I know, clearly you can open windows, but in an "airtight" (not 100% of course) house, is it safe to have a non-working/broken MVHR? Will enough air still come in if you aren't aware the MVHR died? Presumably we have some CO2 meters that might warn us but.. you know?

I don't think it should worry you.  I notice rooms are stuffy around 1500ppm - there's still a long long way to go before it's acutely dangerous:

 

We have CO2 monitor, a mandatory requirement in Scotland, once your airtightness starts to get to a responsible level, I think it starts to glow red above a predefined ppm CO2.

We have a couple of portable CO2 monitors that include an alarm feature. Not mandatory down this neck of the woods yet but a damn good idea. In a power cut all is well for a short while unless you start lighting candles etc then the air quality falls off a cliff (according to the monitor, not so easy to detect yourself). 
 

I’m sure it would take a good many hours in an airtight house with a non functioning MVHR to become a serious health issue. In our case we’ve bought 11-12 hours of extra MVHR if we lose power with an Ecoflow battery that kicks in to power the MVHR in the event of a power cut - mainly so we don’t have to open any windows and throw the heat away. 

3 hours ago, puntloos said:

I know, clearly you can open windows, but in an "airtight" (not 100% of course) house, is it safe to have a non-working/broken MVHR? Will enough air still come in if you aren't aware the MVHR died? Presumably we have some CO2 meters that might warn us but.. you know?

Our MVHR trips to battery supplied power when the mains goes off..... 

5 hours ago, puntloos said:

I know, clearly you can open windows, but in an "airtight" (not 100% of course) house, is it safe to have a non-working/broken MVHR? Will enough air still come in if you aren't aware the MVHR died? Presumably we have some CO2 meters that might warn us but.. you know?

 

What is your plan (if any) for backup power and maintaining power to MVHR and/or home automation?   You could have Loxone alert you to open a window if CO2>threshold or after X number of hours (or if you have a motorized skylight or something open this), but if Loxone also has no power then that limits you to simpler solutions.

 

We don't have a dedicated UPS for Loxone/Network, and are relying on Victron battery system for this.  This has got me thinking though, that it would be wise to implement load-shedding in some way so that in a period of extended power-outage the battery isn't dead in 8hrs, but instead allows for mutliple days of usage with keeping minimal lighting, MVHR network and home automation running.   Not really thought about this much as not really as power hardly goes out and I'm not a 'prepper", but interesting..

 

I wonder though, how many days would you need to be without MVHR for CO2 levels to reach 5,000 ppm?  Anyone know how to calculate this?

 

I would suggest that you have a CO2 monitor to check that the air is good 24/7 as CO2 is very insipid. You’re very unlikely to die, just have a bad headache with high (2500+ ppm) CO2 levels. 

If a person expels 0.7 kg of CO₂ a day, and a house, 10m by 6 m by 5 m, has 300 m³ of air in it, that is 375 kg of air.

After a day, one person would have increased by CO₂ by 0.18%.

So about 5 days to start noticing anything.

Or a day for 5 people.

 

Apollo 13 got back OK, and they had greater problems than just CO₂.

 

Edited December 22, 20232 yr by SteamyTea

This is very interesting: https://protonsforbreakfast.wordpress.com/2021/06/06/estimating-rates-of-air-change-in-homes/

 

He measures increase in OC2 during the night (for 2 people) from 450-1950pp with (calculated) 0.3 ACH..

6 hours ago, Dan F said:

 

What is your plan (if any) for backup power and maintaining power to MVHR and/or home automation?   You could have Loxone alert you to open a window if CO2>threshold or after X number of hours (or if you have a motorized skylight or something open this), but if Loxone also has no power then that limits you to simpler solutions.

 

Honestly I'm probably better prepared than most, my smart home + network is on a UPS that should last about 2 hours, but next to that I have full off-grid capable solar, so if it's just grid power that's gone I'll certainly notice. 

 

Also, I have a bunch of lonxone'd CO2 sensors, so theoretically my home will know things are awry. Not 100% sure if I have standalone CO2 monitors but I wouldn't be surprised, I'd have to look it up.

 

12 hours ago, puntloos said:

my smart home + network is on a UPS that should last about 2 hours, but next to that I have full off-grid capable solar,

 

Dedicated UPS for loxone/network + batteries with Solar PV, or just UPS?   I skipped loxone/network UPS given Victron has <20ms switchover which appears to be sufficient for everything I have.  What I haven't though about is if/how I could have house running off-grid for 8hrs, but loxone/network running for 24hrs+.    I'd need to turn off some circuits in CU when battery reaches a certain threshold, or another approach would be to have a dedicated inverter for loxone/network (this would avoid 20ms switchover time, but would rely on battery never being empty)

 

12 hours ago, puntloos said:

I have a bunch of lonxone'd CO2 sensors,

 

Didn't go for Loxone Touch Pure with CO2?  You using Loxone+KNX in the end?

27 minutes ago, Dan F said:

 

Dedicated UPS for loxone/network + batteries with Solar PV, or just UPS?

Both, Solax batteries/EPS inverter connected to solar, and a separate UPS for the network center of the house. 

 

27 minutes ago, Dan F said:

   I skipped loxone/network UPS given Victron has <20ms switchover which appears to be sufficient for everything I have. 

I bought an online UPS, since there will be no switchover whatsoever which is better for the equipment (you effectively always run off battery, whether or not it's being charged is incidental)

 

27 minutes ago, Dan F said:

What I haven't though about is if/how I could have house running off-grid for 8hrs, but loxone/network running for 24hrs+.    I'd need to turn off some circuits in CU when battery reaches a certain threshold, or another approach would be to have a dedicated inverter for loxone/network (this would avoid 20ms switchover time, but would rely on battery never being empty)

I'm not sure I completely follow. Indeed my entire house could run off grid for maybe 8 hours if I take it easy on my antique kettle collection, and once the solar batteries die I am estimating my UPS can carry the torch for minimal brains for a few more hours (obv if I only run the brains off solar I could go for days but that would mean no light/heat etc). 

Once the UPS runs low it sends that signal to the brains to power down peacefully. 

27 minutes ago, Dan F said:

 

Didn't go for Loxone Touch Pure with CO2?  You using Loxone+KNX in the end?

Yeah I tried to stick with KNX for the bulk of the backbone of the house (lights, sensors, actuators(shutters)) and loxone for mainly brains/interface 

You have a power failure, open the door for a bit, problem solved

34 minutes ago, TonyT said:

problem solved

Not in the middle of winter in an electric house. That’s one problem replaced with another. 

25 minutes ago, Russdl said:

Not in the middle of winter in an electric house

How do gas and oil houses cope in power cuts.

1 hour ago, Russdl said:

Not in the middle of winter in an electric house. That’s one problem replaced with another. 

Not really,  open the door a bit of fresh air in if you are worried about dying due to power failure on equipment

Co2 monitor as suggested or voltage monitor on mvhr supply with low voltage draw alarm so at least you know about a fault?