Does Anyone Monitor Their Home's CO2 Level?

[ano]

I  have CO2 sensors in my house so I know when to exchange the air.   I just tapped into my 18" return air flex duct and ran an 18" flex duct to outside with a 20" x 40" filter rack to filter outside air.  I put an 18" motorized damper in the outside air duct and an 18" motorized damper between my inside return filter rack and the duct tee that runs to the outside.  The outside air damper is NC  and the damper that closes off the return air from indoors is a NO and I just energize a relay to power the damper motors that have a spring return when the power to the dampers  is removed.  This gives me 100% outside air exchange which will exchange all the air in the house in about 10 to 15 minutes.   This is just a hobby. no real concerns for health.  Also works good to get rid of odors in the house from cooking. 
 
I also track the indoor enthalpy vs. the outdoor enthalpy  so as not to introduce energy to the indoor air that will need to be removed by the ac unit.

 
Wow, I have to say I'm pretty impressed. What type of CO2 sensors are you using? 
 
My setup is a bit less "heavy duty."  I have two HVAC units and each has an 8" duct going to outside with a 12x12 filter. First problem is 12x12 filters are hard to find.  Each has a damper then it ties into the return.  One unit has two 18" returns, the other has a single 18" return. 
 
Because mine only works when the HVAC fan is running, I decided to add two booster fans, one for each air intake. I think that will work for me then I can run this all night since my goal is to use free outside cooling as well as ventilation.  One unit is a 3 zone system, so I have three dampers on the output, but when the AC is off, all those dampers open.
 
I like your arrangement, but I have another question. When you have it switched to outside air, where does all the air go?  You didn't mention any duct for exhaust.  For me, I figure the exhaust vents I have for my three bathrooms and the stove hood should be enough, but my flow rate is not that high.  For you, your flow rate is much higher, so do you have a problem with exit air? 
 
Also, did you automate yours, or do you have to activate the dampers manually?  I'm hoping to activate mine 1) when CO2 is high, or 2) when outside air can help heat or cool the house. 

 

[apostolakisl]

The part about these things that bugs me is they say they are 90% etc. efficient, and that may be true from their side, but I don't see it like that.  If its 70 degrees inside and 110 outside (a cool summer day in Phoenix) then AT BEST my air going out is warmed to 90 degrees and the air coming in is cooled to 90 degrees.  And that would be perfect conditions, so I still have to cool this 90 degree air to 70 degrees.  They would call that 100% efficiency. 

 
Actually no.  They use counter current heat transfer.  It doesn't just end up half way in the middle.  
 
But still, the amount of money it saves you in operation doesn't justify the upfront cost.

 

[ano]

For me it wouldn't be a good fit anyway because in most cases I want the outdoor air at the temp it already is.  There are probably times when that isn't the case, but I'm not sure the cost justifies it.
 
I should add, a Phoenix attic can get to 150 in the summer. Even if I insulate this air exchanger, I have trouble believing it will be able to to efficiently drop incoming air to 80 degrees, no matter how efficient they say these things are.

 

[johnlaroux]

I bought my sensors from All Electronics for $10 each, ( Telaire 6004 CO2 Modules) but they have sold all they had.  I have two extras and will probably put one outside.
 
I have one upduct in the ceiling and the rest goes out the fireplace flue and out all the bathroom exhaust ducts. I need to install more upducts but wife says no. She doesn't like the looks of them.
 
I used to have it automated like the following.
 
If the heater or ac came on because they are called for by the thermostat  and any of the three CO2 sensors were above 800ppm and the outside enthalpy is lower then the indoor enthalpy (the enthalpy condition is only if the ac comes on not the heater)
then the outside air damper will open for 10 minutes and then close.
 
Wife does not like automated things , so I had to disable the automation of the outside air.
 
To increase the WAF, I now give her control of the outside air.  I have the CO2 values on the computer screen were they are red when above 800ppm and green when below 800ppm so when she feels she needs or wants to exchange the air indoors she has a point on the computer screen where she can enter a number of minutes and the computer will open the outside air damper and turn on the indoor fan.
When the timer gets to 0 the computer turns off the indoor fan and closes the outside air damper.
 
I was wondering if the method you want to use would push dirt out of your return air filters, as there isn't anything to prevent your booster fans from pushing air thru the filters instead of out the discharge of the airhandlers.

 

[ano]

I was wondering if the method you want to use would push dirt out of your return air filters, as there isn't anything to prevent your booster fans from pushing air thru the filters instead of out the discharge of the airhandlers.

 
Yeah, I understand that "wife" thing. :wacko:
 
The problem of air coming out of the air returns and bringing with it dust has crossed my mind.  My thought was that I tend to use the better air filters that trap dirt better and have a fair air flow resistance. Given the choice, I beleive the air will come out the vents with little resistance and less so out the air returns which have a greater resistance.  The booster fans I'm planning to use only use about 60 watts so I don't expect great airflow when you consider how many vents it will be coming out of.  When you combine all this, I'm hoping the dust won't be a problem. 
 
