I had a hoophouse for about three years, no automatic anything. What I found was that the temp can get very, very high on a sunny day and can drop to the outside temp almost instantly when there is no sun. There will be very little heat retension at night. I kept a hi-lo thermometer in it so I could monitor it pretty regularly.

Polyethylene doesn't reflect IR, so on a clear night the temps can drop very quickly, even below outside temperatures (due to radiation to space). I replaced just the roof of my original greenhouse with polycarbonate and reduced the nighttime cooling dramatically (PC reflects the heat inside).

Thermal mass will regulate temperature better. I used a large bathtub full of water and fish (and water plants, a bog garden, small creek, sphagnum moss garden etc) to regulate my temps. More water will give you an even more uniform temperature (but note in Internodal stretch and your GH temps that keeping your greenhouse too uniform will make some plants grow more compactly). Also, if you need periods of say 25C to make the plants grow during the day and your average daily temp is only 20, then if your thermal mass is large and insulation poor you may prevent the greenhouse every getting hot enough during the day. Add more insulation.

As chris said recently, if you are paying for heating at night and venting during the day you are probably doing something wrong.

With my hoophouse (approx 12' x 20') the temperatures overnight were 10 to 12 degrees above the outside temperature. (I have 6 55gal. steel drums inside filled with water)
Temperatures during the heat of the day in summer (in Zone 5 at 6500 ft. altitude) could quickly soar to 140, so I used a swamp cooler assisted by a large household fan to keep the daytime temperatures down into the 80s and 90s.

We generally have a temperature differential of 40 to 50 degrees between day and night, year-round.

Hope this helps some...
Best Regards,
Junkmanme

My hoophouse easily climbed into the low 110s w. the outside temp as low as 80 I had a section of the back cut out w. an exhaust fan that was programmed to come on when the temperature reached 95°. I also had cross ventilation which seemed to help.

My 10 x 12 hoophouse is covered with single layer IR polyethylene. There is no heating, no heat storage, and no fans. But I did make a solar vent about 2 feet square on the roof. Night temps are only a couple degrees warmer than outside temps. Covering the beds with Remay really improves it a few degrees because the soil has a lot of retained heat.

Before the vent I had daytime temps aver 110 in January and now it is about 85. Without the vent it can hit 150 in the late Spring. Even with the vent I have to open the ends up in the spring to keep it from overheating, which seems more damaging to the plants than being too cold.

Bob B

stanc:

We also have a hoop house.

It came with dual poly and a blower. The blower would inflate the hoop house like a little baloon. This was to add about 40% heat retention.

It worked ok until January that first year then I could barely keep the temp above freezing at night.

Like previously posted, the temp would drop almost instantly.

Here's what I did to insulate it and maintain heat. Perhaps this will give you some ideas.

First I bought 2 large rolls of 1/2 inch bubble wrap. The rolls came in 48" X 250 feet.

I removed the outter layer of plastic (also 6 mil both layers).

I layed out the panels so that I could pull it over the house, right to the ground on the other side. I then cut the panel right at ground level on the side that I was working on. In other words, the panel started at ground level, over the greenhouse and to ground level on the other side.

I layed out these panels from front to back (on our house, it takes 3 panels with a bit of overlap.).

I did this 3 times to make 3 layers of bubblewrap.

I then returned the outter cover to its normal position and re-zippered it all up (our GH uses those wire lock things).

Now, I run the blower all the time which keeps the house inflated plus the bubblewrap, which lays directly on the greenhouse (the bubble created is above the bubblewrap).

That, in itself, INSTANTLY created good insulating that the temps went from freezing inside (while we were working) to around 15C (59F). We keep the GH between 10C to 15C normally.

On the inside, we put 2, 45 gal barrels of water. There's also a 125Gal pond with fish inside.

These 2 water sources really help to buffer the temps.

Also, the GH is full of plants which also absorb heat during the day and release at night.

The heater doesn't run too much and when it does, it heats things up nicely.

Oh yeah, it's VERY important to have ALL air leaks sealed! Around any doors, vents, around the base of the house... anything.

