Monitoring Temperature in a Greenhouse

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adri123

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Re: Monitoring Temperature in a Greenhouse
« Reply #60 on: March 05, 2015, 09:59 »
Well I can calibrate it and compensate if it turns out not to be too accurate.  I couldn't justify 40 for one of the better ones.  They'll all be made in the same factory more than likely...

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Elm street

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Re: Monitoring Temperature in a Greenhouse
« Reply #61 on: March 08, 2015, 16:31 »
These units will only work when connected to a computer/device so are not stand alone!
Therefore you will need a long USB cable or leave your device in the greenhouse  :(

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adri123

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Re: Monitoring Temperature in a Greenhouse
« Reply #62 on: March 08, 2015, 21:15 »
Thx.  I thought that might be the case but fortunately I have a long USB cable and/or a crappy old laptop that can stay in the Pt overnight.

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Headgardener22

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Re: Monitoring Temperature in a Greenhouse
« Reply #63 on: May 09, 2016, 18:39 »
I know this topic has been quiet for a long time but I'be been entertaining myself by creating my own temperature monitoring system using a Raspberry Pi and the DS18B20 waterproof sensors. I've now got to the point where I have run the system for three days with two sensors measuring the temperature every 10 seconds or so and created a graph of the results of the temperature indoors and outdoors.

My next step is to increase the number of sensors and to measure the temperature inside the waterbutt to see if the temperature rises and falls and to compare that with the temperature inside the polytunnel, both just in the atmosphere and on top of the waterbutt.

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Trikidiki

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Re: Monitoring Temperature in a Greenhouse
« Reply #64 on: May 09, 2016, 20:22 »
HG22, as you are aware I was monitoring soil temperatures using DS18B20s and an Arduino. It worked really well as long as my power source held up. I had a blue-tooth connection to an old phone so I could check the temperatures on the fly rather than having to remove the SD card and transfer the data onto the PC. The blue-tooth was a big battery drain especially if they disconnected for some reason as it constantly tried to reconnect.

I am now playing with a 'solar heating system' in my small greenhouse but have been too busy rebuilding my fruit cage and other real gardening chores, to give it the time. Hopefully get back onto it when spring planting subsides.

Basically it is a black painted radiator feeding a dark green oil drum. The water is pumped during daylight hours for 1 minute every 15 minutes. My problem at the moment is the startup current for the pump motor keeps burning out relays.

The plan is eventually to have one radiator painted black feeding the oil drum, the pump will only run when the radiator temperature reaches a certain threshold above the oil drum temperature, thus saving battery power by only pumping when there is heat to be gained. A second radiator will be my propagator bench with a transparent "sun cloche" over it. At night when the temperature drops to a predetermined level another pump will run the water through the bench radiator to heat the cloche. I could also set it to pump the water to cool the bench radiator during the daytime if the temperature starts to rise too high on a very sunny day.

I had thought of keeping the drum on the sunny side of the greenhouse to add to the solar heating effect but am now thinking that using a plastic drum buried in the ground will insulate the drum well, may provide a little geo-thermal heating effect and also free up the floor space in the greenhouse.

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Headgardener22

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Re: Monitoring Temperature in a Greenhouse
« Reply #65 on: May 10, 2016, 14:29 »
Hi Trikidiki,

We're obviously going in similar directions (I'm just a bit slower). My ultimate plan goes something like this:

A solar panel; a water tank; two 12v pumps; a length of hose around the polytunnel; three temperature sensors (in the solar panel, the tank and the polytunnel; a car battery; and a solar panel to charge the battery.

When the temperature in the solar panel is warmer than the temperature in the tank, the water is pumped round the panel and into the tank;
When the temperature in the tank is warmer than the temperature in the polytunnel, the water is pumped around the pie in the polytunnel.

I think I'll also need a fan which runs if the temperature in the polytunnel is higher than (say) 35C.

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Trikidiki

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Re: Monitoring Temperature in a Greenhouse
« Reply #66 on: May 10, 2016, 21:44 »
I have had the prototype running on occasions and also have another oil drum of water next to it which is currently 'stagnant'. Just using touch there is an appreciable difference in the temperatures in the two tanks when it has been running for a while. My gut feel is that it will not produce enough heat to maintain an adequate temperature in a large volume which is why I am focusing on just heating a propagation bench. If it works better than expected I might try to heat more of the greenhouse.

I just need to get some larger relays. The pumps draw 3A when running but they are burning out the tracks on 10A relay modules so must be producing a huge power surge on start up. It may be that although the relays are rated at 10A the circuit boards cannot cope with the 3A the pumps are drawing.


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steved

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Re: Monitoring Temperature in a Greenhouse
« Reply #67 on: May 13, 2016, 07:58 »
You would need a motor rated relay/contactor. Induction motors can draw upto 8x the running current on start up
Political Correctness-a concept based on the idea that its possible to pick up a turd by the clean end.



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