Site Visit: Bahrain Bay district cooling plant
Bahrain Bay's district cooling plant features groundbreaking design
Bahrain Bay’s district cooling plant features some groundbreaking design and engineering, but its keepers have had to be patient as they wait to see how the facility will operate at full capacity
Although now almost three years old, the district cooling plant serving the slowly resurrecting Bahrain Bay development in the north of Manama looks and feels like a brand new facility.
From the outside in, the building is pristinely maintained and the incongruous quietness of the hulking machines which fill its chiller room suggests a project that has yet to truly commence operations. Such an impression isn’t too far wrong.
The Bahrain Bay Utilities (owned by Paragon Utilities) plant was built to serve the entirety of Bahrain Bay’s 1.5 million m² gross floor area but, since the global financial crisis and the consequent stalling of many of the development’s projects, it hasn’t had that much to do.
With Arcapita Bank Headquarters currently the only completed Bahrain Bay project, the plant has only ever had to call one of its 18 chillers into operation on an intermittent basis to service the development’s cooling needs.
The plant may have to wait a few years before it is allowed to reach its full potential but, nevertheless, it is still a project which can and should be admired for the feat of engineering which it represents.
The most notable aspect of its design is its use of seawater as a cooling medium. Venkateswaran Seshadri, projects and maintenance manager for Dalkia (15% owner of Bahrain Bay Utilities) says that Bahrain Bay’s seaside location meant that such a design was a perfect fit.
“The plant needs a very large volume of water and this is a scarce commodity in Bahrain. That’s why we had to use the seawater for its condenser circuit,” he says.
“There are not many seawater cooling plants in the GCC,” he adds. “There is another cooling plant in Bahrain that uses seawater because the distance to the sea [in this country] is not far. But most other plants in the region use freshwater or treated sewage effluent.”
If not distinctive enough through its use of seawater as a cooling source, the plant’s use of that seawater is in fact “a unique design,” according to Shanmugam Apparsamy, Dalkia’s operations manager for Bahrain and Abu Dhabi. While other seawater district cooling plants treat the source liquid with chlorine to eliminate any marine or ecological element that it may contain, the Bahrain Bay plant involves a filtration system design which achieves this without using chemicals.
The system involves two intake pipes buried beneath the seabed, the installation of which saw a coffer dam built in order to excavate the seabed and bury the two pipes which feed the plant.
Crushed gravel was then laid on top of these, with a geotextile membrane on top of that, and a layer of calibrated sand on top of that, all weighed down by heavy river stones to minimise movement of the membrane. The coffer dam was then removed , allowing these various layers to act as a natural fine filter through which the water travels down to the pipes by simple infiltration.
Beyond ensuring the effectiveness of this filtration system, another challenge which the design of the seawater cooling plant had to overcome was the behaviour of the sea itself.
“The coast doesn’t have water continuously due to extreme low tide periods in this region, so the plant doesn’t get any water from the sea at these times,” explains Shanmugam.
“We have two big storage tanks capable of storing enough water to continuously supply the plant when it is running at full load. The tanks are capable of supplying water to the plant for six hours in full load conditions.”
The design of the plant also had to consider how the seawater used by the plant was disposed. Following its use, the temperature of the water rises in the heat exchange process and has to be treated before being returned to its point of origin. The design also had to ensure that this discharged water did not affect the marine environment.
“As per the [environmental] regulations, the outfall water cannot be sent back to the sea [immediately after use],” says Shanmugam.
“We have to put it through a cooling tower, cool it to a certain temperature and send it back to sea through the outfall pipes. These pipes are installed a far distance from the intake pipes so that the intake water and outtake water is not being mixed. Fresh seawater must always come from the filtered pipes.”
Delivering the procurement and construction of this seawater infiltration intake and outfall system was Al Hassanain Contracting Company, which also assisted Dalkia with its design engineering. Meanwhile, Dalkia secured the services of Qatar’s Unicorp to carry out the design engineering, and procurement and construction on the district cooling plant itself.
Construction of the plant began in June 2008 and, after a period for testing and commissioning, was handed over to Bahrain Bay Utilities in August 2011 in conjunction with a sewage treatment plant which sits adjacent.
Although the construction process ran fairly smoothly, Venkateswaran says that executing the design of the building was complicated by the project’s aesthetic considerations.
“This is an industrial plant but there were some restrictions imposed by the master developer [Bahrain Bay] that meant the building should not look like an industrial plant, he says.
“If it was a normal industrial building, all the provisions for construction would have been met much easier as it would have been a completely different design. You could have easily brought in the chillers and the other major equipments. But, this not being an industrial plant from the external view, there were difficulties in handling the equipment and bringing them into the building – especially the chillers.”
In order to accommodate these design stipulations, Venkateswaran says that some parts of the building’s structure were “not built until the chillers were moved in,” at which point the external walls could be constructed. Further care had to be taken with the procurement of the chillers themselves, as he explains.
“Seawater is a very aggressive medium; it corrodes the equipment. There was special selection made of the chillers for handling seawater. The seawater touched components are made of titanium as that is the best material for handling seawater. That’s why these chillers are a bit more expensive than normal chillers.”
Beyond the plant itself, installation of the district cooling piping network by contractor Ahmed Mansoor Al A’Ali (the design engineering and supervision of which was done by Atkins) also presented its own particular challenges.
“The depth of the burial required in some cases was almost five metres,” says Venkateswaran. “We had to do shoring and dewatering as the sea is so nearby that you hit the groundwater quickly, so we had to develop extensive dewatering systems.”
By the time this work and that at the district cooling plant were complete in 2011, it had become apparent that the Bahrain Bay development was experiencing financing problems and that the district cooling utility would not be operating at full capacity for some time.
This has consequently left the Dalkia team with the job of overseeing operations at the plant on a hugely reduced scale. Venkateswaran says that, while the facility has been running well since it was handed over, he and his company are looking forward to a time when it can be tested at full capacity.
“So far we haven’t had any major problems with the plant,” he says. “But from a commercial viewpoint, it would be better for us to have all the chillers running. It is better for us to have the plant running at full capacity because that will mean more revenues for the company.”