ANY cold air entering will have a great effect on heat retention.

In the spring, I'll be installing an automatic fan that I kind of made. What I did was take an old 5000 BTU air conditioner which no longer worked. I got rid of the compressor and all other cooling components.

I just left the fan, the capacitor and the thermostat in. I had to make some minor modifications so that air can only enter when the fan is on (luvers).

This will go above the door and the thermostat will be extended into the GH. When the temp get over whatever I set it to, the fan will come on and bring cooler air in.

Hope that helps give you some ideas.

blondboy: That sounds like a very successful project! do you have a log of inside vs outside temperatures?

You might also be interested in solaroof.

Thanks Nathan.

No, I don't keep actual logs, persay. The remote thermometers do keep a record of MAX/MIN temps only. I do check those out once in a while.

I've thought about, one day, getting one of those outdoor weather stations with remotes that keeps logs.

But, for me, there's really no reason.

I basically keep the GH (this year) at 11C-14C. The temps outside, this winter, have been amazing. Our lowest (in our area) has only hit around -12C or so. With many days up into the teens, which is very unusual for here.

But even last year when we had a low of -18C, I was still able to keep the GH warm. At those temps though, I do need to have the 2nd heater at the ready. They are both on thermostats. The 2nd one set lower than the first one.

This works quite nicely and not too harsh on the electric bill either. :)

Blondboy, your insulation method sounds very promising. Can you tell us a bit more? Regarding the bubble wrap-- why do you use only 48" wide rolls? Do you attach the strips together or overlap when you lay the three layers? What material and dimentions are the panels you refer to? When you refer to the bubble above the bubble wrap do you mean that you are inflating the space next to the cover plastic? Any idea of % light transmitted through? How does the wire lock work to secure three layers of bubble wrap plus the two layers of 6 ml plastic? Do you have a double channel base for your wire? Does your house have roll-up sides or other cooling means other than the fan and louvers? What are the dimentions of your structure?

I would appreciate any feedback. I plan to try something similar this spring when I replace the plastic on my smallest 15x40' GH. I purchased a 20'x40' roll of bubble wrap which I hope to sandwich between two plastic layers and wire lock the 3 sheets in one channel. I also want to inflate the cover on both sides of the bubble wrap. I was really curious of expected lifespan of the bubble wrap in a permanent setup.

I'll try to answer your questions in order. :)

- I used 48" rolls of 250' because that's all I could get locally (locally still meaning that I had to drive over an hour away... north of Toronto if memory serves... 3 years ago now).

I would have loved to get 12' X 250' rolls, but no one at all carried anything close to that around here. I wasn't interested in order through the USA as it would have been cost prohibitive.

- I just overlap them. Here's the EXACT process we now perform.

Lay first layer of 6mi poly on GH.
Then, we put 1 panel at one end, another panel at the other end. We then lay a center panel over the 2 end pieces (overlaping each one a little bit). This method assures that the entire structure is covered, not leaving overlap at either end (except for the poly sheet for tightening).

Then, we keep doing this for 3 layers of bubble wrap.

Once the 3 layers of bubble wrap are on and adjusted, we lay the top piece of poly on top of the whole thing.

In escence, we've now created a poly, bubble wrap sandwich! yummmy! ROFL! ;)

The upper and lower pieces of poly are the exact same size. So we ZIP one end of the GH. Then, we go to the other end and using a piece of wood, roll the poly around the wood and pull tight the plastic sheets.

Once that's done, we ZIP that and then start on one side and tighten/zip along the bottom. Repeat on other side, again, tightening to create a fairly firm structure.

NOT so tight as to not allow a bubble to be formed when the blower is on. There is a little play left in it.

- When you say strips, I'm not sure what you mean. If you mean the locking strips, then no.

- when I refer to the panels, I am refering to the bubble wrap which we've cut. Basically, since the GH is close to 11x11x11 (being 11 feet tall, probably more like 10'5" ish) we cut the panels so that it is aligned at each edge, almost toughing the ground. This is where the wire locks attach, at the bottom, to seal the poly sheets.

