Energy Recovery Ventilation/Heat Recovery Ventilation

[Prof Tournesol]

I thought it would be helpful to start a discussion on this. We have a reasonably well-sealed house in North East Victoria and, several years ago, installed a Netatmo weather station. This includes an internal module that, amongst other things, measures CO2. This has also become topical with Covid as it's an indirect measure of air freshness. To our horror we watched our own Anthropogenic House Warming events, with CO2 levels usually above 2000ppm. This became a problem in winter it isn't practical to open windows. We also have problems with bathroom condensation and cold, not surprising when we discovered that our bathroom fans 'extracted' into a sealed roof cavity!

We looked at several HRV/ERV options. Zehnder had a system that required internal ducting and we had no accessible roof cavity, the Minister for Finance and Aesthetics put her foot down over having exposed ducting or enclosing the ducts with internal bulkheads. We settled on a German-made Lunos system, distributed in Australia by Laros, based in Canberra. This is a very simple system that consists of paired wall mounted fans that work in synchrony, one blows whilst the other (at the other end of the house) sucks. The air passes over a ceramic heat exchanger, then, after a few minutes, they reverse direction in synchrony. We have some additional bathroom units that also control humidity.

Installation was simple, it involved drilling a circular hole in the wall and inserting, then carefully sealing, the Lunos units. They are hard-wired in pairs, so needed connecting by an electrician. They come standard with pollen filters, but after the 2019/20 fires, we've opted for HEPA filters. They are deeper than our wall thickness so we had to enclose them externally in boxes, but if you had a thicker wall or built them into a cupboard, they would be extremely discrete.

It's early days, 3 weeks, I'm keen to see what happens in winter, but so far CO2 levels are below 1000ppm, mostly below 800ppm on the middle fan speed setting, sometimes down to 400ppm. We have no bathroom steam issues, the mirrors haven't even fogged up. Certainly recommended for anyone with a moderately well-sealed house, it's worth checking on your internal air quality. 

What doesn't it do? This unit feels like it was designed in the pre-internet era, totally hard wired, no connectivity, 2 rocker switches per pair of units with 4 switch combos (00, 01, 10, 11) to control the speed options. I'm thinking of changing to automated switches linked to the Netatmo weather station that monitors internal CO2 levels to automate the fan speeds.

The external boxed HRV unit

 

An internal unit

 

[Full Range]

We have different conditions and needs in Queensland 

Several years ago I installed a Cardiff Air system for cooling and air circulation 

It’s basically a very large fan installed in the ceiling, and it draws air in through open windows and then vents through the ceiling cavity and out through the eaves 

Works great in just about all scenarios except on days with high heat and humidity 

[Marc]

Interesting @Prof Tournesol- what was the actual aim, just to reduce CO2 levels within the residence?

[Prof Tournesol]

8 hours ago, Marc said:

Interesting @Prof Tournesol- what was the actual aim, just to reduce CO2 levels within the residence?

CO2 is one consistent measure of air quality and freshness. Hospitals are measuring it to help indicate where Covid may be accumulating in air droplets, for instance. Spring and autumn are easy, we can just open a window to improve ventilation. If we try that in summer or winter we get too much heat transfer. The HRV allows us to ventilate without heat transfer (or minimal) so we can have fresh air, often better quality than outside as it is HEPA filtered on the way in and out, and the two ERV units in the bathrooms manage humidity. I've spoken to many ERV users who tell me that cleaning mould in the bathroom stopped when they installed ERV, so it just controls the internal environment in a way that heating and air conditioning and ordinary extraction fans cannot. The more air-tight your house, the greater the advantage you'd get from HRV.