Measuring Real-World ITE Thermal Phase Shift: An ESPHome and DS18B20 Tutorial

Introduction: Why Measure Real-World Phase Shift?

During an external thermal insulation (ITE) retrofit, the choice of insulation material (such as wood fiber) is often driven by theoretical thermal phase shift. However, there is often a gap between theoretical calculations and real-world performance on historical walls. This tutorial explains how to accurately measure this phase shift by embedding DS18B20 sensors within the wall layers and integrating them into Home Assistant using ESPHome.

Hardware Setup: Multi-Layer Integration

For this measurement, we use an ESP32 microcontroller flashed with ESPHome and three waterproof DS18B20 temperature sensors wired on a OneWire bus:

1. Outdoor Sensor (T_ext): Placed on the exterior facade, sheltered from direct sunlight.
2. Interface Sensor (T_intf): Placed precisely between the old brick/stone wall and the new ITE insulation.
3. Indoor Sensor (T_int): Placed on the inner surface of the wall.

ESPHome Configuration for the OneWire Bus

Here is the YAML configuration to integrate into your ESPHome node to report the three temperatures with ultra-high 12-bit resolution:

dallas:
  - pin: GPIO23

sensor:
  - platform: dallas
    address: 0x2c00000b12a34f28
    name: "ITE Outdoor Temperature"
  - platform: dallas
    address: 0x3c00000b12b45e12
    name: "Insulation Interface Temperature"
  - platform: dallas
    address: 0x4c00000b12c56f23
    name: "Indoor Wall Temperature"

Analyzing Phase Shift in Home Assistant

Thermal phase shift is the time delay between the peak outdoor temperature and the peak interface/indoor temperature. By exporting your Home Assistant data to InfluxDB and Grafana, you can easily calculate the time delta (t2 – t1) of daily maximums. High-performance wood fiber should yield a measured shift of 10 to 12 hours, successfully flattening the summer heat spikes.