Josef, many sincere thank you's for taking the time to review and respond to my post.
2/3 Collector/Thermal mass - We are planning to install a double stack of 55-gallon drums (painted black, filled with water) all along (6" away from the wall surface, to be precise) the back wall to act as our main means of collection and significant thermal mass. We'll have around 50 in total. I will be adding additional means of collection and thermal mass as space and layout permit.
4- Distribution - We are planning on what you describe, and also the installation of radiant heat barrier along all interior walls to prevent the radiant heat from escaping for as long as possible.
5- Control - You are absolutely correct, and as best I can tell at this early stage, the weakest spot in our design is the ability to regulate the higher temps in the hotter months. Having not yet installed the thermal mass, it's difficult to tell how they will help moderate the greenhouse temps either way (cooling down or heating up). The good news is, we have the time to progress in steps, with measurement and consideration in between.
A few notes on your comments:
- Most importantly, we are intending to use this greenhouse primarily during fall, winter and spring, to help bridge the gap between temperate growing seasons. If we had to forego using the greenhouse in the hotter parts of the year, we would be willing to do so as we have plenty of outdoor growing space to utilize during that time.
- We are keeping open the idea of using electric exhaust fans to some degree if need be (although this would not be ideal). I am going to try and utilize every possible method to reduce the need for this. Even if we do need some fans, I'm hoping to make enough progress that we could utilize efficient solar fans. And like I said above, our goal for this greenhouse is not summer use.
- We designed the angle and relative pitches of the roof to collect the most light in winter and shed the most light in summer relative to the angle of the sun at those times. Even so, your comment about the lack of overhang on the south facing roof side is quite valid. We may yet opt to add some sort of overhang over a small portion of the top of the south facing roof to further help shed direct summer sun. Hopefully we can do so in a way that does not interfere with solar collection in the winter. I need to get the barrels in first and then do some measurements.
- We may find that it makes sense to install shade cloth or alumi-net to physically reduce the amount of sunlight the building absorbs in the hotter months.
- I have also considered adding some automatic solar powered roof vents to the north facing roof to vent excess heat. This would involve making holes in the existing roof, but we can do it if needed.
- We are painting the wood framing inside with high quality white paint, to help deflect/diffuse light and to increase longevity in a humid environment. All the insulation we're using is closed-cell and will not absorb moisture.
- I am worried about the smaller size of my top vents as well. We have some room to make them bigger if need be, or add other ones.
- I will be buying a digital temperature logger so that I can chart out the indoor/outdoor temperatures once we get everything installed.
I remain hopeful that the "cooling intake tubes" idea holds some merit.