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   CO2-based demand control for coach ventilation  evaluated  
The ventilation of confined spaces can be controlled according to demand by using CO2-concentration as an indicator for occupancy. This concept can be applied to railway passenger coaches and saves energy since less outside air has to be heated or cooled to inside temperature.
Technology field: Optimisation of comfort functions
close main section General information
  close sub-section Description
   

The ventilation of confined spaces can be controlled according to demand by using CO2-concentration as an indicator for occupancy. This is realised by a feedback loop involving CO2-sensors and ventilation equipment allowing for power variation.

This principle is applicable to railway coaches:

Most of today's passenger coaches are ventilated according to seating capacity rather than actual demand (number of passengers), resulting in a constant outside air intake of some 20 m3 per hour and seat or 1600 m3 for a 80 seat coach. A CO2-controlled operation may considerably reduce these figures while ensuring air quality. This saves energy since less outside air has to be heated or cooled to inside temperature.

Fields of application

  • Buildings with a high variation of occupancy and high occupancy peaks, such as cinemas, theaters, classrooms, meeting rooms and retail establishments.
  • Railways
close main section General criteria
  close sub-section Status of development: in use
    CO2-based demand-controlled ventilation is used in some limited applications in railways, e.g. in some DB trains such as ICE-T tilting trains, new sleepers and couchettes.
  Time horizon for broad application: 5 - 10 years
    (no details available)
  Expected technological development: basically exploited
   

There is still some improvement potential in sensor technology:

  • DB experience: Shortcomings of today‘s sensors: strong sensor drifting. Frequent calibration required.
  • Complementary sensor for „bad smell“ (VOCs etc.) is desirable but not yet available for railway needs.
    Motivation:
    Energy efficiency
  Benefits (other than environmental): none
    (no details available)
  Barriers: medium
   

General barrier

Passenger comfort: Some experts stress that low CO2 levels alone do not always guarantee good air quality.

Specific barriers for retrofit measure

Technological: A pre-condition for CO2-based demand-controlled ventilation is power-controllable ventilation equipment.

Economic: Retrofit expensive: amortisation not always favourable.
    Success factors:
   

Implementation

Combine installation of CO2-based demand-controlled ventilation with a general energetic retrofit (coach insulation etc) in order to obtain optimum cost-benefit ratio.

Technological

Combine CO2-based demand-controlled ventilation with a complementary sensor for „bad smell“ (VOCs etc.) to form a reliable air quality sensor.
  Applicability for railway segments: high
    Type of traction:  electric - DC, electric - AC, diesel
    Type of transportation:  passenger - main lines, passenger - high speed, passenger - regional lines, passenger - suburban lines
    In principle CO2-based demand-controlled ventilation may be applied in all passenger stock. In new stock, there are no principal barriers and CO2-based demand-controlled ventilation could be set as a requirement. Retrofit of existing stock is an option, but cost-benefit ratio is not always favourable. If hardware conditions (variable ventilation equipment) are not given, refit is especially costly. For old coaches with short residual terms such a measure is usually out of question.
    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: < 5%
  Share of newly purchased stock: < 20%
   

German DB AG: ICE-T tilting trains, new sleepers and couchettes. CO2-based demand-controlled ventilation is part of the specification sheet for new high speed stock.

Dutch NS Reizigers: pilot project involving two trainsets

Swiss SBB: Several refurbished coaches in regular service.
  Market potential (railways): high
    No major barriers are visible that could keep CO2-based demand-controlled ventilation from becoming a standard in passenger stock.
    Example:
   

Refitting of B 20-73 at SBB

SBB refitted the B 20-73 coach with a bundle of energy saving measures (CO2-ventilation, coach insulation etc.). The programme reduced total energy consumption (incl. traction) by 14 % and showed a good cost-benefit ratio.
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: 2 - 5%
  Energy efficiency potential throughout fleet: 1 - 2%
   

Empirical data

  • Measurements on retrofitted trainsets at NS Reizigers yielded annual energy savings of 7250 kWh per coach.
  • Measurements on retrofitted Intercity coaches at SBB yielded energy savings of 14% of total consumption. This impressive figure is not only owed to demand-operated ventilation but rather to a bundle of measures including coach insulation and other.

