Overview

A quiet air purifier that can be automated to run at full speed when there is nobody in the room.
Uses MERV11 Filters and Arctic P12  Completely silent when at 40% fan speed while still moving quiet a bit of air.
Integrates with HomeAssistant to report temperature and relative humidity and can be automated to go full speed at night or depending on temperature or people activity.

The 9 fans are connected to one another using a small plastic connector and then mount to the removable top of the air purifier. 

Components used

The model fits air filters that are 16" x 24" x 1" 
I used filters rated MERV 11 /1000 MPR - Filtrete AD25-6PK-1E that i got on sale. 
https://www.amazon.de/dp/B07FNXS7HQ?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

It fits 9x 120mm pc fans. I used Arctic P12 PWM fans and a generic powered fan hub for 12v power to the fans.
5pcs Arctic P12 PWM 
https://www.amazon.de/-/en/gp/product/B096JXXKP5?smid=AUBM4K0YLFI9J&th=1

Fan Hub 
https://www.amazon.de/dp/B0C56ZBP7V?ref=ppx_yo2ov_dt_b_fed_asin_title

For control there is a mount for  esp32 board on a breakout board to step-down from 12v to 5v
Board used -  https://www.amazon.de/dp/B0CLD28SHQ?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

This breakout board accepts 12v so one 12v power adapter is used to power the board and the fan hub.
Power Supply 12v 2A - https://www.amazon.de/dp/B0D7946K8T?ref=ppx_yo2ov_dt_b_fed_asin_ti

The fan hub uses Sata power conector so I'm using this Molex to Sata power cable to connect to 12v. Instructions to follow.
Molex to Sata Power cable to power the fan hub - https://www.amazon.de/dp/B07TWFWZ7Y?ref=ppx_yo2ov_dt_b_fed_asin_title

(Optional) And just because why not, Temperature and Humidity sensor, that can be monitored by HomeAssistant 
https://www.amazon.de/dp/B0DYDHL5K2?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

(Optional) 10x3 magnets to hold the top 
https://www.amazon.de/-/en/Magnets-Strong-Fridge-Neodymium-Magnet/dp/B0CPV7BBKN?th=1

Instructions:

I printed the Frame in PETG it flexes when there are no filters but when fully assembled its quite rigid. Printing in PLA might work but not sure.

Print volume needed around 230x230x250 

After the Frame parts are printed they need to be glued with superglue. There are notches to help align the frame.

The 9 fans need to be screwed to the inner one using the fan connector before inserting them in the frame lid.

- The esp32 mount and 12v jack mount need to be installed with m3 screws.

- The DHT21 temp/humidity sensor has Power/GND/(Digital)Data wire that need to be connected to the ESP32.The DHT21 temp/humidity sensor has Power/GND/(Digital)Data wire that need to be connected to the ESP32.

The fan hub is double sided taped to the flat mount on the fan frame. All the fans are wired to the hub and cable-managed with the plastic clips. 

The fan hub is powered using the Molex to Sata power cable. only 2 of the wires are used the other 2 can be cut. In this case, Yellow - 12v Black - Ground. 

From the ESP32 PWM signal and GND connect to the fan hub input port

 

 

 

 

 

This is my wiring diagram (yes, its AI, sorry):

                         ┌───────────────┐                         
                         │    12V PSU    │                         
                         │ +12V     GND  │                         
                         └───┬──────┬────┘                         
                             │      │                              
                ┌────────────┘      └────────────┐                  
                │                                │                  
        ┌───────▼───────┐                ┌───────▼───────┐          
        │   FAN HUB     │                │  BUCK 12V→5V  │          
        │ SATA +12V ◀───┘                │ IN+  ◀─ +12V  │          
        │ SATA GND  ◀────────────────────│ IN–  ◀─ GND   │          
        │                               │               │          
        │ PWM IN ◀──── GPIO23 (ESP32)   │ OUT+ → +5V    │          
        │ TACH (unused)                 │ OUT– → GND    │          
        └───────────────┘               └───────┬───────┘          
                                                │                  
                                         ┌──────▼───────┐          
                                         │    ESP32     │          
                                         │ VIN ◀─ +5V   │          
                                         │ GND ◀─ GND   │          
                                         │              │          
                                         │ GPIO23 → PWM │          
                                         │ GPIO18 ◀─ DHT│          
                                         │ 3V3   → VCC  │          
                                         │ GND   → GND  │          
                                         └──────────────┘          
                                                 │                  
                                ┌────────────────┴────────────┐     
                                │   AM2301 / DHT21 Sensor     │     
                                │ VCC → 3.3V (ESP32)          │     
                                │ GND → GND (common)          │     
                                │ DATA → GPIO18 (ESP32)       │     
                                └─────────────────────────────┘   

Programing

The esp32 processor is flashed with esphome and its running the following .yaml 
For instructions on installing esphome

 

esphome:
  name: esphome-web-480ba4
  friendly_name: Air Purifier
  min_version: 2025.5.0
  name_add_mac_suffix: false
esp32:
  board: esp32dev
  framework:
    type: esp-idf
logger:
api:
ota:

platform: esphome

wifi:
  ssid: "wifi_name"
  password: "wifi_pass"
PWM: ESP32 GPIO23 -> HUB PWM IN (25 kHz)
output:

platform: ledc
pin: GPIO23
frequency: 25000 Hz
id: fan_pwm

fan:

platform: speed
name: "Air Purifier Fan"
output: fan_pwm
speed_count: 100
id: air_purifier_fan

-------- AM2301 (DHT21/AM2301A) --------
sensor:

platform: dht
pin: GPIO18
model: DHT22      # use DHT22 for AM2301/DHT21
update_interval: 15s
temperature:
  name: "Air Purifier Temperature"
  accuracy_decimals: 1
humidity:
  name: "Air Purifier Humidity"
  accuracy_decimals: 1