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§ 18

Cabin energy and CO₂ per task

How much energy and CO₂ does one coating in the cabin cost?

Answer: Most of the cabin's energy goes into heating air. During the spray phase it is fresh air that must reach spray temperature, and during the dry phase the air must reach dry temperature, but much of it is recirculated. The calculator works out the energy for one task in each phase, the price and CO₂ emissions with the emission factor you enter for your energy source. It is used when you plan multiple cars per drying, calculate the cost per task or make the company's ESG report. Air volume and recirculation are in the cabin's documentation.

Formula

Varmeeffekt (kW) = luftmængde (m³/h) × 0,34 × temperaturløft ÷ 1000

Spray phase: all air is fresh. Dry phase: only (1 − recirculation) needs heating from outdoor temperature

Energi (kWh) = effekt × tid i timer

Naturgas: ca. 56-57 kg CO₂ pr. GJ (Energistyrelsens standardfaktor) ≈ 0,204 kg pr. kWh brændværdi. For el og fjernvarme bruger du leverandørens eller Energistyrelsens aktuelle faktor

Symbols and units in the formula
SymbolMeaningUnit
luftmaengdeCabin air volumem³/h
sproejte_minInjection time per taskmin
delta_sproejtTemperature rise in spray phase (outside → booth)°C
toerre_minDrying time per jobmin
delta_toerreTemperature rise in drying phase (outside → drying temperature)°C
recirk_pctRecirculation in the drying phase%
energiprisEnergy pricekr/kWh
co2_faktorEmission factor for your energy sourcekg CO₂/kWh
=Energy per taskkWh
=Heraf sprojtefasenkWh
=Heraf torrefasenkWh
=Energy price per taskkr
=CO₂ per taskkg

Validity and source

Source
Fysik: luftens varmekapacitet ca. 0,34 Wh/(m³·K) · CO₂ = energi × emissionsfaktor

Does not apply when

  • Estimate without burner efficiency, heating of cabin walls and the car itself and without fan electricity. Burner loss comes on top, see burner's data. Heat recovery in the spray phase can be calculated by lowering the temperature rise.

Worked example

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

Substituted

  • Cabin air volume25,000 m³/h
  • Injection time per task30 min
  • Temperature rise in spray phase (outside → booth)15 °C
  • Drying time per job40 min
  • Temperature rise in drying phase (outside → drying temperature)55 °C
  • Recirculation in the drying phase80 %
  • Energy price0.90 kr/kWh
  • Emission factor for your energy source0.20 kg CO₂/kWh

Giver

  • Energy per task126 kWh
  • Heraf sprojtefasen64 kWh
  • Heraf torrefasen62 kWh
  • Energy price per task113 kr
  • CO₂ per task25.7 kg

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Sådan bruger du den

Kabinen er værkstedets største energiforbruger, og det meste går til at varme luft. Beregneren regner energien for én opgave i sprøjtefasen og tørrefasen, prisen og CO₂-udledningen. Brug den når du regner omkostning pr. opgave, overvejer flere biler pr. tørring, eller laver virksomhedens ESG-opgørelse.

Step by step

  1. Find luftmængden.
  2. Tast tider og temperaturløft.
  3. Tast recirkulation i tørrefasen.
  4. Tast pris og emissionsfaktor.

Typical errors

  • At glemme recirkulationen.
  • At bruge en forkert emissionsfaktor.
  • At glemme brænderens tab.

Examples from everyday life

En personbil i efteråret

Kabinen flytter 25.000 m³/h. Sprøjtefasen er 30 min med 15 graders løft, tørrefasen 40 min med 55 grader og 80 % recirkulation.

Cabin air volume
25,000 m³/h
Injection time per task
30 min
Temperature rise in spray phase (outside → booth)
15 °C
Drying time per job
40 min
Temperature rise in drying phase (outside → drying temperature)
55 °C
Recirculation in the drying phase
80 %
Energy price
0.9 kr/kWh
Emission factor for your energy source
0.204 kg CO₂/kWh

It means: Opgaven bruger 126 kWh, heraf 64 kWh i sprøjtefasen og 62 kWh i tørrefasen. Det koster 113 kr og udleder 25.7 kg CO₂.

Samme opgave om vinteren

Om vinteren er løftet 25 grader i sprøjtefasen og 65 i tørrefasen.

Cabin air volume
25,000 m³/h
Injection time per task
30 min
Temperature rise in spray phase (outside → booth)
25 °C
Drying time per job
40 min
Temperature rise in drying phase (outside → drying temperature)
65 °C
Recirculation in the drying phase
80 %
Energy price
0.9 kr/kWh
Emission factor for your energy source
0.204 kg CO₂/kWh

It means: Energien stiger til 180 kWh og prisen til 162 kr.

Rule of thumb

Uden recirkulation ville tørrefasen koste flere gange så meget som sprøjtefasen. Recirkulationen er den største besparelse.

How to check the answer

Sprøjtefase + tørrefase skal give energien pr. opgave.