Recording / Logging Greenhouse Temperatures

I'm curious to know how the temperature falls compared to outside. It will lag behind the outside, so if temperature drops to freezing outside this time of the year that will normally not be until close to dawn, and then rise as son as the sun is up. If the greenhouse lags far enough behind that might be a 5C difference (but without that data I'm guessing ...) ... then from the forecast I can decide what action I need to take to keep my plants alive. Also when I last did some spread-sheeting the Forecast was incredibly pessimistic on Low temperatures - presumably so that they never get accused of not providing a warning - so I also want to get a feel for whether that is sufficiently "predictably-pessimistic" that I could make my own "adjustment"

And finally an Alarm when I forget to open / close the greenhouse in good time would be handy. At this time of year I want absolutely as little heat as possible so the plants don't grow "soft" ... but equally I don't want any undue cold either, which could send them into hibernation, stress, and leave them impaired and under-performing for the whole season.

As @ricky101 says, the traditional way was with a Max/Min thermometer and make a note (mentally or on paper ) each day.

 

Why worry ?

If you use auto vents it takes care of the daytime heat, if you have a heater set for frost free that takes care of night time frosts.

The type of glazing / insulation you have determimes the differential, last night ours was 0c outside , but 7c inside , though we do have twin wall 10mm polycarb etc.

Using some form of heatsink also help maintain a higher temp overnight, could be a pile of bricks or some trugs full of water, which also serve as a heater for watering the plants, rather than cold mains water.

 

Early days, but i think you'd like these. I'm guessing your Mindshift ones are a bit like the Chinesium one's I've had which do-the-job, but bits of it are a struggle.

I've only got a starter-set to see how I get on, and I've only done CONFIG not actually stuck it in the greenhouse overnight yet - more on that later - but the software is seriously impressive, whereas the stuff I've had before has been "hard work".

Apart from twiddling all sorts of "What Columns would you like in your Download File" it looks like you can set it so that when you plug in it will EMail you the file(s) in your preferred format(s) ... e.g. a PDF with charts and a CSV

Twiddling the log-interval shows me how many days it would record for ... and changing the date format template showed an example of how it would then look. Software that includes that sort of stuff is definitely less likely for me to trip over myself ...



I can see that would be a boon for monitoring e.g. medical supplies in transit - person at the far end plugs it into a USB port and "good stuff happens"

Beware that some models have fixed (non rechargeable, non replaceable) batteries
Hardware - LogTag

 

First set of readings ... impressed with the features and, so far, everything "just works" which is encouraging



Showing tabs:

Report - Details about settings (e.g interval), Hi/Lo temperature (and the date/time it occurred), and graph of the period

Chart - graph with carious Display Options

Data - just the raw data

Summary

 

First full night recording, and all conclusions based on that one single data point ... but

I am trying both the USB-connector type, and the "cradle" type. I reckon the Cradle type is easier (if you have several Loggers) ... just stuff the LogTag into the cradle, it downloads the data (showing a red light) and once the light has turned Green again stuff the next one in. The buttons on the Logger can be used to STOP/reSTART the logging (on collecting, and then after downloading again after replacing in-situ)

Once downloaded (or subsequently by opening all the relevant saved-data-files) a composite chart can be produced. The result is not what I was expecting ...



Overnight the big greenhouse was 3C warmer than outside ... I have always assumed that the small green (at 10x12 probably quite large for a home greenhouse) offered a couple of degrees of protection but by 00:30 it was down to less than 0.5C difference, and 05:00 - 07:00 was basically the same as outside.

So I'd be better off moving my tender plants into the big greenhouse ... also having some free-standing staging in the big greenhouse I could chuck a "significant" thermal blanket over the top at night - no light needed - and if I put my heater under there it would have nothing like the dT to try to overcome compared to the small greenhouse (where it would be neigh on impossible to get a thermal blanket over everything, short of covering the whole greenhouse !)

As expected the temperature change in the small greenhouse is more rapid than the big one (and would be far more dramatic in an even smaller greenhouse). The rise yesterday afternoon at 16:30 is when it was closed up for the night - I've always done that "reasonably early" to "capture some heat" but actually it took the temperature up to nearly 35C (the gain lasted 1.5 hours) ... which won't make the plants at all happy. The big greenhouse only climbed from 24C to 25C after the vents were closed (that gain also lasted 1.5 hours)

I got my LogTag recorders from this lot. They were here "next day" Watch out for the models that do NOT have [user] replaceable batteries

Hardware - LogTag

 

It was after distrusting max/mins and then seeing exactly what was happening (and when) using data loggers in polytunnels that led me have loads of plants in plastic crates on the staging that I could quickly stack into mounds and wrap with old net curtains, fleece, sheets, etc. overnight.

 

You see a lot of such devices saying that these days, as normally they can run for a year or more on the same battery, but often you find if you split the case open they are just standard coin cells that can readily be replaced.

 

I think that is probably the case ... just not sure how easily the case (sorry!) could be split open. I hate that sort of wastage :( but I can imagine in the Health Industry that a logger accompanying a batch of medicine, to check that temperature was safely maintained en route, is too difficult to retrieve for reuse. Pity though ...

 

I put the fan heater in the small greenhouse last night as forecast was to be 7C for nearly all the night. I put a logger in front of the heater (light blue) on a 1-minute log as I wasn't sure how quickly the heater would cycle (nor what the hysteresis on the thermostat would be like). I had it on a low setting, and seems that it was on for 20-30 minutes and off for 60-90 minutes. The thermostat sensor and the (purple) logger were at staging height. The fan heater itself has a dial marked 1-9, I imagine the hysteresis is "poor", but I also have a 13AMP thermostat with an extension prob so that can be put amongst the plants, and looks like that worked well - temperature cycled 1C

Grey day here this morning, vents not opened on the greenhouses as yet

Need to rig up some staging in the big greenhouse as that wouldn't have needed any heat

 

At what level is the outside logger, and is it susceptible to wind chill?

I used to place mine at my plot at 'ground zero' in a plastic carrier bag, which was where my outside plants were, but at home on top of the staging outside my greenhouse, again where my outside veg plants are (only grow/hold stuff there or at window box level), just trying to establish what your outside datum is.

 

Its between my greenhouses - North side of the one in front as I was trying to avoid any direct sun. If the wind howls from East or West it would definitely go through that gap ...

I have a an upturned plastic (mesh) crate, to allow some airflow (upwards) with the sensor on top, and then a large upturned clay flowerpot on top of that. Thus the sensor is 12-18" off the soil. I was hoping that would provide some still air, whilst also allowing some thermal currents sufficient to be accurate.

I've done the same for the ones in the greenhouse, but I wonder if that initial green spike was the clay pot heating up in the sun (but I did also change the ventilation from doors-open to closed-and-vents-open as the breeze was very cold yesterday.

My plan was to make some sort of Stevenson screen