Heating Your Greenhouse in Europe This Winter

Started by Bern, September 03, 2022, 09:59:17 AM

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Quote from: Martin Bohnet on December 21, 2023, 11:53:24 PMColleagues at work dread cold times because my mood will drop with every Kelvin below -5°C at night and every day with an average below 0°C.

I really like the mix of units/scales there Martin  :)  ;)

Martin Bohnet

That's not a mix. The Celsius scale can be used to describe distinct temperatures, but if you want to talk about differences (every *unit* below -5°C) one needs to use Kelvin. Engineers tend to be as pedantic about such things as others are about orthography... Hi Mary Sue ;)
Martin (pronouns: he/his/him)


Quote from: Martin Bohnet on December 22, 2023, 08:40:12 AMThat's not a mix.

Maybe not in Germany, but elsewhere it absolutely certainly is.

1°C may be 1K (as in divisions, not actual temperature) but most people would not have a clue (about the Kelvin scale) and certainly not mix the two.

Hence my comment

Martin Bohnet

OK, I admit that came as a shock reading that English Wikipedia allows °C as unit for temperature differences. I have NEVER seen that in any serious text about thermodynamics and would rather give up my Dipl. Ing. academic title than ever use it like that. But given how the English speaking world clings to completely unusable imperial units, what can you expect?
Martin (pronouns: he/his/him)

David Pilling

If you're measuring in °C then why wouldn't differences be in °C. You have a thermometer it shows XX°C - so you'd write in your notebook values in °C and then take the difference.

As a child I had Imperial units beaten in to me (literally), I was sat at a desk for the first five years of my education memorizing how many furlongs in a mile, chains in a furlong, pennies in a pound, fluid ounces etc. Anyway this education made me what I am, and I measure temperatures above freezing in °F and temperatures below freezing in °C.

We did hear tales that in Germany they used °K, but surely you'd say your plants freeze below 273 °K. You're in a transitional state and one day people will say "it's a fine day, the temperature is 293 °K".

I had more luck with my Physics career, only the first three months (at age 14) used the cgs system (dynes, ergs) and the rest of it was MKS.

I curse the fools who decided the UK would go metric, they doomed us to a 100 years or more of confusion. All the doors in this house are Imperial size as are all the bolts and screws. I have a workshop full of Imperial tools. We have mysterious units in the shops, why are things sold in 453gm packets (because it is 1 pound weight).

Good luck to the USA in keeping the old units.

It's not as if broad and sunny uplands where everyone uses the same units lie ahead. People are tinkering with the definition of a kilo-byte as 1024 bytes (the latter is now properly a kibibyte).

Martin Bohnet

Oh boy. the trouble is, again, that 0°C, 10°C or 20°C describe discrete states a system can be in, not a distance between them. the "coincidence" that the distance between 0°C and 10°C are 10 K is there "by design" to not have complications in the form of strange factors like in the imperial units. Think of 10°C as of a point in a landscape. London, Sheffield and Edinburgh are roughly on one line, and while Edinburgh is roughly 2.3 times further away from London than Sheffield, would you ever try to say Edinburgh is 1.3 Sheffield from Sheffield?

 And don't torture me with imperial tools. IF you'd at least stay in one "unit" it would be fine, lets say in multiples of 1/16 ", but already sorting the tools from 3/8, 7/16, 1/2, 9/16, 5/8, 11/16, 3/4, 13/16, 7/8 to 15/16 gives one a headache...

1024 bytes, on the other hand, is useful - just think of it as $400. At least in early days of computing it was highly useful and relevant for addressing and timing to think in memory pages ranging from $00 to $FF, a.k.a the address space that can be indexed using 8 bit as pointer. At the end of the day it may still be after all the optimization and branch prediction and what not of modern processors and compilers is done.
Martin (pronouns: he/his/him)


My background, ecucation and career are all science. I have no problem working with any units in the imperial or metric systems and can generally convert between most of the "equivalent ones", in my head to a close enough approximation.

The first and only time that I have ever known anyone outside of science use Kelvin was 7 posts above this. To be honest, I don't recall anyone using Kelvin outside of academia, although it must have happened - even when I worked with industrial ventilation systems, I was almost certainly the only person that knew why 273 was added to C gas temperatures to achieve mass balances.
In the UK, only a small % of people will know anything about Kelvin, even the people who quote them as the CCT for lamps will generally have not the very first clue. It is, after all, a totally unneccessary complication.

In many everyday uses, imperial units are far more flexible/useful.
I use imperial when wood working for instance - 12 inches - divide it by almost any number and accurately mark out a length of timber. Halve it, halve it again, and again and again, now mark that accurately. All quite easy
Do the same with 30cm.

If measuring something, I remember whatever is easiest - the nearest to a whole number - I would remember 1 foot rather than 30.5cm (actually 30.48cm, but no quick and simple measurement device can measure that accurately.)

Martin Bohnet

Quote from: CG100 on December 23, 2023, 01:34:38 AMDo the same with 30cm.

