How not to fail the IAQ test
Speaking to the CIBSE Journal, SAV’s Lars Fabricius has outlined the benefits of low noise MVHR (mechanical ventilation with heat recovery) units, individually mounted within each space, for maintaining acceptable indoor air quality (IAQ) in classrooms. “Such units are easily retrofitted to existing classrooms and can be configured to provide true demand controlled ventilation by modifying the ventilation rate in relation to the key IAQ parameters of CO2 concentration or relative humidity. Control can also be arranged via PIR movement sensors, simple timers or through an interface with a BMS,” he observed.
“A large measure of temperature control is provided by a combination of automatic bypass, speed differential between fans, night cooling and optional cooling modules,” he added.
“The common alternative, opening windows, offers no opportunity to recover heat from the outgoing air. Additionally, school staff tend to open windows in response to rising temperatures rather than ‘stuffiness’ caused by elevated CO2 levels. There are also issues of security, air pollution and noise ingress associated with opening windows,” he continued.
He also noted that traditional centralised ventilation systems are typically specified on the assumption that all of the spaces will be fully occupied all of the time. However, as occupancy of teaching spaces varies considerably through the course of the day and evening, this can waste energy through continuous ventilation of unoccupied or partially occupied spaces.
“Decentralised units use high efficiency, EN308-compliant counter-flow aluminium heat exchangers that recover at least 84% (dry bulb) of the heat energy in outgoing air (91% at 80% relative humidity). An integral data logger constantly measures the performance of the unit. Further energy savings are achieved by the use of variable speed EC motor technology to minimise the energy consumed by the ventilation drives,” he concluded.
“As classrooms become better insulated with improved air-tightness, ventilation design becomes increasingly important for maintaining acceptable (IAQ) without energy wastage.”
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