Hoop House Issue...How to Solve Please!

I put the cover on the HH today. It was a great day to play with the temps inside the thing. Well, observe is more like it. I wanted to know how hot it might get, and how the sun affected things.

Well, we had a great day of varying sunshine. Sometimes, full and intense sun for half an hour. Other times, a high overcast that really screened out the sunshine, but nothing even close to shady/cloudy. Actually, perfect lighting for outdoor photography of animals and buildings, etc......diffused lighting.

My air temp was in the mid to upper 60's today. When the sun was blazing, it got to 97F in the HH. When the sun was diffused by high clouds, it was around 79F. So, quite the variance in temperature. I don't know that I like that. Question 1....are those normal fluctuations?

I also noticed sun angle means a lot, too. During midday, the HH had no problems heating up. After 4pm, though, the temps dropped rapidly. I was outside about an hour ago, and the sun was shining on the HH directly. The air temp was 70F, but the HH temp was only 73F. Question 2...should I be concerned by how quickly this drops off at night...and it's ability to hold steady temps?

It seems it makes no difference if I get to 500 degrees during the day if I'm still going to drop back to 27F at night....in a matter of hours.

Here are some things that "may" help you help me.

- 3.5mm thickness on the plastic covering. I had choices from .7mm to 6mm. I thought about buying the 6 for any help it may provide, but the 3.5mm was just the right size for the dimensions of my garden.

- We had only a 10-15mph breeze today, if that. So, it's not like it was windy. And, I became concerned about air getting in. I shored up some more spots, but it is making me think this thing has to be completely airtight....and that can't be necessary. After all, warm air comes predominantly out the top, right?

Tomorrow, I will check the temps of the air and inside the HH first thing in the morning and compare. I will also fill and add my gallon jugs of water in hopes I get a better differential Friday morning.

I know it's trial and error, but man.

One other thing I realize that may avert some of the panic.......the cover will only need to trap "some" heat after frost dates. And, it can't stop weeklong stretches of subfreezing weather and cloudy days. The cover will keep most of the frost off after the soil temps heat up. Which could also be part of the problem.....the soil just 3 inches down is still really cold. That may help explain the rapid cool off when the sun ducks behind a cloud.

Please help me discuss. As you can tell, when trying something new, I like to nip any potential issues in the bud.....so to speak....lol.

This time of year, as you know, the hoops are going to extend your season by adding warmth to the bed so you can plant a few weeks earlier and the seedling can get a head start. You are well on your way. I am not an expert; I do have a little experience with cold frames in particular, but I will address a few questions.

If it is getting very hot under the hoop, plan on venting somehow.
To retain heat into the dark, colder hours, you will need mass that will absorb heat during the day and slowly release it at night. The water jugs are good. I painted mine black.

I cannot give you all the details in this brief post, but I will encourage you, and anyone else reading this post,to try an internet search on subjects like hoop house, cold frames, hot beds, passive solar, things like that, you will find a lot of your questions answered and plan how to use your hoop to the greatest advantage.
It is a learning curve. But I think my best advice would be don't forget to open the tent on those days you know it is going to be sunny.

Absolutely. Once I saw 82 this morning, I thought.....Well, even on a day like today I need to plan to roll up the sides. 97 was crazy. But, today, I wanted to see how long it could hold that heat.....and was disappointed.

The water will help no doubt. And, so will warmer soil. And, at 97F, that soil ought to warm up quickly enough to get some ambient heat flowing along with water juggies.

I am wondering if I buy thicker plastic....6mm....and double it over.....effectively making it 12mm....if that will slow down heat loss. It should, but each level of thickness will also cut sunlight allowed in.

I'll search. Thanks for the help.

There may be some benefit to thicker film, but an envelope would be better, me thinks.

What do you mean by an envelope Camp?

I would like to know that, too, Jennie.

