Produced in Association with


SERIES 22 / Module 05 Ventilation


maintain airflow and reduce fan energy consumption. ● Periodically calibrate sensors and controls to ensure that they are operating as intended. ● Regularly check for and repair air leaks in ductwork to reduce energy losses. ● Check and adjust control time schedules to match actual occupancy patterns e.g. if low to zero occupancy on Friday afternoons the ventilation can be turned off earlier. ● Check & adjust temperature set points e.g. for an office space energy efficient set points would be to heat up to 20°C and cool down to 23°C.


2. Use of low-pressure drop filters ● Review the air handling unit air filtration requirements and consider if lower pressure drop equivalent air filters can be used, or, if a lower air filtration standard can be tolerated. ● Select filters that have low-pressure drops to reduce the energy required for air movement. This will save fan power energy consumed. For example using Medium (‘M’ type filters) in place of Fine (‘F’ type filters).


3. Optimise ventilation rates ● In many cases the original design of an air handling unit has been superseded by actual operations. It is therefore prudent to review design and actually required airflow rates and to reset ventilation rates to meet but not exceed regulatory requirements, avoiding over-ventilation. ● Where possible implement zoning in the ventilation system, allowing different areas to be ventilated according to their specific needs rather than ventilating the entire building uniformly e.g. separating


spaces that require 24/7 ventilation from those that require only 0900/1700 air treatment.


4. Optimise for night cooling and free cooling ● Consider night cooling ventilation strategies and utilise cooler night air to ventilate and cool the building, reducing the need for air conditioning during the day. ● Consider free cooling strategies utilising outside air when it is cooler than the indoor air for cooling purposes, bypassing the need for mechanical cooling.


Figure 2: Thermal image of an air handling unit heating coil in operation. Equipment


Automated controls and sensors Fans


Heat pump Humidifier


Motors: drive elements Packaged chillers units


Packaged steam generators/ancillaries Plate heat exchanger Pumps


Run-around heat recovery coil Thermal insulation


Thermal wheel: rotary heat (recuperator)


Economic life - years 10 15 15 10 15 20 25 20 20 25 30 15


Table 3: Economic life of ventilation components extracted from CIBSE Guide M3


5. Demand controlled ventilation ● Demand controlled ventilation is a method of adjusting ventilation rates based on real-time occupancy levels or indoor air quality measurements, typically using CO₂ or occupancy sensors and variable speed fans. ● For example an office space could be provided with 100% ventilation whilst its CO₂ sensor reports 1,000ppm CO₂, 50% ventilation at 600ppm CO₂ and 25% at 400ppm CO₂. ● By only ventilating spaces as needed, rather than at a constant rate demand controlled ventilation reduces unnecessary energy use. This saves fan power and heating and cooling energy inputs and can yield significant savings.


6. Efficient fan systems ● Ideally replace existing older life expired fans with high-efficiency fans e.g. EC Drives. The replacement of belt fans with EC fans can save approximately 25% of fan energy. It is notable that EC Fans are also able to be variably speed controlled. ● Ensure that fans are correctly sized for the application to avoid excess energy use due to oversizing.


7. Ventilation heat recovery (VHR) ● The most efficient method is the use of thermal wheels where heat recovery efficiencies can be as high as 80%. However, in retrofit applications it may be more suitable to install run around coils but these have lower efficiencies of 40-50%.


REFERENCES


1. Average values obtained from a sample of recent energy audits by the author.


2. CIBSE Guide A Table (A)1.1 Recommended comfort criteria for specific applications.


Figure 3: A life expired belt driven AC fan with poor efficiencies. Figure 4: A replacement EC fan in practice


3. CIBSE Guide M Appendix 13.A1 : Indicative life expectancy factors.


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