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§ 15

Grundlast: strommen der lober, nar I er gaet hjem

How much power do we use when not working, and what does it cost per year?

Answer: The fastest measurement on an energy course: read the electricity meter when the last person leaves, and again when the first person arrives. What is used between is the base load: ventilation, compressors, cooling, servers, lighting and machines on standby. The calculator finds the base load in kW and multiplies it by the hours per year when the company is closed. You enter your own readings and your own electricity price.

Formula

Grundlast (kW) = (aflæsning ved åbning − aflæsning ved lukning) ÷ timer imellem

Forbrug uden for drift = grundlast × lukkede timer pr. år

Udgift = forbrug × elpris

Closed hours: a year has 8,760 hours. 1 shift on weekdays (approx. 2,000 hours running) gives approx. 6,700 closed hours

Symbols and units in the formula
SymbolMeaningUnit
kwh_lukningMeter reading at closurekWh
kwh_aabningMeter reading at openingkWh
timer_maaltHours between the two readingstimer
lukkede_timer_aarHours per year when you are closedtimer/år
elprisYour electricity price (from your electricity bill)kr./kWh
=GrundlastkW
=Consumption outside operating hours per yearkWh/år
=Expenditure outside operating hours per yearkr./år
=Saving if basic load is halvedkr./år

Validity and source

Source
Energy review according to SparEnergi/Energy Agency method: read the metre outside operating hours

Does not apply when

  • Measure a normal night, not a night when a wash, charging or frost protection runs that otherwise wouldn't. If you have hourly readings from the electricity company or Eloverblik.dk, you can read the base load directly from the curve at night. Use electricity price without VAT if the company can deduct VAT.

Worked example

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

Substituted

  • Meter reading at closure48,210 kWh
  • Meter reading at opening48,322 kWh
  • Hours between the two readings14 timer
  • Hours per year when you are closed6,000 timer/år
  • Your electricity price (from your electricity bill)1.60 kr./kWh

Giver

  • Grundlast8.00 kW
  • Consumption outside operating hours per year48,000 kWh/år
  • Expenditure outside operating hours per year76,800 kr./år
  • Saving if basic load is halved38,400 kr./år

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Sådan bruger du den

Energikursets første måling i jeres egen virksomhed: hvad bruger I, når ingen er der? Grundlasten kan være en stor del af elregningen, og meget af den kan slukkes uden at nogen mærker det.

Step by step

  1. Aflæs elmåleren, når sidste mand går, og skriv klokkeslættet.
  2. Aflæs igen, når første mand kommer.
  3. Skriv timerne imellem og de lukkede timer i et år: 8.760 minus driftstimerne.
  4. Aflæs grundlasten og udgiften. Gå så en runde om natten og find det, der står og summer.

Typical errors

  • At måle en nat, hvor noget særligt kørte, fx opladning af trucks.
  • At glemme weekender og ferier i de lukkede timer.
  • At aflæse en måler, der kun dækker en del af bygningen.

Examples from everyday life

Smedeværksted en almindelig nat

Måleren viser 48.210 kWh kl. 16 og 48.322 kWh kl. 6 næste morgen, 14 timer. Værkstedet er lukket ca. 6.000 timer om året, og elprisen er 1,60 kr.

Meter reading at closure
48,210 kWh
Meter reading at opening
48,322 kWh
Hours between the two readings
14 hours
Hours per year when you are closed
6,000 timer/år
Your electricity price (from your electricity bill)
1.6 kr./kWh

It means: Grundlasten er 8 kW. Det giver 48,000 kWh/year og 76,800 kr./år, mens ingen arbejder. Halveres grundlasten, sparer I 38,400 kr./år. Trykluft og udsugning er de første at tjekke.

Lille kontor over en weekend

Et rengøringsfirmas kontor aflæses fredag kl. 16 (12.040 kWh) og mandag kl. 6 (12.052 kWh), 62 timer. Kontoret er lukket ca. 6.700 timer om året.

Meter reading at closure
12,040 kWh
Meter reading at opening
12,052 kWh
Hours between the two readings
62 hours
Hours per year when you are closed
6,700 timer/år
Your electricity price (from your electricity bill)
1.6 kr./kWh

It means: Grundlasten er 0.19 kW, altså 1,297 kWh/year og 2,075 kr./år. Det er printere, netværk og køleskab. Her er gevinsten lille, men en stikdåse med afbryder er gratis.

Rule of thumb

1 kW der står tændt døgnet rundt, koster ca. 14.000 kr om året ved 1,60 kr/kWh.

How to check the answer

Grundlasten må ikke være højere end jeres gennemsnitlige forbrug i arbejdstiden. Er den det, er aflæsningerne byttet om.