Manufacture of a greenhouse tunnel market gardening

[Rabbit]

Superb greenhouse!

I could almost envy you, if I didn't have one.


What is the diameter of the tubes?
What are the dimensions of the greenhouse?

[dedeleco]

Suggestion:
The cylinder wears out, probably, because it loses its gas, and therefore it is enough to replace it to reactivate it.

An easy volatile gas like acetone or even with a lower point of liquid passage, vapor, around 20 ° C, should work.

Even butane or propane under adequate pressure, low to very cold, should work, since the pressure increases very quickly with T.

You have to see the force of the cylinder and its diameter, which fixes its pressure and the nature of the liquid gas. (P (T)).

Total error, it is a solid liquid wax, "wax":
http://www.baylissautovents.co.uk/shopc ... nformation

and wikipedia:
http://en.wikipedia.org/wiki/Wax_thermostatic_element


It should suffice to replace it cold with the right quantity, if it degrades.

The Autovents are operated by the expansion of a mineral wax. The high rates of expansion are concentrated over the phase change solid-liquid. The piston works directly in contact with the wax and the lowest temperature we have so far been able to utilize is about 55 ° Fahrenheit. Other waxes and blends of wax can be used to give higher opening temperatures.

The viscosity of the wax causes a hysteresis giving a temperature difference of 5 ° Fahrenheit to 10 ° Fahrenheit, opening to closing, although this may be possibly reduced by careful blending of the wax.

Response time is somewhat governed by the load on the piston. The energy to move the load is collected from the surroundings and is governed by the surface area of ​​the tube in which the wax is contained. For the smaller units we use a plain aluminum tube but for the larger we use a tube which is finned on both the outside and the inside bore. Wax is a poor conductor of heat.

and a supplier of this "wax":
http://www.paramelt.com/files/Pdf/dilav ... 012_03.pdf

and precise measurements:
http://www.sasolwax.com/sasolwaxmedia/B ... fin_en.pdf

[bleusideral]

well Delaco; good study of the system!
Without going into the gas too much, I would simply like to experiment with air in a canister to supply a cylinder, knowing the expansion of the hot air, I think it should work with a reserve of hot air supplying a cylinder ... in a well sealed system of course!

[dedeleco]

The air will not work, because small diameter which requires a big pressure tens of Bars (measure the necessary force and the diameter of the piston of the jack is essential) and the variation of P with T is not brutal enough, because as RT / V linear in T roughly.

You might as well take liquid paraffin that solidifies around 20 ° C or very heavy fuel oil, which changes by 10% in volume when liquefied.

[manitou22]

Bonsoir
It is also possible to adapt a system like this: http://www.ebay.de/itm/Feuerungsregler-Feuerzugregler-Holzkessel-3-4-/280598619032?pt=Systemkomponenten_Heizung&hash=item4154fb2398, it's not too expensive and it can be set, disconnected easily.
A+

[dedeleco]

This has existed for at least 80 years and is very classic, on wood boilers, without any electricity and is much easier with a much greater range of T between 60 and 100 ° C.
But not between 18 and 25 ° C, much more difficult.

[bleusideral]

Hello

for the cylinder I think a range of T ° 30 to 60, did not go to check, acetone would therefore be more appropriate!

Rabbit: it is a classic market garden greenhouse, the galvanized tubes of approx. 60, spacing of the arches of 2m, I have 5 complete arches (they are in two parts) therefore 10m long, and 6 m wide (originally they were 8 m, but lack of space and reconciled with the means available between two trees and reduced to 6, this is why they are not very regular and that to catch up I placed Teflon spacers to "equalize" the tension wires and not have a warped cover!)

estimate for a similar greenhouse in new between 1500 and 2000 €
mine: tarpaulin half bought new: 90 € (75m²), the other I got it free
hoops and tubing and hardware: I had one for a 14m greenhouse, I have one left for a shelter for my motorhome! : 250 €

the door: recovery in carpentry, aluminum and tempered glass
front facade with the door: corrugated "sheets" in anti-UV fiberglass at a large brico store: 60 €
total 400 €!
for an objective that pays for itself in one year: plants and vegetable growing, fruit growing for fewer plants: more spread out production, less treatment, more productivity, micro-drip irrigation and mulching in winter
+ 50 years of ornamental plants and hedges

voili voilou

[dedeleco]

for the cylinder I think a range of T ° 30 to 60, did not go to check, acetone would therefore be more appropriate!

above 30, at 40 ° C, the plants burn and die, like us, in 2003 with the heat wave !! With our old men who checked them, with the dead !!!

So maximum opening around 30 ° C required.

How much force is needed? several kilos ???
What is the diameter of the piston, less than 1cm to see the photos ???

Acetone 1 bar at 56 ° C, too high for 1 Kilo per cm2 of piston, and at 20 ° C at, 228Bars !! The variation is not huge and rapid.
http://fr.wikipedia.org/wiki/Ac%C3%A9tone

You need a liquid at a lower point:
ether?
T at 1bar 35 ° C closer, but at 20 ° C pressure 0,56 Bars quite high.
http://fr.wikipedia.org/wiki/%C3%89ther ... A9thylique

if the diameter of the piston is sufficient to have the necessary force, to be measured, it can work with a precise threshold of opening.

Ether explodes easily with air (usual chemical accidents).

Liquid paraffin, at T melting around 25 ° C seems to me much more powerful for a small diameter.

[Alain G]

above 30, at 40 ° C, the plants burn and die, like us, in 2003 with the heat wave !! With our old men who checked them, with the dead !!!

So maximum opening around 30 ° C required.

Poor Dede!

You obviously don't have a greenhouse to conclude that plants die at this temperature!


I have spikes of 65C at the top of my greenhouse or the tomato plants remain very healthy even at this height!

[dedeleco]

I have spikes of 65C at the top of my greenhouse

not long, like we do in a sauna, sweating, compensating by full of evaporating water which cools, and if too long without enough water on the ground which arrives, the tomato dies desiccated and overheated !!!

The tomato is warm country with water.