GreenHouse Condensation

Question for those that have built their own Greenhouses.
Water condensation,
drops falling on your head, sort of like rain when wall and roof get below dew point.
Is there a roof angle that you should stay above to where drops would run down the roof instead of falling like rain.

I heard Gothic was the best!!!

It is said that 6:12 pitch or greater will work. Also, there are anti-condensate greenhouse films as well as sprays. SB

Let me restate my question
I feel I was not clear
I would like the roof angled so that condensation would reliably run down the glazing to a gutter system.

It seems to me, that as the roof angle gets lower a higher percentage of the condensation will fall as drops. At some angle the drops start falling instead of running down.
I'm in southern Indiana and temp 12 - 25 at nights with some nights of course colder. so the glazing could be cold
This is something I can't test very well with out building one

Not familiar with the mist systems as to how they would keep condensation down.

I was thanking that you have humidity and the surface of the glazing was below dew point you would have condensation
I don't know if condensation is a real problem or not.
what has been your experiences.

Hi Larry,

Condensation is a problem for every greenhouse in use in the winter. As you may know, generally speaking there are two ways to handle condensation. First, reduce the amount of condensation, and second, control the drips. You are really asking about the second method.

You are right, increasing the pitch will make the water droplets run off better. The anticondensate polyethylene films are really misnamed...they don't reduce the amount of condensation, but they reduce water surface tension and reduce dripping in this way. The sprays I mentioned above work the same way, I believe.

The vertical and horizontal framing supports are as important as the glazing or the pitch. A steeper pitch won't do much good if the droplets are just going to fall off of the framing members instead of straight off of the glazing itself. My GH is built with channels in the horizontal came which move the water off to the vertical members (I beams) and down to the sidewall. There are greenhouses with "internal gutters." All of this is designed direct the movement of the condensate rather than letting it sit on the glazing until it falls on the plants.

I recall only one reference which gave a pitch, and that was 6:12 or greater. I have 6:12 (by coincidence only) and I have virtually no drips.

Reducing the amount of condensation is a different discussion!

I hope that this answers your question. SB

can you run a dehumidafier? what would be the formula for how big of a unit you would need to supprt your particuler gh? mines an 8x16 rion on a 2ft sub wall and with our humidity levels im concerned on how to handle the problem...

Thopicman, Yes, I believe gothic is best for it gives more head room compared to, say, an aframe.

Bulbhound, Yes a dehumidifier will reduce the humidity. But, during winter time even inside the house you’re living in, it will have very low humidity (so low its not healthy) with single panes of glass you get condensation. It seems to me the only choice is to control the run off.

Stressbaby, Fulton, MO should be about the same in the winter as I am here in Indiana.
Question1, 6:12, I read that as a 6 inch rise in 12 inches. Would that not be a 45 deg angle.
Question2, is your gh a commercially designed unit, very few that build from scratch use channels and gutters. I was thinking of rafters with polycarbonate glazing. One piece length for the roof giving a clear span, down to the walls with a collection gutter where the roof meets the wall.
I’m not sure how bad a problem condensation is, But here I set planning and the question pops into my mind. I need to minimize the problem with design instead of trying to fix it later. Reducing water surface tension could make a marginal design work.
I wonder how they clean those internal gutters I would sure hate to get mold in them.(grin)
Thanks, I will not go lower than 6:12

Larry, a 45 degree angle would be 12:12; 12 inches rise for every 12 inches of run.

My GH is a hobby GH kit out of aluminum.

I would say that if you stay at 6:12 or steeper and if you have a clear span of polycarb, without any crossing pieces, you probably will be ok... it would be nice if an owner/builder in our climate chimed in here!

Bulbhound, the traditional ways of minimizing the amount of condensation are 1) circulating the air better and 2) venting in a small amount of outside air (usually in the evening) and then reheating to reduce the RH.

Stressbaby, Dang wrong again, now that you point it out, it's obvious.
I keep trying to think of a way to test roofs.
Looks like the best thing is to just design a steep roof
Thank you for your comments.

Howdy folks...
Condensation will often depend on what the moisture is condensing on.

If you have a single barrier (i.e. glass, poly, whatever) and it is much much warmer in the g-house than outside you will see some build-up. However, if you have double-ply (poly double-walled/fan inflated; honey-combed poly, etc) you will see either NO condensation or very little. The angle of the roof will not come into play.

Larry...can you give us more info as to what kind of g-house covering you are considering using? That would help us to give you a more definitive answer.

Shoe.

Horseshoe
planning for polycarbonate glazing (double wall)
I have no feel for this.
I plan for extending growing season so it would
be heated as needed.
around here winter temps most of the time
fall around +10 to +20 with top +35 to +40
however, we do get the -20 ever 30 to 40 years
As you plan, you think, what happens when the temp
is low, say, -5
got to wondering about condensation and how much of a problem it is.
any comments?
thanks

I don't believe you'll run into into bigtime problems with condensation if you keep in mind just a couple things. Your double-glazing will certainly help restrict condensation, so that's a big plus! The amount of heat inside the g-house vs the cold temperature outside plays a big role...condensation, of course, will form where there is the two temp differences.

