Carbon dioxide levels in a MVHR home

[Seeoda]

Hi all,

 

I have a three bed (118m2) with a Ventaxia MVHRV. I am there alone at the moment. In my bedroom I usually leave the bedroom door open and it allows great ventilation. I can measure this with a Co2 senor that I own. In the mornings I wake up with about 700 ppm. However, with the bedroom door closed, Co2 gets surprisingly high given the low occupancy and the MVHR. It may get to 1200 ppm. Is this normal? 

[JohnMo]

Our bedroom normally has me, wife and dog (don't ask), last night's peak was around 750ppm.  Door was open, prior to dog in room, the door would be closed and it would peak around 1000ppm.  Think it's the reduced flow moving air under the door undercuts.

[jamieled]

We get similar numbers. Building regs require us to have a CO2 monitor but we don't really pay attention to the numbers much now.

[TimCx]

What CO2 monitors are you guys using? I was thinking if getting one but I am struggling to find any that are good, most of the YouTube reviews seem to be for cheap Chinese units and I would like something that is likely to be accurate.

[JohnMo]

In Scotland they have to be hard wired, record actual, peak and average over the last 24hrs.  Mine is a DETA 1142 (I think)

[Russdl]

@TimCx I’m using these Analox ones. No complaints so far (and the price on that site I linked is very good but no idea if it’s a good site)
 

 

[JohnMo]

I bought mine of gumtree, 5x for £50, sold two for £50, installed one on bedroom and another in the lounge, one spare.

 

Amazing what you can find

[SteamyTea]

19 hours ago, Russdl said:

@TimCx I’m using these Analox ones. No complaints so far (and the price on that site I linked is very good but no idea if it’s a good site)
 

 

Ummm

 

"Reduce the risk of airborne viruses being spread and give your people true peace of mind - give them an Air Quality Guardian."

 

Extraordinary claims need extraordinary evidence.

[Adrian Walker]

2 hours ago, SteamyTea said:

Ummm

 

"Reduce the risk of airborne viruses being spread and give your people true peace of mind - give them an Air Quality Guardian."

 

Extraordinary claims need extraordinary evidence.

 

 

 

The name "Analox Air Quality Guardian" is just a marketing term IMHO, but CO2 monitoring is the BEST way to confirm the air quality and correct functioning of a MVHR. I have spent time with @Russdl and it was hugely beneficial to have accurate CO2 levels in all the rooms while setting up the MVHR system in his lovely home.

 

[SteamyTea]

9 minutes ago, Adrian Walker said:

but CO2 monitoring is the BEST way to confirm the air quality and correct functioning of a MVHR

A few years ago, @DamonHD sent me some data from classrooms. There was a very good correlation between RH and CO2 levels and classroom occupancy.

RH may be of more importance for comfort than CO2, people are quite susceptible to bringing outside of an optimal RH window.

Fungi are also very susceptible to RH levels, too many of the wrong fungal spores and all sorts of health issues can manifest themselves.

I am not sure what the upper health limit is for CO2 concentration, probably quite high (I think our @Ed Davies did some work on this), I doubt many homes would get close to it.

 

Monitoring and controlling RH and temperature would probably have a greater impact on comfort levels than CO2 and temperature, but in reality, in the UK, the 3 go together.

Very different for other climate regimes and lifestyles.

[jonM]

My bedroom hits a maximum of around 1200 ppm at 5-30 am if window and/or door is shut. 

I am using Netatmo monitoring in three rooms which also capture temperature and humidity. It is very easy to set up and you can download the data if required. 

https://www.netatmo.com/en-gb/weather/weatherstation

Edited October 3, 2022 by jonM

[Seeoda]

On 02/10/2022 at 12:45, SteamyTea said:

A few years ago, @DamonHD sent me some data from classrooms. There was a very good correlation between RH and CO2 levels and classroom occupancy.

RH may be of more importance for comfort than CO2, people are quite susceptible to bringing outside of an optimal RH window.

Fungi are also very susceptible to RH levels, too many of the wrong fungal spores and all sorts of health issues can manifest themselves.

I am not sure what the upper health limit is for CO2 concentration, probably quite high (I think our @Ed Davies did some work on this), I doubt many homes would get close to it.

 

Monitoring and controlling RH and temperature would probably have a greater impact on comfort levels than CO2 and temperature, but in reality, in the UK, the 3 go together.

Very different for other climate regimes and lifestyles.

As you say, the two go together, but I get the impression when a room is at the lower temperature range Co2 is a much better measure of human presence. 

[TimCx]

On 02/10/2022 at 12:45, SteamyTea said:

A few years ago, @DamonHD sent me some data from classrooms. There was a very good correlation between RH and CO2 levels and classroom occupancy.

RH may be of more importance for comfort than CO2, people are quite susceptible to bringing outside of an optimal RH window.

Fungi are also very susceptible to RH levels, too many of the wrong fungal spores and all sorts of health issues can manifest themselves.

I am not sure what the upper health limit is for CO2 concentration, probably quite high (I think our @Ed Davies did some work on this), I doubt many homes would get close to it.

 

Monitoring and controlling RH and temperature would probably have a greater impact on comfort levels than CO2 and temperature, but in reality, in the UK, the 3 go together.

Very different for other climate regimes and lifestyles.

Am I right in thinking that RH is Relative Humidity in this context?

[SteamyTea]

28 minutes ago, TimCx said:

Am I right in thinking that RH is Relative Humidity in this context?

Yes.

It is the easy one to measure.

Absolute Humidity, AH, is more useful as you can calculate the total mass of water in the air.

You can convert between the two, but it is messy.

 

Relative humidity (RH)
The ratio of the actual amount of water vapor in the air to the amount it could hold when saturated is expressed as a percentage, or the ratio of the actual vapor pressure to the saturation vapor pressure is expressed as a percentage.

Absolute humidity (AH)
The mass of water vapor in a unit volume of air. It is a measure of the actual water vapor content of the air.

Thanks to the World Meteorological Organization, we can find saturation vapor pressure given the temperature and atmospheric pressure (read more at Saturation vapor pressure)

From the relative humidity and saturation vapor pressure, we can find the actual vapor pressure.

Then we can use the general law of perfect gases

In our case this is

where R is the universal gas constant defined as 8313.6, and Rv is the specific gas constant for water vapor defined as 461.5

Thus we can express mass to volume ratio as
,
which is absolute humidity.

So, for 25 degrees centigrade and 60% relative humidity, one cubic meter of moist air contains about 14 grams of water, which corresponds to conversion table values I've found before.