Thailand’s 2 IAQ Seasons: Completely Different Challenges
Rainy Season (May-October):
- Relative humidity 70-90% RH
- Mold grows rapidly in poorly ventilated rooms
- Dust mites at annual peak
- PM2.5 low — outdoor air is clean
Dry / Haze Season (November-April):
- Relative humidity 30-55% RH
- Bangkok PM2.5 frequently exceeds 50 μg/m³, especially March-April
- Northern Thailand (Chiang Mai, Chiang Rai) can exceed 200 μg/m³
- Cross-border smoke from Myanmar and Laos wildfires
Rainy Season Mode: War Against Humidity and Mold
Target: maintain humidity at 50-60% RH in all rooms.
Key equipment:
- Dehumidifier: Daikin or Mitsubishi 10-20L/day for 20-30 m² rooms
- Bathroom exhaust fan: auto-run 30 minutes after showering
- ERV mode adjustment: reduce fresh air intake to avoid importing outdoor humidity
Rainy Season Automation:
yaml
alias: "Rainy Season Dehumidifier"
trigger:
- platform: numeric_state
entity_id: sensor.bedroom_humidity
above: 65
action:
- service: switch.turn_on
target:
entity_id: switch.bedroom_dehumidifier
- delay:
hours: 2
- service: switch.turn_off
target:
entity_id: switch.bedroom_dehumidifier
Mold prevention measures:
- Check TVOC sensor after heavy rain: mold releases Microbial VOCs as it grows
- Apply anti-mold solution on high-risk areas (bathroom walls, wardrobes) every 3 months
- Never dry clothes indoors in closed rooms: adds significant moisture load
PM2.5 Season Mode: Seal Out External Pollution
Target: maintain indoor PM2.5 < 12 μg/m³ even when outdoor exceeds 50 μg/m³.
PM2.5 Season Automation:
yaml
alias: "PM2.5 Season Lockdown"
trigger:
- platform: numeric_state
entity_id: sensor.outdoor_aqi
above: 100
action:
- service: switch.turn_off
target:
entity_id: switch.erv_fresh_air_damper
- service: fan.set_percentage
target:
entity_id: fan.air_purifier_living
data:
percentage: 100
- service: notify.line
data:
message: "Outdoor AQI is high — please close all windows now."
HEPA H13 filter replacement frequency during PM2.5 season:
- Normal season: replace every 12 months
- PM2.5 season: inspect monthly, may need replacement every 6 months
- HA tracks filter runtime hours and sends automatic alerts
Automatic Seasonal Mode Switch
HA can use an Input Select entity for Season Mode:
- PM2.5 Season (1 November - 30 April): HEPA full speed + close fresh air if AQI > 100
- Rainy Season (1 May - 31 October): dehumidifier mode + exhaust fan boost
Set date-based automations to switch modes automatically, or let the outdoor AQI sensor be the deciding trigger.
Required Sensors for Seasonal IAQ System
SHT31/Sonoff SNZB-02 (temperature + humidity): 300-600 THB. Plantower PMS5003 (PM1.0, PM2.5, PM10): 500-800 THB. SenseAir S8 (CO2 NDIR): 1,800-2,500 THB. Sensirion SCD40 (CO2 + temp + humidity): 1,500-2,200 THB. SGP30/TVOC: 400-700 THB.
For a 3-bedroom home: total sensor investment 8,000-15,000 THB provides complete data for year-round seasonal IAQ management.