01/30/2012
Approximately 50% of
energy could be saved by replacing the existing AC belt driven backward-curved
fans throughout a building with EC Plug Fans. A retrofitting project in the
government-owned Wakefield Building in Adelaide achieved great energy-savings
and performance increases.
Fan energy is typically the most significant consumer of energy within a
commercial building. Approximately 50% of energy can be saved by replacing the
existing AC belt driven backward-curved fans throughout a building with EC Plug
Fans.
Wakefield House Building, Adelaide
The original fan and air handling unit (AHU) arrangement for level 14,
which is typical throughout all floors of the building, comprises a coil face bypass
arrangement, with air distributed via a belt driven backward curved centrifugal
fan arrangement.
In October 2011, the existing fan was replaced by an ebm-papst EC Plug Fan.
Minor works to the damper were also performed. The project was managed by System
Solutions Engineering Pty Ltd, an engineering firm and consultancy based in
Adelaide.
The main issues with the arrangement and system related to performance
and the ability to adequately distribute the air to the floor. Due to the
system type and the fans proximity to the cooling coil, cooling capacity of the
AHU is reduced as only part of the coil face is utilised. Air from the fan is
only incident on part of the cooling coil, which then is reflected by
insufficient capacity being delivered to the floor.
Contributing to the insufficient capacity is the reduction in supply air
to deliver cooling to the floor. Locating the fan so close to the cooling coil
creates turbulence and increases the system static, which in turn reduces the
supply air quantity by approximately 10-15% from design. When combined with the
reduced performance of the cooling coil, the net reduction in capacity to the
floor is approximately 45% from design.
Old fan current
Starting currents for each day, which exceed 80 Amps, whereas the average
current across the phases throughout daily fan operation is 8.55 Amps.
New system
In October 2011, the existing centrifugal belt driven fan was replaced
with an EC Plug fan. Minor works to the damper arrangement and operation were
also performed.
The new EC Plug Fan was installed away from the cooling coil, and the
damper was rearranged above the cooling coil in the bypass ductwork. The new
damper was installed to provide an equivalent pressure drop to the cooling
coil, which provides more stable distribution and controllability of supply
air. The EC Plug Fan pressurises the plenum chamber and rather than delivering
an uneven air profile as per a centrifugal fan as indicated in the figure
above, provides uniform air pressure and therefore volume across the whole
cooling coil, achieving greater capacity from the coil. As part of the upgrade
works, airflow was increased by 10% returning the supply air quantity to the
design figure and combined with the resultant increased coil efficiency, cooling
delivered to the floor was increased by approximately 15-20%.
New fan current
Starting currents now approach 6 Amps (before 80 Amps), and the average
current across the phases throughout daily operation of the EC Plug Fan is 4.7
Amps.
Summary - Energy and
Operating Cost
Annual savings of
· 9,470.7 kWh
· $1,799.43
· 6.5 tonnes of CO2 Emissions.
For commercial office buildings, up to 70% of the total energy use is
attributed to the heating,ventilation, and air conditioning (HVAC) systems. As
fan energy is typically the most significant consumer of energy within a
commercial building, the reduction of approximately 50% from the replacement of
the existing AC belt driven fans throughout the building to EC Plug Fans, will
have a significant impact on the total energy consumed, as well as reduction in
green house gas emissions.
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