- yes, when I refer to the bubble above the bubble wrap (I knew that would confuse when I wrote it hehehehe) I was refering to how the outter sheet of poly expands and creates kind of a bubble when inflated.

- As for lighting penetration, I'm not sure what the % would be. What I can say is that the first year, we used 3 layers and it worked nicely. The 2nd year, we thought that if 3 layers insulated well, 5 layers would be better.

WRONG! 5 layers cut the light so much that there wasn't enough sun penatration to even heat up the structure in the day time. So we went back to 3 layers this year and it's much brighter in there.

It's bright enough that we now have some plants flowering that we didn't expect to flower. Enough that the banaana plants are happily putting on new leaves. One of those bad boys has even hit the top of the roof!

- I'm not sure what you mean by double channel for the wire.

Here's a URL that show exactly what I'm using:

http://www.griffins.com/images/products/09-16501_lrg.jpg

- As for rollup sides, no, not really. In the fall, I just put the wire lock from top to about 1/2 way down the 2 ends and nothing at the bottom. I then use a 12' piece of wood and roll the plastic over this until the real cold comes. I do the same in late March, early April.

- dimentions about (not exact) 11x11x11. I wanted to make it bigger, but due to space contraints and city codes..... well, you get the pix. :)

By the way, for the inflator, I did NOT buy the inflator that is normally used for Double Poly Hoop Green Houses.

Those things suck anywhere from 60watts to 150 watts. That's too much to be running 24/7.

Rather, I got my hands on an older style, all-metal muffin fan. Same as the 5" fans used in some computers to cool them, just not those crappy plastic, low output ones.

This thing inflates the GH nicely. The plastic is good and ridged and hail bounces right off. Helps it stand up to high winds too.

This fan only takes 20 watts of power.

To connect it to the GH, I used on of those dryer vent attachments with the square output. I removed the louvers and the fan fit right it. I bolted it into it. I attached that plastic dryer flex hose and that, attached to an adapter (home depot) that then attaches to the plastic thing that goes into the inner layer of plastic (designed for green houses).

As for life span, that depends on the sun I guess. I did NOT buy the bubblewrap that is UV protected. It's blue or pink. Didn't want to change the color of the light.

So, it's the 6mil poly that has the UV protection.

This is the 3rd year using the bubble wrap and it seriously looks like new.... well, except for some fungus here and there! ROFL! ;)

Done! :)

Because the outisde is windproof I think that layering is going to be almost as good as a single sheet. I found that in UV and the wind the bubble wrap died fairly quickly, but with a protective outer layer it should last decades :)

Bubble wrap is a marvel.

Blondboy.
Your bubblewrap seems to work quite well, especially with the water for heat storage. But why do you have to inflate the covering? The purpose of an inflator is to keep 2 layers of covering film separated so there is an air space in between them for insulation. The bubblewrap wil do this for you quite nicely, so can you eliminate the inflator?

Bob B

Bob B,

I would advise keeping the inflator but not using it for one reason. High winds. I posted back in May 05 this...

"Protecting covering in high or gusting winds." http://forums2.gardenweb.com/forums/load/strucs/msg0501305219728.html

I didn't reply to it because, 1. My poly was as tight as I could get it, and 2. It was single layer.

A couple of weeks ago we had very high winds and gusts here and it was unseasonly warm and sunny, My nice new double layer poly was taking a beating.

I could not turn on the exhaust fans because they were and are still stored in the garage. So, rigged up the inflation blower.

WOW!!! when the poly inflated that nasty banging and slapping sound stopped.

Keep the blower just for high wind protection, you do not need it for the insulation function with the bubble wrap.

Just my contribution...

I've actually conducted some tests for that very reason.

I reasoned that the bubblewrap does basically the same thing as the inflator... providing air gaps to increase insulating power.

So last year, during a cold week, I ran tests to see what, if any, was the difference in heating performance as well as maintaining the heat.

I found that with the blower OFF, it took more time to heat the GH and when the heaters stopped, the heat disappated faster.