Well, actually all mechanical technicians and engineers i know and work with think in milimeters, anyway, and do not flinch at all when going down to µm. From an engineers view, an inch is almost a kilometer. The only smaller imperial length unit I ever encountered is mil, which is used for wall thickness for catalysts, and guess what, it's 1/1000 of an inch, so it's almost a breach of imperialism, so to speak.
Martin (pronouns: he/his/him)

David Pilling

The Centigrade scale existed and was in use before Kelvins were invented... that'd be when I was a lad in the 1960's.

Actually the Kelvin scale was proposed by William Thompson in 1848, but the Kelvin scale was only standardised and named in 1954.

So pre 1954 people measured differences in degrees C.

Mr Celsius invented his scale in 1742, but outside of Sweden it was called the centigrade scale until 1948.

In the 1960's it was commonly still called centigrade and we struggled to come to terms with cycles per second becoming Hertz.

5-bob on them dropping the blokes' names from units and just going with letters at some point?


Quote from: Martin Bohnet on December 23, 2023, 02:52:19 AMWell, actually all mechanical technicians and engineers i know and work with think in milimeters, anyway, and do not flinch at all when going down to µm.

I do not doubt that for half a moment (imperial measurement, I believe), but another red herring.
When I worked in the plastic films/coatings industry, pretty much everything in terms of thickness was measured in microns, or fractions thereof. Only roll lengths and widths did not - m and mm respectively.

Horses for courses. As I said, a vanishingly small percentage of people in the UK have the first clue what the Kelvin scale or 1K is.

The unit(s) is/are Kelvin, there is no plural - 1 Kelvin, 50 Kelvin. The Kelvin scale also adopted the convention that both K and C scales used the same scale, in that a 1K interval was a 1C interval, so the K scale "stole" the interval size/scale from C.

Quote from: David Pilling on December 23, 2023, 04:50:52 AM5-bob on them dropping the blokes' names from units and just going with letters at some point?

Most people that I have worked with have used K rather than Kelvin - the CCT is 2700K is said as twenty-seven hundred kay.
Who uses anything but C and F? Very, very seldom does anyone hear centigrade (or celcius) or fahrenheit.

David Pilling

It is true that people say K and not Kelvin. But do they say H or Hertz. N or Newton.

Commonly people talk of kilo Watt hours 'units' not Joules. Would be interesting to put food (Calories (a metric but non-SI unit)) in the same units as battery capacities (Amp hours (x Volts)) and that unit would be the Joule.

Could link all this with plants, the common names or the long since botanical names stick around after the professionals have set the world to rights and moved on.

Lets hear it for the BTU (British Thermal Unit, 'therm'), the horsepower hour and gasoline gallon equivalent.


The calorie that everyone talks of is actually the kcal.

As for kWhr - it produces a "reasonable number" for most uses. Who wants to be routinely talking about energy use in units of 10^6 joules?

It happens all over the place - pick something that produces convenient numbers to remember, what anyone calls it is irrelevant for 99% of the time.

Another hobby of mine is hifi. Tonearms (on record-players) have what is known as effective mass and this varies in the region 5-30 grammes (roughly speaking).
It isn't a mass, so the units are not g, and the convention is to ignore the decimal place.
It is actually inertia, so the units are mass multiplied by distance squared. The real position of the decimal point is ignored to get that simple figure of a one or two digit number around 10-20. Everyone does it, very, very few people know what it really means, but the system works. (The inertia (effective mass) of the tonearm interplays with the compliance of the cartridge suspension, so is important).

The symbol for hertz is Hz  :)


The WWI Christmas Truce in 1914

"The Christmas truce was a series of widespread unofficial ceasefires along the Western Front of the First World War around Christmas 1914. The truce occurred five months after hostilities had begun. Soldiers along the western front broke into spontaneous truces of Christmas celebration, song and even exchange of gifts. For a brief moment they wondered why they were juxtaposed in lethal combat along the jaws of hell." Sadly, the war would continue for almost 4 more years.

"British Field Artillery Lieutenant John Wedderburn-Maxwell described the event as "probably the most extraordinary event of the whole war – a soldier's truce without any higher sanction by officers and generals....""

"numerous accounts in letters and journals attest to the fact that on Christmas 1914, German and English soldiers played soccer on the frozen turf of No Man's Land."

A detailed account of this event by Will Grigg is detailed here.


I'm hoping for a Christmas truce this 2023 and that it will extend well into the coming years.  It can be done.

Merry Christmas to All!

David Pilling

They were more sporting at the start of WW1. My great uncle Jack was captain of a merchant ship off South America, in 1914 it was sunk by SMS Leipzig, but first he and the crew were taken off and eventually deposited on land, uncle Jack receiving a gift from the captain of the German cruiser.

For his part, he did not rejoin the war, having been freed, but set up the local nautical college.

Quote from: Bern on December 23, 2023, 01:41:37 PMMerry Christmas to All!

'God bless us, everyone' said Tiny Tim.


New Year's Eve Party at the Brandenburg Gate

Great photo of an iconic location. 


Let's hope for a good year in 2024.

Happy New Year to All!