The good old ventilation issue

[Yéri]

Hello everyone,

I'm not that active on the forums, but I pay a visit once in a while

I'm moving through the last stages of building my "greenhouse", but I can't help but notice (and especially now that winter is at our doorsteps) a certain...unhealthy feeling to the atmosphere inside my greenhouse.

I started off with a tower fan (see end of post) and opening up my door every day for fresh air. This helped avoiding fungi, but always caused a drier period during the day. Combined with a central heating and young plants, this wasn't the ideal solution.

So I added 2 ventilation grills:
One on top at the end


And one below on the other end of the greenhouse


And in order to take advantage of that aeration, I decided to replace my tower fan with 2 smaller fans


Check out the specs if you like.

I installed on at the ventilation grill below, and one on the other end of the greenhouse, but opposite to the ventilation grill there


This in order to have a good airflow rotating through the whole greenhouse.
Here's a panorama of the greenhouse, with my old bigger fan on the red arrow and the locations of the new smaller fans on the yellow arrows (I hope it's not too confusing). The greenhouse itself is roughly 4m x 3m x 2m


Now that I've given you an idea of my setup, let's move onto the issue itself...
I can't shake the feeling that those small fans aren't going to cut it. They do cause some air movement, but it doesn't seem much to me.

On the other hand, my big fan seemed to cause to blow too hard, and as it was in a central position and on the floor, I think I was creating pools of stagnant air.

So here I am, asking for your opinion!
Now that you've seen the airflow the small fans cause (in the specs), do you think this would be sufficient for my setup?
Or would there be another kind of fans I could use, more appropriate to my needs? (I'll add that I can't install a ceiling fan, I'm not the proprietor of the house and I'm not allowed to make holes in order to hang it)

I know it's all a bit vague! I've been reading several articles and guides on how to have correct ventilation inside a greenhouse, but I'm still doubting myself.

As always, advice from firsthand orchid growers is so much more valuable than general guides.

Best regards and happy holidays

Yéri~

[spetrizio]

i can try to help but few things are not clear to me.
do you measure humidity in GH or it is just feeling that the air is not ok?
what are the target temp/RH for day and for night?

what is on the top of GH? glass roof?
do you have possibility to throw outside air into GH or only from the room( I suppose it is some kind of room in front of GH)?

current small fans are too small I think. If i understood correctly one of them is used as exhaust fun and one of them as circulation fan.
as circulation fan I would suggest fan which is able to swing left/right. usually you can buy it at some megastore.
regarding exhaust fan sizing you have to think also about summer time. How big influence of hot sunny day you expect to inside temp? it could be big influence if the roof is transparent even in winter if you have direct sun.

I would prefer stronger ventilation in combination with some humidifier to keep RH in the desired boundaries. you can connect fans through timer or thermostat (or both) to avoid running vents all the day.

[Yéri]

Hi Spetrizio,

Thank you for the reply, I will answer your questions as best as I can.

do you have possibility to throw outside air into GH or only from the room

I realise now you don't actually see it, but in the first picture, you can basically imagine a double glass door to the outside on the left.

do you measure humidity in GH or it is just feeling that the air is not ok?

I have a Hydrofogger coupled to a humidifier, so I can keep the humidity to a certain level. I try to go for 70% during the summer and 60% in the winter, although I'm not too sure whether I should reduce humidity during winter.

what are the target temp/RH for day and for night?

It's my first greenhouse so temperature control is a bit new to me, but this winter I try to keep it around 21-23°C daytime and 16-18°C during the night.

If i understood correctly one of them is used as exhaust fun and one of them as circulation fan.

As for the fans, they are both inside the greenhouse so no exhaust fan.
Let's say I just made 2 holes at both ends of the greenhouse in order to have fresh air enter on its own, but no exhaust fans. (should I have one?)

The tower fan has a swing function, but I have the feeling it was blowing too hard on the plants so I just kept it on stationary.

Temperatures can go up quite a bit as this is actually a part of the sunporch. The roof is made out of polycarbonate.

I hope I have shed some light on the situation

[spetrizio]

I think exhaust fan (or intake or both) is must have.
I have both and sizing is 1 complete air change in minute. my GH is full sun exposed so maybe it is oversized to you, but your small fun with 30cfm would change complete air in cca 30 minutes so I think you need something stronger especially for summer.

if you feel that tower fan is too strong try something smaller, but that small fan looks for me more usefull for terrarium not for GH.
with one or two smaller swinging fans you can cover all spots and it will not blow allways into one fixed point.

[DavidCampen]

You want fans with large blades turning relatively slowly so that you create a large volume of slow moving air rather than a small volume of rapidly moving air.

[Rasheeka]

A couple of small fans on opposite sides of the room, blowing in opposite directions, parallel to the walls will create a circular air flow. I had a 15'x15' room in my basement for years and this worked well. Only opened the door a bit after watering to let some excess humidity out.

[AliWay]

Ventilation is perhaps one of the most important component in a successful greenhouse. You should install a mechanical ventilation in your greenhouse as it can be automated to keep a greenhouse’s environmental conditions consistent regardless of the conditions outdoors. I don't have any greenhouse but we had ventilation system installed in our home called to keep the environment fresh and humidity free. The air is much lighter (due to reduced humidity) and definitely fresher all round.