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Experimental Greenhouse, Which Data Loggers?

01/19/2021 3:55 AM

I'm building a 10 sq. meter greenhouse, (Legal max size here) and I hope to make it useful to other people by collecting data on how well or how badly it works. We are at about 48 degrees north and its a Mediterranean climate, wet cool dull winters and dry summers. I plan to have it pretty airtight when necessary, to better retain heat, and also maybe (if possible) to recycle moisture from the air in summer. Because it is potentially airtight, I was going to use either an integrated compost bin or tiny rocket stove to generate CO2 to bring CO2 levels up from 400ish ppm to the plant daytime optimum (around 1200 ppm). I was going to store rainwater from the roof in rainbarrels and also in compartments under the growing beds. Probably 300 to 500 liters under the beds. In winter time, and maybe in summer too, I was going to collect heat from the daytime and either store it in the planter soil or in the water under the planter. To collect heat, I was going to pump warm air from inside the greenhouse near its roof through pipes in the soil and in the water. And also, I will have a solar thermal collector on the north wall of the greenhouse, to directly absorb solar heat and transfer it under the soil quickly. Hopefully some of these collection methods will also condense water from the air for reuse. Any suggestions for data loggers or an alternative to accurately measure of temperature (to about 0.1 degrees C), atmospheric moisture content and humidity, and CO2 ppm? I include diagrams of what I hope to do, and pictures of the progress so far. (It has been a very wet muddy time.

Here are pics of it.

I'm nearly ready to put glass on the roof, and today, and tomorrow, I'll be putting glass and cutting acrylic sheets to go in the triangle pieces above the door and at the back of the greenhouse. One way to capture heat from near the roof is a solar powered fan up there to pump the air into pipes that go under the water in the planter.

Below is a pic of the back (north wall) It is 27 inches high of brick, the planter will be around 24 inches high, for a total soil depth of around 18 inches and there will be 8 or more inches of water below that, it will be contained in rubber pond liner. Below the pond rubber, I'm going to have either concrete pavers or a thin concrete layer (to prevent rats from digging in). I have done rough calculations about how much compost I need to rot to have the CO2 levels I want. The plants in this size greenhouse likely could use up to 0.2 Kg of CO2 in Winter and around 0.3 kg of Co2 in the Summer. Here are some of the ways to get 0.3 kg of CO2 into the air in the greenhouse. 70 kg human resting in the greenhouse for about 10 hours. Or Burn 200 grams of wood, or have an enclosed compost bin attached to the greenhouse and add about 3.5 kg of yard waste to the compost every day in the summer. A problem is that 1200 ppm of CO2 isn't recommended for long term human exposure. (Though it is ok). A bigger worry is if I overshot it and I didn't know. So, Data loggers for Temp, humidity and CO2. I have no clue what to get or what might be the best solution. If data loggers are too expensive, maybe an old camera set to take a pic of the displays of all the thermometers and humidity meters every 20 minutes? Anyways, any ideas are appreciated, Thanking you in Advance

Brian White Victoria BC Canada

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#1

Re: Experimental Greenhouse, which data loggers, etc.

01/19/2021 4:17 AM

<...accurately measure of temperature (to about 0.1 degrees C)...>

Of what value is the information to the first decimal point? At what spot within the structure? The temperature within it will vary with where it is measured and will be noticeable in the difference between readings if that is the sort of accuracy ambition. Would this mean several sensors, for example, and what is the intent of capturing all these data?

<...condense water from the air for reuse...>

One needs to be careful as there is the prospect of aerosols conveying soil-based pathogens around the place by doing that, especially if the footprint is only <....10 sq. meter...> and, say, no more than 2.5m high.

<...collect heat from the daytime...store it in the...water under the planter...>

That's a great way of growing bacteria in the <...water...>...

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#3
In reply to #1

Re: Experimental Greenhouse, which data loggers, etc.

