Greenhouse Temperatures 100 deg!

Mine hit 99.5f, and that's WITH shading. I use a generic 'greenhouse shading' that I got from a local G/C. I've left it in place since putting it up last year. However, quite a lot of plants grown from seed went quite 'leggy'. I'm now thinking I'll have to take it down, especially for the early part of the season. What MIGHT be better would be to use blinds, are these available ?
Cheers...freddy.

 

"What MIGHT be better would be to use blinds, are these available ?"

Yes, tend to be expensive though ... and they need to be on the outside, so subject to wind effect

Look smart :thumb:

but if smart is not important then something like scaffolder's debris netting will do - and its pretty durable, so should last several seasons.

http://www.groblinds.com/


Prices range from £59 for a 2' wide blind to £99 for a 6' width

 

Hi Kristen. Maybe I didn't make it clear. I already have netting, but the problem is it's semi-permanent as it's fixed to the outside using drawing pins, therefore a bit of a pain to keep putting it up/taking it down. Oh yes, those prices ! Better get my thinking cap on, methinks.
Cheers...freddy.

 

I`m of the same opinion, the more vertical distance you can get between bottom and top vents, the more air will flow for a given in/out temperature difference. You are a lucky one, not much height in most greenhouses :wink:
I have 30 sqft of base vents (excl the door) and 8sqft of top vent with about 9ft of height difference. I can supplement the natural ventilation with upto 45 airchanges/hour through 30 tons of cool clay soil.
Shading and misting are effective for controlling heat, its best to have lots of options available :wink:

 

"30 sqft of base vents"

I am curious as to what type they are? Seems like a decent area to me :thumb:

"excl the door"

The trouble with opening the door is that it is a top-to-bottom opening, so doesn't encourage the convection-type ventilation. Air rushes in, straight out the vents, and that doesn't cause any heat-loss at the far end of the house - well, that's what I reckon anyway!

 

Hi Kristen
They are pretty much just rectangular holes at the minute, (in the attached pic they`re at the bottom :wink rest assured they will become almost 360 degree of base vents :wink:
The top vent frame is in the 2nd pic and fits to the top dead center of the dome (9.5ft off the ground) so the air just hasn`t anywhere else it can go except up and out. To give some scale the outside length of the seat its resting against is 4.5ft long, i think the vent area may be 12 sqft rather than 8sqft..its been a while since i worked it all out.

 

What a fabby greenhouse! NOW I see how you can get so much bottom ventilation. :thumb:

Shouldn't you be called "Pent", rather than "Hex"?!! - or am I mixing my Latin with my Greek?

 

They had a greenhouse that shape in "Its Not Easy to be Green" with Dick Strawbridge

P.S. Apparently a geodesic dome from http://www.grow-dome.co.uk/

 

You can`t rush out and buy one like this, John. Its not operational as its constantly evolving, it will use a flooded floor type system with 5 seperate 600L beds plus a vertical growing system to make use of the nice height.
This one is a copy except in size obviously to the Eden dome, it uses almost the same geometry.. note the big holes for the pillows. The strawbridge dome is a standard timber panel dome,its design weaknesses are that it uses silicon sealer between the polythene to make it weathertight and you have to disassemble the whole thing to replace the covering. This one uses marine grade aluminium to clamp the triple glazed pillows in place and each one can be replaced seperately.
Its like comparing a jalopy to the farrari.. silly price tag on those Kristen ..£2500? not a hope :wink:

Another unique feature of the greenhouse is it has a subsoil heat exchange system in place. It was a lot of hard work but should pay benefits in the long run. This beast is buried 4ft below the greenhouse floor.

 

"silly price tag on those Kristen ..£2500? not a hope"

Indeed, and I've never seen one one eBay - tuppence-halfpenny, or otherwise

"What's a flooded floor system?"

I think you put an old, dodgy, washing machine in the corner :hehe:

Hydroponics me-thinks.

"sub-soil heat exchanger"

I'm presuming it takes heat out of the soil? My 2p worth is that would be better at a distance away from the greenhouse itself? (to not reduce soil temperature near the things growing in the greenhouse itself)

 

i would have to make a pentagonal picnic table then..not keen :wink:

 

They have advertised several on ebay, materials wise they cost about £500 so £2500 is a good markup.
My greenhouse holds about 900ft3 of air which will heat up very rapidly when the sun shines, the greenhouse shelters the soil mass which also uses 2ft deep perimeter insulation. When a greenhouse heats up the usual method is to open all the vents to exchange it with cooler outside air..maybe even on a sunny winter day too :wink:
The air is circulated underground by a duct fan so the entire air volume can be passed through the ground loops upto 45 times per hour. The plenum (the wooden cylinder) design allows for a variable percentage (0-100%) of the air to be constantly recirculated underground without returning to the greenhouse.It uses the venturi principle.
The fan is controlled by a differential thermostat which senses and compares the soil temp with the air temp, and it fires up the fan if theres enough of a differential.
Venting a greenhouse on a day like today means you have 80F outside air with 100F greenhouse air to cool..the best you`ll do is 80F if you have a very powerful fan.
With the heat exchanger the air leaves the plenum at pretty much soil temperature 55F-60F, it`ll do the same thing in winter when the air temps are 32F :wink:

 

HOW COOL IS THAT !!!!!!!!!!!

I definitely can't afford not to have one of those .... <gets birthday list out!>

I saw some Grand Designs programme, or somesuch, and the owner had installed a MHRV**. However, he had also installed a large (10" maybe? perhaps it was just 4" drainage pipe) the 50 or more yards alongside his driveway to his entrance, and then up the pillar for the air intake. He used that as the air inlet for the MHRV system, so in Winter it pre-heated to sub-soil temperature, and in Summer cooled.

** Mechanical Heat Recovery Ventilation system. Air from the house is pumped out through a heat exchanger, with fresh external air coming the other way. The heat exchanger transfers "most" of the temperature to the incoming air, so that heat is not lost (and when the house is cooler than outside the reverse in Summer)

I wonder how quick the heat transmission is through the soil - how much does the temperature vary from 55F-60F - i.e. how quickly does the heat/cold radiate away from the underground pipe? Moist soil helps, I presume?