[BabbyAnn]

interesting results

[Maarten]

Your temperature differences are very consistent over the days. Quite interesting; consistently a degree more can make a real difference. Now that this is clear, would you consider swapping the two plastics without changing the sensors and see whether it is truly the plastic, or a difference due to exact location?

All the best,

Maarten

[Trikidiki]

I can do that. It could show an anomaly but I suspect not, they are only a couple of feet apart and in one bed so has had the same treatment over the past few years.

The original data which isn't on those graphs may have shown an anomoly as the black end was very slightly shaded by the very top of an oak tree about 50m away but after the first week the sun is well clear of the tree now, the results were very similar until we started to get some consistent sun. They now receive equal sunlight from sunrise to sunset.

I tested the sensors by clustering them together and measuring temperatures in a variety of situations from on top of the log burner to inside the fridge, they never showed more than 0.25°C variance and that wasn't by any particular sensor.

I'll try and get them swapped over during the weekend.

[sweetpea84]

i read somewhere else (one of the gardening magazines) recently that clear plastic is the winner when it comes to achieving higher temps under plastic.

[Trikidiki]

You could have said that a month ago.

[Goneterseed]

You could have said that a month ago.

sweetpea84 wasn't a member a month ago. 

[sweetpea84]

  exactly!! I'm using clear plastic and the weeds aren't too bad. They are big enough to pull out in one go but not so big they've overtaken each of the warmed beds.

[Trikidiki]

Duplicated from the original thread for my own future reference.

Your temperature differences are very consistent over the days. Quite interesting; consistently a degree more can make a real difference. Now that this is clear, would you consider swapping the two plastics without changing the sensors and see whether it is truly the plastic, or a difference due to exact location?
.....

Maarten

Attached are the results from about three days of logging.

The surface temperatures react very quickly to ambient temperature changes so the immediate effect of changing the sheets over settles down really quickly. What is telling is that the underground sensor that was under the black polythene shows a steady rise in temperature in the first few hours when covered with clear polythene and the underground sensor that was under the clear polythene shows a corresponding steady fall when under the black polythene. Then the results show the normal pattern under the respective polythene.

I think this shows as I suspected that the individual sensors, the soil nor the location are skewing the results.

I will run this until the end of the week then may swap the black polythene for bubble-wrap and see if that is an improvement over clear polythene.

[Maarten]

Hi Trikidiki,
Thanks for doing this. That was a very quick change. That also means that the effect of the cover only lasts for as long as it is on. I guess that is another benifit of clear plastic. You can leave it a bit longer on when something starts growing, in contrast to black plastic.
Maarten

[mrsbean]

Oh my, this is now beyond me. It seems more like a science lesson. I think i will just stick to old fashioned weeding.

[Trikidiki]

I replaced the black polythene with bubble wrap to see if it had any benefit over the clear polythene. The attached graph shows that the bubble wrap had a very slightly better warming effect than clear polythene but not by any significant amount and pretty much tracked with the clear polythene as it heated and cooled.

I am putting this to bed now and will re-purpose the sensors etc for my solar greenhouse heater project.