Heat Retension at Sub-zero

[digitS']

Recently, I recorded how my, so far, unheated greenhouse was only staying about 4 or 5F above outdoor temperature by dawn.

Here is the Deal

Since then, we have 2 mornings when the thermometer has fallen below zero! The greenhouse did better! . . . well, not really.

The morning the temperature was -4F, the greenhouse was 16.

The moring the temperature was -10, the greenhouse was 15.

Now, this morning the temperature at dawn was 23, the greenhouse was back to being 4 warmer than outdoors: 27.

There's probably a formula for all this but it is a bit beyond me counting on my fingers and toes this morning. But, it seems to me that there is a fairly simple reason the greenhouse temperature can be 25 above the outdoors when it is extremely cold: 16 and 15 is a long, long drop from the 90 I allowed the greenhouse to heat to during the sunny days that preceded those cold, cold mornings.

So, there is certainly heat retention in my sunshed greenhouse. I just need to figure out what I can grow in there that will tolerate a temperature range of from 15 to 90 !

Or, and here is an important solution (at least partial) that was suggested by Lesa last year: Cover the greenhouse with an insulated blanket during the night.

Steve

 

[chris09]

So, there is certainly heat retention in my sunshed greenhouse. I just need to figure out what I can grow in there that will tolerate a temperature range of from 15 to 90 wink!

Well you can always grow Cacti.

Steve what type of Greenhouse do you have?



Chris

 

[wifezilla]

How much thermal mass do you have in there? A greenhouse without thermal mass will have big temperature swings.

Over on www.sufficientself.com, SKR8PN build a greenhouse of the side of his garage and the whole back wall is water containers. He is still growing tomatoes and he is in Ohio.

I kept some chinese cabbage alive in a hoop house using 2 liter bottles filled with water.

 

[digitS']

Cacti! Well there's an idea! A high desert variety accustomed to wide swings of temperature that would naturally occur.

There is a picture of my sunshed on last year's thread where I covered similar thoughts. And no, I still haven't painted it . . .

I once had a lean-to greenhouse against my garage and thought about putting an opening thru the wall. A tight building, much larger than the greenhouse space, would do a good job of maintaining consistency of temperature.

No water containers in my greenhouse, Wife'. For thermal mass, I look to the insulated walls and roof and the concrete foundation to help me out there. Of course, the earth beneath any protected space, especially those without floors, will help to some degree, so to speak.

I have toyed with the idea of putting a large tank beneath the bench in the greenhouse. It would help some by retaining heat during the winter. I could drain it and pull it out during the spring when I need every inch of space and replace it and stock it with tilapia thru the summer !

Anyway, the idea might be fun but I couldn't keep tilapia in there during the winter nor have the tank around during the gh's busiest weeks.

S'

 

[lighthawk]

I suspect that wind speed and direction overnight may also play a big part in how quickly you are losing heat.

 

[digitS']

It has a certain advantage, Lighthawk. The protection of the neighbor's garage, a board fence and my garage on what is usually the windward side.

That protection is especially important to the plastic tunnel and it is protected by the greenhouse, as well. Otherwise, I suppose, it would have blown into the next county on more than 1 occasion.

I used to regularly visit a small commercial greenhouse. It was actually part of a larger range of greenhouses but the entire enterprise was fairly small. The entire thing has been gone for about 20 years.

The greenhouse was very old. If I remember right, it was built in the 1920's. It looked like a glass roof sitting on the ground. The structure was only about 8' wide and the central pathway was about 3' below grade.

It had very little exposure to the wind and open air. That little old greenhosue was hardly up to today's commercial standards but still useful.

Steve
edited to correct the width, it certainly couldn't have only been 6'.

 

[chris09]

That little old greenhosue was hardly up to today's commercial standards but still useful.

I grow some good plants in my little hole in the wall greenhouse that is way under today's commercial standards.

I been kicking around the idea of building a Pit Greenhouse but just seem to part with the old A-Frame Greenhouse .
Maybe I will dig the pit then move the A-Frame over the pit then I wont have to part with the old A-Frame Greenhouse. :/ That might be a thought.

Chris

 

[digitS']

I had forgotten about that thread, Chris!

My complaint on there was about ventilating the greenhouse in July !

See? It just never ends . . .

S'

 

[chris09]

I had forgotten about that thread, Chris!

My complaint on there was about ventilating the greenhouse in July !

See? It just never ends . . .

S'

I see what you mean.
Even that Greenhouse of mine can/ has been up to 120* on a good sunny Feb. day with a outside temp of 20*.

With a pit style greenhouse you would almost have to have windows up at the ridge that opens up and vents a ground level for some good ventilation along with a good exhaust fan.

Chris

 

[Organics North]

I have a 12x48 single layer hoop house, with 3 raised beds in it. I covered the 4' center bed with a second layer of hoops and plastic. (Sort of a mini quonset inside the big quonset. Inside the center hoop frost is 2 inches out of the ground.

That inner hoop buys me a couple extra weeks to a month on each end of the season.

I too struggle with the challenge of heat retention. I am going to switch to an IR retention greenhouse film, also by next fall I am going to add a second layer and an inflation blower. It is my understanding from a family member who is a life long large scale greenhouse operator, that the inflated second layer is the best bang for the buck on heat retention. (I also dream of using a foil/bubble/foil blanket I close at night.)

As Zilla says thermal mass is good too!

ON