Demand driven ventilation on a budget, part 1 : the options

Introduction

Our house dates from the ages where energy efficiency was an afterthought, meaning that half of the windows are single glazed, the walls are solid brick and isolation was nowhere to be found. A perfect place to burn lots of dinosaur piss!

Well, I'd rather not. The roof already has been renewed, windows soon will be, and a layer of isolation will cover the existing brick walls. In Belgium, renovations of this order require me to get my ventilation in order: being able to extract air in the order of 400 m3 / hour.

A quick calculation tells me that the energy required to heat the air coming from outside to room temperature is in the order of 1 KWh per 400 m3. Pretty significant if you would keep this system turned on 24/24.

That brings us to demand driven ventilation. Let's just extract air whenever the air in a room is too polluted or humid. Or in Belgian Technical terms: a C+ ventilation system.

Options

What are our options? I'll pick a few popular brands. The configuration is one that I assume to be very common in similar renovations, a thorough one in which you do not want to have ducts through the entire house, to avoid losing space. In particular, this means that I will use both vents in my roof to extract from the attic and the first floor and vents in the cellar to extract from the ground floor and the cellar.

An important consequence is that I can't use one central extraction unit, I will have two separate small technical spaces in which I will centralize extraction hardware.

Renson

The Renson Healthbox is a system that is supposed to run on minimal power for each of the connected vents, and increases power based on measurement performed on the incoming air. As it comes with valves, I assume it adjusts the airflow using these valves to avoid extracting at max power everywhere when there is just one room that has bad air quality.

Sensors and valves are present inside the central unit, installation seems simple enough, you just attach the passive hardware and you're good to go.

In my case, I would have to buy this piece of active hardware twice, once for the attic and once for the basement, resulting in a total cost of EUR 2500 for the active hardware.

Duco

Duco is a bit more modular, the ducobox focus comes without the sensors and actuators. The box is EUR 650, a CO2 sensor/valve is EUR 200 and a humidity sensor/valve is EUR 150. In my case this would result in a total of about EUR 2000, probably a bit more including the remote etc.

Custom solution

Given my use case and me looking for a toy project, it quicly became obvious that I was going for a custom solution. As I'm - no idea why - documenting it, I'll try to make it easy to make, use and understand.

The basic design requirements : 

• Based on tube fans, which are compact and high performance. I'll go for models with a built-in valve preventing reverse airflow.
• The tube fans ideally have adjustable power. Depending on the room / use case this might not be the case for every single fan. E.g. a toilet might be ok with a simpler tube fan.
• The sensors should be affordable but still yield useable numbers. This might be one of the more interesting and research intensive parts.
• Home Assistant integration
• It should be trivial to hook up manual and semi automatic controls for people not wanting to use Home Assistant. In other words, a very simple IO interface exposing sufficient controls.

Cost estimation: between EUR 100 and 200 for a single tube fan, depending on the fanciness. Sensors : about EUR 50 for the raw hardware, including accessories might go up to EUR 100 per measuring spot. A raspberry pi, EUR 50. Other accessories : EUR 100.

As I've got 4 rooms where I'd like to have extraction, the active hardware will cost me an estimated EUR 1000. We'll see whether that holds once the hardware has been selected, the subject of the next post.