At any rate, here is what I found with a quick search. http://www.ehow.com/how_7557713_collect-suns-heat-hoop-greenhouse.html

This statement really helped me understand the drop in temperature was to be expected. "At night, hoop houses lose heat rapidly due to lack of insulation."

So, the best approach is to likely put in the water jugs and paint them black.

I have a 24'x14' HH around Nashville TN. I get about a 7degree differential in the coldest nights and am happy with that. I do have a 6mil covering. I would think that anything less than that would be easily damaged. Depending on how large your HH is you may need alot of water to make a difference. I have three 55 gallon drums in mine plus another 400 gallons in my aquaponics system that I heat. On the coldest nights I cover my plants in the greenhouse with another covering called agribon 15 that I get from Johnny's Seeds. With all of this I haven't lost any plants even when it got down to 11. I didn't even use an air heater this winter.

Hope this helps.
Richard

camprn wrote:There may be some benefit to thicker film, but an envelope would be better, me thinks.

In this case I mean 2 layers of film separated by a space, thus creating an envelope. Kind of like double pane window.
something like this

I got the above image from http://thenauhaus.com/blog/index.php/tag/chapter-5/

I've also heard of people buying a clear solar pool cover (the on that looks like bubble rap) and turning it so the bubbles are down and putting it over the top cover. I do agree that to get any benefit from two layers your going to have to put some space between them. The space acts as the insulation.

Richard, thanks a bunch. I originally thought the same thing about 6mm....durability. However, I was told somewhere that the "thickness" didn't make much difference in heat retention, so I went with the 3.5mm.

Mine only measures 4'x12'. So, I don't have a ton of space to heat. However, I'm sure it's going to require more water than I can fathom. I may have to cut the size down since I won't have all 64 squares going right out of the shoot. I just thought it looked better to have the whole bed covered instead of part of it. And, the added expense was so minimal.

Camprn, I was envisioning something else when you said envelope, but that makes sense. One thing I read last night was stating that you need to "trap" the heat. And, multiple layers help do that. I am thinking of a floating row cover that would provide at least one extra layer. Along with that, it would stay in place once I take the plastic off the house. But, we'll see. As with everything, it's a "work in progress."

Sort of stinks, though, I sure thought the HH was a simple concept. But, once again, I've been shocked by reality...lol.

Don't get discouraged. Though we have a greenhouse we also grow a 4'x20' bed outside all winter here under just a row cover. Also we only have one layer on our greenhouse and it does fine. Like I said we do cover those beds as well on really cold nights. As for the thickness we have walnut trees that rain down walnuts 2 1/2" that almost puncture our 6mil. I have used 3mil for row covers and have some of that left that's 3 years old. We are really into "use what you got".

Good luck

VENTILATION ! ie: open the doors , raise the sides , buy fans you can put on thermostats,, I purchase a vent kit from Intlernational greenhouse supply co it had two vent lovers with motors a tstat and a fan all for under 300 bucks works great! but even on a 75 deg day with vents open fan on, the temps still get in the low 90 range , next step is a shade cloth 50%

Jay birds right about the other end of the seasons. I love my greenhouse, but unless you spend more money than I want to I am always in a battle to moderate temps. I have two fans in mine and it does still get too hot on the hottest days of summer. This next year I might get a sun screen. Last year I trained my tomatoes so they offered everything else in the greenhouse shade. As for my fans I used two old roof fans that my Dad replaced an gave me.

I'm a bit confused. BBG are you talking hoop HOUSE or hoops over your individual SFG beds only?

Don't forget you want to measure the temperature of your hoop-house at GROUND LEVEL. The temperatures near the plastic cover will fluctuate dramatically while the temperatures near the ground will be much more stable.

Also you might want to check out Eliot Coleman's book: "Four Season Harvest" which clearly explains the use of double layers in hoop houses. He grows vegetables year round in Harborside, ME using UNHEATED hoop-houses in near SFG conditions. It's true that his farm is HUGE compared to most SFG's - but that doesn't mean his ideas can't be adapted to our smaller areas. It's good reading!