Optimizing Air Flow for CO2 and Heat Loss in Vans

In summary, I calculated that I need to add 1.3 cubic feet of air before I start to get sick from CO2.
  • #1
mess
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TL;DR Summary
I am working on a campervan project that i intend to take far up north in extreme cold climates, as such ive sealed it very well with thick foam insulation. There is nearly 0 air flow between the outside of the van and the inside.

On one of my test trips it was very cold, i kept all the windows and vents closed, and by the morning i had a severe migrain.
My goal is to determine the ideal amount of air flow, in order to keep CO2 below 1000ppm and to minimize heat loss.

I calculated the following based off a similar post in this forum, and I am hoping this can be verified so I know that i am in the right ballpark and going in the right direction as far a solution.
Fresh air has about 0.04% (400ppm) co2, non ideal air has a high limit of 0.1% CO2 (<1000ppm). the difference is .06%.
in a van with typical sprinter dimensions that's about 500 cubic feet minus any things you might have added in your build, but ill say 500.
so 500 cuft * .06% = .3 cuft can be added in order to pass non ideal co2.
and 500 cuft * .26% = 1.3 cuft can be added before you start to get sick from co2. because 0.3% (co2 sickness concentration) - 0.04% (fresh) = .26% difference.
A single occupant adds about 12 cubic feet per day of co2, or about .5 cuft per hour of co2.
That means at best, a single occupant has less than an hour before CO2 levels become not ideal, and just under 3 hours before they might get headache, lack of concentration and sleepiness from too much co2.
now getting into fatal numbers.
500 cuft * 1% = 50 cuft can be added before you might die from co2. This will happen in 100 hours for a single occupant, that's about ~4 days, ~2 days for double, less than that with pets.

Next to figure out a solution through venting in air from the outside:

when the inside air reaches nearly 1000ppm (i have a sensor that controls a vent fan and valve that's attached to the roof of my van now), the vent will open and the fan will suck air from the outside, and mix it in with the return air going into my diesel heater.

Inside air:
500 cf @ 0.1% co2

air coming in from vent :
20cfm @ 0.4% co2

500 cf / 20 cfm = 25 minutes
in 25 minues the entire volume will have been diluted. with would bring it to 50% of the co2%, 500ppm.

therefore at 20cfm, .05% (500ppm) can be removed in 25 min

in one hour that's about ~1000ppm.

but one human is adding .5% (5000ppm) CO2 in one hour. Or 5x more than I am removing.

Therefore in order to maintain around 500ppm in the van i need a flow rate of 20cfm*5 or 100cfm.

And to maintain around 1000ppm CO2 I need a flow rate of about 50cfm? (I think i might have done this part wrong)

(pic of my 3d printed contraption)
Any help appreciated! thank you!
DSC_0037.JPG
 
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  • #2
Get masks for the people with an exhale valve plumbed to the outside.
You removed your CO2 source.
 
  • #3
Here's my calculation for 1000 PPM of ##\rm{CO_2}##, where X = Cubic feet per hour of air (CFH). A quantity, X, of air at 0.04% ##\rm{CO_2}## enters, 0.5 CFH of ##\rm{CO_2}## is added, and the same quantity of air (plus the 0.5 CFH of ##\rm{CO_2}##) leaves at 0.1% ##\rm{CO_2}##:

##0.0004X + 0.5 = 0.001(X + 0.5)##, where ##X## is CFH of air.

Solve for X, and I get 833 CFH, or 14 CFM of air required.
 
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  • #4
jrmichler said:
Here's my calculation for 1000 PPM of ##\rm{CO_2}##, where X = Cubic feet per hour of air (CFH). A quantity, X, of air at 0.04% ##\rm{CO_2}## enters, 0.5 CFH of ##\rm{CO_2}## is added, and the same quantity of air (plus the 0.5 CFH of ##\rm{CO_2}##) leaves at 0.1% ##\rm{CO_2}##:

##0.0004X + 0.5 = 0.001(X + 0.5)##, where ##X## is CFH of air.

Solve for X, and I get 833 CFH, or 14 CFM of air required.
Thanks so much for this!

What was your process for arriving at that equation? I would like to learn :D
 
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  • #5
It's a simple flow balance, as illustrated in the sketch for the ##\rm{CO_2}##:
CO2 balance.jpg

The equation says that flow in is equal to flow out, with the flow being unknown ##X##. Set up the equation, solve for ##X##.

There is a tiny error because oxygen is taken from the incoming air stream and converted into ##\rm{CO_2}## that is not shown in the sketch or the equation. That error is so small as to be meaningless in the scope of this problem.
 
  • #6
jrmichler said:
It's a simple flow balance, as illustrated in the sketch for the ##\rm{CO_2}##:
View attachment 273756
The equation says that flow in is equal to flow out, with the flow being unknown ##X##. Set up the equation, solve for ##X##.

There is a tiny error because oxygen is taken from the incoming air stream and converted into ##\rm{CO_2}## that is not shown in the sketch or the equation. That error is so small as to be meaningless in the scope of this problem.
Thanks for the explanation! I tried to do that on my own and after about 30 minutes I kind of got some fleeting partial clarity on the equation. What subjects should I study in order to develop equations like these modeling real world behavior?
 
  • #7
mess said:
What subjects should I study in order to develop equations like these modeling real world behavior?
The primary subject to study is physics. Of course, you need calculus to study physics, and algebra to study calculus. Other core subjects are statics and dynamics. Those subjects will not only give you a solid foundation, but get you about 1/3 of the way to a degree in either physics or engineering.
 
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  • #8
https://www.epa.gov/indoor-air-qual...-do-i-need-my-home-improve-indoor-air-quality

...homes receive 0.35 air changes per hour but not less than 15 cubic feet of air per minute (cfm) per person. as the minimum ventilation rates in residential buildings in order to provide IAQ that is acceptable to human occupants and that minimizes adverse health effects. ASHRAE also suggests intermittent exhaust capacities for kitchens and bathroom exhaust to help control pollutant levels and moisture in those rooms. ASHRAE also notes that "dwellings with tight enclosures may require supplemental ventilation supply for fuel-burning appliances, including fireplaces and mechanically exhausted appliances.

Cheers,
Tom
 
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Related to Optimizing Air Flow for CO2 and Heat Loss in Vans

1. How does optimizing air flow affect CO2 levels in a van?

Optimizing air flow in a van can help reduce the levels of CO2 by allowing fresh air to circulate and replacing the stale air that contains higher levels of CO2. This can help create a more comfortable and healthy environment inside the van.

2. What are some ways to optimize air flow in a van?

Some ways to optimize air flow in a van include installing ventilation fans, opening windows or vents, using a roof vent or fan, and using air conditioning or heating systems to regulate the temperature and air flow.

3. How does optimizing air flow impact heat loss in a van?

Optimizing air flow can help regulate the temperature inside a van, which can reduce heat loss. By allowing air to circulate, heat can be evenly distributed throughout the van, making it more comfortable and reducing the need for excessive heating.

4. Are there any specific designs or modifications that can help optimize air flow in a van?

Yes, there are various designs and modifications that can help optimize air flow in a van. Some examples include installing roof vents, adding insulation to the walls and ceiling, and using window deflectors to direct air into the van.

5. How can optimizing air flow in a van benefit the overall driving experience?

Optimizing air flow in a van can improve the overall driving experience by creating a more comfortable and healthy environment. It can also help regulate the temperature, reduce humidity, and eliminate odors, making the journey more enjoyable for passengers and drivers alike.

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