Buildings consume more than 90% of Hong Kong’s electricity. In commercial and industrial buildings, more than 50% of the energy is used to provide central air conditioning. As a result, improving the efficiency of air conditioning systems can have a significant impact on the city’s power consumption, not only saving money but also helping the environment.

Professor Wang Shengwei (second from left) and his research team

A PolyU research team led by Ir Professor Wang Shengwei, Chair Professor at the Department of Building Services Engineering, has spent a number of years formulating optimisation strategies to enhance the energy performance of air conditioning systems. Their solutions have found ways to reduce energy usage by between 15% and 40% in a range of commercial and industrial buildings, including factories, hotels, commercial and office complexes, and underground facilities.

 

In many cases, the low efficiency of air conditioning systems is the result of poor or obsolete design, improper operation and controls, and a lack of maintenance. To help buildings save energy, Professor Wang and his team took a three-pronged approach to the problem, looking at life-cycle optimisation, adaptive commissioning, and fault diagnosis in air conditioning systems.

Life-cycle optimisation

The team took a holistic approach to optimizing the efficiency of air conditioning systems. Under a process they referred to as “life-cycle optimisation”, air conditioning systems were subjected to a thorough examination at every stage, from design to construction to operation, to maximise their performance.

At the design stage, the researchers ensured the most appropriate energy-efficient technologies were used for the air conditioning system. They then optimised the system by simulating electrical loads and working conditions, including integrating and connecting different building services, to come up with a design that had the highest chance of meeting the air conditioning demand with the minimum energy consumption.

Adaptive commissioning

Traditionally, a central air conditioning system is designed so that it is tuned to certain specific conditions or balance points. However, the characteristics of the actual system after construction may deviate significantly from the design. To minimise this discrepancy, the team employed the concept of adaptive commissioning, under which different operational options are included in the design to allow more flexibility at the construction stage.

Professor Wang explains: “Instead of building one big pump of full capacity in a cooling tower, for example, we could build three small pumps that add up to the same capacity. That gives the leeway of running one to three pumps according to the actual need. When the water-loop hydraulic resistance is low, we may operate only two small pumps to save energy.”

Fault diagnosis

When the air conditioning systems were in use, the team looked at different operation modes to see how they affected energy consumption, with a view to meeting the same cooling demand with less energy. Fault diagnosis plays a key role in this process.

“Components may fail over time, leading to performance degradation. They may also need to be cleaned or tuned up from time to time. Thus, when an air conditioning system is not performing optimally, we need a mechanism to check where the fault is and to fix the problem as soon as possible,” Professor Wang says.

The team used big data analytics to effectively locate faults in information-super-rich buildings, which are equipped with built-in Internet-of-Things sensors and building automation systems that collect a huge volume of data every day. Even in information-poor buildings, where very little data is available, the team was still able to analyse energy use to discover the pain points that lead to wastage.

Promoting energy-efficient buildings

Professor Wang and his team have been providing optimisation solutions for air conditioning systems for a number of buildings through offering consultancy services. They have also used the same strategy to optimise lighting, lifts, and other systems in 25 buildings, including 10 buildings on PolyU’s campus, to improve overall energy efficiency.

In one high-rise commercial complex in Hong Kong, to which the PolyU team has been providing services for more than 10 years, the optimisation strategies reduced annual electricity consumption by more than 10 million kWh, leading to an annual saving of more than HK$10 million on electricity bills.

“Our solutions not only save electricity cost, but also contribute to power grid stability by using energy stored in buildings and shutting down part of the cooling plant for short periods of time, without sacrificing user comfort,” Professor Wang explains.

By improving the power efficiency of individual buildings in the private and public sectors, the PolyU team is helping to deliver significant energy-saving benefits to society.

The systematic approach to life-cycle smart optimisation and diagnostics solutions for buildings’ air conditioning systems