Experimental Greenhouse, Which Data Loggers?

<...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...>...

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.

Do let the forum know how it all goes.

<unsubscribes>

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.

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

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

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.

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.

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

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.

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.

What you have there is a terrarium....

A really big one....

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.