Pseudo Glasshouse... advice appreciated

[OzPhal]

Hi everybody,

I live in Southern Australia and grow Phalaenopsis spp. All of my plants at this stage are seedlings with leaf spans of around 100mm. I also have one deflasked P. lobbii. I plan on growing more flasks up in the future along with seedlings so I'm wanting to build a small 'mini' glasshouse. I'm planning on building a table - around 2m X 1m which will have heat cable installed under a bed of propagating sand and then covered in coarse gravel. The Phals will sit on the gravel. The sides and roof i'm planning on covering in with twinwall polycarbonate and then i'm going to incorporate some style of door at the front (maybe something that is hinged at the top and i can simply lift up). Internally i'm going to have temperature control, an air circulation system, and also install a small scale fogging system to control the humidity/temperature, I also want to set-up some sort of system so that if the temperature gets too high then vents in the top and at the bottom edges will open to allow some fresh air to flow through. My goal will be about 28oC and 80% RH and then i'll need to take in to consideration the intricacies of some Phal species... I may install lighting down the track if it's necessary. This unit will sit outside so obviously everything will need to be waterproof etc. I might consider moving it inside if I find that the costs associated with keeping it warm are too high. I'm wondering if anybody has any advice on:

1) Grade of twinwall polycarbonate to use
2) Suggestions for thermostats/humidity controllers
3) DIY high pressure fogging systems (1,000PSI units)
4) Suggested heating cable to use
5) Any pitfalls i may come across

Thanks for your time...

[DavidCampen]

What are your outside environmental conditions - high, low temperatues and humidity?

For fog/humidification you will have difficulty finding a high pressure pump that will operate at the low volumes you will need. For your size setup I would suggest using ultrasonic fog units - they produce finer fog particles than the high pressure units. If I could get a reasonable sized ultrasonic fogger that had the capacity I need I would use it instead of the high presuure rig that I have.

For polycarbonate I would suggest somewhere between 8 mm double wall to 16 mm triple wall.

I suggest that you incorportae some thermally actuated vent openers so that your plants won't cook if you are not there to open the vents.

[OzPhal]

In regard our climatic conditions:

Average maximum summer temp is 26oC (78oF) (although we get spikes up to 40oC or 104oF)
Average minimum temperature is 6oC (42.8oF) although we do get as low as 0oC (32oF)

Average maximum humidity is 80%
Average minimum humidity is 50%

Do ultrasonic fog units produce sufficient volume of fog for something that large? I've only ever seen the ones that are used for water features etc that normally have coloured leds with them and they produce a small amount of fog.

I was thinking of the 8mm double wall for the outer skin also, are there any small vent openers? I know there are larger ones for large setups - where could i get these?

Thanks for your advice

Cheers

Originally Posted by DavidCampen

What are your outside environmental conditions - high, low temperatues and humidity?

For fog/humidification you will have difficulty finding a high pressure pump that will operate at the low volumes you will need. For your size setup I would suggest using ultrasonic fog units - they produce finer fog particles than the high pressure units. If I could get a reasonable sized ultrasonic fogger that had the capacity I need I would use it instead of the high presuure rig that I have.

For polycarbonate I would suggest somewhere between 8 mm double wall to 16 mm triple wall.

I suggest that you incorportae some thermally actuated vent openers so that your plants won't cook if you are not there to open the vents.

[Discus]

I use(d) an ultrasonic humidifier for a balcony area considerably larger than your proposed growing area; sadly they seem to die after about 6 months, and are quite expensive (over US$100 each). The ones I had have integrated humidistats, which is quite handy, but they only went as high as 75%, which is probably enough. There was also an option to run continuously regardless of humidity.

With regards to controlling your microclimate, one of those herpetological control units would probably work quite well. I would be tempted to use it to automate fans when hot and heater when cold; you can also use them to automate various humidification devices. I have no experience with these units, but they look quite nifty:
Digital Aquatics

I made my own "controller" out of industrial electromechanical doohickeys - a humidistat and a thermostat, along with a light sensor, relay (to "reverse" the light sensor, which turns on in the dark, which is the opposite of what I wanted for seasonal light signals) and a timer. Most of it was DIN rail mountable which was quite handy, and things that weren't were easily cable tied on there. It's a bit rough and ready, but it doesn't rain inside my house; I would ideally house it inside a plastic box with a small "muffin fan" continuously ventilating the enclosure. (There is already one blowing past the sensors). RS Components sell pretty much anything you might need for this. RS Australia | World Leading Distributor of Electronics, Electromechanical and Industrial Components

With regards to ventilation/cooling, not only would I use forced air ventilation (perhaps having the inlet as a DIY or otherwise "wet wall), I would be sorely tempted to put in "just in case" greenhouse auto-openers on a panel.

You'll probably want some kind of shadecloth too, which ought to be mounted some distance above the polycarbonate.

Don't forget a few additional fans for turbulent flow inside the structure.