Dubai, UAE, 1 November 2018: With metro projects being part of the public transport system, there are key considerations that should be kept in mind while designing its HVAC and tunnel ventilation systems, said Pramod Kumar Jha, Senior Mechanical Engineer, Building Services, Middle East, Atkins, member of SNC Lavalin. “In regular building projects – hotels, residences and office complex projects – the buildings have got a typical layout for many floors and hence a standard design solution can be adopted,” Jha explained. “In a metro project, all the buildings – stations, depots, tunnels, tunnel ventilation/emergency egress shafts – differ from each other in terms of shapes, sizes, location, approach and operation.”

Jha stressed these buildings are also interconnected with each other operationally, meaning an issue in any of the buildings may also impact the other buildings  in terms of train operation and other system-related operations, which is not the case for regular building projects.

Jha highlighted other key differences. Firstly, the metro buildings accommodate special systems such as rail power, automated platform screen doors, automated fare collection system, rail signaling and communication system, smoke ventilation system and/or tunnel ventilation system. “Being an infrastructure project,” Jha added, “the MEP services are designed with a consideration of future demands, expected expansions and replacement of equipment. Being part of public transport services, the metro MEP services are designed with stringent reliability, availability, maintainability and safety (RAMS), as per international requirements. This also means that MEP services are designed with sufficient space allowances for easy and quick maintenance, for continuous functional requirements.”

Jha added that the quantity of stakeholders, government authorities, service providers, manufacturers, services designers and third-party reviewers involved in metro projects is also considerably more, compared to a regular building project and, therefore, communication and coordination among stakeholders is a big challenge. Due to train movement, noise and vibration control measures is a bigger challenge in metro projects, Jha said, and the average cooling per area in metro projects is much higher than regular building projects. “Therefore, the large HVAC system design with respect to the location of the metro station/building is a challenge by itself,” he said. Lastly, high ambient temperature in the Middle East poses a big challenge on tunnel cooling and ventilation system design.

With the aforementioned considerations, Jha outlined key factors that must be kept in mind in designing the station HVAC and tunnel ventilation systems:

a) Passenger safety is the first and foremost consideration.

b) Consideration of the future requirements (e.g. passengers to be transported in 10 years’ time ahead from the year of beginning of metro operation).

c) Safety, reliability, availability and maintenance.

d) Demand-based operation of the HVAC and Tunnel ventilation system.

e) Energy-efficient system design (e.g. use of free cooling, energy recovery from the cool exhaust air, reduce infiltration/exfiltration, use of high efficiency equipment, etc).

f) Adequate space allowance for delivery, installation, replacement, maintenance of all equipment is to be considered right from the initiation of the design, as the equipment are very large and heavy (e.g. a tunnel ventilation fan size could be of 3,200mm diameter and the noise attenuator could be of size 4,000mm x 5,000mm x 3,000mm).

g) Air infiltration and exfiltration (from the tunnel to the station or vice versa, due to piston effect of the train movement in the tunnel) to be considered while sizing the HVAC equipment.

h) Tunnel ventilation systems are sized for high pressure variation due to the train’s piston effect and allow less time for tunnel ventilation fans to reach to 100% design speed in one direction and in reverse direction as per NFPA 130 standard, based on tunnel ventilation system operation mode.

i) Use of innovative means of cooling, such as radiant floor cooling (recommended only for central parts of the buildings, which are not exposed to direct ambient air).

Underscoring the importance of having the right knowledge for such niche projects, Jha said that as the world economy is looking towards the Middle East region, United Arab Emirates, Saudi Arabia and other GCC countries are opening new opportunities for metro professionals to utilise their knowledge to support the upcoming metro projects, which are being developed to resolve the traffic congestion, environment challenges, pollution, and provide more economic and efficient transportation in the region. Sharing some of the metro projects in the pipeline in Middle East region, Jha pointed to the Dubai Metro Green Line and Red Line Extensions; enhancement of Dubai Metro Stations; Abu Dhabi Metro; Makkah Metro; Jeddah Metro and Kuwait Metro.

Jha will hold a seminar on ‘Design of environmental control and ventilation systems for metro projects in the Middle East region’ during the HVAC R Expo, part of The Big 5 Dubai. The talk will be held on Tuesday, November 27, from 1:00-1:45pm.

Hannah Jo Uy is Assistant Editor at Climate Control Middle East magazine. She may be contacted at hannah@cpi-industry.com