Topic: Blowaway / Tunnel in Greenhouse

[kGarden]

In the past I have put a tunnel, or a blowaway, in the greenhouse for an enclosure to look after seedlings in early Spring in order that I am only heating a small volume.  Chatter on various forums suggested that some folk don't bother with any heat assuming that the blowaway would provide enough additional protection, so I stuck my 4-shelf jobbie in the greenhouse:



and some logging thermometers: one on the top shelf, another on a plant in a pot stood on the greenhouse border (plastic bag / upturned pot at bottom left of the blowaway), and the last one on a brick outside the North/shaded end of the greenhouse for an external temperature.

The Blowaway was colder, over night, than the greenhouse!! ... presumably because the thermometer in the greenhouse was at border-soil level and that was generating / releasing some heat compared to 3' higher up on the blowaway shelf, but at best the blowaway offered no additional insulation at all.

The blowaway would be easy / cheaper to heat of course.  A Tea-light might be enough, for example.


(Click for larger image)

There is an article on my Blog with more indepth details
https://kgarden.wordpress.com/2015/03/01/using-a-tunnel-blowaway-in-a-greenhouse-for-seedling-protection/

[caroline7758]

What is a blowaway, please?

[kGarden]

Plastic "greenhouse" that is flimsy and inclined to "blow away". like the 4-shelf one in my picture above, or a tunnel that just has a loose cover and isn't dug into the ground to anchor it down.

[galina]

I am really surprised that the minimum temperatures are so similar.  That the internal greenhouse doesn't stay warmer. 

No doubt it will be easier to heat, but not without heatsource it appears.

Have you ever experimented with 'brown water' or with any water storage.  For example diluted 'brown' fertiliser in milk bottles which heat up during the day and give off heat more slowly during the night.  Should keep heat a bit longer, especially if you can have several gallons of stored water.  Brown because it heats up more than clear water.  And you can use the bottles later when plants need fertilising. 

[kGarden]

I am really surprised that the minimum temperatures are so similar.  That the internal greenhouse doesn't stay warmer.

Doesn't surprise me as I can't see the polythene cover providing any insulation quality at all ... its thin and not the sort of type / quality used for polytunnels.

I'd like to try putting some sort of Thermal Mass in there to see if I can store day-heat to release at night.  I don't suppose it needs much, its a tiny volume, and if it gets reasonable hot during the day (assuming any seedlings in there were not allowed to fry!!) the thermal mass would be able to gain some decent heat.

I'll chuck something in there tomorrow and leave it a week if I have time ... and I'll move the Greenhouse thermometer to be at the same height, rather than cheating by having it on the ground!

[Duke Ellington]

I use the same plastic greenhouse inside my glass greenhouse but on one of the shelves I have one or two of those electric propagators switched on. One propagator probably has the same effect as your tea light.

[Jayb]

Interesting to see the results you recorded. I have to admit, I was under the impression a glass greenhouse at best offered an increase of a couple of degrees in overnight temperatures. I think the use of a 'blowaway' for an indoor heated area sounds good and as noted it can be quite economical. Not in the same league as you recordings, but in previous winters I've noticed the difference in temperature on my greenhouse benches to the border, usually by several degrees.

[kGarden]

in previous winters I've noticed the difference in temperature on my greenhouse benches to the border, usually by several degrees.

Colder on the bench, than the border, or did you get a different result?

I am never sure how much "heat" is coming up from Mother Earth.  Folk talk of covering tender plants with, say, a duvet to trap rising heat (and let the snow / frost sit on top of the duvet), but I've never been sure it was "enough".

I would have expected heat-to-rise and cold-to-fall in the greenhouse, so would have thought that the border would be colder than the bench, on that basis.

I'll stick the logging thermometers are different heights in the greenhouse and see how they perform.

[Tee Gee]

I'm curious Kg what is all the greenery around the mini greenhouse?

The bloke on the next plot to me does similar to you!

He erects a flat pack plastic greenhouse in his tunnel then fetches his stuff on in that.

I am not sure if he heats it but I do know he has a 12" square voltaic solar panel on his shed roof which he uses for his automatic watering system in the summer months, perhaps he uses this power to heat his mini greenhouse in the winter!

I think the best indoor set up I ever saw was when I grew Dahlias big time and it was an old pool table a friend got from a pub!

What he did was; he put the pool table in his cellar which stays at around 50° F (10°C) summer and winter then he fitted a soil cable on the table top  and growlights into the light canopy above the table, this was on a timer and brought all his stuff on in this way.

Amazing what you can do with a bit of imagination and recycled materials.

Another I saw was a lead lamp fitted with a 100 watt bulb.

The lamp cable was threaded through the bottom of a tin can ( bean can if you like) then the lamp holder and bulb  was fitted in the bottom of the tin.

This was then placed under a slatted shelf and the heat from the bulb warmed up the tin and radiated the heat upwards.

The tin also acted as a shield from dripping water/condensation.

As I said great what you can do with a little imagination, then of course there is the tea light method as already mentioned!

[kGarden]

I'm curious Kg what is all the greenery around the mini greenhouse?

Box cuttings (growing on); don't really want them getting ringing wet in the winter because of Box blight ... delusions of grandeur that I will be able to plant a parterre like Versailles :D :D :D

This was then placed under a slatted shelf and the heat from the bulb warmed up the tin and radiated the heat upwards.

I used to do that with my 4-shelf blowaway, stood in my conservatory. I had an incandescent bulb in a biscuit tin as the "radiator". Don't suppose its possible to buy an incandescent bulb any more ... technology has overtaken me though and my socking great big 400W Metal Halide growing lamp chucks out enough waste heat to be global-warming all on its own! Scandalous really ...