Assessing the impact of mechanical ventilation on indoor air quality in homes in subtropical New Zealand

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Dr Terri-Ann Berry, Joanne Low, Shannon Wallis, Roger Birchmore,

Helen Gremillion, Guillermo Prado-Ramirez, Dan Blanchon, Marleen Baling, Erin Doyle, Tianyi Tang and German Hernandez,

Environmental Solutions Research Centre, Unitec

T H I S W O R K B Y E S R C I S L I C E N S E D U N D E R A C R E A T I V E C O M M O N S A T T R I B U T I O N - N O N C O M M E R C I A L - N O D E R I V A T I V E S 4 . 0 I N T E R N A T I O N A L L I C E N S E .

Assessing the impact of mechanical

ventilation on indoor air quality in

homes, in sub-tropical New Zealand

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Introduction

Environmental Solutions Research Centre

• Energy efficient buildings can negatively impact indoor air quality (IAQ)

• Inadequate ventilation can lead in accumulation of indoor pollutants

• Lack of evidence demonstrating mechanical ventilation benefits on IAQ

• Relationship between “occupant perceived”

and data-driven results

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Positive Pressure Ventilation (PPV)

• Mechanical ventilation

• Extracts and filters dry air from roof space and brings it inside

• Creates a slight positive pressure which drives out stale, old air

• May exchange indoor and outdoor air

• What is its effect on IAQ?

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PPV CHARACTERISTICS

• Fan

• Draws air from roofspace into home

• AC centrifugal, 810 m

³

/hr, 92 Watt

• No. of fans selected depends on house size (1 fan = 100 m

²

area).

• Filter

• Filters particles > 0.4 µm

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HUMIDITY & MOLDS

• Healthy Homes 30-60%

(ASHRAE,2016)

• Survival of some viruses is longer at lower relative humidity (20%−30%) (Bing- Yuan, 2018).

• Bacteria and fungi favour

growth/diversity at higher

humidity (Dannemiller,2016).

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Method – Design

15 homes across Auckland and Hamilton Investigated conditions before and after

installation of a positive pressure ventilation system (PPV) using:

1. IAQ – low cost sensors

2. Mold development – PCR & genome sequencing

3. Occupant comfort levels – questionnaires

Collaborative study between

• ESRC (IAQ),

• AMS (Mold),

• School of Computer Sciences (IAQ sensors)

• School of Health & Social

Practice (questionnaires)

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Method -

Recruitment

Monitoring homes six

weeks before and after the installation of PPV

Auckland - 9 houses

• 7 urban, 2 rural

• Ave. house size 117 m

²

Hamilton - 6 houses

• 4 urban, 2 rural

• Ave. house size 134 m

²

House

locations

, Auckland

House locations, Hamilton

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Method – Mould and IAQ

• Mould samples taken in living room, bathroom, and bedroom (swab and vacuuming)

• Three IAQ monitors per house – master bedroom, bedroom, and kitchen/living area.

IAQ monitors measure PM

₁₀

, PM

_2.5,

T & RH

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Method - Questionnaire

• Two adult occupants per home

• Perceived levels of comfort, IAQ and mold

• House construction

• Condensation and mold

• Heating and cooling habits

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Results – Temperature and RH

• Improvement in perception of heating effectiveness and

temperature

• No homes dissatisfied with temperature post-PPV

• Measured temperatures slightly increased (1-10%) in 12, and

decreased in three

• Measured RH reduced in all but

two houses (4-14%)

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Results - Satisfaction

Pre HRV Post-HRV Parameters Mean rank

(Std Dev)

Mean rank (Std Dev) Odour 3.5 (1.3) 4.5 (0.02) Humidity 2.6 (1.2) 4.7 (0.01) Air Flow 3.1 (1.2) 4.4 (0.03) Dust 2.9 (1.1) 3.8 (0.03) Temperature 2.8 (1.0) 4.4 (0.02) Air quality 3.0 (1.0) 4.6 (0.02) Pre-installation:

57% had existing problem with IAQ Post-installation:

93% had no IAQ problem.

Significant increase in ranking post-installation improvement incl. temperature (despite

evidence)

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RESULTS SAMPLE - HAMILTON

Parameters Pre Post Change (%) SD Change (%)

PM_2.5 (µg/m³) 14.89 4.92 -67 -32

PM10 (µg/m³) 16.68 5.46 -67 -33

Temperature (°C) 19.1 17.9 -6 -23

Dew Point (°C) 12.7 10.2 -20 -21

Relative Humidity (%) 67.8 61.3 -10 -26

Shannon please can

you crop off the SD

change column ?

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Results – PM

• Pre installation: 57% of

participants had IAQ issues

• Post: only 7% had IAQ issues

• Measured mean reduction of 86.7% after PPV use

• Two homes had little or no PM reduction

• PM reductions were higher

indoors than outdoors

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Results – Fungal DNA

• Overall decrease in number of fungal DNA measured (not statistically significant)

• No effect from household pets and RH

• Positive correlation found between fungal DNA and temperature and PM

_2.5

(R

²

= 0.73 &

0.62, p = 0.006 & 0.02, respectively)

• Post-installation, Auckland homes had

significantly lower fungal DNA than

Hamilton.

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Conclusions

• Overall greater satisfaction with home heating and less extreme thermal sensations

• Improved environmental comfort likely due to

decrease in humidity

(perceived) and increased

air flow (by PPV)

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