George Berbari presents the pros and cons of a modular chilled water plant.
Modular chilled water plants have several applications. The first application of water-cooled modular plants were inlet turbine cooling, which were used to increase the capacity of a power plant. The modular solution proved to be ideal for existing power plants, where offsite construction and short installation period provided a great advantage for small plants of 10,000 tonnes or less, required for the power plants.
The second great application came in the form of temporary plants of 1,000- to 10,000-tonne capacity, which provided the ideal solution either for entities dealing in plants on a rental basis or those purchased to supply short- to medium-term cooling until the permanent plant room was built. However, modular plants which were designed for 0.9 to 0.95 KW/tonne were often operating at 1.1 to 1.3 KW/tonnes, as integrated industrial controls and operation were not invested in. This was due to the temporary nature of the installation, as reported by key district cooling operators, who typically operate several temporary solutions.
The third application of a modular plant was for a large capcacity district cooling plant. Two such plants have been built in Dubai – the first in the Jumeirah Beach Residence (JBR) plantroom, with 60,000-tonne capacity, and the second at the Dubai Festival City, with 50,000-tonne capacity.
Two aditional plants of 36,000 tonnes each, where phase 1 comprised 18,000 tonnes, were built for Barwa City in Qatar, and a small plant of 5,000 tonnes was built for a capital project in Abu Dhabi.
All the above plants comprised containarised chiller, condenser pumps and primary chilled water pumps, while the cooling tower was built on a separate concrete basin or used FRP basins. The elctric switch gear and water tanks were built in traditional concrete structures and the distribution of chilled water pumping in some cases was containarised, and in other cases, it was built in concrete structures. They, therefore, represented a hybrid approach of traditional concrete structures, a chilled water plantroom and a modular containarised solution.
Despite its advantages, the main drawback of a modular plant is the large footprint it creates. For example, the JBR plant is almost 170 m x 60 m = 10,000 m2 in footprint or 5.9 tonnes per m2 of land. The Dubai Festival City plant is 135 m x 60 m = 8,100 m2 in footprint or 6.2 tonnes per m2 of land, while Barwa City DCP occupies an area of 5,440 m2 for each plant of 36,000-tonne capacity, which translates into a density of 6.6 tonne/m2.
The traditional multi-storey plants are typically constructed on 15 to 20 tonnes per m2 of land, saving prime and expensive city centre real estate land that can be utilised for other purposes.
Here, it needs to be pointed out that one of the best examples of judicious use of land is Qatar Cool West Bay 2 plantroom, where a 37,500 m2 of chiller plant was constructed based on a world record of 22 tonnes per m2 of land, only for the chiller plant, and almost 17 tonnes per m2 of land for the entire plant, with a thermal storage tank.
Now, let us compare the plus points of a traditional plantroom and a package chiller plant.
The main advantages of traditional plantroom over a package chiller plant are:
- Three times better land utilisation
- Better aesthetic appearance in critical city centres
- Easier operation and maintenance as all chillers are accessible on a single plantroom, rather than opening several doors and side openings to clean the condenser or change major component in modular plant
- Much better operating efficiency, as industrial control is integrated in one system, as compared to fragmented communicating controls between several containarised units
- Lower construction cost – the West Bay 2 has cost Qatar Cool around QR 140,000,000 or QR 3,750 tonnage, as compared to QR 5,500 or QR 6,000/tonne for a modular plant built at the same period
The main advantages of a modular plant over a traditional plant are:
- Modularity offers more flexibility in terms of buildup; on the other hand, in a traditional plant, one has to build the entire concrete plant and stageup the chiller component
- Can carry out offsite construction with standarised quality-controlled component that are not dependent on contractor work
- Faster onsite construction period once the module arrives on site – however, a caveat: the module requires a six to 10-month ordering period, depending upon chiller manufacturer’s delivery period, as well as other main components
It is interesting to note that more than 90% of 3,500,000,000 tonnes were built in the GCC region as tradional concrete plants, while less than 10% opted for modular plants, due to the above-stated reasons.
In the final analysis, it is my opinion that a large capacity plant, for example, one above 10,000 tonnes in capcity and up to 60,000 tonnes, should be built in a traditional manner. But where a 100,000-tonne plant is required, the builtup capacity can be staged to minimise initial investment, as it will take a few years before the full capacity is needed. It would be better to build two plants of 50,000 tonnes, preferably at two separate strategic locations, in order to optimise the distribution piping. And if only one plot is available, it is better to build them side by side, where one can be built immediately, and the second one at a later stage. The first 50,000-tonne plant building and thermal storage can be built in one go, while chillers can be staged as and when necessary.
On the other hand, small capacity plantrooms of less than 10,000 tonnes or a temporary or a semi-temporary cooling arrangement could consider the modular plant option, as it offers an advantage, when it comes to construction cost and time.
The writer is the CEO of DC Pro Engineering, Dubai. He can be contacted at gberbari@ dcproeng.com