Posted By: GotanewlifeReally good info. Really. But now do it again with the window being opened in another room, preferably at the end of a corridor on the same floor, that would represent a FreshR type scenario.

The window I've been using to do these tests is exactly in the location where I'd put the unit. So for my particular case, it does represent that scenario.

Posted By: GotanewlifeOK but that is for one room, were you not hoping the unit would have an effect beyond that room. Obviously I started reading this thread half way through. Sorry.

If you have a look back through the thread I think you'll find the answer to your question. Yes I am hoping the unit can have an effect throughout the whole flat. However, I live in a smallish 2 bed flat, not a 10 bed mansion so it seems feasible. The Fresh-R or Blumartin units seem able to turn over a sufficient quantity of air for that volume of space. There is of course the question of whether it will reach the points furthest from the unit, hence the tests described just above (which, ignoring the effect of bedroom doors, represent measurements taken at just about the furthest possible distance from the unit).

A couple of pages back you'll see my tests of what happens in one of the bedroom looking at what goes on with the door open or shut. With the oor shut there is not enough air exchanged with the rest of the flat to keep the CO2 levels reasonably low. Therefore I'll likely be looking as some kind of cascade ventilation system where a standalone fan moves air in/out of the bedroom(s) from the hallway where the unit will be located.

I agree, I can't fully derive what a Fresh-R type device would achieve, because I would be dependent on what rate of air exchange its control system decides to provide given different CO2 concentrations and so on.

Also, I don't know how to calculate what a window, open by X mm, is equivalent to, in terms of an in-wall unit providing a certain rate of air exchange.

What I can however derive - I think - is that if I provide adequate access to fresh air at a certain position in my flat, then it does seem that in the largest room its benefits will reach the parts of that room which are furthest from the unit, without any additional forced air circulation.

This is because my last set of measurements were taken with the sensor placed at the point which is furthest from where the unit would be. The unit would be where the window currently is - the window that I was opening to varying degrees in my tests.

I agree there are lots of vagaries to do with wind and stack effect and so on, which would apply both during my tests and when a Fresh-R unit was installed. I'm unfortunately limited in what I can do about this. All I can say is that all my tests were done on days that weren't particularly windy. Also, the effect of opening the window is very clear in the results; the effect I feel is strong enough that it's not so marginal as to be overwhelmed by variations in conditions. I wouldn't claim to be able to prove that to you objectively though, with the results I have. I can say that when I repeat the tests at different times, the results are fairly consistent. The graphs shows the results of four tests I did when I left things undisturbed for several hours afterwards. There were other occasions where I did it and then opened other windows within an hour or so, because I didn't feel like sitting in a stuffy room. On those occasions the peak values, and the slope of the first part of the graph following them, were fairly similar to those seen in the full-duration tests.

One thing that occurred to me was whether this kind of CO2 test could be an alternative way of testing airtightness. Where for whatever reason a blower test was impractical, or too expensive. You would somehow produce a certain level of CO2 and then measure its rate of decline.

Probably too many variables to make it meaningful.

In my case, the fact that opening a window just a crack produced a significant effect, makes me think that the airtightness I've achieved must be - with the help of some motivated reasoning - "fairly good".

Posted By: Ed DaviesIt frustrates me no end to see all these graphs people produce of temperature, etc, against time. That's interesting as a first look but not really helpful for understanding. Scatter plots and correlations of appropriate variables might be more illuminating though we see them so rarely that it's hard to say.

Maybe that kind of data will become more easily obtainable with an increase in home automation systems.

Doing my tests, the sensor records CO2 levels, but I have to manually record things like: how many people were in the room, when did I start/stop cooking, when did I open and close windows, etc etc. That's labour-intensive and prone to error/gaps. In a house where these things are recorded automatically with occupancy sensors and so on, the kind of scatter plot data you describe would be much easier to produce. I agree it would be much more interesting and informative.

Of course you still have the problem that no two houses are really the same, and where they differ, it can be in a multitude of ways, so comparing between buildings would still be very tricky.

Au contraire, it is entirely clear what it monitors - nothing!

This is very expensive for what it is. Any standard compact MVHR can be plumbed into a cupboard without any pipes other than 2 stubs to outside. The one I have has reduced fan speed frost protection (but mine is adjustable for temp), mine has 3 speeds but mine isn't wireless. Neither can be controlled by an external sensor. Mine is quietish yours is very slightly quieter, notionally, but still too loud IMO to be left out on display as suggested by its mirror finish SS coating. In short, apart from the wireless gimmick the only thing you are getting for the extra £650 is a post heater.

DIY a std one into a cupboard on an outside wall, you'll get a better result niose wide, more controllability and save money! External pipes just finish in 90 ss bull nose vent things will be more effective, and internally you get to choose the best inlet and outlet positions rather than being fixed by the unit and you can have much larger vents.


I parallel wired this into my unit's boost switch input and it is extremely effective and dead cheap - (also for sale in UK)

https://www.amazon.co.uk/gp/product/B00GNT1NJY/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A2I0KD4PFXY56D

There is a thread on it.

I have found this:

https://www.heatraesadia.com/products/heating-and-ventilation/mechanical-ventilation-and-heat-recovery/advance-and-advance-plus.htm

which is starting to look like my favourite. Unit is about £800. It has various add on sensors, including CO2, and what looks like a sensible and fairly comprehensive control system. SFP looks good. As far as I can make out the "trickle" rate can be set down to 25m3/hr - not quite as low as I'd like ideally but better than most others.

The CO2 sensor is pricey at around £380. However, is compensated for by the low price of the unit itself. It seems like the lowest a CO2 sensor is going to cost, as a DIY-type arrangement, is around £100. Unlike the Vent Axia Sentinel mentioned above it doesn't look like this unit has DIY friendly control inputs. However, realistically, the time spent faffing around with semi-unofficial DIY arrangements has a price in itself.

If I go for it I will report back.