Arduino CO2 Sensor Controls PCM Fans in HRV

[AC_Hacker]

Yeah, this CO2 Jihad I'm on is becoming a real education.

I really had not anticipated the effects of CO2 concentration due to gas appliances. I've had all the classes, passed all the tests, etc. but I guess that true awakening comes late to the oxygen-starved brain.

I have a 2 foot wide full-on commercial gas stove (not a commercial style stove, the real thing) in my kitchen that I really love to cook on because of the control and raw power (4x - 35,000 BTU burners + mega oven). The oven does have a big exhaust port on the back, so there's hope, but the burners not only put out awesome heat but, as I am learning awesome CO2 & CO. I might be able to get it all to work out if I got a righteous range hood and restricted the options of escape for the CO2.

So, I'm doing some serious re-thinking of my cooking arrangements.

I do have an exceptional electric convection oven down cellar that I usually use for big meal over-loads. I could make that available for regular service.

I looked previously at induction cook tops, and I understand their efficiency, but considering their payback, I wasn't very impressed. However I wasn't aware then, as I am now, of CO2 concentration problems and how convection tops could eliminate those problems.

Factors that favor induction cooking are that like gas, they are quick-on and quick-off (I have come to regard this as essential) and they all seem to have a timer (timed on & timed off) built in to every element. My bachelor brain really likes this idea.

For me, the argument against induction is that I have acquired over the years a very fine and expensive set of triple ply non-induction cookware.

* * *

I have also become aware that my other gas appliances, a gas dryer and a gas demand water heater, are not venting their exhaust gases completely. The CO2 levels I'm seeing are significant, but not critical... not like the 'ventless' heater. I think I can work on them and improve their performance. Neither of them comes with it's own fresh air input... they were built before fresh air was needed... back when houses leaked like a sieve and CO2 concentrations dissipated out through thousands of cracks.

Although it has not been so bad in recent years, in my area, we have had winters when we lost electricity for up to a week, and it was the gas stove with it's faithful oven that saw my family through the outage. Repeated experiences like this have made me deeply convinced of the wisdom of having multiple heating sources.

* * *

BTW, I just did some quick searches on induction cooktops and have come up with interesting information both pro & con that I will explore more fully in a separate thread.

Best,

-AC

[stevehull]

AC,

Please note that I am not against all gas appliances. But they must be put in properly. I really like vented water heaters in the garage - not in the home. And I never ever recommend the use of spot combustion heaters - even if they say "ventless".

I also put a return plenum in the kitchen to my HRV when I designed my other home some ~20 years ago. It was on low speed 24x7 (20 cfm). Above the propane fired cooktop, we had the required direct vented hood. I also adjusted the HRV fans so that the HRV allowed a very small positive pressure in the house (0.2 inch of water column).

This not only kept out dust, but helped to rid the kitchen of any combustion gas issues.

I measured CO2 in that house many, many times and at the highest it ever got to 425 ppm.

Also note that the pilot light in many gas stoves produce a huge amount of CO2 over 24 hours.

Now I am beginning to better understand your home CO2 issues.


Steve

[AC_Hacker]

Originally Posted by stevehull

...allowed a very small positive pressure in the house (0.2 inch of water column)...

Oh, so you kept your house perpetually pressurized at 50 pascals? Yeah, that would dump a lot of CO2.

Originally Posted by stevehull

I measured CO2 in that house many, many times and at the highest it ever got to 425 ppm.

I'm pretty sure that before I started my insulation & infiltration Jihad, my CO2 concentrations were insignificant.

And the deal is, I'm only partially done, the best is yet to come...

-AC

[AC_Hacker]

I just came across this very useful list of sensors:

List of sensors
MQ-2

Sensitive for Methane, Butane, LPG, smoke.
This sensor is sensitive for flamable and combustible gasses.
The heater uses 5V.
The MQ-2 at seeed: Grove - Gas Sensor(MQ2) - Wiki


Search for datasheet: http://duckduckgo.com/?q=%22mq-2%22+...filetype%3Apdf

MQ-3

Sensitive for Alcohol, Ethanol, smoke
The heater uses 5V
The Arduino blog about the "breathalyzer" using a MQ-3 : Arduino Blog » Blog Archive » Arduino Breathalyzer: Calibrating the MQ-3 Alcohol Sensor
The MQ303A (also on this page) is like this sensor, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq-3%22+...filetype%3Apdf