Lack of air-movement inside the g-house combined with excessive watering of the plants will also be a big factor. I keep a small fan running all the time in my g-house; this not only inhibits dead air pockets but greatly reduces foliage disease and certain insect families.

Another factor that comes into play will be how much you are watering your plants. Excessive watering of the plants will also contribute to condensation, especially in Winter (due to Winter air usually being "dry air"). Excessive water in the g-house (especially to the point of soaking into the ground/floor) will do what water prefers to do, i.e., "seek its own level"...this means it will move into the (drier) air and when the air is saturated then you'll have water particulates (condensation). Restricting the over-use of water will definitely not only reduce the chance of condensation but will offer benefit to your plants as well (too much water during a slow-growth time is not healthy).

Before I continue on in this long-winded post, lemme just mention one last perspective...

I don't believe you'll run into into bigtime problems with condensation if you keep in mind just a couple things. Your double-glazing will certainly help restrict condensation, so that's a big plus! The amount of heat inside the g-house vs the cold temperature outside plays a big role...condensation, of course, will form where there is the two temp differences.

Lack of air-movement inside the g-house combined with excessive watering of the plants will also be a big factor. I keep a small fan running all the time in my g-house; this not only inhibits dead air pockets but greatly reduces foliage disease and certain insect families.

Another factor that comes into play will be how much you are watering your plants. Excessive watering of the plants will also contribute to condensation, especially in Winter (due to Winter air usually being "dry air"). Excessive water in the g-house (especially to the point of soaking into the ground/floor) will do what water prefers to do, i.e., "seek its own level"...this means it will move into the (drier/warmer) air and when the air is saturated then you'll have water particulates (condensation). Restricting the over-use of water will definitely not only reduce the chance of condensation but will offer benefit to your plants as well (too much water during a slow-growth time is not healthy).

Before I continue on in this long-winded post, lemme just mention one last perspective...you mentioned that "I plan for extending growing season so it would be heated as needed". "Extending the season" usually refers to trying to get another couple weeks or months at one or both ends of the growing period (starting earlier in the Spring and growing past frost/freeze date in the Fall/Winter). If that is your goal, as opposed to using the g-house to over-winter plants all Winter, then the only thing you'll really need to do is ventilate your g-house during days when the sun is really heating it up (either lower your curtains or open doors,or have exhaust fans kick in. The hotter it gets in there (and yep, you'll see how warm they can get inside even if the temp outside is in the teens) the more moisture created (picture a terrarium).

Hope this has been helpful and NOT confusing. (By the way, am curious about what you are going to grow in there. I'm the curios sort, ya know!)

I have no idea what the pitch of this gh roof is, but in the pic you can see the angle of the ribs. I've seen very little condensation over the years and the few times I've witnessed it it was as someone above said (Stress baby?), the little bit of moisture collected on the metal ribs and dropped from there, not so much from the plastic glazing.

Horseshoe:
Thank you, I appreciate hearing about your experiences.
The plan is to build the gh this summer. It will be small, about 24’ X 20’ and extend the garden season next fall with tomatoes to get my feet wet. My wife wants flowers, and a way to start seed earlier in the spring. I figure I’ve got a learning curve to over come the first winter. (probably never stops)
If I can soak up some of the experience all you folks have, maybe I won’t make all the mistakes the first year. (I hate reinventing the wheel)
I’m glad to hear that condensation probably won’t be the big problem as I was afraid it might be.
About 20 years ago I played with a 30’ hoop house. The heat gain was a surprise to me (shouldn’t of been but it was), I was scrambling for ventilation, mounted more and bigger fans. The killer was a bad over night storm that took down lots of power lines combined with a car wreck about 3 mile away that took down my power line and we didn’t get power till late afternoon. Just about cooked everything as I was not home to pull the cover off.
This time, I’m planning on big vents in the roof so that if fans go out I have 12 volt battery backup to open the vents.
You always plan for the problems you know, it’s the new ones that get you. (grin)

yep! I hear that! To this day I worry about power outtages...if it happens in the summer (or a warm winter day), things will fry in no time at all! If power goes out in the winter, things could easily die from killing low-temps! (Fortunately for us, we now have a generator that will power the exhaust fans (summer time) and run the heater fan (winter time).

I think you're doing good checking all the possibilities out and gleaning info on what you want/hope to do w/your g-house. Good going! With a mind (and perspective) like you have I feel you will do a great job; you and your wife will really enjoy that greenhouse!

Happy Growing to ya'll!

Shoe.

