Smart Net House: Climate Control for Protected Cultivation

Protected cultivation under net houses and polyhouses is one of the fastest-growing segments of Indian horticulture – but maintaining optimal microclimates manually is laborious and error-prone. A smart net house climate control system for protected cultivation automates temperature, humidity, CO2, and ventilation management, significantly increasing crop yields and reducing labour costs for Indian farmers. This guide covers sensor selection, controller programming, and practical tips for Indian polyhouse conditions.

Table of Contents

• Benefits of Smart Climate Control
• Key Parameters to Monitor
• Hardware and Wiring
• Arduino Control Code
• Actuators and Automation
• India-Specific Considerations
• Frequently Asked Questions

Benefits of Smart Climate Control

Studies from Indian Council of Agricultural Research (ICAR) show that smart climate-controlled net houses achieve 30-50% higher vegetable yields compared to uncontrolled structures. Temperature deviations of just plus or minus 5 degrees Celsius during critical growth stages can reduce flowering by 20-40% in tomatoes, capsicum, and cucumbers – the most profitable polyhouse crops in India. Automated climate control eliminates these losses while reducing irrigation water use by 25-35% through evaporation management.

For Indian farmers in states like Maharashtra, Karnataka, Himachal Pradesh, and Punjab where polyhouse cultivation is government-subsidised (National Horticulture Mission supports up to 50% of project cost), adding smart controls to an existing structure typically recovers investment within one crop cycle.

Key Parameters to Monitor

Hardware and Wiring

Core components for a basic smart net house controller:

• Arduino Mega 2560 – for multiple sensor and relay channels
• 4x DHT22 sensors – distributed at corners and centre of the house
• 4x Capacitive moisture sensors – one per growing bed
• 4-channel relay module (5V) – controls fans, misting, heater, irrigation
• 2-inch exhaust fan (220V) – ventilation when temperature exceeds setpoint
• Ultrasonic mist maker or nozzle system – humidity control
• I2C LCD 20×4 or OLED display – on-site status display
• WiFi module (ESP8266 or ESP32) – remote monitoring via phone

Arduino Control Code

#include <DHT.h>
#include <LiquidCrystal_I2C.h>

// Sensor pins
DHT dht1(2, DHT22);  // Corner 1
DHT dht2(3, DHT22);  // Corner 2
DHT dht3(4, DHT22);  // Centre
DHT dht4(5, DHT22);  // Corner 3

// Relay outputs (active LOW for most modules)
#define FAN_RELAY    8
#define MIST_RELAY   9
#define HEAT_RELAY   10
#define IRRIG_RELAY  11

// Setpoints
#define TEMP_MAX  26.0  // Turn on fan above this
#define TEMP_MIN  16.0  // Turn on heater below this
#define HUM_MIN   60.0  // Turn on mist below this
#define HUM_MAX   82.0  // Turn off mist above this

LiquidCrystal_I2C lcd(0x27, 20, 4);

float avgTemp() {
  return (dht1.readTemperature() + dht2.readTemperature() +
          dht3.readTemperature() + dht4.readTemperature()) / 4.0;
}

float avgHum() {
  return (dht1.readHumidity() + dht2.readHumidity() +
          dht3.readHumidity() + dht4.readHumidity()) / 4.0;
}

void setup() {
  dht1.begin(); dht2.begin(); dht3.begin(); dht4.begin();
  lcd.init(); lcd.backlight();
  pinMode(FAN_RELAY, OUTPUT);  digitalWrite(FAN_RELAY, HIGH);
  pinMode(MIST_RELAY, OUTPUT); digitalWrite(MIST_RELAY, HIGH);
  pinMode(HEAT_RELAY, OUTPUT); digitalWrite(HEAT_RELAY, HIGH);
  pinMode(IRRIG_RELAY, OUTPUT); digitalWrite(IRRIG_RELAY, HIGH);
}

void loop() {
  float temp = avgTemp();
  float hum = avgHum();

  // Temperature control
  digitalWrite(FAN_RELAY,  temp > TEMP_MAX ? LOW : HIGH);
  digitalWrite(HEAT_RELAY, temp < TEMP_MIN ? LOW : HIGH);