Estimate of overall potential

No exact data on saving effects as a percentage of total consumption are available. Therefore an estimate of the potential is derived:

According to a rough estimate by DB AG one third of the energy for air-conditioning is needed to climatise fresh air intake. Since demand-operation ideally reduces air intake from the current 100% to actual occupancy ratio, the corresponding energy savings may be up to "100% - occupancy ratio" of this energy, e.g. for a typical occupancy of 40%, the energy saving potential amounts to 60% of the energy needed for fresh air climatisation.

Collecting these figures and taking into account that climatisation is about 20% of total energy consumption of a passenger train, one gets a saving potential of 4 %:

100 % (total consumption) × 0,2 (climatisation energy) × 1/3 (climatisation of fresh air intake)

× 0,6 (saving potential of demand-operated ventilation for typical occupancy) = 4 %

This is a rough estimate of maximum potential and will only be reached (or exceeded) under favourable conditions.

It is obvious that the saving potential is dependent on

  • potential for regions with extreme conditions such as cold winters or hot summers)
  • average occupancy (high potential for low average occupancies)
  Other environmental impacts: neutral
   

 
close main section Economic criteria
  close sub-section Vehicle - fix costs: medium
    For retrofit measure: Due to pronounced differences between air-conditioning technology of rail vehicles, no general figure can be given. The following figure may give an idea: Retrofit measure for demand-operated ventilation of SBB B 20-73 coach in Switzerland caused additional costs of about 14.000 EUROs. However, this is the cost for a dedicated solution realised on one single coach. This figure could be substantially reduced if a larger number of vehicles is refitted.
  Vehicle - running costs: significant reduction
    Reduced energy costs (cf. Energy efficiency potential)
  Infrastructure - fix costs: none
    (no details available)
  Infrastructure - running costs: unchanged
    (no details available)
  Scale effects: medium
    Installation in new stock: some scale effects are to be expected both for CO2 sensors and in railway industry if the application becomes a standard in railway coaches. Retrofit: Some minor scale effects may come from dropping prices of sensor equipment. Due to the heterogeneity of stock, the retrofit measure will be specific to some extent for every vehicle series. Scale effects are therefore to be expected if large series of the same vehicle type are refitted.
  Amortisation: (no data)
    Amortisation is difficult to assess in a general manner. In new stock, the additional cost for CO2-operated ventilation will usually pay off in a short period of time. Reftrofit measures are often costly and profitability is not always favourable but can be raised by including the feature in a bundle of measures (cf. the refitting of B 20-73 at SBB).
close main section Application outside railway sector
  close sub-section Status of development outside railway sector: test series
    There have been various demonstration projects of CO2-based demand-controlled ventilation in buildings.
  Time horizon for broad application outside railway sector: in 5 - 10 years
    (no details available)
  Expected technological development outside railway sector: basically exploited
    cf. same category in "General criteria".
  Market potential outside railway sector: small
    CO2-controlled ventilation is seen as especially promising for buildings with a high variation of occupancy and high occupancy peaks, such as cinemas, theaters, classrooms, meeting rooms and retail establishments. Its market is therefore limited to a certain class of buildings/establishments.
close main section Overall rating
  close sub-section Overall potential: very promising
  Time horizon: mid-term
    CO2-based demand-controlled ventilation is a very promising option for energy efficiency. The highest savings are achieved for extreme climatic conditions and trains with low occupancy rates. Cost-effectiveness is good for new stock and medium to critical for retrofit measures.
References / Links:  Brunner, Gartner 1999;  Dongen, Fiechter 2000;  Emmerich, Persily 1997
Attachments:
Related projects:  CO2-controlled ventilation;  Savings on Coaches, Type Bpm
Contact persons:
 date created: 2002-10-09
 
© UIC - International Union of Railways 2003