 All right, great. Well, today I wanted the opportunity to talk about high tunnel ventilation high tunnels that are Popular right now. It's kind of a trend people have been wanting to get into for you know, probably the last 10 years and we get a lot of high tunnels in Alabama and then oftentimes they You know kind of Don't get used properly or maybe don't get utilized to their fullest and One of the problems with high tunnels in Alabama is it get really hot, you know, and so I want to talk about Ventilation today. I think I'd start off with How a greenhouse works when we get my slide to advance issue with that There we go. So, you know, the Sun is a powerful thing. It's really amazing and it You know, you get this ball of energy up there It takes eight minutes for a photon of light to reach the Sun to the earth and when it gets here it comes in the form of shortwave radiation and When that goes through greenhouse glazing or the clear covering on a greenhouse It goes in the greenhouse. It hits stuff and gets Rereadiated as these long wavelengths and if you've ever opened a hot car, you know Or open a car up in the middle of summer in the Sun, you know, it gets really hot in there Well, it's the same concept where the shortwave Radiation can get in but then it has a hard time getting out when it's reradiated as long these long waves And so what you get is heat gain and it can get hot fast just like your car does A greenhouse can and that's the same way the earth works. That's why they call it the greenhouse effect And that's how we maintain this temperature Here on earth is through that same same type of process So greenhouses can get really hot. So on a clear summer day A 30 by 96 greenhouse if you had all the doors shut, no ventilation at all You're gonna pick up about a million BTUs per hour And that's a lot of energy to give you an idea what that is So it's like burning 10 gallons of propane or natural gas or 10 terms of natural gas Every hour, okay It's like burning three car tires every hour or having 50 kitchen ovens open Excuse me running full blast open in the greenhouse. It's a lot of energy and it's all free from the Sun What the problem is it gets really hot very quickly And we all think when we're thinking about greenhouses or high tunnels that we want it warm in there because plants like it hot but actually Just like us plants like it when the temperature is comfortable and after you get over 85 degrees you start losing some productivity the plants Metabolism slows down and they're having to do things to cool themselves off and sometimes that's cost energy and Or may prevent some metabolic processes that Would otherwise be increasing your yield So when it gets over a certain temperature plants become less productive just like they become less productive at Some lower temperatures. So just about all crops have an optimum operating range and we try to get close to that as we can So like tomatoes, you know, they have an optimum Daytime temperature. We have an optimal nighttime temperature same thing with most crops And if it gets too hot or too cold you start getting problems like over 85 degrees Like a ping that's what makes tomatoes red becomes inhibited Palm production becomes reduced almost non-existent sometimes, you know, and if night temperatures get less than 50 degrees the plant won't set fruit and less than 60 degrees The flowers will abort. So let us the same thing if it gets too hot in there you get bolting tipburn bitterness You know, definitely increase pest pest pressure. So this is Lettuce that I've grown in a greenhouse down here and I've got just a really poorly designed greenhouse It does not ventilate well and I know once it gets to about May early June I can't grow less in that greenhouse anymore because it gets too hot and when it gets really hot the plant gets stressed and then It becomes a lot more susceptible Pythium and I get pythium almost on the clock, you know Once it gets a certain temperature in that greenhouse Consecutively, I'm gonna lose that crop because it gets too hot So it gets really hot in the greenhouse and it happens really quick And so we have to try to get rid of that heat and with high tunnels our primarily mechanism for getting rid of that It's through natural ventilation You know and wind is the major driving force behind natural ventilation It doesn't take a lot of wind to push that air that hot air through the house if the greenhouse is designed or excuse me The high tunnel of design properly, you know two to three mile per hour wind is a lot of air ball You moving through that greenhouse and it can push out that hot air pretty fast So natural ventilation with wind you can have a pushing effect and in some cases if you have some root vents Roof vents you can get a pooling or a vacuum effect as that air moves through the house So the idea is, you know, you got hot air constantly being made in that greenhouse or heat is constantly being gained And you get this cooler air from outside getting pushed in and it pushes out that hot air Boy see if you have roof vents or really high Gable vents can also help out with natural ventilation, you know hot humid air Rises because it's less dense and it can go out of the greenhouse or the high tunnel if you have roof vents And when it does it pulls in cooler air from the outside from the side vents and this does help But it's not as big of effect as the wind driven ventilation So it's really important when you're talking about ventilating a Structure like this is to consider especially if you're purchasing one to keep in mind the height of the greenhouse the air volume and even the crop height and You know those the tendency in the past Say Pre 1990s, I would say was to have shorter greenhouses So a shorter ceiling in that greenhouse. The idea was to keep that warm air closer to the crop We've since kind of moved away from that and structures are getting taller and taller and taller And that's kind of what I recommend is getting a tall structure. And so what is the optimum height of a structure? I don't really know yet. We're still trying to figure that out But I definitely think it's important to get if you can greater than an 8 foot Eve