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Today 15°C / 11°C
Tomorrow 15°C / 13°C
7 messages
03/04/2013 at 00:41

It's been quite cold recently barely managing to keep above freezing but yesterday the sun came out and it hit 50 degrees C in my Greenhouse at some point. 

Thats not good either is it. It's a plastic greenhouse around 8 foot by 16 foot by around 6 ft 6 so while it has vents there is no way to automate the opening and closing.

I read somewhere about using milk cartons painted black to store a little heat, I did it with the black inside of a compost bag sellotaped to milk cartons and they do end up full of warm water   

Theres also a suggestion of having a water barrel in the greenhouse to help absorb some of the daytime heat. 

I do have a domestic thermostat which can easily be wired into a battery operated fan. this has a common and 2 outputs normally open and normally closed so can be used as a heat / cool activated switch. it'd also be relatively simple to hook up a solar powered battery charger (not a huge output but it was good enough for a radio when i was fishing).

what temperature range should I be aiming for in my greenhouse ? I don't think my seedlings will appreciate going from 3 to 50 degrees C in a day.

 

03/04/2013 at 00:50

Hi blackest, I use a 12V, 20W solar panel to power four 12V 120mm computer type fans, two blowing cool air in at the bottom of one end of the greenhouse and two extracting hot air at the top of the other end.  This works great as the fans only blow when the sun is shining (no thermostat needed), and it keeps a nice gentle breeze of fresh air flowing through the greenhouse, which I'm sure helps prevent fungal diseases.  You can easily get all the bits from ebay.

04/04/2013 at 14:53

I think you may need a new thermometer. I can't imagine any UK greenhouse getting to those sorts of temperatures in the current weather. 50F I could believe but not 50C. That temperature would fry humans never mind plants!

 

Good tip on the solar fans. I have a few old PC fans lying around and had been thinking of doing this. I have automatic vents but some additional ventilation during bright Winter weather would also be welcome to keep the greenhouse fresh. What bits do you need? Can you just connect the panel output to the fans?

04/04/2013 at 15:23

http://s4.gardenersworld.com/uploads/images/original/20961.jpg?width=307&height=350&mode=max

This is sat on the bench. Over reading maybe it is in direct sun

http://s4.gardenersworld.com/uploads/images/original/20962.jpg?width=660&height=350&mode=max

 Think you should be able to see the red reaching to 38 degrees 

outside temperature is about 14 degrees C

Took these pictures at 3:02pm but i'm not in the UK , southern Ireland 

 

04/04/2013 at 16:57

Thermometers should be shaded, not exposed to direct sun.

04/04/2013 at 18:50

Will move it and see how it goes tomorrow it's going to be interesting to see if my bags of composting grass succeed in keeping the greenhouse a bit warmer overnight.

The theory is sound enough, I think the great MD said the victorians used green manure in the cold frames to keep up the temperatures in the cold frames.  Having sheep at the back and Cows to the left if the grass doesn't work there is no shortage of alternatives. Prefer the smell of grass thou.

04/04/2013 at 19:25
steephill wrote (see)

Good tip on the solar fans. I have a few old PC fans lying around and had been thinking of doing this. I have automatic vents but some additional ventilation during bright Winter weather would also be welcome to keep the greenhouse fresh. What bits do you need? Can you just connect the panel output to the fans?

Most panels come with a good long length of cable, so not much else is needed.  The fans are connected straight to the panel, but I did put a switch in line so they can be turned off if need be.

The hardest bit is finding somewhere to mount the fans.  I replaced the manual louvre at the bottom of one end with a  sheet of 4mm plywood, cut some fan-sized holes in it and just screwed the fans on the inside with woodscrews.  The fans extracting at the top of the other end are in a similar bit of ply which replaced the triangular piece of glass above the door.  It has all been going for a few years now.  I did have to replace one of the fans last year as it failed, but I too always seem to have old PCs available!

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