Hardwired PoE Smart Air Exchanger: Controlling Venmar Constructo HRV with Waveshare 8-ch Ethernet Relay & Home Assistant

alainmic · September 24, 2026, 2:23pm

Hardwired PoE Smart Air Exchanger: Venmar Constructo + Waveshare 8-ch PoE Relay & Home Assistant

Tired of wireless smart plugs and Zigbee relays dropping offline in basement mechanical rooms? Want to stop freezing Arctic air (-25°C) from entering during Hydro-Québec or dynamic peak pricing events without breaking factory wall switches?

Here is a complete engineering and automation guide for converting a Venmar Constructo 2.5 (Model 45110) or equivalent Broan/Nutone HRV into a local 2-speed smart ventilation fan with hardware button lockout using a Waveshare 8-ch PoE Ethernet Relay Module (SKU 24964).

Full GitHub Guide & Schematics:

gist.github.com

https://gist.github.com/alainmic/620665f9808deeed0f9e573fcd117ad2

venmar_constructo_waveshare_poe_relay_guide.md

# Hardwired PoE Smart Air Exchanger: Controlling a Venmar Constructo HRV with Home Assistant & Waveshare 8-ch Ethernet Relay

A complete engineering and automation guide for converting a **Venmar Constructo 2.5 (Model 45110)** or equivalent **Broan / Nutone Heat Recovery Ventilator (HRV / ERV)** into a fully integrated, local 2-speed smart ventilation system with **hardware button lockout** for cold-climate peak energy management.

---

## 1. Project Motivation: The Cold-Climate Mechanical Room Dilemma

In Canadian and northern US homes equipped with an HRV or ERV, ventilation is vital for indoor air quality and humidity control. However, controlling these units efficiently in a modern smart home presents two major hurdles:

This file has been truncated. show original

Key Highlights & Real-World Findings

100% Local PoE & Modbus RTU over TCP: Single Cat6 drop for 802.3af PoE power and Modbus RTU communication over TCP (port 4196). No Wi-Fi, no Zigbee mesh dropouts through concrete foundations.
The Symmetrical 4-Relay Defragged Architecture:
- Zone 1 (Bathroom OC): Relay 1 (NC) in-series for bathroom button lockout; Relay 2 (NO) across OC & OL for HA High Speed Boost.
- Zone 2 (Upstairs B): Relay 3 (NC) in-series with ground for wall control lockout; Relay 4 (NO) across B & G for HA Low Speed.
Fail-Safe NC (Normally Closed) Lockouts: Relays 1 and 3 are de-energized 99% of the year. Factory bathroom buttons and wall controls function 100% autonomously if Home Assistant or the relay reboots.
Winter Peak Lockdown: Energizing Relays 1 and 3 during peak events physically prevents anyone from accidentally pressing a bathroom boost button and sucking freezing outdoor air inside during 53¢/kWh peaks.
Modern Template Fan Integration: Full YAML for modern template: - fan: schema (no deprecated fan: - platform: template warnings) with mutual interlocks.
Automations Included: Smart Dehumidistat via Nest humidity sensors, 20-min High Speed boost auto-off, and 3-stage Hydro-Québec dynamic peak management.