height and 12 Foot's even better, you know, some of the most advanced greenhouses in the world Might have a 16 to 20 foot Eve or gutter height on that house So the taller the house in my opinion the better and but also it gets more expensive because it requires more metal For that structural load So, you know get that I was talking about eight the ceiling height That would be like your apex the height the ceiling and then your gutter or Eve is kind of the worth your sidewall height would be So there is a thing called a vent the floor ratio and you really want to maximize this so the American side for agriculture engineers recommends a 15 to 25 percent of Bent the floor ratio. So whatever floor area have you want 15 to 25 percent to be represented in in Ventilation area and your goal to keep that greenhouse similar to the outside air temperatures to have about one air exchange Per minute or 60 air exchanges per hour Now you can get that vent the floor ratio with a four foot gutter height So you can see here on this chart. This is a high tunnel. That's got about a four foot gutter Our Eve height to it. So the vinyl and you get a 35 percent Vent the floor ratio, which is actually greater than what is recommended by the American Society for Agriculture Engineers However, here in Alabama with a four foot gutter height that greenhouses or hot tunnels going to get too hot. Okay The reason for that is is it four feet? We don't get a lot of wind shear and how much wind you actually feel You know one to two foot off the ground not a lot, you know, you may start filling it at four feet So even though we have that vent the floor area ratio with it over What is recommended just because we don't get a lot of air movement down low It's not going to properly ventilate. And so it's also important to understand that the bigger the structure is and as far as Surface area the more ventilation are you going to need? So this is a vent the floor area ratios for a freestanding 30 by 96 high tunnel Here it is for a gutter connected high tunnel. And so if you have You know where I had 35% Vent the floor area ratio with a Freestanding greenhouse once I put five bays connected to it my vent the floor area drops to 14% Okay, so I'm not getting nearly the ventilation rate that I should get it when I start adding Bays to that structure so one other thing that's important to consider is that larger volume of Air in the greenhouse when you get a taller greenhouse I'd like to give this example where you have two pots of water on the stove Same size pot one is half full and one is completely full of water and yet that's I'd like to ask which one's going to boil first Well, of course the one that's only half full is going to burn. I mean, excuse me boil first Because it takes a lot less energy to heat that water up There's a lot smaller volume of water and you can kind of think of that same Concept when we're talking about greenhouse air volumes, okay So the bigger the greenhouse or the taller it is the greater the air volume is going to be per square foot of greenhouse All right, and so what that means is with that larger volume of air I'm going to get a greater buffering effective temperature where When the sun is shining it's going to take longer for that air to get hot versus a shorter house So it's that works also when with a heat loss, you know in the winter So if I have a larger volume of air going into the night That means that that air temperature can be buffered against heat loss at a greater effect than a shorter house would Okay, so here's some kind of some of the work we've been doing with these ventilation rates We're just looking at different structures. And so this structure You see he's got about a four-foot Paul ventilation area around the whole greenhouse and On a sunny day, you know, if you look at the blue line That's the inside temperature and the orange line is the outside temperature and I almost have About a 20 degree difference in temperature between outside and side way too hot for any crop at a hundred and ten degrees Even humans, you know, that's that's dangerous to be working in So when I get to a much taller structure that's got a lot greater vent the floor area ratio I Can see a big difference in The excuse me the temperature difference between the inside and outside. So in this case the outside temperature is orange and the inside temperature is blue and With a little bit of shade. I'm actually a little bit cooler inside than I'm outside. I can vent that greenhouse At a much greater effect when I have that huge area of ventilation compared to the floor area So really the take-home message I'd like for you to leave with today would be the taller is better We don't really know what the optimum is it's different Depending on where you are in the world greenhouse or high tunnel Environmental controls are very dynamic and is largely based on the outside temperature sunlight and wind And so, you know greater air volume Generally is a good idea in the greater the ventilation area at the floor area the better You know what you definitely want to do is maximize your ventilation to floor area ratio You know in the wind, you know with a lot of times with high tunnels We think of the wind as kind of an enemy because normally they're street Cheap structures and they don't handle very well in the wind So you pay for what you get if you but if you have a well-designed structure that can handle those winds It's deaf and you have it out in the field with where it can properly ventilate and it's not blocked from Trees or buildings. You're gonna have more success with your crop because it can cool more efficiently If you want to learn a little bit more about controlling the greenhouse environment I had this publication through the Southern Regional Aquilter Center. It's kind of revolves around aquaponics But it works for any crop and it discusses the different ways you can Control or manipulate the greenhouse environment For your crops and you can find that easily through Google if you just search SRAC Aquaculture in a list of their publications should come up pretty easily. So here's my name. I'm using my email and Contact number if I can help you in any way