Guest Blog Post: How Decentralised Ventilation Reduces CO2 Levels While You Sleep

Today's blog post is written by Matt, a customer who recently purchased two LUNOS Nexxt-E decentralised ERV systems.

My "HRV Journey" began after I'd completed a lot of gap sealing in my house, performed in search of better energy efficiency. I had a vague awareness that indoor air quality could become a particular concern with a well-sealed house, so I decided to buy a CO2 meter compatible with my home automation system, Home Assistant, to see what was going on with CO2 levels in my bedroom overnight.

It's fair to say the results shocked me:

Readings well over 2,500ppm overnight, when the maximum "healthy" level is considered to be around 1,000ppm. Not to mention there's research showing once you exceed 900ppm sleep quality rapidly declines. And this was just with one person (and a cat! 😆) in a fairly large bedroom, which while relatively well sealed, certainly can't claim to be airtight (two doors with typical 10-20mm cutouts underneath, and a somewhat-leaky aluminium sliding window).

I even observed that when I had several guests in the dining room downstairs for a few hours - about as far away from the bedroom as you can get in the house - the CO2 readings gradually started to climb, eventually peaking out around 800ppm. I can only imagine what the CO2 levels downstairs were at that time!

Looking for a solution to this problem led me to discovering the concept of mechanical ventilation, and specifically HRV, and doing a lot of reading on the topic. That, combined with some fantastic advice from Cam and Claire at Fresh Ventilation, eventually led to me purchasing and installing two LUNOS Nexxt decentralised HRV units - one in the master bedroom, and another in the living room.

The results speak for themselves:

CO2 levels in the bedroom never exceeding ~850ppm overnight - and despite some additional gap sealing vs when the "before" graph was taken. This is with the Nexxt operating in its second slowest fan speed mode, which is almost completely inaudible.

Apart from their impressive thermal performance and noise characteristics, another key reason I chose LUNOS for my HRV units is that they are one of the few options which allow for easy and comprehensive integration into home automation systems (by allowing the unit mode and fan speed to be controlled via a 0-10V input). This was a key requirement for me, and one which is already letting me automatically adjust the fan speeds based on the "house mode" my house is in (e.g. night, away, day [with someone at home]).

For example, when the house is set to "day" mode in Home Assistant, it automatically sets my units to fan speed 4 [out of 8] - a speed at which they are quiet, but move enough air to keep CO2 levels low. When set to "away", the fan speed is automatically increased to 6 for a maximum of two hours, to quickly ventilate the house at a time when noise is not a concern, before dropping back to fan speed 2 for thermal efficiency reasons until someone returns home. And when set to "night", the unit in the bedroom is automatically slowed down to fan speed 2, allowing it to manage CO2 overnight while keeping noise to a minimum.

I haven't yet gotten any further than that with automating the Nexxt units, but there's plenty more that their home automation integration capabilities allow, and I intend to implement soon. Such as:

• Dynamically adjusting the fan speeds when in "home" mode in response to measured CO2 levels - i.e. slowing the units down for maximum thermal efficiency when CO2 levels are low, and speeding them up only when CO2 levels rise.
• Taking into account external humidity in the aforementioned automation - e.g. keeping the fan speed low even if CO2 levels are rising (within reason), if it is very humid outside.
• Taking into account room presence in the aforementioned automation - e.g. slow down the HRV unit in the living room if there are people actually in the living room, to minimise noise, and speed it up again when the room becomes unoccupied again.
• Setting up a single "switch" in Home Assistant to quickly ventilate the house, e.g. for use in the evening when it is cooler outside than in, which will set both HRV units to only intake fresh air (rather than performing heat recovery functions) and also turn on one or more extractor fans to balance the airflow.

Overall - I'm extremely happy with my two LUNOS Nexxt units, and the automation abilities are an extra cherry on top. They're doing a great job - not just evident through CO2 sensor data, but also the simple fact that the air in the house never feels "stale" anymore - which used to be a problem. It's noticeable to the point where visitors have, unprompted, commented on how "fresh" the house feels, despite the fact that all windows and doors are closed. And of course, this is all being achieved with minimal thermal loss.