01/19/2021 1:14 PM

Hi, PWSlack, I could have normal 1 degree accuracy Temp measurement in most of the greenhouse. But on the wall at the back on the north wall, I will add batches of water to the solar collector, and it will flow down, collect heat, and dump it into the water chamber or soil below. This water in that heat collector will be separate from the rest of the water in the system. There may be condensation on the top where the cool water is stored before being dumped into the solar heat collector. Condensation releases heat, but compared to the amount of water in the cool tank, it won't be enough to raise the temp much. So one highly accurate temp reader on that, and a couple of accurate ones on the output from the solar heat collector and in the soil and in the water below. (Newtons law of cooling probably applies as the water in the storage below the planter releases heat). I want to measure the heat flow from the water where it is stored up to the plants roots. this might mean measurement every 4 inches to get a heat gradient. So for that, probably the sensor needs to be accurate to 0.1 and quick response too.

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#5
In reply to #3

Re: Experimental Greenhouse, which data loggers, etc.

01/20/2021 7:23 AM

Do let the forum know how it all goes.

<unsubscribes>

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#6
In reply to #5

Re: Experimental Greenhouse, which data loggers, etc.

01/21/2021 12:58 PM

So, which data loggers do you recommend? Previously I used a digital oven thermometer with a long lead to the probe. It was always on, displayed temp accurate to 0.1 C and was very responsive to small temperature changes. So, I could calculate how much heat different configurations of a "dripwall" solar collector was collecting and moving under the soil. But they are discontinued. All the ones I can find now or either accurate to about half a degree C or shut off their display after 30 seconds or so. I thought dataloggers would be a much better option, but I have never even used one. I'm looking for temp to 0.1 C so I can measure heat gain from condensation, and also I want humidity and CO2 data. So, anyways, temp and humidity at entrance and exit of the heat exchange tubes or pipes. And ideally a CO2 meter to at least try to optimize Co2 "fertilization" in the greenhouse. It probably needs a display so I can run tests. And logging for day and night heat changes in the air and in the soil and water. I want it to be useful to other people so they can decide how "tight" to have their greenhouses for best growth.

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#2

Re: Experimental Greenhouse, Which Data Loggers?

01/19/2021 6:28 AM

<...Burn 200 grams of wood... it is potentially airtight...>

What is to happen to the smoke and the ashes from this process?

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#4
In reply to #2

Re: Experimental Greenhouse, Which Data Loggers?

01/19/2021 1:18 PM

Just throwing it out there. Ashes would be recycled into the soil or compost. Might occasionally burn rosemary or sage or cedar to kill off spider mites. 200 g isn't much wood. but smoke would probably mostly make it a non starter if burnt inside the greenhouse.

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#7

Re: Experimental Greenhouse, Which Data Loggers?

01/23/2021 11:30 AM

Just because a digital device displays to a resolution of 0.1 does not mean that it is even accurate to the whole number digit, particularly in the consumer market.
In the industrial instrumentation world, the first question when 0.1°C accuracy comes up is "how deep is your pocket book".

Thermocouple sensors and their cold junction reference measurement can't do it outside of some very specialized designs at huge cost.

When BTU calculations that need 0.1° accuracy on chilled water are done for billing purposes in institutions with large centralized utilities, the temp measurement is done with either Class A or Class 1/3DIN 4-wire Pt100 RTDs for sensors, with an analog front end that is a true 4 wire RTD, high accuracy analog input.

Thermistors might be able to produce repeatable accuracy over a nominally narrow range if the analog front end were capable too, but industry doesn't use thermistors because of their narrow range of linearity, lack of commercial calibrators, and relatively low upper temp range, so I've never messed with them.

You might take a look at National Instruments (NI) that has lots of test and measurement PC I/O cards and has Labview, a software package that does PC based data acquisition for temperature. NI tends to be found in university and R&D research labs, as opposed to industry, which matches what you're doing. NI's help files are some of the better ones out there.

But I suspect that you're thinking this a $100 project data acquisiton task nut for 0.1°C, that's a dream.

If you're into programming, the Raspberry Pi micro is targeted at analog I/O, but you'll also quickly discover that things like the shifting temperature of the analog measuring device affects the reported temperature and find yourself in the world of instrumentation design.