  // Humidity control
  if(hum < HUM_MIN) digitalWrite(MIST_RELAY, LOW);
  if(hum > HUM_MAX) digitalWrite(MIST_RELAY, HIGH);

  lcd.setCursor(0,0);
  lcd.print("T:");lcd.print(temp,1);lcd.print("C H:");lcd.print(hum,0);lcd.print("%");
  lcd.setCursor(0,1);
  lcd.print("Fan:");lcd.print(digitalRead(FAN_RELAY)==LOW?"ON ":"OFF");
  lcd.print(" Mist:");lcd.print(digitalRead(MIST_RELAY)==LOW?"ON":"OFF");

  delay(10000);
}

Actuators and Automation

Recommended actuator setup for Indian net houses:

• Ventilation: 2x Crompton or Orient exhaust fans (220V, 6-inch) on relay – triggered 2 degrees above setpoint with 5-minute hysteresis to prevent hunting
• Misting: Solenoid valve (12V) on drip misting line or ultrasonic humidifier – triggered when RH drops below 60%
• Heating (winter in north India): IR heater (500W) on relay with thermal cutout at 30 degrees Celsius for safety
• Shade net: 12V DC motor on roll-up shade net mechanism – triggered by BH1750 lux sensor above crop threshold
• Drip irrigation: Solenoid valve on main drip line – timer-based with soil moisture override

India-Specific Considerations

Indian polyhouses face unique challenges compared to European references:

• Summer peak load: In May-June, inside temperatures can reach 50+ degrees Celsius without active ventilation. Multiple fan banks and external shade nets are essential in Maharashtra, Karnataka, and Rajasthan.
• Monsoon humidity: July-September brings 85-95% RH – misting becomes irrelevant; focus switches to fungal disease prevention through targeted ventilation
• Power cuts: Use a UPS (1kVA) to keep the controller and sensors running during power outages; relay outputs default to safe state (fan on, heater off) when Arduino resets
• Voltage fluctuation: Indian 230V supply can vary 180-260V. Use a servo voltage stabilizer for the climate control system to prevent relay and sensor damage.
• Government subsidy: NHM and RKVY subsidise polyhouse installation; adding a digital climate controller strengthens the project report and increases approval probability

Frequently Asked Questions

What size net house can one Arduino controller manage?

A single Arduino Mega can monitor up to 16 DHT22 sensors and control 8 relay channels – sufficient for a single bay net house up to 500 square metres. For larger multi-bay structures (1000+ sq m), use a modular approach with one ESP32 per bay communicating to a central Raspberry Pi dashboard via WiFi or RS485 Modbus network.

How do I connect the climate controller to my phone for remote monitoring?

Add an ESP8266 (NodeMCU) or ESP32 module to send sensor readings to Blynk, ThingsBoard, or a custom web server. The ESP module queries the Arduino via I2C or Serial and relays data to the cloud every few minutes. Blynk is recommended for Indian farmers due to its simple phone app with configurable alerts and override buttons.

What crops benefit most from climate-controlled net houses in India?

Capsicum (bell pepper) gives the highest returns at Rs 80-180/kg farm gate but requires strict temperature control (18-24 degrees Celsius). Tomato, cucumber, and exotic vegetables (broccoli, colored capsicum) are popular. Cut flowers (gerbera, carnation) under climate control command Rs 3-8 per stem at wholesale – premium income relative to vegetable farming.

Is an IoT-connected system required or can it run standalone?

The system works perfectly standalone – the Arduino reads sensors, applies control logic, and drives relays without any internet connection. IoT connectivity adds remote monitoring and alert capability. Start standalone and add an ESP8266 WiFi module later as a non-invasive addition – no changes to the existing Arduino code required.

What is the return on investment for smart climate control addition?

For a 1000 sq metre net house growing capsicum, the additional electronics cost Rs 8,000-15,000. Improved climate control typically increases marketable yield by 20-30% (avoiding heat/cold stress crop loss) and reduces labour for manual monitoring and ventilation by 2-3 person-hours per day. At Rs 100/hour labour and Rs 100/kg capsicum price, ROI is typically achieved within the first growing season.

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