Optimise Specific Fan Power in AHUs – Complete Guide

Posted: 30th July 2025

Optimising Specific Fan Power in AHUs: A Collaborative Approach by ECE UK Ltd with Design Engineers and HVAC Professionals

At ECE UK Ltd, we are dedicated to advancing energy efficiency and sustainability in building design, particularly in the realm of commercial HVAC systems in UK. As a leading air handling units manufacturer, we understand that a critical factor influencing HVAC energy efficiency is Specific Fan Power calculation and optimisation. Defined as the energy consumption of fans in relation to the airflow they produce, SFP is an essential metric for assessing the performance of ventilation systems. Through collaborative partnerships with design engineers and HVAC professionals, we can significantly reduce HVAC fan energy consumption through strategic ventilation system design, efficient air handling units (AHUs), and advanced motor technologies.

Optimise Specific Fan Power in AHUs - Complete Guide

What Is Specific Fan Power (SFP) in HVAC Systems?

Specific Fan Power is a crucial metric that measures the energy consumption of fans in relation to the airflow they produce, making it an essential indicator for assessing the performance of energy-efficient ventilation systems. This critical measurement is determined by two main components:

Internal resistance of the air handling unit
External resistance caused by the ductwork and air flow resistance

The final SFP figure directly impacts the overall HVAC energy efficiency of the fan system. Unfortunately, many design approaches overlook the comprehensive relationships between ventilation system design, AHU performance, and fan operations, potentially leading to inflated SFP values that compromise sustainable HVAC design.

Why SFP Matters in Energy-Efficient Building Design

Understanding and optimising SFP is fundamental to creating sustainable ventilation solutions that contribute to both environmental goals and operational cost savings. When SFP values are elevated, it indicates that the HVAC commissioning process may need refinement, and the system requires more energy to move the same volume of air.

Key benefits of optimised SFP include:

Reduced energy consumption and operational costs
Enhanced indoor air quality improvement
Better system reliability and longevity
Compliance with sustainable HVAC design standards
Improved overall commercial HVAC systems UK performance

How Duct Length and Air
Velocity Affect SFP

Reducing Duct Length for Optimal Performance

One of the most effective strategies for minimising SFP is to reduce the length of the ductwork. Longer ducts with more bends generate greater friction (Figure 1), resulting in increased resistance that the fan must overcome. By shortening the duct length (Figure 2), we can significantly lower the external pressure losses, making it easier for the fan to operate. This not only reduces energy consumption but also enhances system performance and reliability.

This approach not only reduces HVAC fan energy consumption but also enhances system performance and reliability, contributing to better HVAC commissioning outcomes.

Figure 3: Air moving through gradually expanding duct

Maintaining Low Air Velocity

In conjunction with reducing duct length, maintaining lower air velocities within the ductwork is crucial for minimising SFP and improving ventilation system design (Figure 3). Elevated air velocities lead to increased turbulence and friction losses, which elevate the energy requirements for air movement.

Benefits of Using IE6 Permanent Magnet Motors

The selection of high-performance Air Handling Units (AHUs) is vital in achieving low SFP values and optimal sustainable HVAC design. As an experienced air handling units manufacturer, ECE UK Ltd promotes the use of IE6 permanent magnet motors in modern AHUs, which provide superior efficiency compared to traditional motors.

Enhanced Efficiency Performance

IE6 permanent magnet motors (Figure 4) are engineered for high efficiency across various operational conditions, translating into reduced HVAC fan energy consumption and lower SFP values. These advanced motors represent the pinnacle of energy-efficient ventilation systems technology.

Figure 4: IE6 High Efficiency Fan with Permanent Magnet Motors

Figure 5: £ Savings Per Year for different motor operating schedules

Adaptive Control Features:

These motors integrate seamlessly with sophisticated control systems that monitor and adjust fan speeds in real-time to align with demand. This capability significantly reduces excess energy use during periods when full capacity is unnecessary, optimising Specific Fan Power calculation results.

Lower Internal Resistance:

By choosing AHUs with optimised internal components—including advanced heat exchangers and filters with enhanced nano technology (Figure 6)—internal resistance can be decreased further. This enhancement improves airflow efficiency and reduces SFP while contributing to better indoor air quality improvement.

Regular air handling unit maintenance ensures these advanced components continue operating at peak efficiency throughout their lifecycle.

Figure 6: Filter with Enhanced Nanoclass Technology

Role of Heat Recovery Units in
Reducing SFP

Increased thermal efficiency in heat recovery ventilation units positively influences Specific Fan Power calculation in accordance with the Ecodesign Directive 1253/2014 by reducing the energy consumption associated with the fan system.

Figure 7: Transfer of heat and coolth between the exhaust and supply air

Thermal Energy Transfer Optimisation

Heat recovery components in Air Handling Units (AHUs) facilitate thermal energy transfer between the exhaust and supply air streams (Figure 7), reducing the amount of additional heating or cooling required. This process decreases the heating and cooling coil size, which in turn reduces the resistance across each coil.

Enhanced System Performance

Higher thermal efficiency means more effective heat transfer, leading to:

Reduced thermal loads on downstream heating or cooling systems
Lower auxiliary energy requirements for temperature conditioning
Decreased pressure drop across the heat recovery unit
Improved HVAC energy efficiency overall

When thermal efficiency increases, the temperature difference that the fan needs to overcome diminishes, allowing the fan to operate at lower power for the same airflow rate, directly improving sustainable HVAC design performance.

Ecodesign Directive Benefits

The Ecodesign Directive 1253/2014 incorporates a performance-based approach that allows for adjustments or “bonuses” in compliance criteria based on enhanced heat recovery ventilation efficiency. For units with higher thermal efficiency (exceeding certain thresholds), the regulation provides bonus points or relaxations in SFP limits, recognising superior energy-efficient ventilation systems performance.

Sustainable Ventilation Solutions

At ECE UK Ltd, we believe that achieving optimal SFP values requires a collaborative effort involving engineers and HVAC professionals specialising in commercial HVAC systems UK. By engaging in joint discussions during the early design phase, we ensure that all aspects of the ventilation system design are integrated effectively.

This collaborative approach allows us to:

Analyse both internal AHU resistance and external duct resistance comprehensively
Develop innovative designs that enhance overall system performance
Optimise Specific Fan Power calculation from the outset
Ensure proper HVAC commissioning procedures
Deliver sustainable ventilation solutions that meet environmental goals

Learn more through our comprehensive case study: Hinckley CDC

Conclusion

In our commitment to providing sustainable ventilation solutions, ECE UK Ltd recognises the critical importance of lowering Specific Fan Power in Air Handling Units. Through the strategic implementation of shorter, low-velocity duct designs, coupled with high-efficiency Air Handling Units (AHUs) and IE6 permanent magnet motors, we achieve remarkable reductions in HVAC fan energy consumption.

By fostering collaboration among HVAC professionals and engineers, we pave the way for more efficient commercial HVAC systems UK that contribute to our collective environmental goals. Our comprehensive approach to sustainable HVAC design, combined with expert HVAC commissioning and ongoing air handling unit maintenance, ensures optimal indoor air quality improvement and long-term system performance.

Together, we can address the challenges of HVAC energy efficiency and work toward a greener future through innovative energy-efficient ventilation systems that prioritise both performance and sustainability. Contact ECE UK Ltd today to discover how our expertise in thermal energy transfer and advanced ventilation system design can optimise your next project.

Contact our team today

Get straight through to one of our engineers and start discussing the needs of your new air handling unit. Our team are on hand to work out a custom solution for you and your project. Just call 01634 729 690 or send us an email at sales@eceuk.com to get started.

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