With the blower on, it added that extra air gap on TOP of the bubblewrap. That little extra air gap made a difference on heating and retention. It heated up quicker and maintained the heat longer.

So this year, It's been running since December, non-stop (good little muffin fan) and the GH has been more efficient than ever (of course, 3 layers in stead of 5 of bubblewrap does help too).

Plus, even if there was no difference at all, I'd still leave it on.

THIS IS ONTARIO CANADA! and that means, you NEVER know when the weather will take a drastic change and how violent it can get in minutes. Seriously! LOL :)

So, being that I work about 50 miles from work, I couldn't be there to turn on the fan should a huge wind start up or large hail OR BOTH! hehehehe

Which reminds me. I had better start looking for a backup metal muffin fan. Ya never know when this one will give up the ghost.

If you get a backup fan, put the two in series (one blowing into the next). If you put them side by side, which is the obvious way to do it, when one fails, the other will just blow back through the stationary one. But you knew that anyway.

Thanks for the reply Blondboy. Lots of good info to work with. I was at first confused between "panels" and some other attachment stripping. I see now that you are refering to the bubble wrap itself. The immage of the single wirelock with wiggle wire inserted still has me concerned about your "sandwich". Do you just rely on the inner and outer plastic film pressure to hold your bubble wrap panels in place or do you attach them at the ground level in the wire lock. I assume that you would need to smash the bubbles to compress the bubblewrap enough to wire lock attach three panels of thickness. I know you can buy a double wire lock base but I purchased a large quantity of singles to get quantity discount and planned to screw 2 bases parallel to eachother. You can normally put 2 wiggle wires on top of each other in each base channel (seperately secure 2 plastic layers) so I was planning to use the bottom base for the outermost sheet of plastic.

The muffin fan is a good idea. I had used an old bathroon ceiling exhaust fan for the last 11 years in my GH for an inflation fan. I can't believe it lasted that long and I don't know the electric draw it had but now I bought 2 inflation kits at an auction and I plan to use at least one of them. I may just inflate the outer layer since the other responses don't support all that much benefit from inner and outer inflation. I know that the snow doesn't accumulate on an inflated house as readily.

I was always told by our GH salesman to install the plastic on a 60F day to get the perfect stretch on the cover. For oue 30 foot GH I had to loosen the wirelock and redo the single layer of plastic because it sagged so much that water laid in upper areas. Overstretching is my main concern with the inflatable system.

Thanks again for all the input and my appoligies to Stanc for not starting a new thread for this side topic.

Yeah, the wirelock is all around the structure. The 2 ends from point to ground and on both sides at ground level.

No, I don't pack the bubblewrap in the wirelock. It just lays on top of the inner layer of poly. It kind of bunches up at the ends a bit. It stays put since the BW is 22 feel long. Therefore, from top/center, 11 feet down to the ground on each side.

Also, this makes it easy in the spring to remove. I just remove the wirelock and pull the bubblewrap off. Fold and press! LOL j/k... fold and store.

But, after contacting that company with the pool covers for such a good price, I may decide to go that route next year.

The $$$ available will decide that.

Excellent discussion. I have a 12 x 20 hoophouse that I have been considering modifying for winter production. The ideas and experiences expressed are similar, but better, than my ideas.
I very MUCH appreciate your comments on this subject.
Best Regards,
Bruce (Junkmanme on GardenWeb 6500' elevation in N. New Mexico)

Reading this post with GREAT interest, since my hoop house experiment last winter was a dismal failure...scorching temps in the daytime, outside temps at night. I want to try this system. Blondboy, you mentioned a company that had good pool cover prices. Can you share the name of the company? Thanks for all the great information in this thread!

Anyone in USA who knows of a reliable company to get a solar pool cover from?

MollyD

Dessertgardner & Molly, maybe I can offer some insight since this concept of a solar pool cover has been on other threads of this forum. Try to get the Magni-Clear Solar pool cover when ordering. The company web is americasbestpoolsupply.com They ore located in Ohio but when I wanted to save on the shipping of a larger cover by driving there they told me that they are shipped from Canada.