Wakefield house Case Study – retrofitting for energy efficiency made easy

EC plug fan retrofit saves 50% energy in commercial building using the same space

Fan energy is typically the most significant consumer of energy within a commercial building. Approximately 50% of fan 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 system

Old fan arrangement in AHU

The main issues with the above arrangementand system relate to performance and the ability to adequately distribute the air tothe floor.

Due to the system type and the fan's 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.

New system

New fan arrangement in AHU

In October 2011, the existing centrifugal belt driven fan was replaced by 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%.

Old Fan current

Old fan current

The starting currents for each day exceeded 80 Amps. The average current across the phases throughout daily fan operation was 8.55 Amps.

New fan current

New fan current

Starting currents now approach 6 Amps (before 80 Amps). The average current across the phases throughout daily operation of the EC plug fan is 4.7 Amps.

Summary - Energy and Operating Cost

SystemStarting currentOperating currentAnnual kWhCo2 emissionsAnnual operating cost
Old belt driven fan>80 A8.55 A18,637.312.7 tonnes$ 3,541.09
New EC plug fan<6 A4.7 A9,166.66.2 tonnes$ 1,741.66
Savings  9,470.76.5 tonnes$1,799.43
 Savings
Supply airflow+10%
Cooling capacity+20%
Fan energy used-50%

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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