CO2 levels stay level in an hermetically closed ecosystem for weeks by cycling day and night while passing all air through a marine tank growing phytoplankton. Â When the system is first put together, the CO2 levels spiral until the plants and bacteria cycles get established. Â This biosphere has a diversity of 15 different plants growing in an enclosed space. Â The trick is to balance the plants out depending on their function in the ecosystem.Â (including worms and insects)
Enclosed systems in the past generally consisted of one plant in a bottle. Â They are easy to start. Â Most of the time they are bogs. Â Below is a link to one of them.
Below is a description how the data is collected. Â See other posting for how the Biosphere IV is made.
The following chart shows a typical day in the biosphere. Â The left half of the chart is with lights on. Â The right side is lights off for 12 hours. Â The RH is in yellow. Â You can see the scales on both sides of the graph. Â Twice a day there is a dehumidifier defrosting cycle. Â One in the day and one at night. Â The blue line is CO2 in ppm. Â It's a bit high; however, animals live for weeks at this level.Â
Temperature and DP are always the same. Â The DP is a calculated number by the measuring device. Here is a simplified version of the formula. Â In most cases, air pressure is considered.
Tdew point = T - ((100 - RH)/5.)
And Relative Humidify is also dependent on air pressure and temperature. Â It is not Absolute Humidity, but Relative. Â
When given temperature andÂ dewpoint, the vapor pressure (plugging Td in place of T intoÂ Clausius-ClapeyronÂ equation) and the saturation vapor pressure (plugging T intoÂ Clausius-ClapeyronÂ equation) can be determined. The RH = E/Es*100%.Â
LN(Es/6.11) = (L/Rv )(1/273 - 1/T)
Es = Saturation vapor pressure
L = Latent heat of vaporization = 2.453 Ã 10^6 J/kg
Rv = Gas constant for moist air = 461 J/kg
T = Temperature in Kelvins
â¢ Monitor indoor air quality and carbon dioxide levels in greenhousesÂ
â¢ Displays temperature, relative humidity and CO2 simultaneouslyÂ
â¢ CO2: 0 to 2,000 ppm, Accuracy: Â±5%Â
â¢ Temperature: 14 to 140ÂºF (-10Âº to 60ÂºC), Accuracy: Â±0.9ÂºF (Â±0.5ÂºC)Â
â¢ RH: 0.0% to 99.9%, Accuracy: Â±3%
There is an RS232 output on the side of the unit. Â The RS232 data is 9600 baud at 5 volt levels that needs to be pulled up to 3V3 or 5V using a 300 ohm resistor tied high. Â The data is inverted from the standard RS232 standard. "0" = Â Â -15v Â equal +5v. "1" = Â +15v = 0V. Â This means there is no need to use the MAXUM chip MAX232 converter. Â It can be directly connected to a Bluetooth module. Â (HC-05 or HC-06 will work). Â However, don't forget the pull-up resistor to high data output. Â There is no connection for sending data to the unit, just out.
The RS232 outputs the current data in the format described below. Â
CO2 Â Â Â Â Â Â Â Temp Â Â Â RH Â Â Â Â Â Dew Point
C594ppmÂ Â Â T22.6CÂ Â Â H89.6%Â Â Â d20.7CÂ Â Â w21.3C59
Data comes out every 2 toÂ 3 seconds. Â It is then captured using a terminal software called Putty. Â
It requires opening the CO2 meter up and inserting a HC-06 board. Â The power for the Bluetooth device is connected to the power adapter plug-in. Â The unit can run off batteries, but it dies after a couple of days. Â It's best to run off an adapter.
After the HC-06 is powered by the adapter, connect the connections directly to the "out" of the RS232 1/8 inch mono-audio receptacle.Â Â It appears there are a lot of tricks put into the CO2 meter discouraging what I did. Â They want you to buy the USB to RS232 adapter and software. Â A wire needs to be connected between the ground of the RS232 connector to the mounting ring of the 1/8 inch receptacle. Â It's embedded partly in the plastic housing. Â When the jack is in place, it connects the GND to that ring by default. Â It will not work without that connection in place.
The CO2 trends seem to follow the night and day. Â At night plants make CO2 to grow; during the day they take CO2 and produce O2. Â O2 is around 21% all the time. Â And all air cycles through marine tank throughout the day. Â And it appears the CO2 follows the RH changes. Â This is really noticeable when a biosphere is first put together. Â The CO2 will go as high as 1500ppm and the RH is 100%. Â After a week or two, the CO2 comes down and stabilizes around a range of 380 to 600 ppm at a RH of 65 to 80%. Â The Earth's average CO2 is around 450 ppm. Â Indoor CO2 levels are around 600ppm.
Using three tanks, one for day, another for night and the last for marine phytoplankton CO2 sinking, it's possible to keep a stable CO2 levels. Â