m³/min. Det er 29,700 kWh/year, altså 47,520 kr./år. En lækagejagt betaler sig næsten altid.

Autoværksted med lille kompressor

Værkstedets stempelkompressor kører 45 s og står 315 s, når ingen bruger luft. Den yder 1,2 m³/min, trækker 7,5 kW, og nettet er under tryk 2.500 timer.

Time loaded in measurement (total)
45 s
Time unloaded/stopped in measurement (total)
315 s
Compressor's capacity (type plate)
1.2 m³/min
Compressor's consumed power, loaded
7.5 kW
Hours per year when the network is under pressure
2,500 timer/år
Your electricity price
1.6 kr./kWh

It means: Lækageandelen er 12.5 %, og det koster 3,750 kr./år. Lukker I for luften om natten, falder timerne under tryk, og så falder tallet også.

Rule of thumb

Et hul på 3 mm ved 6-7 bar lækker ca. 0,3-0,4 m³/min. Mange net ligger på 20-30 % lækage, et velholdt net under 10 %.

How to check the answer

Lækageflowet må ikke være større end kompressorens ydelse. Andelen skal ligge mellem 0 og 100 %.