If the dust is a problem, I will need to install dampers like you have.

 

[tmbrown97]

I happen to live in an area with some of the worst allergies imaginable (and I'm especially sensitive), some of the worst electric rates possible, and a big house (builder grade, poor quality) that costs me a FORTUNE to cool!  I haven't gotten around to upgrading the HVAC yet or had an opportunity to add a fresh air vent or anything - but what we did to last year is add a whole house fan.
 
It's loud, the house is dustier, and I have to take 2 zyrtec/day ($12 for 365 generic brand pills!), but it sure cut our cooling costs down!  We're downstairs until the kids' bath time - and we keep an eye on the outside temp which kinda affects when we head upstairs - when it's time, we go open the windows and crank on the whole house fan - then we let it run until the house is about 65°.
 
What I did do - is set it so that whenever the outside temp drops below the inside temp, a red light starts flashing on all my thermostats.  I don't have my own outside temp sensor, but I pull from wunderground (and a neighbor has a sensor like 4 houses down) to feed a value in the elk which it uses to compare to the inside temp of the house and pushes to the thermostat.  When we see the red light, we turn off the AC and kick on the fan.
 
Pretty low-tech mostly aside from the wunderground integration, but I can say that my solution has paid for itself a dozen times over.

 

[ano]

I bought my sensors from All Electronics for $10 each, ( Telaire 6004 CO2 Modules) but they have sold all they had.  I have two extras and will probably put one outside.

 
Looks like they are still selling these for $20 if you buy a device that contains a few temp and humidity sensor as well.  Still seems like a good deal.  The sensors puts out a 0-4V signal which is perfect to connect to my HAI because it can read a 0-4V signal.  Only 256 resolution, but that should be good enough. 
 
Is it linear, so basically 1V is 500, 2V is 1000, 3V is 1500, etc.? 
 
Also, could this CO2 sensor be the elusive occupancy sensor that the home automation folks have been looking for?  Motion sensors only work is you continue to move, which people watching TV or sleeping fail to do.  Do you think it would be a reliable way to detect people? 

 

[johnlaroux]

Looks like they are still selling these for $20 if you buy a device that contains a few temp and humidity sensor as well.  Still seems like a good deal.  The sensors puts out a 0-4V signal which is perfect to connect to my HAI because it can read a 0-4V signal.  Only 256 resolution, but that should be good enough. 
 
Is it linear, so basically 1V is 500, 2V is 1000, 3V is 1500, etc.? 
 
Also, could this CO2 sensor be the elusive occupancy sensor that the home automation folks have been looking for?  Motion sensors only work is you continue to move, which people watching TV or sleeping fail to do.  Do you think it would be a reliable way to detect people? 

 
Yes it is linear and if you buy the $20 one you need to un-solder the device or you could do as I did and apply a 20 to 30 vdc to power the entire  unit and just solder wires to the analog out and ground of the CO2 sensor inside. I also removed the internal fan to get rid of the noise. Also the whole unit is pretty big, its 8x4x2 inches.
 
As far as the occupancy use it would only work if a person was in a bedroom with the door closed, and that would take some time to build up enough CO2 to know someone was there.  CO2 is a gas and like humidity will spread itself out evenly through out the house fairly quickly.   Take a look at my CO2 graph above  and due to me working nights you will see the red line which is the master bedroom at about 8am when I went to bed, it took awhile for the CO2 levels to build up and you can see how fast it dropped when I woke up and opened the door around 2:15pm, and how the entire house rose when the master bedroom mixed with the rest of the house.   You can also see how fast the levels dropped at around 11:15pm when the wife turned on the outside air.

 

[BraveSirRobbin]

Is it linear, so basically 1V is 500, 2V is 1000, 3V is 1500, etc.? 

FYI for those that might need it, you can reference THIS guide on A-D converters for a conversion from voltage to engineering units for your acquisition system.

 

[ano]

I received the "Nose" and unsoldered  the CO2 sensor without a problem.  (Actually used a hack saw, soldering iron, you name it.)  The sensor seems to work quite good. I'm amazed how quickly it can respond.  Its been even helpful for experiments.  I have a pet Tarantula that lives in a 10 gallon aquarium. I always wondered if it was too stuffy in there for her.  Nope. It appears Tarantulas emit very little CO2.
 
Now I just need to figure out a simple way to have the sensor trip a relay when the output exceeds a certain voltage.  I could build something with a comparator, but that is more work than I want. I was looking for a voltage controlled relay, but can't find one.  Maybe something like the ELK sensitive relay can be tweaked to work.

 

[johnlaroux]

That sensor's price is way better then the Honeywell one, isn't it?

 

[ano]

Cheaper yes, and I think inside the Honeywell uses the same sensor, BUT no relay output so you have to carry around a digital volt meter to read it. :unsure: