Environmental conditions data logger and temperature regulator (Help!)

I am conducting bio-remediation research and currently am building a room within a room that measures approximately 10 X 6 X 8 feet. Inside the room is a 8,000 btu air conditioning unit that pulls hot air from the surrounding larger room, blows even hotter air outside the building and cold air only into the 10 X 6 X 8 room. In this smaller room, there are a number of high humidity bio-terrariums that need to be kept in the 70-75 degree F range (cold in comparison to my tropical climate). We can set the ac unit to whatever temp we want but it is not going to be properly functional as it is drawing hot air from the surrounding room that is much warmer and will thus likely never turn off. What we are thinking about doing is creating a circuit scheme with temperature, humidity and CO2 (up to 4,000 ppm) sensors and housing the arduino in a fashion to protect it from the high humidity (>90% relative humidity) and placing it inside the bio-terrarium. The primary functionality we want is to sense temperature inside the bio-terrarium and regulate the air conditioning unit by turning it off(or the power strip it is connected to) whenever temperatures drop below ~74 F. We would also like to log all three of the sensors data and have them stored on a microSD or more preferably have the data accessible via our wifi network.

I have very basic experience with arduino. I haven't done anything more complicated than increasing the frequency of an LED blink with a potentiometer. Can you guys give me some advice on the best way to go about this most effectively and efficiently?

How do you think this sensor will fare? I think the CO2 range is too low

EmerickL:
We can set the ac unit to whatever temp we want but it is not going to be properly functional as it is drawing hot air from the surrounding room that is much warmer and will thus likely never turn off.

...

The primary functionality we want is to sense temperature inside the bio-terrarium and regulate the air conditioning unit by turning it off(or the power strip it is connected to) whenever temperatures drop below ~74 F.

I think you're saying that the AC unit will be trying to control the inlet temperature (on the assumption it's drawing air from the room it is in). Would it be possible to find an AC unit designed to be installed outside the room? I don't think that's particularly unusual for domestic AC units.

PeterH:

EmerickL:
We can set the ac unit to whatever temp we want but it is not going to be properly functional as it is drawing hot air from the surrounding room that is much warmer and will thus likely never turn off.

...

The primary functionality we want is to sense temperature inside the bio-terrarium and regulate the air conditioning unit by turning it off(or the power strip it is connected to) whenever temperatures drop below ~74 F.

I think you're saying that the AC unit will be trying to control the inlet temperature (on the assumption it's drawing air from the room it is in). Would it be possible to find an AC unit designed to be installed outside the room? I don't think that's particularly unusual for domestic AC units.

We have a working AC unit that blows cold air so we are trying to work with what we have and liked the idea of tackling the project with arduino. This isn't a 'domestic' AC unit but rather an 8,000 btu room unit. The bioterrariums are rather small, measuring just a couple cubic feet each, they produce their own heat and it is the air inside these terrariums that needs to be maintained at 74F. While the primary function is to regulate this temperature, it is nearly as important to us to log the CO2, humidity and temp data for the entirety project.

I think you may need to reach out to a refrigeration technician. when you compress freon and then allow it to expand, there is a phase change and a lot of cooling and heating going. on. there is no reason you cannot use a DX system. even in your area. the operation has more to do with pressures than temperatures.

since you should not have any heat load in the space, the amount of cooling will not be that great.
in addition, you should use the controls of the air conditioner and not power the entire unit on and off.
you must include an idle time setting. you have to wait some time between the time the unit is shut off and the time you can turn it back on. the pressurized gas that is liquid will need time to reach equilibrium in the system or you could try to start the compressor with liquid in it and break something.

also, if you use water and air as your heat transfer medium, you will find it much easier to use. I hope you have a stream or a deep lake nearby. efficencies go way up when using water as the medium.

I am not sure about the comment about humidity. the nature of air conditioning is to pass warm air over a cold coil. the moisture will condense and drain away from the unit. the air will increase in temperature as it mixes with the room and and the RH will drop rapidly.

if you have some control over the design of the cooling, look into ice or water storage. your compressor can run to store cold, then you can use that with very precise control into the space.

also understand that humidity is a totally seperate control process from cooling. you can dehumidify without changing temperature. just re-heat the air with the exhaust gas from the compression side of the AC compressor.

for the data logging, get an SD card shield. it will handle the voltages for you.
you should be able to get the data from the unit over your wifi.

dave-in-nj:
I think you may need to reach out to a refrigeration technician. when you compress freon and then allow it to expand, there is a phase change and a lot of cooling and heating going. on. there is no reason you cannot use a DX system. even in your area. the operation has more to do with pressures than temperatures.

since you should not have any heat load in the space, the amount of cooling will not be that great.
in addition, you should use the controls of the air conditioner and not power the entire unit on and off.
you must include an idle time setting. you have to wait some time between the time the unit is shut off and the time you can turn it back on. the pressurized gas that is liquid will need time to reach equilibrium in the system or you could try to start the compressor with liquid in it and break something.

also, if you use water and air as your heat transfer medium, you will find it much easier to use. I hope you have a stream or a deep lake nearby. efficencies go way up when using water as the medium.

I am not sure about the comment about humidity. the nature of air conditioning is to pass warm air over a cold coil. the moisture will condense and drain away from the unit. the air will increase in temperature as it mixes with the room and and the RH will drop rapidly.

if you have some control over the design of the cooling, look into ice or water storage. your compressor can run to store cold, then you can use that with very precise control into the space.

also understand that humidity is a totally seperate control process from cooling. you can dehumidify without changing temperature. just re-heat the air with the exhaust gas from the compression side of the AC compressor.

for the data logging, get an SD card shield. it will handle the voltages for you.
you should be able to get the data from the unit over your wifi.

What is a DX system? I know the relationships between humidity and temperature, I just need to log CO2 in ppm and relative humidity to ensure proper growth parameters for hydrocarbon re-mediating microbes. For the temperature, I have an AC unit cooling a room within a room but there are greenhouse type boxes INSIDE the room within a room that are warmer because of microbial metabolism and thus I need to ensure that the air inside these terrariums stay at 74 F, not the room they are inside or the room that room is in. So I need an arduino to cut the cooling of the AC off when it is 74 F INSIDE the terrariums (small plastic boxes) and to log the temps, CO2 and relative humidity

Does your AC unit come with a remote control? Like Dave-in-nj said, you need to interface with the remove (or not) control, instead of shutting the power to the AC.

Does your room have wifi reception to your wifi network?
Does the wifi network require user name/password or just a secret key?

liudr:
Does your AC unit come with a remote control? Like Dave-in-nj said, you need to interface with the remove (or not) control, instead of shutting the power to the AC.

Does your room have wifi reception to your wifi network?
Does the wifi network require user name/password or just a secret key?

Yes the AC has a remote control and the room has wifi reception that just requires a secret key

OK that's good. The AC remote is likely IR remote that flashes infrared light to the unit to indicate commands. Use this library to detect the right code for each command, such as on and off:

GitHub - Arduino-IRremote/Arduino-IRremote: Infrared remote library for Arduino: send and receive infrared signals with multiple protocols?

If the wifi only needs a secret key, the arduino wifi shield can handle the security:

AC IR remote signals are much longer than standard remote. You may need to make some changeds to the defaults in IRremote to handle the longer signal.

is there a way to use the Arduino to accept the code from the remote ?

yes just use the IRremote (or IRLib) library.

You will need an IR receiver & IR LED (emitter) for testing.

Once you work through the examples in the library, you will understand the requirements a lot better.

So do some background (re)searching on the above.

Depending on your setup, you may actually want the Arduino to be sending the signal to the Aircon unit to control it.