Fan System Replacements In HVAC Equipment To Improve Energy Use

Fig. 1: Wakefield House in Adelaide, site of a major HVAC upgrade
Figure 1: Wakefield House in Adelaide, site of a major HVAC upgrade

Accounting for up to 50% of the energy consumed in Australian buildings, fans are the major contributor of energy used in air conditioning and ventilation systems (HVAC). Therefore the specification of high efficiency fans and fan upgrade projects provides a huge opportunity to significantly reduce energy consumption.

This article discusses the retrofit of high efficiency fans in existing HVAC equipment to drastically reduce energy consumption. It further outlines additional benefits gained by upgrading fans, like the ability to easily speed control. The effectiveness and benefits resulting from high efficiency air movement systems are highlighted and summarized using examples from the field.

The article concludes with a best practice method to select and specify high efficiency fans for HVAC applications.

Introduction

What can be done to existing HVAC equipment to improve efficiency and performance?

Most energy efficiency upgrades in HVAC systems involve updates to control strategies or the installation of variable speed drives (VSD) to existing motors. While these measures reduce energy consumption, the actual fan, the most energy-hungry part of the system, is not replaced. Hence these upgrades miss out on a huge savings opportunity.

This article addresses the replacement of fans in HVAC equipment, the reasons to do it, how it can be done, and what the benefits are; examples are given. A brief introduction to the definition of fans and fan efficiencies in the context to the fan standard (ISO 12759) and the recommendations of the Fan Manufacturers Association of Australia and New Zealand (FMAANZ) are given. This paragraph seeks to assist building owners, facility manages, consultants and contractors with the specification of efficient fans throughout their buildings.

Why fans?

Figure 2: Example of a fan array

HVAC equipment in buildings accounts for around 50% of the total electrical energy usage and therefore is the single most energy hungry component (1). The savings potential in HVAC equipment is huge and therefore it makes sense to focus on it first. So why has this not been addressed earlier? Unfortunately HVAC is not as obvious a target as for example lighting. Fans and compressors in HVAC equipment are hidden energy guzzlers and are not addressed because they are not as visible or as obvious as for example lighting.

Existing fan decks in HVAC
The problems with existing fans are the cost of running and maintaining them, the questionable or unknown performance, the low efficiency of components used to build them, as well as their reliability. Each of these issues is addressed in the following.

Belt driven systems which are typical in HVAC applications require ongoing maintenance and frequent replacement of belts, pulleys, and bearings. Failure to do so ultimately leads to increased inefficiencies and motor and bearing failures which increase cost even further. Indirect maintenance costs also increase due to belt dust and associated costs which will require more frequent filter replacements and cleaning.

Especially in larger systems this mix and match assembly of various components is typically never tested in an air test chamber and as a result the actual system performance is estimated. Inefficiencies and performance inaccuracies in these systems are caused by the drive losses and the mismatch of components or simply by inefficient components like forward curved impellers or old and inefficient motors.

Having a single large fan installation in an AHU instead of multiple fans provides a single point of failure which poses a high risk, especially in critical systems like medical applications or data centres. These are also time consuming and expensive to fix. For example a bearing issue or a failed motor will cause your air conditioning unit to fail and repair can take several days in a large application.

EC fan retrofits

All of the above mentioned problems can be avoided and efficiency can be improved by replacing the existing fan systems with high efficiency direct-drive EC fans.

Various fan manufacturers and some HVAC equipment manufacturers offer a range of EC direct drive replacement fans to replace existing fan system without mechanical alterations to their equipment. One of the simplest examples is an axial fan on an air cooled condenser. The low efficiency fan can simply be removed and replaced with a high efficiency EC fan. Reductions in energy use of approximately 30% are common for these products.

The upgrade examples of conventional belt driven fans in computer room air conditioning units (CRAC units) to direct drive EC fans have on average achieved savings of 51% in current draw across several hundred installations in Australia.

Figure 3: CRAC unit fan upgrade

The first task for larger AHU retrofits is the removal of the existing fan assembly. This can be a challenge due to the large size and weight of some of these fans. The side or top of the AHU is either removed to get access, or the existing fan is disassembled inside the AHU. EC plug fans require separation between suction and pressure side. If a plenum does not exist, a separation wall is inserted into the AHU after the original fan was removed. The wall is usually built in the previous fan chamber to separate the suction from the pressure side and one or several EC direct drive fans are then fitted into the wall. Previous retrofits have achieved energy savings of around 70%.

Larger air conditioning units will require EC fan assemblies that might not look like the original fan assemblies. The achieved savings are nevertheless similarly impressive. This approach aims to match the existing fan’s performance, with both fans being mechanically interchangeable. Performance of the replacement products is tested and therefore savings and cost for the retrofit can be estimated very accurately before the replacement takes place. This method should be the principal way to replace fans in old HVAC equipment.

Figure 6: Example of a foot mounted EC plug fan upgrade

Bigger single fan installations as usually found in large AHUs, however these require a different approach. Even though the work involved in these upgrades seems unreasonably high it is worth looking at these applications in particular as the savings potential in monetary terms is substantial as these units traditionally consume a lot more energy. EC plug fans are the solution for these bigger air-handling requirements. They are backward curved centrifugal impellers mounted on a direct drive EC motor. The electronics and motor form one unit in order to save space, optimise performance and enable easy installation. EC plug fans are available in different configurations and the most common versions are either wall mounted or foot mounted models.

