Inflated Greenhouse Air Pressure Sensor

I was hoping someone could assist me with figuring out how to create a sensor for my new greenhouse I am building this spring. The walls of the greenhouse will be made of 2 layers of polyethylene that I will be pumping air in to. Since I will have it pretty well sealed I was hoping to use the UNO to detect the air pressure in the wall.

Basically:

  1. When it reaches X lbs. of pressure it turns off the blower
  2. When the pressure drops to X lbs. of pressure it turns the blower on
  3. Somehow record/trend pressure changes in relation to outside temperature
  4. Most important of all an alarm siren that goes off if there is catastrophic failure of the wall
    Since the site is off grid, it has very limited internet access, however I am setting up a local WIFI network with a server.

Is this possible or am I dreaming? If it is possible can you suggest where I can find some scripts for it, when I search Google everything I find is for ventilators and medical devices.
Thank you for any ideas your willing to share with me.

Yes it is possible though I have not used the air pressure sensors or the wifi element.

There are several arduino air pressure sensors projects out there, just google ; here's one with code.

For wifi, again lots of turorials around but what distance are you talking about ? - if too great there are other wireless options.

Expect you will be wanting to look at temperature ,indoor/outdoor and humidity reading and control, again all do-able with the Ardunio, use such things a lot on my controllers ( fishkeeping /greenhouse)

TechDave:
Basically:

  1. When it reaches X lbs. of pressure it turns off the blower.
  2. When the pressure drops to X lbs. of pressure it turns the blower on.

You have mentioned the pressure as "X" in both cases. I'm not sure whether you meant that "X" was the same value both times or whether it was two different values.

I would suggest that the blower should turn off at X, and turn back on at Y, where X > Y.
This is called hysteresis, and will prevent unwanted rapid switching on and off of the blower.
.
Good luck with your project, it sounds feasible.
Please keep us updated with your progress, and ask further questions if required

Hi John.. Actually I was meaning X as in since I have not actually built the greenhouse yet (waiting for the ground to thaw out) I really have no idea what values I am looking for.. but yes your right X=max pressure Y minimum pressure. To much I could blow a seal to little defeats the insulation factors. I am wanting to have this greenhouse growing year around it gets very cold winter time up here.

Yes Ricky I will be looking in to all of those controllers also as I am going to put an Aquaponics system in the greenhouse but I didn't want ask for help on everything heheh

Anyhow the WIFI comment I assumed (yup I know what that can do to me) that would be the best way to get the data I was hoping to track. Would I be better off setting something up inside the greenhouse... maybe a raspberry PI or just an old PC?

Just a total side question for you Ricky do you use Hydrometers in your soil? If so may I ask which ones you use, I see a bunch of different ones on the market is there any better then others or are the all about the same?

Hi,

Everyone has there own ideas of monitoring data so I will mention mine and some of the methods I use etc.

Regarding your twin walled polytunnel, like the idea of using air, but from my small use of double layer bubble wrap, wonder how long your “seals” will last in the hot uv light and cold freezing nights ? and will you end up having to keep a pump running 24/7 as the leaks grow ?

Don’t know what air gap you are using but I used some 1" cubes of polystrene every foot of so to keep the two layers apart, expect there are some ready made such spacers for polytunnels, even with leaking seals it should still maintain the air gap.

Hydrometer, assume you mean a soil moisture gauge ? - no never used them as think the cheap stuff is no much use and the rest are rather expensive, though only from what I read.

Would think for a polytunnel ( how large ?) something like a timer /solenoid/seep hose might be more suitable, in warm conditions and open drainage it will not be easy to over water short term.

Readings, I know some folk want to sit and watch every temperature change throughout the day, but I find a simple daily min/max reading is all that needed.
Your automation, be it auto roof vents or cooling fans / or heaters in winter should take care of anything inbetween, though is max temperature that will be your main concern.
( can I ask what country you are in ?)

For controlling am sure an Arduino will do, while I would suggest a simple Uno for developing each module on, you might have to go to an Ardunio Mega 2560 for the complete project.

Regaring wifi and all that, seems a bit old fashioned to me, I made an automatic SMS controller that will send hourly ( or whatever) status and alarm reports to your phone, including a small battery backup so you still get notification when the mains goes off.

Its all there for you to make your own custom controller, just needs putting togther, if you have the time and inclination, as my old schoolteacher used to say ;D

Plenty on help in the forum as you can see.

I dont think it is impossible...more wondering why?

Increasing the pressure in the walls will have a negative effect on insulation. More air = more convection = more heat loss.

Removing the air would mean less convection and transfer between surfaces, much like in vacuum double glazing?

first off, this is very doable. no reason you could not do this.
second, you could do it with a simple switch, but that is another question.

the fan laws indicate that to increase flow, you have to square pressure.
this means that to keep it at or near the low end, might be easier and lower cost than try to have it run to high, then turn off, wait, then go high again.

the flow through the leaks work in reverse, the flow is squared when the pressure doubles. so, those leaks will leak more at the higher pressures.

all that said, you can easily run your blower at different speeds, faster as the pressure drops, and slower as the pressure builds.