I'm not familiar with the RH consumer market, but consumer interest in home weather stations and home air conditions, I suspect that some web searching will come up with an affordable RH sensor with either data storage or an analog output.
For CO2 check out this OMEGA which does CO2 and RH and logs 32K values.

https://www.omega.com/en-us/test-inspection/air%2C-soil%2C-liquid%2C-and-gas/gas-analyzers/p/AQM-102-CO2-Monitor

Probably others out there, too.

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#8
In reply to #7

Re: Experimental Greenhouse, Which Data Loggers?

03/26/2021 1:28 AM

Thank you very much! I still haven't bought any data loggers. I'm happy to report that my experiments are coming along in spite of that. The main thing for me at the moment, is to bring as much heat as possible down into the soil and water compartment from the air during the hot parts of the day. I have very little ventilation in the greenhouse (that's an experiment too). I'm using 2 little computer fans to drive air down through 2 pipes, one goes into the soil and one goes into the water compartment. The air temperature drops by about 5 degrees C through the soil and about 8 C through the water. I cannot measure how much condensation there is in the soil pipe, because the water just runs out through a hole into the soil but I can in the pipe that goes into the water compartment. (I'm just going to wait before I take measurements because I can't measure the air volume through the system. (I was thinking to use a dandelion "clock" in as a visual clue to the speed of the air in a clear plastic tube) . I have used lengths of J-strip to direct and collect drips of condensation on the roof. On hot days, it's just drip drip drip, (I'm trying to simulate a cloud and concentrated rain). So, here is a question. When, say 200 ml of water condenses in the pipe going through the water chamber (the cold water around it causes moisture to condense inside the pipe), where does the heat of condensation go? is it just heating the air a bit or does it get sucked into the cold water, or maybe a bit of both? Here is the project so far as a youtube playlist. https://www.youtube.com/playlist?list=PLkzXlmAwZTZeWOz3H5ua7q5ItqnJww2G6 Thanks, Brian

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#9

Re: Experimental Greenhouse, Which Data Loggers?

04/23/2021 1:49 AM

I finally splurged and bought some a thermometer with 4 sensors, a thermometer data logger with 4 sensors and a combined humidity, temperature monitor and CO2 monitor. I have a few issues to solve, can you give me suggestions?

Here is the CO2/humidity/ temp monitor. Its pretty cool! I was a bit in shock when the greenhouse came out as 98% humidity and maybe 650 ppm C02, but then I put the monitor outside and it dropped down to 410 ppm. But, anyways, it makes sense because there is organic material under the soil and it's rotting and releasing CO2 in the heat. Another thing that the meter made clear is that houses have a lot of CO2 and maybe we should be piping air from houses to greenhouses to make the plants grow a bit faster.

There are a couple of difficulties with the thermometers. First of all, the sensors are a bit wimpy. and they are unprotected. I'll be poking these into the soil. Is there anything I can do or a sleeve I can make to protect them? The probe wires are about 3 ft long and I will have to put some of them about a foot deep into the soil.

Here are the other ones (for the datalogger) and they are thinner. So they also need protection.

The other problem is that the boxes are rated for 80% humidity max. but my first reading was 98% so I have to protect the boxes or keep them outside the greenhouse.

That's the datalogger. and below is the thermometer.

Its way cheaper of course. But you have to be there while doing detailed readings.

So, anyway, any suggestions to make these thing work out?

Thanks, Brian.

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#10
In reply to #9

Re: Experimental Greenhouse, Which Data Loggers?

04/23/2021 4:00 AM

Your humidity should be maintained at 50 - 70%, too high and you get problems...

..."When humidity gets too high in greenhouses, plant leaves stand a much better chance of getting wet. Wet foliage, unfortunately, is one of the best ways to ensure a fungal infection or an outbreak of mildew. Fungal diseases such as the Botrytis pathogen or powdery mildew are common greenhouse culprits. When moisture builds up on the roof of the greenhouse and then drips back down, it can splash infected plant leaves and the resulting spray can contaminate nearby plants."...

https://homeguides.sfgate.com/ideal-humidity-level-greenhouse-77050.html

https://zipgrow.com/how-to-reduce-humidity-in-a-greenhouse/#:~:text=Most%20indoor%20growers%20will%20want,%2D80%25%20is%20usually%20tolerable.

