Request ID: FOI-1665-2324 Date published: 07 September 2023
You asked
Dear team,
Regarding the air conditioning systems on the subsurface lines (Metropolitan, District, Hammersmith and City, and Circle), known as the s7 and s8 stock.
I have some questions regarding the saloon air conditioning/ air cooling systems.
1. Do the trains use air conditioning (using typical refrigeration and humidity/air extraction) and/or air cooling systems (without humidity extraction)?
2. What is the target saloon temperature of both the s7 and s8 stocks?
If there is no set target temperature, what is the target saloon temperature at the following external ambient temperatures?
1. 20ºc
2. 25ºc
3. 40ºc
3. Does the previously mentioned system monitor and control the humidity of the saloons? If so, what is the target relative humidity?
4. What is the previously mentioned system's maximum power consumption (in watts) under full load (train contains maximum passengers and 40ºc+ ambient temperature)?
5. What is the average rate of failure for the previously mentioned systems (meaning when necessary the air is not cooled or heated, requiring mechanical or technical repair) during their lifetime, measured in average unit distance (Miles) until technical failure?
We answered
TfL Ref: 1665-2324
Thank you for your request received by Transport for London (TfL) on 21 August 2023 asking for information about Sub Surface lines AC systems.
Your request has been considered in accordance with the requirements of the Environmental Information Regulations and our information access policy. I can confirm that we hold the information you require. Your questions and our replies are as below:
Regarding the air conditioning systems on the subsurface lines (Metropolitan, District, Hammersmith and City, and Circle), known as the s7 and s8 stock.
I have some questions regarding the saloon air conditioning/ air cooling systems.
Do the trains use air conditioning (using typical refrigeration and humidity/air extraction) and/or air cooling systems (without humidity extraction)? Yes, the trains use air conditioning (HVAC) units. Each HVAC module contains a refrigerant circuit using R407C and is hermetically sealed. The HVAC units have passive ventilation but not humidity extraction.
What is the target saloon temperature of both the s7 and s8 stocks? If there is no set target temperature, what is the target saloon temperature at the following external ambient temperatures?
20ºc
25ºc
40ºc
The saloon internal set point temperature is automatically adjusted depending on the external temperature. In its normal operating mode, the saloon HVAC uses a type of algorithm called fuzzy logic to generate the required mode.
3.Does the previously mentioned system monitor and control the humidity of the saloons? If so, what is the target relative humidity?The system doesn’t monitor/control humidity 4. What is the previously mentioned system's maximum power consumption (in watts) under full load (train contains maximum passengers and 40ºc+ ambient temperature)?31kW Cooling, 21kW Heating (Including the floor heater capacity).
5. What is the average rate of failure for the previously mentioned systems (meaning when necessary the air is not cooled or heated, requiring mechanical or technical repair) during their lifetime, measured in average unit distance (Miles) until technical failure?At the moment our failure rate is high relate to low pressure intermittent fault during start up but this failure mode doesn’t cause service delay.
If this is not the information you are looking for, or if you are unable to access it for any reason, please do not hesitate to contact me.
Please see the attached information sheet for details of your right to appeal as well as information on copyright and what to do if you would like to re-use any of the information we have disclosed.
Yours sincerely
Sara Thomas FOI Case Management Team General Counsel Transport for London