Horseshoe
Your generator, would it be auto-start with loss of power. Then if you were not at home you would still be protected.
Our local water dept put in a generator that’s diesel with auto-start and an automatic transfer box. (big town, 550 people) The man trips the breaker about once a month to prove that it works. once, that I know of, a bad battery connection and it failed the test. Then they were glad he was doing this monthly test.
This is a big generator, I was just wondering if they have auto-start for smaller generators.

Larry...yes, they have auto-start for residentialj-sized operations. As for me, I don't have that. (Sure would be nice though!) However, I work here on the premises and if there is any bad weather or any potential for power outtage I'm most definitely here at that time.

Are the auto-start generators hard-wired? SB

SB...yes, they 'can' be hard-wired if you choose, or they can be wired so you can plug them in (or unplug them). (If un-plugged they don't automatically turn themselves on, of course.)

Normally you need to have a permit and electrician hook them up for you and while doing so you can determine which circuits you want to be activated when the generator comes on (kitchen, heater, LR lights, well pump, etc).

For me, I fed my generator line into the breaker box and hand-select which breakers I want powered up at that time (G-house fans/heater, well pump, shoffice lights/outlets, for example). Since I'm here all the time (entirely too much!) it seems I am the "automated power cut-on"!

Stressbaby
Don’t have to be hardwired. Normally they are hardwired, the plugs and receptacles for 50 plus amps are expensive and one more thing to give trouble down the road. By hardwiring you bypass the need for them.
A 30 amp plugs rating is about 6000 watts max (220 times 30 amps = 6600 watts)
A 50 amp plugs rating is about 10000 watts (220 times 50 amps = 11000 watts)
I just never wanted to run the max. If you ever get to that stage be talking to an electrician.

Generally, the wiring lay out to the load devices (Fan or Heaters) are on separate circuits with thought on balancing the load to the generator if some of the devices are 110 volt. The generators 220 volts is split into two 110 circuits and its best if they have close to the same load.

However, you must have a transfer box so that generator voltage can’t back onto the power lines, can be deadly to linemen if that happens.

Basically this transfer box has a relay that when the generator starts up, the generator voltage operates the relay to transfer the load (Fans or heaters) from the power line to the generator.

In using any generator if the devices are not plugged directly into the generator you must use a transfer box (most likely manual transfer) for safety.
This is not one for the backyard wiring wizard to do. The safety of the linemen is on the line and Legally you have to have an electrician involved. (For as I know, just about any where in the country)

Yes, excellent advise, LarryH. (and thanks for the info regarding the plug loads..I had been wondering how that worked.)

SB, transfer boxes are available at Home Despot/Lowes types places, however as LarryH says, if you're not familiar w/electricity hookup it's best to let your electrician hook them up.

LarryH, my "back feed" hookup has worked great for me over the years. What I do is throw the main breaker (incoming) so it doesn't have an affect on the line-men. Seems efficient to me...any comment on that?

Thanks, folks.

Is the generator voltage backup into the line the reason we are told to shut off the main breaker when power is lost? I thought it had something to do with damage to circuits and motors when the power comes back on...

Decisions, decisions... if it's hard-wired, you have to find room for it permanently in the GH, but certainly there is greater security.

SB...yes, always turn off the main breaker when using a generator (unless you have the auto-transfer box as that will do the job for you). And yes, you turn the main breaker off so power doesn't go out of your breaker box and, as LarryH mentioned, zap some lineman who is working on the lines.

As for keeping your generator in the g-house all the time, that is not necessary (and actually not a good place for it anyway since the exhaust fumes would easily accumulate in there). I keep my generator under an overhang that comes off the side of my "shoffice" and it plugs into an outlet there that feeds back to the breaker box. From the breaker box is where the wires to the g-house begin, so you really want your generator within range of your breaker box, not necessarily next to or in your g-house.

Stressbaby
Question, Is the generator voltage backup into the line the reason we are told to shut off the main breaker when power is lost? No, that’s to disconnect you from power till they get it fixed right. while they are working on it, power could kick in and out a few times, maybe low voltage for a while (low voltage is death on motors) once power is really back on for 10-15 min then turn the breaker back on. less damage to equipment this way.

Horseshoe
Generators need a transfer box. It is designed so the generator can never be connected to the line and back feed into it.
Say power drops, you turn the main breaker off then fire up your generator. When power is fixed , you shut off the generator and turn on the main breaker
This works great it seems.
You’re the man in charge, You’ve done this for 10 years. Its part of your job.
Something happens to you, you’re in the hospital for a week.
During that week there is a power failure, there is someone who gets the job of firing up the generator. They may not understand the whole story, They know that they have to get the fans running again, they could fire up the generator with out turning off the main breaker.
The transfer box prevents that from happening, he/she has to throw the switch to connect the generator and that switch also disconnects the power lines.
One handle does the disconnect from power lines and connects to the generator.

I believe it’s a legal requirement to have a transfer box.
And if your not legal your insurance may not be good. (just a thought)