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#11
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Re: Experimental Greenhouse, Which Data Loggers?

05/01/2021 10:33 PM
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#12

Re: Experimental Greenhouse, Which Data Loggers?

05/02/2021 5:44 AM

I use to build and install data logging systems. Mostly military spec weather stations. The first question I would ask you is how many sensor inputs do you want to log? Then build double that. You got two choices. Buy a commercial logger and transducers. You need a fat wallet for that. Especially with multiple inputs. I'll bet that has not changed.

Or one could use an old laptop and some com input hardware. This takes some sensor wiring, hardware circuitry, and programming experience. One should be able to find open source programming for windows and office, or linux and libre for display tables and charts.

I would complete the construction, then place 4 cheap ebay temp/humid recorders in house to see what's happening first. One might need to change initial construction before installing custom permanent sensor array. CO2 detectors, water temp and flow. Possibly water pH. Outside temp and humidity...and wind direction and speed. One might automatically control re-cir and exhaust fans, louvers and water pump. Even humidity control. Light timers. If you go to the trouble and time for logging and measuring your greenhouse, why not control it too?

You might horse trade for some old or surplus PLC gear.

If you need this quick, you'll have to shop around and buy. The only equipment I'm familiar with is old and very expensive.

I marked this off topic because I haven't seen one for 20 yrs.

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#13
In reply to #12

Re: Experimental Greenhouse, Which Data Loggers?

05/02/2021 12:03 PM

Hi, Haymaker, I think it is very much on topic, thanks! I bought a datalogger, Around 100 bux with 4 input probes, and a thermometer about 18 bux with 4 input probes. But the probes are flimsy and I will have to armor them to place them under the soil. I haven't figured out how just yet. I also got a CO2/humidity meter/ thermometer around a hundred bux too and that is pretty cool. I now wish that I had got one for control instead (only a little more expensive). There is a solar panel that powers fans that send the air down under ground and under water to cool the air. (About 10 C drop as it passes through the pipe under water). And I could just use the controller to switch the power to blow air out of the greenhouse if Temp or humidity is too high or if CO2 level is too low. My greenhouse is shaded part of the day, and it's amazing how quickly temp drops when a cloud passes over the sun. Or how quickly CO2 rises when I sit in the greenhouse for a while. It's a much more interesting project now that I have that combo meter. Another thing that is very interesting is humidity. It varies a lot. My moisture collection can be "raining" from the roof even while humidity isn't very high. (Depends on the temperature differential quite a lot). I think also the air circulation from the computer fans make a big difference. Cool air blowing up to the roof in places triggers the condensing earlier. I might end up having fans going at night to prevent condensation on plants in the morning, (to get that rain flowing at night too).

Pepper in flower today and Tomatoes need staking.

I haven't been paying much attention to the greenhouse last couple of days, sorry. But the fans through pips under the soil and the solar thermal panel (also sending heat to the soil) are definitely reducing temperature swings and humidity. (Its a lot less humid than Brasília in January, for instance). Maybe, I'll bring up the CO2 monitor and do an hour or 2 in the greenhouse today. (But I gotta work :( too).

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#14

Re: Experimental Greenhouse, Which Data Loggers?

05/02/2021 2:11 PM

The Tenmars TM-747D 4 ch temperature monitor manual at this link
https://www.voake.com/product/tenmars-tm-747d/?attachment_id=10715&download_file=5d5d862de0bd5
says that the unit takes 'thermocouple' (T/C) sensors, as opposed to RTD's or thermistors.

The exposed junction style (exposed wires and welded bead) shown in your photograph is indeed, not very robust; that style is VERY quick responding, but with the trade-off of being overly delicate and subject to breakage.
The yellow jacks shown in your photo are probably indicative that the unit is using Type K thermocouples - the North American standard color for a Type K is yellow (color of the external insulation and the associated plug or jack).