Figure 5: Example of a wall mounted EC plug fan array with additional space above and below

Using multiple EC fans to replace one existing fan assembly has several benefits. Smaller fans are easier to handle and can usually be carried and installed by two people without special lifting equipment. In most installations access is restricted and lightweight and small products significantly reduce install cost and time. Using 3, 4 or even more fans in one AHU significantly increases the reliability, as a single fan failure will not cause the HVAC equipment to fail. Additionally these smaller fans can be easily replaced, with a typical replacement taking between 30 to 45 Minutes. It is relatively easy to accommodate room for further upgrades to the building by allowing space to add additional fans at a later stage, for example if demand for the required airflow increases. This approach also allows for the use of only one fan model across several AHUs in a building, hence reducing the number of spare part variations. This can further increase the reliability and reduce down-time of HVAC equipment.

This approach is scalable to any size of AHU. Figure 5shows how the addition of one or two more EC fans is possible at a later stage should the need arise.

Benefits

Figure 6: Benefits of speed control: noise reduction

EC fan retrofits have additional benefits besides reducing power consumption.

1) EC fans have built in speed controllability, which enables very easy and inaudible speed control (cf. Fig. 6). Most EC fans will accept standard signals from existing building management systems (BMS). Even a basic potentiometer can be used to modify air flows.

2) Backward curved fans allow for easy measurement of air volume via a differential pressure sensor. This is convenient considering fan applications do not ask for fan speed but air volume.

This information can be made accessible to the BMS or via a digital display. It is therefore possible to not only monitor speed but actually measure, monitor and control air volume.

Figure 7: Power savings using EC technology

Speed control and therefore air volume control should be implemented wherever possible for the following reasons:

  • Power savings by reducing air flows to minimum requirements
  • Noise reduction, again by reducing air flows
  • Increase life time of the equipment due to the reduced demand
  • Increase comfort level due to lower noise and air velocities
  • Easy maintenance of desired conditions in air conditioned space due to more accurate control

But where are the savings coming from when speed controlling EC fans? A reduction in speed and therefore air flow of only 5% results in savings of 14%. A reduction by 50% reduces input power by 87% (cf. Figure 7)! This is possible because EC fans follow fan laws and maintain their high efficiency over a wider performance range than other fan motor technologies. It is important to remember that these savings through speed control are in addition to the reductions achieved by simply switching to EC technology. As shown above, savings of 40% to 70% in input power can be achieved before speed control.

3) EC fans typically have a soft start function built in, significantly reducing in-rush current when the fans are switched on and ramping up in a defined time period.

4) EC fans from ebm-papst offer a high level interface on larger fans. This allows for easy integration of EC fans into the existing or future BMS system. This allows to access fan status, operation parameters and even switching fans on and off.

5) Gone are the days of changing bearings and belts, greasing, and adjusting pulleys. ebm-papst EC fans have maintenance-free bearings and do not require servicing.

Fan selection for new equipment or retrofit

How common is EC technology?

EC fans are not new. Electronically commutated motors were developed in the early seventies and have found their way into the majority of fan applications globally. First introduced into computer room air conditioning units (CRAC) in 2005, EC technology can now be found in international and Australian manufactured commercial air conditioning and air handling units, very often as standard technology. Many industry-leading commercial air conditioning companies have been offering EC-based systems for many years. Even domestic ducted air conditioning and gas heaters are now available with high efficiency direct drive EC fans with backward curved impellers.

What is an efficient fan?

The Australian standard for fan efficiency, ISO 12759:2010, defines what a fan is and how efficiencies are measured. It paves the way for further legislation and best practice as it ensures that any information provided by a manufacturer that refers to the standard is comparable.

One method that resulted from the standard is the voluntary performance code of practice which was introduced by the Fan Manufacturers Association of Australia and New Zealand (FMAANZ) in 2013. High efficiency fan systems are “HEPS compliant” and efficiency levels are equal to European ErP 2015 regulations. The code is a tool to enable specifying engineers and consultants the identification of efficient fan systems without going into details about type of fan, size, technology and application.

Most recently the carbon credits methodology determination as part of the Emissions Reduction Fund (ERF) introduced minimum efficiency levels which are 5% above the ErP 2015 levels (3).

Now it is possible to ensure the use of high efficiency fans in HVAC applications by simply specifying that “fans have to be compliant with HEPS (equal to ErP 2015)” or “fans have to be compliant with minimum efficiency requirements under the ERF”.

What financing options or rebates are available?

Some states and councils in Australia offer incentives to improve energy efficiency of fans, for example energy savings certificates (ESCs) in NSW or Energy Upgrade Agreements (EUAs) in Victoria. This can result in energy-efficiency upgrades as cash-flow positive investments. Abatements for fan retrofits are also available nationally under the ERF as mentioned above.

Recommendations

Fans are a major contributor to energy consumption in buildings. Replacing existing low efficiency fan systems with new high efficiency EC direct drive products can reduce the fan power consumption by up to 70%.

Furthermore it was shown that EC fans are more versatile, increase reliability and reduce maintenance and service cost.

Different design options for retrofits were given which are possible due to the modular design of EC fans.

To ensure that high efficiency fans are used in new HVAC equipment, the specification according to FMA-ANZ high efficiency performance standards and its relation to European ErP guidelines was outlined.

References

(1) Simon Bradwell, ‘AS/NZS ISO 12759:2013 – Implications and effects on fans and fan efficiencies in existing buildings’, Fan Manufacturers Association of Australia and New Zealand, 2013, www.fmaanz.com.au.

(2) Department of Climate Change and Energy Efficiency, ‘Council of Australian Governments (COAG) National strategy on energy efficiency, baseline energy consumption and greenhouse gas emissions in commercial buildings in Australia’, Part1, Nov 2012, p 20.

(3) Federal Register of Legislative Instruments F2015L01712, ‘Carbon Credits (Carbon Farming Initiative—Refrigeration and Ventilation Fans) Methodology Determination 2015’, 27/10/2015.