Here are the charts for last night with everything except the circulation fan turned off:
Looks basically the same as with the lights on. Last night was mostly clear, but thin hazy clouds. I am at only 250 ft elevation and less than a mile from the Salish Sea (Puget Sound), though. Here are what the skies above the greenhouse looked like at sunset and a couple hours after sunrise:
Thanks for the update. Maybe that’s real and maybe it’s a measurement issue. At any rate 5F isn’t a big deal. My measurements could be an issue also. But for 18 years I’ve been amazed how quickly the temperature in mine drops when the sun goes down. All winter mine hits 90F for about 8 hours on about 80% of the days. By one hour after sunset it’s similar to outside, often 30s or 40s. When it drops that fast after a warm day I just can’t see it staying warmer than outside for another 12 hours on a winter night.
I think I’m going to end up double layering the greenhouse, building it with the ability to install the glass panes from both the exterior and the interior.The southern exposure and the radiant heat seeping from the house ought to contribute to an environment where better insulation would matter. The problem here is that a wide gap between panes is not a great insulator; a big gap promotes air movement within the panes which transfers heat. I need to find out how much of an effect this is.
Also as stated; I’m not fighting the winter, I just want to fight the early spring. Even if the greenhouse hits -20f, just getting stuff out of the howling winds would be a win.
Heck now I’m thinking about burring more insulation (specially buried deep in the perimeter) and running PEX tubbing on the gravel, in case I eventually want to pump some radiant heat in… I have to think about this. Basically radiant heat sucks at pumping heat in a hurry so it is not an ‘on demand’ system, but on a thermostat it would keep an eye on ambient temperature and start slowly pumping heat as needed. It would be expensive (money and effort) but it would nail that extra month of seasonal growth I want, if not more.
This is very possible. I use sensors hanging in mylar-wrapped PVC tubes, with one mounted on the outer north wall of the greenhouse and one mounted in the rafters. The outside one is definitely closer to the ground than an official weather reading should be, so on calm/clear nights when cold air pools near the ground, it could be reading a few degrees lower than a similar sensor would ~8 feet up (this is intentional because I’m wanting to know what temperature seedlings at ground level in the yard are experiencing). Here’s my sensing setup outside:
And inside:
The rafter one is probably reading warmer than at plant working level. Every iota of warm air molecules are going up.
I have been thinking of adding another lower, but the circulation fan does a pretty good job mixing the air. There’s a noticeable “breeze” throughout the greenhouse. But yes, that’s one reason it’s at 8’ (eventual avocado tree canopy height) rather than 11’ (exhaust fan height above rafters), is to not catch the most extreme heat at the highest points.
EDIT: By the way, if anyone wants tips on making a cheap temperature sensor and has some minimal tinkering abilities with electronics (soldering a few connections on the sensor chip, writing an image to an SD card), I highly recommend the raspberry pi & ADT-7410 chip, and would be happy to share my python script for uploading the reading to a web server (which can be on the local network or any website).
It works great with the pi zero W ($10), the sensor chip is just $8, and incredibly accurate/precise. I tested my two chips next to each other for a few hours before installing them separately and the readings were within 0.05°C of each other.
I have a large unheated high tunnel. In 6b WV.
With a mix of Perennial fruit and annual vegetables .
During the cold season , if closed up ,it definitely heats up during the day, can be close to outside temperature at night.
The tunnel Extends the growing season a month or so on each end of the season.
I often use remay Frost blankets to cover vegetables when a freeze is happening outside. This can protect something like peppers for an extra month or so. Keeping the heat from the ground near the pepper plants. So a tunnel within a tunnel .
The perennials are often confused !
So mid winter on a sunny day it can be 90f in there, then suddenly
Drop below freezing at night.
The dilemma then becomes , Do I keep it open and cool or closed and hot. The extra heat is good for most vegetables but not for perennials in mid winter. They can break dormancy thinking its spring, then freeze and die. While the same plant could be sitting out in the snow and be fine !
If I had a heat source that I could just keep it say 35°F that should eliminate most of this issue.
Or
A separate one for perennials and one for vegetables that could be kept at different temperatures.
I hear ya. Fortunately my plants for world domination is more for overwintering and an early start, not for extending the season on the tail end. Come end of September I would keep the vents open until April when is time to get the perennials to start waking up for real.
I would still get to use the warmer greenhouse for warm weather veggies during the summer and fall, the soil and nights are too chilly here for tomatoes to have enough of a grow window.
similar problems to what I’m trying. I want to get my figs in ground under a hoophouse. I can run a tiny heater from my solar battery for 6 hours, is necessary, to keep it above 35-40F, but in the day it might get hot enough to wake them up; I’m not sure what to do. my only idea so far is to use reflective mylar facing onward or a shade to block sunlight in the day to keep it a more steady temperature?
I don’t have time every single day to be opening and closing vents or running fans, and I don’t have any more money to throw at it for fans or vents anyway
it’s a dilemma. I’m zone 6, very hot dry summer, very cold wet winter. like high desert.