Industrial thermocouples are typically sold with the thermocouple element inside of a Stainless Steel (SS) sheath that completely covers the junction. The space between the thermocouple wire and the sheath is typically filled with a white insulating powder, Magnesium Oxide, or MgO, hence the style is often referred to as an MgO thermocouple. The combination of a SS sheath and insulating powder creates a lag between a temperature change at the tip of the sheath and when the junction 'sees' the temperature change, but for what you're doing, the lag time is inconsequential.
What's important about thermocouples is that the all the wiring in the circuit MUST be the same 'Type' alloyed metals as the thermocouple junction itself, which means that the extension wire from the thermocouple AND the plug that the extension wire connects to and which plugs into the monitor. A mismatch of thermocouple components or the use of copper wire in a thermocouple circuit gives you garbage temperature readings.

Those yellow jacks undoubtably have screw connectors holding the T/C extenstion wiring, so if it were me, I'd get replacement Type K, MgO thermocouples with SS sheath with enough leadwire coming out the sheath to give you the amount of wire needed to make the measurements. The two internal Type K wires are color coded, too: red is negative and yellow is positive. If you connect a thermcouple backwards, an increase in temperature drives the reading negative, a decrease temperature drives the reading positive. It doesn't hurt the meter, just swap the wires.

That meter can handle all the major Thermocouple types: J, K, T, for which there's selection setting, but using a Type T or a Type J would mean having to replace the plugs (which are most likely the 'Mini' style plug).

Sources:
A local guy was selling a carton of 30-40 MgO T/C's for $10 on Facebook marketplace. Ebay has hundreds of T/C listings. Local industrial distributors frequently stock T/C's, wire, and plugs, but finding one is a chore if you're not in the biz.

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#15

Re: Experimental Greenhouse, Which Data Loggers?

05/12/2021 1:52 PM

I took some measurements yesterday (May 11th) in the greenhouse. Air blown from the top of the greenhouse and through the black pipe under the water (I think the speed is at most 30 cubic ft per minute) One cubic ft is 28.3 liters. At 1.20 pm the air in was at 32.6 C and it came out at 22.2 C so that's significant cooling. So, I calculate roughly 17 grams per second of air passing at that time. And with the heat capacity of air roughly a joule per gram per degree C rise in temperature, that means that the cooling of air by passing it through the pipe transfers 170 watts to the water surrounding the pipe "at its optimum operation". I also measured some of the water dripping from the roof condensation collection system and the water that condensed out in the black pipe. So from 9.20 am until 8.45 pm, The 3 glasses on the path in the greenhouse collected drops of water (from Door towards the east side) 21 ml, 12 ml and 1ml. The east side is where the fans blowing air down is. So 34 ml of water. Not much, but it is a passive system. Meanwhile we got the 10 C cooling from that one pipe and air driven through by the computer fan, PLUS we got 361 ml of water condensed in that pipe! 2257 joules per ml released when water condenses multiplied by 361 ml is 814777 joules in 11 hours and 25 minutes. (685 minutes) which is 41,100 seconds. And divide 814,777 by 41,100 and we get part of the wattage that we are charging the climate battery with. and it is 19.8 Watts! That's just for the condensation in that pipe submerged in the water storage. There are also 2 pipes going under the soil and fans blow air through them too but I don't have a way of measuring the condensed water there. There is probably less condensation in those because the soil is a bit warmer than the water so less heat transfer. So, even though the system is far from perfect, a 15 watt solar panel running 3 computer fans is acting very much like a heat pump. Moving and storing a lot more energy than it could ever produce. The next stage will probably be to hook up my 2 other water cooling systems to a "radiator" somewhere on the roof and pump cool water through that radiator while blowing a fan downwards on it too. This should get a better "cloud effect" where I will collect the water and have cool dry air descending towards the plants. I will run this off a solar panel too because I want the fans and water pump working hardest and getting the most cooling when the sun is shining the most.

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