Information about clothes

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Usage of energy in laundries

In laundries, energy is necessary to generate process heat (steam, hot water). Energy sources are gas, electricity and fuel oil (extra light) and fuel oil (heavy: S). gas and electricity are used for

  • direct machine heating as well as for
  • indirect application to heat transfer media

Heavy fuel oil is normally applied in industrial plants only due to complex legal requirements for its application

The following processes require process heat:

  • washing
  • drying
  • calendering
  • ironing, pressing, finishing

Distribution of energy in laundries

Distribustion energy laundry.png

Energy consumption of the different processes

General data in MJ of energy per kg of dry textile:

  • Washing (washer extractors) : 2,7 MJ/kg
  • Washing (tunnel washer) : 1,8 MJ/kg
  • Tumble drying (Gas) : 2,7 MJ/kg
  • Tumble drying (Steam) : 4,7 MJ/kg
  • Ironing (Steam) : 4,5 MJ/kg
  • Tunnel Finisher (Gas) : 2,5 MJ/kg
  • Tunnel Finisher (Steam) : 3,0 MJ/kg

Energy sources in laundries

Energy sources.png

High pressure steam:

Steam pressure > 1,0 bar, usually: 8 -12 bar (above atmospheric pressure), temperatures: 175 - 191 °C

Steam characteristics

  • high heat capacity
  • excellent transfer capacity
  • constant efficiency at max. power

Application technology

+ direct steam flow (washing and steam process, therefore short heating up of heating washing liquor)

+ high efficiency (economic)

+ reserve at high peaks of consumption (big boiler)

- high acquisition costs

- inspection by legislation required

Low pressure steam:

Steam pressure 0,5 - 1,0 bar, usually: 0,5 bar (above atmospheric pressure), temperatures: max. 120 °C

Steam characteristics

  • high heat capacity
  • excellent transfer capacity

Application technology

+ short heating up intervals

+ simple handling and maintenance

+ low acquisition costs

+ no legal requirement of inspection (TÜV),registration of boiler only

- temperature max. 120 ºC, therefore inapplicable for mangles, tumblers, presses etc.

Heat supply in small laundries

Local supply (heating)

  • Individual heating of each machine
  • for laundries at a capacity of up to 500 kg textiles/day
  • Gas or electricity (prerequisite: local favourable fees)
  • Advantage of individual heating: flexible usage of resources dependent on amount of textiles
  • Economical: no higher use of energy than required
  • Efficient and environmentally friendly

Small laundry.png

Heat supply in industrial laundries

Central supply

  • for laundries at a capacity of more than 500 kg laundry
  • most important medium is steam, sometimes hot water or thermal oil
  • Advantage: distribution of heating medium constantly possible as well as the possibility of direct heating of the washing liquor
  • Performance of steam generator is very important
  • At high utilization, all machines may require heating energy at same time -> boiler should be capable to supply all machines with enough steam,even at high production peaks

Steam boiler.png

Measures to reduce energy consumption

Organisational measures: concerning work processes

  • Sorting of textiles: cotton, linen, coloureds, wool
  • Intelligent combination of washing programmes: Temperatures/energy demand for heating, time for the washing cycles, time for loading and unloading,
  • Avoid overload (check weight), high rejects require another washing cycle
  • Work processes shall be organized in a way that steam generator can deliver constantly
  • Steam consumption shall be continuously all over the day
  • Avoidance of “steam spikes” = shifted start of machines

Technical measures: can be influenced at the laundry (e.g. washing program)

The Sinner's Circle describes the main influences of the washing process. Temperature is related to thermal energy demand.


Temperature reduction can be compensated by

  • Low temperature washing (more chemistry, more mechanics)
  • Reduction of liquor ratio (higher mechanics)
  • Optimization of washing times (prolonged time)

Optimization of steam generation

  • High efficiency (constantly monitoring of CO2 – concentration)
  • Optimal burner-adjustment (soiled heating surfaces decrease heating efficiency)
  • Thorough deaeration of heat exchangers
  • Functionality check of all steam traps
  • Re-usage of condensate
  • Installation free from leakages
  • Isolation of steam pipes (to avoid waste heat)

Application of low-pressure steam (2 to 4 bars)

  • Economical more efficiently than high-pressure steam (10 to 16 bars)
  • Application possible for heating of water for steam for finisher process only
  • BUT: Mangling and drying require high-pressure steam or gas

Waste heat recovery by heat exchangers:

  • waste water of the washing process
  • waste water of the drying process
  • waste water of the finishing process

Re-usage of washing liquor


  • Saving of water and saving of energy
  • Nowadays common process design in tunnel washers
  • Application also possible in washer extractors
  • Rinsing baths collected in tanks
  • Application of gathered rinsing liquor in next pre- or main wash
  • Pumping of liquor by exploitation of height differences into machines


  • Storage demand for tanks
  • Technological complex, e.g. pumps, valves
  • Isolation of tanks necessary
  • Lint generation (filter systems shall avoid carry-over into next compartment)
  • Particularly problematic if there will be linen/white laundry after coloured laundry (should be avoided even with filter systems)

Low temperature washing

  • Increased mechanics and/or chemistry necessary
  • Heating energy can be saved
  • Adapted detergents necessary (special ingredients such as PAP)
  • Higher prices of those special detergents
  • Washing efficiency as well as optimal action of chemicals may be decreased
  • Application of low-temperature process shall be individually adapted for each laundry

Reduction of liquor ratio at increased mechanics

  • In practice often too high liquor ratios because of defective measuring and controlling devices, process controlling “by hand” and no consideration of load
  • Low liquor ratios enable energy savings without decreased washing efficiency
  • exceptions: blended fibres, mechanically sensitive textiles (wool), heavily soiled textiles, incontinence goods, PES/CO blended fibres tend to crumple

Optimization of washing times

  • Optimisation of time also leads to energy saving
  • Processes with shorter residence times: higher temperatures or higher machine power/mechanical agitation
  • BUT: Washing efficiency may decrease

Technological measures: concerning the construction of machinery


  • Adequate dimensioning and form of paddles (also see module 2)
  • Adjustment of revolutions per minute to achieve g-factors of about 0,7 g (also see module 3)
  • Rotating drum revolutions instead of oscillating
  • Reverse rhythms
  • Longer running times/shorter idle times (e.g. running times 12s, idle time 2s) cause more intensive mechanics than short running times/long idle times (gentle wash)
  • Low liquor ratios
  • One bath: Without pre-wash and/or wetting
  • 60°C – washing process: Alternation of thermal disinfection by chemical-thermal
  • Intermediate spin: high number of revolutions per minute between rinsing baths -> Heating energy demand for drying and demand of rinsing water will decrease
  • Reduce residual moisture: by higher dewatering power


Adapted air circulation

  • Low waste air
  • Fresh air/recycled air
  • Circulation through textiles (crosswise)

Adapted controlling of drying time

  • Controlling by time (disadvantageous, because in practice mostly overdrying)
  • Controlling by moisture (measurements of temperature difference in waste heat)
  • IR textile- and surface temperature measurement

Gas heating

Active environmental protection:

Optimize energy consumption by

  • Burner optimization
  • Use of adapted burners
  • Reduced washing temperatures
  • Optimized washing mechanics (without negative influence on washing performance as well as life cycle of textiles!)

Passive environmental protection:

Reduce energy consumption by

  • Technical measures to reduce energy consumption
  • Application of heat exchangers to reduce temperature of effluent water


Leonardo da Vinci project Laundry Sustainability