Since the invention of the centrifugal chiller, in 1922, the traditional approach for designing a large chiller plant always involved typical centrifugal chiller plants, due to their durability, energy efficiency and cost-effectiveness. There is no doubt that centrifugal chillers’ efficiency has improved massively over the past 100-plus years, but it is still 100% dependent on electricity.

The way to net zero carbon

To meet net zero carbon by 2050, utilising centrifugal chillers will depend on achieving a 100% zero-carbon power grid at the city/country level, a challenge that all countries face, particularly the Middle East. The best practical way to achieve this target is to reduce the power demand of cities to optimise the capital cost of this transformation.

In our field, one of the key points is the optimisation of cooling demand that has been going on for a few decades. I believe this has reached its best, and further improvement will not reduce the carbon emission of the cooling system dramatically. Therefore, we must now look at the elephant in the room – that is the chiller plant.

In the Middle East, solar power is the main player when it comes to neutralisation of the grid. However, the available technologies that convert solar energy – around 1,370 Watts/square metre – to electricity can convert only a small portion – around 200-250 Watts/square metre. This means we should investigate utilising solar energy more efficiently in one way or another.

Considering a hybrid approach

Car manufacturers could be cited as a good example of a hybrid approach. Electric cars were invented in 1888; however, the combustion engine cars were seen as a better option and dominated the market for decades. Today, electric cars constitute a key player towards net zero carbon, but they are not yet the best option for all users. This is why hybrid cars have become a good alternative option for this transition period. A hybrid model on wheels utilises both technologies and creates a win-win situation for manufacturers, who need time to phase out their combustion engine plants and invest more in electric cars, and for consumers, who want practical cars at a reasonable price.

From what I see, just like combustion cars, centrifugal chillers and all other traditional chillers may not be part of the future, and manufacturers will need to reinvest in new technologies and existing ones, such as absorption chillers.

To create a similar win-win scenario during the current transition period in the industry, the designer and the client should encourage a hybrid approach utilising traditional chillers as well as absorption chillers in chiller plant design.

Why absorption chillers

The current technologies allow us to utilise solar energy directly as heat or any other waste heat to generate chilled water with almost 40% less electrical power compared to centrifugal chiller plants.

Chillers Energy Comparison

Smart investment

Investment is always the main driving factor in construction, and the hybrid plant approach should be attractive to building owners and operators, so it can be implemented on a large scale. Investing in a chiller plant with 100% absorption chillers will not suit most projects for many reasons, such as the area and the cost of the solar panels.

One of the ideas is to replace the standby chiller in District Cooling (or large plants) with a combination of air-cooled and absorption chillers with photovoltaic thermal panels (PV-T) that can generate electricity and hot water simultaneously. This combination – absorption CH and PV-T – will use the solar energy more efficiently for the cooling system, with a very limited impact on the capital cost.

Designing this type of system will need an accurate computational analysis for the annual operational cooling load, though, along with the weather data to ensure the right combination of the system, including:

§ The absorption chiller operation temperature and capacity

§ The PV-T areas and energy generation

§ The capacity of the hot and/or cold buffers

§ The system payback

The writer is Head of Mechanical (Middle East) at Ramboll. He may be contacted at s.mohamed@ramboll.com