MQ-4

Sensitive for Methane, CNG Gas
The heater uses 5V.
Search for datasheet: http://duckduckgo.com/?q=%22mq-4%22+...filetype%3Apdf

MQ-5

Sensitive for Natural gas, LPG
The heater uses 5V.
The MQ-5 at seeed: Electronic brick - Gas sensor(MQ5) - Wiki and Gas Sensor - MQ5 - Wiki


Search for datasheet: http://duckduckgo.com/?q=%22mq-5%22+...filetype%3Apdf

MQ-6

Sensitive for LPG, butane gas
The heater uses 5V.
The MQ-6 at seeed: Electronic brick - Gas sensor(MQ6) - Wiki
The MQ306A (also on this page) is like this sensor, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq-6%22+...filetype%3Apdf

MQ-7

Sensitive for Carbon Monoxide
The heater uses an alternating voltage of 5V and 1.4V.
A library for the MQ-7 : MQ-7 Breakout Arduino Library
The MQ307A (also on this page) is like this sensor, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq-7%22+...filetype%3Apdf

MQ-8

Sensitive for Hydrogen Gas
The heater uses 5V.


Search for datasheet: http://duckduckgo.com/?q=%22mq-8%22+...filetype%3Apdf

MQ-9

Sensitive for Carbon Monoxide, flammable gasses.
The heater uses an alternating voltage of 5V and 1.5V. It depends on the gases how to use that alternating voltage. If only Carbon Monoxide is tested, the heater can be set at 1.5V.
The MQ309A (also on this page) is like this sensor, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq-9%22+...filetype%3Apdf

MQ131

Sensitive for Ozone
The heater uses 6V.


The load-resistor is 100k...200k, which is a lot higher than for other sensors. This sensor is also very sensitive. It measures in ppb (parts per billion) where other sensors measure in ppm (parts per million).


Search for datasheet: http://duckduckgo.com/?q=%22mq131%22...filetype%3Apdf

MQ135

For Air Quality
Sensitive for Benzene, Alcohol, smoke.
The heater uses 5V.
An example how to use it: AirQualityMQ135 \ Learning \ Wiring


Search for datasheet: http://duckduckgo.com/?q=%22mq135%22...filetype%3Apdf

MQ136

Sensitive for Hydrogen Sulfide gas.
The heater uses 5V.
Search for datasheet: http://duckduckgo.com/?q=%22mq136%22...filetype%3Apdf

MQ137

Sensitive for Ammonia.
The heater uses 5V.
Search for datasheet: http://duckduckgo.com/?q=%22mq137%22...filetype%3Apdf

MQ138

Sensitive for Benzene, Toluene, Alcohol, Acetone, Propane, Formaldehyde gas, Hydrogen gas.
The heater uses 5V.
Search for datasheet: http://duckduckgo.com/?q=%22mq138%22...filetype%3Apdf

MQ214

Sensitive for Methane, Natural gas.
The heater uses 6V.
Search for datasheet: http://duckduckgo.com/?q=%22mq214%22...filetype%3Apdf

MQ216

Sensitive for Natural gas, Coal gas.


Search for datasheet: http://duckduckgo.com/?q=%22mq216%22...filetype%3Apdf

MQ303A

Sensitive for Alcohol, Ethanol, smoke (just like the MQ-3)
The heater uses 0.9V
An example for the MQ302A MQ3 (or MQ303a) Alcohol Sensor Arduino Guide | insapio polymath
It detects the same gasses as the MQ-3, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq303a%2...filetype%3Apdf

MQ306A

Sensitive for LPG, butane gas
The heater uses 0.9V.
It detects the same gasses as the MQ-6, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq306a%2...filetype%3Apdf

MQ307A

Sensitive for Carbon Monoxide
The heater uses an alternating voltage of 0.2V and 0.9.
It detects the same gasses as the MQ-7, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq307a%2...filetype%3Apdf

MQ309A

Sensitive for Carbon Monoxide, flammable gasses.
The heater uses an alternating voltage of 0.2V and 0.9V. It depends on the gases how to use that alternating voltage.
It detects the same gasses as the MQ-9, but uses a lower heater voltage.


