It is February now. With this in mind, people are about to start their seeds and many are building or buying greenhouses with little thought about what this will effect in the summer. Many are just throwing it together with little thought to just how effective it may be during the colder months. I want to get to you before you get this idea. I want to explain how you can use forced air for year round plants.
We know to allow airflow and rain during the summer, but what about winter? First, you will need to water your plants, and second, we will want to keep the space warm. This is pretty easy right? We have the sun giving us its radiant energy and that will keep our greenhouse warm.
This is a little shortsighted and not fully accurate. It depends where you live, first of all. Secondly, what about night. When it is getting down to 15 degrees at night and you have an extremely poorly insulated greenhouse, you are losing all of that warmth and the plants will still freeze.
My first suggestion for something quick would be to have a small space heater, but even that would just prolong the growing season in the building. A space heater will also be a power hog over time.
We could spend a little more time upfront and have this problem corrected, or at least much more functional and reliable for the price.
Think geothermal. You dig a trench about 2-3 feet deep and bury tubing into the ground. The best for heat transfer is copper, but I think going with Geothermal HDPE for your coil, which is hundreds of times less efficient than copper, but it will not corrode on you nearly as fast as copper and is MUCH cheaper. It would be best if you use many small tubes instead of a few large tubes. This provides more surface area for faster heat transfer. The most efficient for transfer is water, but if you don’t want to have to run a ton of piping into your greenhouse to create a closed loop system, it would be easiest to just allow air to be your transfer medium in an open-loop system.
I really like the idea of a thermal pump for air flow by having one side of the tubing higher in the space than the other, allowing the heat transfer to drive the entire engine, but the realist in me says to just grab one marine battery and a 75Watt solar panel to run a low draw fan. It doesn’t have to be high velocity flow, but the higher the flow, the better the heat transfer… to a certain point.
Another awesome thing to do is to add a rocket mass heater with the exhaust going into a berm. The berm could be a big pile of dirt, or could be made a large square slab of cement for a wall. It could also be drums full of water, for a large section of gravel… anything that will take and hold heat. Make the berm part of or close to your north facing wall (above the equator) and you can be harvesting tropical plants in the U.S.!
For heat, you will have a rocket mass, wood burning heater going into a mass on the north in conjunction with the geothermal transfer. Next, would be cooling. The awesome thing about geo-thermal is that the same loop is heating and cooling all in one. All you are doing is making the air space the same temp as the ground, which, if you dig far enough, will be constant. The further north you are, the deeper you would have to dig.
Another option that reduces the amount of digging needed is to add geothermal heat sinks to a pond. You have to consider fish and the changes in water temp in your decisions for this, but it is a proven and viable option. I may be easy and cheap if you decide to do this and you have a pond already. I just stumbled on this idea and I haven’t really researched it too much.
I hope I got you guys thinking a bit about some easy and inexpensive ways to temperate a space, be it an outbuilding, greenhouse, or even your home.
I also have a question that was asked by Greg from Colorado. I made a two part series. I will post at least one of those next week, Greg, but I WILL get to both parts.
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