Drives & Controls March 2023

41 www.drivesncontrols.com March 2023 BUILDING SERVICES n Singapore HVAC retrofit delivers 45% energy savings A Singapore landmark, the 18-storey Keppel Bay Tower, has cut the energy needed to run its AHUs (air-handling units) by more than 45% following a retrofit which included AC drives, axial fans and high-efficiency motors. In 2018, the building’s owner Keppel Land secured a grant from Singapore’s Building and Construction Authority (BCA) under its Green Buildings Innovation Cluster (GBIC) programme to implement and test new energy-efficient technologies. The tower block had already achieved the BCA’s Green Mark Platinum status, but the new initiative aimed to cut energy use by a further 20%. Danfoss and the Danish high-efficiency fans specialist Novenco suggested replacing the existing centrifugal fans in the air handling units (AHUs) with an alternative designed to boost the efficiency of HVAC systems. The proposal included using axial fans driven by IE4 and IE5 permanent magnet motors, in combination with dedicated HVAC drives. It was reviewed by industry experts appointed by the BCA and independent researchers who agreed that there was potential to save energy by combining these technologies. Being an easy retrofit, it would also minimise downtime and inconvenience. The concept is characterised by two key factors – the high efficiencies of the individual components, and their intelligent interaction. Unlike centrifugal fans, the unidirectional ZerAx axial fans chosen for the project harness both static and the dynamic pressures. They are thus more efficient, and reduce carbon emissions as well as sound levels. To maximise the energy efficiency of any ventilation system, its fans need to use both static and dynamic pressures. But the efficiencies of conventional centrifugal HVAC fans are calculated solely on the basis of the static pressure. They are unable to utilise the dynamic pressure which, according to Novenco,“disappears into thin air”. Axial fans, on the other hand, exploit both static and the dynamic pressures, leading to efficiencies above 90%, compared to 65-70% for typical centrifugal fans. Although centrifugal fans may appear simpler and more flexible, they can turn out to be an expensive choice – both in terms of operating costs and environmental impact. In centrifugal fans, air flows perpendicular to the fan axis and thus loses energy. In axial fans, an aerodynamic design results in straight airflows parallel to the fan axis, with little or no turbulence, thus reducing losses. The fans used in the Singapore project are claimed to be the most energy-efficient on the market, with efficiencies of up to 92%. The fan lifetimes are claimed to be at least 20 years, contributing to sustainability and cutting maintenance costs. The fans are driven by Danfoss VLT HVAC Drive FC 102 VSDs dedicated to building services applications. Working together, Danfoss and Novenco have come up with a concept they call EC+ which they claim is most efficient system for AHUs. The motor and drive efficiencies are both above 95%, while the axial fan efficiency is 92%, resulting in a total system efficiency of 85%. This is claimed to be 20–25% higher than the nearest alternatives, such as direct-driven centrifugal plug fans with electronically commutated motors. Because of these high efficiencies, the AHUs can be up to 30% shorter and lighter than traditional designs, yet deliver the same performance. Plug-and-play designs allow rapid installation. The Keppel Bay retrofit was completed in less than 10 hours. The retrofit has delivered energy savings of more than 45%, as well as improving the environment for the building’s occupants because of the lower noise levels. It has played a significant role in a 22.3% reduction in the building’s annual energy consumption – higher than the initial target of 20%. The high-efficiency AHU drives are one of five technologies chosen for the GBIC initiative – the others being smart sensors for fresh air control, an intelligent building control system, a smart activity-based lighting system, and an intelligent water management system for the cooling towers. The BCA has now certified Keppel Bay Tower as a Green Mark Platinum Zero Energy building – the first commercial building to achieve this in Singapore. n High-efficiency motors, fans and drives have been retrofitted to AHUs in a Singapore tower block, resulting in energy savings of 45% and making it the city-state’s first commercial building to achieve net-zero status. An energy-saving retrofit has made the Keppel Bay Tower the first net-zero commercial building in Singapore In centrifugal fans (top) the air flows perpendicular to the fan axis, losing energy, while in axial fans (below), the flows are parallel to the axis with little turbulence, making them more efficient.