Search for datasheet: http://duckduckgo.com/?q=%22mq309a%2...filetype%3Apdf

MG811

Sensitive for Carbon Dioxide (CO2).
The heater uses 6V.
The signal from this gas sensor can be connected to the Arduino, but it's better to amplifly the signal with a OpAmp.
An example of this sensor (without an OpAmp) : Sensor Workshop at ITP :: Reports / MG 811


Search for datasheet: http://duckduckgo.com/?q=%22mg811%22...filetype%3Apdf

AQ-104

For air quality


Search for datasheet: http://duckduckgo.com/?q=%22aq-104%2...filetype%3Apdf

AQ-2

Sensitive for Flamable gasses, smoke


Search for datasheet: http://duckduckgo.com/?q=%22aq-2%22+...filetype%3Apdf

AQ-3

Sensitive for Alcohol, Benzine


Search for datasheet: http://duckduckgo.com/?q=%22aq-3%22+...filetype%3Apdf

AQ-7

Sensitive for Carbon Monoxide


Search for datasheet: http://duckduckgo.com/?q=%22aq-7%22+...filetype%3Apdf

[Daox]

How is this project coming along? I've been awol lately and haven't been able to keep up!

[AC_Hacker]

Originally Posted by Daox

How is this project coming along? I've been awol lately and haven't been able to keep up!

Welcome back. Were you warming yourself on some sunny shore?

The project is going pretty good.

The CO2 sensor has occasionally exhibited some anomalous behavior, like cruising along at 700 ppm and then pegging itself at around 6000 ppm. The other CO2 sensors I have aren't exhibiting this odd behavior. It could be a bad sensor, or it could be an artifact that is only present in the analog mode. I have some information that should enable me to get the sensor working in digital mode, but I'll need help.

I also don't have so much confidence in the humidity/temp sensor that I bought. So I bought a precision Swiss sensor which is laying on my desk awaiting installation.

I also ordered a 24v switcher power supply (has arrived), and also a DC to DC step down circuit (not yet in) so that I can power the Teensy and the CO2 sensor and the fans all off of the same supply.

The LCD display is working just great, and has a subtle green back light that is tied to the PWM, so when the CO2 level goes high, the fans run faster AND the display glows brighter. All very satisfying.

In the meantime, I learned a great deal about the CO2 situation in my living room. I also learned that my gas appliances are all introducing CO2 into my house. No problem in the summer, but winter is another story.

Because of the CO2 increases in my house, I am giving a very serious look at induction cooking as an alternative to gas cooking. I'm not even considering electric resistance cooking, I really don't like it. I have gained some interesting information about induction cooking through research and now through experience, which I will share on the Induction Cooking Efficiency thread I started previously. The cost analysis I did before is still holding up, but when I started considering indoor air pollution, and the need to dump all that air, I have reconsidered.

It's interesting how you can't always predict where something will lead you. When I started out to build a smart HRV, I really didn't anticipate the other changes that would follow.

Stay tuned.

-AC

[Exeric]

deleted comment.

[AC_Hacker]

xxxxxxxxxxx

[Exeric]

Ok, done.

[AC_Hacker]

The Sensorion SHT15 breakout board arrived from Sparkfun.

I already had a SHT10 laying about, but honestly, it is so small, I'm not sure if I can work with it... besides, the SHT15 is much more accurate.

Above is a close-up of the SHT15, balanced on a couple of pennies. As you can see, life becomes much easier with the breakout board. I mean, it may be possible to solder directly to the SHT15 (which is already mounted on an incredibly tiny board), but life is too short and my fingers are too thick.

I soldered some pins to the thru-holes on the board so that I could plug it in to the proto-board so that I could get it going.

Then I read through the specs... the SHT15 uses 3.3v. Unfortunately, my proto-board is only supplied with GND, +5v, +12v, -12v.

So I will need to get a 3.3v regulator.

Also, further reading of the specs indicated that:

IMPORTANT: After soldering the devices should be stored at >75%RH for at least 12h to allow the polymer to re-hydrate. Otherwise the sensor may read an offset that slowly disappears if exposed to ambient conditions. Alternatively the re-hydration process may be performed at ambient conditions (>40%RH) during more than 5 days.

So, I had to construct a re-hydration chamber so that the SHT15 would deliver the accuracy I am looking for.

The above picture is my re-hydration chamber, skillfully crafted from a Thai Food To-Go box.

So while the sensor is re-hydrating, I'm off to find a 3.3v regulator.

Best,

-AC