I had been using a blower we found in the greenhouse to get the fire in our wood-stove roaring, but then I realized that it already had a purpose! In the greenhouse! To keep the greenhouse warm in the winter I want to both absorb as much heat during the day and store it in things such as the pond and other high thermal mass materials and also insulate the greenhouse at night to keep in as much of the heat as possible. Our greenhouses are double glazed, meaning they have two layers of the plastic sheeting that covers the outside. Apparently this is actually a great way to insulate a greenhouse, and if you can get a nice amount of air between these two layers, then all the better. So we are trying out blowing up the greenhouse.
It is apparent from the holes that were already present in the inner layer of glazing and the fact that there are blowers in every greenhouse, that this was something the previous owners already were already doing. Hopefully this means that it will work!
I’ve been doing a ton of research about heating and insulating the greenhouses. This post from Midwest Permaculture seems awesome and has great information about things such as TMV and R values of different materials which is super useful.
THERMAL MASS VALUE BTU/Sq. Ft./degree F.
- Water 63
- Steel 59
- Stone 35
- Concrete 35
- Brick 24
- Sand 22
- Earth 20
- Wood 10.6
R-Value Measurements (hr°Fsq.ft/BTU)
- Fiberglass glazing- single layer R = .83
- Glass double layer R = 1.5 – 2.0
- Polyethylene Double 6mil film R = 1.7
- Glass triple layer 1 / 4 “ air space R = 2.13
- Polycarbonate 16mm triple wall R = 2.5
- Polystyrene (styrofoam) 1 inch thick R = 4.0
I need to check them out some more and read up on Midwest Permaculture
And then there’s always THIS
It looks so tropical in there, right?! It sure feels tropical because it is humid as all hell in the greenhouse. Like so humid it is literally raining in there. The sun was out in full force today and someone (no idea at all who that could be) apparently didn’t twist the wires to the fan together enough and the fan quit working!
(You can see the untwisted white wires up at the top, along with the rogue wire nut at the bottom. Don’t get me started on the black wire connected to the white wire in there, seriously I have no idea, but it works)
So during the day at some point it got up to almost 105 degrees, leading to the pond relocating onto the greenhouse film making it steamy and rainy inside. So, I did some research about this humidity issue, and I’m almost convinced it is an issue, but also not convinced that it needs an immediate or high-tech resolution. Apparently most plants don’t like a lot of humidity – it messes with their respiration and can lead to the spread of diseases, especially fungus and mildew issues. I also am pretty sure it’s not great for the materials in the greenhouse, mainly the electrical work in there, but that is less of a concern.
The goal of this particular greenhouse is to be somewhat tropical, so the humidity might not be that big of an issue. I assume that some plants don’t mind the humidity and would enjoy the steaminess. The drawback of this is that I want to grow tomatoes and other veggies in there and I know that tomatoes and squash are especially susceptible to fungus/blight and powdery mildew. I could try to make some sort of division between the pond area and the veggie areas, but that seems counter-productive to the whole heat-sink idea of the pond, and I have four other greenhouses, so if I was going to do that, I should just use a different one.
A couple of commercial/industrial solutions exist: non-condensing greenhouse glazing, condensation reducing sprays, circulation fans, and dry-air heat. I’m not particularly interested in trying out most of these. I know I need more circulation, but I’m trying to balance that with keeping the heat in, so I need to try to figure that out. I also could keep the water in a container that didn’t allow evaporation, but I really like the idea of a greenhouse pond, so I’m really set on making this work. So…
Solutions I am willing to try that might work:
- The greenhouse glazing is double thick and there is a blower which can inflate between the two layers and allow for better insulation leading to less of a temperature differential between the inside and outside air which is a large cause of condensation.
- I could try to come up with something that could force the condensation to happen in a certain place – a metal tube or some sort of upside-down pointy thing? This would hopefully lead to less dripping in random areas and if possible, reduce the humidity.
- Venting – yes I know I need more of this, but my highest hope is that maybe this isn’t an issue at all. Maybe if the fan had been working the humidity would never have risen too far to start with and we would all be millionaires… yeah…
I spent a lot of time messing with this greenhouse fan – a lot, like the better part of three days. I googled a million things, I texted my friend who is an electrical engineer, I twisted and untwisted and retwisted wires (luckily without electrocuting myself), I emailed the old owners, and I called the manufacturer. See, I was convinced that the vent in one of the greenhouses was installed backwards, or the fan ran the wrong way. The way the fan works it sucks hot air out of the greenhouse, but the vent opens outward, meaning that it doesn’t open automatically when the fan turns on. In fact it becomes harder to open it since the fan is sucking it closed. I rigged the door to swing open when the fan turns on, and I figured that there was something wrong with the set up of the fan and the vent since they didn’t work in the same way.
It turns out that I was wrong – the fans are only meant to run in exhaust mode and the vent is supposed to open against this flow because if the vent opens inward, a stiff wind could blow open the vent and ruin the temperature control. Apparently we are missing a crucial piece of the greenhouse set-up which automatically opens the vent right before the fan turns on.
So lessons learned?
- Sometimes calling people is much easier than trying to research things yourself on the internet. Sure there was a lot of information out there, but some of it wasn’t relevant, was hard to understand, or was just plain wrong. Adding to that was the fact that I wasn’t even entirely certain what I was even looking for – was it the fan or the vent that was wrong? But one call to Dave at the ACME Fan and Greenhouse supply company had me straightened out.
- Drawing electrical diagrams is HARD! This is not pretty:
- Sometimes things don’t need fixing. Technically the fan/vent set up is completely correct, minus the missing part. But….
Lessons NOT learned:
- I’m still not 100% convinced that it is correct! (I know, I am a very hard-headed, stubborn know-it-all!). I understand that it was correct at one point and possibly had all the parts it needed, but that is no longer the case. I could go out and buy one of those automatic openers and hook it up and it would work as intended, or I could figure out how to work with what I have.
- I’m still going to try to kludgy this together somehow. Maybe flip the vent for the summer and wedge it closed for the winter? Maybe some Rube Goldberg machine can open that vent when the fan turns on? Maybe automatic venting that doesn’t even need a fan?
- Ideally the fan will be unnecessary and I would like to not depend on these automatic thingamajigs. Not because I’m a Luddite or hate technology, but because they fail and are hard to fix and make me angry (and the irrigation system battery died and killed all my squash babies earlier this summer). I figure that people managed at one point without all those things, and I can figure out how to as well. Living part time in Philly does make it more complicated, but that sounds like a challenge…