Air handling units can be significant energy consumers. Modern technologies dramatically reduce consumption while maintaining or improving performance.
Where AHUs Use Energy
Understanding consumption patterns identifies saving opportunities:
Fan Energy
Fans move air through the AHU and distribution system. Fan energy is proportional to airflow and pressure, and varies with the cube of speed – halving speed reduces energy by 87.5%.
Heating
Warming supply air in winter consumes significant energy in UK climates. Heating loads depend on ventilation rate, temperature rise required, and operating hours.
Cooling
Removing heat from supply air in summer. Less dominant than heating in UK but increasingly significant with climate change and internal gains.
Humidification
Adding moisture to supply air. Can be significant energy consumer where required, particularly steam humidification.
Energy Saving Technologies
Heat Recovery
Captures energy from exhaust air to pre-condition supply air. Reduces heating loads by 50-80% depending on efficiency. Primary energy saving technology for ventilation.
Types include plate heat exchangers, rotary wheels, and run-around coils. Selection depends on application requirements.
EC Fans
Electronically commutated fans are significantly more efficient than AC motors, particularly at part load. Direct drive eliminates belt losses. Variable speed is inherent.
EC fan retrofits often pay back within two to three years through energy savings.
Variable Speed Drives
For AC motor fans, VSDs enable speed control. Reducing speed at part load saves substantial energy. Essential for demand-controlled ventilation.
Demand-Controlled Ventilation
Matching ventilation to actual occupancy via CO2 sensing or other indicators. Reduces unnecessary ventilation when spaces are lightly occupied.
Savings depend on occupancy patterns. Intermittently occupied spaces benefit most.
Economy Cycle (Free Cooling)
Using cool outside air for cooling when conditions suit. Reduces mechanical cooling loads in mild weather.
Works best in climates with significant cooling requirements but cool ambient temperatures. UK climate offers good free cooling potential in spring and autumn.
Enthalpy Control
Considers humidity as well as temperature when selecting between fresh and recirculated air. More effective than temperature-only economy cycles.
Optimum Start/Stop
Controls learn building response and start equipment just in time to achieve conditions by occupancy. Avoids running equipment longer than necessary.
Night Cooling
Using cool night air to pre-cool building thermal mass. Reduces next-day cooling loads. Requires suitable building construction and control systems.
Low Pressure Drop Design
Minimising resistance through AHU and ductwork reduces fan energy. Filter selection, coil sizing, silencer design, and ductwork layout all contribute.
Measuring and Verifying Savings
Energy saving claims need verification:
Sub-metering
Monitor AHU energy consumption directly. Compare before and after any changes.
Normalisation
Account for weather differences, occupancy changes, and operational variations when comparing periods.
Commissioning
Ensure systems operate as designed. Poorly commissioned systems waste energy regardless of efficient components.
Ongoing Monitoring
Energy consumption drifts over time as components degrade and controls drift. Regular monitoring identifies problems before they become significant.
Whole-Life Cost Perspective
Higher efficiency equipment often costs more initially. Evaluate on whole-life cost:
- Higher purchase price
- Lower energy consumption
- Potentially lower maintenance
- Longer service life
Present value calculations demonstrate true economics. For equipment running continuously, energy costs typically dwarf purchase price over equipment life.
Our Efficient Equipment
i-Flow designs AHUs with efficiency in mind. Heat recovery, EC fans, and low-pressure-drop construction come as standard in many applications. Contact us to discuss energy-efficient solutions for your project.
